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Interacting effects of climate change and agricultural BMPs on nutrient runoff entering Lake Erie
Abstract
Agricultural best management practices (BMPs) have been implemented in the watersheds around Lake Erie to reduce nutrient transfer from terrestrial to aquatic ecosystems and thus protect and improve the water quality of Lake Erie. However, climate change may alter the effectiveness of these BMPs by altering runoff and other conditions. Using the Soil and Water Assessment Tool (SWAT), we simulated various climate scenarios with a range of BMPs to assess possible changes in water, sediment, and nutrient yields from four agricultural Lake Erie watersheds. Tile drain flow is expected to increase as is the amount of sediment that washes from land into streams. Predicted increases in tributary water flow (up to 17%), sediment yields (up to 32%), and nutrient yields (up to 23%) indicate a stronger influence of climate on sediment compared to other properties. Our simulations found much greater yield increases associated with scenarios of more pronounced climate change, indicating that above some threshold climate change may markedly accelerate sediment and nutrient export. Our results indicate that agricultural BMPs become more necessary but less effective under future climates; nonetheless, higher BMP implementation rates still could substantially offset anticipated increases in sediment and nutrient yields. Individual watersheds differ in their responsiveness to future climate scenarios, indicating the importance of targeting specific management strategies for individual watersheds.
... Modeling flow and nutrient transport under future climate scenarios are thus critical to manage nutrient pollution. Within the Lake Erie Basin, while climate projections predict a warmer and wetter winter with more extreme events, modeling studies provide somewhat conflicting results on the impact of these changes on streamflow and nutrient losses (Rahman et al., 2012;Ahmadi et al., 2014;Bosch et al., 2014;Verma et al., 2015;Cousino et al., 2015;Culbertson et al., 2016;Robertson et al., 2016;Wallace et al., 2017;Kalcic et al., 2019). For example, using the SWAT model, Bosch et al. (2014) predicted higher flows and greater sediment and nutrient (nitrogen and phosphorus) losses under future climate scenarios in the western and central regions of the Lake Erie basin, driven largely by wetter spring periods. ...
... Within the Lake Erie Basin, while climate projections predict a warmer and wetter winter with more extreme events, modeling studies provide somewhat conflicting results on the impact of these changes on streamflow and nutrient losses (Rahman et al., 2012;Ahmadi et al., 2014;Bosch et al., 2014;Verma et al., 2015;Cousino et al., 2015;Culbertson et al., 2016;Robertson et al., 2016;Wallace et al., 2017;Kalcic et al., 2019). For example, using the SWAT model, Bosch et al. (2014) predicted higher flows and greater sediment and nutrient (nitrogen and phosphorus) losses under future climate scenarios in the western and central regions of the Lake Erie basin, driven largely by wetter spring periods. Green and Wang (2008) predicted decreased N:P ratios in runoff due to an increase in surface runoff. ...
... The projected shift from surface to subsurface flow in winter is likely a result of the warmer air temperatures, as well as the temporal distribution of precipitation and snow cover under future climates. Warmer winter temperatures will likely reduce the extent of frozen ground (Sinha & Cherkauer, 2010), and this can contribute to increased infiltration and decreased surface runoff within the SWAT model (Bosch et al., 2014). This was also reported by Jyrkama and Sykes (2007), who projected increased infiltration and groundwater recharge in a southern Ontario watershed due to decreased ground frost, demonstrating the importance of soil freezing dynamics in controlling projected pathway losses (Xiuqing and Flerchinger, 2001). ...
... In 2011, the largest algal bloom to date was recorded in Lake Erie and in 2014, a Lake Erie algal bloom contaminated the city of Toledo's water supply, eliminating their drinking water for >2 days (Michalak et al. 2013;Molder et al. 2015;Steffen et al. 2017). To mitigate the loss of pollutants and contaminants into these waterways, which impair water quality and biodiversity, best management practices (BMPs) can be implemented (Bosch et al. 2014). A critical issue with BMPs in highly agricultural areas such as Chatham-Kent is the cost and/or space it takes to implement these practices, as they are often deemed to be not 'economically viable due to the amount of land it takes out of production' (Cole, Stockan, and Helliwell 2020). ...
... As a result, more attention is being paid to BMPs because of the positive outcome they bring to water quality, which is one of the largest implications of BMPs. For example, Lake Erie receives high levels of sediment and nutrient loads from agricultural drains, which is one reason we have seen a substantial increase in algal blooms over the last decade (Bosch et al. 2014). Bosch et al. (2014) highlights the efforts that have been made by numerous groups to implement BMPs to reduce the nutrient and sediment loads entering Lake Erie. ...
... For example, Lake Erie receives high levels of sediment and nutrient loads from agricultural drains, which is one reason we have seen a substantial increase in algal blooms over the last decade (Bosch et al. 2014). Bosch et al. (2014) highlights the efforts that have been made by numerous groups to implement BMPs to reduce the nutrient and sediment loads entering Lake Erie. While this is useful for those looking to implement the different BMPs, it is still relevant to understand and quantify the impacts of DMPs as they are still frequently implemented across the region. ...
... Climate change affects the atmospheric CO 2 level and hydrological parameters such as precipitation, temperature, evaporation, and streamflow. This situation also affects nutrient dynamics and water quality in the basins (Bosch et al. 2014). In addition, rising temperatures as a result of climate change cause a decrease in water potential and dissolved oxygen in water resources and an increase in fish mortality and algae growth (Ahiadu 2019). ...
... In addition, hydrological models are preferred for the effects of climate change on the environment (Aawar and Khare 2020), interbasin water transfer (Sanlı et al. 2021), water resources management (Avcı et al. 2022), and the impact of water resources management on neighboring basins (Sanlı et al. 2022). SWAT is one of the widely used models in the literature since it is a useful tool for establishing a watershed model, determining the effectiveness of different management scenarios in reducing nutrient loss, and improving water quality (Bosch et al. 2014). Also, it can simulate the sediment yield over long periods in large and complex basins. ...
... Considering the significant decrease in runoff due to climate change, a decrease in N and P loads in t/year in the basin is an expected result since changes in flow result in changes in nutrient loads. A high flow volume increases nutrient loads and reduces pollutant concentrations, while a low flow volume reduces nutrient loads and increases pollutant concentrations (Bosch et al. 2014;Tong et al. 2007 The effects of climate change on N and P concentrations in the North Aegean Basin were evaluated at IST_KEN014 station. Increases in nutrient concentration values caused changes in water quality classes; TP concentration is 0.172 mg/l and TN concentration is 2.407 mg/l as a result of baseline model simulation; these values increased to 0.214 mg/l and 0.216 mg/l for TP and increased to 3.814 mg/l and 3.763 mg/l for TN, respectively, as a result of RCP4.5 and RCP8.5 climate change simulations. ...
Climate change is a global phenomenon that directly affects agriculture by altering crop yield, nutritional quality, pests, and plant diseases. The North Aegean Basin located in Turkey has considerable agricultural importance due to its fertile soils. Agricultural activities have increased significantly and uncontrollably in the last decade, resulting in dramatic changes in nitrate and phosphorus levels in surface water within the watershed. Changes in climatic conditions have the potential to impact the quantity and quality of water resources. Best management practices (BMPs) are presently utilized as a planning tool to enhance the quality of water resources. To develop policies in this regard, it is necessary to evaluate the effectiveness of BMPs. To this end, this study aims to investigate the potential effect of climate change on the surface water quality of the North Aegean Basin. For the period between 2010 and 2030, global climate data retrieved from Concentration Pathway (RCP) scenarios 4.5 and 8.5 and regionally downscaled were used to feed the Soil and Water Assessment Tool (SWAT) model. The various potential BMP scenarios were developed and simulated in the hydrological model by considering the effects of climate change. The RCP4.5 scenario reduced the precipitation by 15.11%, while the RCP8.5 scenario reduced the precipitation by 10.97%. Decreased precipitation also affected the runoff and the nutrient loads and concentrations. As a result of the RCP4.5 simulation, TP and TN concentrations increased by 24.42% and 58.45%, respectively, in the IST_KEN014 station. Improvements were observed in TN and TP concentrations with the effect of applied BMP simulations. Also, the results revealed that the applied BMP scenarios may contribute to considerable reductions in nutrient loads. Considering the RCP4.5 scenario, BMPs reduced TN loads in the basin by 2.42–10.97%, while reducing TP loads by around 3.60–16.81%. Considering the RCP8.5 scenario, the BMPs reduced the TN loads in the basin between 2.21 and 10.04%, while they reduced the TP loads between 3.57 and 16.67%.
... The watershed model ensemble was built with SWAT. SWAT is a watershed model commonly used to assess nonpoint source pollution in watersheds, as well as climate change impacts on hydrology and nutrients (e.g., Bosch et al. 2014;Verma et al. 2015;Culbertson et al. 2016;Scavia et al. 2017;Čerkasova et al. 2018;Wang et al. 2018). The model uses inputs of elevation, land use and land cover, climate, and soils, runs on daily time scales, and is able to simulate a wide range of agricultural and landmanagement practices (Neitsch et al. 2009;Arnold et al. 2012). ...
... Cousino et al. (2015) simulated 100% no-till on agricultural areas and found this lowered sediment yields by 16% compared to corresponding climate scenarios under historical management with conventional tillage (nutrient data not included in findings). Bosch et al. (2014) evaluated modest adoption rates of agricultural conservation practices: 25% of cropland with cover crops and no-till and 20% with filter strips. They found this scenario of agricultural conservation practices with modest changes in climate showed annual loading reductions of 6% TP, 4% DRP, and 4% TN. ...
... They found this scenario of agricultural conservation practices with modest changes in climate showed annual loading reductions of 6% TP, 4% DRP, and 4% TN. Similar to this study, Bosch et al. (2014) also found conservation practices (no-till, cover crops, filter strips) to be less effective in a future climate. Bosch et al. (2014) and Cousino et al. (2015) chose to focus on variability caused by the different climate scenarios and only include one watershed model. ...
This study investigates the combined impacts of climate change and agricultural conservation on the magnitude and uncertainty of nutrient loadings in the Maumee River Watershed, the second‐largest watershed of the Laurentian Great Lakes. Two scenarios — baseline agricultural management and increased agricultural conservation — were assessed using an ensemble of five Soil and Water Assessment Tools driven by six climate models. The increased conservation scenario included raising conservation adoption rates from a baseline of existing conservation practices to feasible rates in the near future based on farmer surveys. This increased adoption of winter cover crops on 6%–10% to 60% of cultivated cropland; subsurface placement of phosphorus fertilizers on 35%–60% to 68% of cultivated cropland; and buffer strips intercepting runoff from 29%–34% to 50% of cultivated cropland. Increased conservation resulted in statistically significant (p ≤ 0.05) reductions in annual loads of total phosphorus (41%), dissolved reactive phosphorus (18%), and total nitrogen (14%) under the highest emission climate scenario representative concentration pathway (RCP 8.5). While nutrient loads decreased with increased conservation relative to baseline management for all watershed models, different conclusions on the true effectiveness of conservation under climate change may be drawn if only one watershed model was used.
... Implementation of ACPs varied across studies, but applications commonly implemented ACPs on varying percentages of land area in the modeled watershed, targeted ACP implementation to critical source areas with high nutrient loads, or compared individual vs. combinations of ACPs in the same watershed. Other scenarios included varying levels of projected climate change severity (e.g., Bosch et al., 2014;Cousino et al., 2015;Culbertson et al., 2016) or implementation of ACPs corresponding to farmer survey input (e.g., Palm-Forster et al., 2016;Pyo et al., 2017). ...
... While none of the SWAT modeling studies modeled subsurface drainage management as a distinct ACP, multiple studies included a description of how tile drainage was simulated, and the extent of implementation within a watershed, as part of the baseline model of existing conditions. For example, Bosch et al. (2011Bosch et al. ( , 2013Bosch et al. ( , 2014 simulated subsurface drainage in all of their watershed models for areas under row crops and hay with soil types C and D, as defined by the soil hydrologic group (USDA NRCS, 2020). Additionally, they set the depth to the impermeable layer at 2500 mm, the depth to subsurface drains at 1000 mm, the time to drain soil to field capacity at 24 h, and the tile drain lag time at 96 h. ...
... Xu et al. (2018) found that ACP implementation plans that were optimized for current climate conditions were much less effective when applied under future climate scenarios. Overall, these studies concluded that widespread, adaptive implementation of combined ACPs across the WLEB would be needed to overcome excess nutrient loading both now and in the future (Michalak et al., 2013;Bosch et al., 2014;Cousino et al., 2015;Muenich et al., 2016;Culbertson et al., 2016;Wallace et al., 2017;Xu et al., 2018). ...
Lake Erie is threatened by eutrophication and harmful algal blooms due to excess nutrient loading from agricultural sources. Agricultural conservation practices (ACPs) have been developed and implemented to reduce nutrient losses but estimating ACP effectiveness is challenging. The Soil and Water Assessment Tool (SWAT) has been used to investigate ACP effectiveness for water quality improvement. Many SWAT applications have been developed by different investigators to evaluate ACP effectiveness for reducing nutrient, particularly phosphorus (P), loading in the agriculturally-dominated Western Lake Erie Basin (WLEB). Our objective is to establish what has been achieved by past modeling research and make suggestions for future applications and improvements. We synthesized the findings of 28 SWAT modeling studies within the WLEB. Models generally performed satisfactorily against accepted criteria for streamflow and sediment, but performance for P loads, like soluble reactive P, was mostly “unsatisfactory”. The “unsatisfactory” performance maybe due to imperfections and idealizations in model formulations and/or parameterization. Thus, simulations of P transport and transformation processes need improvement. In addition, model parameter selection is the key part of model set-up. Most SWAT modeling studies used default values during initial set-up, then performed calibration and validation. It was found that the calibrated P related parameter values varied widely across different studies, even within the same watershed with some values unrealistic for the study areas. The phenomena of different combinations of model parameters producing similar outputs indicates equifinality. Equifinality in the baseline model may impact results when ACPs are incorporated. Furthermore, the unrealistic values used in ACP assessment undermine the credibility of ACP effectiveness. Future model applications should try to re-examine the calibrated P parameters and make sure they are realistic for the study area as well as reduce equifinality by constraining the model with characterization of watershed conditions, better understanding of hydrologic processes, and parameter values based on real-world observations. In summary, future model applications should focus on improving P transport and transformation processes, using measured watershed characteristics for parameterization, and improving reflections of climate change, which could result in more accurate assessments of ACP effectiveness to meet targeted goals.
