Increase In Total Phosphorus Concentrations Research Articles

Biogeochemical response of subtropical treatment wetlands to different flow conditions

The biogeochemical response to different flow conditions within two parallel, well-performing flow-ways (FWs) in Everglades Stormwater Treatment Area (STA)-2 was studied. Three flow events in FW1, an emergent aquatic vegetation (EAV) based system and three flow events in FW3, a submerged aquatic vegetation (SAV) dominated system, were carried out between August 2015 and July 2017. These flow events included either low or moderate flow that was preceded and/or followed by no flow. These flow scenarios were designed to simulate different hydraulic and hydrologic conditions that STAs experience during full-scale operations. Hydraulic loading rates (HLRs, flow volume per day/wetland effective treatment area) during the flow events ranged from 0.5 to 10.4 cm d−1 with resulting phosphorus loading rates (PLRs, daily load/wetland effective treatment rate) of 1 to 20 mg P m−2 d−1. The ability of these flow-ways to remove and transform P in the water column under different flow conditions was evaluated using water quality data from autosamplers and weekly grab samples collected at six monitoring stations along each flow-way.Distinct water column concentration gradients of total phosphorus (TP) from inflow to outflow at all phases of the flow events for both flow-ways were observed. The magnitude at which P is removed from the water column increased with fractional distance from the inflow and was greater for the EAV-dominated system (FW1) than the SAV-based system (FW3). This system response translated to higher TP concentration reduction in EAV than SAV. Inflow to outflow TP concentration reductions for EAV were 94, 88, and 86% for moderate (MF), low (LF), and no flow (NF), respectively. For SAV, TP concentration reductions were 73, 71, and 64% for MF, LF, and NF, respectively. A significant increase in TP concentrations [largely dissolved organic P (DOP) and particulate P (PP)] in the SAV-dominated system was observed under no flow condition. The increase was attributed to in-situ production of PP through several mechanisms that likely include phytoplankton growth, periphyton sloughing, litter fragmentation, and resuspension via entrainment or bioturbation. While soluble reactive P (SRP) was the dominant form of inflow TP removed along the EAV FW, PP accounted for most of the reduction in TP concentration along the SAV FW, under both flow and no flow conditions. Particulate P and DOP comprised the residual P pool at the outflow region of each FW with slightly higher concentrations in the SAV than the EAV FW under no flow condition. The removal of P from the water column in the EAV FW was largely attributed to biotic processes (i.e., P uptake by biota) while coupled biotic and abiotic processes regulated P reduction in the SAV FW.

Abrupt chlorophyll shift driven by phosphorus threshold in a small subtropical estuary

Chlorophyll trends in subtropical and tropical estuaries are under characterized and may reveal patterns not shared by their temperate analogues. Detection of trends requires long-term monitoring programs, but these are uncommon. In this study, we utilized an 18-year chlorophyll-a time series from 2002 to 2020 in Weeks Bay, AL, to detect and quantify trends in chlorophyll variability over multiple time scales. Our analysis included up to 30 years of contemporaneous data for variables such as river discharge, nitrogen, and phosphorus to relate the chlorophyll-a trends to environmental drivers. We detected an abrupt shift in chlorophyll-a that was linked to changes in phosphorus and hydrology. The shift followed an abrupt increase in total phosphorus concentration from upstream of the primary river system that discharges into Weeks Bay. Total phosphorus continued to rise after the abrupt shift, but there was no detectable change in chlorophyll-a. We propose that the exceedance of a total phosphorus threshold at 0.1 mg l-1, combined with a period of very low river discharge variability, induced the shift in chlorophyll-a. This shift opposed the pattern of proportional change usually observed as a result of nutrient enrichment. Not all monitoring stations underwent the abrupt shift, which demonstrated the complexity of phytoplankton response to environmental drivers and the significance of spatial differences even over small estuaries.

