Total Maximum Daily Load Research Articles

Pay-for-practice or Pay-for-performance? A coupled agent-based evaluation tool for assessing sediment management incentive policies

Cost-shared programs have been applied to incentivize the adoption of agricultural best management practices (BMPs) to address the long-standing water quality issue in the Chesapeake Bay watershed, US. However, the business-as-usual (BAU) incentive program (i.e., pay-for-practice, paying cost share for implementing BMPs) is likely to miss the Total Maximum Daily Load target to reduce 20% of the total suspended sediment (TSS) in 2010 by 2025. Some field experiments indicate that pay-by-performance (PFP; paying lower cost share but with additional bonus payment per unit sediment reduction) can better motivate community involvement leading to greater water quality control outcomes. However, the effectiveness of different incentive policies is still unclear at a basin scale. We propose a coupled agent-based modeling tool to quantify the performance of different incentive policies. The tool considers farmers’ (i.e., agents’) BMP adoption dynamics affected by the social norm and the potential bonus payment. Specifically, we compare individual-based PFP (PFPi) and group-based PFP (PFPg) with BAU. Results of our proposed model applied to the selected study area, the Susquehanna River Basin, Chesapeake Bay’s largest tributary watershed, suggest that PFP can achieve higher TSS reduction with less cost. PFPg shows the best basin-wide TSS reduction associated with the least uncertainty among all tested policies. Also, the performance of PFPg is less impacted by the change in the bonus payment compared to PFPi attributed to farmers’ collaboration efforts. Potentially, the proposed policy evaluation tool can better inform an achievable target with policy suggestions in assistance with social studies (e.g., surveys and behavioral experiments).

Water quality impacts of climate change, land use, and population growth in the Chesapeake Bay watershed

AbstractThe 2010 Chesapeake Bay Total Maximum Daily Load was established for the water quality and ecological restoration of the Chesapeake Bay. In 2017, the latest science, data, and modeling tools were used to develop revised Watershed Implementation Plans (WIPs). In this article, we examine the vulnerability of the Chesapeake Bay watershed to the combined pressures of climate change and growth in population, agricultural intensity, and economic activity for the 60‐year period 1995–2055. The results will be used to revise WIPs, as needed, to account for expected increases in loads. Assessing changes relative to 1995 for the years 2025, 2035, 2045, and 2055, mean annual precipitation increases of 3.11%, 4.21%, 5.34%, and 6.91%, respectively, air temperature increases of 1.12, 1.45, 1.84, and 2.12°C, respectively, and potential evapotranspiration increases of 3.36%, 4.43%, 5.54%, and 6.35%, respectively, are projected. Population in the watershed is expected to grow by 3.5 million between 2025 and 2055. Watershed model results show incremental increases in streamflow (2.3%–6.2%), nitrogen (2.6%–10.8%), phosphorus (4.5%–26.7%), and sediment (3.8%–18.8%) loads to the tidal Bay due to climate change. Growth in population, agricultural intensity, development, and economic activity resulted in relatively smaller increases in loads compared to climate change.

Assessing Feasibility of Water Resource Protection Practice at Catchment Level: A Case of the Blesbokspruit River Catchment, South Africa

The operationalization of water resource protection initiatives for surface water resource quality and equitable water quality allocation is critical for sustainable socio-economic development. This paper assessed Blesbokspruit River Catchment’s water quality status, using the South African Water Quality standards and Water Quality Index (WQI). Protection levels for quality, and waste discharge for point sources were set and evaluated using the total maximum daily loads (TMDLs) and chemical mass balance (CMB) techniques, respectively. The study found that the water quality results for the analysed physico-chemical parameters (Na+, Ca2+, Mg2+, Cl−, F−, pH, EC, SO42−) of the data collected from 2015 to 2022 were within the limits of the water quality standards, except for NO3− and PO42−. The water quality from the study area was categorized as acceptable for drinking purposes with the WQI of 54.80. The application of the TMDL approach resulted in the 77.96 mS/m for electrical conductivity (EC), 9.92 mg/L for phosphate (PO42−), and 15.16 mg/L for nitrate NO3− being set as the protection levels for the catchment. The CMB was found to be a useful tool for the evaluation of point source discharges into water resources. The study recommends the application of TMDL and CMB techniques in water resource protection practice.

