Management Practice Scenarios Research Articles

Quantifying the impacts of agricultural management and climate change on soil organic carbon changes in the uplands of Eastern China

In order to implement optimal farming practices for increasing soil organic carbon (SOC) in agro-ecosystems, there is a need for understanding how management practices and climate change alter SOC levels. This study quantified the influence of agricultural management practices and climatic factors on SOC changes in Eastern China’s upland-crop fields in northern Jiangsu Province for the period of 2010–2039, by using the DeNitrification-DeComposition (DNDC, version 9.5) model. We utilized the currently most detailed soil database, which is at a scale of 1:50,000, containing 17,024 soil polygons derived from 983 upland soil profiles. Across all the examined scenarios of agricultural management practices, our results show that the carbon sequestration potential in the upper layer soil (0–50cm) of the study area varied from 6.93 to 155.11Tg C during 2010–2039, with an average rate of 59 to 1317kg C ha−1 year−1. As a promising alternative, the combined scenario of crop residue return rate of 50% and farmyard manure incorporation rate of 50% is recommended for agricultural management practice in this region. Meanwhile, climate conditions play a significant role in the annual SOC changes as well. Air temperature increase of 2–4°C leads to 3.41–7.51Tg C decrease in SOC under conventional management for the entire study region. Decreasing or increasing precipitation by 20% would increase 0.57 Tg C or decrease 1.09Tg C under the conventional management scenario, respectively. Additionally, among all the soil groups, the fluvo-aquic soils have the highest C sequestration rate in most scenarios. Our findings could be used to inform optimal agricultural management toward climate mitigation.

Hydrologic modeling and evaluation of Best Management Practice scenarios for the Grand River watershed in Southern Ontario

Abstract The Grand River is the largest river in Southern Ontario feeding Lake Erie with water, sediment, and nutrients. Understanding the watershed hydrological processes is crucial to support decision making on reducing non-point source pollution from the watershed into Lake Erie. In this study, the Soil and Water Assessment Tool (SWAT) was adapted to Canadian conditions and applied to the Grand River watershed in Southern Ontario to simulate hydrologic processes based on available geospatial, climate, management, flow, and water quality data. The SWAT was calibrated based on flow, sediment, and nutrient concentrations at eight flow gauging stations and seven water quality stations. The calibrated model was then applied to evaluate the potential effects of Best Management Practices (BMPs) including nutrient management, buffer strip, cover crop, and wetland restoration on water quantity and water quality in the watershed. The evaluated results showed that the BMPs of nutrient management and wetland restoration have more significant impacts on nutrient reduction at the watershed outlet to Lake Erie based on the BMP implementation and extent that were applied in this study. The SWAT modeling, findings, challenges, and recommendations for future research in the Grand River watershed are also discussed in this paper.

Modeling Impacts of Residential and Agricultural Development and Beneficial Management Practice Scenarios on Phosphorus Dynamics in a Small Watershed

<abstract> <b><sc>Abstract.</sc></b> Both agricultural land uses and residential on-site wastewater systems (OWS) have the potential to be nonpoint sources of phosphorus (P) in rural watersheds. Watershed-scale computer models are a commonly used tool for evaluating the impacts of increased human development on P dynamics and for evaluating how beneficial management practices (BMPs) can reduce P loading. Many agricultural field BMPs have been evaluated using watershed-scale models; however, no studies have compared their efficacy to OWS BMPs in a mixed land use watershed. The objectives of this research were to (1) use the P on-site wastewater simulator (POWSIM) and the Soil and Water Assessment Tool (SWAT) to simulate different agricultural and residential development scenarios in the Thomas Brook watershed in Nova Scotia, Canada, and evaluate their impacts on sediment and total P (TP) loads and TP concentrations and (2) simulate and evaluate different individual and combinations of select agricultural and OWS BMPs. A 50-year simulation period was used for both the development and BMP scenarios. The development scenarios evaluated included increasing the residential population and conversion of hay fields or pastures to corn-based cropping regimes. The agricultural BMPs evaluated were (1) corn and rotational crop replacement with no-till agricultural land uses and (2) no-till corn. Decreased failure rates, increased watercourse setbacks, disposal field replacement, and the use of high P sorption filter media were the OWS BMPs evaluated. The agricultural development scenarios increased cumulative sediment and P loads at the watershed outlet, while the residential scenarios increased the frequency of hyper-eutrophic conditions in the stream during the last 20 simulated years. Agricultural crop replacement BMPs produced the highest reductions in cumulative sediment (13% to 46%) and TP loads (26% to 34%) but had no observable change on the in-stream trophic status. The OWS BMPs produced small reductions in TP loading (2% to 15%), no sediment load reductions, but had a positive effect on the trophic status. The best ranked combination of agricultural and OWS BMPs resulted in a cumulative TP load reduction of 58%, and the dominant trophic state at the end of the 50-year period was mesotrophic, as compared to eutrophic for the reference simulation. The best combination BMP scenario included replacing corn and rotational crops with pastures, using high P sorption filter media (5000 mg P kg^-1 media), and lowering of the OWS failure rate to 5%. The results of these modeling scenarios showed that agricultural BMPs were most effective in reducing cumulative P loads, while OWS BMPs were effective in mitigating in-stream eutrophication impacts. This study highlights the importance of identifying specific water quality issues that need to be targeted prior to implementing a watershed BMP strategy. Further model refinement and testing are required with improved field measurements to improve model confidence before the model should be used for planning and design purposes.