Spatiotemporal variation and influencing factors of nitrogen and phosphorus in lake sediments in China since 1850

Chinese lakes have been affected by climate change, agricultural intensification and population increases since 1850. However, the spatiotemporal variations in nitrogen and phosphorus in lake sediments and the factors influencing these variations are poorly understood. This research analysed the spatiotemporal variations in the mass accumulation rate (MAR) and total nitrogen (TN) and total phosphorus (TP) concentrations of sediments since 1850 and the responses of these factors to the influence of natural and anthropic factors through the collection of data from 56 lake sediment samples in China. After 2000, the average MAR value (2794 g/m2/yr), TN concentration (0.35%) and TP concentration (0.96‰) of lake sediments were significantly higher than the average values during 1850–1900 (p < 0.05). During the study period, the MAR of the lake sediments in the eastern plain (EP) was the highest in the country, and the increase was also largest in this region. The TN concentrations of lake sediments in the Northeast Plain (NEP) were the highest in the country, and the TN concentrations of lakes in the Yunnan-Guizhou Plateau (YGP) underwent the largest increase. The TP concentrations in the sediments of the YGP were higher than the national average during the study period, and the lakes in the NEP had the highest increase in TP concentrations. The result showed climate and lake morphology are important factors controlling the indices in lakes' sediment in Qinghai-Tibet Plateau (QTP) since 1900. Climate and lake morphology are major impact factors for lakes’ sediment indices in NEP, EP, Mongolia- Xinjiang Plateau (MXP) and YGP in 1900–1950. After 1950, anthropic factors gradually replaced natural factors and became the main factors affecting these four regions and anthropic factors promoted the increase of nutrient concentration in lake sediments. The results of this study show that sustainable agricultural development policies and population policies can help control the quality of nutrients entering lakes, thereby reducing the concentrations of nutrients in lake sediments in the future.

Climate change impact on water quality in the integrated Mahabad Dam watershed-reservoir system

Climate change, besides global warming, is expected to intensify the hydrological cycle, which can impact watershed nutrient yields and affect water quality in the receiving water bodies. The Mahabad Dam Reservoir in northwest Iran is a eutrophic reservoir due to excessive watershed nutrient input, which could be exacerbated due to climate change. In this regard, a holistic approach was employed by linking a climate model (CanESM2), watershed-scale model (SWAT), and reservoir water quality model (CE-QUAL-W2). The triple model investigates the cumulative climate change effects on hydrological parameters, watershed yields, and the reservoir’s water quality. The SDSM model downscaled the output of the climate model under moderate (RCP4.5) and extreme (RCP8.5) scenarios for the periods of 2021–2040 and 2041–2060. The impact of future climate conditions was investigated on the watershed runoff and total phosphorus (TP) load, and consequently, water quality status in the dam’s reservoir. The results of comparing future conditions (2021–2060) with observed present values under moderate to extreme climate scenarios showed a 4–7% temperature increase and a 6–11% precipitation decrease. Moreover, the SWAT model showed a 9–16% decline in streamflow and a 12–18% decline in the watershed TP load for the same comparative period. Finally, CE-QUAL-W2 model results showed a 3–8% increase in the reservoir water temperature and a 10–16% increase in TP concentration. It indicates that climate change would intensify the thermal stratification and eutrophication level in the reservoir, especially during the year’s warm months. This finding specifies an alarming condition that demands serious preventive and corrective measures.

Calculation of total phosphorus loads from rivers around Lake Taihu and analysis of total phosphorus fluctuation in the lake in 2015-2016

