Article

Interacting effects of climate change and agricultural BMPs on nutrient runoff entering Lake Erie

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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.

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... 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). ...
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Article
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). ...
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Article
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.
... In support of this postulation, [13] predicted that streamflow will increase during winter season in the future in several southern Ontario watersheds. As well, [68] found that tile flow is expected to increase based on their study of four Lake Erie watersheds. ...
... In support of this postulation, [13] predicted that streamflow will increase during winter season in the future in several southern Ontario watersheds. As well, [68] found that tile flow is expected to increase based on their study of four Lake Erie watersheds. . Hence, the concentration of nitrate must increase in tile water during spring to account for this steady increase in load. ...
... In a study using SWAT model, [70], found that annual P loading would decrease in the future from a watershed in Lake Erie basin due to increased evapotranspiration and decreased snowfall. On the other hand, [14,18,19,68,71,72] all found that nutrient losses may increase in future in Ontario and Quebec watersheds. ...
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Article
The detrimental impacts of agricultural subsurface tile flows and their associated pollutants on water quality is a major environmental issue in the Great Lakes region and many other places globally. A strong understanding of water quality indicators along with the contribution of tile-drained agriculture to water contamination is necessary to assess and reduce a significant source of non-point source pollution. In this study, DRAINMOD, a field-scale hydrology and water quality model, was applied to assess the impact of future climatic change on depth to water table, tile flow and associated nitrate loss from an 8.66 ha agricultural field near Londesborough, in Southwestern Ontario, Canada. The closest available climate data from a weather station approximately 10 km from the field site was used by the Ontario Ministry of Natural Resources and Forestry (MNRF) to generate future predictions of daily precipitation and maximum and minimum air temperatures required to create the weather files for DRAINMOD. Of the 28 models applied by MNRF, three models (CGCM3T47-Run5, GFDLCM2.0, and MIROC3.2hires) were selected based on the frequency of the models recommended for use in Ontario with SRA1B emission scenario. Results suggested that simulated tile flows and evapotranspiration (ET) in the 2071–2100 period are expected to increase by 7% and 14% compared to 1960–1990 period. Results also suggest that under future climates, significant increases in nitrate losses (about 50%) will occur along with the elevated tile flows. This work suggests that climate change will have a significant effect on field hydrology and water quality in tile-drained agricultural regions.
... Research has been done to assess how BMPs affect in-stream water quality (e.g., Holmes et al., 2016;Tomer et al., 2014); however, few studies have measured the response of sediment nutrient processes to BMPs. Land use effects will likely be exacerbated by climate change, which may alter the effectiveness of BMPs (Bosch et al., 2014;Kaushal et al., 2014), making it necessary to understand how BMPs affect sediment nutrient processes now and in the future. For example, many of the streams and rivers that flow into the Laurentian Great Lakes of North America drain substantial agricultural and urban areas (LaBeau et al., 2014). ...
... As a result, these watersheds deliver elevated nutrient loads to the lakes, which are associated with increasing eutrophication (Robertson & Saad, 2011). Nutrient runoff from agricultural and urban landscapes is projected to intensify due to potential climate change (Bosch et al., 2014). Within the next century, discharge to the Great Lakes is predicted to increase in spring and winter months and decrease in the summer months (Gyawali et al., 2014). ...
... In addition, urban and agricultural land use is expected to increase which may increase nutrient export from these watersheds (LaBeau et al., 2014). Thus, BMPs may become more necessary but less effective in the future (Bosch et al., 2014), which will affect nutrient loading and sediment nutrient processes. ...
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Article
Contemporary land use can affect sediment nutrient processes in rivers draining heavily modified watersheds; however, studies linking land use to sediment nutrient processes in large river networks are limited. In this study, we developed and evaluated structural equation models for denitrification and phosphorus retention capacity to determine direct and indirect linkages between current land use and sediment nutrient processes during base flow in the Fox River watershed, WI, USA. A large spatial‐scale dataset used for this study included sediment nitrogen and phosphorus retention measurements and land use information for 106 sites. The structural equation models for the Fox River watershed identified direct links between current land use and in‐stream sediment nutrient processes. Subwatersheds with agricultural land consisting of more natural land cover had lower surface water nitrate concentrations and higher denitrification enzyme activity than subwatersheds with less alternative cover. This indicates that best management practices implemented in the Fox River watershed that restore natural land cover can improve water quality through nitrogen removal on the agricultural landscape and in the river network. Best management practices are not having the same measurable effects on phosphorus in the river network, most likely due to legacy phosphorus stored in the sediment.
... 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). ...
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Article
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. ...
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Article
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. ...
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Article
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.
... A number of studies explored potential impacts of climate on nutrient loads to Lake Erie; some based on adjusted historical climate data (e.g., Daloğlu et al., 2012;Bosch et al., 2014;Jarvie et al., 2017) and others based on output from climate models (e.g., Johnson et al., 2015;Verma et al., 2015;Culbertson et al., 2016;Kalcic et al., 2019;Kujawa et al., 2020). Some of these studies suggest P loads will increase in response to climate change, while others suggest a decrease. ...