Diffuse pollutant load predictions in areas that implement the total maximum daily load due to climate change

Total maximum daily load (TMDL), which is implemented for water quality management in a watershed, necessitates the use of a watershed model to predict the load. However, such a model consumes a lot of time and effort until the results are simulated. Therefore, the present study aimed to compare and evaluate load changes following the revision of the land-based diffuse pollutant unit load values, which are used to calculate the diffuse pollutant discharge loads in the total maximum daily load (TMDL) guidelines established for TMDL control by watersheds in South Korea, using the Natural Resources Conservation Service (NRCS) method. When the revised unit load was used, the loads were reduced by an average of 56.8% compared with the prior unit load. The descending order of load change rate was biochemical oxygen demand (BOD) > total phosphorus (TP) > total nitrogen (TN). Although the difference in load discharge trends between the Representative Concentration Pathway (RCP) 2.6 and RCP8.5 scenarios was insignificant, the load discharge under the worst scenario (RCP8.5) may increase. When the future period was split into 30-year increments, the load of precipitation and diffuse pollutants increased in the intermediate future (2041–2070). This study examined how the management ratio of diffuse pollutants in a watershed changes when the legal standard value of institutionally managed diffuse pollutants changes. The findings of this study provide useful information for the efficient management of present and future diffuse pollutants.

Progress in reducing nutrient and sediment loads to Chesapeake Bay: Three decades of monitoring data and implications for restoring complex ecosystems

AbstractFor over three decades, Chesapeake Bay (USA) has been the focal point of a coordinated restoration strategy implemented through a partnership of governmental and nongovernmental entities, which has been a classical model for coastal restoration worldwide. This synthesis aims to provide resource managers and estuarine scientists with a clearer perspective of the magnitude of changes in water quality within the Bay watershed, including nitrogen (N), phosphorus (P), and sediment for the River Input Monitoring (RIM) watershed and the unmonitored below‐RIM watershed. The flow‐normalized N load from the RIM watershed has declined in the period of 1985–2017, but P and sediment loads have lacked progress. Reductions of riverine N are largely driven by reductions of point sources and atmospheric deposition. Future reductions will require significant progress in managing agricultural nonpoint sources. The below‐RIM watershed, which comprises a disproportionately high fraction of inputs to the Bay, has shown long‐term declines in major sources, including point sources (N and P), atmospheric deposition (N), manure (N and P) and fertilizer (P), based on a combination of monitoring and modeling assessments. To date, the Bay cleanup efforts have achieved some progress toward reducing nutrients from the watershed, which have resulted in improving water quality in the estuary. However, further reductions are critical to achieve the Chesapeake Bay Total Maximum Daily Load goals, and emerging challenges due to Conowingo Reservoir, legacy nutrients, climate change, and population growth should be considered. Continued monitoring, modeling, and assessment are critically important for informing the restoration of this complex ecosystem.This article is categorized under: Science of Water > Water Quality Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness

The development of an action plan for the Jeneberang River pollution control based on the calculation of the total maximum daily load

