Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Carbon sequestration in different wetland plant communities in the Big Cypress Swamp region of southwest Florida

Carbon sequestration in different wetland plant communities in the Big Cypress Swamp region of... International Journal of Biodiversity Science, Ecosystem Services & Management, 2015 Vol. 11, No. 1, 17–28, http://dx.doi.org/10.1080/21513732.2014.973909 Carbon sequestration in different wetland plant communities in the Big Cypress Swamp region of southwest Florida a,b,c a,b Jorge A. Villa and William J. Mitsch * a b Environmental Science Graduate Program, The Ohio State University, Columbus, OH, USA; Everglades Wetland Research Park, Florida Gulf Coast University, 4940 Bayshore Drive, Naples, FL, USA; Grupo de Investigación GAMA, Corporación Universitaria Lasallista, Caldas, Antioquia, Colombia (Submitted 16 February 2014; accepted 3 October 2014; edited by Blanca Bernal) Wetlands offer many ecosystem services, including the long-term sequestering of carbon (C) in soil. Here we present a study of C sequestration rates in a relatively undisturbed wetland landscape of southwest Florida. Accordingly, carbon sequestra- tion was determined in four wetland plant communities and an adjacent hydric pine flatwood community that represent a gradient of inundation extent. Going from the wettest to the driest, communities were designated as: deep slough, bald cypress (Taxodium distichum), wet prairie and pond cypress (Taxodium distichum var. imbricarium). An adjacent hydric pine flatwood community was also included in the study as a reference upland site. Three soil cores were collected from 137 210 each of these communities and were analyzed for total C content. Core samples were also analyzed for Cs and Pb −2 −1 activity to estimate accretion rates. C sequestration rates (g-C m yr ) were the highest in the deep slough (98 ± 9) and bald cypress (98 ± 5) followed by the pond cypress (64 ± 7), wet prairie (39 ± 1) and pine flatwood (22 ± 5). These results suggest that impediment of decomposition by anaerobic conditions caused by prolonged wet cycles, may not account for all the variability in C sequestration rates observed in this subtropical setting. Instead, this variability could also be attributed to other factors like the quantity and chemical composition of the organic material reaching the soil. When methane emissions are taken into account, cypress-dominated (bald and pond cypress) and the deep slough communities act as net carbon sinks. Keywords: carbon sequestration; subtropical wetland; cypress swamp; Everglades; climate regulation; Taxodium distichum Introduction terrestrial world (Whiting & Chanton 2001; Frolking et al. 2006; Page et al. 2011; Mitsch et al. 2013). Climate regulation through carbon (C) sequestration in Values for C fluxes in wetlands, however, are far from wetlands soils may be one of the most important ecosys- definitive (Roulet 2000). For instance, early estimates of C tem services of wetlands in the long term. Carbon is −1 sequestration rates for North America (52.7 Tg-C yr ) sequestered in wetlands when C inputs (productivity and/ −1 and the world (137 Tg-C yr ) had an uncertainty of or sedimentation) surpasses C outputs (decomposition and more than 100% according to Bridgham et al. (2006). C exports) and the remaining organic material, mostly More recently, Mitsch et al. (2013) revised this number senesced plant material, is accumulated in the wetland's and after including a revised area for tropical wetlands and anaerobic sediment layer as a mat of partially decayed their sequestration rates, they estimated that the worldwide organic material, or peat. A fraction of this organic matter −1 sequestration may be around 830 Tg-C yr . Much of our may also be incorporated into the mineral fraction of the current knowledge of wetlands as carbon sources and soil as soil organic C. Globally, it is estimated that 455– sinks comes from extensively studied northern peatlands 700 Pg-C (1 Pg = 10 g) of carbon in organic form is (Gorham 1991; Maltby & Immirzi 1993). In general, wet- stored in wetlands (Mitsch & Gosselink 2015). By com- lands in boreal and subarctic biomes experience low tem- parison, Lal (2008) estimates that there is 1550 Pg-C peratures that are partially responsible for inhibit organic stored in the earth's soil organic C pool. This pool includes matter decomposition and also limit productivity (Clymo various forms of organic C, from highly active humus to 1984; Roulet et al. 2007). In the case of wetlands in warm relatively inert charcoal (Lal 2008). Considering that wet- subtropical and tropical climates, this temperature effect lands occupy only 5–8% of the terrestrial land surface seems to be more complex and less understood. On the (Mitsch & Gosselink 2015), these global estimates rank one hand, wetlands are generally more productive in lower them as the terrestrial ecosystems with the highest C latitudes. On the other hand, higher temperatures in these density (Kayranli et al. 2010), leading scientists from regions could lead to a rate of decomposition that exceeds different disciplines to emphasize the key role that wetland that of productivity (Franzluebbers et al. 2001; Mitsch ecosystems may play in the Earth's radiative forcing et al. 2010). despite their relatively low percent coverage of the *Corresponding author. Email: wmitsch@fgcu.edu © 2014 Taylor & Francis 18 J.A. Villa and W.J. Mitsch Beyond the controlling effect that macroclimate may communities and speculate about their impact on radiative have on productivity and decomposition, C sequestration forcing, as possible net GHG sinks. seems also to differ according to the wetland type or hydrogeomorphic setting and the plant communities therein. For example, in a study of temperate wetlands in Methods different hydrogeomorphic settings, Bernal and Mitsch Study site (2012) found depressional and isolated wetlands to This study was conducted in Corkscrew Swamp Sanctuary sequester two times more C than riverine flow-through −2 −1 in southwest Florida (26° N 23ʹ W, 81° N 35ʹ W). This wetlands (317 versus 140 g-C m yr , respectively). nature preserve, within the Corkscrew Regional Conversely, in a follow-up study in the tropics, the same Ecosystem Watershed, is a collection of relatively undis- authors found that C sequestration rates in tropical, slow- turbed freshwater wetlands characteristic of southwest flow-through wetlands were as much as three to four times Florida (Figure 1). Climate in this portion of Florida is higher than in tropical, depressional and seasonal riverine wetlands (Bernal & Mitsch 2013). They attributed the characterized by very warm and wet summers, mild win- observed differences in C sequestration in these studies ters with occasional light frost and spring droughts. Mean to site-specific factors such as the extent of inundation or annual precipitation and temperature in the headwater of the form of organic matter (recalcitrant versus labile) the watershed are 1201 mm and 23.2°C, respectively entering the systems. The effect of these factors has also (values from 35-yr records since 1971, Station COOP: been noted in other studies of tropical peatland ecosystems 084210, Immokalee, FL, South Florida Water (Chimner & Ewel 2005; Hirano et al. 2009). Management District). A complete ecological description Despite the apparent benefit that wetland ecosystems of Corkscrew Swamp is presented by Duever et al. (1984). have on the reduction of Earth's radiative forcing through C Briefly, Corkscrew Swamp is a riverine cypress strand on sequestration, possible feedbacks to the atmosphere of C in a relatively small and flat watershed (i.e. 32,030 ha). Low the form of methane (CH ) are a real concern (Gedney et al. erosive force of the waterways allows the development of 2004;Bridghamet al. 2006;Kayranliet al. 2010;Bastviken vegetation and accumulation of peat in what would nor- mally be the main stream channel, leading to a diffuse et al. 2011). CH is a greenhouse gas (GHG) produced in system of shallow irregular channels. Mineral substrate wetlands by organic matter decomposition under anaerobic profiles, consisting mainly of sands overlying limestone, conditions (Whalen 2005). Once in the atmosphere, CH has decline along a line perpendicular to the general flow an adverse effect on the radiation budget of earth because of direction, from the surrounding pinelands to the deepest its global warming potential (GWP) that is 25 times greater than the potential of the same mass of carbon dioxide (CO ) over 100 years (Forster et al. 2007). Calculations made in 2005 based on carbon equivalents (i.e. taking into account the GWP of CH ) of the global wetland area and its organic C stock suggested that these ecosystems should be regarded as a relatively small net source of GHG (Mitra et al. 2005). More recently, Mitsch et al. (2013) used a dynamic model of C fluxes from 21 wetlands in different climates to estimate that wetlands in the world may be currently acting as net C −1 sinks of about 830 Tg yr , with an average of −2 −1 118 g-C m yr of net C retention. Accurate estimation of C sequestration in wetlands across different landscapes is critical for developing better C budgets that will ultimately help us understand the role of wetlands as GHG sinks or sources in future climate scenarios. Here, we present a study of C sequestration rates from different wetland plant communities and an adjacent hydric pine flatwood community that are charac- teristics of southwest Florida. These wetland plant com- munities are situated in a single hydrogeomorphic setting, but represent a gradient of inundation. We expected a gradient in C sequestration of the wetland plant commu- nities that will follow the gradient of inundation. Then, we Figure 1. Location of the study sites corresponding to four compare the C sequestration rates with previously pub- different wetland plant communities and an adjacent upland lished CH emissions rates for these same plant commu- community in southwest Florida. The black circles indicate the nities to assess their role as sources or sinks of C GHG. sites from which soil cores were extracted. DS = deep slough, We follow this with a discussion of possible causes for the BC = bald cypress, WP = wet prairie, PC = pond cypress and variability in C sequestration among these wetland PF = pine flatwood (upland). International Journal of Biodiversity Science, Ecosystem Services & Management 19 channels in the strand. Ground surface, however, is rela- Once in the lab, samples corresponding to each tripli- tively flat because organic soils have accumulated in low- cate depth interval were dried at 55°C for 48 hr. After lying areas, creating a generally level topography. The drying, samples were weighed to calculate the soil bulk most significant factor affecting the distribution of the density. Then, debris (small branches) and roots, when plant communities is the hydroperiod (i.e. inundation present, were carefully removed and all samples were extent) that can last for more than 250 days in deep ground to a 2-mm particle size, homogenized and stored sloughs, depending on the amount and distribution of in sealed bags until analysis. Core depths varied between yearly rainfall. Maximum wet season water levels and, to and within sites. Only depth intervals that had the three a lesser extent, minimum dry season water levels can also replicates were used in the analyses and calculations. be important in determining plant community zonation Maximum analyzed core depths (cm) were 32, 48, 32, (Duever et al. 1984). 26 and 14 for deep slough, bald cypress, wet prairie, We selected four distinct wetland plant communities pond cypress and pine flatwood, respectively. across the gradient of inundation in the Corkscrew Swamp landscape. The plant communities investigated were desig- Accretion rates nated as: (1) Deep slough, mostly bare soil with sparse emergent macrophytes like Peltandra virginica, Thalia Accretion rates were determined non-destructively by 137 210 geniculata and Pontederia cordata, a subcanopy domi- Cs and Pb activity in each 2-cm soil measuring nated by Annona glabra, Fraxinus caroliniana and interval (Craft & Richardson 1993; Bernal & Mitsch Cephalanthus occidentalis and an open canopy of tall 2013). Composite subsamples (~10 g) corresponding to Taxodium distichum, (2) Bald cypress, also bare soil with each depth interval at each plant community were run in a a sparse understory dominated by Osmunda regalis in high-efficiency Germanium Detector (GL 2820R, small mounds created by dead trees and roots and Canberra). Cs is a man-made radionuclide distributed Crinum americanum in small depressions; both under a worldwide primarily as the consequence of atmospheric canopy and subcanopy similar in composition to that of deposition after nuclear weapons testing (Smith et al. deep slough, (3) Wet prairie, co-dominated by Cladium 2000). Depositional patterns of this isotope normally exhi- jamaicense, P. cordata, Ludwigia sp., Alisma subcordatum bit a distinct peak in the activity in the soil profile that Raf. with no bare soil, and (4) pond cypress, a dense stand corresponds to year 1964, one year after the Test Ban of Taxodium distichum var. imbricarium relatively smaller Treaty (Ritchie & McHenry 1990). Thus, by knowing than the trees in the bald cypress community but with a the depth interval with the peak in Cs activity, the relatively closed canopy, with Ludwigia sp. and Sagittaria average accretion rate can be estimated as the depth of graminea primarily covering the forest floor. A hydric the interval with the peak in Cs activity divided by the pine flatwood (Pinus elliottii, Serenoa repens and time from 1964 to the year of sampling. 