... The diversity of projected climate impacts on P loads could be attributed in part to the range of time scales used in these regional analyses. For example, Johnson et al. (2015), Bosch et al. (2014), Daloğlu et al. (2012), Jarvie et al. (2017), and Kujawa et al. (2020) evaluated responses at annual scales, whereas Kalcic et al. (2019) analyzed spring (March-July) loads and Culbertson et al. (2016) and Verma et al. (2015) analyzed monthly loads. This diversity of results could also be influenced by the climate and watershed models chosen for analysis, whether or not model outputs have been bias corrected, or how modeling techniques were linked. ...
Article
In response to increased harmful algal blooms (HABs), hypoxia, and nearshore algae growth in Lake Erie, the United States and Canada agreed to phosphorus load reduction targets. While the load targets were guided by an ensemble of models, none of them considered the effects of climate change. Some watershed models developed to guide load reduction strategies have simulated climate effects, but without extending the resulting loads or their uncertainties to HAB projections. In this study, we integrated an ensemble of four climate models, three watershed models, and four HAB models. Nutrient loads and HAB predictions were generated for historical (1985–1999), current (2002–2017), and mid-21st-century (2051–2065) periods. For the current and historical periods, modeled loads and HABs are comparable to observations but exhibit less interannual variability. Our results show that climate impacts on watershed processes are likely to lead to reductions in future loading, assuming land use and watershed management practices are unchanged. This reduction in load should help reduce the magnitude of future HABs, although increases in lake temperature could mitigate that decrease. Using Monte-Carlo analysis to attribute sources of uncertainty from this cascade of models, we show that the uncertainty associated with each model is significant, and that improvements in all three are needed to build confidence in future projections.
... One frequently used model is the Soil Water Assessment Tool (SWAT), which has over 3350 peer-reviewed articles (https://www.card.iastate.edu/swat_articles/index.aspx). In agricultural landscapes, this model is frequently used in BMP and climate change impact assessments in the Great Lakes area (Ahmadi et al., 2014;Bosch et al., 2014;Liu et al., 2016;Robertson et al., 2016;Rahman et al., 2012;Wallace et al., 2017). This is a semi-distributed, process and empirically based watershed scale eco-hydrological model. ...
... Although this model was developed in a warm, dry region (Neitsch et al., 2011), it has been calibrated successfully in more northern regions with complex agricultural practices and hydro-climatic conditions to assess water quality issues associated with climate change El-khoury et al., 2015;Mehdi et al., 2015;Shrestha & Wang, 2018). However, to date, there have been few detailed modeling studies focusing on providing a better understanding of how future precipitation characteristics and temperature changes will influence flows, water balance, and water quality responses within the Great lakes region, particularly over the different seasons (Ahmadi et al., 2014;Bosch et al., 2014;Robertson et al., 2016;Rahman et al., 2012;Wallace et al., 2017). Therefore, in this study, the objectives were to predict how climate change will affect the water balance, flow regimes, sediment, and nutrient loads in the Medway Creek Watershed (MCW) using the SWAT model at the (a) annual scale and (b) seasonal scale (Cousino et al., 2015;Crossman et al., 2013;Verma et al., 2015;Wang et al., 2018). ...
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Thesis
Within the Great Lakes region, agricultural non-point source nitrogen (N) and phosphorus (P) contamination contribute to algal blooms and decreased water quality, particularly from tile-drained landscapes. These water quality challenges are accompanied by anthropogenically induced increases in greenhouse gases within the atmosphere, which are leading to changes in climate, which may in turn exacerbate water quality issues by changing hydrological and biogeochemical cycling. This may be particularly important during the non-growing season (NGS), during which most of the annual nutrient export and flow occurs in the Great Lakes region. However, hydrologic and biogeochemical processes during the NGS are less well understood compared to the growing season. The implementation of beneficial management practices (BMP) such as controlled tile drainage (CD) have the potential to mitigate both current and future water quality issues. However, there is little information on the potential water quality tradeoffs associated with this particular practice under both contemporary and future climates. Such information is necessary before CD may be widely recommended and adopted as a BMP. In this thesis, the Soil Water Assessment Tool (SWAT) model was used to demonstrate the potential for CD to reduce nutrient losses in midwestern Ontario, under both current and future climates, and to understand the processes affecting nutrient export responses through the analyses of the water balance, flow regimes, and weather patterns, and to examine seasonal differences in these variables. In this study, two Soil Water Assessment Tool (SWAT) models were applied at varying scales. One was generated for the Medway Creek watershed, near London, ON, to understand the impact of climate change on water quality and quantity by forcing the model with a bias corrected general circulation model (GCM) ensemble. The second SWAT model was run at the field scale, for a field site near Londesborough, ON to understand the potential water quality tradeoffs associated with CD for a field with low-sloped clay loam soil. Results indicate that future changes in climate will cause shifts in seasonal water budgets, resulting in much greater nutrient export during the NGS and an overall increase in annual nutrient losses by the 2080-2100 period. These changes will be driven by precipitation quantity, but also changing precipitation characteristics (timing, form, magnitude, and frequency) and temperature, which will influence runoff pathways. The use of CD will not mitigate water quality issues and will instead exacerbate TP losses in runoff by increasing soil moisture and consequently increasing surface runoff. Although reductions of tile flow were greater than the simulated increases in surface runoff, the approximately 10X greater TP concentrations in surface runoff resulted in an overall increase in simulated edge-of-field TP losses. This will be particularly problematic where CD is used both during the NGS and growing season. This thesis has provided an improved understanding of the impacts of climate change on water quality in the MCW, and has demonstrated that CD has little potential to mitigate water quality issues in the present or future. This thesis has also demonstrated that understanding nutrient export processes during the NGS will be increasingly important for increasing BMP efficacy, reducing NPS contamination, and the occurrence of harmful algal blooms. iv
... Their study concluded that total nutrient loading will increase in response to increase in magnitude and changes in the timing of runoff. Other studies have also used the SWAT model to simulate nutrient loading scenarios under climate change (Bosch et al., 2014;Xu et al., 2019). While more attention is being given to climate change impacts on water quantity and hydrological risks, relatively less number of studies have focused on water quality impacts (Whitehead et al., 2009). ...
