Excessive Phosphorus Loading Research Articles

Water quality in a large complex catchment: Significant effects of land use and soil type but limited ability to detect trends

Globally, significant societal resources are devoted to mitigating negative effects of eutrophication from excessive phosphorus (P) and nitrogen (N) loading. Potential effectiveness of mitigation measures and possible confounding factors are often assessed using studies conducted in headwater catchments. However, success is often evaluated based on trends in river mouth water chemistry. It is not clear how transferrable insights from headwater catchments are to larger rivers. Here, relationships between P and suspended solids (SS) identified in small agricultural headwater catchments were applied to 30 larger, mixed land use catchments draining into Mälaren, a Swedish great lake. Relationships identified in headwater streams between SS concentration, catchment agricultural land percentage and arable land clay content were corroborated for the larger catchments (R2 = 0.59, p-value<0.001. The same was true for connections between SS and particulate P (R2 = 0.74, p-value<0.001). This study highlights the importance of agricultural land, clay content and SS for P transport, on both smaller headwater as well as larger catchment scales, supporting the use of headwater findings on larger, management relevant scales. Consequently, these relationships should be used to target mitigation measures to reduce SS and P losses. To explore the effectiveness of mitigation measures on water quality, we assessed long-term (20 year) trends in tributary water quality and compared these trends to the amount of mitigation measures implemented in the catchment. Overall improving trends were detected using regional Mann Kendall tests, but few decreasing trends in nutrient concentrations were found for individual sites using Generalized Additive Models (GAM). The lack of significant trends and identifiable connections to amount of mitigation measures implemented could be due to several reasons, e.g. insufficient time for recently implemented measures to have an effect, ongoing release of legacy P as well as low areal coverage and poor spatial placement of implemented measures. In addition, trend detection requires large amounts of data and the results should be carefully interpreted and communicated.

Research note: Recreational boating, sewage production, and potential implications for phosphorus loading in Lake Champlain

The impacts of recreational boating on lake ecosystems are often not well characterized, including for Lake Champlain (US/Canada) where excess watershed phosphorus loading drives cyanobacteria blooms. Improperly disposed boater-generated sewage has not been considered as a source of phosphorus in total maximum daily load models or implementation plans for the Lake. Surveys of marinas and boaters informed sewage production estimates by marina-using boaters. Annual boater-generated sewage volume was estimated to range between 2,445 and 5,184 m 3 . These volumes allowed estimation of potential phosphorus contributions to Lake Champlain by improperly disposed sewage at varied rates of discharge. Such contributions were negligible compared to known Lake Champlain phosphorus sources, suggesting use of Clean Water Funds to reduce phosphorus inputs may not be warranted. Nonetheless, due to potential for pathogen contamination, continued financial support through other means was recommended to allow marinas to operate and maintain pumpout facilities at rates reasonable to boaters. Improperly disposed sewage was estimated to represent <0.01% of annual phosphorus contributions to Lake Champlain (USA/Canada). As such, Clean Water Funds targeted to address significant phosphorus inputs to the lake may not be warranted. Nonetheless, continued governmental support for marinas to provide and maintain sewage pumpout facilities for free or at rates most boaters were willing to pay is recommended to minimize introduction of pathogens associated with fecal pollution. To further help ensure compliance with sewage disposal regulations, educational materials and messaging to boaters to encourage use of pumpout facilities should be made available in English and French due to significant populations of boaters speaking each language.