... In agricultural dominated watersheds, sediment and nutrient runoff are a widespread concern (Bosch et al. 2014). In Lake Erie's western basin, increased sediment load from surrounding areas has been affecting the region's water quality (Cousino, Becker, and Zmijewski 2015;Stow et al. 2015;Larson et al. 2018). ...
... In Lake Erie's western basin, increased sediment load from surrounding areas has been affecting the region's water quality (Cousino, Becker, and Zmijewski 2015;Stow et al. 2015;Larson et al. 2018). It is predicted that, with varying levels of climate change, the western Lake Erie watersheds will receive more annual precipitation and more intense springtime rain events in the future, which may further increase the sediment load (Bosch et al. 2014). Bosch et al. (2014) found that surface sediment runoff increases by 13% under a moderate climate change scenario and up to 39% under a more pronounced climate change scenario. ...
... It is predicted that, with varying levels of climate change, the western Lake Erie watersheds will receive more annual precipitation and more intense springtime rain events in the future, which may further increase the sediment load (Bosch et al. 2014). Bosch et al. (2014) found that surface sediment runoff increases by 13% under a moderate climate change scenario and up to 39% under a more pronounced climate change scenario. These increases in surface sediment runoff would increase river SSC by 9% and 23%, respectively (Bosch et al. 2014). ...
Satellite remote sensing has been widely used to map suspended sediment concentration (SSC) in waterbodies. However, due to the complexity of sediment-water interactions, it has been difficult to derive linear and non-linear regression equations to reliably predict SSC, especially when trying to estimate depth of integrated sediment. This study uses Landsat 8 OLI (Operational Land Imager) sensor to map SSC within the Maumee River in Ohio, USA, at multiple depth intervals (15, 61, 91, and 182 cm). Simple linear least squares regression (LLSR), and three common machine learning models: random forest (RF), support vector regression (SVR), and model averaged neural network (MANN) were used to estimate SSC at the depth intervals. All machine learning models significantly outperformed LLSR while RF performed the best. In both RF and MANN, R² (coefficient of determination) increases with depth with a maximum R² of 0.89 and 0.83, respectively, at a depth of 0–182 cm. The results show that machine learning models can implement nonlinear relationships that produce better predictions than traditional linear regression methods in estimating depth integrated SSC, especially when samples are limited.
... The Maumee River has delivered relatively consistent N loads to Lake Erie in recent decades (Choquette et al., 2019) even though total N and nitrate (NO 3 -) concentrations in the river have slightly decreased (Rowland et al., 2021;Stow et al., 2015) because precipitation and discharge have increased in the basin (Williams and King, 2020). On agricultural fields, increases in precipitation cause increases in hydrologic N loss (Hanrahan et al., 2019), which may be exacerbated with climate change (Bosch et al., 2014). Agricultural conservation practices have been implemented throughout the basin with some success in reducing N in runoff, but nutrients are still transported to adjacent streams and downstream rivers (USDA-NRCS, 2016). ...
... Agricultural conservation practices have been implemented throughout the basin with some success in reducing N in runoff, but nutrients are still transported to adjacent streams and downstream rivers (USDA-NRCS, 2016). Incorporating climate-change projections indicates that additional agricultural conservation may be needed to offset increases in discharge (Bosch et al., 2014;Fraker et al., 2023), although warmer temperatures may lead to reduced runoff (Kalcic et al., 2019). This uncertainty in future nutrient run-off scenarios indicates that a combination of agricultural conservation practices may be needed to reduce N loads to Lake Erie. ...
... As a result, it was seen that cover crop and terracing practices for both climate change simulations were more effective in reducing erosion than zero tillage and vertical tillage. Although some BMPs seem to be less effective on erosion corresponding to climate change impacts, increasing BMP application rates in the future has distinctive contributions to balancing erosion in the basins [69]. ...
... As a result, it was seen that cover crop and terracing practices for both climate change simulations were more effective in reducing erosion than zero tillage and vertical tillage. Although some BMPs seem to be less effective on erosion corresponding to climate change impacts, increasing BMP application rates in the future has distinctive contributions to balancing erosion in the basins [69]. The use of cover crops and terracing practices, which have a greater effect on reducing erosion, were examined on a sub-basin basis. ...
Climate change and agricultural activities are significant sources of stress to the natural environment and water resources. These also affect erosion and the associated estimation of sediment yields, which is also a crucial task in the hydrological models. The presented study is significant for the development of sustainable watershed management practices. It also aims to determine the effects of climate change and different agricultural best management practices (BMPs) on the sediment loads of the North Aegean Basin in Türkiye by using the Soil and Water Assessment Tool (SWAT) model. While sediment calibration was performed for 2014, streamflow calibration and verification were performed using the SWAT Calibration and Uncertainty Program (SWAT-CUP) for the period 2012–2013 and 2014–2015, respectively. The obtained results showed that the climate change scenarios reduce the surface waters of the basin and sediment yield in accordance with the hydrological transport processes. During the 2012–2030 time period, runoff in the basin for the RCP4.5 and RCP8.5 climate change scenarios decreased by 38.5% and 31.8%, respectively, and the basin sediment yield decreased by 55.7% and 50.7%, respectively. The sediment yields to water resources had distinctive reductions due to BMPs such as zero tillage, vertical tillage, cover crop, and terracing. Considering the RCP4.5 and RCP8.5 scenarios, BMPs reduced the sediment yield in the range of 0.93–4.03% and 0.89–3.85%, respectively. Determining the sediment transport by using hydrological modeling and the effects of climate change for different agricultural practices on erosion will be useful for decision-makers.
... Similar results were shown for Shell and Logan Creek watersheds in Nebraska (Van Liew et al. 2012). Bosch et al. (2014) simulated practice responses to climate change scenarios using the SWAT model in four rivers draining to Lake Erie (the Raisin, Maumee, Sandusky, and Grand Rivers). SWAT simulations suggested that conservation practices, such as no-till practices, cover crops, and filter strips will become less effective in removing pollutants under future climate due to increased flows, lessened contact time, and reductions in filter strip vegetation density under drought. ...
... Success of forest regeneration is likely to be impacted by climate changes, such as increased frequency and intensity of floods and drought (USGS 1997;Ogden & Innes 2008). More frequent storms and drought conditions would harm canopy trees and reduce the ability of seedlings to establish (Swetnam & Betancourt 1997;USGS 1997;Borja 2014). Seedlings will also likely have to compete with more vines and, potentially, invasive species as climate change continues (Rustad et al. 2011). ...
Water quality practices are commonly implemented to reduce human impacts on land and water resources. In series or parallel in a landscape, systems of practices can reduce local and downstream pollution delivery. Many practices function via physical, chemical, and biological processes that are dependent on weather and climate. Climate change will alter the function of many such systems, though effects will vary in different hydroclimatic and watershed settings. Reducing the risk of impacts will require risk-based, adaptive planning. Here, we review the literature addressing climate change effects on practices commonly used to mitigate the water quality impacts of urban stormwater, agriculture, and forestry. Information from the general literature review is used to make qualitative inferences about the resilience of different types of practices. We discuss resilience in the context of two factors: the sensitivity of practice function to changes in climatic drivers, and the adaptability, or relative ease with which a practice can be modified as change occurs. While only a first step in addressing a complex topic, our aim is to help communities incorporate consideration of resilience to climate change as an additional factor in decisions about water quality practices to meet long-term goals. HIGHLIGHTS
Many water quality practices function via physical, chemical, and biological processes sensitive to weather and climate.;
Climate change presents a risk to practice-based investments in water quality protection; more resilient practices can help reduce this risk.;
Practice resilience can be characterized in terms of sensitivity to changes in weather and climate and ability to modify the practice over time.;
This review is intended to help communities and water resource managers consider climate resilience when adopting practices to meet water quality goals.;
... In addition, by implementing the SWAT model, Bosch et al. (2014) studied the impact of climate change and, using a range of BMPs, on water, sediment, and nutrient yields of four agricultural Lake Erie watersheds, during three 30-year periods between 2010 and 2099. The results showed increases in streamflow, sediment yield, and total phosphorus (TP) loading. ...
... It was also reported by Azadi et al. (2021) and Akomeah et al. (2021), and Woznicki and Nejadhashemi (2012). Some studies, such as Bosch et al. (2014) and Olaoye et al. (2021), found an increase in flow and nutrient load in their case studies located in North America. Azadi et al. (2021) and Akomeah et al. (2021) found similar results, including intensification of thermal stratification, increase in reservoirs water temperature and increase in phosphorus concentration under climate change scenarios. ...
Climate change, besides global warming, is expected to intensify the hydrological cycle, which can impact watershed nutrient yields and affect water quality in the receiving water bodies. The Mahabad Dam Reservoir in northwest Iran is a eutrophic reservoir due to excessive watershed nutrient input, which could be exacerbated due to climate change. In this regard, a holistic approach was employed by linking a climate model (CanESM2), watershed-scale model (SWAT), and reservoir water quality model (CE-QUAL-W2). The triple model investigates the cumulative climate change effects on hydrological parameters, watershed yields, and the reservoir’s water quality. The SDSM model downscaled the output of the climate model under moderate (RCP4.5) and extreme (RCP8.5) scenarios for the periods of 2021-2040 and 2041-2060. The impact of future climate conditions was investigated on the watershed runoff and total phosphorus (TP) load, and consequently, water quality status in the dam’s reservoir. The results of comparing future conditions (2021-2060) with observed present values under moderate to extreme climate scenarios showed a 4-7% temperature increase and a 6-11% precipitation decrease. Moreover, the SWAT model showed a 9-16% decline in streamflow and a 12-18% decline in the watershed TP load for the same comparative period. Finally, CE-QUAL-W2 model results showed a 3-8% increase in the reservoir water temperature and a 10-16% increase in TP concentration. It indicates that climate change would intensify the thermal stratification and eutrophication level in the reservoir, especially during the year’s warm months. This finding specifies an alarming condition that demands serious preventive and corrective measures.
... The Maumee River delivers significant P to the western basin and has an agricultural watershed that has been the study of the effectiveness of BMPs on nutrient load reductions (e.g., [14,41]). Therefore, to explore the impacts of phosphorus loading reduction scenarios on water quality changes, the nutrient loads from the Maumee River were varied in two management scenarios. ...
... The USEPA [12] established the target of limiting March-July dissolved reactive phosphorus loading from the Maumee River to 186 metric tonnes and total phosphorus loading to 860 metric tonnes, an approximately 40% reduction from 2008 loads (closest to the original 1978 Annex 3 target of 11,000 MT), in order to reach 'mild bloom' threshold of 9600 MTA [42]. Nutrient loads may be controlled by BMPs (best management practices) in the Maumee River watershed to reduce the P loads entering into the western basin [14,41]. However, the direct effect of the loads recommended in the Annex 4 targets, as well as the direct effect of achievable loads from the implementation of BMPs, has not been simulated over decadal timescales. ...
During the 1970s, harmful cyanobacteria (HFCB) were common occurrences in western Lake Erie. Remediation strategies reduced total P loads and bloom frequency; however, HFCB have reoccurred since the mid-1990s under increased system stress from climate change. Given these concurrent changes in nutrient loading and climate forcing, there is a need to develop management tools to investigate historical changes in the lake and predict future water quality. Herein, we applied coupled one-dimensional hydrodynamic and biogeochemical models (GLM–AED) to reproduce water quality conditions of western Lake Erie from 1979 through 2015, thereby removing the obstacle of setting and scaling initial conditions in management scenarios. The physical forcing was derived from surface buoys, airports, and land-based stations. Nutrient loads were reconstructed from historical monitoring data. The root-mean-square errors between simulations and observations for water levels (0.36 m), surface water temperature (2.5 °C), and concentrations of total P (0.01 mg L−1), PO4 (0.01 mg L−1), NH4 (0.03 mg L−1), NO3 (0.68 mg L−1), total chlorophyll a (18.74 μg L−1), chlorophytes (3.94 μg L−1), cyanobacteria (12.44 μg L−1), diatoms (3.17 μg L−1), and cryptophytes (3.18 μg L−1) were minimized using model-independent parameter estimation, and were within literature ranges from single year three-dimensional simulations. A sensitivity analysis shows that 40% reductions of total P and dissolved reactive P loads would have been necessary to bring blooms under the mild threshold (9600 MTA cyanobacteria biomass) during recent years (2005–2015), consistent with the Annex 4 recommendation. However, these would not likely be achieved by applying best management practices in the Maumee River watershed.
... Such studies show that implementing a combination of BMPs may counteract climate-change induced increases in nitrogen loadings (Woznicki andNejadhashemi 2014, Ghimire et al 2021). However, it has been noted that BMP selection must be guided by local knowledge due to small scale changes in nitrogen export and responses to climatic changes (Bosch et al 2014, Johnson et al 2022. ...