... Journal of Hydrology 586 (2020) 124868 The goal of this study is to examine how changes in precipitation and streamflow translate into changes in the magnitude and timing of nutrient loading in the Cannonsville watershed using a physically based watershed model. Earlier studies that investigated the impact of climate change on water quality have used one to three GCMs (Bosch et al., 2014;Jayakody et al., 2014;Woznicki et al., 2011). Recognizing that the greatest source of uncertainty in hydrological modeling of climate change has been attributed to GCMs (Teng et al., 2012), we used a suite of 20 GCMs. ...
Article
In this study we investigated the impact of climate change on nutrient loading in the Cannonsville Reservoir watershed of the New York City (NYC) water supply system where management practices have reduced nutrient inputs in the last 25 years. A modified version of the SWAT hydrological and water quality model (SWAT-HS) that had been previously tested and verified for streamflow and phosphorus for this watershed was calibrated for nitrate to estimate contributions from point and nonpoint sources. Model simulations show that forests that occupy 64% of the watershed area contribute the greatest proportion of nitrate at 39%, while pastures that are in close proximity to streams and runoff generating areas contribute the greatest proportion of total nitrogen at 34%. Point sources contribute less than 5% of the annual nitrate load. Stream export accounts for only about 23% of the annual total N input to the watershed from anthropogenic sources, suggesting significant storage or loss from the landscape. We assumed stationary land use and management practices to assess the change in nutrient loading from baseline (2001-2010) to middle of the century (2051-2060) period due to a change in climate. Results indicated no change to moderate increase in the annual loading of dissolved forms of nutrients (N and P) whereas particulate forms of nutrients and sediment loadings are projected to increase due to an increase in the frequency and magnitude of large storm events. A seasonal shift in streamflow due to warmer winter temperatures, greater amounts of precipitation falling as rain, and earlier melting of snowpack may play an important role in controlling the seasonal pattern of nutrient loading. The methodology used in this study can be adapted in other watersheds to estimate the relative importance and partition contributions from various nonpoint sources to water quality, and to investigate the impacts of climate change.
... Specifically, the vertical distribution of suspended particulate material and nutrients was strongly influenced by the thermal structure (Wang et al. 2012), while extreme low flows could change the concentration of dissolved and suspended material, which was attributed primarily to the lack of flushing; additionally, sediment resuspension increased as the lakes became shallower (Mosley et al. 2012). Additionally, above certain thresholds, warming has a stronger influence on sediments because it may markedly accelerate the release of sediments (Bosch, Evans et al. 2014); in particular, the issues of heavy metal pollution in sediments received much attention during this time (Fujita et al. 2014). Additionally, in the context of global climate change, the impacts of thermokarst and retreat of mountain glaciers on water quality received considerable attention (Kokelj and Jorgenson 2013;Clarke et al. 2015). ...
... First, conservation agriculture (CA) is becoming more popular, which is beneficial for improving soil properties and processes, thereby increasing topsoil organic matter, reducing erosion, and runoff, improving water quality and protecting Environ Sci Pollut Res (2020) 27:14322 14341 -14330 biological biodiversity (Palm et al. 2014). Specifically, climate change above a certain threshold will significantly accelerate nutrient export; hence, attention should be paid to integrated nutrient management to protect and improve water quality (Bosch et al. 2014). The establishment of vegetation buffers on agricultural fields could partially reduce the negative impacts of climatic extremes for aquatic ecosystems (Goldstein et al. 2012;Thomson et al. 2012). ...
