Water Quality Problems Research Articles

Impact of waterborne E. coli outbreaks on local communities: evidence from housing transactions in Michigan

Abstract Waterborne Escherichia coli (E. coli) represents a pervasive water quality problem across the United States. In Michigan, the presence of E. coli has become problematic for many areas where agricultural run-off and ineffective policies have made these outbreaks endemic. Combining the universe of housing transaction datasets from 2009 to 2017 with the State of Michigan water sampling dataset, we investigate and quantify the negative impacts of E. coli outbreaks on local housing prices. Our difference-in-differences model estimates an overall impact of −8.94% for houses in the treatment group relative to the control group. However, this effect is only short term, as sales prices recover after the outbreak has ended.

Nanobubble-enabled foam fractionation to remove algogenic odorous micropollutants

Due to climate change and environmental pollution, natural lakes and reservoir water suffer increasingly serious algal blooms and associated water quality problems due to the presence of algal or algogenic organic matter (AOM) such as algal odour and toxins. Effective removal of these micropollutants, especially in the event of algal blooms, is critical to aesthetic values of water bodies, drinking water security and human health. The study investigated the removal efficiency of two common odorous compounds, trans-1,10-dimethyl-trans-9-decalol (geosmin) and 2-Methylisoborneol (2-MIB), using foam fractionation enabled by air nanobubbles with addition of two common cationic and anionic surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), to enhance foaming ability and stability. The results showed that the cationic surfactant (i.e., CTAB), a low pH, and high ionic strength significantly promoted the removal of geosmin and 2-MIB. For example, the removal tests using the synthetic water determined that the conditions of pH = 7, [CTAB] = 20 mg·L−1 and IS = 10 mM as NaCl resulted in both the highest geosmin removal rate of 91.81% and highest 2-MIB removal rate of 85.0%. The removal of two odorous compounds in real lake water was evaluated, which yielded removal rates of 83.2% for geosmin and 48.1% for 2-MIB, highlighting the minor inhibition from water matrixes on the removal performances. Compared to microbubbles, nanobubbles enabled greater surface areas of foam and higher removal efficiencies. The study provided new insights into the use of foam fractionation with air nanobubbles to enhance the removal of odorous compounds from impaired water and mitigate the negative environmental and health impacts of harmful algal blooms (HABs).

Impacts of land use changes on the spatiotemporal evolution of groundwater quality in the Yinchuan area, China, based on long-term monitoring data

Agricultural activities and rapid urbanization have significantly impacted groundwater quality, especially in semi-arid and arid regions. This study comprehensively evaluated the quality of phreatic and confined groundwater in the Yinchuan area, China, using long-term monitoring data from 1991 to 2018. Geospatial analysis model was employed to explore the spatiotemporal evolution of groundwater hydrochemistry. The effects of land use changes on groundwater quality were assessed using correlation analysis and a multiple linear regression model (MLR). The findings indicate significant temporal variations in groundwater quality, with phreatic water consistently exhibiting high salinity and hardness. The groundwater quality indices for phreatic water were frequently more polluted than confined water. From 1991 to 2018, the hydrochemical composition of phreatic water evolved from HCO3-Mg and HCO3•SO4-Mg to more complex forms such as HCO3•SO4•Cl-Mg and HCO3•Cl-Mg. In contrast, confined water predominantly maintained its HCO3-Mg type and HCO3•Cl-Na (Na•Mg) type water. Urban land had rapidly expanded in the past three decades, increasing by 318.75% compared to 1991. The water body and urban area diminished the quality of phreatic water. High salt water in increase of TDS, Cl–, SO42–, Mn, TH, NO3–, F–, and Fe into phreatic water. NO3–, NH4+, and F− in phreatic water could be impacted by human and industrial activity in urban areas. This study provides valuable insights for local decision-makers to effectively manage groundwater resources and solve issues of groundwater scarcity and water quality problems in arid and semi-arid locations.