Jeneberang Watershed is one of the priority watersheds set by the Ministry of Environment and Forestry in the Sulawesi Island region and is the location of various important economic activities that contributes around 2% to the national gross domestic product (GDP). The results of water quality monitoring in 2018 and 2019 show that the average water quality status of the Jeneberang river was moderately polluted. This study aimed to develop an action plan for water pollution control derived from the calculation of the total maximum daily load (TMDL) to meet the river water quality standard. The method used in this study was the application of a numerical model of water quality combined with the spatial approach for calculating the TMDL. The calculation results indicated that the load of existing pollutants entering the Jeneberang river was 4,844.87 kg- BOD/day while the TMDL was 3,552.97 kg-BOD/day, therefore a load reduction of 1291.9 was required. Furthermore, it was necessary to reduce the water pollution load from domestic, industrial, and livestock activities by 871.37, 14.86, 337.28 kg-BOD/day, respectively, and from the combination of agriculture and built-up land by 68.39 kg-BOD/day. The action plan resulting from the development of TMDL is the construction of 122 units of communal sewage treatment plant with a budget of IDR 121.86 billion and 350 units of biodigester with a total budget of IDR 7.35 billion. Meanwhile, 46 inspectors and a budget of IDR10 billion per year are required to supervise industries. Thus, the study revealed that TMDL can be used as the basis for the development of an action plan.

Risk quotient analysis and total maximum daily load estimation for Kedah River, Malaysia

Kedah River plays an important role in providing habitat for aquatic plants, animals, and it has been widely used by humans for recreation purposes. However, rapid development and urbanization activities along the river have significantly impacted the surface water quality in the watershed. Nowadays, Total Maximum Daily Load (TMDL) is one of the best approaches for restoring an impaired watershed. TMDL is used to identify the maximum concentration of pollutants that a waterbody can receive without violating the water quality standards. This study was intended to conduct a TMDL assessment for five water quality parameters which are turbidity, suspended solids (SS), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and Ammoniacal Nitrogen (NH3N). The calculation includes identifying the existing load, target pollutant load, and the endurance capacity of load using secondary data adopted from DOE. Risk Quotients (RQs) analysis was included in this TMDL study to address the water health systematically. From the result, most of the existing pollutant from year 2013 to 2017 exceeded the standard value of Class IIA by NWQS especially for SS, BOD, and NH3N.

Long-term trends in inflowing chlorophyll a and nutrients and their relation to dissolved oxygen in a large western reservoir

Naymik J, Larsen CA, Myers R, Hoovestol C, Gastelecutto N, Bates D. 2023. Long-term trends in inflowing chlorophyll a and nutrients and their relation to dissolved oxygen in a large western reservoir. Lake Reserv Manage. XX:XXX–XXX. Anoxia in Brownlee Reservoir is one of the numerous water quality issues associated with eutrophic conditions in the Snake River as it flows through southern Idaho and parts of eastern Oregon. The states of Idaho and Oregon have developed total maximum daily loads (TMDLs) for multiple reaches of the Snake River and its tributaries upstream of Brownlee Reservoir intended to address poor water quality. Despite the emphasis on developing TMDLs throughout the Snake River and its tributaries, published long-term trend monitoring to evaluate the results of the TMDLs is lacking. Trends in Snake River concentrations and loads summarized using weighted regressions on time, discharge, and season show that combined efforts to improve water quality upstream of Brownlee Reservoir have realized decreasing trends in concentrations of chlorophyll a, total phosphorus, and suspended solids (80%, 46%, and 61% reductions, respectively) from 1995 to 2021. Brownlee Reservoir, a large mainstem reservoir with short residence time, has responded quickly to inflowing reductions of chlorophyll a and total phosphorus. Since 2005, dissolved oxygen (DO) has improved in the reservoir, with a 33% reduction in the volume of the reservoir having DO less than 1 mg/L. This supports the primary premise of upstream TMDLs and demonstrates that inflowing water quality improvements are effective at improving in-reservoir dissolved oxygen.