210 210 Aristida stricta) community that was never flooded during Pb is a naturally occurring radioisotope. Pb can the study period was also included as a reference upland be formed in wetlands from in situ decay of Ra (sup- 210 210 community. Inundation during 2011 and 2012 had a dura- ported Pb). Pb can also be deposited in wetlands tion in days of 264 and 198; 181 and 149; 138 and 117; from the decay of Rn in the atmosphere, or indirectly and 125 and 67 for deep slough, bald cypress, wet prairie via the water column (unsupported Pb) (MacKenzie and pond cypress, respectively (Villa 2014). et al. 2011). This unsupported component of the Pb inventory can be used to establish chronologies of wetland sediments or peat because once it is incorporated in the soils it decays exponentially with time in accordance with Sample collection and preparation its half-life (22.2 yr) (Oldfield & Appleby 1984). To Three 6.5-cm-diameter cores were collected in each plant establish peat chronologies in our plant communities, we community (15 cores total) using a universal core head assumed a constant rate of supply of unsupported Pb sediment sampler (WaterMark) equipped with ~60-cm and applied the constant-rate-of-supply (CRS) model polycarbonate barrels. Cores in deep slough, wet prairie described by Appleby and Oldfield (1978, 1983) and and pond cypress were collected between June and Oldfield and Appleby (1984). The average of the relatively September 2011. Cores in bald cypress and pine flatwood constant down-core total Pb activity in the soil profile were collected between March and June 2012. Distance was assumed to represent the supported Pb activity between cores was less than 1 m, except for those from the (Craft & Richardson 1998; Brenner et al. 2001). bald cypress community, in which one core was collected about 5 m apart from the other two. When sites had Soil analyses and carbon sequestration rates standing water, surface water in the corer was siphoned off before processing the soil core. Processing in the field Duplicate samples corresponding to each core 2-cm depth consisted of sectioning the core into 2-cm depth intervals, interval in each plant community were analyzed for total then packaging and sealing them in separate plastic bags. carbon (TC%) and inorganic carbon (IC%) in a Total During sectioning, we cleaned the work area after packa- Carbon Analyzer for soil samples (TOC-V series, SSM- ging each sample to avoid any possible soil mixing. 5000A; Shimadzu Corporation, Kyoto, Japan). TC was 20 J.A. Villa and W.J. Mitsch determined by total combustion at 900°C, whereas IC was this analysis because it acted as a net sink for CH during −1 determined by digestion with 10 mol L H PO at 200°C. the study period considered in Villa and Mitsch (2014). 3 4 The organic carbon (OC) fraction per depth was calculated as The GWPs used were the three reported in Forster et al. the difference between TC and IC. The soil bulk density at (2007) (i.e. 72 for 20 yr, 25 for 100 yr and 7.6 for 500 yr). each depth interval was calculated with the dry weight and This GWP is an emission metric proposed by the the volume. Intergovernmental Panel on Climate Change to assess the −1 Soil TC concentration (g-C kg )ofeachdepth interval overall climate response associated with a forcing agent was obtained by multiplying the percentage value of C by 10. (i.e. GHGs). It compares integrated radiative efficiencies TC was then multiplied by the corresponding dry weight to of GHGs to that of CO , assumed as the standard gas, over obtain the mass of TC per interval. The mass of TC was specified time periods. Decrease over time of the GWPs integrated in the profile down to the age of the peat that was results from the reduced radiative forcing of CH given its 137 210 estimated with Cs and Pb. As these depths did not lifetime of 12 yr (Forster et al. 2007). coincide with the 2-cm intervals, we calculated the dry weight To determine if the soil in a plant community was acting as in each bottommost interval by multiplying its height by the a source or sink of C GHG we established a GHG compensa- corresponding bulk density and dividing by the area of the tion boundary, in which the GWP multiplied by CH /CO 4 2 core. Then, the integrated mass of C and the integrated dry ratio was equal to 1 [GWP (CH /CO ) = 1] (Whiting & 4 2 weights were divided by the area of the core and the number of Chanton 2001). This boundary was constructed by plotting years from the age of the peat to the year of sampling to first the three GWPs (y-axis) versus their respective compen- −2 −1 estimate the C sequestration rates (g-C m yr )and mass sation boundary value [GWP = (CO /CH )] and then tracing 2 4 −2 −1 accretion rates (g m yr ), respectively. an empirical best fit line for these three points. Then, we plotted the CH /CO ratios calculated for our plant commu- 4 2 nitiesversusthe GWPofCH for 20, 100 and 500 yr. Accordingly, given a specific GWP, a system would be acting Carbon sequestration versus methane emissions as a net GHG source if a system has a CH /CO ratio that falls 4 2 To assess the role that wetland plant communities in south- in the area above and to the right of this boundary. Conversely, west Florida may be playing in a climate change context, it would be acting as a GHG sink if the ratio falls into the area we related the CH /CO ratio to the GWPs of CH in an 4 2 4 below and to the left of this boundary. approach similar to that presented by Whiting and Chanton (2001). The CH /CO ratio was calculated using 4 2 the average 2-yr CH emissions measured by Villa and Results −2 −1 Mitsch (2014) (26.9 g CH m yr in deep slough, 2.7 g −2 −1 −2 −1 Soil profiles CH m yr in bald cypress, 25.9 g CH m yr in wet 4 4 −2 −1 prairie and 3 g CH m yr in pond cypress). The C The variation of soil bulk density and carbon concentra- sequestration rates in this study assumed as the net atmo- tions with depth for each plant community is shown in spheric CO assimilated by the system (e.g. Mitsch et al. Figure 2 (a and b respectively). The cores extracted at the 2013). The pine flatwood community was excluded from bald cypress community had a thick root zone between 20 Figure 2. Soil profile at each wetland plant community showing: (a) bulk density and (b) carbon concentration. International Journal of Biodiversity Science, Ecosystem Services & Management 21 and 28 cm depth that was not included in the analyses. wet prairie and the pine flatwood tend to be more subject Bulk density remained low through most of the depth to erosive and re-distribution processes. −3 sampled in deep slough and bald cypress (i.e. <1 g cm ), The CRS model applied to these unsupported inven- −3 averaging 0.30 and 0.10 g cm respectively. In turn, bulk tories dated soil intervals back to 1897 in the deep slough density showed a significant increase with depth in the wet community (Figure 3). However, the mean ± standard prairie, pond cypress and pine flatwood communities as error of the minimum detection limits (MDL) for the the peat layer was gradually replaced by sand. unsupported Pb measurements in all communities, −3 Accordingly, bulk density (g cm ) in these communities including the pine flatwood community, was −1 went from 0.39, 0.17 and 0.63 in the surface, 2-cm depth 1.4 ± 0.03 pCi g . According to MacKenzie et al. −1 interval, to values over 1.00 at the 8, 10 and 4 cm depth (2011), MDL of 0.27 pCi g lead to potential bias intervals, respectively. towards erroneous old values for ages older than about Most of the C measured in the different communities 80 yr. To avoid bias induced by the MDL in our measure- was in organic form (>99%). Soil TC concentrations ments, we calculate carbon sequestration rates since ~1950 (i.e. ~60 yr) in the four wetland communities. In the pine decreased with depth in all wetland communities and the upland site. In the deep slough and bald cypress, this flatwood, only the top interval could be dated to 1956 with decrease was less pronounced than in the other commu- the CRS model and therefore C sequestration and bulk −1 nities, going from 435.8 and 415.6 g-C kg at the soil accretion were determined in this community since that −1 surface to 76.5 and 35 g-C kg at the deepest depth year. Table 1 summarizes mean accretion rates using the interval, respectively. TC concentrations decreased sharply Cs peak activity and the CRS model, as well as the net from the soil surface in the wet prairie and pond cypress and mass accretion rates and the carbon concentration communities and remained low throughout the sandy since 1950. The accretion rates estimated with Cs layer. In the hydric pine flatwood community, where the were fairly similar to those estimated using the Pb soil consisted primarily of fine sand, TC concentration was CRS model in the pond cypress and pine flatwood. −1 low throughout the profile. Values (g-C kg ) in these However, in the case of the wet prairie, the rate from the three communities (wet prairie, pond cypress and pine Cs peak was considerably lower. Carbon sequestration flatwood) went from 145.3, 391.8 and 5.9 at the soil sur- rates (mean ± standard error) in wetland plant commu- −2 −1 face to 10.8, 3.81 and <0.01, respectively. nities ranged from 98 ± 9 g-C m yr in deep slough and −2 −1 bald cypress 98 ± 5, to 39 ± 1 g-C m yr in wet prairie. Carbon sequestration in the upland pine flatwood commu- −2 −1 Soil accretion and carbon sequestration rates nity was 22 ± 5 g-C m yr , representing a more than Cs activity showed distinct peaks in the wet prairie, 4-fold increase from the surrounding upland communities pond cypress and pine flatwood community. Peaks in the to the wettest wetland communities (Figure 5). deep slough and bald cypress communities were not clearly identifiable. High Cs activity in the profile of Carbon sequestration versus methane emissions these two communities was rather evenly distributed across different depth intervals (Table 1, Figure 3). Our assessment indicated that soil in the bald and pond Therefore we used only Pb to determine the accretion cypress communities function as a net C GHG sink, inde- rates in the different communities. Total integrated unsup- pendent of the time horizon for which uptake and emis- 210 −2 ported Pb ranged from 5.2 pCi cm in wet prairie to sions are considered. The deep slough community acts as a −2 28.6 pCi cm in bald cypress and had a mean ± standard net GHG source when considered on a 20- and 100-yr −2 error of 15.6 ± 4.4 pCi cm (Figure 4). The distribution of horizon, but it switches to a net sink when the analysis is this unsupported Pb suggests that there is preferential considered for 500 yr. The wet prairie community deposition towards the forested communities dominated remained a GHG source regardless of the time horizon by cypress (deep slough, bald and pond), whereas the used in the analysis (Figure 6). 137 210 Table 1. Mean accretion rates using the Cs peak activity and the CRS model ( Pb), net and mass accretion rates, and the mean (range) of carbon concentration since 1950 for the soils in each community. Mean Mean accretion accretion Net accretion Mass Mean carbon Carbon 137 210 rate ( Cs) rate ( Pb) since 1950 accretion rate concentration sequestration −1 −1 −2 −1 −1 −2 −1 Plant community (mm yr ) (mm yr ) (cm) (g-m yr ) (g-C kg ) (g-C m yr ) Deep slough – 1.6 9.7 229.8 438 (321–511) 98 ± 9 Bald cypress – 2.4 12.2 217.6 380 (242–425) 98 ± 5 Wet prairie 0.4 0.9 5.3 508.7 83 (35–156) 39 ± 1 Pond cypress 0.9 1.1 6.5 238.1 257 (27–422) 64 ± 7 Pine flatwood* 0.4 0.3 2 226.7 59 (37–91) 22 ± 5 Note: *This plant community was never inundated during the period between June 2011 and June 2013. The accretion rate of this community was calculated from 1956. 22 J.A. Villa and W.J. Mitsch 137 210 Figure 3. Cs and Pb activity in four different wetland plant communities (a, b, c and d) and an adjacent upland site (e). Left and 137 210 137 center columns represent total Cs and Pb activity through the soil profile, respectively. Dates corresponding to the peak of Cs and those obtained using the constant rate of supply of unsupported Pb (CRS) model are presented in the second y-axis. Right column contains Pb as a function of cumulative mass in log scale. International Journal of Biodiversity Science, Ecosystem Services & Management 23 Figure 4. Integrated unsupported Pb activity for four differ- ent wetland plant communities and an adjacent upland commu- Figure 6. Wetland plant communities in southwest Florida as nity. DS = deep slough, BC = bald cypress, WP = wet prairie, sinks or sources of greenhouse gases (i.e. CH and CO ) eval- 4 2 PC = pond cypress and PF = pine flatwood (upland). uated for three different time horizons. The curved line represents the greenhouse gas compensation boundary and is an empirical best fit of three global warming potentials contemplated in Forster et al. (2007). Values below or left of the compensation boundary indicate a net sink of GHG, whereas values above and right of the boundary net source of GHG. and pine flatwood), Cs peaks were measured, yet the accretion rates estimated with the two methods ( Cs peak and Pb CRS model) were somehow different, leading to further discrepancies in the calculation of the C sequestration rates. Moreover, the use of Cs in envir- onments where sands dominate the profile, as is the case in these three communities, must be regarded with caution because an increase in sand-size particles in soil profiles Figure 5. Carbon sequestration and inundation extent in wet- will cause a decrease in the activity of Cs that cannot be land plant communities of southwest Florida. Bars represents related to the atmospheric fallout rates of Cs (Ritchie & mean carbon sequestration rates (n = 3) for: DS = deep slough, BC = bald cypress, WP = wet prairie, PC = pond cypress and McHenry 1990). Altogether, our results highlight the PF = pine flatwood. Error bars denote the standard error of the potential value of using Pb as an alternative, yet inde- mean. Circles represent the annual average 2011 and 2012 inun- 137 pendent method to date soils using Cs in wetlands with dation extent for each corresponding plant community. high organic matter and low clay content or those with profiles that are dominated by sands, like the ones found in this study. Mean accretion rates since 1950 in the cypress-domi- Discussion nated communities