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Effect of Phosphorous Loadings on Macrophytes Structure and Trophic State of Dam Reservoir on a Small Lowland River (Eastern Poland)

Effect of Phosphorous Loadings on Macrophytes Structure and Trophic State of Dam Reservoir on a... The main objective of the study was to evaluate if macrophytes structure and trophic status of dam reservoir Kranik on a small lowland river Wynica are determined by phosphorous loadings. Studies were conducted seasonally in May, July and October during the years 2008­2009. Samples were taken at four sites: Site 1 ­ inflow of the Wynica River to pre-dam, Site 2 - pre-dam, Site 3 - dam reservoir and Site 4 ­ outflow of the Wynica River from dam reservoir. Physical and chemical parameters (temperature, Secchi disc depth, dissolved oxygen, pH, conductivity, total suspension, chlorophyll-a, TP and P-PO4) were measured in water samples. Together with water parameters there were estimated biomass of phytoplankton and species composition and biomass of emergent, floating-leaved and submerged macrophytes. Concentrations of TP, chlorophyll-a and Secchi disc depth were used to calculate trophic state index of Carlsson for dam reservoir and its pre-dam. Based on mean water current, mean residence time of water in dam reservoir and concentrations of TP and P-PO4 loadings (g m) flowing into dam reservoir with the Wynica River were calculated. The results showed visible negative effect of phosphorous loadings on both macrophytes composition and trophic state of the reservoir. The marked changes concerned soft vegetation. High P loadings (7.74 g m of TP and 6.03 g m P-PO4) during the spring of 2008 caused the disappearance of characeans meadows. In 2009, the presence of rigid hornwort (Ceratophyllum demersum L.), the species typical for eutrophic lakes was noted. This unrooted submerged plant uptakes dissolved orthophosphates directly from the water column. Values of Carlsson index (51.4 TSI 68.2) indicate the eutrophic state of dam reservoir Kranik. During summer season in dam reservoir there were observed algal blooms (biomass of phytoplankton exceed 10 mg WW dm-3) and low water transparency (Secchi disc depth ranged from 0.4 to 0.65 m). During the two-year studies in dam reservoir Kranik a high reduction of P loadings, mostly dissolved orthophosphates was observed. Dependently on season, reduction of P-PO4 loadings ranged from 52% (July 2008) up to 91% (May 2009). The reduction of TP was lower and reached values from 15% (May 2008) to 48% (July 2009). INTRODUCTION Phosphorus is a key limiting factor controlling primary production in river ecosystems [40, 30, 20]. Enhanced inputs of phosphates from human sources (together with other nutrients such as nitrates) may stimulate the process of eutrophication. In lentic ecosystems this process can promote intensive growth of planktonic algal biomass which led to decrease of oxygen content and a subsequent decrease in diversity of water biocenosis as well the reduction of the economical and aesthetic values of the reservoir (surface scums, production of toxins, bad taste of water) [34, 38]. The major sources of P entering rivers are sewage/industrial effluents (point sources) and agricultural runoff (diffuse sources) [15]. Sewage is one important route by which inorganic phosphorous compounds may enter rivers. The principal sources of phosphates in sewage are human faeces and urine, food wastes (together around 75% of phosphates in sewage), detergents and industrial effluent that are discharged to reservoirs [14, 23]. In pre-dams and dam reservoirs the concentrations of phosphorous compounds may be reduced substantially, the process lead to improve the quality of inflowing water [25, 26]. In the reservoirs phosphorous loadings are diminished under two main processes: settling of particles and adsorbed phosphorous and incorporation of dissolved orthophosphates into phytoplankton biomass, which is then eliminated from the water by sedimentation [18, 34]. The negative, frequently observed effect of P loadings is increase of trophic status of reservoir. As a consequence, algal blooms, decrease of water transparency and biomass of soft vegetation are observed in the reservoir [31, 13]. The most vulnerable for eutrophication process are newly created reservoirs. Such reservoirs are intensively colonized by different phyto and zoocenosis, thus the trophic structure of the ecosystems is very unstable [11]. The main objective of the study was to recognize the influence of high P loadings on macrophytes structure and trophic status of a new man-made dam reservoir. SRUDY AREA, MATERIALS AND METHODS The dam reservoir Kranik (50° 56' 32.23" N, 22° 11' 37.06" E) and its pre-dam are small and shallow reservoirs (Table 1), created on the Wynica River near the town of Kranik (eastern Poland). The Wynica River is a right-bank tributary of the Vistula River and is about 42,5 km long. Water current shows seasonal variability and rangs from 0.11 to 0.42 m3s-1 (mean 0.29 m3s-1) [3]. The river catchment covers 508 km2 and it is dominated by arable lands and pastures. The main problems of water quality of the Wynica River are high loads of sewage from district dairy of Kranik, diffuse sewage sources (runoff from intensively managed agricultural lands) and storm runoffs. The dam reservoir Kranik was created in 2006 for the purpose of water discharge, recreation and fishery management. All banks of the reservoir are rampart, except for the south side, where the natural slope of river valley was retained. The reservoir was built on the area comprised by meadows, pastures and fishery ponds. One year after filling algal blooms appeared in the reservoir, which was closed for recreation use. High constant supply of organic matter and nutrients (mostly P-PO4) caused remarkable reduction of water transparency and deterioration of water quality. The studies were conducted during the years 2008­2009 at four sites (Fig. 1): Site 1 ­ inflow of the Wynica River to pre-dam; Site 2 ­ pre-dam; Site 3 ­ dam reservoir; Site 4 ­ outflow of the Wynica River from dam reservoir. Water samples were taken in spring (May), summer (July) and autumn (October). Water temperature, pH, conductivity and dissolved oxygen were measured in situ using YSI 556 MPS electrode. Total suspension content was estimated by gravimetric method. Concentrations of chlorophyll-a were determined by spectrophotometric method following Table 1. Main hydrological parameters of pre-dam and dam reservoir Kranik pre-dam Volume (m ) dam reservoir 996000 39.06 2.5 1180 570 40.2* Surface (ha) Mean depth (m) Maximum length (m) Maximum width (m) Water residence time (days) * according Pczula and Suchora [28] Fig. 1. Location of studied sites on WynicaRiver, pre-dam and dam reservoir Kranik a 24 h