Agricultural best management practices (BMPs) are often implemented to reduce nutrient transport from farmland to downstream waterbodies. However, under the scenario of a changing climate, nutrient transport processes may be altered and BMPs may not be as effective. Using an ensemble of downscaled climate projections under moderate and high radiative forcings, we perform a hybrid climate assessment of BMPs in a large, flat, and primarily agricultural watershed in the Canadian Prairies. We quantify the total nitrogen delivery under current and future climate scenarios, with and without BMPs. Our findings reveal that BMP combinations, which are currently sufficient under historical climate conditions, may become inadequate to handle increased nitrogen under future climate conditions. We examine the enhancement of BMPs, conditioned to mean ensemble projections. Although updated combinations of BMPs show improvements in both the magnitude and cost of nitrogen removal compared to historical practices, their efficiency systematically declines as temperature rises. The decline rate of BMP efficiency is significantly larger under the high radiative forcing. Even by implementing all considered BMPs, we show that, at least under some realizations of future climate, the historical status-quo nitrogen state, in which no BMP is implemented, cannot be maintained. Our study demonstrates the reduced effectiveness of BMPs as the climate warms. To combat this, we recommend the immediate implementation of updated BMPs to slow down the build up of nitrogen. However, in innovations in physical, chemical, and biological remediation technologies would be needed in long term to control nitrogen loads coming from farmlands.
... The most important factors that determine the variation of river water and sediment flux are mainly attributed to the influence of climate change and human activities in the basin. Climate change can impact sediment transport rates, influencing overall runoff [16][17][18] . Li et al. conducted a non-parametric trend analysis of long-term data series to identify important trends in water OPEN ...
The sediment content and transport rate of rivers are crucial indicators reflecting soil erosion, water quality, and water resource management in a region. Studying changes in river sediment transport rates within a basin is essential for evaluating water quality, restoring water ecosystems, and implementing soil and water conservation measures. This study focused on the Shule River Basin and utilized various methods such as moving average, cumulative anomaly, Mann–Kendall mutation test, Mann–Kendall (M–K) trend test, Sen’s slope estimation, Correlation analysis, wavelet analysis, R/S analysis, ARCGIS10.7 interpolation, non-uniformity coefficient, and concentration to analyze data from hydrologic stations at Changmapu (CMP), Panjiazhuang (PJZ), and Dangchengwan (DCW). The research examined the temporal and spatial characteristics of sediment transport rates and identified key driving factors. Findings revealed significant increases in annual sediment transport rates at CMP and PJZ by 12.227 and 4.318 kg/s (10a)⁻¹, respectively, while DCW experienced a decrease of 0.677 kg/s (10a)⁻¹. The sediment transport rate of the three stations had a sudden change around 1994. The average annual sediment transport rates displayed distinct cycles, with CMP, PJZ, and DCW showing cycles of 51a, 53a, and 29a respectively. Additionally, while CMP and PJZ exhibited a continuous upward trend in sediment transport rates, DCW showed a consistent decline. The annual average sediment transport rates of CMP, PJZ, and DCW were 1305.43 kg/s, 810.06 kg/s, and 247.80 kg/s, respectively. These research findings contribute to enhancing the comprehension of sediment dynamics in the arid region of northwest China and offer a theoretical basis for the restoration and management of ecological environments in similar areas in the future.
... The data revealed an increase in annual precipitation compared to historical conditions (624.5 mm/year), accompanied by an enhanced interannual variability. It is therefore essential to consider the uncertainties in the effectiveness of control measures resulting from climate change, rather than solely relying on historical conditions (Arnell et al., 2015;Bosch et al., 2014;Xu et al., 2019). Under historical conditions, the candidate plans had TN and TP loads ranging from 25.6 to 73.6 tons/year and 5.7 to 14.3 tons/ year, respectively. ...
... For example, Wagena and Easton (2018) found that targeting critical source areas with ACPs could offset some projected negative effects of climate change on water quality as well as widespread implementation of ACPs. Similarly, Bosch et al. (2014) found that ACP implementation could offset some forecasted increases in runoff, but also found that the responses varied among watersheds and that ACP effectiveness tended to decrease with increasing climate change. Additional studies have found contrasting results in the interactions between land management and climate change and between climate change and hydrological and biological processes, including the potential for reductions in lake nutrient loading due to climate change (e.g., Cousino et al., 2015;Culbertson et al., 2016;Robertson et al., 2016;Hall et al., 2017;Kalcic et al., 2019;Mehan et al., 2019;Scavia et al., 2021;Kujawa et al., 2022). ...
... under RCP8.5 scenario. Intensification of heavy rainfall events due to climate change can affect soil moisture and runoff and affect productivity, plant growth, and water quality in watersheds (Arroyo et al. 2016;Bosch et al. 2014;Carpenter et al. 2018;Delpla et al. 2011;Mahmoudi et al. 2021;Ragno et al. 2018;Rahmani et al. 2016). Changes in climate, land use and vegetation expose ecosystems to change. ...
In this study, the effect of climate change on the reliability (Rel), resilience (Res), and vulnerability (Vul) has been evaluated in Atrak watershed located in northeastern Iran. Monthly rainfall data were used for 28 weather stations. The precipitation data of the Canadian Earth System Model (CanESM2) for the period 2025–2075 under Representative Concentration Pathways (RCPs) 4.5 and 8.5 scenarios for the selected stations were then extracted and downscaled by the delta method. Next, the Standardized Precipitation Index (SPI) was determined for the baseline and future periods at a 1-month time scale. To determine the health status of the watershed, RelResVul were calculated in temporal and spatial scales. The results showed that rainfall in both periods (2025–2050 and 2051–2075) will be decreased − 1.45 and − 2.9% under RCP4.5, respectively, and will be decreased 0.56% in the period 2025–2050 and will be increased 5.18% in the period 2051–2075 under RCP8.5. In terms of mean annual rainfall, rainfall will be decreased − 2.20% under RCP4.5 climate scenario and will be increased 2.26% under RCP8.5. Mean indices of Rel, Res, and Vul for the near period (2025–2050) under RCP4.5 climate scenario will be 180, 52.5, and 33.33, respectively, and under RCP8.5 climate scenario, 200, − 2.50, and − 11.11%. In the far period (2051–2075), under RCP4.5 climate scenario, these indices will be 200, 25, and 22.22%, respectively, and under RCP8.5 climate scenario, will be 212, − 10, and 38.89%, respectively. The average changes in the health index also show that the health index under RCP4.5 for the near and far periods and the whole period increase 66.67, 58.33, and 62.5%, respectively. While under RCP8.5, this index increased 37.50, 54.17, and 45.83%, respectively. According to the results of the present study, it is suggested different management methods such as rainwater harvesting, use of low water use species and increasing production efficiency in agriculture should be considered.
... A variety of best management practices (BMPs) have been implemented on farms, at the edges of fields, and in urban and suburban areas to decrease nutrient runoff (Sharpley et al. 2006). However, excess nutrients persist and may be exacerbated by projected future climate conditions, requiring additional strategies to improve water quality in the western Lake Erie Basin and throughout the Great Lakes (Bosch et al. 2014). The restoration and creation of wetlands are rapidly emerging as a novel BMP designed to further reduce P export from target watersheds including those located in the Great Lakes region, while also providing benefits to the habitat, decreasing flood risk, improving water Constructed and restored wetlands have previously been used to capture particulate and dissolved P prior to surface water export in a variety of settings, including as engineered treatment wetlands, although they remain less common than other agricultural BMPs (for example, reduced tillage or grassed buffer strips) (Berkowitz et al. 2020). ...
Historical loss of wetlands coupled with excess phosphorus (P) loading at watershed scales have degraded water quality in portions of the western Lake Erie Basin (WLEB). In response, efforts are underway to restore wetlands and decrease P loading to surface waters. Because wetlands have a finite capacity to retain P, researchers have developed techniques to determine whether wetlands function as P sources or sinks. The following technical report evaluates the soil P storage capacity (SPSC) at locations under consideration for wetland restoration in collaboration with the Great Lakes Restoration Initiative (GLRI) and the H2Ohio initiative. Results indicate that the examined soils display a range of P retention capacities, reflecting historic land-use patterns and management regimes. However, the majority of study locations exhibited some capacity to sequester additional P. The analysis supports development of rankings and comparative analyses of areas within a specific land parcel, informing management through design, avoidance, removal, or remediation of potential legacy P sources. Additionally, the approaches described herein support relative comparisons between multiple potential wetland development properties. These results, in conjunction with other data sources, can be used to target, prioritize, justify, and improve decision-making for wetland management activities in the WLEB.
... Similarly, greater P loss can be expected if more severe storms occur at times of the year when soils are more vulnerable to runoff and erosion. Unfortunately, the effects of timing and severity of rainfall have been suggested as some of the factors causing recent increases in the severity and extent of algal blooms in Lake Erie, for example (Bosch et al., 2014). During extreme rainfall and flooding, the critical source areas of a watershed contributing P and sediment can increase dramatically. ...
Conservation practices that reduce nutrient and soil loss from agricultural lands to water are fundamental to watershed management programs. Avoiding trade‐offs of conservation practices is essential to the successful mitigation of watershed phosphorus (P) losses. We review documented trade‐offs associated with conservation practices, particularly those practices that are intended to control and trap P from agricultural sources. A regular theme is the trade‐off between controlling P loss linked to sediment while increasing dissolved P losses (no‐till, cover crops, vegetated buffers, constructed wetlands, sediment control basins). A variety of factors influence the degree to which these trade‐offs occur, complicated by their interaction and uncertainties associated with climate change. However, acknowledging these trade‐offs and anticipating their contribution to watershed outcomes are essential to the sustainability of conservation systems.
... Respective Coupled Model Intercomparison Project (CMIP) experiments, the CMIP3 (Meehl et al., 2007) using the SRES and the CMIP5 (Taylor et al., 2011) using the RCPs, provided GCM projections from climatic modeling centers around the world. Some of the climate change studies in the GL basin using IPCC AR4 scenarios quantified impacts on hydrology (Kutzbach et al., 2005;Cherkauer and Sinha, 2010;Rahman et al., 2010), lake level (Angel and Kunkel, 2010;Hayhoe et al., 2010), water quality (Bosch et al., 2014;Hall et al., 2017), ecosystem (Hellmann et al., 2010), infrastructure and commercial navigation (Millerd, 2005). Similarly, some of the climate change studies in the GL basin using IPCC AR5 scenarios quantified impacts on hydrology (Wang et al., 2016;Basile et al., 2017;Byun et al., 2019), NBS (Music et al., 2015), lake level (Notaro et al., 2015), fluvial flood risk (Xu et al., 2019), water quality (Cousino et al., 2015;Verma et al., 2015;Wallace et al., 2017) and fisheries industry (Collingsworth et al., 2017). ...
The freshwater resources of the Laurentian Great Lakes basin contribute significantly to the environment and economy of the region. With the impacts of climate change becoming more evident, sustainable management of the freshwater resources of the Laurentian Great Lakes basin is important. This study uses 36 simulations from 6 regional climate models to quantify trends and changes in land-area precipitation and temperature in two future periods (mid-century, 2035-2064 and end-century, 2065-2094) with reference to a baseline period (1951-2005) for two emission scenarios (RCP 4.5 and RCP 8.5). Climatic forcings from these 36 simulations are used as input to a calibrated and validated hydrological model to assess changes in land snowpack and actual evapotranspiration, and runoff to lake. Ensemble results show wetter (7 to 15% increase in annual precipitation) and warmer (2.4-5.0 • C increase in annual mean temperature) future conditions on GL land areas. Seasonal and monthly changes in precipitation and mean temperature are more sporadic, for instance although precipitation is projected to increase overall, in some scenarios, summer precipitation is expected to decrease. Projected increases in highest one-day precipitation and decreases in number of wet days indicate possible increases in extreme precipitation in future. Minimum temperature is expected to increase in a higher rate than maximum temperature. Ensemble results from the hydrological model show projected decrease in snowpack (29-58%). Similarly, actual evapotranspiration is projected to increase, especially during summer months (up to 0.4 mm/day). Annually, runoff is expected to increase (up to 48% in Superior, 40% in Michigan-Huron, 25% Erie and 28% in Ontario). Seasonal and monthly changes in runoff are more sporadic (e.g., projected decrease up to 17% in Erie subdomain in October). Such contrasting patterns of changes in land hydroclimatology of the GL basin will pose challenges to sustainable management of the water resources of the basin in future.
... Several simulation studies exist that evaluate the effectiveness of nutrient management in reducing nutrient loading under various climate scenarios [19,20]. Nutrient management models are typically deterministic and have limited ability to account for weather variability in the definition of optimal farming practices, balancing farmers' income with environmental impacts. ...
Phosphorus (P) is an essential nutrient to boost crop yields, but P runoff can cause nutrient over-enrichment in agricultural watersheds and can lead to irreversible effects on aquatic ecosystems and their biodiversity. Lake Erie is one prominent example as this watershed has experienced multiple episodes of harmful algal blooms over the last decades. Annual P loads crucially depend on yearly weather variations, which can create the risk of years with high runoff and excessive nutrient loads. Here we apply stochastic modeling to derive sustainable management strategies that balance crop yield optimization with environmental protection, while accounting for weather variability as well as weather trends as a result of climate change. We demonstrate that ignoring annual weather variations results in mitigation efforts for environmental pollution that are largely insufficient. Accounting explicitly for future variations in precipitation allows us to control the risk of emissions exceeding the P target loads. When realistic risk targets are imposed, we find that a package of additional measures is required to avoid P over-enrichment in the Lake Erie watershed. This package consists of a substantial reduction of P inputs (approximately 30% for different accepted risk levels), adoption of cover crops throughout the near- and mid-century, and cultivation of less nutrient-intensive crops (30% more soy at the expense of corn). Although climate change reinforces these conclusions, we find that the accepted risk level of exceeding P target loads is the predominant factor in defining a sustainable nutrient management policy.