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Article
Research on the impacts of climate change on water quality helps to better formulate water quality strategies under the challenge of an uncertain future, which is critical for human survival and development. As a result, in recent years, there has been growing attention given to research in the field, and the attention has led to an increasing number of publications, which is why a systematic literature review on this topic has been proposed in the current paper. This study reviewed 2998 related articles extracted from the Science Citation Index-Expanded (SCI-E) database from 1998 to 2018 to analyse and visualize historical trend evolution, current research hotspots, and promising ideas for future research by combining a traditional literature review, bibliometric analysis, and scientific knowledge mapping. The results revealed that the impacts of climate change on water quality mainly included the aggravation of eutrophication, changes in the flow, hydrological and thermal conditions, and the destruction of ecosystems and biodiversity. Further exploration of the influence mechanism of climate change on cyanobacteria is an emerging research topic. Additionally, the water quality conditions of shallow lakes and drinking water are promising future research objects. In the context of climate change, the general rules of water quality management and the scientific planning of land use are of great significance and need to be further studied. This study provides a practical and valuable reference for researchers to help with the selection of future research topics, which may contribute to further development in this field.
... 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). ...
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Technical Report
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. ...
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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 Abbreviations: CEAP, Conservation Effects Assessment Project; CP, conservation practice. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 10.1002/ael2.20084
... 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). ...
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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. ...
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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. ...
Article
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]. ...
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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. ...
Article
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). ...
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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 data set 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 behaviour 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 to 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 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. ...
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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. ...
Article
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]. ...
... However, these studies focus on individual decision making and most do not explicitly consider downstream water quality impacts and, thus, are unable to fully evaluate policy effectiveness. On the other hand, a growing number of hydrological process-based models have been developed for Lake Erie and other areas of the Great Lakes region; however, these models omit behavioral or economic considerations and therefore must impose assumptions about BMP adoption (e.g., assuming full or random adoption, see Scavia et al. 2017 andBosch et al. 2014). We demonstrate the value and necessity of integrated assessment models to identify realistic policy impacts of nutrient management policies and quantify the social cost of water quality. ...
... Increased global temperatures have been predicted to alter hydrological processes, with a tendency towards more frequent hydrological extremes such as droughts and floods (Trenberth, 2011). The projected increase in the intensity of heavy precipitation events with warming (Mallakpour and Villarini, 2017;Ragno et al., 2018) is expected to affect soil moisture and runoff (Rahmani et al., 2016); plant productivity and growth (Arroyo-Cosultchi et al., 2016;Gorton et al., 2019); and water quality in watersheds (Delpla et al., 2011;Bosch et al., 2014;Carpenter et al., 2018). Developing strategies to adapt to and/or mitigate the impacts of climate change requires a better understanding of the effects of future climate trends on watershed hydrology (Null et al., 2010). ...
Article
Evaluation of hydrological response to future climate change is essential for water quality risk assessment and adaptive management implementation within a watershed context. In this study, we present a modeling framework that integrates a hydrological model with projections of General Circulation Models (GCMs). Temperature and precipitation projections of six GCMs with two downscaling methods are used to force the Soil and Water Assessment Tool (SWAT) model in the Hamilton Harbour watershed in Ontario, Canada. A flow-based weighting strategy was developed to integrate the projections of multiple GCMs based on their ability to recreate empirical flow frequency distributions in multiple monitoring sites. Our study renders support to the ability of the weighted model ensemble to draw meaningful hydrological forecasts. Nonetheless, we also note that the ensemble strategy understates the frequency and magnitude of flow extremes, and therefore the domain that is collectively delineated by individual GCMs can still provide complementary planning information. Climate change is projected to trigger a distinct increase in air temperature and precipitation during the late winter-early spring period, which in turn will likely result in an earlier snowmelt and changes in the magnitude and timing of peak flow events. Analysis of the water cycle shows that the sensitivity of the individual hydrological components to climate change may vary along the urban-to-agriculture gradient. The projected declining soil-water content in agricultural catchments highlights the likelihood of more intensified drought conditions in the croplands. Evapotranspiration rates will likely increase across the entire watershed, whereas surface runoff could be reduced but less so in urbanized locations. Overall, our findings suggest that any future planning exercise to ameliorate the prevailing water quality conditions will only be insightful if we consider the interplay between climate change and urbanization processes in the area.
... Similarly, Robertson et al. (2016) concluded that a −5 to +17% change in total annual precipitation results in a −21% to +9% change in total annual discharge and a −29 to +17% change in total annual P loading in the Lake Michigan basin. Bosch, Evans, Scavia, and Allan (2014) found that increases of +3 and +6% in precipitation result in changes in average annual discharge of +6 to +12% and total average annual P loading of +4 to +6%. Whereas water quality in rivers is documented to be greatly related to land cover (Arnold et al., 2013;Robertson & Saad, 2011), discharge is reported to be strongly linked to precipitation (Miao & Ni, 2009;Yang, Yan, & Liu, 2012). ...