were similar to those reported for Soil accretion rates ~100 yr in different cypress communities in Georgia by 137 −1 The estimation of soil accretion using the Cs peak Craft and Casey (2000) (i.e. 0.8–2.2 cm yr ). We could activity in the soil profile was not a reliable method for not find in the literature accretion rates for sites with plant the deep slough and bald cypress communities. The communities similar to the wet prairie and pine flatwood absence of Cs-binding clay particles (Schell et al. communities considered in this study. However, the accre- 1989; MacKenzie et al. 1997; Brenner et al. 2001) and tion rate in the wet prairie was lower than those reported for possibly active uptake of Cs by plants (Oldfield et al. ~30 yr by Craft and Richardson (1993)in unenriched 1979) could explain the profiles with evenly distributed marshes of the Everglades with short inundation periods 137 137 −1 Cs near the topsoil depth intervals. Moreover, Cs (i.e. 1.6–2.4 cm yr ). The mean accretion rates in the activity in these two communities was measured at depths different communities followed closely the trend of the 210 210 that, according to our Pb dating, were decades older distribution of unsupported Pb in the soil profiles than the start of atomic bomb testing. This is not an (Table 1, Figure 4). This distribution of unsupported Pb unusual finding in wetland environments of Florida (e.g. also suggests that particles from wet prairie and pine flat- Brenner et al. 2001) and supports the idea of post-deposi- wood (lower values) are being either eroded and deposited tional mobility of this radionuclide through the soil profile. in the adjacent forested communities (higher values) or For the other three communities (wet prairie, pond cypress re-deposited within the same community. More Pb 24 J.A. Villa and W.J. Mitsch profiles in different sites within each community should T. geniculata and C. jamaicense, respectively (i.e. 17% help determine which of these two processes is dominant. versus 6.9% and 9.8%, respectively), and also has higher Also, despite the fact that wet prairie had low integrated C:N ratios (i.e. 51.5 versus 14.1 versus 24.1, respectively) unsupported Pb in the soil profile, the specific mass (Osborne et al. 2007). Secondly, decomposition rates, and accretion rate was more than double the rate of the other therefore C turnover, are up to one order of magnitude communities. We can only explain this by a relative higher higher in other co-dominant plant species of the wet proportion of sand in the profile of this particular site that prairie when compared with that of cypress (Deghi et al. has accumulated since 1950. 1980; Battle & Golladay 2001; Chimney & Pietro 2006). Differences measured in C sequestration rates of Corkscrew plant communities can also be attributed to the Carbon sequestration in the different wetland plant quantity of the organic matter entering the system. For communities instance, Cohen (1973) estimated that 40% of the peat in High C sequestration rates in tropical wetlands of warm the Okefenokee Swamp, southern Georgia, was produced in and wet climates have been attributed primarily to the low situ by roots. Cypress-dominated communities in decomposition rates in such environments (Chimner & Corkscrew have a belowground productivity in the top −2 (Duever et al. Ewel 2005; Jauhiainen et al. 2005; Hirano et al. 2009). 30 cm ranging from 1633 to 1946 g m 1984), whereas belowground productivity in communities Prolonged cycles with standing water above the soil sur- face or waterlogged soils may well enhance C accumula- dominated by sawgrass, one of the co-dominant species in −2 tion by impeding aerobic decomposition and attenuating the wet prairie, is around 390 g m (Miao et al. 1997). warm air temperatures. Our results, which show the varia- Despite existing differences in quality of the organic tion in C sequestration along a gradient of inundation in a matter litter composition and quantity of organic matter single hydrogeomorphic setting, partially support this being incorporated into the soils, the fate of the organic claim. We found a general trend in the inundation gradient matter that reaches the soil surface is not clear yet in this with lower C sequestration rates corresponding with com- dynamic environment of contrasting dry and wet conditions munities with shorter inundation periods, confirming our (i.e. aerobic versus anaerobic processes). Future research initial prediction (Figure 5). However, this gradient was should focus on the synergistic effects that alternating aero- not straightforward. The deep slough community and bald bic and anaerobic conditions (McLatchey & Reddy 1998; cypress had very similar C sequestration rates regardless Chimner & Ewel 2005), timing of litter fall, quantity and of having different inundation periods. Also, the wet quality of litter (Pettit et al. 2011;Chowet al. 2013), and prairie community had lower C sequestration rates than microbial and fungal community activity (Pettit et al. 2011; the pond cypress community despite having a longer Todd-Brown et al. 2012) may be playing in the decomposi- inundation period. Therefore, the slowing of decomposi- tion of organic matter and hence in the variability observed tion by prolonged inundation periods can only explain to in the C sequestration rates. some extent the differences in C sequestration between the plant communities studied in Corkscrew Swamp. Carbon sequestration in southwest Florida wetland Differences in C sequestration rates between wetlands ecosystems in tropical and subtropical wetlands can be attributed to the quality of the organic matter entering the system. For To better assess the role that wetland ecosystems of south- instance, Bernal and Mitsch (2013) speculated about the west Florida may be playing in the sequestering of carbon at a wider scale, we compared the rates measured in this study effect of recalcitrant matter in the higher C sequestration rates observed in sites dominated by forested communities to those reported in previous studies from tropical and sub- when compared to macrophyte-dominated sites in different tropical zones of America and Africa (Table 2). To avoid wetlands of Costa Rica and Botswana. Day (1982), in a confusion introduced by the use of different methodologies study in the Great Dismal Swamp, Virginia, attributed in the estimation of the carbon sequestration rates, we only differences in the decay rates to the chemical characteris- selected studies which used radiometric dating, either with 137 210 tics of the litter, rather than to the environmental condi- Cs or with Pb.We thenarrangedwetlandsbygeo- tions resulting from flooding. Specifically, increases in morphic setting (Brinson 1993). According to these studies, decay rates were the result of relatively higher nutrient C sequestration in tropical and subtropical zones ranges −2 −1 content (nitrogen and phosphorus), and low lignin and between 18 and 232 g-C m yr . Also, rates (mean ± stan- tannic acid content, and C:N ratios. These litter composi- dard error) tend to be higher in riverine, low-gradient allu- −2 −1 tion differences could help explain why, in our study, C vial (100 ± 25 g-C m yr ), than in depressional −2 −1 sequestration rates in the wet prairie were lower when (62 ± 18 g-C m yr ) or riverine, low-gradient, non-alluvial −2 −1 compared with the adjacent cypress-dominated commu- wetlands (56 ± 12 g-C m yr ). The rate for the latter nities. In the first place, leachates from cypress leaves, geomorphic setting, excluding the data in this study, is −2 −1 the dominant taxa and main input of organic matter in 57 ± 17 g-C m yr . bald cypress and pond cypress communities, have higher The C sequestration in the wetland communities that we −2 −1 percent lignin content than leachates from co-dominant studied ranged from 39 to 98 g-C m yr , in the lower species in the deep slough and wet prairie like middle portion of the rates observed along the tropical/ International Journal of Biodiversity Science, Ecosystem Services & Management 25 Table 2. Mean carbon sequestration rates from tropical and subtropical wetlands of America and Africa featuring their geomorphic setting, type, dominant plant species and general location. 137 210 The rates were calculated using Cs to estimate the accretion rates or Pb (*). Values in parentheses indicate reported ranges. ND = Not described. Geomorphic setting and C sequestration rate −2 −1 wetland type Dominant plant sp Location Latitude (g-C m yr ) Reference Depressional Rainforest swamp Spathiphyllum friedrichsthalii Costa Rica 10 N 61* Bernal and Mitsch (2013) Cypress swamp Taxodium distichum var. imbricarium, Nyssa aquatica, Georgia, USA 31 N 31 Craft and Casey (2000) Cephalanthus occidentalis Cypress swamp Taxodium distichum var. imbricarium, emergent grasses Georgia, USA 31 N 31 Craft and Casey (2000) Marsh Acalypha diversifolia, Gynerium sagittatum Costa Rica 10 N 131* Bernal and Mitsch (2013) Marsh ND Georgia, USA 31 N 56* Craft and Casey (2000) Mean ± SE 62 ± 18 Riverine, low gradient alluvial Rainforest swamp Chamaedorea tepejilote, S. Friedrichsthalii, Costa Rica 10 N 232* Bernal and Mitsch (2013) P. macroloba, Calathea crotalifera Cypress-Tupelo swamp Taxodium distichum, Nyssa aquatica Georgia, USA 31 N 18 Craft and Casey (2000) Marsh S. friedrichsthalii Costa Rica 10 N 222* Bernal and Mitsch (2013) Marsh Eichhornia crassipes, Thalia geniculata Costa Rica 10 N 80* Bernal and Mitsch (2013) Marsh T. domingensis Costa Rica 10 N 84* Bernal and Mitsch (2013) Marsh Eleocharis sp., Paspalidium sp., Oxycaryum cubense Costa Rica 10 N 89* Bernal and Mitsch (2013) Marsh Oryza longistaminata, Schoenoplectus corymbosus Botswana 19 S 42 (33–53) Bernal and Mitsch (2013) Marsh ND Florida, USA 27 N 202 (127–259)* Brenner et al. (2001) Marsh Cladium jamaicense Florida, USA 26 N 127 (86–158) Reddy et al. (1993) Mean ± SE 100 ± 25 Riverine, low gradient non alluvial Cypress swamp ND Florida, USA 29 N 122 Craft et al. (2008) Cypress swamp ND Georgia, USA 31 N 36 (15–56) Craft et al. (2008) Cypress swamp Taxodium distichum, Annona glabra, Fraxinus caroliniana, Florida, USA 26 N 98 (81–112) This study Cephalanthus occidentalis, Peltandra virginica, Thalia geniculate Cypress swamp Taxodium distichum, Annona glabra, Fraxinus caroliniana, Florida, USA 26 N 98 (88–106) This study Cephalanthus occidentalis, Crinum americanum Cypress swamp Taxodium distichum var. imbricarium, Ludwigia sp., Florida, USA 26 N 64 (49–71) This study Sagittaria graminea Marsh ND Georgia, USA 30 N 24 Craft et al. (2008) Marsh Cladium jamaicense Florida, USA 26 N 94 (54–130) Craft and Richardson (1993) Marsh Cladium jamaicense Florida, USA 26 N 19 Craft et al. (2008) Marsh Cladium jamaicense Florida, USA 26 N 46 (37–56) Craft et al. (2008) Wet prairie Cladium jamaicense, Pontederia cordata, Ludwigia sp., Alisma Florida, USA 26 N 39 (37–40) This study subcordatum Raf. Mean ± SE 62 ± 12 26 J.A. Villa and W.J. Mitsch subtropical latitudinal range. Bernal and Mitsch (2013)in a measure or for water diversion. Considering the impor- study of 12 freshwater wetland communities in contrasting tance that the duration of inundation and the maximum wet and dry tropical climates found a Shelford-type nonlinear and minimum water levels have on the plant community relationship between C sequestration rates and the P/T zonation (Duever et al. 1984), it is also reasonable to ratio (ratio of mean annual precipitation and air temperature, expect a shift in the plant communities. In general, −2 −1 10 mm yr /°C). According to this study, this ratio, a proxy changes favoring the areal expansion of cypress-domi- for water availability, suggests a midpoint of the P/T ratio at nated forest could enhance the net sink of GHG of the which C sequestration in wetlands from lower latitudes whole landscape. However, the practice of predicting the seems to be enhanced. Based on the finding in their study, trajectory of plant communities in Corkscrew is rather this point is around a P/T ratio of 1.2 with minimum and challenging. Despite the fact that inundation is the main maximum sequestration rates at ratios near 0.2 and 1.8, variable in the distribution of the plant communities, the respectively. However, regardless of the P/T ratios, the isolated effects of this single variable could be hard to same authors also noted that the hydrogeomorphic type predict. was a key factor in determining the carbon sequestration Some studies on the successional dynamics of pond capacity of their different wetland soils. Located in one single cypress-dominated communities in depressional swamps hydrogeomorphic setting, our wetland communities have a in central Florida (Casey & Ewel 2006) and riparian forests P/T ratio of 0.5 (35-yr average), suggesting that wetlands in in South Carolina (Giese et al. 2000) suggest that increased southwest Florida may not be at the optimal climatic location inundation periods and water levels may induce a shift in for sequestering carbon when compared with other tropical the pond cypress community towards a plant community and subtropical freshwater wetlands. However, the lack of dominated by species of hardwood forest like Nyssa spp., organic matter-binding parent materials in the soils of Salix spp., Gordonia lasianthus and Cephalanthus occiden- Corkscrew, where organic soils develop on top of a mineral talis. Whether or not bald cypress stands will develop later substrate consisting typically on sands (Duever et al. 1984), in the succession is still to be determined, but regardless, may also be a factor determining the comparatively lower the new community will likely continue to function as a carbon sequestration rates (Trumbore & Harden 1997). GHG sink. Conversely, dryer conditions with shorter inun- Nonetheless, the role that these wetland communities are dation periods and lower water levels may lead to a dom- playing in carbon sequestration at a landscape scale should inance of pine flatwood communities, that could possibly not be undervalued. Our results indicate that