... Crossman et al. (2013) revealed that shifts in rainfall and air temperature could result in an increase of up to 30% in the P loadings into Lake Simcoe which offset the P reduced through improved agricultural practices. Bosch et al. (2014) revealed that with climate change, there would be a 17% increase in the runoff and a 23% increase in nutrient yield in the Lake Erie basin in the USA. ...
A quantitative understanding of riverine phosphorus (P) export in response to shifts in anthropogenic inputs, terrestrial retention, and climate is important for developing mitigation measures at a watershed scale. In this study, we simulated a decadal change in the riverine P export in a human-dominated watershed from a cold climatic region located in Northeast Asia. A process-based catchment model nested within a delicate land P module was applied to simulate the dynamics of P retentions and its exports in the watershed. We found that the terrestrial P retention capacities declined for 2008–2017, and the decline rates would accelerate under three representative concentration pathways (i.e. RCP2.6, RCP4.5 and RCP8.5). The P released from the diffused source and historical legacy could partly offset the effort through point-source P reduction by the improved wastewater treatments. Climate changes (e.g., duration and frequency of extreme rainfall event) could accelerate P deliveries from the P legacy retained in soils. We suggest that a long-term watershed P management strategy should be targeted to reduce historical P legacy input into river rather than solely focusing on the short-term changes in the riverine P concentration.
... The simulation results suggest the need for adaptive measures against an aggravating threat in deterioration of water quality due to increased inflow of pollutants into rivers carried by increased surface runoff. Especially for the Bocheongcheon basin, an area subject to intensive management of agricultural non-point pollutants, appropriate best management practices (BMPs) must be carefully selected and placed to secure quality water near agricultural land [50][51][52]. The effect of BMPs can be enhanced when coupled with maintenance of soil loss reduction infrastructure in high-altitude arable lands, which were identified as major sources of agricultural non-point pollutants in South Korea [53]. ...
Highly concentrated precipitation during the rainy season poses challenges to the South Korean water resources management in efficiently storing and redistributing water resources. Under the new climate regime, water resources management is likely to become more challenging with regards to water-related disaster risk and deterioration of water quality. To alleviate such issues by adjusting management plans, this study examined the impact of climate change on the streamflow in the Bocheongcheon basin of the Geumgang river. A globally accepted hydrologic model, the HEC-HMS model, was chosen for the simulation. By the calibration and the validation processes, the model performance was evaluated to range between “satisfactory” and “very good”. The calibrated model was then used to simulate the future streamflow over six decades from 2041 to 2100 under RCP4.5 and RCP8.5. The results indicated significant increase in the future streamflow of the study site in all months and seasons over the simulation period. Intensification of seasonal differences and fluctuations was projected under RCP 8.5, implying a challenge for water resources managers to secure stable sources of clean water and to prevent water-related disasters. The analysis of the simulation results was applied to suggest possible local adaptive water resources management policy.
... This is because PS are strictly controlled by environmental agencies coupled with the low loadings from the treatment plants (Muyibi et al., 2008). Therefore, BMPs are the most effective management tools in this category of watersheds, and these BMPs depend on the site, soil condition, target pollutant removal level, climate, and available budget (Bosch et al., 2014;Randhir et al., 2017). The proposed management solutions can provide a more flexible plan regarding the tradeoff between urban development and water quality protection. ...
Nutrient pollution is considered as a primary factor of water quality deterioration in urban-dominated watersheds in which an informed decision on the management strategies are required to improve the water quality condition. The Hydrological Simulation Program Fortran (HSPF) model is used to evaluate the impacts of pollution by these nutrients using the Skudai River watershed in Malaysia as a case study. A developed land-use/land-cover (LU/LC) scenarios were used to evaluate these impacts. Statistical methods were employed to assess the extent of these impacts and their significance in shifting the trophic state of the rivers in the watershed. The study shows that when urban development increases from 18.2 to 49.2%, the total nitrogen (TN) and total phosphorus (TP) loads increase from 3.08 to 4.56 × 10 ³ kg/yr and from 0.13 to 0.27 × 10³ kg/yr, respectively. Streamflow and stream concentrations (NH3N, NO3N, and PO4-P) produce varying responses as the watershed land-use changes (from 1989 to 2039). As the rivers in the watershed shift their trophic state with respect to the level of anthropogenic disturbance within their catchments, the TN and TP concentrations at the estuaries are likely to change from oligotrophic to eutrophic state. This is an indication that the Johor Strait and the coastal rivers will be exposed to eutrophication, subsequently resulting in harmful algal bloom. This condition can be prevented by integrating water quality management alongside urban development because it is observed that a control of non-point source (NPS) pollutants from 1% of the urban development will decrease TN and TP concentration in Skudai River by 0.023 mg/L and 0.004 mg/L respectively.
... Concentration-discharge (C-Q) relationships therefore provide valuable information on processes controlling nutrient availability and connectivity in catchments (Creed et al. 2015, Ali et al. 2017, Moatar et al. 2017. Understanding these processes is especially important in light of the increasing frequency of extreme climatic events (Burn and Whitfield 2016) which will increase hydrological nutrient export (Bosch et al. 2014). ...
Concentration‐discharge (C‐Q) relationships have been widely used to assess the hydrochemical processes that control solute fluxes from streams. Here, using a large regional dataset we assessed long‐term C‐Q relationships for total phosphorus (TP), soluble reactive phosphorus (SRP), total Kjeldahl nitrogen (TKN), and nitrate (NO3) for 63 streams in Ontario, Canada, to better understand seasonal regional behavior of nutrients. We used C‐Q plots, Kruskal‐Wallis tests, and breakpoint analysis to characterize overall regional nutrient C‐Q relationships and assess seasonal effects, anthropogenic impacts, and differences between “rising” and “falling” hydrograph limbs to gain an understanding of the dominant processes controlling overall C‐Q relationships. We found that all nutrient concentrations were higher on average in catchments with greater levels of anthropogenic disturbance (agricultural and urban land use). TP, SRP, and TKN showed similar C‐Q dynamics, with nearly flat or gently sloping C‐Q relationships up to a discharge threshold after which C‐Q slopes substantially increased during the rising limb. These thresholds were seasonally variable, with summer and winter thresholds occurring at lower flows compared with autumn and greater variability during snowmelt. These patterns suggest that seasonal strategies to reduce high flows, such as creating riparian wetlands or reservoirs, in conjunction with reducing related nutrient transport during high flows would be the most effective way to mitigate elevated in‐stream concentrations and event export. Elevated rising limb concentrations suggest that nutrients accumulate in upland parts of the catchment during drier periods and that these are released during rain events. NO3 C‐Q patterns tended to be different from the other nutrients and were further complicated by anthropogenic land use, with greater reductions on the falling limb in more disturbed catchments during certain seasons. There were few significant NO3 hydrograph limb differences, indicating that there was likely to be no dominant hysteretic pattern across our study region due to variability in hysteresis from catchment to catchment. This suggests that this nutrient may be difficult to successfully manage at the regional scale.
... Thus, our results support targeted restoration of wetlands in high nitrogen yield or source areas but suggest that efforts may be less successful where tile-drains continue to bypass wetlands, limiting wetland capacity to receive and remove -NO 3 from the landscape. Tile drainage should be considered in addition to other landscape characteristics and processes -e.g., climate change (Bosch et al 2014), and nutrient legacies (Van Meter et al 2018) -in prioritizing restoration efforts and projecting river-basin scale effects. ...
Wetland restoration is a primary management option for removing surplus nitrogen draining from agricultural landscapes. However, wetland capacity to mitigate nitrogen losses at large river-basin scales remains uncertain. This is largely due to a limited number of studies that address the cumulative and dynamic effects of restored wetlands across the landscape on downstream nutrient conditions. We analyzed wetland restoration impacts on modeled nitrate dynamics across 279 subbasins comprising the ∼0.5 million km2 Upper Mississippi River Basin (UMRB), USA, which covers eight states and houses ∼30 million people. Restoring ∼8,000 km2 of wetlands will reduce mean annual nitrate loads to the UMRB outlet by 12%, a substantial improvement over existing conditions but markedly less than widely cited estimates. Our lower wetland efficacy estimates are partly attributed to improved representation of processes not considered by preceding empirical studies - namely the potential for nitrate to bypass wetlands (i.e., via subsurface tile drainage) and be stored or transformed within the river network itself. Our novel findings reveal that wetlands mitigate surplus nitrogen basin-wide, yet they may not be as universally effective in tiled landscapes and because of river network processing.
... However, all the partial effects of precipitation on both chlorophyll-a and phytoplankton biomass were consistent showing a positive effect. This relationship has been evidenced by numerous limnological analyses ( Bosch et al., 2014 ;Jeppesen et al., 2009 ;Sinha et al., 2017 ) and shows that high precipitation is linked with higher inputs of nutrients in water bodies that enhance algal growth. Concerning the total runoff we found a negative effect on both chlorophyll-a and phytoplankton biomass. ...
Understanding the climatic drivers of eutrophication is critical for lake management under the prism of the global change. Yet the complex interplay between climatic variables and lake processes makes prediction of phytoplankton biomass a rather difficult task. Quantifying the relative influence of climate-related variables on the regulation of phytoplankton biomass requires modelling approaches that use extensive field measurements paired with accurate meteorological observations. In this study we used climate and lake related variables obtained from the ERA5-Land reanalysis dataset combined with a large dataset of in-situ measurements of chlorophyll-a and phytoplankton biomass from 50 water bodies to develop models of phytoplankton related responses as functions of the climate reanalysis data. We used chlorophyll-a and phytoplankton biomass as response metrics of phytoplankton growth and we employed two different modelling techniques, boosted regression trees (BRT) and generalized additive models for location scale and shape (GAMLSS). According to our results, the fitted models had a relatively high explanatory power and predictive performance. Boosted regression trees had a high pseudo R² with the type of the lake, the total layer temperature, and the mix-layer depth being the three predictors with the higher relative influence. The best GAMLSS model retained mix-layer depth, mix-layer temperature, total layer temperature, total runoff and 10-m wind speed as significant predictors (p<0.001). Regarding the phytoplankton biomass both modelling approaches had less explanatory power than those for chlorophyll-a. Concerning the predictive performance of the models both the BRT and GAMLSS models for chlorophyll-a outperformed those for phytoplankton biomass. Overall, we consider these findings promising for future limnological studies as they bring forth new perspectives in modelling ecosystem responses to a wide range of climate and lake variables. As a concluding remark, climate reanalysis can be an extremely useful asset for lake research and management.
... The simulation results suggest the need for adaptive measures against an aggravating threat in deterioration of water quality due to increased inflow of pollutants into rivers carried by increased surface runoff. Especially for the Bocheongcheon basin, an area subject to intensive management of agricultural non-point pollutants, appropriate best management practices (BMPs) must be carefully selected and placed to secure quality water near agricultural land [50][51][52]. The effect of BMPs can be enhanced when coupled with maintenance of soil loss reduction infrastructure in high-altitude arable lands, which were identified as major sources of agricultural non-point pollutants in South Korea [53]. ...
Science is fundamental to sound policies, particularly when it comes to implementing an Ecosystem Approach. Science can and should inform nearly all facets of an Ecosystem Approach, yet challenges remain to realizing this goal. To help identify and better understand these challenges we used a qualitative comparative case study approach to identify and characterize the challenges and successes of implementing a science-driven Ecosystem Approach in the Laurentian Great Lakes. These case studies include delisting of Areas of Concern, improving coastal resilience, and addressing declining offshore lake productivity. These case studies were selected because they provide a set of very different, yet complementary, cases for assessing implementation, as well as the factors influencing the science-policy exchange. Through this comparative study, we identified a diverse set of challenges and successes, that were both systemic and case specific. Emerging from this comparative assessment were principles and enabling conditions (e.g. scale, governance, shared goals) we believe are critical to consider when establishing or improving a science-driven Ecosystem Approach.
Lake eutrophication caused by nitrogen and phosphorus has led to frequent harmful algal blooms (HABs),
especially under the unknown challenges of climate change, which have seriously damaged human life and
property. In this study, a coupled SWAT-Bayesian Network (SWAT-BN) model framework was constructed to
elucidate the mechanisms between non-point source nitrogen pollution in agricultural lake watersheds and algal
activities. A typical agricultural shallow lake basin, the Taihu Basin (TB), China, was chosen in this study, aiming
to investigate the effectiveness of best management practices (BMPs) in controlling HABs risks in TB. By
modeling total nitrogen concentration of Taihu Lake from 2007 to 2022 with four BMPs (filter strips, grassed
waterway, fertilizer application reduction and no-till agriculture), the results indicated that fertilizer application
reduction proved to be the most effective BMP with 0.130 of Harmful Algal Blooms Probability Reduction (HABs-
PR) when reducing 40% of fertilizer, followed by filter strips with 0.01 of HABs-PR when 4815ha of filter strips
were conducted, while grassed waterway and no-till agriculture showed no significant effect on preventing HABs.
Furthermore, the combined practice between 40% fertilizer application reduction and 4815ha filter strips con
struction showed synergistic effects with HABs-PR increasing to 0.171. Precipitation and temperature data were
distorted to model scenarios of extreme events. As a result, the combined approach outperformed any single BMP
in terms of robustness under extreme climates. This research provides a watershed-level perspective on HABs
risks mitigation and highlights the strategies to address HABs under the influence of climate change.
