Excessive Phosphorus Loading Research Articles

Integrating soil testing phosphorus into environmentally based manure management in peri-urban regions: A case study in the Beijing area

Rapid growth in intensive peri-urban livestock farming has led to excessive manure phosphorus (P) loads in some regions of China, with an increasing risk of eutrophication of watercourses. There is an urgent need to assess the potential regional landbank available to receive these manures to both satisfy crop demand and reduce environmental pollution. In this case study, we assessed the potential distribution of manure P applications to arable land in the Beijing area, based on the exclusion of land above a critical value of soil Olsen-P, with a slope >25°, and land designated as water protection zones. The effects of different cropping area structures and contrasting P application strategies on changes in soil P status were assessed using scenario analysis. Results show that current manure generation (2011) has resulted in high P surpluses, with an average manure P loading rate to arable land of 53kgPha−1. We estimate that 11% of arable land is unsuitable for continuous P applications due to high soil P levels, which exceed the P environmental risk threshold. Under the traditional P management scenario, the Olsen-P in vegetable and orchard land will be saturated (more than soil P environmental threshold) before 2030, whilst the Olsen-P of cereal land will be close to the soil P environmental threshold in 2030. Scenario analysis results suggested that increasing the proportion of manure applied to cereal fields reduced the annual P surplus, which in turn alleviated the over-accumulation of P in orchards and vegetable fields. The annual total manure P excretion is expected to increase from 21.3 Gg in 2011 to 30.8 Gg in 2030, and the predicted soil Olsen-P levels for 2030 are estimated to increase to 55, 106 and 132mgkg−1 in cereal, orchard and vegetable land, respectively. However, a balanced P management strategy could maintain much lower soil Olsen-P levels, i.e., 24, 22 and 27mgkg−1 in cereal, orchard and vegetable land, respectively. Applying manure to cereal fields with relatively low Olsen-P levels, and exporting surplus manure out of the peri-urban regions of Beijing are regarded as the key strategies to minimize environmental P risk.

Developing a 21st Century framework for lake-specific eutrophication assessment using quantile regression

Over the past 30+ years, researchers and water resource managers have often relied on a set of regression-based equations to describe the relationships between secchi depth (SD), chlorophyll (Chl) and total phosphorous (TP) and quantitatively assess lake trophic status after Carlson (1977). Here, we develop a revised framework for eutrophication assessment that incorporates recent statistical advances in ecology and leverages the increasing availability of lake-specific datasets in the 21st Century. Long-term (1992–2012) water quality data from Lake Champlain (LC) are used to revisit and revise classic equations of tropic state indices (TSIChl/TP). The upper boundaries of SD–ln(Chl) and ln(Chl)–ln(TP) distributions within this dataset fit well with quantile regression (99th, QR) to generate LC-specific TSIChl/TP equations. Our results illustrate that Carlson (1977)'s original TSIChl/TP equations overestimate the trophic status of LC relative to LC-specific equations, and highlight the power of the QR-derived TSIChl/TP metric. We combine TSISD and TSIChl into one metric to indicate pseudoeutrophication and pseudomesotrophication of oligotrophic waters as well as pseudoeutrophication of mesotrophic waters to identify waters threatened by potential trophic shift. Additionally, TSIChl and TSITP were coupled as a complimentary dual metric to indicate potential risks of excessive phosphorus loading to oligotrophic and mesotrophic waters. With these dual metric schemes, we performed cluster analysis of 15 locations to spatially assess trophic status and phosphorous risks across LC. This study describes a relatively simple and robust approach for lake-specific status assessment, the structure of which can be broadly utilized within monitoring and research communities.

Controlling cyanobacterial blooms by managing nutrient ratio and limitation in a large hyper-eutrophic lake: Lake Taihu, China

Excessive nitrogen (N) and phosphorus (P) loading of aquatic ecosystems is a leading cause of eutrophication and harmful algal blooms worldwide, and reducing nutrient levels in water has been a primary management objective. To provide a rational protection strategy and predict future trends of eutrophication in eutrophic lakes, we need to understand the relationships between nutrient ratios and nutrient limitations. We conducted a set of outdoor bioassays at the shore of Lake Taihu. It showed that N only additions induced phytoplankton growth but adding only P did not. Combined N plus P additions promoted higher phytoplankton biomass than N only additions, which suggested that both N and P were deficient for maximum phytoplankton growth in this lake (TN:TP=18.9). When nutrients are present at less than 7.75–13.95mg/L TN and 0.41–0.74mg/L TP, the deficiency of either N or P or both limits the growth of phytoplankton. N limitation then takes place when the TN:TP ratio is less than 21.5–24.7 (TDN:TDP was 34.2–44.3), and P limitation occurs above this. Therefore, according to this ratio, controlling N when N limitation exists and controlling P when P deficiency is present will prevent algal blooms effectively in the short term. But for the long term, a persistent dual nutrient (N and P) management strategy is necessary.