extraction with 90% acetone in the dark [10]. The concentrations of P compounds were estimated using spectrophotometric method with ammonium heptamolybdate [29]. For the analysis one liter of water was filtered (3 replicates at each site). Trophic status of pre-dam and dam reservoir were evaluated by calculating Trophic State Index (TSI) of Carlsson [5]. Loadings of TP and P-PO4 were estimated using Vollenveider [41] criteria, including concentrations of total phosphorous and dissolved orthophosphates in pre-dam and dam reservoir, mean water current and mean water residence time. Biomass of phytoplankton was estimated in 100 ml water samples preserved with Lugol's liquid. Algal biomass was calculated using the lengths and widths of algal cells and common geometric equations [32]. The species structure of macrophytes was estimated along horizontal transects [16] starting from the land-water ecotone and ending at the depth of macrophytes occurrence. In pre-dam, due to its small area, transects ranged between banks. In pre-dam 5 transects were marked and in dam reservoir ­ 18 transects. Along the transects macrophytes were sampled at points located every 20 m using floristic fork. The plant material was collected for species identification. Species identification was done according to Klosowski and Klosowski [17] and Pelechaty and Pukacz [27]. The density of emergent macrophytes (helophytes) was estimated at 10 randomly chosen sites by counting the shoots on the area of 0.25 m2 limited by a floristic fork. The biomass of floating-leaved (nympheids) and submerged vegetation (elodeids) was estimated using Bernatowicz rake [2] of the area 0.16 m2 and calculated per m2 of bottom surface. All data collected during field studies were analyzed statistically. The influence of the water of the Wynica River on physical and chemical parameters of pre-dam and dam reservoir was analyzed by means of two-way ANOVA (site, season). For pre-dam and dam reservoir Pearson's correlation coefficients between biomass of phytoplankton and macrophytes and environmental variables were calculated. All analysis were performed by STATISTICA 6.0. RESULTS Physical and chemical water parameters During the years 2008­2009 physical and chemical parameters of the water of the Wynica River, pre-dam and dam reservoir Kranik differed between studied sites and seasons (Table 2). Most of studied parameters showed a significant variability (Table 3). Temperature of water, independently on site and season, showed the lowest values at Site 1 (inflow of the Wynica River to pre-dam). The highest water temperature, in spring and summer, was observed at Site 4 (outflow of the Wynica River from dam reservoir); in autumn at Site 3 (dam reservoir). Values of pH ranged from 7.35­8.65. In 2008 the highest values of pH were noted in summer (July) and the lowest in spring (May). In 2009 the highest pH was observed in spring (May) and the lowest in autumn (October). Secchi disc visibility in pre-dam in all studied seasons reached the bottom and rose from spring to autumn from 0.9 to 1.1 m. In dam reservoir an opposite pattern was observed, the highest water transparency, 1.5 m (2008) and 1.1 m (2009) was noted in spring (May). During summer and autumn seasons, Secchi disc depth rapidly decreased and amounted to 0.65 and 0.4 m (2008) and to 0.5 and 0.9 m (2009). The highest concentrations of dissolved oxygen (10.74­16.47 mg dm-3) were observed in spring, while the lowest, dependently on the year in summer (4.93­10.11 mg dm-3) or in autumn (5.66­7.02 mg dm-3). Conductivity, in both studied years, reached the highest values (404­642) in spring and the lowest in summer (351­483). Concentrations of total suspension ranged from 3.3 to 52.2 mg dm-3. In 2008, the lowest amounts were noted in spring and the highest in autumn. In general, the content of total suspension was about 2­4 times lower in the outflow of the Wynica River from dam reservoir than in the water of the Wynica River inflowing to pre-dam. In 2009, the lowest content of total suspension was noted at most sites in autumn and the highest in summer. Concentrations of chlorophyll-a showed high variability, dependently on season and site. The lowest concentration of chlorophyll-a, 1.85 g dm-3 was observed in July Table 2. Seasonal variations of physical and chemical water parameters at studied sites on WynicaRiver, pre-dam and dam reservoir Kranik during the years 2008­2009 2008 Stanowisko 3 Maj 14.4 1.5 7.72 6.89 16.47 8.32 10.16 11.78 7.73 376 9.0 8.7 19.0 13.4 642 445 504 524 12.1 455 11.8 8.65 8.30 7.60 7.78 7.53 8.39 7.79 7.77 8.39 7.77 7.74 0.65 0.4 1.0* 1.1* 1.2* 1.1 8.40 21.8 12.9 15.1 22.1 12.4 12.7 18.0 8.6 13.1 23.5 9.4 13.9 22.3 0.5 8.18 Lip Pa Maj Lip Pa Maj Lip Pa Maj Lip Pa Maj Lip Pa 9.9 0.9 7.91 Stanowisko 4 Stanowisko 1 Stanowisko 2 Stanowisko 3 Lip 19.4 1.0* 7.63 5.66 11.90 11.69 7.02 10.74 4.93 528 15.8 11.4 52.2 53.0 4.1 7.0 444 360 350 421 351 7.56 1.1* 12.7 Pa Maj 16.2 8.39 8.57 10.92 10.11 13.97 9.87 495 7.1 434 19.6 360 21.2 387 6.3 404 24.8 2009 Stanowisko 4 Lip 25.2 8.50 Pa 9.2 7.79 8.45 12.14 354 13.7 370 3.3 9.82 24.43 10.39 35.02 22.90 17.91 11.38 Stanowisko 1 Stanowisko 2 Maj Lip Pa Maj Temperature (°C) Secch disc depth (m) 0.9* pH Dissolvedoxygen (mg dm-3) 455 13.6 Conductivity (S cm-1) Total suspension (mg dm-3) Chlorophyll-a (g dm-3) TP (mg dm-3) P-PO4 (mg dm-3) 58.6 51.3 51.4 68.2 62.3 - 0.195 0.261 0.101 0.278 0.419 0.129 0.063 0.082 0.086 0.054 0.125 0.034 0.078 0.130 0.101 0.066 0.224 0.131 0.018 0.023 0.036 0.007 0.019 0.031 54.5 50.3 52.9 55.4 56.9 58.4 - TSI Site 1 ­ inflow of Wynica River to pre-dam; Site 2 ­ pre-dam; Site 3 ­ dam reservoir; Site 4 ­ outflow of Wynica River from dam reservoir; TSI ­ Trophic State Index; * ­ to the bottom 2009 at Site 2 (pre-dam) and the highest ­ 72.45 g dm-3 in July 2008 at Site 3 (dam reservoir). Concentrations of total phosphorous and dissolved orthophosphates in all studied seasons were visibly higher at Site 1 (the inflow of thge Wynica River to pre-dam) than at Site 4 (the outflow of the Wynica River from dam reservoir) (Table 2). During the years 2008­2009 the highest decrease of concentration of P-PO4 was noted in spring (May); in 2008 the concentration of P-PO4 decreased 4-times, from 0.195 mg dm-3 to 0.054 mg dm-3 and in 2009 as many as 11-times, from 0.078 mg dm-3 to 0.007 mg dm-3. Differences in total phosphorous concentrations along the studied sites were much lower. In 2008, the highest decrease of TP concentration was observed in spring (May); from 0.327 mg dm-3 (Site 1) to 0.194 mg dm-3 (Site 4). In 2009, the highest difference of concentration of TP was noted in summer (July), from 0.274 mg dm-3 (Site 1) to 0.141 mg dm-3 (Site 4). Table 3. Results of two-way ANOVA (site, season) for selected physical and chemical parameters of water of