wetlands in lead also to the establishment of sedge and grass-dominated southwest Florida can sequester up to four times more C in communities (Marois & Ewel 1983), altogether leading to a the soils than adjacent pine flatwood upland communities. net increase in GHG emissions. Implication of the balance between carbon sequestration Conclusions and methane emissions In this study, C sequestration in the soil of four different In its present state, the Corkscrew Swamp watershed repre- major wetland communities of southwest Florida was sents a relatively undisturbed mosaic of wetland ecosystems investigated. Sequestration rates were the highest in the that have developed in response to long-term climatic, hydro- community with the longest inundation, but did not follow logic, edaphic and fire influences (Duever et al. 1984). a discernible pattern with the duration of inundation for Therefore, the 500-yr time horizon (GWP = 7.6) used in the rest of communities considered across the landscape. our analysis may be more realistically describing the emis- Overall, the slowed decomposition caused by prolonged sions/uptake status of GHG in the Corkscrew wetland plant anaerobic periods brought about by high water levels and communities studied. Any possible positive radiative poor drainage observed in other tropical wetlands could strength caused by CH emissions during the first stages of 4 only partially explain the rates of C accumulation found in peat formation in the deep slough in the past, represented by this subtropical setting. Rather, the rates observed in these the CH /CO ratios in the 20- and 100-yr horizons, might 4 2 communities that alternate between prolonged wet and dry have been offset by now by its long-term C sequestration cycles may also be determined to some extent by the (e.g. Frolking et al. 2006; Frolking & Roulet 2007). chemical composition of the organic matter reaching the Accordingly, conservation strategies to maintain and soil. Over an extended time period (500 yr), the long-term enhance the wetland GHG sinking potential should focus C sequestration of the cypress-dominated (bald and pond) on the cypress-dominated and deep slough communities. and deep slough communities outweighs their CH emis- Current efforts to restore the historical hydrological sions. These communities should therefore be the focus of flows in the Everglades region (southern portion of conservation strategies to enhance ecosystem service of Florida) features the redirection of unused freshwater for climate regulation offered by wetlands in south Florida. restoration purposes and human demands (Chimney & Goforth 2001; Perry 2004). Under this scenario, it is reasonable to expect that the inundation cycles will be Acknowledgments modified in the different wetland ecosystems of the entire This study was conducted first at the Olentangy Wetland Research region including Corkscrew, either as a restoration Park at The Ohio State University (mid 2010–mid 2012) and later at International Journal of Biodiversity Science, Ecosystem Services & Management 27 the Everglades Wetland Research Park at Florida Gulf Coast Craft C, Washburn C, Parker A. 2008. Latitudinal trends in University (mid 2012–mid 2014). Authors wish to acknowledge organic carbon accumulation in temperate freshwater peat- the numerous volunteers that helped with field and laboratory work. lands. In: Vymazal J, editor. Wastewater treatment, plant Also, to Blanca Bernal for her help in the initial stages of this dynamics and management in constructed and natural wet- research. Anonymous reviewers provided key directions for the lands. New York (NY): Springer Science and Business data analysis and discussion of results that considerably improved Media B. V.; p. 23–31. the final version of this manuscript. Director Jason Lauritsen, Dr. Craft CB, Casey WP. 2000. Sediment and nutrient accumulation Shawn Liston and Dr. Michael Knight provided permission and in floodplain and depressional freshwater wetlands of help with logistics at the Corkscrew Swamp Sanctuary. Georgia, USA. Wetlands. 20:323–332. Craft CB, Richardson CJ. 1993. Peat accretion and N, P and organic C accumulation in nutrient-enriched and unenriched Everglades peatlands. Ecol Appl. 3:446–458. Funding Craft CB, Richardson CJ. 1998. Recent and long-term organic Funding for this project came from the National Science soil accretion and nutrient accumulation in the Everglades. Foundation (Grants CBET [1033451] and [0829026]). Partial Soil Sci Soc Am J. 62:834–843. funding for this study was also provided by the Society of Day Jr. FP. 1982. Litter decomposition rates in the seasonally Wetland Scientist through its RAMSAR Students Grants Program. flooded Great Dismal Swamp. Ecology. 63:670–678. Deghi GS, Ewel KC, Mitsch WJ. 1980. Effects of sewage efflu- ent application on litter fall and litter decomposition in cypress swamps. J Appl Ecol. 17:397–408. References Duever MJ, Carlson JE, Riopelle LA. 1984. Corkscrew Swamp: Appleby PG, Oldfield F. 1978. The calculation of lead-210 dates a virgin cypress strand. In: Ewel KC, Odum HT, editors. assuming a constant rate of supply of unsupported Pb to Cypress Swamps. Gainsville (FL): University Presses of the sediment. Catena. 5:1–8. Florida; p. 334–348. Appleby PG, Oldfield F. 1983. The assessment of Pb data Forster P, Ramaswamy V, Artaxo P, Berntsen T, Betts R, Faney from sites with varying sediment accumulation rates. DW, Haywood J, Lean J, Lowe DC, Myhre G, et al. 2007. Hydrobiologia. 103:29–35. Changes in atmospheric constituents and in radiative forcing. Bastviken D, Tranvik LJ, Downing JA, Crill PM, Enrich-Prast A. In: Solomon S, Qin M, Manning D, Chen Z, Marquis M, 2011. Freshwater methane emissions offset the continental Averyt KB, Tignor M, Mill HL, editors. Climate change carbon sink. Science. 331:50. 2007: the physical science basis. Cambridge: Cambridge Battle JM, Golladay SW. 2001. Hydroperiod influence on break- University Press; p. 129–234. down of leaf litter in Cypress-gum wetlands. Am Midl Nat. Franzluebbers AJ, Haney RL, Honeycutts CW, Arshad MA, 146:128–145. Schomberg HH, Hons FM. 2001. Climatic influences on Bernal B, Mitsch WJ. 2012. Comparing carbon sequestration in active fractions of soil organic matter. Soil Biol Biochem. temperate freshwater wetland communities. Glob Change 33:1103–1111. Biol. 18:1636–1647. Frolking S, Roulet N, Fuglestvedt J. 2006. How northern peat- Bernal B, Mitsch WJ. 2013. Carbon sequestration in freshwater lands influence the Earth’s radiative budget: sustained wetlands in Costa Rica and Botswana. Biogeochemistry. methane emission versus sustained carbon sequestration. J 115:77–93. Geophys Res. 111:G01008. Brenner M, Schelske CL, Keenan LW. 2001. Historical rates of Frolking S, Roulet NT. 2007. Holocene radiative forcing impact sediment and nutrient accumulation in marshes of the Upper St. of northern peatland carbon accumulation and methane emis- Johns River Basin, Florida, U.S.A. J Paleolimnol. 26:241–257. sions. Glob Change Biol. 13:1079–1088. Bridgham S, Megonigal J, Keller J, Bliss N, Trettin C. 2006. The Gedney N, Cox PM, Huntingford C. 2004. Climate feedback from carbon balance of North American wetlands. Wetlands. wetland methane emissions. Geophys Res Lett. 31:L20503. 26:889–916–916. Giese LA, Aust WM, Trettin CC, Kolka RK. 2000. Spatial and Brinson MM. 1993. A hydrogemorphic classification for wet- temporal patterns of carbon storage and species richness in lands. Washington (DC): Wetland Research Program, US three South Carolina coastal plain riparian forests. Ecol Eng. Army Corps of Engineers. 15:S157–S170. Casey WP, Ewel KC. 2006. Patterns of succession in forested Gorham E. 1991. Northern peatlands: role in the carbon cycle depressional wetlands in north Florida, USA. Wetlands. and probable responses to climatic warming. Ecol Appl. 26:147–160. 1:182–195. Chimner RA, Ewel KC. 2005. A tropical freshwater wetland: II. Hirano T, Jauhiainen J, Inoue T, Takahashi H. 2009. Controls on Production, decomposition, and peat formation. Wetl Ecol the carbon balance of tropical peatlands. Ecosystems. Manag. 13:671–684. 12:873–887. Chimney MJ, Goforth G. 2001. Environmental impacts to the Jauhiainen J, Takahashi H, Heikkinen JEP, Martikainen PJ, Everglades ecosystem: a historical perspective and restora- Vasander H. 2005. Carbon fluxes from a tropical peat tion strategies. Water Sci Technol. 44:93–100. swamp forest floor. Glob Change Biol. 11:1788–1797. Chimney MJ, Pietro KC. 2006. Decomposition of macrophyte Kayranli B, Scholz M, Mustafa A, Hedmark Å. 2010. Carbon litter in a subtropical constructed wetland in south Florida storage and fluxes within freshwater wetlands: a critical (USA). Ecol Eng. 27:301–321. review. Wetlands. 30:111–124. Chow AT, Dai J, Conner WH, Hitchcock DR, Wang J-J. 2013. Lal R. 2008. Carbon sequestration. Philos Trans R Soc B Biol Dissolved organic matter and nutrient dynamics of a coastal Sci. 363:815–830. freshwater forested wetland in Winyah Bay, South Carolina. MacKenzie AB, Farmer JG, Sugden CL. 1997. Isotopic evidence Biogeochemistry. 112:571–587. of the relative retention and mobility of lead and radiocae- Clymo RS. 1984. The limits to peat bog growth. Philos Trans R sium in Scottish ombrotrophic peats. Sci Total Environ. Soc Lond B Biol Sci. 303:605–654. 203:115–127. Cohen AD. 1973. Petrology of some Holocene peat sediments MacKenzie AB, Hardie SML, Farmer JG, Eades LJ, Pulford ID. from the Okefenokee swamp-marsh complex of southern 2011. Analytical and sampling constraints in Pb dating. Georgia. Geol Soc Am Bull. 84:3867–3878. Sci Total Environ. 409:1298–1304. 28 J.A. Villa and W.J. Mitsch Maltby E, Immirzi P. 1993. Carbon dynamics in peatlands and Reddy KR, DeLaune RD, DeBusk WF, Koch MS. 1993. Long other wetland soils regional and global perspectives. term nutrient accumulation rates in the Everglades. Soil Sci Chemosphere. 27:999–1023. Soc Am J. 57:1147–1155. Marois KC, Ewel KC. 1983. Natural and management-related Ritchie JC, McHenry JR. 1990. Application of radioactive fallout variation in cypress domes. For Sci. 29:627–640. Cesium-137 for measuring soil erosion and sediment accu- McLatchey GP, Reddy KR. 1998. Regulation of organic matter mulation rates and patterns: a review. J Environ Qual. decomposition and nutrient release in a wetland soil. 19:215–233. J Environ Qual. 27:1268–1274. Roulet NT. 2000. Peatlands, carbon storage, greenhouse gases, Miao SL, Miao SL, Sklar FH. 1997. Biomass and nutrient and the Kyoto Protocol: prospects and significance for allocation of sawgrass and cattail along a nutrient gradient Canada. Wetlands. 20:605–615. in the Florida Everglades. Wetl Ecol Manag. 5:245–264. Roulet NT, Lafleur PM, Richard PJH, Moore TR, Humphreys Mitra S, Wassmann R, Vlek PLG. 2005. An appraisal of global ER, Bubier J. 2007. Contemporary carbon balance and late wetland area and its organic carbon stock. Curr Sci. 88:25–35. Holocene carbon accumulation in a northern peatland. Glob Mitsch WJ, Bernal B, Nahlik A, Mander Ü, Zhang L, Anderson Change Biol. 13:397–411. C, Jørgensen S, Brix H. 2013. Wetlands, carbon, and climate Schell WR, Tobin MJ, Massey CD. 1989. Evaluation of trace change. Landsc Ecol. 28:583–597. metal deposition history and potential element mobility in Mitsch WJ, Gosselink JG. 2015. Wetlands. 5th ed. Hoboken selected cores from peat and wetland ecosystems. Trace Met (NJ): John Wiley & Sons. Lakes. 87–88:19–42. Mitsch WJ, Nahlik A, Wolski P, Bernal B, Zhang L, Ramberg L. Smith JT, Clarke RT, Saxén R. 2000. Time-dependent behaviour 2010. Tropical wetlands: seasonal hydrologic pulsing, carbon of radiocaesium: a new method to compare the mobility of sequestration, and methane emissions. Wetl Ecol Manag. weapons test and Chernobyl derived fallout. J Environ 18:573–586. Radioact. 49:65–83. Oldfield F, Appleby PG. 1984. Empirical testing of Pb-dating Todd-Brown KO, Hopkins F, Kivlin S, Talbot J, Allison S. 2012. A framework for representing microbial decomposi- models for lakes sediments. In: Haworth EY, Lund JWG, editors. Lake sediments environmental history. Minneapolis tion in coupled climate models. Biogeochemistry. (MN): University of Minnesota Press; p. 93–124. 109:19–33. Oldfield F, Appleby PG, Cambray RS, Eakins JD, Barber KE, Trumbore SE, Harden JW. 1997. Accumulation and turnover of 210 137 Battarbee RW, Pearson GR, Williams JM. 1979. Pb, Cs carbon in organic and mineral soils of the BOREAS northern and Pu profiles in ombrotrophic peat. Oikos. 33:40–45. study area. J Geophys Res. 102:28817–28830. Osborne TZ, Inglett PW, Reddy KR. 2007. The use of senescent Villa JA. 2014. Carbon dynamics of subtropical wetland com- plant biomass to investigate relationships between potential munities in south Florida [Ph.D. Dissertation]. Columbus particulate and dissolved organic matter in a wetland ecosys- (OH): The Ohio State University. tem. Aquat Bot. 86:53–61. Villa JA, Mitsch WJ. 2014. Methane emissions from five wetland Page SE, Rieley JO, Banks CJ. 2011. Global and regional impor- plant communities with different hydroperiods in the Big tance of the tropical peatland carbon pool. Glob Change Cypress Swamp region of Florida Everglades. Ecohydrol Biol. 17:798–818. Hydrobiol. doi:10.1016/j.ecohyd.2014.07.005 Perry W. 2004. Elements of South Florida’s comprehensive Whalen SC. 2005. Biogeochemistry of methane exchange Everglades restoration plan. Ecotoxicology. 13:185–193. between natural wetlands and the atmosphere. Environ Eng Pettit N, Davies T, Fellman J, Grierson P, Warfe D, Davies P. Sci. 22:73–94. 2011. Leaf litter chemistry, decomposition and assimilation Whiting GJ, Chanton JP. 2001. Greenhouse carbon balance of by macroinvertebrates in two tropical streams. wetlands: methane emission versus carbon sequestration. Hydrobiologia. 1–15. doi:10.1007/s10750–011–0903–1. Tellus B. 53:521–528. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Biodiversity Science, Ecosystem Services & Management Taylor & Francis

Carbon sequestration in different wetland plant communities in the Big Cypress Swamp region of southwest Florida

Loading next page...