Stochastic sequential dispersal and nutrient enrichment drive beta diversity in space and time

Nutrient pollution constitutes a major threat to biodiversity, one whose magnitude is predicted to increase greatly in the near future. While the negative effects of excessive nitrogen and phosphorus loading on local species diversity are widely appreciated, a growing body of evidence indicates that increases in productivity (a correlate of nutrient supply) can also reduce predictability in community composition by driving community divergence and increases in beta diversity (or compositional dissimilarity among communities). Stochastic variation in dispersal history has frequently been cited as a cause of such patterns. However, underlying mechanisms have not received strong experimental scrutiny. I present results of a microcosm experiment testing the effects of enrichment and dispersal mode on zooplankton community structure. I show that beta diversity increases with enrichment but only in the presence of sequential dispersal and variation in dispersal history. Sequential dispersal and enrichment enhanced beta diversity by driving increases in temporal compositional turnover (or beta diversity in time). These results suggest that nutrient enrichment and dispersal may have interactive effects on community organization by facilitating persistent compositional flux and reducing our ability to predict the structure of communities in both space and time.

Impacts of wind waves on sediment transport in a large, shallow lake

AbstractLake Okeechobee is a large, shallow subtropical lake, located in south Florida. Over the last several decades, Lake Okeechobee has experienced accelerated eutrophication due to excessive phosphorus loads from agricultural run‐off. Recycling of phosphorus from bottom sediments through resuspension is critical to addressing eutrophication of the lake and for water quality management. The present study investigates the impacts of wind waves on sediment transport in Lake Okeechobee, using measured data and the Lake Okeechobee Environmental Model (LOEM). The LOEM was fully calibrated and verified with more than 10 years of measured data in previous studies. Analysis of the measured data indicates significant wave height (SWH) and suspended sediment concentration are closely correlated to the wind speed in the lake. The nonlinear interaction of high‐frequency wind waves with relatively low‐frequency currents in the boundary layer plays a key role in sediment deposition/resuspension. Without considering the effects of wind waves, the bottom shear stress can be greatly underestimated. The spatial variations of key variables for sediment modelling, including SWH, water depth, orbital velocity, current velocity, bottom shear stress and sediment concentration, are discussed. In general, the near‐bottom wave velocity (and the associated bottom shear stress) is greater than or the same order of magnitude as the near‐bed current velocity (and the associated bottom shear stress) in this shallow water system. Although the sediment zones of Lake Okeechobee were described in previous studies, few published papers discussed its formation mechanisms. The findings of the present study include that the multiyear averaged bottom shear stress with wind‐wave effect plays a key role in forming the spatial patterns of the sediment zones. The study results are currently being used in lake management and in developing strategies for reducing phosphorus in the lake.

Remote sensing models using Landsat satellite data to monitor algal blooms in Lake Champlain

Lake Champlain is significantly impaired by excess phosphorus loading, requiring frequent lake-wide monitoring for eutrophic conditions and algal blooms. Satellite remote sensing provides regular, synoptic coverage of algal production over large areas with better spatial and temporal resolution compared with in situ monitoring. This study developed two algal production models using Landsat Enhanced Thematic Mapper Plus (ETM(+)) satellite imagery: a single band model and a band ratio model. The models predicted chlorophyll a concentrations to estimate algal cell densities throughout Lake Champlain. Each model was calibrated with in situ data compiled from summer 2006 (July 24 to September 10), and then validated with data for individual days in August 2007 and 2008. Validation results for the final single band and band ratio models produced Nash-Sutcliffe efficiency (NSE) coefficients of 0.65 and 0.66, respectively, confirming satisfactory model performance for both models. Because these models have been validated over multiple days and years, they can be applied for continuous monitoring of the lake.