This review summarized the past and current studies on forest nutrient export and existing watershed water quality models that are capable of predicting nutrient loadings from forest-dominated watersheds. Emphasis was given to the watershed models used under cold climate conditions and their capacities and limitations in assessing the impacts of forest best management practices (BMPs) and climate change scenarios on nutrient loadings at a watershed scale. The nutrient export rates in forest-dominated watersheds were found to vary significantly controlled by local climate and landscape conditions. Some watershed water quality models can estimate nutrient loadings from forests either with a simplified forest growth function or without a forest growth component. No existing watershed water quality models have explicit representation forest BMP functions. Combining or coupling with a forest growth model is required for a realistic simulation of nutrient dynamics and assessing the impact of forest BMPs in a forest-dominated watershed. The review also considered the suitability of models for exploring the potential effects of climate change on hydrologic and nutrient processes relevant to forest management. Discussions on the challenges and limitations of forested watershed water quality models and recommendations for future development were made following the review. The findings of this study can provide valuable references for water quality modeling studies in forest-dominated watersheds under cold climate conditions.
The objective of this study is to identify the optimal spatial distribution of Best Management Practices (BMPs) to reduce total phosphorus (TP) runoff from agricultural land in the largest Canadian watershed draining into Lake Erie, the Great Lake most vulnerable to eutrophication. BMP measures include reduced fertilizer application, cover crops, buffer strips, and the restoration of wetlands. Environmental SWAT model results feed into a spatial optimization procedure using two separate objective functions to distinguish between public BMP program implementation costs (PIC) on the one hand and farmers’ private pollution abatement costs (PAC) on the other hand. The latter account for the opportunity costs of land retirement and changing land productivity. PAC are initially lower than PIC but exceed the latter after 30% of the annual TP baseline load is eliminated. This suggests that under optimal conditions existing grant and incentive payments cover the economic costs farmers face up to a maximum of 30% of the baseline load reduction. Imposing further reductions of up to 40% results in a cost to farmers of almost $52 million per year. This is 45% higher than the optimal solution based on PIC and therefore not deemed incentive-compatible under the watershed’s existing cost-sharing scheme.
As part of federal programs to reduce nutrient pollution, states across the Midwest have developed nutrient reduction strategies, which focus on implementation of agricultural conservation practices (ACPs) or best management practices (BMPs). Despite several decades of federal investment in implementing ACPs/BMPs for reducing nutrient pollution, nutrient pollution is a continuing and growing challenge with profound implications for water quality and public health as well as ecological functions. Pollutant transport depends on water and sediment fluxes, which are governed by local hydrology. Therefore, knowing how flow conditions affect nutrients export is critical to develop effective nutrient reduction strategies. The objective of this study was to investigate the role of streamflow duration curve in controlling nutrient export in the western Lake Erie Basin and the Mississippi River Basin. To achieve this goal, we used long-term monitoring data collected by the National Center for Water Quality Research. We focused on the percentage of the annual pollutant load (nitrate-NO3-N, dissolved reactive phosphorus-DRP, total phosphorus-TP, and total suspended solids-TSS) exported during five flow intervals that spanned the flow duration curve: High Flows (0-10th percentile), Moist Conditions (10-40th percentile), Mid-Range Flows (40-60th percentile), Dry Conditions (60-90th percentile), and Low Flows (90-100th percentile). The results show that the top 10% of flows (i.e., high flows) transported more than 50% of the annual nutrient loads in most of the studying watersheds. Meanwhile, the top 40% of flows transported 54-98% of the annual NO3-N loads, 55-99% of the annual DRP loads, 79-99% of the annual TP loads, and 86-100% of the annual TSS loads across the studying watersheds. The percentage of the annual loads released during high flows increased as the percentage of the agricultural land use in the watershed increased, but it decreased as the watershed area increased across different watersheds. Finally, flow condition/nutrient export relationships were consistent over studying period. Therefore, reducing nutrient loads during high flow condition is the key for effective nutrient reduction.
Nonpoint source pollution from cultivated croplands has often been associated with downstream water quality impairment in various watersheds. Given projected changes in global climate patterns, this study contributes to the existing literature by elucidating the impacts of climate projections on edge-of-field surface runoff and sediment and nutrient losses. We apply a well-tested ecohydrological model, Agricultural Policy Environmental eXtender (APEX), to continuous corn and corn–soybean fields in Buchanan County, Iowa, using climate scenarios developed from three well-known representative concentration pathway (RCP) climate projections: RCP 2.6, RCP 4.5, and RCP 8.5. Our results indicate that there will be a moderate to substantial increase in surface runoff, sediment, and nutrient losses depending upon the reference point of comparison (baseline scenario) and upon which climate scenario actually materializes. However, regardless of which climate scenario materializes and regardless of the baseline for comparison, soluble nitrogen losses are bound to increase, the magnitude depending upon the climate scenario. We find also that nutrient losses will be higher from continuous corn fields than from corn–soybean fields, given the tillage practices implemented on corn versus soybeans in the study area. Similarly, we find that nutrient losses may be higher from fields that receive manure than fields that receive only inorganic fertilizer, though this latter finding may be predicated upon the specific nutrient application rates utilized.
Planning of Best Management Practices (BMPs) is increasingly dependent on Process-based Watershed Models (PWMs) and suffers from large uncertainties. The large complexity and long runtimes of such models make prudential watershed management a difficult undertaking. In this study, we aimed to bridge the gaps between PWMs and uncertainty-based BMP planning with Bayesian Belief Network (BBNs). A new modeling framework of Process-guided Hybrid BBNs (PH-BBNs) was developed to represent the probabilistic cascade of critical modules in Soil & Water Assessment Tool (SWAT), a widely-used PWM, across external stressors (e.g., weather and various BMPs), parametric uncertainties, and watershed predictors. The PH-BBN modeling framework was used for decision support of Nonpoint Source (NPS) pollution mitigation in an intensively-cultivated area adjacent to Lake Dianchi, one of the three most eutrophic lakes in China. Our findings suggest that PH-BBNs can capture the critical pathways of water, sediment, and Total Phosphorus (TP) loss. Watershed projections are subject to large uncertainties to varying degrees in different landscapes. According to variance-based sensitivity analysis, precipitation accounts for >80% of the projection variability, which underlines watershed vulnerability to climate change. As the effectiveness of parallel terraces, filter strips, and fertilization management would degrade with increasing rainfall intensity, they should be conservatively designed for BMP sustainability. Implementation of parallel terraces and filter strips is recommended as they are projected to reduce 80% of TP loads with >90% compliance confidence. PH-BBNs can render effective decision support for BMP risk assessment and adaptive watershed management under climate change.
Cyanobacterial harmful blooms have been increasing worldwide, due in part to excessive phosphorus (P) losses from agriculture-dominated watersheds. Unfortunately, cyanobacteria bloom management is often complicated by uncertainty associated with river P cycling. River P cycling mediates P exports during low flow but has been assumed to be unimportant during high flows. Thus, we examined interactions between dissolved reactive phosphorus (DRP) and suspended sediment P during high flows in the Maumee River network, focusing on March–June Maumee River DRP exports, which fuel recurring cyanobacteria blooms in Lake Erie. We estimate that during 2003-2019 March to June high flow events, P sorption reduced DRP exports by an average of 13-27%, depending upon the colloidal-P:DRP ratio, decreasing the bioavailability of P exports, and potentially constraining cyanobacteria blooms by 13-40%. Phosphorus sorption was likely lower during 2003-2019 than 1975-2002 due to reductions in suspended sediment loads, associated with soil-erosion-minimizing agricultural practices. This unintended outcome of erosion management has likely decreased P sorption, increased DRP exports to Lake Erie, and subsequent cyanobacteria blooms. In other watersheds, DRP–sediment P interactions during high flow could have a positive or negative effect on DRP exports; therefore, P management should consider riverine P cycles, particularly during high flow events, to avoid undermining expensive P mitigation efforts.
Harmful algal blooms (HABs) impose major costs on aquatic ecosystems worldwide, including the Laurentian Great Lakes. Microbial consumers, including fungi, can have important interactions with bloom-forming algae and cyanobacteria, although relatively few studies have investigated the relationship between fungi and HABs. We examined changes in the aquatic fungal community coincident with the occurrence of large cyanobacterial blooms in two areas of the Great Lakes (western Lake Erie and Saginaw Bay, Lake Huron). We collected water samples over the course of bloom development, peak, and decline from 3 sites in western Lake Erie on 11 dates and 2 sites in Saginaw Bay on 4 dates. Single molecule sequencing (PacBio RS II) with two molecular markers (the internal transcribed spacer (ITS) of the rRNA locus using fungal-specific primers and the 18S rRNA with primers targeting early-diverging lineages of fungi) was used to estimate fungal community composition. Results indicate a diverse fungal community within the lakes, including several major fungal phyla. The Chytridiomycota were particularly well-represented (54.8% and 45.4% of ITS and 18S sequences, respectively), and we also found representation from both Cryptomycota and Aphelidiomycota, which are putatively obligate intracellular parasites. Further, we found associations between the fungal community (alpha diversity; community composition) and measures of bloom magnitude (chlorophyll a, phycocyanin, and microcystin concentrations) in western Lake Erie. Our results suggest potentially important spatial and temporal heterogeneity in the fungal community that motivates further research on functional importance of fungi in the Great Lakes and consequences for HABs and freshwater ecosystems more broadly.
Reinforcing the small water cycle is considered to be a holistic approach to both water resource and landscape management. In an agricultural landscape, this can be accomplished by incorporating agricultural conservation practices; their incorporation can reduce surface runoff, increase infiltration, and increase the water holding capacity of a soil. Some typical agricultural conservation practices include: conservation tillage, contour farming, residue incorporation, and reducing field sizes; these efforts aim to keep both water and soil in the landscape. The incorporation of such practices has been extensively studied over the last 40 years. The Soil and Water Assessment Tool (SWAT) was used to model two basins in the Czech Republic (one at the farm-scale and a second at the management-scale) to determine the effects of agriculture conservation practice adoption at each scale. We found that at the farm-scale, contour farming was the most effective practice at reinforcing the small water cycle, followed by residue incorporation. At the management-scale, we found that the widespread incorporation of agricultural conservation practices significantly reinforced the small water cycle, but the relative scale and spatial distribution of their incorporation were not reflected in the SWAT scenario analysis. Individual farmers should be incentivized to adopt agricultural conservation practices, as these practices can have great effects at the farm-scale. At the management-scale, the spatial distribution of agricultural conservation practice adoption was not significant in this study, implying that managers should incentivize any adoption of such practices and that the small water cycle would be reinforced regardless.
Lake Erie is located in North America with its southern shoreline bordering Ohio, as well as parts of Michigan, Pennsylvania and New York. A one-year study investigated nutrient pollution in a Central Basin Lake Erie headwater tributary watershed near Cleveland Ohio. Results suggest that the 2019 annual phosphorus load entering Lake Erie from the Euclid Creek watershed was approximately 22,600 pounds, over four times the watershed’s target of 5,545 pounds. Multiple upstream sites were the major nonpoint sources of nutrient pollution. Four sampling sites averaged phosphorus levels 12 to 15 times the watershed target of 0.05 mg/L. Leaking sanitary sewers in residential areas were believed to contribute more pollution than the three golf courses and the regional airport located within the watershed. The presence of the Cleveland Metroparks along the riparian corridor in the Main Branch significantly reduced (p < 0.05) nutrients during dry weather. In particular, stream restoration within the Acacia Reservation lowered phosphorus levels by an average 0.31 mg/L. Spring storms contributed the most to the annual phosphorus load (∼47%). To mitigate nutrient pollution in urban watersheds, best management practices (BMPs) would require a two-fold strategy. During dry weather, BMPs should incorporate stream restoration and forested riparian buffers where feasible. Green infrastructure should be designed to mitigate the impact of wet-weather storm-induced flows.
An enhanced understanding of nonpoint source (NPS) nutrient export to the lower Great Lakes is needed to inform land use and land management decisions within southern Ontario. However, this understanding is limited by a lack of long-term, temporally-intensive monitoring. To address this knowledge gap, we revisit six agriculturally-dominated subwatersheds in southern Ontario, which were intensively studied during the mid-1970s, to assess changes in hydrology and NPS nutrient contributions. We compared 1975-1977 to 2016-2018 stream runoff, nutrient export (kg/day•km 2), and flow-weighted mean concentrations (FWMCs) of total phosphorus (TP), total dissolved phosphorus (TDP), total nitrogen (TN), nitrates (NO 3-+NO 2-) and Total Kjeldahl Nitrogen (TKN). Relative to the 1970s, runoff increased at three of six watersheds (by~20-35%) while TP and TDP export increased at five watersheds (by~50-125%). The increases in TP and TDP FWMCs were lower relative to phosphorus export changes at the three watersheds with increased runoff, suggesting that hydrology is an important driver of phosphorus export at these sites. Interestingly, export of TN and nitrates increased while TKN export decreased at most watersheds. We further note a shift in the timing of nutrient export at most sites, with~40-70% of export now occurring during the winter and fall seasons whereas~40-85% of past export occurred during spring and summer. These findings support an enhanced importance of non-growing season nutrient export from agricultural watersheds since the mid-1970s and stresses the need for targeted best management practices specific to the fall and winter seasons.