 
/lp/taylor-francis/carbon-sequestration-in-different-wetland-plant-communities-in-the-big-L1m1CXXISs

References (67)

Publisher
Taylor & Francis
Copyright
© 2014 Taylor & Francis
ISSN
2151-3732
eISSN
2151-3740
DOI
10.1080/21513732.2014.973909
Publisher site
See Article on Publisher Site

Abstract

International Journal of Biodiversity Science, Ecosystem Services & Management, 2015 Vol. 11, No. 1, 17–28, http://dx.doi.org/10.1080/21513732.2014.973909 Carbon sequestration in different wetland plant communities in the Big Cypress Swamp region of southwest Florida a,b,c a,b Jorge A. Villa and William J. Mitsch * a b Environmental Science Graduate Program, The Ohio State University, Columbus, OH, USA; Everglades Wetland Research Park, Florida Gulf Coast University, 4940 Bayshore Drive, Naples, FL, USA; Grupo de Investigación GAMA, Corporación Universitaria Lasallista, Caldas, Antioquia, Colombia (Submitted 16 February 2014; accepted 3 October 2014; edited by Blanca Bernal) Wetlands offer many ecosystem services, including the long-term sequestering of carbon (C) in soil. Here we present a study of C sequestration rates in a relatively undisturbed wetland landscape of southwest Florida. Accordingly, carbon sequestra- tion was determined in four wetland plant communities and an adjacent hydric pine flatwood community that represent a gradient of inundation extent. Going from the wettest to the driest, communities were designated as: deep slough, bald cypress (Taxodium distichum), wet prairie and pond cypress (Taxodium distichum var. imbricarium). An adjacent hydric pine flatwood community was also included in the study as a reference upland site. Three soil cores were collected from 137 210 each of these communities and were analyzed for total C content. Core samples were also analyzed for Cs and Pb −2 −1 activity to estimate accretion rates. C sequestration rates (g-C m yr ) were the highest in the deep slough (98 ± 9) and bald cypress (98 ± 5) followed by the pond cypress (64 ± 7), wet prairie (39 ± 1) and pine flatwood (22 ± 5). These results suggest that impediment of decomposition by anaerobic conditions caused by prolonged wet cycles, may not account for all the variability in C sequestration rates observed in this subtropical setting. Instead, this variability could also be attributed to other factors like the quantity and chemical composition of the organic material reaching the soil. When methane emissions are taken into account, cypress-dominated (bald and pond cypress) and the deep slough communities act as net carbon sinks. Keywords: carbon sequestration; subtropical wetland; cypress swamp; Everglades; climate regulation; Taxodium distichum Introduction terrestrial world (Whiting & Chanton 2001; Frolking et al. 2006; Page et al. 2011; Mitsch et al. 2013). Climate regulation through carbon (C) sequestration in Values for C fluxes in wetlands, however, are far from wetlands soils may be one of the most important ecosys- definitive (Roulet 2000). For instance, early estimates of C tem services of wetlands in the long term. Carbon is −1 sequestration rates for North America (52.7 Tg-C yr ) sequestered in wetlands when C inputs (productivity and/ −1 and the world (137 Tg-C yr ) had an uncertainty of or sedimentation) surpasses C outputs (decomposition and more than 100% according to Bridgham et al. (2006). C exports) and the remaining organic material, mostly More recently, Mitsch et al. (2013) revised this number senesced plant material, is accumulated in the wetland's and after including a revised area for tropical wetlands and anaerobic sediment layer as a mat of partially decayed their sequestration rates, they estimated that the worldwide organic material, or peat. A fraction of this organic matter −1 sequestration may be around 830 Tg-C yr . Much of our may also be incorporated into the mineral fraction of the current knowledge of wetlands as carbon sources and soil as soil organic C. Globally, it is estimated that 455– sinks comes from extensively studied northern peatlands 700 Pg-C (1 Pg = 10 g) of carbon in organic form is (Gorham 1991; Maltby & Immirzi 1993). In general, wet- stored in wetlands (Mitsch & Gosselink 2015). By com- lands in boreal and subarctic biomes experience low tem- parison, Lal (2008) estimates that there is 1550 Pg-C peratures that are partially responsible for inhibit organic stored in the earth's soil organic C pool. This pool includes matter decomposition and also limit productivity (Clymo various forms of organic C, from highly active humus to 1984; Roulet et al. 2007). In the case of wetlands in warm relatively inert charcoal (Lal 2008). Considering that wet- subtropical and tropical climates, this temperature effect lands occupy only 5–8% of the terrestrial land surface seems to be more complex and less understood. On the (Mitsch & Gosselink 2015), these global estimates rank one hand, wetlands are generally more productive in lower them as the terrestrial ecosystems with the highest C latitudes. On the other hand, higher temperatures in these density (Kayranli et al. 2010), leading scientists from regions could lead to a rate of decomposition that exceeds different disciplines to emphasize the key role that wetland that of productivity (Franzluebbers et al. 2001; Mitsch ecosystems may play in the Earth's radiative forcing et al. 2010). despite their relatively low percent coverage of the *Corresponding author. Email: wmitsch@fgcu.edu © 2014 Taylor & Francis 18 J.A. Villa and W.J. Mitsch Beyond the controlling effect that macroclimate may communities and speculate about their impact on radiative have on productivity and decomposition, C sequestration forcing, as possible net GHG sinks. seems also to differ according to the wetland type or hydrogeomorphic setting and the plant communities therein. For example, in a study of temperate wetlands in Methods different hydrogeomorphic settings, Bernal and Mitsch Study site (2012) found depressional and isolated wetlands to This study was conducted in Corkscrew Swamp Sanctuary sequester two times more C than riverine flow-through −2 −1 in southwest Florida (26° N 23ʹ W, 81° N 35ʹ W). This wetlands (317 versus 140 g-C m yr , respectively). nature preserve, within the Corkscrew Regional Conversely, in a follow-up study in the tropics, the same Ecosystem Watershed, is a collection of relatively undis- authors found that C sequestration rates in tropical, slow- turbed freshwater wetlands characteristic of southwest flow-through wetlands were as much as three to four times Florida (Figure 1). Climate in this portion of Florida is higher than in tropical, depressional and seasonal riverine wetlands (Bernal & Mitsch 2013). They attributed the characterized by very warm and wet summers, mild win- observed differences in C sequestration in these studies ters with occasional light frost and spring droughts. Mean to site-specific factors such as the extent of inundation or annual precipitation and temperature in the headwater of the form of organic matter (recalcitrant versus labile) the watershed are 1201 mm and 23.2°C, respectively entering the systems. The effect of these factors has also (values from 35-yr records since 1971, Station COOP: been noted in other studies of tropical peatland ecosystems 084210, Immokalee, FL, South Florida Water (Chimner & Ewel 2005; Hirano et al. 2009). Management District). A complete ecological description Despite the apparent benefit that wetland ecosystems of Corkscrew Swamp is presented by Duever et al. (1984). have on the reduction of Earth's radiative forcing through C Briefly, Corkscrew Swamp is a riverine cypress strand on sequestration, possible feedbacks to the atmosphere of C in a relatively small and flat watershed (i.e. 32,030 ha). Low the form of methane (CH ) are a real concern (Gedney et al. erosive force of the waterways allows the development of 2004;Bridghamet al. 2006;Kayranliet al. 2010;Bastviken vegetation and accumulation of peat in what would nor- mally be the main stream channel, leading to a diffuse et al. 2011). CH is a greenhouse gas (GHG) produced in system of shallow irregular channels. Mineral substrate wetlands by organic matter decomposition under anaerobic profiles, consisting mainly of sands overlying limestone, conditions (Whalen 2005). Once in the atmosphere, CH has decline along a line perpendicular to the general flow an adverse effect on the radiation budget of earth because of direction, from the surrounding pinelands to the deepest its global warming potential (GWP) that is 25 times greater than the potential of the same mass of carbon dioxide (CO ) over 100 years (Forster et al. 2007). Calculations made in 2005 based on carbon equivalents (i.e. taking into account the GWP of CH ) of the global wetland area and its organic C stock suggested that these ecosystems should be regarded as a relatively small net source of GHG (Mitra et al. 2005). More recently, Mitsch et al. (2013) used a dynamic model of C fluxes from 21 wetlands in different climates to estimate that wetlands in the world may be currently acting as net C −1 sinks of about 830 Tg yr , with an average of −2 −1 118 g-C m yr of net C retention. Accurate estimation of C sequestration in wetlands across different landscapes is critical for developing better C budgets that will ultimately help us understand the role of wetlands as GHG sinks or sources in future climate scenarios. Here, we present a study of C sequestration rates from different wetland plant communities and an adjacent hydric pine flatwood community that are charac- teristics of southwest Florida. These wetland plant com- munities are situated in a single hydrogeomorphic setting, but represent a gradient of inundation. We expected a gradient in C sequestration of the wetland plant commu- nities that will follow the gradient of inundation. Then, we Figure 1. Location of the study sites corresponding to four compare the C sequestration rates with previously pub- different wetland plant communities and an adjacent upland lished CH emissions rates for these same plant commu- community in southwest Florida. The black circles indicate the nities to assess their role as sources or sinks of C GHG. sites from which soil cores were extracted. DS = deep slough, We follow this with a discussion of possible causes for the BC = bald cypress, WP = wet prairie, PC = pond cypress and variability in C sequestration among these wetland PF = pine flatwood (upland). International Journal of Biodiversity Science, Ecosystem Services & Management 19 channels in the strand. Ground surface, however, is rela- Once in the lab, samples corresponding to each tripli- tively flat because organic soils have accumulated in low- cate depth interval were dried at 55°C for 48 hr. After lying areas, creating a generally level topography. The drying, samples were weighed to calculate the soil bulk most significant factor affecting the distribution of the density. Then, debris (small branches) and roots, when plant communities is the hydroperiod (i.e. inundation present, were carefully removed and all samples were extent) that can last for more than 250 days in deep ground to a 2-mm particle size, homogenized and stored sloughs, depending on the amount and distribution of in sealed bags until analysis. Core depths varied between yearly rainfall. Maximum wet season water levels and, to and within sites. Only depth intervals that had the three a lesser extent, minimum dry season water levels can also replicates were used in the analyses and calculations. be important in determining plant community zonation Maximum analyzed core depths (cm) were 32, 48, 32, (Duever et al. 1984). 26 and 14 for deep slough, bald cypress, wet prairie, We selected four distinct wetland plant communities pond cypress and pine flatwood, respectively. across the gradient of inundation in the Corkscrew Swamp landscape. The plant communities investigated were desig- Accretion rates nated as: (1) Deep slough, mostly bare soil with sparse emergent macrophytes like Peltandra virginica, Thalia Accretion rates were determined non-destructively by 137 210 geniculata and Pontederia cordata, a subcanopy domi- Cs and Pb activity in each 2-cm soil measuring nated by Annona glabra, Fraxinus caroliniana and interval (Craft & Richardson 1993; Bernal & Mitsch Cephalanthus occidentalis and an open canopy of tall 2013). Composite subsamples (~10 g) corresponding to Taxodium distichum, (2) Bald cypress, also bare soil with each depth interval at each plant community were run in a a sparse understory dominated by Osmunda regalis in high-efficiency Germanium Detector (GL 2820R, small mounds created by dead trees and roots and Canberra). Cs is a man-made radionuclide distributed Crinum americanum in small depressions; both under a worldwide primarily as the consequence of atmospheric canopy and subcanopy similar in composition to that of deposition after nuclear weapons testing (Smith et al. deep slough, (3) Wet prairie, co-dominated by Cladium 2000). Depositional patterns of this isotope normally exhi- jamaicense, P. cordata, Ludwigia sp., Alisma subcordatum bit a distinct peak in the activity in the soil profile that Raf. with no bare soil, and (4) pond cypress, a dense stand corresponds to year 1964, one year after the Test Ban of Taxodium distichum var. imbricarium relatively smaller Treaty (Ritchie & McHenry 1990). Thus, by knowing than the trees in the bald cypress community but with a the depth interval with the peak in Cs activity, the relatively closed canopy, with Ludwigia sp. and Sagittaria average accretion rate can be estimated as the depth of graminea primarily covering the forest floor. A hydric the interval with the peak in Cs activity divided by the pine flatwood (Pinus elliottii, Serenoa repens and time from 1964 to the year of sampling. 