Controls for multi-temporal patterns of riverine nitrogen and phosphorus export to lake: Implications for catchment management by high-frequency observations

Intensifying human activity coupled with climate change increase the transport of excess riverine nitrogen (N) and phosphorus (P) loading from catchment to lake, leading to eutrophication and harmful algal blooms worldwide. To improve understanding of multi-temporal patterns of riverine N and P export and their hydro-biogeochemical controls over both episodic events and long-term trend, we analyzed and interpreted high-frequency data of total nitrogen (TN), ammonia-nitrogen (NH4–N), and total phosphorus (TP) provided by an automatic water quality monitoring station in a typical agricultural catchment draining to Lake Chaohu, China. Mann-Kendall test revealed a significant decreasing trend of riverine N and P concentration most of the time during 2018–2020. At the sub-daily scale, intraday TN concentrations varied by more than 1 mg/L in 31.8% of the period. Monthly TN and TP concentrations were particularly high in December 2019, indicating combined effect of hydrologic (long dry antecedent period and subsequent intensive rainfall events) and anthropogenic controls (fertilization and agricultural drainage). Significantly higher TN concentrations in winter and TP concentrations in summer reflected coupled dominances of precipitation and temperature on hydrologic and biogeochemical processes. Rainfall events with very heavy intensity drove disproportionate N and P loads (more than 20% of the total export) in only 3.2% of the period. Moderate and very heavy events registered the highest TN and TP concentrations, respectively. Our results highlighted the importance of automatic water quality monitoring station to reveal dynamics of riverine N and P export, which may imply future nutrient loading abatement plans for lake-connected catchment.

Quantifying the social benefits and costs of reducing phosphorus pollution under climate change

Excess phosphorus loading to waterbodies has led to increasing frequency and severity of harmful algal blooms, negatively impacting economic activity and human health. While interventions to improve water quality can create large societal benefits, these investments are costly and the value of benefits is often unknown. Understanding the social and economic impacts of reduced phosphorus loading is critical for developing effective land use policies and for generating public and political support for these initiatives. Here, we quantify the social benefits and costs of improving water quality in Lake Champlain under a range of phosphorus reduction and climate change scenarios between 2016 and 2050. We use statistical models to link water quality outputs from an established integrated assessment model with three categories of benefits: tourism expenditures, property sales, and avoided human health impacts. We estimate the costs of reducing phosphorus loading using data reported by the State of Vermont. We find that under the most aggressive phosphorus reduction scenario, the total benefits of improved water quality are $55 to $60 million between 2016 and 2050. Over this 35 year time horizon, the combined benefits do not outweigh the costs under any scenario. If the time horizon is extended to 2100 or beyond, however, the benefits may exceed the costs if the applied discount rate is less than 3%. Importantly, we almost certainly underestimate the value of clean water, due to the omission of other types of benefits. Despite this uncertainty, our study provides a tractable framework for disentangling the complex relationships between water quality and human well-being, and illuminates the value of reductions in phosphorus loading to society.

Dark adaptation and ability of pulse-amplitude modulated (PAM) fluorometry to identify nutrient limitation in the bloom-forming cyanobacterium, Microcystis aeruginosa (Kützing)

Harmful algal blooms in inland waters are widely linked to excess phosphorus (P) loading, but increasing evidence shows that their growth and formation can also be influenced by nitrogen (N) and iron (Fe). Deficiency in N, P, and Fe differentially affects cellular photosystems and is manifested as changes in photosynthetic yield (Fv/Fm). While Fv/Fm has been increasingly used as a rapid and convenient in situ gauge of nutrient deficiency, there are few rigorous comparisons of instrument sensitivity and ability to resolve specific nutrient stresses. This study evaluated the application of Fv/Fm to cyanobacteria using controlled experiments on a single isolate and tested three hypotheses: i) single Fv/Fm measurements taken with different PAM fluorometers can distinguish among limitation by different nutrients, ii) measurements of Fv/Fm made by the addition of DCMU are comparable to PAM fluorometers, and iii) dark adaptation is not necessary for reliable Fv/Fm measurements. We compared Fv/Fm taken from the bloom-forming Microcystis aeruginosa (UTEX LB 3037) grown in nutrient-replete treatment (R) and N-, P-, and Fe-limited treatments (LN, LP, LFe, respectively), using three pulse-amplitude modulated (PAM) fluorometers and the chemical photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and evaluated the effects of dark adaptation prior to PAM measurement. There were significant differences in Fv/Fm estimates among PAM fluorometers for light- versus dark-adapted cell suspensions over the whole experiment (21 days), which were all significantly higher than the DCMU-based measurements. However, dark adaptation had no effect on Fv/Fm when comparing PAM-based values across a single nutrient treatment. All Fv/Fm methods could distinguish LN and LP from R and LFe treatments but none were able to resolve LFe from R, or LN from LP cultures. These results indicated that for most PAM applications, dark adaptation is not necessary, and furthermore that single measurements of Fv/Fm do not provide a robust measurement of nutrient limitation in Microcystis aeruginosa UTEX LB 3037, and potentially other, common freshwater cyanobacteria.