太湖流域水环境综合治理力度空前，太湖总磷浓度却于2015、2016年重回升势，蓝藻大面积暴发情况也未得到有效遏制.本文从2015和2016年环太湖河道的进出太湖水量、总磷负荷量计算入手，结合雨情、水情、太湖调蓄以及人为影响等各方面因素，分别开展水量和总磷负荷质量的平衡分析.在此基础上，结合2010-2017年环太湖河流多年平均进出太湖总磷负荷量对比，分析太湖总磷的外源、内源变化趋势及来源，探讨2015和2016年太湖总磷升高的原因及控制重点方向.结果表明，2015和2016年为太湖流域丰水年，尤其是2016年发生特大洪水，太湖年内最高水位达4.87 m，仅次于1999年的4.97 m的历史最高水位.2015和2016年大量外源总磷负荷进入太湖，其中环太湖河道带入的总磷负荷量占年度太湖总磷负荷总量的66.8%和74.2%，成为进入太湖的总磷负荷的主要外源；加之，2015年太湖水生植物收割造成当年沉水植物面积较上年同期下降88.7%，水生植物骤减导致对磷的吸收转化能力下降，滞留在湖体中的总磷负荷量占年度太湖总磷负荷总量的21.5%和27.5%，成为影响太湖水体总磷浓度的重要内源.太湖总磷浓度升高又为太湖蓝藻暴发进一步提供了营养盐基础，亟需强化太湖总磷源头的控制、减少总磷入湖总量.;Government has strengthened the comprehensive management and restoration of the water environment in Taihu Basin. Despite the great efforts, the total phosphorus concentration in Lake Taihu rebounded in 2015-2016. Occurrence of cyanobacterial blooms has not been effectively inhibited. Thus, this essay is going to examine the reasons behind and figure out the key direction in controlling the total phosphorus in Lake Taihu. The water quantity balance analysis and the total phosphorus mass balance analysis will be carried out through the calculation of the total phosphorous fluxes and the water flows between Lake Taihu and the surrounding rivers. Affecting factors, including rainfall, lake storage regulation and human factors, will also be considered. Based on the analysis, we will investigate the sources of total phosphorus change in Lake Taihu as well as the reasons of variations. The results showed that Taihu Basin had abundant rainfall in 2015-2016, especially in 2016, there was a severe basin flooding. The maximum water level of Lake Taihu reached 4.87 m, only 0.1 m lower than that of the historical record in 1999. Enormous total phosphorus load flowed from the surrounding rivers to Lake Taihu, which became the main external source of Lake Taihu's total phosphorus load. The load from rivers occupied 66.8% and 74.2% of the annual total phosphorus load in Lake Taihu in 2015 and 2016, respectively. On the other hand, for internal source, the massive reduction of submerged plants played an important role in affecting the total phosphorus concentration in Lake Taihu. The area of submerged aquatic plants in Lake Taihu decreased by 88.7% in 2015. The large-scale harvest of aquatic plants hindered the phosphorus absorption and transformation capacity of the lake. In 2015 and 2016, the total phosphorus load retained in Lake Taihu accounted for 21.5% and 27.5% of the total phosphorus load. The increase in total phosphorus concentration in Lake Taihu provided a strong foundation for cyanobacterial blooms. It is urgent to lower the amount of total phosphorus into Lake Taihu and tighten the control of the total phosphorus sources.

The role of turbulence in internal phosphorus release: Turbulence intensity matters

Hydrodynamic fluctuations can trigger sediment suspension concomitantly with internal phosphorus release, while the interactive effect of turbulence mixing and sediment suspension on the regulation of phosphorus dynamics is in need of deep understanding. This study addressed the changes in total phosphorus (TP), phosphate (PO43--P) and suspended sediment (SS) in the overlying water, and measured the profile of dissolved oxygen (DO), Fe(II) and soluble reactive phosphorus (SRP) across the sediment-water interface in the simulated environmental turbulence scenario, For a turbulence intensity (ε) of 3.6 × 10−3 m2/s3, the SRP flux increased hence PO43--P showed a 36.36% increase relative to its initial level. Although ε of 1.3 × 10−2 m2/s3 benefited the delivery of oxygen from the bulk aqueous phase to the upper sediment which can trigger the formation of Fe oxides and hydroxides, the turbulence-induced phosphorus diffusion from the sediment exceeded its inactivation and resulted in a large SRP flux. However, a protion of the released PO43--P can be immobilized through SS adsorption and biotic (likely cyanobacteria) assimilation. Higher turbulence intensities (ε of 3.3 × 10−2 and 7.4 × 10−2 m2/s3) led to an approximately 40-fold increase in TP concentration and a significant increase in sediment suspension, which contributed to the immobilization of a majority of the phosphate through adsorption; thus, the PO43--P concentrations in the overlying water displayed 47.75% and 41.67% decline, respectively. This study also confirmed the sequential phosphorus buffer mechanisms associated with increasing turbulence intensities. With an ε of 3.6 × 10−3 m2/s3, bounding to Fe ion had a significant impact on phosphorus inactivation but with an ε of 7.4 × 10−2 m2/s3, the main immobilization mechanism is switched to phosphorus adsorption from the large quantity of suspended sediment.