Human-driven land-use/cover (LULC) changes threaten the integrity of ecosystems in many ways. To evaluate possible impacts of future changes in LULC on ecosystem services and support more sustainable environmental management, it is essential to understand how land-use patterns affect both ecological and economic outcomes, and how alternative spatial land-use and -management strategies may improve sustainability in land-use systems. I developed and tested a spatial simulation approach that can help improve our understanding of how human-driven landscape conditions at the watershed scale might reshape impacts on both water quality and economic performance in a Lake Erie watershed under a changing climate. The dissertation is organized into three chapters. The first chapter describes a study in which I evaluated sensitivity of a stochastic land-change model (LCM) to pixel versus polygonal land unit derived from parcel maps. Performance of pixel- and polygon-based simulations suggest that using polygonal unit is helpful with generating more realistic landscape patterns, but at the cost of spatial allocation accuracy. For the second chapter, I developed the first integrated modeling approach that compares the relative economic efficiency of alternative spatial land-use and -management strategies for addressing non-point source (NPS) nutrient pollution. Using the Soil Water Assessment Tool (SWAT) and data on crop costs and prices, I evaluated joint impacts on nutrient reduction and economic returns for optimized patterns of land-use changes (LUCs) versus conservation practices (CPs) at the field scale. Simulated results showed relying on CPs alone might not be sufficient to restore water quality in Lake Erie, and a combination strategy including both LUCs and CPs would be necessary and more efficient. Finally, I examined sensitivity of optimized spatial patterns of land-use and -management (CPs) approaches to climate change. I found optimal land-use and -management placement can be quite sensitive to change in climatic conditions. CP targeting was found to be more robust to climate change than land-use change, but integration of both strategies would be necessary to achieve high DRP reduction (>65%) targets. Results from this study highlight the need for future spatial optimization studies to consider adaptive capacity of conservation actions under a changing climate.
Policy processes traditionally dominated by government increasingly are open to participation by diverse non-governmental actors. This can result in more inclusive policy making, but undue influence that undermines democratic processes is also possible. We use insights from critical discourse analysis and framing theory to assess the discursive influence of non-state actors in the context of a government-led policy process to address eutrophication problems in the Lake Erie basin, shared by Canada and the United States. We analyze the actions of the Ontario Federation of Agriculture and the Ohio Farm Bureau Federation within the policy process to develop Domestic Action Plans to deal with nutrient runoffs. This research provides novel insights into how policy influence may occur in a process with multiplicity of stakeholders. In the context of efforts towards inclusive resource governance, this approach helps us reveal hurdles to the achievement of goals for sustainable resource use.
Elevated phosphorus (P) loading from the watersheds draining into Lake Erie, particularly from agricultural (53%) and urban (43%) sources, is identified as one of the main drivers of the severe eutrophication. In this study, we present a comprehensive evaluation of 11 process-based models to characterize the water cycle as well as nutrient fate and transport within a watershed context, and to find a robust and replicable way to optimize the modelling strategy for the Lake Erie watershed. Our primary objective is to review the conceptual/technical strengths and weaknesses of the individual models for reproducing surface runoff, groundwater, sediment transport, nutrient cycling, and channel routing, and to collectively guide the management of the Lake Erie Basin. Our analysis suggested that the available models either opted for simpler approximations of the multifaceted, nonlinear dynamics of nutrient fate and transport, and instead placed more emphasis on the advanced representation of the water cycle or, introduced a greater degree of biogeochemical complexity but simplified their strategies to recreate the roles of critical hydrological processes. Notwithstanding its overparameterization problem, the MIKE SHE model provides the most comprehensive 3D representation of the interplay between surface and subsurface hydrological processes with a fully dynamic description, whereby we can recreate the solute transport that infiltrates from the surface to the unsaturated soil layer and subsequently percolates into the saturated layer. Likewise, the physically based submodels designed to represent the sediment detachment and erosion/removal processes (DWSM, HBV-INCA, HSPF, HYPE, and MIKE SHE), offer a distinct alternative to USLE-type empirical strategies. The ability to explicitly simulate the daily plant growth (SWAT and APEX) coupled with a dynamic representation of soil P processes can be critical when evaluating the long-term watershed responses to various agricultural management strategies. Drawing parallels with the (sub)surface and sediment erosion processes, a more complicated physically based approach, e.g., the dynamic wave model provided by MIKE SHE (coupled with MIKE URBAN or MIKE HYDRO) and SWMM may be more appropriate for realistically simulating the pressurized flow and backwater effects of water routing in both open channels and closed pipes. While our propositions seem to favor the consideration of complex models that may lack the commensurate knowledge to properly characterize the underlying processes, we contend this issue can be counterbalanced by the joint consideration of simpler empirical models under an ensemble framework, which can both constrain the plausible values of individual processes and validate macroscale patterns. Finally, our study discusses critical facets of the watershed modelling work in Lake Erie, such as the role of legacy P, the challenges in reproducing spring-freshet or event-flow conditions, and the dynamic characterization of water/nutrient cycles under the nonstationarity of a changing climate.
Changes to water resources are critical to all sectors of the economy. Climate change will affect the timing and quantity of water available in the environment as well as have an adverse effect on the quality of that water. Floods, droughts, and changing patterns of water scarcity—when water is not available in sufficient enough quantities or of a suitable quality at the right time to fulfill demand—are all critical factors when considering how and where Indiana will be able to economically develop in the future. Management of water resources will become even more important as different sectors try to minimize the risk of water scarcity in the face of increasing climate variability. This paper focuses on observed changes to Indiana’s water resources and how the availability and quality of those resources are likely to change in the face of future climate. Generally, Indiana is becoming wetter but with the projected increase coming primarily in the winter and spring. Summer water use will increase the likelihood of water shortages and the need for improved water management. In particular, Indiana may benefit from investment in methods to increase short-term storage of water—retaining more of the overabundance from winter and spring to relieve summer shortages.
The nonpoint source pollution problem can be controlled by implementing various best management practices (BMPs) in the watershed. However, before such practices are adopted, their effectiveness at various spatial and temporal scales must be evaluated. The objective of this research was to evaluate a suite of BMPs in a pasture-dominated watershed in their effectiveness at controlling nutrient losses. A total of 171 different BMP combinations incorporating grazing and pasture management, riparian and buffer zones, and poultry litter applications were evaluated for their effectiveness using the Soil and Water Assessment Tool (SWAT) model.The SWAT model was parameterized using detailed farm and watershed-scale data. The stochasticity in weather was captured by generating 250 various possible weather realizations for a 25-year period, using measured historical climate data for the watershed. Model results indicated that losses of both total nitrogen, mineral phosphorus, and total phosphorus increased with an increase in litter application rates. For the same application rates, greatest losses were predicted for fall application timings compared to spring and summer applications. Overgrazing resulted in greater nutrient losses compared to baseline conditions for all application rates, timings, and litter characteristics, indicating that overgrazing of pasture areas must be avoided if any improvement in the water quality is to be expected. Variability in weather conditions significandy affected BMP performance; under certain weather conditions, an increase in pollutant losses can be greater than reductions due to BMPs implemented in the watershed. Buffer strips and grazing management were two most important BMPs affecting the losses of total nitrogen and total phosphorus from the pasture areas.
In 2011, Lake Erie experienced the largest harmful algal bloom in its recorded history, with a peak intensity over three times greater than any previously observed bloom. Here we show that long-term trends in agricultural practices are consistent with increasing phosphorus loading to the western basin of the lake, and that these trends, coupled with meteorological conditions in spring 2011, produced record-breaking nutrient loads. An extended period of weak lake circulation then led to abnormally long residence times that incubated the bloom, and warm and quiescent conditions after bloom onset allowed algae to remain near the top of the water column and prevented flushing of nutrients from the system. We further find that all of these factors are consistent with expected future conditions. If a scientifically guided management plan to mitigate these impacts is not implemented, we can therefore expect this bloom to be a harbinger of future blooms in Lake Erie.
After a 20-year absence, severe cyanobacterial blooms have returned to Lake Erie in the last decade, in spite of negligible change in the annual load of total phosphorus (TP). Medium-spectral Resolution Imaging Spectrometer (MERIS) imagery was used to quantify intensity of the cyanobacterial bloom for each year from 2002 to 2011. The blooms peaked in August or later, yet correlate to discharge (Q) and TP loads only for March through June. The influence of the spring TP load appears to have started in the late 1990 s, after Dreissenid mussels colonized the lake, as hindcasts prior to 1998 are inconsistent with the observed blooms. The total spring Q or TP load appears sufficient to predict bloom magnitude, permitting a seasonal forecast prior to the start of the bloom.
1] Water yield responses to two climate change scenarios of different spatial scales were compared for the Missouri River Basin. A coarse-resolution climate change scenario was created from runs of the Commonwealth Scientific and Industrial Research Organization General Circulation Model (CSIRO GCM). The high-resolution climate change scenario was developed using runs of the Regional Climate Model RegCM, for which the GCM provided the initial and lateral boundary conditions. Water yield responses to the high-and low-resolution climate change scenarios were investigated using the Soil and Water Assessment Tool (SWAT). Basin-wide water yield increased for both GCM and RegCM scenarios but with an overall greater increase for the RegCM scenario. Significant differences in water yields were found between the GCM and RegCM climate scenarios.
The quantification of point and non-point losses of Nitrogen (N) and Phosphorus (P) to surface waters is currently a major
issue for the implementation of Environmental Directives, such as the Water Framework Directive in Europe. However, the drivers
behind nutrient pollution are location specific and are affected by regional hydroclimatic and geomorphological characteristics.
In this study the river basin model SWAT was used in order to improve the process-based understanding of mechanisms behind
nutrient transport from land to water recipients in two European catchments with significantly different meteorological conditions:
the Greek catchment of Ali Efenti, representative of the Mediterranean climate, and the Norwegian catchment of Vansjø-Hobølv,
representative of the cold climate typical in Scandinavia. The models were firstly calibrated according to measured river
flows and nutrient loads, and then four Best Management Practices (BMPs), related to nutrient application and soil management
were applied in order to examine their effectiveness under the different geoclimatic conditions of the two catchments. The
results of the baseline indicated that diffuse agricultural sources were the largest contributor of N losses in both catchments
and of P losses in the Greek catchment, while point sources were significant contributors to P levels in Norwegian rivers.
Nutrient losses to surface waters in Ali Efenti exhibited high seasonal variation, attributed to the extremeness of precipitation
events that is typical in the Mediterranean, as well as to the temporal distribution of sediment losses to waters. On the
other hand, in Scandinavia, the losses of N and P occurred with less deviation throughout the year and independently of the
freezing of soils. The values of the calibrated parameters that mainly governed the hydrological and erosion processes in
the catchments demonstrated the natural driving forces of nutrient losses to waters and their temporal distribution indicating
that these forces are also crucial in determining the appropriate implementation of agricultural management practices in various
geoclimatic regions.
KeywordsBMPs–Diffuse pollution–Geoclimatic conditions–Nitrogen–Phosphorus–Sediments–SWAT
Climate-induced increase in surface temperatures can impact hydrologic processes of a watershed system. This study uses a
continuous simulation model to evaluate potential implications of increasing temperature on water quantity and quality at
a regional scale in the Connecticut River Watershed of New England. The increase in temperature was modeled using Intergovernmental
Panel on Climate Change (IPCC) high and low warming scenarios to incorporate the range of possible temperature change. It
was predicted that climate change can have a significant affects on streamflow, sediment loading, and nutrient (nitrogen and
phosphorus) loading in a watershed. Climate change also influences the timing and magnitude of runoff and sediment yield.
Changes in variability of flows and pollutant loading that are induced by climate change have important implications on water
supplies, water quality, and aquatic ecosystems of a watershed. Potential impacts of these changes include deficit supplies
during peak seasons of water demand, increased eutrophication potential, and impacts on fish migration.
The Bosque River Watershed in Texas is facing a suite of water quality issues including excess sediment, nutrient, and bacteria.
The sources of the pollutants are improperly managed cropland and grazing land, dairy manure application, and effluent discharge
from wastewater treatment facilities. Several best management practices (BMPs) have been proposed for pollution reduction
and watershed protection. The overall objectives of this study were to demonstrate a modeling approach using Soil and Water
Assessment Tool (SWAT) model to simulate various BMPs and assess their long-term impacts on sediment and nutrient loads at
different spatial levels. The SWAT model was calibrated and validated for long-term annual and monthly flows at Valley Mills
and for monthly sediment, total nitrogen (TN) and total phosphorus (TP) at Hico and Valley Mills monitoring locations. The
BMPs including streambank stabilization, gully plugs, recharge structures, conservation tillage, terraces, contour farming,
manure incorporation, filter strips, and PL-566 reservoirs were simulated in the watershed areas that met the respective practice’s
specific criteria for implementation. These BMPs were represented in the pre- and post-conditions by modifying one or more
channel parameters (channel cover, erodibility, Manning’s n), curve number (CN), support practice factor (P-factor), filter
strip width, and tillage parameters (mixing efficiency, mixing depth). The BMPs were simulated individually and the resulting
Hydrologic Response Units (HRUs), subwatershed, and watershed level impacts were quantified for each BMP. Sensitivity of model
output values to input parameters used to represent the BMPs was also evaluated. Implementing individual BMPs reduced sediment
loads from 3% to 37% and TN loads from 1% to 24% at the watershed outlet; however, the changes in TP loads ranged from 3%
increase to 30% decrease. Higher reductions were simulated at the subwatershed and HRU levels. Among the parameters analyzed
for sensitivity, P-factor and CN were most sensitive followed by Manning’s n. The TN and TP outputs were not sensitive to
channel cover. This study showed that the SWAT modeling approach could be used to simulate and assess the effectiveness of
agricultural best management practices.