Rotifer functionality as a potentially useful indicator of lake browning

Lake browning is considered a severe water quality problem in lake ecosystems, but it has received considerably less attention in water protection than eutrophication. Current metrics used in lake surveillance monitoring programmes, including the European Union’s Water Framework Directive, do not reflect browning sufficiently. The aims of the study were to explore the potential role of the functionality of rotifers as browning indicators and to improve understanding of the environmental parameters driving the functionality and diversity of rotifers. Seasonal data on rotifer communities and water quality from seven lakes with differing water colour and trophic conditions were analysed. The feeding guilds of rotifers enabled differentiation between lakes in terms of their ecological conditions, and, in particular, eutrophic and brown-water lakes were clearly distinguished from other lakes. The guild ratio of rotifers was positively affected by water colour, but inversely related to total phosphorus concentration. Our results suggest that zooplankton functionality provides a potential tool to assess ecosystem dynamics, particularly when assessing lake browning. Thus, our results suggest that application of the guild ratio of rotifers is a promising method to estimate the general browning status of lakes and may complement the metrics used in Water Framework Directive.

Challenges and Urgent Need of Solid Waste Management in Rudrapur City, US Nagar Uttarakhand

The rapid expansion of urban areas (horizontal and vertical) that occurred throughout the 20th century transformed urban areas into areas that required environmental problems that most urban cities have to face on a global scale. With the rapidly growing population in the urban centers, SWM is turning into a notable environmental challenge and an advent issue, especially in the urban areas (MC) of Uttarakhand. Open throwing and dumping of un-segregated SW pollute the freshwater streams also and open disposal and burning of SW are the main reasons for the adversely affected urban environment, i.e., air pollution, air quality, smog etc. The lack of appropriate SWM facilities has seriously threatened the urban areas. Growing amounts of consumption and waste production combined high-density low-income living Cities, i.e. Rudrapur. Improper management of SWM is just one of the major present problems facing the Rudrapur MC, which are environmental loss, degradation of water and air quality and urban health problems also related to untreated SW throwing, depositing in different parts of urban areas. The present study is based on observation and exploratory research methods by using both primary and secondary data which was collected during a field survey of Rudrapur MC. The entire Rudrapur MC generated a huge amount of SW in quantities comparable to the very small amount collected and transferred to a disposal and treatment site by the MC. Insufficient methods of solid waste collection and transportation in Rudrapur city are not so much improved and there is little access to municipal vehicles for SW collection, transfer and transportation to the final disposal.

Case study: Nutrients distribution and assessment of the current trophic status of Plastiras lake in Thessaly (central Greece) after tropical storm Daniel

Based on the interactions of three water quality variables, chlorophyll-a (Chl-a), secchi depth (SD – water transparency) and total phosphorus (TP), this study was aimed to assess the trophic state of Plastiras Lake through the modified method of Carlson's trophic state index (CTSI). Eutrophication is one of the most serious problems for water quality and CTSI is an important index for monitoring water quality status and eutrophication assessment. The classification scale for Trophic State Index (TSI) fluctuates from 0 to 100 and the results of this study showed that the mean TSI for Chl-a was 42.95, for SD was 45.50 and for TP was 75.15. The overall CTSI finally was 54.53. These show that Plastiras Lake is presently classified as mesotrophic to eutrophic which reflects the current levels of nutrients in the lake.

Identifying manning roughness coefficient using automatic calibration method and simulation of pollution incidents in the Nile River, Egypt