Balancing multiple stakeholder objectives for floodplain reconnection and wetland restoration

Floodplain reconnection and wetland restoration projects are increasingly implemented to enhance flood resiliency, and these nature-based solutions can also achieve co-benefits of nutrient storage and improved habitats. Considering the multiple and sometimes incompatible objectives of stakeholders for uses of riverside lands, a decision-support tool linked to a hydraulic model would enable planners to simulate floodplain restoration scenarios while also quantifying and assessing the trade-offs between the stakeholder objectives to arrive at optimal restoration designs. We illustrate a simple ranking approach using an n-dimensional objective function to represent key stakeholders engaged in restoration. We applied our approach in a watershed in central Vermont (USA) that has been identified by regional and state-level stakeholders as an important location to mitigate flooding damages but also to improve water quality – all within a context of increasing development pressures on riparian lands and limited financial resources to accomplish restoration. Eleven different floodplain reconnection and wetland restoration modifications were combined in six scenarios and simulated with 2D Hydrologic Engineering Center's River Analysis System (2D HEC-RAS), along with a baseline (no-action) scenario. Only modest attenuation of peak flows for 2-, 25-, 50- and 100-year design storms was achieved by the floodplain restoration scenarios due to the steep setting, and flashy nature of the watershed. Yet, several scenarios of floodplain reconnection projects more than met the necessary annual phosphorus load reductions targeted under a Total Maximum Daily Load implementation plan. Our approach provided planners with a ranking of restoration scenarios that best met multiple stakeholder objectives and allowed effectiveness of alternate design scenarios to be quantified, justified, and visualized to promote consensus decision-making.

Seasonal trends of PCBs in air over Washington DC reveal localized urban sources and the influence of Anacostia River

Semi-volatile organic compounds like polychlorinated biphenyls (PCBs) undergo diffusive exchange flux between a water body and the overlying air. The magnitude of this exchange can be a substantial component of the overall pollutant mass balance and needs to be determined accurately to identify major pollutant sources to the water body and to plan appropriate remedies. For the PCB-impacted Anacostia River in Washington DC (USA), quantification of air-water exchange has been a major data gap. In the present study, polyethylene passive samplers were used to measure PCB concentrations in air phase at six locations in DC over a period of one year to capture spatial and seasonal variations. Concurrent water phase PCB measurements were used to quantify the direction and magnitude of air-water exchange in the Anacostia River. Two locations had nearly an order of magnitude higher air phase PCB concentrations that could be related to localized sources. Remaining four locations provided similar air phase PCB concentrations that averaged from 270 ± 44 pg/m3 (summer) to 32 ± 4.3 pg/m3 (winter). ∑PCB water-air exchange fluxes were positive across all seasons, with net PCB volatilization of 180 ± 19 g/year from the surface water. Volatilization rate was an order of magnitude lower than previously estimated from a fate and transport model. PCB load from atmospheric deposition based on previous studies in this watershed was an order of magnitude lower than the volatilization rate. Results refuted a long-standing understanding of the air phase serving as a source of PCBs to the river as per the currently approved Total Maximum Daily Load assessment. The study demonstrates the utility of passive air phase measurements in delineating local terrestrial sources of pollution as well as providing estimates for air-water exchange to complete a robust mass balance for semi-volatile pollutants in an urban river.

A Gap-Filling Tool: Predicting Daily Sediment Loads Based on Sparse Measurements

Sediment load in streams is known as both a carrier and a potential source of contaminants, while sediment deposition can alter stream flow, stage and morphology, and thereby has broad impacts on stream hydrology, aquatic life, and recreation activity. For vast amounts of watersheds around the world, sparse daily measured sediment data may exist, but continuous and multi-year daily measured sediment data are largely unavailable because of time-consuming and budget constraint for measurements. However, when developing total maximum daily load (TMDL) and calibrating/validating watershed models for sediments, such continuous and multi-year datasets are inevitably required. This study extended the flow-weighted method, developed by Ouyang (Ouyang, Y. Environ. Monit. Assess. 193, 422 (2021)) to predict the continuous and multi-year daily sediment loads based on sparse, limited, and discontinuous measured data. This daily sediment load gap-filling tool was validated using measured data from six different US Geological Survey (USGS) gage stations across US. Results showed that the flow-weighted method well predicted daily sediment loads when a good linear correlation existed between measured seasonal sediment loads and measured seasonal stream discharges, which is a prerequisite to apply the flow-weighted method. Five out of six selected USGS gage stations used in this study met this prerequisite. The flow-weighted method (along with an example R script for implementing the method) is a useful tool for filling the daily sediment load gaps.