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Phosphorus supplies (concentrations and fluxes) are essential drivers for biological activities in rivers and should be controlled to prevent eutrophication that usually results from urbanization and agricultural expansion. In this paper, data from 26 sub‐catchments in the Mississippi Basin, the United States, were compiled for the period from 2013 to 2017 to identify how catchment area, precipitation, and land cover affect discharge and total phosphorus (TP), and how TP yield diverges from a generalized local response mode. Results revealed that area‐weighted discharge (Qarea) is controlled by precipitation and land cover (i.e., increases with precipitation and with both urban and forest land covers, and decreases with both shrub/scrub and pasture/grassland covers). TP concentration increases with agricultural land cover and decreases with both forest and water/wetland covers. TP yield (product of Qarea and concentration) is mainly governed by Qarea as the latter changes by a higher order of magnitude compared to concentration in the current study. Hence TP yield is following the same trends that Qarea exhibits with precipitation and land cover. In all catchments, TP yield varied significantly (p < 0.05) and positively with instantaneous discharge. However, the rate of yield variations with discharge exhibited a significant (p < 0.0001) strong negative (r2 = −0.74) correlation with catchment area. This study provided a robust model that can predict the TP concentration and yield across different catchment scales in the Mississippi Basin by means of discharge readings. This article is protected by copyright. All rights reserved
... For example, annual US phosphorus loads are forecasted to increase by 3.4-5.8% from 2010 to 2040 without accounting for the effect of climate change on hydrology (LaBeau et al., 2014), which could increase the frequency of large runoff events and thereby increase annual loads even more (Bosch et al., 2014;Michalak et al., 2013). This is particularly important for the planktivorous bigheaded carps for which simulation studies have demonstrated that growth is notably responsive to differences in phosphorus loads under different scenarios for Lakes Michigan (Alsip et al., 2020) and Erie (Zhang et al., 2016). ...
Article
Bioenergetics and food web models are tools available for understanding and projecting the impacts of aquatic species invasions on food web structure and energy allocation of an ecosystem. However, uncertainty is inherent in modeling the impact of invasive species in novel ecosystems as assumptions must be made about physiological responses to novel environments and interactions with existing (native and non-native) species. Here we use the four major Chinese carps (FMCC) in the Laurentian Great Lakes as a case study to categorize and describe the suite of uncertainties inherent in projecting the impact of invasive species with bioenergetics and food web models. We approach this case study in a decision analytic framework, describing structural uncertainties, environmental variation, partial observability, partial controllability, and linguistic uncertainty. Finally, we review and give suggestions for how the use of methods including adaptive management, scenario planning, sensitivity analyses, and value of information as well as efforts to ensure clarity in language and model structure can enable modelers and managers to reduce and account for key uncertainties and make better decisions for the control of invasive species.
... 132,133 It is expected that under climate change, not only will the nutrient levels entering waterways increase, but that there will also be a decrease in the effectiveness of BMPs. 110,134 Increased flow depth and number of runoff events are expected to diminish the ability of agricultural BMPs to trap nutrients. 128,135 Urban BMPs that receive higher nutrient loads and flows due to changing climatic conditions are expected to decrease removal efficiency. ...
Article
Extensive time and financial resources have been dedicated to address nonpoint sources of nitrogen and phosphorus in watersheds. Despite these efforts, many watersheds have not seen substantial improvement in water quality. The objective of this study is to review the literature and investigate key factors affecting the lack of improvement in nutrient levels in waterways in urban and agricultural regions. From 94 studies identified in the academic literature, we found that although 60% of studies found improvements in water quality after implementation of Best Management Practices (BMPs) within the watershed, these studies were mostly modelling studies rather than field monitoring studies. For studies that were unable to find improvements in water quality after the implementation of BMPs, the lack of improvement was attributed to: lack of knowledge about BMP functioning, lag times, non-optimal placement and distribution of BMPs in the watershed, post-implementation BMP failure, and socio-political and economic challenges. We refer to these limiting factors as known unknowns. We also acknowledge the existence of unknown unknowns that hinder further improvement in BMP effectiveness and suggest that machine learning, approaches from the field of business and operations management, and long-term convergent studies could be used to resolve these unknown unknowns.
... Climate change may also affect the biological character of the Great Lakes by altering the timing of phytoplankton blooms (Winder and Schindler 2004), affecting the availability and transport of nutrients throughout the water column in deep lakes (Brooks and Zastrow 2002), and increasing the volume of favorable thermal habitat available to most fish species thereby affecting growth and consumption rates (Collingsworth et al. 2017). Meanwhile, more frequent and intense runoff events due to changing precipitation patterns (Michalak et al. 2013;Bosch et al. 2014), paired with recent trends in urbanization and population growth (Pijanowski and Robinson 2011), threaten to increase non-point and point-source nutrient inputs in areas of the Great Lakes already struggling with eutrophication, such as Green Bay, Saginaw Bay, and Lake Erie's Western Basin (Stow et al. 2015;Choquette et al. 2019). ...