Study regionA reach of the Nile River located between Naga Hammadi barrage and Asyut barrage, Egypt Study focusAn accurate representation of hydrodynamics of an important water source helps cope with expected future climate changes, pollution incidents and water quality problems. Here, a comparison between HEC-RAS 1D and TELEMAC-2D model was conducted by identifying different Manning coefficients. Moreover, an automatic calibration using Dual-Annealing optimization method was applied for first time to calibrate the model with non-uniform Manning coefficients. The transport of tracer (pollution) was simulated by computing tracer residence times. Pollution transport scenarios were discussed to draw a picture of pollution incidents which will continue to happen in the future. An equation indicating the relation between flow discharge and residence time was derived to hurriedly help decision makers in water management during sudden pollution incidents. New hydrological insights for the regionA model with spatially variable Manning coefficients using TELEMAC-2D was set up and calibrated achieving good accuracyies with average errors of approximately 4 cm and 7 cm between field and simulated water levels for two different discharge scenarios. Moreover, an equation for relation between flow discharge and residence time was derived producing a strong correlation coefficient of 0.95. This study, integrating advanced hydrodynamic models and automatic calibration techniques, provides a robust framework for assessing and managing water resource challenges under varying flow conditions.

Identify the seasonal differences in water quality and pollution sources between river-connected and gate-controlled lakes in the Yangtze River basin

The river-connected Dongting Lake (DT) and Poyang Lake (PY), and the gate-controlled Taihu Lake (TH) and Chaohu Lake (CH) are the four important lakes in the Yangtze River Basin. The comprehensive Water Quality Index (WQI), the Eutrophication Integrated Index (TLI(Σ)), and the Positive Matrix Factorization (PMF) model were employed to evaluate water quality and the contribution of pollution sources for these lakes. The results show that WQI for all lakes indicated generally good water quality, with DT scoring 73.52–86.18, the highest among them. During the wet season, the eutrophication degree of river-connected lake was medium, and that of gate-controlled lakes was high. The surface runoff and agricultural non-point sources are the main pollution sources for both types of lakes, but their impact is more pronounced in gate-controlled lakes during the wet season. The study provides evidence support for scientific understanding of water quality problems and management strategies in these areas.

Timescales of Ecological Processes, Settling, and Estuarine Transport to Create Estuarine Turbidity Maxima: An Application of the Peter–Parker Model

The estuarine exchange flow increases the longitudinal dispersion of passive tracers and trap sinking particles, potentially creating an estuarine turbidity maximum (ETM): a localized maximum of suspended particulate matter concentration in an estuary. The ETM can have many implications: dead zones due to increased turbidity or hypoxia from organic matter decomposition, naval navigation challenges, and other water quality problems. Using timescales, we investigate how the interaction between exchange flow and particle sinking leads to ETMs by modeling a sinking tracer in an idealized box model of the Total Exchange Flow (TEF) first developed by Parker MacCready. Results indicate that the balance of particle sinking and vertical mixing is critical to determining ETM size and location. We then focus on the role of ecology in ETM formation through the use of the Peter–Parker Model, a new biophysical model which combines the TEF box model with a Nutrient–Phytoplankton–Zooplankton–Detritus (NPZD) model, the likes of which were first developed by Peter J.S. Franks. Detritus sinking rates similarly influence detritus peak concentration and location (an ETM), but detritus ETMs occur in a different location than the sinking tracer due to the influence of biological factors, which create a time lag of about 1 day. Lastly, we characterize the flow of the models with a dimensionless parameter that compares timescales and summarizes the dynamics of the sinking tracer in ETM formation and that can be used across systems.

Optimization of green infrastructures for sustaining urban stormwater quality and quantity: An integrated resilience evaluation

Coupling natural green infrastructure with artificial gray infrastructure is considered a key solution for mitigating the risk of waterlogging and water quality problems caused by rapid urbanization. However, further research is needed to evaluate and optimize the utility of gray–green system considering multiple key factors. Here, the effects of gray–green system on both the water quality and quantity were investigated based on the Storm Water Management Model-InfoWorks ICM (SWMM-ICM) and bivariate copula functions. A resilience index that integrates reliability, bearing capacity, recovery speed, and recovery capacity was then proposed. Taking a typical catchment area in Beijing as an example, the results showed that the resilience index proposed is effective for evaluating the stormwater management of gray–green system. The integration of gray–green infrastructures improved the resilience of urban stormwater management, particularly in terms of controlling the water quality (improved by 1.0–4.0 %) rather than the water quantity (only 0.04–0.3 %). Direct confluence and average distribution strategies of gray–green system were more effective for water quality management, as resilience ranged from 0.7478 to 0.7605. To mitigate the ever-increasing water risks under climate change, the direct confluence, and average or downstream renovation strategies are hot spots for system renovation in the future. These results contribute to a better understanding of gray–green system and provide the foundation for sustainable water quality and quantity management in global cities.