Stream corridor and upland sources of fluvial sediment and phosphorus from a mixed urban-agricultural tributary to the Great Lakes

Like many impaired Great Lakes tributaries, Apple Creek, Wisconsin (119 km2) has Total Maximum Daily Load (TMDL) targets for reducing suspended sediment and total phosphorus by 51.2 % and 64.2 %, respectively. From August 2017 - October 2018, a stream sediment budget and fingerprinting integrated study was conducted to quantify upland and stream corridor sources of suspended sediment and sediment-bound phosphorus. Phosphorus concentrations varied among source groups and fluvial sediments, with higher concentrations among suspended sediment and cropland soils. Eroding streambanks identified in the stream corridor sediment budget accounted for 100 % of the TMDL Soil and Water Assessment Tool (SWAT) suspended sediment load but only 20 % of the total phosphorus load. Fine-grained streambed sediment equated to approximately-three years of modeled suspended sediment load but only one third of total phosphorus load. The two primary sources of fine-grained streambed sediment were streambanks and cropland, with relative streambank contributions increasing with downstream direction and watershed area. The relative proportion of suspended sediment varied by season and streamflow; however, cropland and streambank erosion accounted for 54 % and 23 % of the suspended sediment when weighted by of the proportion for representative streamflow. Urban land was a source in the upper watershed, but the signature was sequestered by a mid-watershed detention basin. Contributions from construction sites were higher in the fall 2018, likely corresponding to increased activity following a wet spring. These integrated techniques helped describe sources, transport, and sinks of fluvial sediment and phosphorus throughout the watershed at a range of spatial and temporal scales.

Trend Analysis Using Long-Term Monitoring Data of Water Quality at Churyeongcheon and Yocheon Basins

In this study, we investigated the interrelationships between organic matter and water quality indices in the total maximum daily load basins, namely, Churyeongcheon and Yocheon of the Seomjin River system, and identified trends. Churyeong A and Yocheon B, the basins being analyzed, have high proportions of nonpoint pollution sources and pollutant loads from terrestrial sources. During the study period, biochemical oxygen demand (BOD) decreased in both basins, whereas chemical oxygen demand (COD) and total organic carbon (TOC) increased in Churyeong A and decreased in Yocheon B. The increase in organic matter in Churyeong A correlated with the flow rate, whereas organic matter in Yocheon B showed little correlation with flow rate. Variations in organic matter (BOD, COD, and TOC) in Churyeong A exhibited seasonality under the influence of increased flow rate. Organic matter in Yocheon B was affected by increased flow rate, wherein with time, BOD decreased and COD and TOC increased. This study provides basic data that can be used as a reference to facilitate continuous water management and appropriate strategy implementation by analyzing the influencing factors and trends of organic matter using long-term measurement data.

Total Maximum Daily Loads and Escherichia coli Trends in Texas Freshwater Streams

AbstractFecal indicator bacteria are routinely used to assess surface water sanitary quality. The State of Texas uses Total Maximum Daily Loads to address water bodies that exceed the allowable fecal indicator bacteria criteria. The effectiveness of these processes in decreasing the fecal indicator bacteria concentrations has been debated due to the diversity and nature of fecal indicator bacteria sources. We assessed actual and flow‐adjusted trends in measured Escherichia coli (E. coli) concentrations at 721 freshwater stream sites from 2001 through 2021. We also compared odds of statistical improvement of E. coli concentrations at sites before and after the adoption of Total Maximum Daily Loads (adopted from 2008 through 2014). Results indicate non‐significant differences in the odds of statistically detected improvements in E. coli concentration between pre‐Total Maximum Daily Load and post‐Total Maximum Daily Load sites. Although the State of Texas and numerous watershed stakeholders have made efforts to address water quality impairments, these results join a body of evidence that water quality improvements are stagnating in the state. Furthermore, this study leverages water quality data used for state water quality standards assessment purposes and highlights that robust monitoring program design is needed to effectively assess the progress of water quality planning efforts.