210 210 Aristida stricta) community that was never flooded during Pb is a naturally occurring radioisotope. Pb can the study period was also included as a reference upland be formed in wetlands from in situ decay of Ra (sup- 210 210 community. Inundation during 2011 and 2012 had a dura- ported Pb). Pb can also be deposited in wetlands tion in days of 264 and 198; 181 and 149; 138 and 117; from the decay of Rn in the atmosphere, or indirectly and 125 and 67 for deep slough, bald cypress, wet prairie via the water column (unsupported Pb) (MacKenzie and pond cypress, respectively (Villa 2014). et al. 2011). This unsupported component of the Pb inventory can be used to establish chronologies of wetland sediments or peat because once it is incorporated in the soils it decays exponentially with time in accordance with Sample collection and preparation its half-life (22.2 yr) (Oldfield & Appleby 1984). To Three 6.5-cm-diameter cores were collected in each plant establish peat chronologies in our plant communities, we community (15 cores total) using a universal core head assumed a constant rate of supply of unsupported Pb sediment sampler (WaterMark) equipped with ~60-cm and applied the constant-rate-of-supply (CRS) model polycarbonate barrels. Cores in deep slough, wet prairie described by Appleby and Oldfield (1978, 1983) and and pond cypress were collected between June and Oldfield and Appleby (1984). The average of the relatively September 2011. Cores in bald cypress and pine flatwood constant down-core total Pb activity in the soil profile were collected between March and June 2012. Distance was assumed to represent the supported Pb activity between cores was less than 1 m, except for those from the (Craft & Richardson 1998; Brenner et al. 2001). bald cypress community, in which one core was collected about 5 m apart from the other two. When sites had Soil analyses and carbon sequestration rates standing water, surface water in the corer was siphoned off before processing the soil core. Processing in the field Duplicate samples corresponding to each core 2-cm depth consisted of sectioning the core into 2-cm depth intervals, interval in each plant community were analyzed for total then packaging and sealing them in separate plastic bags. carbon (TC%) and inorganic carbon (IC%) in a Total During sectioning, we cleaned the work area after packa- Carbon Analyzer for soil samples (TOC-V series, SSM- ging each sample to avoid any possible soil mixing. 5000A; Shimadzu Corporation, Kyoto, Japan). TC was 20 J.A. Villa and W.J. Mitsch determined by total combustion at 900°C, whereas IC was this analysis because it acted as a net sink for CH during −1 determined by digestion with 10 mol L H PO at 200°C. the study period considered in Villa and Mitsch (2014). 3 4 The organic carbon (OC) fraction per depth was calculated as The GWPs used were the three reported in Forster et al. the difference between TC and IC. The soil bulk density at (2007) (i.e. 72 for 20 yr, 25 for 100 yr and 7.6 for 500 yr). each depth interval was calculated with the dry weight and This GWP is an emission metric proposed by the the volume. Intergovernmental Panel on Climate Change to assess the −1 Soil TC concentration (g-C kg )ofeachdepth interval overall climate response associated with a forcing agent was obtained by multiplying the percentage value of C by 10. (i.e. GHGs). It compares integrated radiative efficiencies TC was then multiplied by the corresponding dry weight to of GHGs to that of CO , assumed as the standard gas, over obtain the mass of TC per interval. The mass of TC was specified time periods. Decrease over time of the GWPs integrated in the profile down to the age of the peat that was results from the reduced radiative forcing of CH given its 137 210 estimated with Cs and Pb. As these depths did not lifetime of 12 yr (Forster et al. 2007). coincide with the 2-cm intervals, we calculated the dry weight To determine if the soil in a plant community was acting as in each bottommost interval by multiplying its height by the a source or sink of C GHG we established a GHG compensa- corresponding bulk density and dividing by the area of the tion boundary, in which the GWP multiplied by CH /CO 4 2 core. Then, the integrated mass of C and the integrated dry ratio was equal to 1 [GWP (CH /CO ) = 1] (Whiting & 4 2 weights were divided by the area of the core and the number of Chanton 2001). This boundary was constructed by plotting years from the age of the peat to the year of sampling to first the three GWPs (y-axis) versus their respective compen- −2 −1 estimate the C sequestration rates (g-C m yr )and mass sation boundary value [GWP = (CO /CH )] and then tracing 2 4 −2 −1 accretion rates (g m yr ), respectively. an empirical best fit line for these three points. Then, we plotted the CH /CO ratios calculated for our plant commu- 4 2 nitiesversusthe GWPofCH for 20, 100 and 500 yr. Accordingly, given a specific GWP, a system would be acting Carbon sequestration versus methane emissions as a net GHG source if a system has a CH /CO ratio that falls 4 2 To assess the role that wetland plant communities in south- in the area above and to the right of this boundary. Conversely, west Florida may be playing in a climate change context, it would be acting as a GHG sink if the ratio falls into the area we related the CH /CO ratio to the GWPs of CH in an 4 2 4 below and to the left of this boundary. approach similar to that presented by Whiting and Chanton (2001). The CH /CO ratio was calculated using 4 2 the average 2-yr CH emissions measured by Villa and Results −2 −1 Mitsch (2014) (26.9 g CH m yr in deep slough, 2.7 g −2 −1 −2 −1 Soil profiles CH m yr in bald cypress, 25.9 g CH m yr in wet 4 4 −2 −1 prairie and 3 g CH m yr in pond cypress). The C The variation of soil bulk density and carbon concentra- sequestration rates in this study assumed as the net atmo- tions with depth for each plant community is shown in spheric CO assimilated by the system (e.g. Mitsch et al. Figure 2 (a and b respectively). The cores extracted at the 2013). The pine flatwood community was excluded from bald cypress community had a thick root zone between 20 Figure 2. Soil profile at each wetland plant community showing: (a) bulk density and (b) carbon concentration. International Journal of Biodiversity Science, Ecosystem Services & Management 21 and 28 cm depth that was not included in the analyses. wet prairie and the pine flatwood tend to be more subject Bulk density remained low through most of the depth to erosive and re-distribution processes. −3 sampled in deep slough and bald cypress (i.e. <1 g cm ), The CRS model applied to these unsupported inven- −3 averaging 0.30 and 0.10 g cm respectively. In turn, bulk tories dated soil intervals back to 1897 in the deep slough density showed a significant increase with depth in the wet community (Figure 3). However, the mean ± standard prairie, pond cypress and pine flatwood communities as error of the minimum detection limits (MDL) for the the peat layer was gradually replaced by sand. unsupported Pb measurements in all communities, −3 Accordingly, bulk density (g cm ) in these communities including the pine flatwood community, was −1 went from 0.39, 0.17 and 0.63 in the surface, 2-cm depth 1.4 ± 0.03 pCi g . According to MacKenzie et al. −1 interval, to values over 1.00 at the 8, 10 and 4 cm depth (2011), MDL of 0.27 pCi g lead to potential bias intervals, respectively. towards erroneous old values for ages older than about Most of the C measured in the different communities 80 yr. To avoid bias induced by the MDL in our measure- was in organic form (>99%). Soil TC concentrations ments, we calculate carbon sequestration rates since ~1950 (i.e. ~60 yr) in the four wetland communities. In the pine decreased with depth in all wetland communities and the upland site. In the deep slough and bald cypress, this flatwood, only the top interval could be dated to 1956 with decrease was less pronounced than in the other commu- the CRS model and therefore C sequestration and bulk −1 nities, going from 435.8 and 415.6 g-C kg at the soil accretion were determined in this community since that −1 surface to 76.5 and 35 g-C kg at the deepest depth year. Table 1 summarizes mean accretion rates using the interval, respectively. TC concentrations decreased sharply Cs peak activity and the CRS model, as well as the net from the soil surface in the wet prairie and pond cypress and mass accretion rates and the carbon concentration communities and remained low throughout the sandy since 1950. The accretion rates estimated with Cs layer. In the hydric pine flatwood community, where the were fairly similar to those estimated using the Pb soil consisted primarily of fine sand, TC concentration was CRS model in the pond cypress and pine flatwood. −1 low throughout the profile. Values (g-C kg ) in these However, in the case of the wet prairie, the rate from the three communities (wet prairie, pond cypress and pine Cs peak was considerably lower. Carbon sequestration flatwood) went from 145.3, 391.8 and 5.9 at the soil sur- rates (mean ± standard error) in wetland plant commu- −2 −1 face to 10.8, 3.81 and <0.01, respectively. nities ranged from 98 ± 9 g-C m yr in deep slough and −2 −1 bald cypress 98 ± 5, to 39 ± 1 g-C m yr in wet prairie. Carbon sequestration in the upland pine flatwood commu- −2 −1 Soil accretion and carbon sequestration rates nity was 22 ± 5 g-C m yr , representing a more than Cs activity showed distinct peaks in the wet prairie, 4-fold increase from the surrounding upland communities pond cypress and pine flatwood community. Peaks in the to the wettest wetland communities (Figure 5). deep slough and bald cypress communities were not clearly identifiable. High Cs activity in the profile of Carbon sequestration versus methane emissions these two communities was rather evenly distributed across different depth intervals (Table 1, Figure 3). Our assessment indicated that soil in the bald and pond Therefore we used only Pb to determine the accretion cypress communities function as a net C GHG sink, inde- rates in the different communities. Total integrated unsup- pendent of the time horizon for which uptake and emis- 210 −2 ported Pb ranged from 5.2 pCi cm in wet prairie to sions are considered. The deep slough community acts as a −2 28.6 pCi cm in bald cypress and had a mean ± standard net GHG source when considered on a 20- and 100-yr −2 error of 15.6 ± 4.4 pCi cm (Figure 4). The distribution of horizon, but it switches to a net sink when the analysis is this unsupported Pb suggests that there is preferential considered for 500 yr. The wet prairie community deposition towards the forested communities dominated remained a GHG source regardless of the time horizon by cypress (deep slough, bald and pond), whereas the used in the analysis (Figure 6). 137 210 Table 1. Mean accretion rates using the Cs peak activity and the CRS model ( Pb), net and mass accretion rates, and the mean (range) of carbon concentration since 1950 for the soils in each community. Mean Mean accretion accretion Net accretion Mass Mean carbon Carbon 137 210 rate ( Cs) rate ( Pb) since 1950 accretion rate concentration sequestration −1 −1 −2 −1 −1 −2 −1 Plant community (mm yr ) (mm yr ) (cm) (g-m yr ) (g-C kg ) (g-C m yr ) Deep slough – 1.6 9.7 229.8 438 (321–511) 98 ± 9 Bald cypress – 2.4 12.2 217.6 380 (242–425) 98 ± 5 Wet prairie 0.4 0.9 5.3 508.7 83 (35–156) 39 ± 1 Pond cypress 0.9 1.1 6.5 238.1 257 (27–422) 64 ± 7 Pine flatwood* 0.4 0.3 2 226.7 59 (37–91) 22 ± 5 Note: *This plant community was never inundated during the period between June 2011 and June 2013. The accretion rate of this community was calculated from 1956. 22 J.A. Villa and W.J. Mitsch 137 210 Figure 3. Cs and Pb activity in four different wetland plant communities (a, b, c and d) and an adjacent upland site (e). Left and 137 210 137 center columns represent total Cs and Pb activity through the soil profile, respectively. Dates corresponding to the peak of Cs and those obtained using the constant rate of supply of unsupported Pb (CRS) model are presented in the second y-axis. Right column contains Pb as a function of cumulative mass in log scale. International Journal of Biodiversity Science, Ecosystem Services & Management 23 Figure 4. Integrated unsupported Pb activity for four differ- ent wetland plant communities and an adjacent upland commu- Figure 6. Wetland plant communities in southwest Florida as nity. DS = deep slough, BC = bald cypress, WP = wet prairie, sinks or sources of greenhouse gases (i.e. CH and CO ) eval- 4 2 PC = pond cypress and PF = pine flatwood (upland). uated for three different time horizons. The curved line represents the greenhouse gas compensation boundary and is an empirical best fit of three global warming potentials contemplated in Forster et al. (2007). Values below or left of the compensation boundary indicate a net sink of GHG, whereas values above and right of the boundary net source of GHG. and pine flatwood), Cs peaks were measured, yet the accretion rates estimated with the two methods ( Cs peak and Pb CRS model) were somehow different, leading to further discrepancies in the calculation of the C sequestration rates. Moreover, the use of Cs in envir- onments where sands dominate the profile, as is the case in these three communities, must be regarded with caution because an increase in sand-size particles in soil profiles Figure 5. Carbon sequestration and inundation extent in wet- will cause a decrease in the activity of Cs that cannot be land plant communities of southwest Florida. Bars represents related to the atmospheric fallout rates of Cs (Ritchie & mean carbon sequestration rates (n = 3) for: DS = deep slough, BC = bald cypress, WP = wet prairie, PC = pond cypress and McHenry 1990). Altogether, our results highlight the PF = pine flatwood. Error bars denote the standard error of the potential value of using Pb as an alternative, yet inde- mean. Circles represent the annual average 2011 and 2012 inun- 137 pendent method to date soils using Cs in wetlands with dation extent for each corresponding plant community. high organic matter and low clay content or those with profiles that are dominated by sands, like the ones found in this study. Mean accretion rates since 1950 in the cypress-domi- Discussion nated