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Anthropogenic stressors that affect ecological processes in the Laurentian Great Lakes can impact their susceptibility to bioinvasions. Bighead Hypophthalmichthys nobilis and Silver Carp H. molitrix, collectively ‘bigheaded carps’ (BHC), are planktivorous fishes threatening to invade Lake Michigan. While previous studies indicate the lake contains habitat suitable for BHC growth, there is a need to understand how anthropogenic-driven changes to the abiotic and biotic environment could alter its vulnerability to BHC. We applied a spatially explicit model of BHC growth rate potential (GRP; g g−1 d−1) to nine biophysical model scenarios to evaluate changes in habitat suitability in Lake Michigan. Scenarios differed in meteorology (cool, reference, warm), annual tributary phosphorus loads (0, 3300, and 5600 MTA), and the presence/absence of invasive dreissenid mussels. Mussel effects on BHC GRP relied on their contact with the surface mixed layer (SML), the depth of which was affected by meteorology. The warm year advanced the expansion of Bighead Carp habitat by increasing temperature-dependent foraging rates and lessening the time of competitive interaction with mussels due to earlier stratification separating mussels from the SML. Phosphorus loads were the most influential driver of the lake’s suitability. Compared to present conditions, we estimate BHC could have grown an additional 8–40% annually in the 1980s when mussels were not in the lake and phosphorus loads were higher. Our study demonstrates how climate change and nutrient enrichment can increase Lake Michigan’s vulnerability to BHC by affecting thermal regime and productivity, thereby limiting negative effects of dreissenid mussels on BHC growth.
... Examples of common BMPs intended to improve water quality include seasonal practices such as reduced tillage, contour farming, and the use of cover crops to reduce soil erosion as well as long-term practices like grassed waterways, filter strips, and riparian buffers that capture sediment and nutrient runoff prior to discharge into surface water (Sharpley et al., 2006). In general BMPs reduce P inputs; however, their implementation often fails to meet dissolved P reduction targets required to improve water quality of nearby water bodies (Novotny, 2003;Dunne et al., 2006;Cullum et al., 2009;Lemke et al., 2011) and additional measures will be required to further reduce P inputs especially under projected climatic conditions (Bosch et al., 2014). ...
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Article
Constructed and restored wetlands can be effective sinks for particulate and dissolved phosphorus (P) if properly managed, but identifying suitable P retention wetland locations remains challenging. From a landscape perspective, Soil and Water Assessment Tool (SWAT) models identify locations within target watersheds with high nutrient loads that exhibit appropriate site characteristics and hydrodynamics. However, soil properties vary at the field scale, dictating the capacity of wetland systems to remove P and ultimately determining if a given wetland will operate as a sink or source of P over time. Land ownership and site access further complicate identification of P retention wetland locations. As a result, optimization and identification of P retention wetland locations requires analysis at both 1) watershed and 2) field scales, and 3) public engagement. In response, a survey effort linked SWAT model results that identified locations with target watersheds with field soil P storage capacity data and interested landowners. Results suggest that several locations recommended for their high SWAT-predicted P loading and landowner interest were in fact not well suited for project implementation due to soil P saturation and legacy P constraints. These findings highlight the need to couple watershed models with field scale soils analysis to identify locations for P retention wetlands in order to avoid unintended P release. Additionally, increased collaboration with social scientists and others familiar with public engagement strategies is needed to improve outreach activities targeting regional water quality improvements. Practical applications for nutrient retention wetland site selection are also discussed.
... This is in agreement with the findings of Cousino et al. [271], who estimated the increment of sediment loads under RCP 8.5 mostly during winter due to the high frequency of large storm events. These results also agreed by Bosch et al. [272] who projected by the end of century Maumee River tends to increase 6-10% and 8-32% of flow and sediment yields, respectively. These results also recommended that oil palm managers could sufficiently add two fertiliser application months from existing months (May, June and November) to the most active growing season (February and September) in the future to encourage optimum phosphorus uptake with less potential to leach. ...
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The character of land-use, oil palm nutrient processes and climate change on agriculture watershed system are essential for optimum fertilization and reduces nutrient losses and leaching from the land surface. This study assesses the response of a tropical agriculture watershed, Johor River and its tributaries to land used changes, oil palm fertilization schemes and climate change scenarios derived from the long-term meteorological data. Four land-use scenarios from the year 2000 to 2014 were used and one projected climate change scenarios obtained from United States Centre for Atmospheric Research is used. These land-use and climate model were incorporated into the Hydrological Simulation Program-FORTRAN to determine the impact of long-term land-use, climate, and contaminants control via oil palm uptake and nitrate leaching in a tropical watershed. The model was calibrated and validated from 2000 to 2015 using data from two stations, Johor River at Rantau Panjang and Sayong River at Jambatan Johor Tenggara. Good correlation was obtained between observed and simulated streamflow, total sediment concentration, water temperature, biochemical oxygen demand (BOD), dissolved oxygen (DO), nitrate nitrogen (NO3-N), ammonia nitrogen (NH3-N), and orthophosphate (PO4).The simulated model shows that the hydrological water balance and yield of the watershed vary under different land-use scenarios and evapotranspiration is the primary source of water deficit. Proper soil management practices and improved water infiltration will reduce sediment yield and suspended solids concentration by almost 70% and 30% respectively. Water quality analysis indicates lower dissolved oxygen from August to October when lower water flow and high water temperatures lead to higher oxygen depletion. For oil palm nutrient components, organic mineralization is most sensitive since the mineralization rate was related to soil temperature via air temperature and microbial activity. As agriculture development expanded from 68% to 90%, total nitrogen and total phosphorus loads increase to 2.9% and 2.1% respectively. Annual total nitrogen and total phosphorus loads from the agricultural land are expected to increase 1% each with every 1% decrease in streamflow. Climate change analysis suggests that nitrate leaching decreases with the application of 30% less fertilizer rate and frequent fertilization (from three times to five times per year) from conventional practices. The phosphorus yield from oil palm plantation is more from June to August due to the surface runoff and sediment attachments. This study offers a nutrient management on different oil palm fertilization schemes and water quality management in a tropical agriculture dominated watershed.