Iron filings application to reduce lake sediment phosphorus release

Natarajan P, Gulliver JS, Arnold WA. 2021. Iron filings application to reduce lake sediment phosphorus release. Lake Reserv Manage. 27:143–159. Surface water impairments due to excess phosphorus loading from the watershed and internal recycling from sediments have been reported worldwide. This study investigated the application of iron metal filings to lake sediments as a method to control sediment phosphorus release. Using batch studies, a zero-valent iron filings material was selected for laboratory dosing experiments with lake sediment cores. Iron filings doses of 0 (control), 0.01, 0.1, and 1 g/cm2 were added to sediment cores collected from a eutrophic lake in Minnesota, United States, to determine the impacts of iron addition on the oxic and anoxic phosphate (PO4-P) flux at 20 C and 10 C in the laboratory. Under oxic conditions, PO4-P release did not occur from the sediments, and low water column PO4-P concentrations were maintained in the iron-dosed and control cores. After switching to anoxic conditions, the 0.1 and 1 g/cm2 iron doses continued to reduce or fully prevent sediment PO4-P flux. The enhanced supply of iron in the sediments was found to reduce the porewater PO4-P, resulting in no apparent PO4-P diffusion across the sediment–water interface and low PO4-P in the overlying water under oxic and anoxic conditions. Further evaluation using in situ experiments is needed to assess the effectiveness of iron filings addition in sequestering sediment phosphorus under natural conditions.

Outsized nutrient contributions from small tributaries to a Great Lake

Excessive nitrogen (N) and phosphorus (P) loading is one of the greatest threats to aquatic ecosystems in the Anthropocene, causing eutrophication of rivers, lakes, and marine coastlines worldwide. For lakes across the United States, eutrophication is driven largely by nonpoint nutrient sources from tributaries that drain surrounding watersheds. Decades of monitoring and regulatory efforts have paid little attention to small tributaries of large water bodies, despite their ubiquity and potential local importance. We used a snapshot of nutrient inputs from nearly all tributaries of Lake Michigan-the world's fifth largest freshwater lake by volume-to determine how land cover and dams alter nutrient inputs across watershed sizes. Loads, concentrations, stoichiometry (N:P), and bioavailability (percentage dissolved inorganic nutrients) varied by orders of magnitude among tributaries, creating a mosaic of coastal nutrient inputs. The 6 largest of 235 tributaries accounted for ∼70% of the daily N and P delivered to Lake Michigan. However, small tributaries exhibited nutrient loads that were high for their size and biased toward dissolved inorganic forms. Higher bioavailability of nutrients from small watersheds suggests greater potential to fuel algal blooms in coastal areas, especially given the likelihood that their plumes become trapped and then overlap in the nearshore zone. Our findings reveal an underappreciated role that small streams may play in driving coastal eutrophication in large water bodies. Although they represent only a modest proportion of lake-wide loads, expanding nutrient management efforts to address smaller watersheds could reduce the ecological impacts of nutrient loading on valuable nearshore ecosystems.