Impact of Water Quality on the Growth Performance of Clarias gariepinus in Fish Farms within Fako Division, Cameroon

Aquaculture in South-West Cameroon has evolved although not exponentially due to a qualified workforce. The problem of water quality in fish farms that could be associated with poor feeding and water quality management impacts the life of aquatic animals. Fish needs a healthy environment for its optimal growth and development (case study of Catfish). The objective of this studied was to determine the impact of water quality on the growth performance of Clarias gariepinus in some fish farms within Fako Division-South West Region of Cameroon. Material and methods: The method used in this research topic is descriptive, with 4 different localities, namely IRAD Batoke (A), Bakingili (B), Cornelius Fish Center (C) and Oumarou fish farm (D) Mile 2 Limbe. Collection of physicochemical and biological data was conducted from the period of March 8th to May 15th 2023 in Fako Division. Results: The results revealed highest mean temperature value (28.22±0.94ºC) in IRAD Batoke broodstocks tanks while Cornelius fish Center had the highest mean pH, electrical conductivity and total dissolved solid with values of 8.16±1.25; 0.84±0.35 ms/cm; and 0.38±1.8ppt in the broodstocks tanks and table fish tanks. The highest dissolved oxygen (<8mg/l); highest nitrite level (<0.025 mg/l) and highest Ammonium (<0.05 mg/l) were noted in three localities except the Bakingili locality. The physicochemical parameters of water had no negative impacts on the growth performance of this species. Conclusion: The results of physicochemical parameters such as water temperature, pH, and electrical conductivity, total dissolved solid, NH4, NO2, O2 obtained during the study experienced a relative variation and were very suitable for the growth and development of Clarias gariepinus.

Developing a tile drainage module for the Cold Regions Hydrological Model: lessons from a farm in southern Ontario, Canada

Abstract. Systematic tile drainage is used extensively in poorly drained agricultural lands to remove excess water and improve crop growth; however, tiles can also transfer nutrients from farmlands to downstream surface water bodies, leading to water quality problems. Thus, there is a need to simulate the hydrological behaviour of tile drains to understand the impacts of climate or land management change on agricultural surface and subsurface runoff. The Cold Regions Hydrological Model (CRHM) is a physically based, modular modelling system developed for cold regions. Here, a tile drainage module is developed for CRHM. A multi-variable, multi-criteria model performance evaluation strategy was deployed to examine the ability of the module to capture tile discharge under both winter and summer conditions (NSE > 0.29, RSR < 0.84 and PBias < 20 for tile flow and saturated storage simulations). Initial model simulations run at a 15 min interval did not satisfactorily represent tile discharge; however, model simulations improved when the time step was lengthened to hourly but also with the explicit representation of capillary rise for moisture interactions between the rooting zone and groundwater, demonstrating the significance of capillary rise above the saturated storage layer in the hydrology of tile drains in loam soils. Novel aspects of this module include the sub-daily time step, which is shorter than most existing models, and the use of field capacity and its corresponding pressure head to provide estimates of drainable water and the thickness of the capillary fringe, rather than using detailed soil retention curves that may not always be available. An additional novel aspect is the demonstration that flows in some tile drain systems can be better represented and simulated when related to shallow saturated storage dynamics.