KeywordsSWAT-Watershed modeling-Best Management Practice (BMP)-Streambank stabilization-Gully plugs-Recharge structures-Terrace-Filter strips
The concept of critical source areas of phosphorus (P) loss produced by coinciding source and transport factors has been studied since the mid 1990s. It is widely recognized that identification of such areas has led to targeting of management strategies and conservation practices that more effectively mitigate P transfers from agricultural landscapes to surface waters. Such was the purpose of P Indices and more complex nonpoint source models. Despite their widespread adoption across the U.S., a lack of water quality improvement in certain areas (e.g. Chesapeake Bay Watershed and some of its tributaries) has challenged critical source area management to be more restrictive. While the role of soil and applied P has been easy to define and quantify, representation of transport processes still remains more elusive. Even so, the release of P from land management and in-stream buffering contribute to a legacy effect that can overwhelm the benefits of critical source area management, particularly as scale increases (e.g. the Chesapeake Bay). Also, conservation tillage that reduces erosion can lead to vertical stratification of soil P and ultimately increased dissolved P loss. Clearly, complexities imparted by spatially variable landscapes, climate, and system response will require iterative monitoring and adaptation, to develop locally relevant solutions. To overcome the challenges we have outlined, critical source area management must involve development of a 'toolbox' that contains several approaches to address the underlying problem of localized excesses of P and provide both spatial and temporal management options. To a large extent, this may be facilitated with the use of GIS and digital elevation models. Irrespective of the tool used, however, there must be a two-way dialogue between science and policy to limit the softening of technically rigorous and politically difficult approaches to truly reducing P losses.
Agriculture and urban activities are major sources of phosphorus and nitrogen to aquatic ecosystems. Atmospheric deposition further contributes as a source of N. These nonpoint inputs of nutrients are difficult to measure and regulate because they derive from activities dispersed over wide areas of land and are variable in time due to effects of weather. In aquatic ecosystems, these nutrients cause diverse problems such as toxic algal blooms, loss of oxygen, fish kills, loss of biodiversity (including species important for commerce and recreation), loss of aquatic plant beds and coral reefs, and other problems. Nutrient enrichment seriously degrades aquatic ecosystems and impairs the use of water for drinking, industry, agriculture, recreation, and other purposes. Based on our review of the scientific literature, we are certain that (1) eutrophication is a widespread problem in rivers, lakes, estuaries, and coastal oceans, caused by over-enrichment with P and N; (2) nonpoint pollution, a major source of P and N to surface waters of the United States, results primarily from agriculture and urban activity, including industry; (3) inputs of P and N to agriculture in the form of fertilizers exceed outputs in produce in the United States and many other nations; (4) nutrient flows to aquatic ecosystems are directly related to animal stocking densities, and under high livestock densities, manure production exceeds the needs of crops to which the manure is applied; (5) excess fertilization and manure production cause a P surplus to accumulate in soil, some of which is transported to aquatic ecosystems; and (6) excess fertilization and manure production on agricultural lands create surplus N, which is mobile in many soils and often leaches to downstream aquatic ecosystems, and which can also volatilize to the atmosphere, redepositing elsewhere and eventually reaching aquatic ecosystems. If current practices continue, nonpoint pollution of surface waters is virtually certain to increase in the future. Such an outcome is not inevitable, however, because a number of technologies, land use practices, and conservation measures are capable of decreasing the flow of nonpoint P and N into surface waters. From our review of the available scientific information, we are confident that: (1) nonpoint pollution of surface waters with P and N could be reduced by reducing surplus nutrient flows in agricultural systems and processes, reducing agricultural and urban runoff by diverse methods, and reducing N emissions from fossil fuel burning; and (2) eutrophication can be reversed by decreasing input rates of P and N to aquatic ecosystems, but rates of recovery are highly variable among water bodies. Often, the eutrophic state is persistent, and recovery is slow.
Agricultural runoff is a major contaminant source threatening water quality in streams, lakes, and public drinking water reservoirs. Agricultural pollution control practices and programs are traditionally based on the assumption that overland flow is only generated when rainfall intensities exceed soil infiltration capacity. This paper challenges this assumption, noting that overland flow associated with agricultural pollutant transport is often physically consistent with the variable source area hydrology concept, for which overland flow is generated in parts of the landscape where the soil saturates to the surface. Incorporation of variable source area hydrology into watershed management practices reconceptualizes nonpoint source pollution as "variable source pollution," in which pollution control efforts can be focused on relatively small hydrologically sensitive areas recognizing that the extent of these areas will vary throughout the year. There are substantial technical, economic, social, and institutional barriers to implementing strategies for managing variable source pollution partially because of massive institutional inertia of existing agroenvironmental policies and programs and best management practices. Substantial research is needed to quantify the water quality risks associated with variable source pollution, expand the capacity to identify the critical management areas, and eliminate the institutional barriers for managing variable source pollution in agricultural watersheds.
Watershed models are powerful tools for simulating the effect of watershed processes and management on soil and water resources. However, no comprehensive guidance is available to facilitate model evaluation in terms of the accuracy of simulated data compared to measured flow and constituent values. Thus, the objectives of this research were to: (1) determine recommended model evaluation techniques (statistical and graphical), (2) review reported ranges of values and corresponding performance ratings for the recommended statistics, and (3) establish guidelines for model evaluation based on the review results and project-specific considerations; all of these objectives focus on simulation of streamflow and transport of sediment and nutrients. These objectives were achieved with a thorough review of relevant literature on model application and recommended model evaluation methods. Based on this analysis, we recommend that three quantitative statistics, Nash-Sutcliffe efficiency (NSE), percent bias (PBIAS), and ratio of the root mean square error to the standard deviation of measured data (RSR), in addition to the graphical techniques, be used in model evaluation. The following model evaluation performance ratings were established for each recommended statistic. In general, model simulation can be judged as satisfactory if NSE > 0.50 and RSR < 0.70, and if PBIAS + 25% for streamflow, PBIAS + 55% for sediment, and PBIAS + 70% for N and P. For PBIAS, constituent-specific performance ratings were determined based on uncertainty of measured data. Additional considerations related to model evaluation guidelines are also discussed. These considerations include: single-event simulation, quality and quantity of measured data, model calibration procedure, evaluation time step, and project scope and magnitude. A case study illustrating the application of the model evaluation guidelines is also provided.
The presence of subsurface tile drainage systems can facilitate nutrient and pesticide transport, thereby contributing to environmental pollution. The Soil and Water Assessment Tool (SWAT) water quality model is designed to assess nonpoint and point source pollution and was recently modified for tile drainage. Over 25% of the nation's cropland required improved drainage. In this study, the model's ability to validate the tile drainage component is evaluated with nine years of hydrologic monitoring data collected from the South Fork watershed in Iowa, since about 80% of this watershed is tile drained. This watershed is a Conservation Effects Assessment Program benchmark watershed and typifies one of the more intensively managed agricultural areas in the Midwest. Comparison of measured and predicted values demonstrated that inclusion of the tile drainage system is imperative for obtaining a realistic watershed water balance. Two calibration/validation scenarios tested if the results differed in how the data set was divided. The optimum scenario results for the simulated monthly and daily flows had Nash-Sutcliffe efficiency (E(NS)) values during the calibration/validation (1995-1998/1999-2004) periods of 0.9/0.7 and 0.5/0.4, respectively. The second scenario results for the simulated monthly and daily flows had E(NS) values during the calibration/validation (1995-2000/2001-2004) periods of 0.8/0.5 and 0.7/0.2, respectively. The optimum scenario reflects the distribution of peak rainfall events represented in both the calibration and validation periods. The year 2000, being extremely dry, negatively impacted both the calibration and validation results. Each water budget component of the model gave reasonable output, which reveals that this model can be used for the assessment of tile drainage with its associated practices. Water yield results were significantly different for the simulations with and without the tile flow component (25.1% and 16.9%, expressed as a percent of precipitation). The results suggest that the SWAT2005 version modified for tile drainage is a promising tool to evaluate streamflow in tile-drained regions when the calibration period contains streamflows representing a wide range of rainfall events.
Studies have demonstrated some P loss reduction following implementation of remedial strategies at field scales. However, there has been little coordinated evaluation of best management practices (BMPs) on a watershed scale to show where, when, and which work most effectively. Thus, it is still difficult to answer with a degree of certainty, critical questions such as, how long before we see a response and where would we expect to observe the greatest or least response? In cases where field and watershed scales are monitored, it is not uncommon for trends in P loss to be disconnected. We review case studies demonstrating that potential causes of the disconnect varies, from competing sources of P at watershed scales that are not reflected in field monitoring to an abundance of sinks at watershed scales that buffer field sources. To be successful, P-based mitigation strategies need to occur iteratively, involve stakeholder driven programs, and address the inherent complexity of all P sources within watersheds.
In the last part of the twentieth century, recognition became widespread of the important effect of agricultural runoff on the health of aquatic ecosystems in the Lake Erie basin and elsewhere. Because of the efforts to remediate Lake Erie, the "dead lake" among the Laurentian Great Lakes, a number of research and demonstration projects were undertaken in the Lake Erie basin to evaluate and foster adoption of conservation tillage and other farming techniques that would reduce runoff while maintaining productivity. In addition, intensive water quality studies of long duration were begun on major tributaries to Lake Erie during this time. The Lake Erie Agricultural Systems for Environmental Quality (LEASEQ) project examined governmental programs, changes in agriculture, and changes in water and soil quality during the period 1975-1995, and sought to evaluate the linkages among these factors. The study area is characterized by extensive agricultural land use of soils developed from glacial materials deposited on Paleozoic sedimentary bedrock, mostly limestone. Tile drainage is extensive, particularly in slow-draining clay-rich lacustrine soils in the lower reaches of the watersheds. This paper introduces the study area, its geology, geography, soils, and agricultural history. In addition, we provide an overview of the LEASEQ concept and introduce the 11 other papers in this series, which provide a detailed exposition of the results of our studies.
The Soil and Water Assessment Tool (SWAT) model is a continuation of nearly 30 years of modeling efforts conducted by the U.S. Department of Agriculture (USDA), Agricultural Research Service. SWAT has gained international acceptance as a robust interdisciplinary watershed modeling tool, as evidenced by international SWAT conferences, hundreds of SWAT-related papers presented at numerous scientific meetings, and dozens of articles published in peer-reviewed journals. The model has also been adopted as part of the U.S. Environmental Protection Agency's BASINS (Better Assessment Science Integrating Point & Nonpoint Sources) software package and is being used by many U.S. federal and state agencies, including the USDA within the Conservation Effects Assessment Project. At present, over 250 peer-reviewed, published articles have been identified that report SWAT applications, reviews of SWAT components, or other research that includes SWAT. Many of these peer-reviewed articles are summarized here according to relevant application categories such as streamflow calibration and related hydrologic analyses, climate change impacts on hydrology, pollutant load assessments, comparisons with other models, and sensitivity analyses and calibration techniques. Strengths and weaknesses of the model are presented, and recommended research needs for SWAT are provided.
As climate changes, the uncertainty of water availability, changing magnitudes of nonpoint-source pollution, and uncertainty of best management practice (BMPs) effectiveness are issues that watershed managers and stakeholders must consider and plan for. The objective of this study was to determine how BMP effectiveness will be affected by climate change using the Soil and Water Assessment Tool (SWAT). Using downscaled monthly precipitation and temperature data output from the Community Climate System Model (CCSM), daily precipitation and temperature data were produced based on observed weather station data for the Tuttle Creek Lake watershed in Kansas and Nebraska. The A1B, A2, and B1 SRES emissions scenarios were compared to historical CCSM model output. Eight agricultural BMPs were physically represented within SWAT and compared across climate scenarios. Water yield, surface runoff, baseflow, sediment load, nitrogen load, and phosphorus load increased in all three future climate scenarios. Terraces, contour farming, and native grass were determined to be the most effective in pollution load reduction and percent efficiency at the field and watershed scales in future scenarios. Porous gully plugs and filter strips showed no significant changes in pollution load or percent reduction. Grazing management, no-tillage, conservation tillage, and grazing management percent and load reduction in future scenarios varied at the field and watershed scales. This study demonstrates that BMP performance in terms of sediment, nitrogen, and phosphorus reduction significantly changes in future climate scenarios at the field scale, while performance generally does not change significantly at the watershed scale. © 2011 American Society of Agricultural and Biological Engineers.
Joosse, P. J. and Baker, D. B. 2011. Context for re-evaluating agricultural source phosphorus loadings to the Great Lakes. Can. J. Soil Sci. 91: 317-327. Over the past decade, scientists have been discussing the re-emergence of harmful algal blooms and excessive growth of Cladophora in some areas of the Great Lakes. An observation that has emerged from these discussions is that management of non-point or diffuse sources of phosphorus will be more important in the future in order to address symptoms of eutrophication in the nearshore. This paper provides context for this renewed focus on managing non-point source tributary loads and is based primarily on materials and discussions from the Great Lakes P Forum. There are changes that have occurred in the lakes and tributaries in the past 15 yr that indicate a greater need to focus on non-point sources, whether urban or rural. Changes have also occurred in land management to reduce non-point P losses from agriculture. While these changes have reduced sediment and particulate P loading in some Ohio tributaries, the more bioavailable, dissolved P forms have increased. As there is incomplete knowledge about the mechanisms that are influencing algal growth, it could be a challenge to demonstrate, in the near term, improvements in water quality with further P reductions from agriculture alone. Regardless, there appears to be a desire for improved accountability and transparency for agricultural non-point source P management.