Wynica River, pre-dam and dam reservoir Kranik Parameter Temperature Secchi disc depth pH Dissolved oxygen Conductivity Total suspension Chlorophyll-a TP P-PO4 N = 72; ns ­ not significa Season F = 129.68; p < 0.001 ns ns F = 15.17; p < 0.001 F = 4.88; p = 0.012 ns F = 4.16; p = 0.021 F = 5.62; p = 0.006 F = 0.55; p = 0.016 ns Site F = 3.25; p = 0.034 F = 3.19; p = 0.037 ns F = 45.59; p < 0.001 F = 4.67; p = 0.044 F = 10.79; p < 0.001 F = 6.89; p < 0.001 F = 5.01; p = 0.010 Phosphorous loadings Loadings of TP and P-PO4 introduced to dam reservoir Kranik with the Wynica River showed visible seasonal variability (Fig. 2). In 2008, the highest loadings of phosphorous inflow to the reservoir were in spring and summer and amounted to 7.56 g m TP and 4.49 g m P-PO4 in May and to 7.74 g m TP and 6.03 g m P-PO4 in July. In 2009, the highest loadings were observed in July, 3.08 g m P-PO4 and 6.33 g m TP. In all studied seasons in dam reservoir Kranik important reduction of P loadings was observed. The highest retention of P-PO4 was noted in May; 72% in 2008 and 91% in 2009. Reduction of TP loadings was much lower. In 2008, the highest, 42% reduction of TP was observed in October and in 2009 in July ­ 48%. Biomass of phytoplankton During the years 2008­2009 biomass of phytoplankton in dam reservoir was from 1.5 up to 26-times higher than in pre-dam. Observed differences were significant (ANOVA, F = 5.17; p = 0.042). In pre-dam, in both studied years, the lowest phytoplankton biomass was observed in July, 1.07 and 1.23 mg WW dm-3. The highest biomass of planktonic M ay08 Jul08 inflow Oct08 M ay08 Jul08 Oct08 M ay09 Jul09 inflow Oct09 M ay09 Jul09 Oct09 outflow gm outflow TP P-PO4 Fig. 2. Loadings of total phosphorous (TP) and dissolved orthophosphates (P-PO4) in inflow and outflow of Wynica River to dam reservoir Kranik in studied seasons during the years 2008­2009 algae in 2008 was noted in May (3.68 mg WW dm-3) and in 2009 in October (2.71 mg WW dm-3). The biomass of phytoplankton was negatively correlated with water temperature (r = -0.62; p = 0.006) and pH (r = -0.71; p = 0.001) and positively with conductivity (r = 0.72; p = 0.001). In dam reservoir the highest biomass of planktonic algae, in both studied years, was observed in summer, 32.97 mg WW dm-3 (2008) and 23.41 mg WW dm-3 (2009) and the lowest in spring, 5.24 mg WW dm-3 (2008) and 3.77 mg WW dm-3 (2009) (Fig. 3). All the differences were significant (ANOVA, F = 7.87; p = 0.011). The biomass of phytoplankton was positively correlated with water temperature (r = 0.84; p < 0.001), total suspension (r = 0.67; p = 0.003) and concentrations of TP (r = 0.48; p = 0.013) and P-PO4 (r = 0.73; p = 0.001). Also, biomass of planktonic algae was negatively affected by Secchi disc depth (r = -0.64; p = 0.004). mg WW dm -3 30 25 20 15 10 5 0 M ay08 Jul08 Oct08 M ay09 Jul09 pre-dam Oct09 M ay08 Jul08 Oct08 M ay09 Jul09 dam reservoir Oct09 Fig. 3. Biomass of phytoplankton (mean values, +SD) in pre-dam and dam reservoir Kranik in studied seasons during the years 2008­2009 stems m 100 80 60 40 20 0 M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 pre-dam M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 dam reservoir Fig. 4. Density of emergent macrophytes (mean values, +SD) in pre-dam and dam reservoir Kranik in studied seasons during the years 2008­2009 Structure of macrophytes In pre-dam and dam reservoir, during two-year studies 11 macrophyte species were noted (Table 4). In pre-dam the number of species was constant through the sampling period and included 2 species of emergent macrophytes, 2 floating-leaved species and 1 species of submerged macrophytes. In dam reservoir the structure of submerged macrophytes varied between studied years and seasons. In 2008, the highest number of species was noted in May (10 species) in remaining two seasons the number of species was lower (7 species). In spring season, in reservoir there were presented characean meadows formed by Chara tomentosa L., Chara rudis (A. Braun) Leonh. and Chara intermedia A. Braun. In 2009, submerged macrophytes were represented by 8 species. Instead of characeans rigid hornwort (Ceratophyllum demersum L.) appeared. Density of emergent macrophytes, in both studied years, differed significantly between seasons (ANOVA, F = 7.96; p = 0.002) (Fig. 4). The highest density of emergent vegetation, in pre-dam and dam reservoir was observed in summer (mean 87­118 stems m) and the lowest in spring (mean 56­67 stems m). In pre-dam the density of emergent macrophytes was negatively correlated with pH (r = -0.65; p = 0.004) and dissolved oxygen content (r = -0.52; p = 0.027) and positively with concentrations of TP (r = 0.49; p = 0.036) and P-PO4 (r = 0.63; p = 0.005). In dam reservoir there was noted a negative correlation of emergent plant density with Secchi disc depth (r = -0.64; p = 0.004) and conductivity (r = -0.80; p = 0.001) and a positive correlation of helophytes density with chlorophyll-a concentration (r = 0.61; p = 0.006), TP (r = 0.64; p = 0.004) and phytoplankton biomass (r = 0.57; p = 0.013). A significant influence of season was observed also for the biomass of floating-leaved (ANOVA, F = 5.07; p = 0.035) and submerged macrophytes (ANOVA, F = 5.12; p = 0.015) (Fig. 5). During two-year studies, the highest biomass of nympheids, in both reservoirs was noted in May (mean 156.3­386.4 g WW m) and the lowest in July (mean 419.3­722.8 g WW m). In pre-dam the biomass of floating-leaved plants was positively correlated with total suspension (r = 0.71; p = 0.001) and P-PO4 (r = 0.59; p = 0.011) and negatively correlated with dissolved oxygen (r = -0.83; p < 0.001). In Table 4. Species structure of macrophytes in pre-dam and dam reservoir Kranik during the years 2008­2009 2008 PD May Jul Emergent macrophytes Phragmites australis (Cav.) Trin. ex Steud Typha latifolia L. Alisma plantago-aquatica L. Floating-leaved macrophytes Lemna minor L. Polygonum amphibium L. Potamogeton natans L. Submerged macrophytes Potamogeton filiformis Pers. Ceratophyllum demersum L. Chara tomentosa L. Chara rudis (A. Braun) Leonh. Chara intermedia A. Braun Ogólem liczba gatunków PD ­ pre-dam, DR ­ dam reservoir 2009 DR PD Oct May Jul DR Oct May Jul Oct Oct May Jul + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 5 5 5 10 7 7 5 5 5 8 8 8 dam reservoir, the concentrations of chlorophyll-a (r = 0.53; p = 0.026) and TP (r = 0.51; p = 0.031) positively affected the biomass of floating-leaved macrophytes, also conductivity showed negative correlation with biomass of these plants (r = -0.52; p = 0.027). Submerged macrophytes in pre-dam, in both years, showed the highest biomass in summer (mean 861.3 g and 979.8 g WW m) and the lowest in spring (mean 447.8 g and 555.6 g WW m). Biomass of submerged plants was negatively correlated with dissolved