Revisiting the total maximum daily load total phosphorus goal in Lake Okeechobee

In 2000, a total maximum daily load (TMDL) total phosphorus (TP) goal of 40 µg/L was established for Lake Okeechobee, Florida. The goal was selected to reduce the “imbalance to flora and fauna” caused by excessive phosphorus loading in the lake. We recalculate the TMDL TP goal using a water quality data series of TP and chlorophyll-a concentrations from 1986 to 2018 for the original 30 in-lake stations plus an additional 29 stations. Using the cross-tabulation approach used to generate the original TMDL TP goal, we determined a new goal of 42 µg/L, nominally different from the original. We also reevaluate the goal’s ability to maintain an implicit goal of 11.5% bloom frequency. We conclude substantial changes in the frequency and scope of the water quality sampling scheme prevent a determination on the effectiveness of the TMDL TP goal. The implementation, however, appears to have failed as the median TP concentration has increased by 93 µg/L to 133 µg/L and bloom frequency, after correcting for the declining sampling frequency, has increased from 1986 to 2018. An increased sampling frequency of TP and chlorophyll-a sampling is needed, or else tracking responses of chlorophyll-a to future TP reductions will be virtually impossible.

Modelling the impact of runoff generation on agricultural and urban phosphorus loading of the subtropical Poyang Lake (China)

Water quality degradation and eutrophication in surface water bodies caused by excessive phosphorus loads from agriculture and urbanisation are widespread problems. Although phosphorus (P) is often the limiting factor of aquatic ecosystems, only few studies have characterised the primary factors that influence P export in subtropical monsoon catchments. This study aims to assess the temporal and spatial variations in P fluxes, and to investigate the factors controlling P export in a subtropical catchment. Runoff and P export in the Le An River catchment, which flow to Poyang Lake (China) were evaluated using the HYPE model. Sensitivity analysis and calibration of hydrological and P transport parameters were undertaken using PEST. Results show that: (a) HYPE reproduced sufficiently well (NSE ≥ 0.73, |PBIAS| ≤ 14.5%) the stream flow dynamics for widely varying climatic conditions and across six sub-catchments of contrasting physiographic characteristics; (b) HYPE captured intra-annual patterns of total P (TP) loads, although with overestimation of annual TP loads by 8.5–47.0% across two monitoring sites; (c) TP loads had the ranges between 0.24 and 0.88 kg/ha/yr and 4.31–4.69 kg/ha/yr from forest-dominant upstream areas and the downstream plains region, respectively, with the latter being more urbanised and having higher percentage of agriculture; (d) Soil erosion from surface runoff and adsorption/desorption of soil P are the main factors controlled P export from the catchment; (e) most P export occurred during March-August when rainfall-runoff is highest and agricultural practices are most active; (f) stream TP concentrations were greatly affected by point source inputs, especially during low-flow conditions in downstream plains region. This study indicates that measures to reduce TP export to receiving water bodies in subtropical monsoon areas, like Poyang Lake, should focus on managing diffuse sources from soil erosion and surface runoff etc., whereas improvements to sewage management is more likely to reduce river TP concentrations during low-flow periods.

Animal‐Based Organic Amendments and Their Potential for Excessive Nitrogen Leaching and Phosphorus Loading

Nitrate contamination of groundwater has been attributed to application of poultry litter to amend soil organic matter on raspberry farms in British Columbia, Canada. A field study assessed the risk of organic amendments that cause nitrate leaching and nutrient accumulation. The amendments, poultry litter, municipal compost, horse manure, and three types of dairy manure solids, were applied at 25 or 50 Mg dry matter ha–1 to match farm rates before new plantings. Plots were either unseeded or seeded with a grass mix to simulate berry establishment with grass alley crop. Soil was sampled at 0‐ to 15‐, 15‐ to 30‐, and 30‐ to 60‐cm depths 15 times over 14 mo and analyzed for concentrations of NH4+ and NO3–, and at 0 to 15 cm for total C, N, and P at 6 mo after application. Three grass harvests were analyzed for yield and N offtake. Poultry litter supplied more than twice the total mineral N and total P compared to the dairy solids and horse manure, while the compost was intermediate. At 25 Mg ha–1, poultry litter increased concentrations of soil (0–15 cm) NH4+ and NO3– (&gt;150 and &gt;300 mg kg–1, respectively), compared with small short‐term increases by compost (∼70 and 100 mg kg–1, respectively). There was almost no increase from dairy and horse amendments. Grass N offtake reduced soil NO3– concentrations but did not eliminate the risk of leaching from poultry litter. We conclude that dairy solids and horse manure present less risk of nitrate leaching and P loading than poultry litter or municipal compost.Core Ideas Poultry manure and compost amendments greatly increased soil NH4+, NO3– and P. Grass ‘alley’ crop did no sufficiently mitigate soil mineral N from poultry manure. Little risk of nitrate leaching or P loading with dairy solids or horse amendments.