The use of the integrated trophic state index in evaluation of the restored shallow water bodies

The aim of this study was to determine the trophic status of five restored shallow lakes from a group of 30 water bodies in the Olsztyn Lakeland, which were dried in the 19 century as part of a land reclamation program. The effectiveness of the Integrated Trophic State Index (ITS) in the evaluation process was analyzed. ITS is a relatively new method for diagnosing eutrophication intensity. It analyzes the balance between production processes and organic matter decomposition through simultaneous measurements of oxygen saturation and pH of water. ITS is a versatile tool which can be applied in various types of water bodies. In this study, it was used to evaluate shallow water bodies characterized by excessive phosphorus loads and susceptibility to blue-green algal blooms in summer. During a three-year study carried out in 2010–2012, significant correlations were observed between %O2 and pH, which is a basic prerequisite for applying the ITS method. In the analyzed water bodies, correlation coefficients were determined in the range of r = 0.68–0.83. ITS values varied in successive years ITS (from 7.73 to 8.67), ranging from eutrophy to hypertrophy. Most ITS scores were consistent with the values of Carlson’s TSI, which indicates that used integrated trophic state index, based on the values of water pH and oxygen saturation, accurately reflect the ecological status of degraded water bodies.

Drivers of long-term trends and seasonal changes in total phosphorus loads to a mesotrophic lake in the west of Ireland

Excess phosphorus (P) loading is a major cause of deterioration in surface water quality. In Ireland, regulation has focussed on control of P losses from agriculture and wastewater treatment plants (WWTPs): the two main sources of excess P. Hindcast modelling for Lough Leane, south-west Ireland, indicated that, while the only municipal (point) source contributed up to 41% of the annual TP loading until the mid 1980s, over 90% of the TP load was from diffuse sources following upgrading of the WWTP. Field data from 2000–2006 confirmed that most of the TP load came from agriculture, with 73% being exported between September and February, generally the wettest months in the region. However, the WWTP contributed up to 60% of daily loads during summer. Short lake residence times (two to four months) between October and February indicated that external loadings during these months were unlikely to make a significant contribution to summer phytoplankton growth in the lake. In contrast, the potential effects of point sources during low flows were maximised by longer residence times between April and September. The results highlight the importance to aquatic pollution impacts of, and therefore the need for regulatory responses to respect, seasonal variations in loading and residence time.

Innovative Strategies to Achieve Low Total Phosphorus Concentrations in High Water Flows

Eutrophication caused by excess phosphorus (P) loading poses a serious environmental risk to freshwater bodies around the world. While conventional P-removal technologies often satisfy maximum effluent levels of 1,000 μg-P/l, the resulting environmental P concentrations can still contribute to eutrophication. The challenge remains to achieve low total P levels of ≤ 10 μg-P/l in very large water flows. This issue is often exacerbated by the presence of unreactive organic phosphorus. The authors critically assess innovative developments in advanced oxidation, adsorption, biological uptake, and ion exchange for their ability to achieve very low total P concentrations in high-flow systems. Adsorption appears to have the greatest potential for near-term implementation. Biological uptake and ion exchange show promise based on laboratory-scale research and may be long-term options. Pretreatment using advanced oxidation may be valuable in converting organic P to the more readily removable orthophosphate form.

Year-round patterns in bacterial production and biomass in Lake Simcoe, Ontario, Canada: are heterotrophic bacteria a significant contributor to low hypolimnetic oxygen?

Bacteria serve an important function in aquatic environments and are associated with nutrient regeneration, carbon (C) metabolism, and secondary production. This is the first study to measure heterotrophic bacterial production, abundance, biomass, and biovolume in Lake Simcoe, Ontario. Excessive phosphorus loading resulting in low hypolimnetic oxygen concentrations has impacted the cold-water fishery in Lake Simcoe. We tested the hypothesis that bacteria contributed to dissolved oxygen declines in Lake Simcoe and examined the environmental factors impacting bacterial activity. Spatial and temporal variations in the microbial community were measured from June 2010 to July 2011. A dual-isotope method (3H-TdR and 14C-leu) was used, resulting in mean (± standard deviation) annual epilimnetic bacterial production estimates of 0.130 ± 0.173 and 0.268 ± 0.304 μg C L−1 h−1, respectively. The mean annual bacterial abundance was 1.49 ± 1.53 cells × 109 L−1, with a mean biomass of 1.21 ± 1.34 μg C L−1 and a mean biovolume of 0.0043 ± 0.0030 μm3 cell−1. These estimates had distinct seasonal patterns, with consistently lower bacterial activity in the winter relative to the spring, summer, and fall. Differences between epilimnetic and hypolimnetic bacterial activity were inconsistent for the 4 bacterial parameters measured. Lake temperature, chlorophyll a, and dissolved organic C concentrations were the most significant factors influencing the annual epilimnetic patterns in the examined bacterial parameters. Annual bacterial production was low in Lake Simcoe and does not seem to be a major contributor to the low hypolimnetic oxygen concentrations in the lake.