oxygen (r = -0.66; p = 0.003) and positively with total suspension (r = 0.58; p = 0.011) and concentrations of TP (r = 0.61; p = 0.007) and P-PO4 (r = 0.78; p < 0.001). In dam reservoir the highest biomass of elodeids, in both years, was observed in May (mean 2675.9 g and 1841.2 g WW m) and the lowest in October (mean 541.8 g and 694.3 g WW m). The biomass of submerged plants was positively affected by Secchi disc depth (r = 0.90; p < 0.001) and conductivity (r = 0.92; p < 0.001) and negatively by pH (r = -0.52; p = 0.031), total suspension (r = -0.54; p = 0.021), concentration of TP (r = -0.56; p = 0.016), chlorophyll-a (r = -0.59; p = 0.019) and phytoplankton biomass (r = -0.58; p = 0.012). g WW m M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 pre-dam floating-leaved macrophytes M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 dam reservoir submerged macrophytes Fig. 5. Biomass (mean values, +SD) of floating-leaved and submerged macrophytes in pre-dam and dam reservoir Kranik in studied seasons during the years 2008­2009 Trophic state Values of Carlsson index calculated for pre-dam and dam reservoirs, for both years and all seasons indicate the eutrophic state of both reservoirs (Table 2). For pre-dam the values of TSI ranged from 50.3 to 59.7 and for dam reservoir, dependently on season, index of Carlsson reached higher values, from 51.4 to 68.2. The observed changes of TSI index for dam reservoir Kranik seem to be related to the share of P-PO4 in total P loadings. The highest value of Carlsson index, 68.2, was noted in July 2008, at time the highest loading of P-PO4 (6.03 g m) inflow the reservoir and they amounted to 78% of TP loading. The lowest value of TSI, 55.4, was calculated in May 2009, the P-PO4 loading amounted to 1.82 g m and reached 44% of loading of TP. DISCUSSION Phosphorous loadings into dam reservoir Kranik with the Wynica River caused the process of eutrophication of the reservoir and negative changes of species composition and biomass of vegetation. Studies began at spring 2008, two years after the creation of dam-reservoir, thus low diversity of macrophytes in the reservoir and its pre-dam resulted from initial stage of succession. Usually similar structure of vegetation is observed in newly man-made reservoirs [37]. In dam reservoir, among submerged vegetation characeans were noted. These plants are usually the pioneer community in newly created habitats [39]. However, in July 2008, due to high P loadings (4.5­6.0 g m of P-PO4 and 7.5 g m of TP), in dam reservoir there were observed algal blooms (biomass of phytoplankton exceeded 30 mg MM dm-3) and high decrease of water transparency (Secchi disc visibility reached only 0.4 m). At time characean meadows disappeared from the reservoir. Submerged macrophytes responded very quickly to eutrophication process and showed rapid decline of biomass and occurrence of more sensitive species [6, 36]. These relations confirmed significant negative correlations between submerged macrophytes biomass and chlorophyll-a concentration and phytoplankton biomass, as well as a positive correlation of plants biomass with Secchi disc depth. Also, in summer season, rapid development of emergent macrophytes density (form 67 up to 109 stems m) was noted in dam reservoir. The community of helophytes was dominated by common reed (Phragmites australis (Cav.) Trin. ex Steud.). The intensive growth of emergent macrophytes could be related to vegetation period and to increasing concentration of phosphorous compounds in dam reservoir Kranik. This observation confirms positive correlation of helophytes density with concentration of TP. Rooted emergent plants utilize external P loadings during the growing season [20]. P. australis is an emergent species, sensitive to the increase of nutrients concentrations in water and shows a visible increase of its biomass and is a good indicator of eutrophication of water ecosystems [12, 24]. In 2009, in dam reservoir Kranik rigid hornwort, Ceratophyllum demersum L appeared. This unrooted, submerged plant shows ability to uptake dissolved orthophosphates directly from water column and may successfully conquer with phytoplankton [7, 8]. C. demersum was presented in all seasons of 2009 and reached the highest biomass (mean above 1600 g WW m) in May. Relatively high biomass of rigid hornwort (mean above 700 g WW m) was noted in July, despite high biomass of planktonic algae (above 23 mg WW dm-3). Similar results were obtained by Melzer [21], who observed floating mats of C. demersum in highly eutrophic lakes. During two-year studies, a high reduction of P-PO4 loadings was observed in dam reservoir Kranik. The highest retention of dissolved orthophosphates was noted during spring season and amounted to 72% in 2008 and even to 91% in 2009. Usually the highest reduction of P-PO4 (60­80%) in dam reservoirs is observed in summer [26, 33, 35]. High retention of P-PO4 observed in May in dam reservoir Kranik was probably a consequence of rapid growth of soft vegetation. Due to the production of high biomass, submerged macrophytes, are able to accumulate high amounts of inorganic phosphorous in their tissues [1, 9] and affect the concentrations of phosphorous and chlorophyll-a in water column [8]. Trophic state of dam reservoir Kranik depended on season and main biological processes of P loadings elimination. During spring season, values of TSI were the lowest, at time P-PO4 was incorporated mostly into macrophyte biomass and retention of P-PO4 was the highest. Index of Carlsson raised in summer season, in July 2008, TSI amounted to almost 70, value typical for hypertrophic lakes. At time, due to high P-PO4 loadings, in dam reservoir Krasnik a massive development of phytoplankton and algal blooms was observed. CONCLUSIONS Dam reservoir Kranik plays an important role in the reduction of high P loadings in the Wynica River, and led to improvement of quality of river waters. Dependently on season, the retention of total phosphorous ranged from 15 to 48% and dissolved orthophosphates from 52 up to 91%. In dam reservoir, a reduction of P-PO4 loadings is determined by biological processes, phosphorous is incorporated mainly into biomass of macrophytes and planktonic algae. High loadings of P caused eutrophication of dam reservoir Krasnik. Increase of trophic state of reservoir resulted in blooms of planktonic algae and decrease in water transparency. Current loading of P influenced negatively species composition and biomass of macrophytes, mostly sort submerged plants. During two-year studies, the number of submerged macrophytes species was reduced by half and increased biomass of macrophyte species typical for nutrient rich habitats. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Environmental Protection de Gruyter