Multiple stressor effects on biological quality elements in the Ebro River: Present diagnosis and predicted responses

Multiple abiotic stressors affect the ecological status of water bodies. The status of waterbodies in the Ebro catchment (NE Spain) is evaluated using the biological quality elements (BQEs) of diatoms, invertebrates and macrophytes. The multi-stressor influence on the three BQEs was evaluated using the monitoring dataset available from the catchment water authority. Nutrient concentrations, especially total phosphorus (TP), affected most of the analyzed BQEs, while changes in mean discharge, water temperature, or river morphology did not show significant influences. Linear statistical models were used to evaluate the change of water bodies' ecological status under different combinations of future socioeconomic and climate scenarios. Changes in land use, rainfall, water temperature, mean discharge, TP and nitrate concentrations were modeled according to the future scenarios. These revealed an evolution of the abiotic stressors that could lead to a general decrease in the ecosystem quality of water bodies within the Ebro catchment. This deterioration was especially evidenced on the diatoms and invertebrate biological indices, mainly because of the foreseen increase in TP concentrations. Water bodies located in the headwaters were seen as the most sensitive to future changes.

Effects of Precipitation and Topography on Total Phosphorus Loss from Purple Soil

The Sichuan Basin is the main agricultural production area of the upper reaches of the Yangtze River and is also an extremely important ecological area because it is rich in biodiversity and has complex and diverse landscape types. The dominant soil type, purple soil, is prone to rapid soil erosion and weathering processes because it is shallow and rich in phosphorus and other nutrients. Field experiments were conducted to reveal the effects of precipitation and topography characteristics on nonpoint source pollutants from purple soil. The results showed that total phosphorus (TP) load and TP concentration both increased with increasing rainfall amount, and there was an initial time of runoff and sediment yield before runoff generation. Moreover, the TP load generally increased with precipitation intensity as setting a coincident value of rainfall amount; however, the difference between TP load at 30 and 60 mm/h was minimal as was the difference between 90 and 120 mm/h. Similarly, TP concentration increased with increasing precipitation intensity. In terms of topographical conditions, TP load increased with increasing gradient, but began to decline when the gradient was about 20°, which indicates that 20° is the critical gradient for TP loss. There was a significant positive correlation between gradient and TP concentration when the gradient was &lt;15°, whereas the increase in TP concentration slowed as the gradient increased.

Insights into organic farming of European sea bass Dicentrarchus labrax and gilthead sea bream Sparus aurata through the assessment of environmental impact, growth performance, fish welfare and product quality

The organic farming of sea bass and sea bream was investigated in a commercial farm by assessing environmental impact, growth performance, fish welfare and product quality in a multidisciplinary approach. Organic and conventional juveniles were reared in four circular 3.800m3 floating sea cages at a maximum final stocking density of 15kg/m3 and fed on organic or conventional commercial feeds. Conventional farming was started simultaneously and monitored as the reference condition. Environmental and biological samplings were performed after 16months at the first fish harvesting. No environmental impact was observed in the organic farming area, whereas a significant increase in total phosphorus concentration in the sediment and some changes in the structure and species composition of benthic assemblages were detected just beneath the conventional sea cages with no impact 25m from the cages. Organic fish showed a better growth performance consistent with the lower feed conversion ratio and higher metabolic status, as evidenced from the protein and energy profiles, compared with conventional fish. No dietary influence on stress and immune response was observed. A higher incidence of fin splitting occurred, probably due to nutritional factors and/or to the larger size of organic fish.Similar good morphological, physical and sensory traits between organic and conventional fish were observed, as denoted by the high fillet yield, low flesh lipid content, long freshness and shelf life both in sea bream and in sea bass. Conversely, the fillet fatty acid composition was different, being poorer in n-3 PUFA and richer in linoleic acid (C18:2 n-6) in organic versus conventional fish, mirroring the fatty acid profile of the diet.The organic farming of sea bass and sea bream exhibited an overall good performance. Husbandry and feeding practices did not produce any evident environmental impact although long-period investigations covering several full production cycles are needed. Organic fish grew well, displayed an overall state of well-being and had good quality features despite a lower EPA and DHA content. Improvement of organic feed formulation and quality of feed ingredients emerge as important issues to be addressed to optimize the nutritional quality of organic sea bass and sea bream.