... Joseph et al., 2018;Kay et al., 2008;Poulin et al., 2011;Vetter et al., 2017;Wilby and Harris, 2006). This variability among hydrologic models in this study is similar to the collection of other efforts simulating the effects of climate change on the Maumee River Watershed where only one hydrologic model was used across studies and results were mixed across discharge, TP, DRP, and TN loadings (Bosch et al., 2014;Cousino et al., 2015;Culbertson et al., 2016;Johnson et al., 2015;Kalcic et al., 2019;Verma et al., 2015; Table S11). Taken together, these results suggest that use of a single climate or hydrologic model may produce a misleading level of confidence to decision-makers seeking advice on managing watersheds with phosphorus impairments. ...
Article
Hydrologic models are applied increasingly with climate projections to provide insights into future hydrologic conditions. However, both hydrologic models and climate models can produce a wide range of predictions based on model inputs, assumptions, and structure. To characterize a range of future predictions, it is common to use multiple climate models to drive hydrologic models, yet it is less common to also use a suite of hydrologic models. It is also common for hydrologic models to report riverine discharge and assume that nutrient loading will follow similar patterns, but this may not be the case. In this study, we characterized uncertainty from both climate models and hydrologic models in predicting riverine discharge and nutrient loading. Six climate models drawn from the Coupled Model Intercomparison Project Phase 5 ensemble were used to drive five independently developed and calibrated Soil and Water Assessment Tool models to assess hydrology and nutrient loadings for mid-century (2046–2065) in the Maumee River Watershed, the largest watershed draining to the Laurentian Great Lakes. Under those conditions, there was no clear agreement on the direction of change in future nutrient loadings or discharge. Analysis of variance demonstrated that variation among climate models was the dominant source of uncertainty in predicting future total discharge, tile discharge (i.e. subsurface drainage), evapotranspiration, and total nitrogen loading, while hydrologic models were the main source of uncertainty in predicted surface runoff and phosphorus loadings. This innovative study quantifies the importance of hydrologic model in the prediction of riverine nutrient loadings under a future climate.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
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Article
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.
Article
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.
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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.
Thesis
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.
Article
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.
Article
We present a comprehensive evaluation of eleven process-based models to characterize the water cycle, 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 to reproduce surface runoff, groundwater, sediment transport, nutrient cycling, channel routing and collectively guide the management in Lake Erie Basin. Our analysis suggests that the available models either opted for simpler approximations of the multifaceted, non-linear 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 role of critical hydrological processes. Notwithstanding its overparameterization problem, MIKE-SHE 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. 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, that 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 non-stationarity of a changing climate.
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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.
Article
Appropriate land use planning plays an active role in soil and water conservation. Considering the financial investment and grain security limitations, land use planning practices should be applied focusing on the critical source areas (CSAs) rather than the complete region. In this study, the Soil and Water Assessment Tool (SWAT) model was used to identify CSAs for sediment control in the upper Huaihe River basin. A novel one‐at‐a‐time removal approach was proposed which involves individually removing the land use planning programme at sub‐basin level, after which the related runoff and sediment results were simulated by the validated SWAT model. Then, two influencing indexes (i.e., runoff yield and sediment yield) were used to evaluate the influences on runoff and sediment responses at the watershed outlet, caused by the removal of that land use planning programme. Finally, critical sub‐basins for land use planning were prioritized based on the weighted average of those influencing indexes. Calibration and validation results showed that the SWAT model well represented the monthly streamflow and sediment at the watershed outlet. The Nash–Sutcliffe efficiency values of monthly streamflow and sediment were generally greater than 0.75. Results of the integrated priorities revealed that the most CSAs affecting land use planning implementation were in sub‐basin 11, which was not the sub‐basin yielding the most sediment. The CSAs prioritization determined by the one‐at‐a‐time removal approach can achieve a better erosion control performance than that identified by the simulated sediment loads, which can be applied widely in targeting CSAs for implementation of watershed conservation practices with limited investment and disturbance.