Optimizing sampling location for water quality degradation monitoring in distribution systems: Assessing global representativeness and potential health risk

Selecting the optimal monitoring points in a water distribution network is challenging due to the complex spatiotemporal variability of water quality degradation. The lack of a standardized methodology for monitoring point selection forces operators to rely on general recommendations, historical data and professional experience, which can mask water quality problems and increase the risk to consumers. This study proposes a new methodology to optimize the selection of monitoring points in distribution networks. The method considers the spatiotemporal degradation of water quality, the definition of representative zones and two selection criteria: global representativeness and potential health risk. Representative zones were determined for each node of the network based on hydraulic paths and their water quality spatial variability. Part of the distribution network in Quebec City, Canada was used as the case study, in which four water quality parameters were investigated: free chlorine residual (FRC), heterotrophic plate counts (HPC), trihalomethanes (THMs) and haloacetic acids (HAAs). Seasonal variabilities (summer and winter) were also analyzed. The results obtained for the two criteria and for both seasons were compared, and methodological and practical recommendations were established for dynamic monitoring programs that respond to the needs of operators.

Estimating thresholds of natural vegetation for the protection of water quality in South African catchments

Many of South Africa's current water quality problems have been attributed to diffuse pollution derived from poorly regulated land use/land cover (LULC) transformations. To mitigate these impacts, the preservation of an adequate amount of natural vegetation within catchment areas is an important management strategy. However, it is not clear how much natural vegetation cover is required to provide adequate levels of protection, nor at which scale(s) this strategy would be most effective. To investigate the possibility of estimating minimum thresholds of natural vegetation required to protect water resources, regression analysis was used to model relationships between water quality (measured using Nemerow's Pollution Index) and metrics of natural vegetation at multiple scales across a sample of sub-catchments located along the western, southern, and south-eastern coast of South Africa. With conspicuous outliers removed, the models were able to explain up to 82 % of the variability in the relationship between land use and water quality. Moreover, a statistically significant, nonlinear, and inverse relationship was found between proportions of natural vegetation cover and pollution levels. This relationship was strongest when measured (1) across the whole catchment and (2) within a 200 m riparian buffer zone. The models further indicated that approximately 80 to 90 % natural vegetation cover was necessary at these scales to maintain water quality at ecologically acceptable levels. Additional nonlinear thresholds estimated using breakpoint analysis suggested that if proportions of natural vegetation fall below 45 % (across the whole catchment) and 60 % (within a 200 m riparian buffer zone) a dramatic increase in pollution levels can be expected. The estimated thresholds are recommended as guidelines that can be used to inform integrated land and water resources management strategies aimed at protecting water quality in the study area. Likewise, the methods described are recommended for the estimation of similar thresholds in other regions.

Use of multiple sampling techniques for cyanobacteria and cyanotoxin monitoring in the Sacramento-San Joaquin Delta under different hydrologic regimes

Cyanobacteria harmful algal blooms (CHABs) are a growing water quality problem in the upper San Francisco Estuary (California), also known as the Sacramento-San Joaquin Delta. We conducted cyanobacteria and cyanotoxin monitoring from 2020 to 2023, which spanned California's driest consecutive 3-year period and one of the wettest years on record (2023). To assess the impact of CHABs over this range of hydrologic conditions, we monitored invasive Asian Clams (Corbicula fluminea) for microcystin contamination and used molecular tools (qPCR and sequencing) to characterize cyanobacteria in the water column. We also used solid phase adsorption toxin tracking (SPATT) samplers to track microcystins (MCs) and other cyanotoxins in 2023. During the drought years, record breaking MCs, in excess of 1000 μg/L, were documented in water grab samples and Asian clams also accumulated higher MCs relative to the wet year. However, MCs were present in Asian clams during the entire study period. SPATT's confirmed MC presence during wet 2023 and sequencing results corroborated the integrative sampler findings. Yet, no MC was detected in water grab samples at our primary sampling sites during the drought year of 2022 or the wet year of 2023. This highlights the importance of using multiple sampling modalities to provide a more accurate assessment of MC contamination, especially in large estuaries where traditional discrete monitoring can easily miss episodic and transient CHAB events.