Effect of Phosphorous Loadings on Macrophytes Structure and Trophic State of Dam Reservoir on a Small Lowland River (Eastern Poland)

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de Gruyter
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2083-4772
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Abstract

The main objective of the study was to evaluate if macrophytes structure and trophic status of dam reservoir Kranik on a small lowland river Wynica are determined by phosphorous loadings. Studies were conducted seasonally in May, July and October during the years 2008­2009. Samples were taken at four sites: Site 1 ­ inflow of the Wynica River to pre-dam, Site 2 - pre-dam, Site 3 - dam reservoir and Site 4 ­ outflow of the Wynica River from dam reservoir. Physical and chemical parameters (temperature, Secchi disc depth, dissolved oxygen, pH, conductivity, total suspension, chlorophyll-a, TP and P-PO4) were measured in water samples. Together with water parameters there were estimated biomass of phytoplankton and species composition and biomass of emergent, floating-leaved and submerged macrophytes. Concentrations of TP, chlorophyll-a and Secchi disc depth were used to calculate trophic state index of Carlsson for dam reservoir and its pre-dam. Based on mean water current, mean residence time of water in dam reservoir and concentrations of TP and P-PO4 loadings (g m) flowing into dam reservoir with the Wynica River were calculated. The results showed visible negative effect of phosphorous loadings on both macrophytes composition and trophic state of the reservoir. The marked changes concerned soft vegetation. High P loadings (7.74 g m of TP and 6.03 g m P-PO4) during the spring of 2008 caused the disappearance of characeans meadows. In 2009, the presence of rigid hornwort (Ceratophyllum demersum L.), the species typical for eutrophic lakes was noted. This unrooted submerged plant uptakes dissolved orthophosphates directly from the water column. Values of Carlsson index (51.4 TSI 68.2) indicate the eutrophic state of dam reservoir Kranik. During summer season in dam reservoir there were observed algal blooms (biomass of phytoplankton exceed 10 mg WW dm-3) and low water transparency (Secchi disc depth ranged from 0.4 to 0.65 m). During the two-year studies in dam reservoir Kranik a high reduction of P loadings, mostly dissolved orthophosphates was observed. Dependently on season, reduction of P-PO4 loadings ranged from 52% (July 2008) up to 91% (May 2009). The reduction of TP was lower and reached values from 15% (May 2008) to 48% (July 2009). INTRODUCTION Phosphorus is a key limiting factor controlling primary production in river ecosystems [40, 30, 20]. Enhanced inputs of phosphates from human sources (together with other nutrients such as nitrates) may stimulate the process of eutrophication. In lentic ecosystems this process can promote intensive growth of planktonic algal biomass which led to decrease of oxygen content and a subsequent decrease in diversity of water biocenosis as well the reduction of the economical and aesthetic values of the reservoir (surface scums, production of toxins, bad taste of water) [34, 38]. The major sources of P entering rivers are sewage/industrial effluents (point sources) and agricultural runoff (diffuse sources) [15]. Sewage is one important route by which inorganic phosphorous compounds may enter rivers. The principal sources of phosphates in sewage are human faeces and urine, food wastes (together around 75% of phosphates in sewage), detergents and industrial effluent that are discharged to reservoirs [14, 23]. In pre-dams and dam reservoirs the concentrations of phosphorous compounds may be reduced substantially, the process lead to improve the quality of inflowing water [25, 26]. In the reservoirs phosphorous loadings are diminished under two main processes: settling of particles and adsorbed phosphorous and incorporation of dissolved orthophosphates into phytoplankton biomass, which is then eliminated from the water by sedimentation [18, 34]. The negative, frequently observed effect of P loadings is increase of trophic status of reservoir. As a consequence, algal blooms, decrease of water transparency and biomass of soft vegetation are observed in the reservoir [31, 13]. The most vulnerable for eutrophication process are newly created reservoirs. Such reservoirs are intensively colonized by different phyto and zoocenosis, thus the trophic structure of the ecosystems is very unstable [11]. The main objective of the study was to recognize the influence of high P loadings on macrophytes structure and trophic status of a new man-made dam reservoir. SRUDY AREA, MATERIALS AND METHODS The dam reservoir Kranik (50° 56' 32.23" N, 22° 11' 37.06" E) and its pre-dam are small and shallow reservoirs (Table 1), created on the Wynica River near the town of Kranik (eastern Poland). The Wynica River is a right-bank tributary of the Vistula River and is about 42,5 km long. Water current shows seasonal variability and rangs from 0.11 to 0.42 m3s-1 (mean 0.29 m3s-1) [3]. The river catchment covers 508 km2 and it is dominated by arable lands and pastures. The main problems of water quality of the Wynica River are high loads of sewage from district dairy of Kranik, diffuse sewage sources (runoff from intensively managed agricultural lands) and storm runoffs. The dam reservoir Kranik was created in 2006 for the purpose of water discharge, recreation and fishery management. All banks of the reservoir are rampart, except for the south side, where the natural slope of river valley was retained. The reservoir was built on the area comprised by meadows, pastures and fishery ponds. One year after filling algal blooms appeared in the reservoir, which was closed for recreation use. High constant supply of organic matter and nutrients (mostly P-PO4) caused remarkable reduction of water transparency and deterioration of water quality. The studies were conducted during the years 2008­2009 at four sites (Fig. 1): Site 1 ­ inflow of the Wynica River to pre-dam; Site 2 ­ pre-dam; Site 3 ­ dam reservoir; Site 4 ­ outflow of the Wynica River from dam reservoir. Water samples were taken in spring (May), summer (July) and autumn (October). Water temperature, pH, conductivity and dissolved oxygen were measured in situ using YSI 556 MPS electrode. Total suspension content was estimated by gravimetric method. Concentrations of chlorophyll-a were determined by spectrophotometric method following Table 1. Main hydrological parameters of pre-dam and dam reservoir Kranik pre-dam Volume (m ) dam reservoir 996000 39.06 2.5 1180 570 40.2* Surface (ha) Mean depth (m) Maximum length (m) Maximum width (m) Water residence time (days) * according Pczula and Suchora [28] Fig. 1. Location of studied sites on WynicaRiver, pre-dam and dam reservoir Kranik a 24 