Ecodynamic assessment of the submerged aquatic vegetation in lake okeechobee, florida under natural and anthropogenic stress

Lake Okeechobee, a large, shallow lake in southern Florida, is the liquid heart of the Everglades. The lake’s hydrodynamic patterns and water depths have been impacted by four major hurricanes in the past decade, including Irene (1999), Frances and Jeanne (2004), and Wilma (2005), and intermittent water level variations due to droughts in 2000–2001 and 2007–2008. In the past few decades, conditions in Lake Okeechobee have changed signifi cantly, largely as a result of nutrient inputs to the ecosystem from agriculture and other human activities in the watershed. The excessive phosphorus loads from the lake’s watershed have led to an increase in eutrophication and contributed to the accumulation of phosphorus-rich mud sediments on the lake bottom. The cumulative effect of these continuous natural hazards and anthropogenic impacts in Lake Okeechobee resulted in resuspending a large quantity of sediment, lowering light transparency, and releasing a large amount of nutrients into the water column, followed by long-standing shallow water depths. Such collective impacts led to a drastic change of sediment bed and ecosystem stability, especially the submerged aquatic vegetation (SAV). This study quantifi es the ecodynamics of SAV to elucidate the coupled impact of natural and anthropogenic stress by a numerical model, the Lake Okeechobee Environment Model (LOEM) that links the spatial and temporal distributions of SAV as a whole.

Dietary phosphorus in bone health and quality of life

Awareness of phosphorus intake is important because both phosphorus deficiency and overloading impair bone health and quality of life. Phosphorus consumption is increasing in many countries. Most dietary phosphorus is contained in protein-rich foods such as meat, milk, cheese, poultry, fish, and processed foods that contain phosphate-based additives to improve their consistency and appearance. Elevation of extracellular phosphorus levels causes endothelial dysfunction and medial calcification, which are closely associated with the development of cardiovascular disease (CVD). Long-term excessive phosphorus loading, even if it does not cause hyperphosphatemia, can be a risk factor for CVD. In epidemiological studies, higher levels of phosphorus intake have been associated with reduced blood pressure. Interestingly, when examined further, phosphorus from dairy products, but not from other sources, was usually associated with lower blood pressure. A dietary approach to phosphorus reduction is particularly important to prevent bone impairment and CVD in patients with chronic kidney disease. In order to improve bone health and quality of life in the general population, the impact of phosphorous, including in processed foods, should be considered, and measures to indicate the amount of phosphorous in food products should be implemented.

Water quality trading in the Lake Winnipeg Basin: A multilevel architecture

Excess nutrients or eutrophication are degrading freshwater bodies worldwide which is undermining human wellbeing. Some of the world's large lakes, such as Lake Victoria, Lake Tai and Lake Winnipeg, have become eutrophic due to excess nutrients from point and non-point sources. Novel approaches that can prevent excess nutrients from over fertilizing surface water bodies are required. Water quality trading (WQT) is a market mechanism that could cost-effectively provide a means to remediate eutrophication by reducing nutrient loads from point and non-point sources. This paper provides WQT design considerations to remediate water quality within large multi-jurisdictional basins by examining Lake Winnipeg which has become the most eutrophied large lake in the world due to excessive phosphorus loads. The multilevel architecture proposed is designed to simultaneously remediate water quality and encourage integrated water resource management. Inter-sub-basin trading allows for meeting a phosphorus load target for the lake while intra-sub-basin trading allows for meeting phosphorus load targets at the sub-basin outflows. The paper also provides regulatory frameworks (Boundary Waters Treaty, United States Clean Water Act, the Canadian Environmental Protection and the Canada Water Acts) and institutional support (International Joint Commission, United States Environmental Protection Agency and Environment Canada) required to manage an international WQT system within the Lake Winnipeg Basin. To reduce transaction costs a composite market with clearing house and exchange characteristics is likely best suited. By providing design considerations in the form of a multilevel WQT system, this paper makes a contribution towards WQT research within large multi-jurisdictional basins.