Integrated Water, Nutrient, and Pesticide Management of Huanglongbing-Affected Sweet Oranges on Florida Sandy Soils-A Review.

Citrus greening (huanglonbing (HLB)) disease has drastically reduced citrus fruit production in Florida over the last two decades. Scientists have developed sustainable nutrient management practices to live with the disease and continue fruit production. Best pesticide management practices have been devised to reduce the spread of HLB by Asian citrus psyllid (ACP). However, soil application of excessive nutrients and the use of soil drench application of pesticides to huanglongbing-infected citrus groves have been a serious environmental concern since the recent development of resistance to some pesticides. It is important to understand the consequences of applying pesticides and nutrients beyond the recommended application rates with an inappropriate method for citrus growth and development. Alternatively, foliar sprays of some nutrients proved effective to meet plants’ requirements, and foliar sprays of effective insecticide products could provide an adequate mode of action for group rotation to minimize insecticide resistance by ACP and other pests. Sustainability in citrus production systems should include best management practices that improve pesticide and nutrient efficiency by including the total maximum daily load exiting the grove to reduce pesticide and nutrient exports into waterbodies.

Effects of Nitrogen in Sewage Treatment Plant Effluent on Organic Matter Target Indicator of TMDLs in Korea

This study examined the relationship between water quality indicators (five-day biochemical oxygen demand (BOD5) and ammonia nitrogen (NH3-N)) by modeling them at sewage treatment plants (STPs) and receiving waters. Discharge loads from 2016 to 2018 were input into the QUAL-MEV water quality model, which is used for the total maximum daily loads (TMDLs) in Korea, and the results showed that the simulated BOD5 values decreased according to the reduction in the BOD discharged pollution load, while the observed water quality increased. This was caused by an increase in the total nitrogen discharged pollution load and the NH3-N effluence ratio from the STPs. Hence, the model was modified to reflect real-world conditions. After inputting a calibration factor calculated based on real data and the measured ratio of each type of nitrogen, the simulation was repeated, achieving results within ±20% of observed values. This model confirmed that BOD5 in the lower part of the river varies according to the change in the NH3-N ratio of the STP effluent. To better manage BOD5 and to establish achievable water quality targets, a plan that reflects the linkage among water quality indicators, such as the TMDLs used in the United States, should be introduced in Korea.

Time is money: Water quality's impact on home liquidity and property values

Policymakers grappling with how to meet EPA water quality standards within the Chesapeake Bay must weigh the cost of water quality restoration against the benefits accrued to nearby homeowners. Missing from this analysis are the benefits homeowners receive from increased home liquidity – or how quickly a home is sold once listed. In this paper, we exploit variation in water clarity data to examine its relationship with prices and liquidity using real estate data (2008–2015) from the Baltimore region. We find a one-foot improvement in Secchi depth, needed to meet the total maximum daily load recommendation for the central and northern portion of the Chesapeake Bay, increases housing prices by $9600, decreases time on market by 19.7 days, and reduces seller holding costs by $1280. This cost-savings is welfare-enhancing for many home sellers, especially absentee homeowners who are likely to net an additional 13.3% in water quality benefits when liquidity changes are considered alongside property value increases. Not accounting for the additional benefits and losses accrued through home liquidity suggests water quality restoration projects and damages from impairment will be undervalued.