Stable isotope compositions of aquatic flora as indicators of wetland eutrophication

Abstract Carbon and nitrogen stable isotopes (δ13C and δ15N) have been used as indicators for environmental changes in aquatic ecosystems. In this study, δ13C and δ15N values of select flora taxa were evaluated as indicators of human-induced eutrophication in an Everglades wetland which has been impaired by the source and quality of inflow and the alteration of hydrological pattern. Results showed that δ13C of cattail (Typha domingensis Pers.) increased with the decrease in total phosphorus (TP) concentration. Limited data for sawgrass (Cladium jamaicenses Crantz) collected at three study sites along the nutrient gradient also show a similar change in δ13C. However, δ13C of periphyton and bladderwort (Utricularia sp.) decreased with the decrease in TP concentration. The elevated δ13C values of emergent vascular plants (cattail and sawgrass) were likely the results of decreases in stomatal conductance, carboxylation and 13C fractionation under nutrient stress. This is supported by corresponding decreases in photosynthetic rate of cattail along the decreasing nutrient gradient. In contrast, δ15N values of all flora taxa increased with the increase in TP concentration. Findings from this study indicate that δ13C of emergent plants is a sensitive indicator for nutrient stress while δ15N of major flora species may serve as a robust indicator for wetland eutrophication.

Biodiversity of constructed wetlands for wastewater treatment

Constructed wetlands are often built for wastewater treatment to mitigate the adverse effects of organic pollution in streams and rivers caused by inputs of municipal wastewater. However, there has been little analysis of biodiversity and related factors influencing the ecosystem functioning of constructed wetlands. The purpose of this study was to evaluate the biodiversity of two free-water-surface integrated constructed wetlands in subtropical Taiwan by analyzing the water quality, habitat characteristics, and biotic communities of algae, macrophytes, birds, fish, and aquatic macroinvertebrates in the treatment cells. Our results indicated that the two integrated constructed wetlands (Hsin-Hai II and Daniaopi Constructed Wetlands) achieved good performance in reducing the concentrations of total nitrogen (TN) and total phosphorus (TP), and loadings of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) from municipal sewage. In total, 58 bird species, 7 fish species, and 34 aquatic macroinvertebrate taxa were recorded in the two wetlands. The results of stepwise multiple regressions showed that the richness, abundance, and diversity of birds increased with wetland area. Fish richness and abundance respectively increased with wetland area and dissolved oxygen, while the diversity decreased with increases in TP concentrations. The richness and density of aquatic macroinvertebrates increased with the cover of aquatic macrophytes, while the diversity increased with wetland area. Ordination analyses indicated that variations in the community structures of birds, fishes, and aquatic macroinvertebrates were respectively best explained by water temperature, wetland area, and species richness of fish. Our results suggest that wetland area, cover of aquatic macrophytes, and water quality were the most important factors governing the diversity in the constructed wetlands, and that the factors influencing community structures varied among different taxonomic groups. In addition to improving water quality, this study implied that the biodiversity of constructed wetlands for wastewater treatment can be enhanced through proper design and management.

Contaminación producida por piscicultura intensiva en lagunas andinas de Junín, Perú

We report the changes produced by intensive farming of rainbow trout Oncorhynchus mykiss in seven Andean lagoons. The observations were made in 1996 and between 2002– 2007 and allowed to observe the deterioration of the lakes, characterized by the increase in total phosphorus concentrations and decreased dissolved oxygen and transparency. The benthic community was evaluated in seven lakes in 2007, resulting low number of species and diversity indices (H '<1,26; <8 spp.). The abundance ranged from 7 to 35 ind. /0,04 m 2 . Organic matter and carbonates were high in the bottom (from 30,22 to 42,45%).