Soil phosphorus testing on alkaline calcareous soils

Soil phosphorus testing made great strides with multiple chemical tests proposed and implemented for crop fertilizer management programs during the previous century. In the latter part of the previous century, the environmental impact of excess nonpoint phosphorus loading from the landscape (e.g., agricultural lands) to waterbodies became an issue of increased concern, and soil phosphorus testing came to the forefront of management and monitoring. This article will provide a general overview of the usage of phosphorus testing for agronomic purposes in the United States Earn 0.5 CEUs in Nutrient Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/725.

Economic Analysis of Water Treatments for Phosphorus Removal in Florida

Excessive phosphorus loads in urban and agricultural runoff are identified as one of the greatest threats to the natural environment of Central and South Florida. This study compares the cost effectiveness of two different water treatment systems that have demonstrated an enhanced phosphorus removal ability utilizing aquatic plants and biomass: Wetland Stormwater Treatment Areas (STA) and Managed Aquatic Plant Systems (MAPS). Cost effectiveness, expressed as dollars per kilogram (kg) of phosphorus removed, is calculated from the net present value cost for capital, operation and management, including residue management, and benefits from water storage/supply and recreational use, divided by the projected total phosphorus removal over fifty years. MAPS demonstrated the lowest cost at $24 per kg for systems designed to treat waters with 300 ppb (parts per billion) phosphorus to a level of 155ppb. Reservoir-Assisted STA, which treated 540 ppb to 40 ppb phosphorus concentration in Central Florida, had an estimated cost of $77. STAs starting with concentrations ranging from 40 to 180 ppb and facing a target of 10 ppb phosphorus concentration in South Florida had much higher cost estimates, ranging between $268 and $1,346 per kg. This document is FE576, one of a series of the Food and Resource Economics Department, UF/IFAS. Original publication date November 2005. This is an excerpt of “Economic Analysis of Water Treatments for Phosphorus Removal in Florida,” Food and Resource Economics Department, University of Florida, 2004.&#x0D; FE576/FE576: Economic Analysis of Water Treatments for Phosphorus Removal in Florida (ufl.edu)

Essential cryoglobulinemia: A case report

Excess phosphorus (P) loading due to anthropogenic activities has been identified as a primary cause of surface water eutrophication, but it is controversial whether P is a contributor to groundwater contamination. In this study, subsurface transport of P to groundwater and its environmental risk across different land uses was investigated in a karstic springs basin, Florida, USA. Eleven sites including 5 agricultural sites, 5 urban, and 1 pine plantation were selected. Boreholes were drilled to collect soils from surface, vadose zone, and aquifer at 0.6 m depth intervals. Water-extractable P (WSP), Mehlich 3-P, Al, and Fe, soil P storage capacity (SPSC), and P sorption isotherm parameters were obtained for soils from selected depths. We found that agricultural sites particularly horse farms, and urban sites with golf courses and septic tanks showed high risk of P leaching with TP concentrations in the groundwater above the numeric criteria for streams in the north central Florida (0.3 mg L−1). Besides land use which reflected P loadings in the surface soils, significant positive correlations of P sorption maximum (Smax) with M3-Fe, Al, and organic matter, and the precipitation of P by calcium bicarbonate, imply the mechanism regulating soil P attenuation in vadose and saturated zones, respectively. Negative SPSC values were significantly negatively correlated with WSP in all the zones, suggesting the applicability of SPSC in deep soils. Moreover, high TP concentration was observed in the groundwater at one site where the SPSC value changed from positive in the surface soils to negative in the subsoils, indicating that an additive SPSC value to water table would be more robust for evaluating the potential of P leaching before moving down to the limestone area.