The Application of Total Maximum Daily Load (TMDL) Approach in Water Quality Assessment for The Batu Pahat River

An increased number of rivers categorized as polluted is alarming that their repercussions are so severe that the rivers can no longer be rehabilitated. This pollution might result from rapid urbanization and population growth, uncontrolled development, which produces a high volume of water pollution that is discharged into the river. Rapid development has led to a large discharge of point source (PS) and nonpoint source (NPS) pollution into the water supply. As a result, the deterioration in water quality, a decline of safe water supply, and the difficulties in accessing clean water have emerged as massive concerns for water authorities attempting to fulfill the increasing supply of clean water resources. To resolve these issues, several approaches were implemented to determine the best approach that could effectively control water quality pollution in Malaysia. One of the best methods that could be used to manage the water quality is Total Maximum Daily Load (TMDL). TMDL seeks to establish or restrict the amounts of a pollutant allowed to enter the river and is assisted by identifying physical, chemical, and organic qualities in the river water body. In this study, six parameters were measured such as dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N), total suspended solids (TSS), and pH. QUAL2K software was utilized to model the water quality and test several scenarios to reduce the pollutant concentration. The analysis shows that the commercial sector poses the most contributor to the pollution loading (kg/day) in Batu Pahat River, mainly from workshop, wet market and restaurant. In addition, low tide flow produced a higher pollution load (kg/day) than high tide flow due to larger discharge during high flow. In conclusion, the development TMDL plan could improve water quality at the Batu Pahat River by analysing pollution loading reduction and future management of watersheds area.

Climate Change‐Legacy Phosphorus Synergy Hinders Lake Response to Aggressive Water Policy Targets

AbstractWith mounting scientific evidence demonstrating adverse global climate change (GCC) impacts to water quality, water quality policies, such as the Total Maximum Daily Loads (TMDLs) under the U.S. Clean Water Act, have begun accounting for GCC effects in setting nutrient load‐reduction policy targets. These targets generally require nutrient reductions for attaining prescribed water quality standards (WQS) by setting safe levels of nutrient concentrations that curtail potentially harmful cyanobacteria blooms (CyanoHABs). While some governments require WQS to consider climate change, few tools are available to model the complex interactions between climate change and benthic legacy nutrients. We present a novel process‐based integrated assessment model (IAM) that examines the extent to which synergistic relationships between GCC and legacy Phosphorus release could compromise the ability of water quality policies to attain established WQS. The IAM is calibrated for simulating the eutrophic Missisquoi Bay and watershed in Lake Champlain (2001–2050). Water quality impacts of seven P‐reduction scenarios, including the 64.3% reduction specified under the current TMDL, were examined under 17 GCC scenarios. The TMDL WQS of 0.025 mg/L total phosphorus is unlikely to be met by 2035 under the mandated 64.3% reduction for all GCC scenarios. IAM simulations show that the frequency and severity of summer CyanoHABs increased or minimally decreased under most climate and nutrient reduction scenarios. By harnessing IAMs that couple complex process‐based simulation models, the management of water quality in freshwater lakes can become more adaptive through explicit accounting of GCC effects on both the external and internal sources of nutrients.

농경지역의 대규모 축산단지에서 배출되는 축산계 부하의 점오염과 비점오염 분류와 정량화

Livestock manure discharged from agricultural areas has different treatment and fertilization processes depending on the type of livestock. Swine manure is generally treated in livestock wastewater treatment plants and then sprayed as liquid fertilizer or discharged into rivers, whereas cattle manure is composted in livestock excreta resource facilities such as biogas plants, and a large amount is applied to the land. However, the source unit of the livestock manure load applied in Korea''s total maximum daily load (TMDL) is not divided into point pollution type and non-point pollution type. The species and pollution load of livestock manure generated in Yongji Watershed where swine are the main livestock, and Dukcheon Watershed where cattle are mainly raised were investigated through a series of measurements and calculations. The result of this study showed the pollution load of livestock manure was clearly classified into PS type and NPS type, and in particular, the NPS pollution load was relatively large. As for the results measured in two watersheds of different livestock breeds, swine and cattle, BOD and TP showed high EMC concentrations in cattle breeding areas, whereas TN showed significantly higher values in swine breeding zones. This finding led us to conclude that there are differences in the water quality management criteria to be focused on depending on the type of livestock. In addition, the load of NPS was fluctuated sensitively to the rainfall intensity, and it implied that the rainfall intensity should be considered as one of the influencing factors when a pollution load of livestock manure is applied to the TMDL.