h extraction with 90% acetone in the dark [10]. The concentrations of P compounds were estimated using spectrophotometric method with ammonium heptamolybdate [29]. For the analysis one liter of water was filtered (3 replicates at each site). Trophic status of pre-dam and dam reservoir were evaluated by calculating Trophic State Index (TSI) of Carlsson [5]. Loadings of TP and P-PO4 were estimated using Vollenveider [41] criteria, including concentrations of total phosphorous and dissolved orthophosphates in pre-dam and dam reservoir, mean water current and mean water residence time. Biomass of phytoplankton was estimated in 100 ml water samples preserved with Lugol's liquid. Algal biomass was calculated using the lengths and widths of algal cells and common geometric equations [32]. The species structure of macrophytes was estimated along horizontal transects [16] starting from the land-water ecotone and ending at the depth of macrophytes occurrence. In pre-dam, due to its small area, transects ranged between banks. In pre-dam 5 transects were marked and in dam reservoir ­ 18 transects. Along the transects macrophytes were sampled at points located every 20 m using floristic fork. The plant material was collected for species identification. Species identification was done according to Klosowski and Klosowski [17] and Pelechaty and Pukacz [27]. The density of emergent macrophytes (helophytes) was estimated at 10 randomly chosen sites by counting the shoots on the area of 0.25 m2 limited by a floristic fork. The biomass of floating-leaved (nympheids) and submerged vegetation (elodeids) was estimated using Bernatowicz rake [2] of the area 0.16 m2 and calculated per m2 of bottom surface. All data collected during field studies were analyzed statistically. The influence of the water of the Wynica River on physical and chemical parameters of pre-dam and dam reservoir was analyzed by means of two-way ANOVA (site, season). For pre-dam and dam reservoir Pearson's correlation coefficients between biomass of phytoplankton and macrophytes and environmental variables were calculated. All analysis were performed by STATISTICA 6.0. RESULTS Physical and chemical water parameters During the years 2008­2009 physical and chemical parameters of the water of the Wynica River, pre-dam and dam reservoir Kranik differed between studied sites and seasons (Table 2). Most of studied parameters showed a significant variability (Table 3). Temperature of water, independently on site and season, showed the lowest values at Site 1 (inflow of the Wynica River to pre-dam). The highest water temperature, in spring and summer, was observed at Site 4 (outflow of the Wynica River from dam reservoir); in autumn at Site 3 (dam reservoir). Values of pH ranged from 7.35­8.65. In 2008 the highest values of pH were noted in summer (July) and the lowest in spring (May). In 2009 the highest pH was observed in spring (May) and the lowest in autumn (October). Secchi disc visibility in pre-dam in all studied seasons reached the bottom and rose from spring to autumn from 0.9 to 1.1 m. In dam reservoir an opposite pattern was observed, the highest water transparency, 1.5 m (2008) and 1.1 m (2009) was noted in spring (May). During summer and autumn seasons, Secchi disc depth rapidly decreased and amounted to 0.65 and 0.4 m (2008) and to 0.5 and 0.9 m (2009). The highest concentrations of dissolved oxygen (10.74­16.47 mg dm-3) were observed in spring, while the lowest, dependently on the year in summer (4.93­10.11 mg dm-3) or in autumn (5.66­7.02 mg dm-3). Conductivity, in both studied years, reached the highest values (404­642) in spring and the lowest in summer (351­483). Concentrations of total suspension ranged from 3.3 to 52.2 mg dm-3. In 2008, the lowest amounts were noted in spring and the highest in autumn. In general, the content of total suspension was about 2­4 times lower in the outflow of the Wynica River from dam reservoir than in the water of the Wynica River inflowing to pre-dam. In 2009, the lowest content of total suspension was noted at most sites in autumn and the highest in summer. Concentrations of chlorophyll-a showed high variability, dependently on season and site. The lowest concentration of chlorophyll-a, 1.85 g dm-3 was observed in July Table 2. Seasonal variations of physical and chemical water parameters at studied sites on WynicaRiver, pre-dam and dam reservoir Kranik during the years 2008­2009 2008 Stanowisko 3 Maj 14.4 1.5 7.72 6.89 16.47 8.32 10.16 11.78 7.73 376 9.0 8.7 19.0 13.4 642 445 504 524 12.1 455 11.8 8.65 8.30 7.60 7.78 7.53 8.39 7.79 7.77 8.39 7.77 7.74 0.65 0.4 1.0* 1.1* 1.2* 1.1 8.40 21.8 12.9 15.1 22.1 12.4 12.7 18.0 8.6 13.1 23.5 9.4 13.9 22.3 0.5 8.18 Lip Pa Maj Lip Pa Maj Lip Pa Maj Lip Pa Maj Lip Pa 9.9 0.9 7.91 Stanowisko 4 Stanowisko 1 Stanowisko 2 Stanowisko 3 Lip 19.4 1.0* 7.63 5.66 11.90 11.69 7.02 10.74 4.93 528 15.8 11.4 52.2 53.0 4.1 7.0 444 360 350 421 351 7.56 1.1* 12.7 Pa Maj 16.2 8.39 8.57 10.92 10.11 13.97 9.87 495 7.1 434 19.6 360 21.2 387 6.3 404 24.8 2009 Stanowisko 4 Lip 25.2 8.50 Pa 9.2 7.79 8.45 12.14 354 13.7 370 3.3 9.82 24.43 10.39 35.02 22.90 17.91 11.38 Stanowisko 1 Stanowisko 2 Maj Lip Pa Maj Temperature (°C) Secch disc depth (m) 0.9* pH Dissolvedoxygen (mg dm-3) 455 13.6 Conductivity (S cm-1) Total suspension (mg dm-3) Chlorophyll-a (g dm-3) TP (mg dm-3) P-PO4 (mg dm-3) 58.6 51.3 51.4 68.2 62.3 - 0.195 0.261 0.101 0.278 0.419 0.129 0.063 0.082 0.086 0.054 0.125 0.034 0.078 0.130 0.101 0.066 0.224 0.131 0.018 0.023 0.036 0.007 0.019 0.031 54.5 50.3 52.9 55.4 56.9 58.4 - TSI Site 1 ­ inflow of Wynica River to pre-dam; Site 2 ­ pre-dam; Site 3 ­ dam reservoir; Site 4 ­ outflow of Wynica River from dam reservoir; TSI ­ Trophic State Index; * ­ to the bottom 2009 at Site 2 (pre-dam) and the highest ­ 72.45 g dm-3 in July 2008 at Site 3 (dam reservoir). Concentrations of total phosphorous and dissolved orthophosphates in all studied seasons were visibly higher at Site 1 (the inflow of thge Wynica River to pre-dam) than at Site 4 (the outflow of the Wynica River from dam reservoir) (Table 2). During the years 2008­2009 the highest decrease of concentration of P-PO4 was noted in spring (May); in 2008 the concentration of P-PO4 decreased 4-times, from 0.195 mg dm-3 to 0.054 mg dm-3 and in 2009 as many as 11-times, from 0.078 mg dm-3 to 0.007 mg dm-3. Differences in total phosphorous concentrations along the studied sites were much lower. In 2008, the highest decrease of TP concentration was observed in spring (May); from 0.327 mg dm-3 (Site 1) to 0.194 mg dm-3 (Site 4). In 2009, the highest difference of concentration of TP was noted in summer (July), from 0.274 mg dm-3 (Site 1) to 0.141 mg dm-3 (Site 4). Table 3. Results of two-way ANOVA (site, season) for selected physical and chemical parameters of water of