Chapter
Nutrient loading from agriculture is a critical threat to aquatic ecosystems, affecting their ability to provide safe drinking water, and limiting the provision of ecosystem services such as water-based recreation. Efforts to manage the problem typically focus on encouraging, incentivising, or requiring use of best management practices to reduce nutrient inputs on farms and limit their transport to water systems. For example, protecting and restoring wetlands and riparian ecosystems, which filter nutrients from run off and offer co-benefits such as carbon sequestration, terrestrial and in-stream habitat, and recreational opportunities, are important strategies. However, in many agricultural catchments, nutrient concentrations in waterbodies remain high despite such interventions. Reasons for this are myriad and include low uptake of best management practices on farms, timelags in ecosystem response, legacy phosphorus stored in soil and lake sediments, and changing weather patterns associated with climate change. This chapter explores the potential contributions of resilience thinking to reducing nutrient loading to waterbodies and minimising its impacts by treating agricultural watersheds as social-ecological systems, recognising the pressures on freshwater ecosystems caused by human activities throughout the watershed as well as the reliance of such activities on functioning aquatic ecosystems and the services they provide. This involves more explicitly accounting for interactions within agricultural social-ecological systems, planning at the catchment scale, adaptive management, and new governance arrangements. We draw on some lessons learned from a range of innovations developed for technical management practices, policy and governance approaches. We translate these lessons into pathways for reduced nutrient loading for sustainable management of lakes in the face of changing climate, degrading aquatic ecosystems and increasing demand for land and food.
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How anticipated climate change might affect long-term outcomes of present-day agricultural conservation practices remains a key uncertainty that could benefit water quality and biodiversity conservation planning. To explore this issue, we forecasted how the stream fish communities in the Western Lake Erie Basin (WLEB) would respond to increasing amounts of agricultural conservation practice (ACP) implementation under two IPCC future greenhouse gas emission scenarios (RCP4.5: moderate reductions; RCP8.5: business-as-usual conditions) during 2020–2065. We used output from 19 General Circulation Models to drive linked agricultural land use (APEX), watershed hydrology (SWAT), and stream fish distribution (boosted regression tree) models, subsequently analyzing how projected changes in habitat would influence fish community composition and functional trait diversity. Our models predicted both positive and negative effects of climate change and ACP implementation on WLEB stream fishes. For most species, climate and ACPs influenced species in the same direction, with climate effects outweighing those of ACP implementation. Functional trait analysis helped clarify the varied responses among species, indicating that more extreme climate change would reduce available habitat for large-bodied, cool-water species with equilibrium life-histories, many of which also are of importance to recreational fishing (e.g., northern pike, smallmouth bass). By contrast, available habitat for warm-water, benthic species with more periodic or opportunistic life-histories (e.g., northern hogsucker, greater redhorse, greenside darter) was predicted to increase. Further, ACP implementation was projected to hasten these shifts, suggesting that efforts to improve water quality could come with costs to other ecosystem services (e.g., recreational fishing opportunities). Collectively, our findings demonstrate the need to consider biological outcomes when developing strategies to mitigate water quality impairment and highlight the value of physical-biological modeling approaches to agricultural and biological conservation planning in a changing climate.
Chapter
The coupled nature of FEW systems means the human and natural systems are linked such that human behavior impacts natural processes, and the outcomes of these natural processes influence human behavior. Effectively managing FEW systems requires understanding how humans behave and interact with their natural and social environments, as well as understanding the environmental impacts of social changes (e.g., population growth and urbanization). We discuss the importance of including more sophisticated models of human behavior in the study of FEW systems and provide examples of how past research has incorporated complexity in human behavior into models of these systems. We do so from the perspectives of psychology, economics, and decision science—all social sciences with well-developed theories and models of human behavior that are useful in informing models and policies. We present two case studies as examples of how research can explicitly account for human behavior in these systems. Finally, we discuss challenges in incorporating human behavior and adaptation into models of these systems and identify future directions for work in this field.
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Whether bottom hypoxia has long-lasting consequences for pelagic fish populations remains speculative for most ecosystems. We explored hypoxia’s influence on two pelagic zooplanktivores in Lake Erie that have different thermal preferences: cold-water rainbow smelt (Osmerus mordax) and warm-water emerald shiners (Notropis atherinoides). To assess acute effects, we combined predictive bioenergetics-based modeling with field collections made across the hypoxic season in central Lake Erie during 2005 and 2007. To assess chronic effects, we related fishery-independent and fishery-dependent catches with hypoxia severity and top predator (walleye, Sander vitreus) abundance during 1986-2014. As our modeling predicted, hypoxia altered rainbow smelt movement and distributions, leading to avoidance of cold, hypoxic bottom waters. In response, diets shifted from benthic to pelagic organisms, and consumption and energetic condition declined. These changes were lacking in emerald shiners. Our long-term analyses showed rainbow smelt abundance and hypoxia to be negatively related and suggested that hypoxia-avoidance increases susceptibility to commercial fishing and walleye predation. Collectively, our findings show that hypoxia can negatively affect pelagic fish populations over the long-term, especially those requiring cold water.
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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.
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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.
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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.
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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.
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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
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
Article
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.
Article
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.
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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.
Article
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.
Article
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