The research was conducted as part of the USDA's Conservation Effects Assessment Project. The objective of the project was to evaluate the environmental effects of land-use changes, with a focus on understanding how the spatial distribution throughout a watershed influences their effectiveness. The Soil and Water Assessment Tool (SWAT) water quality model was applied to the Squaw Creek watershed, which covers 4,730 ha (11,683 ac) of prime agriculture land in southern Iowa. The model was calibrated (2000 to 2004) and validated (1996 to 1999) for overall watershed hydrology and for streamflow and nitrate loadings at the watershed outlet on an annual and monthly basis. Four scenarios for land-use change were evaluated including one scenario consistent with recent land-use changes and three scenarios focused on land-use change on highly erodible land areas, upper basin areas, and floodplain areas. Results for the Squaw Creek watershed suggested that nitrate losses were sensitive to land-use change. If land-use patterns were restored to 1990 conditions, nitrate loads may be reduced 7% to 47% in the watershed and subbasins, whereas converting row crops to grass in highly erodible land, upper basin, and floodplain areas would reduce nitrate loads by 47%, 16%, and 8%, respectively These SWAT model simulations can provide guidance on how to begin targeting land-use change for nitrate load reductions in agricultural watersheds.
Woznicki, Sean A. and A. Pouyan Nejadhashemi, 2011. Sensitivity Analysis of Best Management Practices Under Climate Change Scenarios. Journal of the American Water Resources Association (JAWRA) 48(1): 90-112. DOI: 10.1111/j.1752-1688.2011.00598.x
Abstract: Understanding the sensitivity of best management practices (BMPs) implementation as climate changes will be important for water resources management. The objective of this study was to determine how the sensitivity of BMPs performance vary due to changes in precipitation, temperature, and CO2 using the Soil and Water Assessment Tool. Sediment, total nitrogen, and total phosphorus loads on an annual and monthly basis were estimated before and after implementation of eight agricultural BMPs for different climate scenarios. Downscaled climate change data were obtained from the National Center for Atmospheric Research Community Climate System Model for the Tuttle Creek Lake watershed in Kansas and Nebraska. Using a relative sensitivity index, native grass, grazing management, and filter strips were determined to be the most sensitive for all climate change scenarios, whereas porous gully plugs, no-tillage, and conservation tillage were the least sensitive on an annual basis. The monthly sensitivity analysis revealed that BMP sensitivity varies largely on a seasonal basis for all climate change scenarios. The results of this research suggest that the majority of agricultural BMPs tested in this study are significantly sensitive to climate change. Therefore, caution should be exercised in the decision-making processes.
A 1-dimensional, linked hydrodynamic and eutrophication model was developed and calibrated with 19 years of observations (1987–2005) for the summer stratification period in the central basin of Lake Erie, corroborated by comparison with observed process rates and areal hypoxic extents, and confirmed with observations from the 1960s and 1970s. The model effectively captures observations of both vertical and temporal trends in dissolved oxygen, as well as temporal trends in chlorophyll-a, phosphorus, zooplankton biomass, and several key processes. The model was used to develop a relationship between external phosphorus load and hypolimnion oxygen conditions, and then to establish load–response envelopes that account for inter-annual variability in physical conditions driven by variation in meteorological drivers. The curves provide a valuable tool for reassessing phosphorus loading targets with respect to reducing hypoxia in Lake Erie.
Hypoxic conditions, defined as dissolved oxygen (DO) concentrations below 2 mg/L, are a regular summertime occurrence in Lake Erie, but the spatial extent has been poorly understood due to sparse sampling. We use geostatistical kriging and conditional realizations to provide quantitative estimates of the extent of hypoxia in the central basin of Lake Erie for August and September of 1987 to 2007, along with their associated uncertainties. The applied geostatistical approach combines the limited in situ DO measurements with auxiliary data selected using the Bayesian Information Criterion. Bathymetry and longitude are found to be highly significant in explaining the spatial distribution of DO, while satellite observations of sea surface temperature and satellite chlorophyll are not. The hypoxic extent was generally lowest in the mid-1990s, with the late 1980s (1987, 1988) and the 2000s (2003, 2005) experiencing the largest hypoxic zones. A simple exponential relationship based on the squared average measured bottom DO explains 97% of the estimated variability in the hypoxic extent. The change in the observed maximum extent between August and September is found to be sensitive to the corresponding variability in the hypolimnion thickness.
Current research has shown that reductions in nonpoint nutrient loading are needed to reduce the incidence of harmful algal blooms and hypoxia in the western and central basins of Lake Erie. We used the Soil and Water Assessment Tool (SWAT) to test various sediment and nutrient load reduction strategies, including agricultural best management practice (BMP) implementation and source reduction in various combinations for six watersheds. These watersheds, in order of decreasing phosphorus loads, include the Maumee, Sandusky, Cuyahoga, Raisin, Grand, and Huron, and together comprise 53% of the binational Lake Erie Basin area. Hypothetical pristine nutrient yields, after eliminating all anthropogenic influences, were estimated to be an order of magnitude lower than current yields, underscoring the need for stronger management actions. However, cover crops, filter strips, and no-till BMPs, when implemented at levels considered feasible, were minimally effective, reducing sediment and nutrient yields by only 0–11% relative to current values. Sediment yield reduction was greater than nutrient yield reduction, and the greatest reduction was found when all three BMPs were implemented simultaneously. When BMPs were targeted at specific locations rather than at random, greater reduction in nutrient yields was achieved with BMPs placed in high source locations, whereas reduction in sediment yields was greatest when BMPs were located near the river outlet. Modest nutrient source reduction also was minimally effective in reducing yields. Our model results indicate that an “all-of-above” strategy is needed to substantially reduce nutrient yields and that BMPs should be much more widely implemented.
The Soil and Water Assessment Tool (SWAT), a physically-based watershed-scale model, holds promise as a means to predict tributary sediment and nutrient loads to the Laurentian Great Lakes. In the present study, model performance is compared across six watersheds draining into Lake Erie to determine the applicability of SWAT to watersheds of differing characteristics. After initial model parameterization, the Huron, Raisin, Maumee, Sandusky, Cuyahoga, and Grand SWAT models were calibrated (1998–2001) and confirmed, or validated (2002–2005), individually for stream water discharge, sediment loads, and nutrient loads (total P, soluble reactive P, total N, and nitrate) based on available datasets. SWAT effectively predicted hydrology and sediments across a range of watershed characteristics. SWAT estimation of nutrient loads was weaker although still satisfactory at least two-thirds of the time across all nutrient parameters and watersheds. SWAT model performance was most satisfactory in agricultural and forested watersheds, and was less so in urbanized settings. Model performance was influenced by the availability of observational data with high sampling frequency and long duration for calibration and confirmation evaluation. In some instances, it appeared that parameter adjustments that improved calibration of hydrology negatively affected subsequent sediment and nutrient calibration, suggesting trade-offs in calibrating for hydrologic vs. water quality model performance. Despite these considerations, SWAT accurately predicted average stream discharge, sediment loads, and nutrient loads for the Raisin, Maumee, Sandusky, and Grand watersheds such that future use of these SWAT models for various scenario testing is reasonable and warranted.
Sediment is an important pollutant for Lake Erie and its tributaries, both as a carrier of other substances, particularly phosphorus, and as a pollutant in its own right. Environmental managers have called for major reductions in sediment and phosphorus loadings from Lake Erie tributaries. In this study, thirty-year datasets (Water Years 1975-2004) with daily resolution are analyzed to identify and interpret trends in suspended sediment and particulate phosphorus concentrations and loads in two major US tributaries to Lake Erie. The Maumee and Sandusky Rivers in agricultural northwest Ohio show continual decreases in concentrations and loads throughout this period. The greatest decreases are observed in summer and fall and under low flow conditions, whereas the smallest decreases are observed in the spring and under high flow conditions. Analysis of concentration-flow relationships indicates that these changes are not due to weather but reflect the successful use of agricultural practices to reduce erosion and prevent sediment loss. Opportunities for further reductions in suspended sediment and particulate phosphorus loads and concentrations lie in better management of sediment losses during winter and spring.
In the last part of the twentieth century, recognition became widespread of the important effect of agricultural runoff on the health of aquatic ecosystems in the Lake Erie basin and elsewhere. Because of the efforts to remediate Lake Erie, the “dead lake” among the Laurentian Great Lakes, a number of research and demonstration projects were undertaken in the Lake Erie basin to evaluate and foster adoption of conservation tillage and other farming techniques that would reduce runoff while maintaining productivity. In addition, intensive water quality studies of long duration were begun on major tributaries to Lake Erie during this time. The Lake Erie Agricultural Systems for Environmental Quality (LEASEQ) project examined governmental programs, changes in agriculture, and changes in water and soil quality during the period 1975–1995, and sought to evaluate the linkages among these factors. The study area is characterized by extensive agricultural land use of soils developed from glacial materials deposited on Paleozoic sedimentary bedrock, mostly limestone. Tile drainage is extensive, particularly in slow-draining clay-rich lacustrine soils in the lower reaches of the watersheds. This paper introduces the study area, its geology, geography, soils, and agricultural history. In addition, we provide an overview of the LEASEQ concept and introduce the 11 other papers in this series, which provide a detailed exposition of the results of our studies.
Please view the pdf by using the Full Text (PDF) link under 'View' to the left. Copyright © 2002. American Society of Agronomy, Crop Science Society of America, Soil Science Society . Published in J. Environ. Qual.31:6–16.
We report on the emergence of the potentially toxic filamentous cyanobacterium, Lyngbya wollei as a nuisance species in western Lake Erie. The first indication of heavy L. wollei growth along the lake bottom occurred in September 2006, when a storm deposited large mats of L. wollei in coves along the south shore of Maumee Bay. These mats remained intact over winter and new growth was observed along the margins in April 2007. Mats ranged in thickness from 0.2 to 1.2 m and we estimated that one 100-m stretch of shoreline along the southern shore of Maumee Bay was covered with approximately 200 metric tons of L. wollei. Nearshore surveys conducted in July 2008 revealed greatest benthic L. wollei biomass (591 g/m2±361 g/m2 fresh weight) in Maumee Bay at depth contours between 1.5 and 3.5 m corresponding to benthic irradiance of approximately 4.0–0.05% of surface irradiance and sand/crushed dreissenid mussel shell-type substrate. A shoreline survey indicated a generally decreasing prevalence of shoreline L. wollei mats with distance from Maumee Bay. Surveys of nearshore benthic areas outside of Maumee Bay revealed substantial L. wollei beds north along the Michigan shoreline, but very little L wollei growth to the east along the Ohio shoreline.
We compare the results of lakewide plankton studies conducted during 1996–2002 with data reported in the literature from previous years to evaluate the effectiveness of continued nutrient control, the relationship between external phosphorus loading and plankton abundance, and the many predicted outcomes of the dreissenid invasion. We found that although recent external annual phosphorus loading has not changed since reaching mandated target levels in the early- to mid-1980s, phytoplankton communities have. Total phytoplankton biomass, measured through enumeration and size-frequency distributions has increased since minima were observed in 1996 or 1997, with summer (July–September) biomasses generally greater than before the dreissenid establishment in the late 1980s. Cyanobacteria biomass also increased during summer in all basins after the dreissenid invasion. In contrast, chlorophyll a concentration has decreased in all basins during both spring and summer. However chlorophyll a concentration was poorly correlated with total phytoplankton biomass. Relative to the mid-1980s, crustacean zooplankton biomass during the years 1996–2002 increased in the western basin during spring and summer, increased in the central basin during spring but remained the same during summer, and decreased to low levels in the eastern basin. Several of these observations are consistent with predictions made by previous researchers on the effects of reduced total external phosphorus loading and the stimulatory or inhibitory effects of dreissenid mussels. However, several were not. Results from this study, particularly the inconsistencies with tested predictions, highlight the need for further research into the factors that regulate plankton community dynamics in Lake Erie.
Hypolimnetic oxygen depletion has been recognized as a problem in the central basin of Lake Erie since the 1970s. However, recent expansion in distribution of the depletion after several years of low depletion rates in the 1990s has led investigators to explore the factors that influence the extent of the depletion. We have investigated the vertical oxygen budget in the central basin, which is influenced by the following factors: 1) vertical mixing; 2) exchange across the air-water interface; 3) photosynthesis; 4) respiration of plankton; and 5) sediment oxygen demand. We tested the importance of these factors using a 1-D vertical oxygen budget and transport simulations through sensitivity analysis and by estimating vertical mixing parameters using a temperature gradient microprofiler. Epilimnetic factors were found to be robust and the present monitoring efforts are sufficient; while epilimnetic production is ultimately the source of the hypolimnetic oxygen depletion, epilimnetic factors do not directly influence on hypolimnetic oxygen depletion. However, hypolimnetic depletion was sensitive to sediment oxygen demand and hypolimnion respiration, which are the results of primary production in the epilimnion, and hypolimnetic mixing, which is not related to eutrophication. These parameters, especially the physical mixing measurements, and their links with eutrophication and primary production require greater monitoring and analysis because of their influence on the expansion of oxygen depletion in the central basin of Lake Erie.
The Lake Erie basin remains one of the most intensely monitored areas in the Great Lakes, largely because of continued interest by government agencies and the public in its trophic status. Total lake phosphorus loading estimates require data from three essential pathways: tributaries, point sources, and the atmosphere. Point source and atmospheric deposition monitoring results are available to allow continued estimation of these components. Several key watersheds are still being monitored, making some tributary load estimation possible. The problem is to make estimates for unmonitored areas, which are now substantially greater than encountered previously. Except for 2 years, the total annual load estimates for 1996–2002 (11,584, 16,853, 12,710, 6,608, 8,456, 7,333, and 9,733 metric tonnes per year, respectively) were near or substantially below the target load set by the Great Lakes Water Quality Agreement of 11,000 metric tonnes per year. The estimates for 1997 and 1998 markedly exceeded the target load due mainly to elevated tributary loads because of heavy precipitation. The margin of error or half-width of approximate 95% confidence intervals varied from 4% to 11% of the total estimated load depending on year. Detailed tables of the yearly (1996–2002) estimates are provided, as well as summaries by Lake Erie sub-basin for 1981–2001.