communities were similar to those reported for Soil accretion rates ~100 yr in different cypress communities in Georgia by 137 −1 The estimation of soil accretion using the Cs peak Craft and Casey (2000) (i.e. 0.8–2.2 cm yr ). We could activity in the soil profile was not a reliable method for not find in the literature accretion rates for sites with plant the deep slough and bald cypress communities. The communities similar to the wet prairie and pine flatwood absence of Cs-binding clay particles (Schell et al. communities considered in this study. However, the accre- 1989; MacKenzie et al. 1997; Brenner et al. 2001) and tion rate in the wet prairie was lower than those reported for possibly active uptake of Cs by plants (Oldfield et al. ~30 yr by Craft and Richardson (1993)in unenriched 1979) could explain the profiles with evenly distributed marshes of the Everglades with short inundation periods 137 137 −1 Cs near the topsoil depth intervals. Moreover, Cs (i.e. 1.6–2.4 cm yr ). The mean accretion rates in the activity in these two communities was measured at depths different communities followed closely the trend of the 210 210 that, according to our Pb dating, were decades older distribution of unsupported Pb in the soil profiles than the start of atomic bomb testing. This is not an (Table 1, Figure 4). This distribution of unsupported Pb unusual finding in wetland environments of Florida (e.g. also suggests that particles from wet prairie and pine flat- Brenner et al. 2001) and supports the idea of post-deposi- wood (lower values) are being either eroded and deposited tional mobility of this radionuclide through the soil profile. in the adjacent forested communities (higher values) or For the other three communities (wet prairie, pond cypress re-deposited within the same community. More Pb 24 J.A. Villa and W.J. Mitsch profiles in different sites within each community should T. geniculata and C. jamaicense, respectively (i.e. 17% help determine which of these two processes is dominant. versus 6.9% and 9.8%, respectively), and also has higher Also, despite the fact that wet prairie had low integrated C:N ratios (i.e. 51.5 versus 14.1 versus 24.1, respectively) unsupported Pb in the soil profile, the specific mass (Osborne et al. 2007). Secondly, decomposition rates, and accretion rate was more than double the rate of the other therefore C turnover, are up to one order of magnitude communities. We can only explain this by a relative higher higher in other co-dominant plant species of the wet proportion of sand in the profile of this particular site that prairie when compared with that of cypress (Deghi et al. has accumulated since 1950. 1980; Battle & Golladay 2001; Chimney & Pietro 2006). Differences measured in C sequestration rates of Corkscrew plant communities can also be attributed to the Carbon sequestration in the different wetland plant quantity of the organic matter entering the system. For communities instance, Cohen (1973) estimated that 40% of the peat in High C sequestration rates in tropical wetlands of warm the Okefenokee Swamp, southern Georgia, was produced in and wet climates have been attributed primarily to the low situ by roots. Cypress-dominated communities in decomposition rates in such environments (Chimner & Corkscrew have a belowground productivity in the top −2 (Duever et al. Ewel 2005; Jauhiainen et al. 2005; Hirano et al. 2009). 30 cm ranging from 1633 to 1946 g m 1984), whereas belowground productivity in communities Prolonged cycles with standing water above the soil sur- face or waterlogged soils may well enhance C accumula- dominated by sawgrass, one of the co-dominant species in −2 tion by impeding aerobic decomposition and attenuating the wet prairie, is around 390 g m (Miao et al. 1997). warm air temperatures. Our results, which show the varia- Despite existing differences in quality of the organic tion in C sequestration along a gradient of inundation in a matter litter composition and quantity of organic matter single hydrogeomorphic setting, partially support this being incorporated into the soils, the fate of the organic claim. We found a general trend in the inundation gradient matter that reaches the soil surface is not clear yet in this with lower C sequestration rates corresponding with com- dynamic environment of contrasting dry and wet conditions munities with shorter inundation periods, confirming our (i.e. aerobic versus anaerobic processes). Future research initial prediction (Figure 5). However, this gradient was should focus on the synergistic effects that alternating aero- not straightforward. The deep slough community and bald bic and anaerobic conditions (McLatchey & Reddy 1998; cypress had very similar C sequestration rates regardless Chimner & Ewel 2005), timing of litter fall, quantity and of having different inundation periods. Also, the wet quality of litter (Pettit et al. 2011;Chowet al. 2013), and prairie community had lower C sequestration rates than microbial and fungal community activity (Pettit et al. 2011; the pond cypress community despite having a longer Todd-Brown et al. 2012) may be playing in the decomposi- inundation period. Therefore, the slowing of decomposi- tion of organic matter and hence in the variability observed tion by prolonged inundation periods can only explain to in the C sequestration rates. some extent the differences in C sequestration between the plant communities studied in Corkscrew Swamp. Carbon sequestration in southwest Florida wetland Differences in C sequestration rates between wetlands ecosystems in tropical and subtropical wetlands can be attributed to the quality of the organic matter entering the system. For To better assess the role that wetland ecosystems of south- instance, Bernal and Mitsch (2013) speculated about the west Florida may be playing in the sequestering of carbon at a wider scale, we compared the rates measured in this study effect of recalcitrant matter in the higher C sequestration rates observed in sites dominated by forested communities to those reported in previous studies from tropical and sub- when compared to macrophyte-dominated sites in different tropical zones of America and Africa (Table 2). To avoid wetlands of Costa Rica and Botswana. Day (1982), in a confusion introduced by the use of different methodologies study in the Great Dismal Swamp, Virginia, attributed in the estimation of the carbon sequestration rates, we only differences in the decay rates to the chemical characteris- selected studies which used radiometric dating, either with 137 210 tics of the litter, rather than to the environmental condi- Cs or with Pb.We thenarrangedwetlandsbygeo- tions resulting from flooding. Specifically, increases in morphic setting (Brinson 1993). According to these studies, decay rates were the result of relatively higher nutrient C sequestration in tropical and subtropical zones ranges −2 −1 content (nitrogen and phosphorus), and low lignin and between 18 and 232 g-C m yr . Also, rates (mean ± stan- tannic acid content, and C:N ratios. These litter composi- dard error) tend to be higher in riverine, low-gradient allu- −2 −1 tion differences could help explain why, in our study, C vial (100 ± 25 g-C m yr ), than in depressional −2 −1 sequestration rates in the wet prairie were lower when (62 ± 18 g-C m yr ) or riverine, low-gradient, non-alluvial −2 −1 compared with the adjacent cypress-dominated commu- wetlands (56 ± 12 g-C m yr ). The rate for the latter nities. In the first place, leachates from cypress leaves, geomorphic setting, excluding the data in this study, is −2 −1 the dominant taxa and main input of organic matter in 57 ± 17 g-C m yr . bald cypress and pond cypress communities, have higher The C sequestration in the wetland communities that we −2 −1 percent lignin content than leachates from co-dominant studied ranged from 39 to 98 g-C m yr , in the lower species in the deep slough and wet prairie like middle portion of the rates observed along the tropical/ International Journal of Biodiversity Science, Ecosystem Services & Management 25 Table 2. Mean carbon sequestration rates from tropical and subtropical wetlands of America and Africa featuring their geomorphic setting, type, dominant plant species and general location. 137 210 The rates were calculated using Cs to estimate the accretion rates or Pb (*). Values in parentheses indicate reported ranges. ND = Not described. Geomorphic setting and C sequestration rate −2 −1 wetland type Dominant plant sp Location Latitude (g-C m yr ) Reference Depressional Rainforest swamp Spathiphyllum friedrichsthalii Costa Rica 10 N 61* Bernal and Mitsch (2013) Cypress swamp Taxodium distichum var. imbricarium, Nyssa aquatica, Georgia, USA 31 N 31 Craft and Casey (2000) Cephalanthus occidentalis Cypress swamp Taxodium distichum var. imbricarium, emergent grasses Georgia, USA 31 N 31 Craft and Casey (2000) Marsh Acalypha diversifolia, Gynerium sagittatum Costa Rica 10 N 131* Bernal and Mitsch (2013) Marsh ND Georgia, USA 31 N 56* Craft and Casey (2000) Mean ± SE 62 ± 18 Riverine, low gradient alluvial Rainforest swamp Chamaedorea tepejilote, S. Friedrichsthalii, Costa Rica 10 N 232* Bernal and Mitsch (2013) P. macroloba, Calathea crotalifera Cypress-Tupelo swamp Taxodium distichum, Nyssa aquatica Georgia, USA 31 N 18 Craft and Casey (2000) Marsh S. friedrichsthalii Costa Rica 10 N 222* Bernal and Mitsch (2013) Marsh Eichhornia crassipes, Thalia geniculata Costa Rica 10 N 80* Bernal and Mitsch (2013) Marsh T. domingensis Costa Rica 10 N 84* Bernal and Mitsch (2013) Marsh Eleocharis sp., Paspalidium sp., Oxycaryum cubense Costa Rica 10 N 89* Bernal and Mitsch (2013) Marsh Oryza longistaminata, Schoenoplectus corymbosus Botswana 19 S 42 (33–53) Bernal and Mitsch (2013) Marsh ND Florida, USA 27 N 202 (127–259)* Brenner et al. (2001) Marsh Cladium jamaicense Florida, USA 26 N 127 (86–158) Reddy et al. (1993) Mean ± SE 100 ± 25 Riverine, low gradient non alluvial Cypress swamp ND Florida, USA 29 N 122 Craft et al. (2008) Cypress swamp ND Georgia, USA 31 N 36 (15–56) Craft et al. (2008) Cypress swamp Taxodium distichum, Annona glabra, Fraxinus caroliniana, Florida, USA 26 N 98 (81–112) This study Cephalanthus occidentalis, Peltandra virginica, Thalia geniculate Cypress swamp Taxodium distichum, Annona glabra, Fraxinus caroliniana, Florida, USA 26 N 98 (88–106) This study Cephalanthus occidentalis, Crinum americanum Cypress swamp Taxodium distichum var. imbricarium, Ludwigia sp., Florida, USA 26 N 64 (49–71) This study Sagittaria graminea Marsh ND Georgia, USA 30 N 24 Craft et al. (2008) Marsh Cladium jamaicense Florida, USA 26 N 94 (54–130) Craft and Richardson (1993) Marsh Cladium jamaicense Florida, USA 26 N 19 Craft et al. (2008) Marsh Cladium jamaicense Florida, USA 26 N 46 (37–56) Craft et al. (2008) Wet prairie Cladium jamaicense, Pontederia cordata, Ludwigia sp., Alisma Florida, USA 26 N 39 (37–40) This study subcordatum Raf. Mean ± SE 62 ± 12 26 J.A. Villa and W.J. Mitsch subtropical latitudinal range. Bernal and Mitsch (2013)in a measure or for water diversion. Considering the impor- study of 12 freshwater wetland communities in contrasting tance that the duration of inundation and the maximum wet and dry tropical climates found a Shelford-type nonlinear and minimum water levels have on the plant community relationship between C sequestration rates and the P/T zonation (Duever et al. 1984), it is also reasonable to ratio (ratio of mean annual precipitation and air temperature, expect a shift in the plant communities. In general, −2 −1 10 mm yr /°C). According to this study, this ratio, a proxy changes favoring the areal expansion of cypress-domi- for water availability, suggests a midpoint of the P/T ratio at nated forest could enhance the net sink of GHG of the which C sequestration in wetlands from lower latitudes whole landscape. However, the practice of predicting the seems to be enhanced. Based on the finding in their study, trajectory of plant communities in Corkscrew is rather this point is around a P/T ratio of 1.2 with minimum and challenging. Despite the fact that inundation is the main maximum sequestration rates at ratios near 0.2 and 1.8, variable in the distribution of the plant communities, the respectively. However, regardless of the P/T ratios, the isolated effects of this single variable could be hard to same authors also noted that the hydrogeomorphic type predict. was a key factor in determining the carbon sequestration Some studies on the successional dynamics of pond capacity of their different wetland soils. Located in one single cypress-dominated communities in depressional swamps hydrogeomorphic setting, our wetland communities have a in central Florida (Casey & Ewel 2006) and riparian forests P/T ratio of 0.5 (35-yr average), suggesting that wetlands in in South Carolina (Giese et al. 2000) suggest that increased southwest Florida may not be at the optimal climatic location inundation periods and water levels may induce a shift in for sequestering carbon when compared with other tropical the pond cypress community towards a plant community and subtropical freshwater wetlands. However, the lack of dominated by species of hardwood forest like Nyssa spp., organic matter-binding parent materials in the soils of Salix spp., Gordonia lasianthus and Cephalanthus occiden- Corkscrew, where organic soils develop on top of a mineral talis. Whether or not bald cypress stands will develop later substrate consisting typically on sands (Duever et al. 1984), in the succession is still to be determined, but regardless, may also be a factor determining the comparatively lower the new community will likely continue to function as a carbon sequestration rates (Trumbore & Harden 1997). GHG sink. Conversely, dryer conditions with shorter inun- Nonetheless, the role that these wetland communities are dation periods and lower water levels may lead to a dom- playing in carbon sequestration at a landscape scale should inance of pine flatwood communities, that could possibly not be undervalued. Our results indicate that wetlands in lead