Morphometry and stratification of the Bents Basin scour pool, Nepean River, NSW

The Bents Basin scour pool is a large hole eroded into the bed of the Nepean River where it flows through the Lapstone Structural Complex at the downstream and of the Bents Bsin sandstone gorge. The scour pool has a surface area of 17500m², a volume of 157400m³, a mean depth of 9.0m, a maximum depth of 22.8m and is an oval-shaped cone. While the capacity-inflow ration is only 0.00054 and indicated that pool volume is very small in relation to the mean annual flow, the scour pool is not flushed for time period of up to 12 months long. Thermal stratification was measured between Mid-January and March 1996 when the thermocline was usually at a depth of 10m. Temperature differences of between 9.6 and 14.7C were measured between the surface and the bottom at times of stratification. Density differences of 2kg/m³ were calculated as a result of thermal stratification. Oxygen stratification was measured between January and April 1996 when the oxycline varied between depths of 7 and 12m. Anoxic conditions were usually recorded below the oxycline. Oxygen stratification resulted in a large increase in total phosphorus concentrations, due to the release of sediment-bound phosphorus. Cation concentration did not vary with depth. Datalogging on 6-7 March 1996 proved that both thermal and oxygen stratification persisted throughout the night. Stratification was recorded between mid-January and March/April 1996 because climatic and hydrologic conditions were not capable of generating sufficient turbulence to mix and hence destratify the scour pool. Current water quality monitoring programs on the Nepean River by government agencies are flawed because they do not sample the whole water column, only surface waters. As a result, these programs present a biased assessment of current conditions during summer.

Do phytoplankton communities correctly track trophic changes? An assessment using directly measured and palaeolimnological data

Summary1. Measurements of total phosphorus (TP) concentrations since 1975 and a 50‐year time series of phytoplankton biovolume and species composition from Lake Mondsee (Austria) were combined with palaeolimnological information on diatom composition and reconstructed TP‐levels to describe the response of phytoplankton communities to changing nutrient conditions.2. Four phases were identified in the long‐term record. Phase I was the pre‐eutrophication period characterised by TP‐levels of about 6 μg L−1 and diatom dominance. Phase II began in 1966 with an increase in TP concentration followed by the invasion of Planktothrix rubescens in 1968, characterising mesotrophic conditions. Phase III, from 1976 to 1979, had the highest annual mean TP concentrations (up to 36 μg L−1) and phytoplankton biovolumes (3.57 mm3 L−1), although reductions in external nutrient loading started in 1974. Phases II and III saw an expansion of species characteristic of higher nutrient levels as reflected in the diatom stratigraphy. Oligotrophication (phase IV) began in 1980 when annual average TP concentration, Secchi depth and algal biovolume began to decline, accompanied by increasing concentrations of soluble reactive silica.3. The period from 1981 to 1986 was characterised by asynchronous trends. Annual mean and maximum total phytoplankton biovolume initially continued to increase after TP concentration began to decline. Reductions in phytoplankton biovolume were delayed by about 5 years. Several phytoplankton species differed in the timing of their responses to changing nutrient conditions. For example, while P. rubescens declined concomitantly with the decline in TP concentration, other species indicative of higher phosphorus concentrations, such as Tabellaria flocculosa var. asterionelloides, tended to increase further.4. These data therefore do not support the hypotheses that a reduction in TP concentration is accompanied by (i) an immediate decline in total phytoplankton biovolume and (ii) persistence of the species composition characterising the phytoplankton community before nutrient reduction.