Phosphorus dynamics within agricultural drainage ditches in the lower Mississippi Alluvial Valley

Excessive phosphorus loading from fertilizers in agriculture results in enriched runoff and downstream aquatic system eutrophication. This study evaluated phosphorus dynamics in agricultural drainage ditches across eight sites within the Lower Mississippi Alluvial Valley (LMAV). The objective of the study was to examine the capacity of drainage ditches across the LMAV to sorb P. Spatially and temporally, all drainage ditch sediments had very low immediately bioavailable phosphorus (P w), and a very low degree of phosphorus saturation (DPS < 20%) throughout the LMAV. Phosphorus binding energy ( K) (0.34–0.60 L/mg) and P sorption maxima (17.8–26.6 L/mg) were low, with very little variation in space and time. Using these metrics, drainage ditches sampled within the LMAV could be described as P sinks, capable of sorbing varying degrees of P seasonally as a result to changes in the Fe-P pool. Sorption, however, will likely be low due to low P sorption maxima and low binding energies. These results will help in P management within primary aquatic systems (such as drainage ditches) within the agricultural landscape and enhance P mitigation strategies at the source, prior to runoff reaching downstream aquatic systems.

Controlling harmful cyanobacterial blooms in a hyper-eutrophic lake (Lake Taihu, China): The need for a dual nutrient (N & P) management strategy

Harmful cyanobacterial blooms, reflecting advanced eutrophication, are spreading globally and threaten the sustainability of freshwater ecosystems. Increasingly, non-nitrogen (N 2)-fixing cyanobacteria (e.g., Microcystis) dominate such blooms, indicating that both excessive nitrogen (N) and phosphorus (P) loads may be responsible for their proliferation. Traditionally, watershed nutrient management efforts to control these blooms have focused on reducing P inputs. However, N loading has increased dramatically in many watersheds, promoting blooms of non-N 2 fixers, and altering lake nutrient budgets and cycling characteristics. We examined this proliferating water quality problem in Lake Taihu, China’s 3rd largest freshwater lake. This shallow, hyper-eutrophic lake has changed from bloom-free to bloom-plagued conditions over the past 3 decades. Toxic Microcystis spp. blooms threaten the use of the lake for drinking water, fisheries and recreational purposes. Nutrient addition bioassays indicated that the lake shifts from P limitation in winter–spring to N limitation in cyanobacteria-dominated summer and fall months. Combined N and P additions led to maximum stimulation of growth. Despite summer N limitation and P availability, non-N 2 fixing blooms prevailed. Nitrogen cycling studies, combined with N input estimates, indicate that Microcystis thrives on both newly supplied and previously-loaded N sources to maintain its dominance. Denitrification did not relieve the lake of excessive N inputs. Results point to the need to reduce both N and P inputs for long-term eutrophication and cyanobacterial bloom control in this hyper-eutrophic system.

Watershed-Level Optimization of BMP Selection for Cost-Effective Pollutant Load Reduction in the Lower Fox River Basin and Green Bay, Wisconsin

Watershed-Level Optimization of BMP Selection for Cost-Effective Pollutant Load Reduction in the Lower Fox River Basin and Green Bay, WisconsinLower Green Bay is impaired by excessive phosphorus and sediment loading from the Lower Fox River (LFR), which leads to algae growth, oxygen depletion, submerged aquatic vegetation, and water clarity problems. Studies have shown that phosphorus load reductions up to 50% will be necessary to achieve noticeable improvements in algae production and water clarity in the LFR Basin and Green Bay Area of...Author(s)Laura J. BlakeCorey GodfreySourceProceedings of the Water Environment FederationSubjectSession 8 - Watershed TMDL Case Study: Lower Fox River and Green Bay, WisconsinDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2009ISSN1938-6478SICI1938-6478(20090101)2009:6L.570;1-DOI10.2175/193864709793958327Volume / Issue2009 / 6Content sourceTMDLS ConferenceFirst / last page(s)570 - 599Copyright2009Word count604Subject keywordsTMDLoptimizationmodelingGreen Bay

Mapping areas at risk of diffuse phosphorus losses to water: a pilot study of Lake Haderslev Dam, Denmark

Haderslev Dam is a 272 ha lake in southern Denmark with a high recreational value. For decades the lake has been severely eutrophicated due to excessive phosphorus loading. Major point sources were cut off in the early 1990s and an upstream wetland was recreated. However, the ecological quality remains unsatisfactory. In this study we estimate the importance of agriculture on diffuse phosphorus (P) input to the lake by modelling combined with independent estimates for contributions from scattered dwellings not connected to a sewer and from background losses. We apply a newly developed Danish P index to the lake catchment for mapping of risk areas for diffuse phosphorus losses. For risk areas we suggest mitigation measures and estimate the effect of the mitigation measures on the total P loading of the lake as well as the associated costs.