Assessment of drinking water quality using Water Quality Index and synthetic pollution index in urban areas of mega city Lahore: a GIS-based approach

The aim of the present study was to assess the drinking water quality in the selected urban areas of Lahore and to comprehend the public health status by addressing the basic drinking water quality parameters. Total 50 tap water samples were collected from groundwater in the two selected areas of district Lahore i.e., Gulshan-e-Ravi (site 1) and Samanabad (site 2). Water samples were analyzed in the laboratory to elucidate physico-chemical parameters including pH, turbidity, temperature, total dissolved solids (TDS), electrical conductivity (EC), dissolved oxygen (DO), total hardness, magnesium hardness, and calcium hardness. These physico-chemical parameters were used to examine the Water Quality Index (WQI) and Synthetic Pollution Index (SPI) in order to characterize the water quality. Results of th selected physico-chemical parameters were compared with World Health Organization (WHO) guidelines to determine the quality of drinking water. A GIS-based approach was used for mapping water quality, WQI, and SPI. Results of the present study revealed that the average value of temperature, pH, and DO of both study sites were within the WHO guidelines of 23.5 °C, 7.7, and 6.9 mg/L, respectively. The TDS level of site 1 was 192.56 mg/L (within WHO guidelines) and whereas, in site 2 it was found 612.84 mg/L (higher than WHO guidelines), respectively. Calcium hardness of site 1 and site 2 was observed within the range from 25.04 to 65.732 mg/L but, magnesium hardness values were higher than WHO guidelines. The major reason for poor water quality is old, worn-out water supply pipelines and improper waste disposal in the selected areas. The average WQI was found as 59.66 for site 1 and 77.30 for site 2. Results showed that the quality of the water was classified as “poor” for site 1 and “very poor “ for site 2. There is a need to address the problem of poor water quality and also raise the public awareness about the quality of drinking water and its associated health impacts.

Assessment of water quality parameters due to longitudinal salinity inundation at Indus Delta: a case study of Kharo Chan, District Sujawal

Deltas are landforms that are formed at the regions where a river meets an ocean. When the freshwater of a river joins the saline water of an ocean, a transitional state of water is obtained. This zone of transition varies on the quantity of freshwater entering the ocean and the quality of both waters. Indus River is facing severe challenges due to climate change which has resulted in reduced water flow in the river. Consequently, seawater intrusion takes place which causes coastal erosion, stunted mangrove growth, and the narrowing of the river towards the seaside. The groundwater in the deltaic regions is unfit for drinking which forces an increased reliance on surface water. Sindh Province of Pakistan, particularly the coastal regions, suffers from severe water quality problems, affecting approximately 41% of the population. The population of this region is deprived of good-quality water for their daily use. This research aims to evaluate the physiochemical parameters of water in the Indus River to identify the zone of salinity inundation and determine safe zones for accessing surface water in the Indus Delta in the Sujawal district. Water samples were collected from Khobar Creek, ending in the Arabian Sea in the areas of Shah Bandar and Kharo Chan at an approximate interval of 5 km. These samples were analyzed for various physical and chemical properties. Properties were compared spatially to develop a relationship between distance and quality of water. Results indicate that the values of dissolved solids in collected samples are between 21,450 and 900 mg/L, pH was between 6.66 and 7.63, conductivity of the samples varied from 33,000 to 1385 µS/cm, acidity values were between 921.14 and 399.84 mg/L, hardness was in the range of 3654 to 192 mg/L, and the turbidity was in between 21 and57 NTU. It was revealed from the results that seawater is having a severe influence upto 15 km from the mouth of the creek in which not a single parameter except the pH was complying with WHO recommendations. In the interval of 15 to 30 km, some properties of water were complying with WHO recommendations, while some of them were deviating from the limits. It has been concluded that turbidity was improving while going toward the ocean, while Total Dissolved Solids, hardness, and chloride concentrations were increasing as water was getting closer to the sea while pH was found almost unaffected. The findings emphasize the need for addressing environmental degradation, social hardships, and economic challenges caused by these water quality issues. Ultimately, the quality of water is crucial for various activities specifically for drinking purposes, and its suitability for specific purposes is of utmost importance.