The impact of tourism on dune lakes on Fraser Island, Australia

AbstractIn view of the increasing tourism to Fraser Island, Queensland, a tourist pressure index (TPI) was developed to assess the potential threat of tourism to 15 of the most accessible dune lakes on the island. Tourist pressure index scores indicated that the two clear lakes on the island, Lake McKenzie and Lake Birrabeen, are most threatened by tourist activities owing to their accessibility, facilities and prominence in advertising campaigns. In addition, limnological investigations of the same 15 lakes were conducted in February 1999 to determine their current trophic status and potential susceptibility to adverse impacts from tourism, particularly with reference to eutrophication. On the basis of nutrient and chlorophyll a concentrations, the two water table window lakes, Ocean Lake and Lake Wabby, were classed as mesotrophic and oligo‐mesotrophic, while all of the perched dune lakes were oligotrophic. Lake McKenzie and Lake Birrabeen, the two most threatened lakes according to TPI scores, had the lowest nutrient concentrations of all of the lakes examined and, consequently, we suggest that nutrient additions might elicit rapid algal growth responses in these systems. Comparisons between current data and historical data from Arthington et al. (1990) indicate that increases in planktonic chlorophyll a concentrations were not always directly mirrored by increases in total phosphorus concentrations. We found that while chlorophyll a concentrations were significantly higher in the 1999 samples than in the 1990 samples for all lakes, total phosphorus concentrations were higher in Ocean Lake, lower in Lake Jennings and similar in lakes McKenzie, Birrabeen and Wabby.

Response of the Cladoceran Community to Trophic State Change in Lake Apopka, Florida

A paleolimnological evaluation of cladoceran microfossils was initiated to study limnological changes in Lake Apopka, a large (125 km2), shallow (mean depth = 1.6 m), warm, polymictic lake in central Florida. The lake switched from macrophyte to algal dominance in the late 1940s, creating a Sediment Discontinuity Layer (SDL) that can be visually used to separate sediments derived from macrophytes and phytoplankton. Cladoceran microfossils were enumerated as a means of corroborating extant eutrophication data from the sediment record. Inferences about the timing and trajectory of eutrophication were made using the cladoceran-based paleo-reconstruction. The cladoceran community of Lake Apopka began to change abruptly in both total abundance and relative percent abundance just before the lake shifted from macrophyte to algal dominance. Alona affinis, a mud-vegetation associated cladoceran, disappeared before the SDL was formed. Planktonic and benthic species also began to increase below the SDL, indicating an increase in production of both planktonic and benthic species. Chydorus cf. sphaericus, an indicator of nutrient loading, increased relative to all other cladocerans beginning in the layer below the SDL and continuing upcore. Changes in the transitional sediment layer formed before the lake switched to phytoplankton dominance, including an increase in total phosphorus concentration, suggest a more gradual eutrophication process than previously reported. Data from this study supported conclusions from other paleolimnological studies that suggested anthropogenic phosphorus loading was the key factor in the hypereutrophication of Lake Apopka.

Seasonal changes of mechanisms maintaining clear water in a shallow lake with abundant Chara vegetation

The study is based on monitoring data on the seasonal variation during four (1996–1999) vegetation periods, as well as long-term summer data on submerged vegetation, nutrients, light, phytoplankton and zooplankton in Lake Krankesjön, a shallow, calcium-rich, moderately eutrophic lake in southern Sweden. The lake has been in the clear water state with abundant submerged vegetation since the end of the 1980s. Somewhat lower summer biomass of submerged macrophytes during 1997 and 1999 indicates a temporary instability of the clear water state. During these 2 years, summer transparency was about 1.2–2.1 m, while concentrations of total phosphorus and chlorophyll (Chl) a were about 26–40 and 8–18 μg l −1, respectively. Summer biomass of submerged macrophytes was higher during 1996 and 1998. In both years, a distinct increase in light availability and decrease in concentrations of nutrients and chlorophyll occurred simultaneously with the development of dense Chara vegetation. Summer values for transparency were about 2.0–2.5 m, while concentrations of total phosphorus and Chl a were about 20–32 and 4–11 μg l −1, respectively. Summer biomass of crustacean zooplankton was below 250 μg l −1 during all 4 years. A peak abundance of Cladocera (mainly Bosmina longirostris) during May or June caused only a short-term reduction in chlorophyll concentrations that was more pronounced in 1997 than in 1996. Measured light attenuation during 1999 was closely correlated with light attenuation calculated from the amount of suspended solids, chlorophyll concentrations, and water colour. Detritus contributed most to the total amount of suspended solids, while chlorophyll was the main contributor to light attenuation. A long-term decrease of the ratios between chlorophyll and total phosphorus suggests that phytoplankton in the clear water state is limited by factors other than total phosphorus concentrations. Increased sedimentation rate, carbon limitation, allelopathy and a lower bioavailable fraction of the total amount of phosphorus are possible explanations, while nitrogen limitation and grazing from zooplankton probably are of minor importance. Possible reasons for the “instability” of the clear water state during 1997 and 1999 are discussed. Unusually high water level as well as cold and windy weather during the spring of 1996–1999 may have caused a slow and late growth of the plants and thus a temporary instability. However, a tendency for an increase in total phosphorus concentrations and sediment accumulation along the wind-protected shores during the clear water state indicate the possibility of a long-term destabilization which contradicts the alternative stable states model.