Excessive Phosphorus Loading to Dal Lake, India: Implications for Managing Shallow Eutrophic Lakes in Urbanized Watersheds

AbstractExtensive watershed development has resulted in excessive total phosphorus (TP) loads to Dal Lake, a high altitude Himalayan lake known for its tourism and economic potential. External and internal TP loads of 5 and ∼1 g m–2 yr–1, respectively, were estimated for the lake. These loading rates are high in relation to the lake's critical tolerance range of 0.1–0.2 g m–2 yr–1, and, over time, have resulted in severe eutrophication in view of extremely high macrophyte biomass (average = 3.2 kg m–2‐fresh weight) and bottom sediment enrichment (79 tons of TP reserves which contribute 88% of the annual TP budget). This study emphasizes the importance of external TP load reduction as a primary management objective to counteract internal TP loading and P storage within bottom sediments resulting from historic anthropogenic loads. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Patterns of vertical stratification in a subtropical constructed wetland in south Florida (USA)

The South Florida Water Management District (District) has built large treatment wetlands, known as Stormwater Treatment Areas (STAs), to reduce excess phosphorus loading to the Everglades. The District conducted research in a prototype treatment wetland, the Everglades Nutrient Removal Project (ENRP), to study biogeochemical processes that are important to treatment performance. Vertical profile measurements of water temperature, dissolved oxygen, pH, conductivity and transmission of photosynthetically active radiation (PAR) were made in open-water areas and sites dominated by emergent, floating or submersed vegetation over an annual cycle. Relative thermal resistance to mixing was used to infer the strength of thermal stratification. Long-term diel variation in temperature at the surface and bottom of an open-water and a vegetated site also was measured. Open-water sites were nearly isothermal and had minimal thermal stratification, while vegetated sites were all thermally stratified to some degree. The highest surface water temperatures (>35 °C) occurred in submersed vegetation where much of the light absorbed by leaves and stems was reflected as heat. Oxygen was uniformly low (<4 mg L −1) in emergent and floating vegetation and attributed to shading, high biological oxygen demand and limited reaeration at the surface. Depressed oxygen levels at open-water areas were attributed to high sediment oxygen demand. The highest oxygen concentrations occurred in submersed vegetation beds. Water column pH was unstratified and near circumneutral in the open water and at emergent and floating vegetation sites, while pH was markedly stratified in submersed vegetation, where surface values at times exceeded 9.0. High surface oxygen and pH levels in submersed vegetation were consistent with intense photosynthesis. Conductivity increased at the bottom of emergent and submersed vegetation but not at open-water or floating vegetation sites. PAR transmission was strongly reduced at all sites due to shading and/or absorption by dissolved organic carbon. Light extinction coefficients were markedly higher at vegetated sites compared to the open water. Peak irradiance shifted to longer wavelengths (538–643 nm) and both short (<400 nm) and long (>700 nm) wavelengths were largely attenuated at 60 cm relative to the surface. Long-term monitoring at a vegetated site revealed periods of inverse thermal stratification and dampened diel variation in temperatures at the bottom compared to open water.

An Assessment of the Phosphorus Retention Capacity of Wetlands in the Painter Creek Watershed, Minnesota, USA

Lake Minnetonka, located in southeastern Minnesota, U.S.A., is currently experiencing increased eutrophication due to excessive phosphorus (P) loading in runoff from agriculture and urban areas. This phenomenon has been exacerbated by the isolation of wetlands in the surrounding watershed from the surface water drainage network. In order to determine if rerouting surface water through these wetlands would be a feasible method for reducing P inputs, we assessed the P retention capacity of wetlands in a subwatershed of Lake Minnetonka, the Painter Creek Watershed (PCW). The objectives of our study were to determine which of 15 different wetland sites in the PCW had the highest P sorption capacity, identify which soil properties best explained the variability in P sorption, and utilize P fractionation to determine the dominant form of soil P. Our results indicated that despite similar vegetation and hydrogeomorphic settings, wetlands in the PCW had considerably different P sorption capacities. Depth-averaged P sorption index (PSI) values showed considerable variability, ranging from 14.6 to 184. The Katrina Marsh, Painter Marsh, South Highway 26, and West Jennings Bay sites had the highest depth-averaged PSIs. The soil properties that best predicted PSI were soil organic matter, exchangeable calcium, and oxalate extractable iron. Phosphorus fractionation data revealed organic P to be the dominant form of soil P, indicating that organic matter accumulation is another P storage mechanism in these wetlands.