Fixed bed column evaluation of phosphate adsorption and recovery from aqueous solutions using recycled steel byproducts

Excessive phosphorus loading from anthropogenic sources is a major cause of eutrophication of natural waters. Phosphorus is also a non-renewable natural resource that cannot be substituted with other sources. The objective of this study was to determine the feasibility of using recycled steel byproducts to remove and recover phosphate from aqueous solutions. Laboratory fixed bed column experiments were conducted with recycled steel chips of different sizes to evaluate phosphate adsorption characteristics and phosphate recovery efficiencies using alkaline solutions. The results showed that phosphate adsorption onto steel chip filters was characterized by an initial fast breakthrough followed by a stable removal phase. The cumulative phosphate adsorption capacities of the steel chips were 8.43–10.4 mg P/g following 4800 empty bed volumes with a 3 min contact time and an initial concentration of 10 mg P/L. The phosphate adsorption onto steel chips was favored at low flow rates, low pH values, and low organic carbon concentrations. Sodium hydroxide solutions effectively desorbed phosphate from the steel chips. The total phosphate desorption percentages were 58.9%, 64.2%, and 83.4% after 120 empty bed volumes using 0.05 M, 0.10 M, and 0.20 M NaOH solutions, respectively. Steel chips also exhibited high phosphate adsorption and desorption capacities when treating agricultural subsurface drainage water, municipal wastewater, and stormwater runoff. Overall, the results of this study suggest that recycled steel byproducts are efficient and promising low-cost phosphate capturing materials for sustainable phosphorus management.

Influence of turbid flood water release on sediment deposition and phosphorus distribution in the bed sediment of the Three Gorges Reservoir, China

Excessive phosphorus (P) loading was identified as an urgent problem during the post-Three Gorges Reservoir (TGR) period. Turbid water with high suspended sediment loads has been periodically released during the flood season to mitigate sediment deposition in the TGR, but limited attention has been paid to its effect on the distribution of P in bed sediment within the reservoir. In this study, field surveys, historical monitoring data related to sediment deposition, and physiochemical properties and the fractional P content in the mainstream surface sediment and representative column sediment, were used to investigate the effect of turbid flood water release on P distribution in bed sediment. The results revealed that turbid flood water release could discharge approximately 20% of the suspended sediment inflow entering the TGR. Additionally, both the particle size of the inflow sediment and suspended sediment flux tended to decline, and the deposited sediment volume tended to constantly increase in the TGR at a rate of 0.117 billion tonnes per year between 2004 and 2016. The median particle size (MPS) was larger for surface sediment obtained in the flood season than for that obtained in the dry season, and the MPS tended to increase with an increase in the sediment depth from 0 to 20 cm. The total phosphorus (TP) content in sediment ranged from 2.6% to 17.5% lower in the flood water releasing period than in the non-flood water storing period. However, no consistent variation was detected for the vertical distribution of P fraction in the top 20 cm of bed sediment. Compared with lakes with slow deposition rates, the TGR showed a rapid sedimentation rate of >1.0 m/y, which mostly resulted in the uniform distribution of the surface sediment P fraction.

Subsurface transport and potential risk of phosphorus to groundwater across different land uses in a karst springs basin, Florida, USA