also to the establishment of sedge and grass-dominated southwest Florida can sequester up to four times more C in communities (Marois & Ewel 1983), altogether leading to a the soils than adjacent pine flatwood upland communities. net increase in GHG emissions. Implication of the balance between carbon sequestration Conclusions and methane emissions In this study, C sequestration in the soil of four different In its present state, the Corkscrew Swamp watershed repre- major wetland communities of southwest Florida was sents a relatively undisturbed mosaic of wetland ecosystems investigated. Sequestration rates were the highest in the that have developed in response to long-term climatic, hydro- community with the longest inundation, but did not follow logic, edaphic and fire influences (Duever et al. 1984). a discernible pattern with the duration of inundation for Therefore, the 500-yr time horizon (GWP = 7.6) used in the rest of communities considered across the landscape. our analysis may be more realistically describing the emis- Overall, the slowed decomposition caused by prolonged sions/uptake status of GHG in the Corkscrew wetland plant anaerobic periods brought about by high water levels and communities studied. Any possible positive radiative poor drainage observed in other tropical wetlands could strength caused by CH emissions during the first stages of 4 only partially explain the rates of C accumulation found in peat formation in the deep slough in the past, represented by this subtropical setting. Rather, the rates observed in these the CH /CO ratios in the 20- and 100-yr horizons, might 4 2 communities that alternate between prolonged wet and dry have been offset by now by its long-term C sequestration cycles may also be determined to some extent by the (e.g. Frolking et al. 2006; Frolking & Roulet 2007). chemical composition of the organic matter reaching the Accordingly, conservation strategies to maintain and soil. Over an extended time period (500 yr), the long-term enhance the wetland GHG sinking potential should focus C sequestration of the cypress-dominated (bald and pond) on the cypress-dominated and deep slough communities. and deep slough communities outweighs their CH emis- Current efforts to restore the historical hydrological sions. These communities should therefore be the focus of flows in the Everglades region (southern portion of conservation strategies to enhance ecosystem service of Florida) features the redirection of unused freshwater for climate regulation offered by wetlands in south Florida. restoration purposes and human demands (Chimney & Goforth 2001; Perry 2004). Under this scenario, it is reasonable to expect that the inundation cycles will be Acknowledgments modified in the different wetland ecosystems of the entire This study was conducted first at the Olentangy Wetland Research region including Corkscrew, either as a restoration Park at The Ohio State University (mid 2010–mid 2012) and later at International Journal of Biodiversity Science, Ecosystem Services & Management 27 the Everglades Wetland Research Park at Florida Gulf Coast Craft C, Washburn C, Parker A. 2008. Latitudinal trends in University (mid 2012–mid 2014). Authors wish to acknowledge organic carbon accumulation in temperate freshwater peat- the numerous volunteers that helped with field and laboratory work. lands. In: Vymazal J, editor. Wastewater treatment, plant Also, to Blanca Bernal for her help in the initial stages of this dynamics and management in constructed and natural wet- research. Anonymous reviewers provided key directions for the lands. New York (NY): Springer Science and Business data analysis and discussion of results that considerably improved Media B. V.; p. 23–31. the final version of this manuscript. Director Jason Lauritsen, Dr. Craft CB, Casey WP. 2000. Sediment and nutrient accumulation Shawn Liston and Dr. Michael Knight provided permission and in floodplain and depressional freshwater wetlands of help with logistics at the Corkscrew Swamp Sanctuary. Georgia, USA. Wetlands. 20:323–332. Craft CB, Richardson CJ. 1993. Peat accretion and N, P and organic C accumulation in nutrient-enriched and unenriched Everglades peatlands. Ecol Appl. 3:446–458. Funding Craft CB, Richardson CJ. 1998. Recent and long-term organic Funding for this project came from the National Science soil accretion and nutrient accumulation in the Everglades. Foundation (Grants CBET [1033451] and [0829026]). Partial Soil Sci Soc Am J. 62:834–843. funding for this study was also provided by the Society of Day Jr. FP. 1982. Litter decomposition rates in the seasonally Wetland Scientist through its RAMSAR Students Grants Program. flooded Great Dismal Swamp. Ecology. 63:670–678. Deghi GS, Ewel KC, Mitsch WJ. 1980. Effects of sewage efflu- ent application on litter fall and litter decomposition in cypress swamps. J Appl Ecol. 17:397–408. References Duever MJ, Carlson JE, Riopelle LA. 1984. Corkscrew Swamp: Appleby PG, Oldfield F. 1978. The calculation of lead-210 dates a virgin cypress strand. In: Ewel KC, Odum HT, editors. assuming a constant rate of supply of unsupported Pb to Cypress Swamps. Gainsville (FL): University Presses of the sediment. Catena. 5:1–8. Florida; p. 334–348. Appleby PG, Oldfield F. 1983. The assessment of Pb data Forster P, Ramaswamy V, Artaxo P, Berntsen T, Betts R, Faney from sites with varying sediment accumulation rates. DW, Haywood J, Lean J, Lowe DC, Myhre G, et al. 2007. Hydrobiologia. 103:29–35. Changes in atmospheric constituents and in radiative forcing. Bastviken D, Tranvik LJ, Downing JA, Crill PM, Enrich-Prast A. In: Solomon S, Qin M, Manning D, Chen Z, Marquis M, 2011. Freshwater methane emissions offset the continental Averyt KB, Tignor M, Mill HL, editors. Climate change carbon sink. Science. 331:50. 2007: the physical science basis. Cambridge: Cambridge Battle JM, Golladay SW. 2001. Hydroperiod influence on break- University Press; p. 129–234. down of leaf litter in Cypress-gum wetlands. Am Midl Nat. Franzluebbers AJ, Haney RL, Honeycutts CW, Arshad MA, 146:128–145. Schomberg HH, Hons FM. 2001. Climatic influences on Bernal B, Mitsch WJ. 2012. Comparing carbon sequestration in active fractions of soil organic matter. Soil Biol Biochem. temperate freshwater wetland communities. Glob Change 33:1103–1111. Biol. 18:1636–1647. Frolking S, Roulet N, Fuglestvedt J. 2006. How northern peat- Bernal B, Mitsch WJ. 2013. Carbon sequestration in freshwater lands influence the Earth’s radiative budget: sustained wetlands in Costa Rica and Botswana. Biogeochemistry. methane emission versus sustained carbon sequestration. J 115:77–93. Geophys Res. 111:G01008. Brenner M, Schelske CL, Keenan LW. 2001. Historical rates of Frolking S, Roulet NT. 2007. Holocene radiative forcing impact sediment and nutrient accumulation in marshes of the Upper St. of northern peatland carbon accumulation and methane emis- Johns River Basin, Florida, U.S.A. J Paleolimnol. 26:241–257. sions. Glob Change Biol. 13:1079–1088. Bridgham S, Megonigal J, Keller J, Bliss N, Trettin C. 2006. The Gedney N, Cox PM, Huntingford C. 2004. Climate feedback from carbon balance of North American wetlands. Wetlands. wetland methane emissions. Geophys Res Lett. 31:L20503. 26:889–916–916. Giese LA, Aust WM, Trettin CC, Kolka RK. 2000. Spatial and Brinson MM. 1993. A hydrogemorphic classification for wet- temporal patterns of carbon storage and species richness in lands. Washington (DC): Wetland Research Program, US three South Carolina coastal plain riparian forests. Ecol Eng. Army Corps of Engineers. 15:S157–S170. Casey WP, Ewel KC. 2006. Patterns of succession in forested Gorham E. 1991. Northern peatlands: role in the carbon cycle depressional wetlands in north Florida, USA. Wetlands. and probable responses to climatic warming. Ecol Appl. 26:147–160. 1:182–195. Chimner RA, Ewel KC. 2005. A tropical freshwater wetland: II. Hirano T, Jauhiainen J, Inoue T, Takahashi H. 2009. Controls on Production, decomposition, and peat formation. Wetl Ecol the carbon balance of tropical peatlands. Ecosystems. Manag. 13:671–684. 12:873–887. Chimney MJ, Goforth G. 2001. Environmental impacts to the Jauhiainen J, Takahashi H, Heikkinen JEP, Martikainen PJ, Everglades ecosystem: a historical perspective and restora- Vasander H. 2005. Carbon fluxes from a tropical peat tion strategies. Water Sci Technol. 44:93–100. swamp forest floor. Glob Change Biol. 11:1788–1797. Chimney MJ, Pietro KC. 2006. Decomposition of macrophyte Kayranli B, Scholz M, Mustafa A, Hedmark Å. 2010. Carbon litter in a subtropical constructed wetland in south Florida storage and fluxes within freshwater wetlands: a critical (USA). Ecol Eng. 27:301–321. review. Wetlands. 30:111–124. Chow AT, Dai J, Conner WH, Hitchcock DR, Wang J-J. 2013. Lal R. 2008. Carbon sequestration. Philos Trans R Soc B Biol Dissolved organic matter and nutrient dynamics of a coastal Sci. 363:815–830. freshwater forested wetland in Winyah Bay, South Carolina. MacKenzie AB, Farmer JG, Sugden CL. 1997. Isotopic evidence Biogeochemistry. 112:571–587. of the relative retention and mobility of lead and radiocae- Clymo RS. 1984. The limits to peat bog growth. Philos Trans R sium in Scottish ombrotrophic peats. Sci Total Environ. Soc Lond B Biol Sci. 303:605–654. 203:115–127. Cohen AD. 1973. Petrology of some Holocene peat sediments MacKenzie AB, Hardie SML, Farmer JG, Eades LJ, Pulford ID. from the Okefenokee swamp-marsh complex of southern 2011. Analytical and sampling constraints in Pb dating. Georgia. Geol Soc Am Bull. 84:3867–3878. Sci Total Environ. 409:1298–1304. 28 J.A. Villa and W.J. Mitsch Maltby E, Immirzi P. 1993. Carbon dynamics in peatlands and Reddy KR, DeLaune RD, DeBusk WF, Koch MS. 1993. Long other wetland soils regional and global perspectives. term nutrient accumulation rates in the Everglades. Soil Sci Chemosphere. 27:999–1023. Soc Am J. 57:1147–1155. Marois KC, Ewel KC. 1983. Natural and management-related Ritchie JC, McHenry JR. 1990. Application of radioactive fallout variation in cypress domes. For Sci. 29:627–640. Cesium-137 for measuring soil erosion and sediment accu- McLatchey GP, Reddy KR. 1998. Regulation of organic matter mulation rates and patterns: a review. J Environ Qual. decomposition and nutrient release in a wetland soil. 19:215–233. J Environ Qual. 27:1268–1274. Roulet NT. 2000. Peatlands, carbon storage, greenhouse gases, Miao SL, Miao SL, Sklar FH. 1997. Biomass and nutrient and the Kyoto Protocol: prospects and significance for allocation of sawgrass and cattail along a nutrient gradient Canada. Wetlands. 20:605–615. in the Florida Everglades. Wetl Ecol Manag. 5:245–264. Roulet NT, Lafleur PM, Richard PJH, Moore TR, Humphreys Mitra S, Wassmann R, Vlek PLG. 2005. An appraisal of global ER, Bubier J. 2007. Contemporary carbon balance and late wetland area and its organic carbon stock. Curr Sci. 88:25–35. Holocene carbon accumulation in a northern peatland. Glob Mitsch WJ, Bernal B, Nahlik A, Mander Ü, Zhang L, Anderson Change Biol. 13:397–411. C, Jørgensen S, Brix H. 2013. Wetlands, carbon, and climate Schell WR, Tobin MJ, Massey CD. 1989. Evaluation of trace change. Landsc Ecol. 28:583–597. metal deposition history and potential element mobility in Mitsch WJ, Gosselink JG. 2015. Wetlands. 5th ed. Hoboken selected cores from peat and wetland ecosystems. Trace Met (NJ): John Wiley & Sons. Lakes. 87–88:19–42. Mitsch WJ, Nahlik A, Wolski P, Bernal B, Zhang L, Ramberg L. Smith JT, Clarke RT, Saxén R. 2000. Time-dependent behaviour 2010. Tropical wetlands: seasonal hydrologic pulsing, carbon of radiocaesium: a new method to compare the mobility of sequestration, and methane emissions. Wetl Ecol Manag. weapons test and Chernobyl derived fallout. J Environ 18:573–586. Radioact. 49:65–83. Oldfield F, Appleby PG. 1984. Empirical testing of Pb-dating Todd-Brown KO, Hopkins F, Kivlin S, Talbot J, Allison S. 2012. A framework for representing microbial decomposi- models for lakes sediments. In: Haworth EY, Lund JWG, editors. Lake sediments environmental history. Minneapolis tion in coupled climate models. Biogeochemistry. (MN): University of Minnesota Press; p. 93–124. 109:19–33. Oldfield F, Appleby PG, Cambray RS, Eakins JD, Barber KE, Trumbore SE, Harden JW. 1997. Accumulation and turnover of 210 137 Battarbee RW, Pearson GR, Williams JM. 1979. Pb, Cs carbon in organic and mineral soils of the BOREAS northern and Pu profiles in ombrotrophic peat. Oikos. 33:40–45. study area. J Geophys Res. 102:28817–28830. Osborne TZ, Inglett PW, Reddy KR. 2007. The use of senescent Villa JA. 2014. Carbon dynamics of subtropical wetland com- plant biomass to investigate relationships between potential munities in south Florida [Ph.D. Dissertation]. Columbus particulate and dissolved organic matter in a wetland ecosys- (OH): The Ohio State University. tem. Aquat Bot. 86:53–61. Villa JA, Mitsch WJ. 2014. Methane emissions from five wetland Page SE, Rieley JO, Banks CJ. 2011. Global and regional impor- plant communities with different hydroperiods in the Big tance of the tropical peatland carbon pool. Glob Change Cypress Swamp region of Florida Everglades. Ecohydrol Biol. 17:798–818. Hydrobiol. doi:10.1016/j.ecohyd.2014.07.005 Perry W. 2004. Elements of South Florida’s comprehensive Whalen SC. 2005. Biogeochemistry of methane exchange Everglades restoration plan. Ecotoxicology. 13:185–193. between natural wetlands and the atmosphere. Environ Eng Pettit N, Davies T, Fellman J, Grierson P, Warfe D, Davies P. Sci. 22:73–94. 2011. Leaf litter chemistry, decomposition and assimilation Whiting GJ, Chanton JP. 2001. Greenhouse carbon balance of by macroinvertebrates in two tropical streams. wetlands: methane emission versus carbon sequestration. Hydrobiologia. 1–15. doi:10.1007/s10750–011–0903–1. Tellus B. 53:521–528.

Journal

International Journal of Biodiversity Science, Ecosystem Services & ManagementTaylor & Francis

Published: Jan 2, 2015

Keywords: carbon sequestration; subtropical wetland; cypress swamp; Everglades; climate regulation; Taxodium distichum

There are no references for this article.