Wynica River, pre-dam and dam reservoir Kranik Parameter Temperature Secchi disc depth pH Dissolved oxygen Conductivity Total suspension Chlorophyll-a TP P-PO4 N = 72; ns ­ not significa Season F = 129.68; p < 0.001 ns ns F = 15.17; p < 0.001 F = 4.88; p = 0.012 ns F = 4.16; p = 0.021 F = 5.62; p = 0.006 F = 0.55; p = 0.016 ns Site F = 3.25; p = 0.034 F = 3.19; p = 0.037 ns F = 45.59; p < 0.001 F = 4.67; p = 0.044 F = 10.79; p < 0.001 F = 6.89; p < 0.001 F = 5.01; p = 0.010 Phosphorous loadings Loadings of TP and P-PO4 introduced to dam reservoir Kranik with the Wynica River showed visible seasonal variability (Fig. 2). In 2008, the highest loadings of phosphorous inflow to the reservoir were in spring and summer and amounted to 7.56 g m TP and 4.49 g m P-PO4 in May and to 7.74 g m TP and 6.03 g m P-PO4 in July. In 2009, the highest loadings were observed in July, 3.08 g m P-PO4 and 6.33 g m TP. In all studied seasons in dam reservoir Kranik important reduction of P loadings was observed. The highest retention of P-PO4 was noted in May; 72% in 2008 and 91% in 2009. Reduction of TP loadings was much lower. In 2008, the highest, 42% reduction of TP was observed in October and in 2009 in July ­ 48%. Biomass of phytoplankton During the years 2008­2009 biomass of phytoplankton in dam reservoir was from 1.5 up to 26-times higher than in pre-dam. Observed differences were significant (ANOVA, F = 5.17; p = 0.042). In pre-dam, in both studied years, the lowest phytoplankton biomass was observed in July, 1.07 and 1.23 mg WW dm-3. The highest biomass of planktonic M ay08 Jul08 inflow Oct08 M ay08 Jul08 Oct08 M ay09 Jul09 inflow Oct09 M ay09 Jul09 Oct09 outflow gm outflow TP P-PO4 Fig. 2. Loadings of total phosphorous (TP) and dissolved orthophosphates (P-PO4) in inflow and outflow of Wynica River to dam reservoir Kranik in studied seasons during the years 2008­2009 algae in 2008 was noted in May (3.68 mg WW dm-3) and in 2009 in October (2.71 mg WW dm-3). The biomass of phytoplankton was negatively correlated with water temperature (r = -0.62; p = 0.006) and pH (r = -0.71; p = 0.001) and positively with conductivity (r = 0.72; p = 0.001). In dam reservoir the highest biomass of planktonic algae, in both studied years, was observed in summer, 32.97 mg WW dm-3 (2008) and 23.41 mg WW dm-3 (2009) and the lowest in spring, 5.24 mg WW dm-3 (2008) and 3.77 mg WW dm-3 (2009) (Fig. 3). All the differences were significant (ANOVA, F = 7.87; p = 0.011). The biomass of phytoplankton was positively correlated with water temperature (r = 0.84; p < 0.001), total suspension (r = 0.67; p = 0.003) and concentrations of TP (r = 0.48; p = 0.013) and P-PO4 (r = 0.73; p = 0.001). Also, biomass of planktonic algae was negatively affected by Secchi disc depth (r = -0.64; p = 0.004). mg WW dm -3 30 25 20 15 10 5 0 M ay08 Jul08 Oct08 M ay09 Jul09 pre-dam Oct09 M ay08 Jul08 Oct08 M ay09 Jul09 dam reservoir Oct09 Fig. 3. Biomass of phytoplankton (mean values, +SD) in pre-dam and dam reservoir Kranik in studied seasons during the years 2008­2009 stems m 100 80 60 40 20 0 M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 pre-dam M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 dam reservoir Fig. 4. Density of emergent macrophytes (mean values, +SD) in pre-dam and dam reservoir Kranik in studied seasons during the years 2008­2009 Structure of macrophytes In pre-dam and dam reservoir, during two-year studies 11 macrophyte species were noted (Table 4). In pre-dam the number of species was constant through the sampling period and included 2 species of emergent macrophytes, 2 floating-leaved species and 1 species of submerged macrophytes. In dam reservoir the structure of submerged macrophytes varied between studied years and seasons. In 2008, the highest number of species was noted in May (10 species) in remaining two seasons the number of species was lower (7 species). In spring season, in reservoir there were presented characean meadows formed by Chara tomentosa L., Chara rudis (A. Braun) Leonh. and Chara intermedia A. Braun. In 2009, submerged macrophytes were represented by 8 species. Instead of characeans rigid hornwort (Ceratophyllum demersum L.) appeared. Density of emergent macrophytes, in both studied years, differed significantly between seasons (ANOVA, F = 7.96; p = 0.002) (Fig. 4). The highest density of emergent vegetation, in pre-dam and dam reservoir was observed in summer (mean 87­118 stems m) and the lowest in spring (mean 56­67 stems m). In pre-dam the density of emergent macrophytes was negatively correlated with pH (r = -0.65; p = 0.004) and dissolved oxygen content (r = -0.52; p = 0.027) and positively with concentrations of TP (r = 0.49; p = 0.036) and P-PO4 (r = 0.63; p = 0.005). In dam reservoir there was noted a negative correlation of emergent plant density with Secchi disc depth (r = -0.64; p = 0.004) and conductivity (r = -0.80; p = 0.001) and a positive correlation of helophytes density with chlorophyll-a concentration (r = 0.61; p = 0.006), TP (r = 0.64; p = 0.004) and phytoplankton biomass (r = 0.57; p = 0.013). A significant influence of season was observed also for the biomass of floating-leaved (ANOVA, F = 5.07; p = 0.035) and submerged macrophytes (ANOVA, F = 5.12; p = 0.015) (Fig. 5). During two-year studies, the highest biomass of nympheids, in both reservoirs was noted in May (mean 156.3­386.4 g WW m) and the lowest in July (mean 419.3­722.8 g WW m). In pre-dam the biomass of floating-leaved plants was positively correlated with total suspension (r = 0.71; p = 0.001) and P-PO4 (r = 0.59; p = 0.011) and negatively correlated with dissolved oxygen (r = -0.83; p < 0.001). In Table 4. Species structure of macrophytes in pre-dam and dam reservoir Kranik during the years 2008­2009 2008 PD May Jul Emergent macrophytes Phragmites australis (Cav.) Trin. ex Steud Typha latifolia L. Alisma plantago-aquatica L. Floating-leaved macrophytes Lemna minor L. Polygonum amphibium L. Potamogeton natans L. Submerged macrophytes Potamogeton filiformis Pers. Ceratophyllum demersum L. Chara tomentosa L. Chara rudis (A. Braun) Leonh. Chara intermedia A. Braun Ogólem liczba gatunków PD ­ pre-dam, DR ­ dam reservoir 2009 DR PD Oct May Jul DR Oct May Jul Oct Oct May Jul + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 5 5 5 10 7 7 5 5 5 8 8 8 dam reservoir, the concentrations of chlorophyll-a (r = 0.53; p = 0.026) and TP (r = 0.51; p = 0.031) positively affected the biomass of floating-leaved macrophytes, also conductivity showed negative correlation with biomass of these plants (r = -0.52; p = 0.027). Submerged macrophytes in pre-dam, in both years, showed the highest biomass in summer (mean 861.3 g and 979.8 g WW m) and the lowest in spring (mean 447.8 g and 555.6 g WW m). Biomass of submerged plants was negatively correlated with dissolved