Excess phosphorus (P) loading due to anthropogenic activities has been identified as a primary cause of surface water eutrophication, but it is controversial whether P is a contributor to groundwater contamination. In this study, subsurface transport of P to groundwater and its environmental risk across different land uses was investigated in a karstic springs basin, Florida, USA. Eleven sites including 5 agricultural sites, 5 urban, and 1 pine plantation were selected. Boreholes were drilled to collect soils from surface, vadose zone, and aquifer at 0.6 m depth intervals. Water-extractable P (WSP), Mehlich 3-P, Al, and Fe, soil P storage capacity (SPSC), and P sorption isotherm parameters were obtained for soils from selected depths. We found that agricultural sites particularly horse farms, and urban sites with golf courses and septic tanks showed high risk of P leaching with TP concentrations in the groundwater above the numeric criteria for streams in the north central Florida (0.3 mg L−1). Besides land use which reflected P loadings in the surface soils, significant positive correlations of P sorption maximum (Smax) with M3-Fe, Al, and organic matter, and the precipitation of P by calcium bicarbonate, imply the mechanism regulating soil P attenuation in vadose and saturated zones, respectively. Negative SPSC values were significantly negatively correlated with WSP in all the zones, suggesting the applicability of SPSC in deep soils. Moreover, high TP concentration was observed in the groundwater at one site where the SPSC value changed from positive in the surface soils to negative in the subsoils, indicating that an additive SPSC value to water table would be more robust for evaluating the potential of P leaching before moving down to the limestone area.

Optimizing best management practices to control anthropogenic sources of atmospheric phosphorus deposition to inland lakes

ABSTRACTExcessive phosphorus loading to inland freshwater lakes around the globe has resulted in nuisance plant growth along the waterfronts, degraded habitat for cold-water fisheries, and impaired beaches, marinas, and waterfront property. The direct atmospheric deposition of phosphorus can be a significant contributing source to inland lakes. The atmospheric deposition monitoring program for Lake Simcoe, Ontario, indicates roughly 20% of the annual total phosphorus load (2010–2014 period) is due to direct atmospheric deposition (both wet and dry deposition) on the lake. This novel study presents a first-time application of the genetic algorithm (GA) methodology to optimize the application of best management practices (BMPs) related to agriculture and mobile sources to achieve atmospheric phosphorus reduction targets and restore the ecological health of the lake. The novel methodology takes into account the spatial distribution of the emission sources in the airshed, the complex atmospheric long-range transport and deposition processes, cost and efficiency of the popular management practices, and social constraints related to the adoption of BMPs. The optimization scenarios suggest that the optimal overall capital investment of approximately $2M, $4M, and $10M annually can achieve roughly 3, 4, and 5 tonnes reduction in atmospheric P load to the lake, respectively. The exponential trend indicates diminishing returns for the investment beyond roughly $3M per year and that focusing much of this investment in the upwind, nearshore area will significantly impact deposition to the lake. The optimization is based on a combination of the lowest cost, most beneficial and socially acceptable management practices that develops a science-informed promotion of implementation/BMP adoption strategy. The geospatial aspect to the optimization (i.e., proximity and location with respect to the lake) will help land managers to encourage the use of these targeted best practices in areas that will most benefit from the phosphorus reduction approach.Implications: Excessive phosphorus loading to inland freshwater lakes around the globe has resulted in nuisance plant growth along the waterfronts, degraded habitat for cold water fisheries, and impaired beaches, marinas and waterfront property. This novel study presents a first-time application of the Genetic Algorithm methodology to optimize the application of best management practices related to agriculture and mobile sources to achieve atmospheric phosphorus reduction targets and restore the ecological health of the lake. The novel methodology takes into account the spatial distribution of the emission sources in the airshed, the complex atmospheric long-range transport and deposition processes, cost and efficiency of the popular management practices and social constraints related to the adoption of BMPs.

Optimal implementation of green infrastructure practices to minimize influences of land use change and climate change on hydrology and water quality: Case study in Spy Run Creek watershed, Indiana