Floods and droughts research progress and its contributions toward sustainability

In 2015, the United Nations General Assembly launched seventeen Sustainable Development Goals (SDGs), aimed at being achieved by 2030. The SDGs 6 (clean water & sanitation) and 13 (climate actions) are two critically important goals concerning water resources that need to be addressed. This study used the Scopus database to explore climate extremes, specifically droughts and floods, in East Asia and highlight the region's efforts and contributions towards achieving SDGs 6 and 13. We found that even before the implementation of SDGs, the topics related to solving the problems of water resources, water quality, and treatment of wastewater using different conceptual models and methodologies were the main concerns in the region. The adoption of SDGs has led to a heightened focus on water and climate sustainability in East Asia, with the considerable surge in climate-related studies after 2019. Under SDG 13, all countries have contributed substantially to climate action research. Keyword analysis indicates that climate change, water management, water treatment, water quality, and adsorption remain prominent. SDGs 6 and 13 have emerged as crucial areas of focus for research and initiatives as the global community grapples with escalating water resources and climate challenges. Under specific keywords search, China has 2nd place in the search with climate and water during the SDGs period, accounting for 21 % of the entire publication from 2015 to 2023. Japan and South Korea account for of 4 % and 3 %, respectively. The research on floods and droughts has garnered significant attention, with half of the ten highly co-cited literature examining the changing pattern of drought, the influence of extreme events on crop yield, and other related topics. Despite the positive contribution of the East Asia region towards SDGs 6 and 13, there is still an urgent need for a more robust framework to improve the complex interconnections between climate actions, clean water, and sanitation for a sustainable soil-water-plant-atmosphere ecosystem.

Characterizing Spatiotemporal Variability in Phosphorus Export across the United States through Bayesian Hierarchical Modeling.

Phosphorus inputs from anthropogenic activities are subject to hydrologic (riverine) export, causing water quality problems in downstream lakes and coastal systems. Nutrient budgets have been developed to quantify the amount of nutrients imported to and exported from various watersheds. However, at large spatial scales, estimates of hydrologic phosphorus export are usually unavailable. This study develops a Bayesian hierarchical model to estimate annual phosphorus export across the contiguous United States, considering agricultural inputs, urban inputs, and geogenic sources under varying precipitation conditions. The Bayesian framework allows for a systematic updating of prior information on export rates using an extensive calibration data set of riverine loadings. Furthermore, the hierarchical approach allows for spatial variation in export rates across major watersheds and ecoregions. Applying the model, we map hotspots of phosphorus loss across the United States and characterize the primary factors driving these losses. Results emphasize the importance of precipitation in determining hydrologic export rates for various anthropogenic inputs, especially agriculture. Our findings also emphasize the importance of phosphorus from geogenic sources in overall river export.

Multi-year three-dimensional simulation of seasonal variation in phytoplankton species composition in a large shallow lake

Lake Erie has been negatively impacted by multiple stressors, including nutrient enrichment and climate change, that have exacerbated eutrophication and harmful algal blooms. Management of these long-term water quality problems requires numerical models that can be run over years to decades. The three-dimensional hydrodynamics and biogeochemistry models applied to date, however, have not been tested for continuous runs longer than one year and have not been shown to accurately reproduce seasonal variation in phytoplankton species composition (e.g., the development of harmful algal blooms) over decadal timescales. We simulated the three-dimensional nutrient and phytoplankton concentrations in western Lake Erie continuously from 2002 to 2014. Using a single parameter set, we were able to reproduce both seasonal and inter-annual variation in phytoplankton species composition. The model qualitatively reproduced the observed seasonal succession (i.e., variation in phytoplankton species composition), including the spring diatom bloom and late summer cyanobacterial growth. This study demonstrates that three-dimensional models can be applied for multi-year simulations of nutrients and phytoplankton to inform large lake research and management.