oxygen (r = -0.66; p = 0.003) and positively with total suspension (r = 0.58; p = 0.011) and concentrations of TP (r = 0.61; p = 0.007) and P-PO4 (r = 0.78; p < 0.001). In dam reservoir the highest biomass of elodeids, in both years, was observed in May (mean 2675.9 g and 1841.2 g WW m) and the lowest in October (mean 541.8 g and 694.3 g WW m). The biomass of submerged plants was positively affected by Secchi disc depth (r = 0.90; p < 0.001) and conductivity (r = 0.92; p < 0.001) and negatively by pH (r = -0.52; p = 0.031), total suspension (r = -0.54; p = 0.021), concentration of TP (r = -0.56; p = 0.016), chlorophyll-a (r = -0.59; p = 0.019) and phytoplankton biomass (r = -0.58; p = 0.012). g WW m M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 pre-dam floating-leaved macrophytes M ay08 Jul08 Oct08 M ay09 Jul09 Oct09 dam reservoir submerged macrophytes Fig. 5. Biomass (mean values, +SD) of floating-leaved and submerged macrophytes in pre-dam and dam reservoir Kranik in studied seasons during the years 2008­2009 Trophic state Values of Carlsson index calculated for pre-dam and dam reservoirs, for both years and all seasons indicate the eutrophic state of both reservoirs (Table 2). For pre-dam the values of TSI ranged from 50.3 to 59.7 and for dam reservoir, dependently on season, index of Carlsson reached higher values, from 51.4 to 68.2. The observed changes of TSI index for dam reservoir Kranik seem to be related to the share of P-PO4 in total P loadings. The highest value of Carlsson index, 68.2, was noted in July 2008, at time the highest loading of P-PO4 (6.03 g m) inflow the reservoir and they amounted to 78% of TP loading. The lowest value of TSI, 55.4, was calculated in May 2009, the P-PO4 loading amounted to 1.82 g m and reached 44% of loading of TP. DISCUSSION Phosphorous loadings into dam reservoir Kranik with the Wynica River caused the process of eutrophication of the reservoir and negative changes of species composition and biomass of vegetation. Studies began at spring 2008, two years after the creation of dam-reservoir, thus low diversity of macrophytes in the reservoir and its pre-dam resulted from initial stage of succession. Usually similar structure of vegetation is observed in newly man-made reservoirs [37]. In dam reservoir, among submerged vegetation characeans were noted. These plants are usually the pioneer community in newly created habitats [39]. However, in July 2008, due to high P loadings (4.5­6.0 g m of P-PO4 and 7.5 g m of TP), in dam reservoir there were observed algal blooms (biomass of phytoplankton exceeded 30 mg MM dm-3) and high decrease of water transparency (Secchi disc visibility reached only 0.4 m). At time characean meadows disappeared from the reservoir. Submerged macrophytes responded very quickly to eutrophication process and showed rapid decline of biomass and occurrence of more sensitive species [6, 36]. These relations confirmed significant negative correlations between submerged macrophytes biomass and chlorophyll-a concentration and phytoplankton biomass, as well as a positive correlation of plants biomass with Secchi disc depth. Also, in summer season, rapid development of emergent macrophytes density (form 67 up to 109 stems m) was noted in dam reservoir. The community of helophytes was dominated by common reed (Phragmites australis (Cav.) Trin. ex Steud.). The intensive growth of emergent macrophytes could be related to vegetation period and to increasing concentration of phosphorous compounds in dam reservoir Kranik. This observation confirms positive correlation of helophytes density with concentration of TP. Rooted emergent plants utilize external P loadings during the growing season [20]. P. australis is an emergent species, sensitive to the increase of nutrients concentrations in water and shows a visible increase of its biomass and is a good indicator of eutrophication of water ecosystems [12, 24]. In 2009, in dam reservoir Kranik rigid hornwort, Ceratophyllum demersum L appeared. This unrooted, submerged plant shows ability to uptake dissolved orthophosphates directly from water column and may successfully conquer with phytoplankton [7, 8]. C. demersum was presented in all seasons of 2009 and reached the highest biomass (mean above 1600 g WW m) in May. Relatively high biomass of rigid hornwort (mean above 700 g WW m) was noted in July, despite high biomass of planktonic algae (above 23 mg WW dm-3). Similar results were obtained by Melzer [21], who observed floating mats of C. demersum in highly eutrophic lakes. During two-year studies, a high reduction of P-PO4 loadings was observed in dam reservoir Kranik. The highest retention of dissolved orthophosphates was noted during spring season and amounted to 72% in 2008 and even to 91% in 2009. Usually the highest reduction of P-PO4 (60­80%) in dam reservoirs is observed in summer [26, 33, 35]. High retention of P-PO4 observed in May in dam reservoir Kranik was probably a consequence of rapid growth of soft vegetation. Due to the production of high biomass, submerged macrophytes, are able to accumulate high amounts of inorganic phosphorous in their tissues [1, 9] and affect the concentrations of phosphorous and chlorophyll-a in water column [8]. Trophic state of dam reservoir Kranik depended on season and main biological processes of P loadings elimination. During spring season, values of TSI were the lowest, at time P-PO4 was incorporated mostly into macrophyte biomass and retention of P-PO4 was the highest. Index of Carlsson raised in summer season, in July 2008, TSI amounted to almost 70, value typical for hypertrophic lakes. At time, due to high P-PO4 loadings, in dam reservoir Krasnik a massive development of phytoplankton and algal blooms was observed. CONCLUSIONS Dam reservoir Kranik plays an important role in the reduction of high P loadings in the Wynica River, and led to improvement of quality of river waters. Dependently on season, the retention of total phosphorous ranged from 15 to 48% and dissolved orthophosphates from 52 up to 91%. In dam reservoir, a reduction of P-PO4 loadings is determined by biological processes, phosphorous is incorporated mainly into biomass of macrophytes and planktonic algae. High loadings of P caused eutrophication of dam reservoir Krasnik. Increase of trophic state of reservoir resulted in blooms of planktonic algae and decrease in water transparency. Current loading of P influenced negatively species composition and biomass of macrophytes, mostly sort submerged plants. During two-year studies, the number of submerged macrophytes species was reduced by half and increased biomass of macrophyte species typical for nutrient rich habitats.

Journal

Archives of Environmental Protection – de Gruyter

Published: Sep 1, 2013

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