Nutrient loading from the Maumee River watershed is a significant reason for the harmful algal blooms (HABs) problem in Lake Erie. The nutrient loading from urban areas needs to be reduced with the installation of green infrastructure (GI) practices. The Long-Term Hydrologic Impact Assessment-Low Impact Development 2.1 (L-THIA-LID 2.1) model was used to explore the influences of land use (LU) and climate change on water quantity and quality in Spy Run Creek watershed (SRCW) (part of Maumee River watershed), decide whether and where excess phosphorus loading existed, identify critical areas to understand where the greatest amount of runoff/pollutants originated, and optimally implement GI practices to obtain maximum environmental benefits with the lowest costs. Both LU/climate changes increased runoff/pollutants generated from the watershed. Areas with the highest runoff/pollutant amount per area, or critical areas, differed for various environmental concerns, land uses (LUs), and climates. Compared to optimization considering all areas, optimization conducted only in critical areas can provide similar cost-effective results with decreased computational time for low levels of runoff/pollutant reductions, but critical area optimization results were not as cost-effective for higher levels of runoff/pollutant reductions. Runoff/pollutants for 2011/2050 LUs/climates could be reduced to amounts of 2001 LU/climate by installation of GI practices with annual expenditures of $0.34 to $2.05 million. The optimization scenarios that were able to obtain the 2001 runoff level in 2011/2050, can also reduce all pollutants to 2001 levels in this watershed.

Evaluation of Eutrophication Control Through Hypolimnetic Oxygenation

The accumulation of nutrients in water bodies occur due to excessive phosphorus and nitrogen loads from the catchments and other external sources, causing buildup of nutrients in sediments. Often, water bodies that present thermal stratification, experience depletion of dissolved oxygen (DO) in the hypolimnion, thereby causing anoxic conditions, favoring the release of nutrients and leading to eutrophic conditions. The use of hypolimnetic oxygenation systems (HOS), which can supply over 50mg/L of DO in the hypolimnion of deeper water bodies, has demonstrated to reverse these conditions in lakes and reservoirs in North America, Europe, and Australia. The objective of this study was to develop a model for forecasting the remediation progress of a eutrophied reservoir using HOS. For this purpose, a mass-balance model was developed that calculates the oxygen accumulation in water bodies, using experimentally obtained oxygen demand (OD) of water and sediment from the reservoir, the extracted OD, the external load of OD, DO provided by natural sources such as photosynthesis and interaction with the atmosphere, and DO supplied by the HOS. The model was applied to forecast DO concentrations in the hypolimnion of a Mexican reservoir under different scenarios of external load of OD and hypolimnetic oxygenation.

Mechanistic study of P retention by dewatered waterworks sludges

Eutrophication caused by excess phosphorus (P) loading poses serious environmental risk to freshwater bodies around the world. Advancing our fundamental understanding towards practical reduction of this risk using novel industrial by-products as P adsorbents is the focus of this study. The study examined the combined effect of solution chemistry and the inherent properties of a novel adsorbent (dewatered waterworks sludges) on their P retention. The overall aim was to contribute to a mechanistic understanding of P retention by the sludges; and to better understand what properties regulate their P retention. Results confirm a strong but variable affinity for P by the sludges. Aluminium (Al)-based sludges generally had higher total specific surface areas; and tended to have higher P sorption capacities (6.09–26.95 mg-P/g) than iron (Fe)-based sludges (5.83–23.75 mg-P/g). In most cases, adsorption data was well fitted with the Freundlich model. However, data for two of the Al-based sludges was best described by the Langmuir model with very minimal leaching of Al, Calcium (Ca) and sulphate (SO42−) ions observed; indicating surface complexation via P binding into the Al hydr(oxide) as the main mechanism for these Al-based sludges. Principal component and multiple linear regression analyses revealed that the metal content (Al, Fe, Aloxalate and Feoxalate) and total specific surface area components had the most significant explanation for the variance of: (i) P-uptake at different initial P concentrations; (ii) the adsorption maxima; and (iii) the Freundlich constant (Kf); (p<0.001). Total carbon (TC), organic carbon, Ca content and exchangeable Ca components explained a significant reasonable variance in P-uptake and Kf. This explanation was demonstrated for the role of Ca content in chemical P precipitation mechanism; and also for exchanging TC sites on the surface of the sludges with phosphate ions via ligand exchange mechanism. Overall, giving the combined effect of intrinsic sludge properties and solution chemistry; dewatered waterworks sludges with high reactive metal content (Al and Fe), Ca and SO42− ions, and total specific surface area would be the best choice for P retention in practical applications.