Impacts of a phosphate detergent ban on concentrations of phosphorus in the James River, Virginia

Phosphorus in the James River, VA, was measured before and after implementation of a state-wide ban on phosphorus containing detergents. Increases in phosphorus concentrations between sites located upriver and downriver from point sources at Richmond, VA, were compared before and after the ban. Prior to the ban, point sources in the Richmond area were responsible for an 85%. (0.11 mg l −1) increase in total phosphorus concentrations between the upriver and downriver sites. After the ban, the increase was reduced to 13% (0.02 mg l −1). Concentrations of dissolved orthophosphate were increased by 88% (0.08 mg l −1) before the ban as compared to 25% (0.02 mg l −1) after the ban.

Quantifying the impact of periphytic algae on nutrient availability for phytoplankton

SUMMARY. Recent laboratory studies demonstrate that periphytic algae growing on the sediment surface reduce nutrient availability in the overlying water. Consequently, periphytic algae may competitively reduce growth of phytoplankton. The aim of this study was to quantify the competitive impact of sediment‐attached periphytic algae on phytoplankton in the presence of all other factors simultaneously affecting nutrient dynamics in natural systems. In enclosure experiments, performed in three lakes of different productivity, the periphytic algal biomass was manipulated. When compared to enclosures with high biomass of periphytic algae, those with reduced biomass showed an increase in total phosphorus concentration in the water of 32–44%. Extrapolation of the experimental results to whole lakes predicts an increase in original total phosphorus concentration of between 1.5% and 8.0%. According to existing regressions between total phosphorus and phytoplankton chlorophyll, the potential increase in original phytoplankton biomass will be between 2.5% and 12.6%. With respect to the shallow parts of lakes, my results support the conclusions revealed from laboratory studies that periphytic algae have a significant impact on the phosphorus concentration in the overlying water. However, when considering whole‐lake dynamics, the competitive impact of periphytic algae on phytoplankton biomass development is probably of minor importance. Rather, the main competitive advantage of growing on the sediment surface, compared to in the water, may be the exclusive access to nutrients in the sediment.

The Eutrophication of Lake Okeechobee

ABSTRACT Average annual total phosphorus concentrations in Lake Okeechobee increased from 0.049 mg/L in 1973 to 0.098 mg/L in 1984. The increases in total phosphorus concentrations were not correlated to external phosphorus inputs, but to changes in lake water levels. It is proposed that the flooding of marshes and exposed lake bottom primarily caused increased total phosphorus concentrations, but that the resuspension of bottom sediments by wind action may also be a major factor influencing in-lake total phosphorus concentrations. Reducing phosphorus inputs by 40 percent as proposed by the Lake Okeechobee Technical Advisory Committee (LOTAC) will not significantly improve water quality in Lake Okeechobee. Average total phosphorus concentrations will not decline significantly. Chlorophyll a concentrations and Secchi transparencies are not correlated to total phosphorus concentrations so massive expenditures of public funds to reduce nutrient inputs will not protect long-term water quality at Lake Okeechobee.