Application of risk-based multiple criteria decision analysis for selection of the best agricultural scenario for effective watershed management

Effective watershed management requires the evaluation of agricultural best management practice (BMP) scenarios which carefully consider the relevant environmental, economic, and social criteria involved. In the Multiple Criteria Decision-Making (MCDM) process, scenarios are first evaluated and then ranked to determine the most desirable outcome for the particular watershed. The main challenge of this process is the accurate identification of the best solution for the watershed in question, despite the various risk attitudes presented by the associated decision-makers (DMs). This paper introduces a novel approach for implementation of the MCDM process based on a comparative neutral risk/risk-based decision analysis, which results in the selection of the most desirable scenario for use in the entire watershed. At the sub-basin level, each scenario includes multiple BMPs with scores that have been calculated using the criteria derived from two cases of neutral risk and risk-based decision-making. The simple additive weighting (SAW) operator is applied for use in neutral risk decision-making, while the ordered weighted averaging (OWA) and induced OWA (IOWA) operators are effective for risk-based decision-making. At the watershed level, the BMP scores of the sub-basins are aggregated to calculate each scenarios’ combined goodness measurements; the most desirable scenario for the entire watershed is then selected based on the combined goodness measurements. Our final results illustrate the type of operator and risk attitudes needed to satisfy the relevant criteria within the number of sub-basins, and how they ultimately affect the final ranking of the given scenarios. The methodology proposed here has been successfully applied to the Honeyoey Creek-Pine Creek watershed in Michigan, USA to evaluate various BMP scenarios and determine the best solution for both the stakeholders and the overall stream health.

Modelling hydrological processes, crop yields and NPS pollution in a small sub-tropical catchment in South Africa using ACRU-NPS

The Agricultural Catchment Research Unit—Nitrates, Phosphorous and Sediments (ACRU-NPS) model, which simulates runoff, sediment and nutrient (NO3 and P) production in agricultural catchments, is used to evaluate the impact of farming practices and land-use changes on crop yields, water discharge, sediment and nutrient loads in the 41-km2 Mkabela catchment in the KwaZulu-Natal midlands, South Africa. The ACRU-NPS model was modified with the following objectives: (a) to develop and incorporate algorithms to simulate crop growth and NPS pollution dynamics in process zones and control features; (b) simulate sediment and nutrient production from land segments for various land uses; (c) model crop yield where crop growth is influenced by water and nitrogen stress; and (d) simulate sediment and nutrient fate at controls and buffers in the stream network. Five management practice scenarios were simulated and run with a series of fertilizer management applications. The resulting crop yields, water discharge, sediment and nutrient loadings were analysed. On average, doubling fertilizer application from base rates resulted in the highest sugarcane yield increase of 5 t/ha, zero fertilizer application resulted in the highest sugarcane yield reduction of 11 t/ha, while applying deficit irrigation, with base fertilizer application rates retained, resulted in 16 t/ha sugarcane yield increase. Flood attenuation and retention capacities for the total non-point source (NPS) pollutants for the period 2006–2012 were also investigated in the study area.

The Necessities of HR practices in RMG Sector of Bangladesh

This study will be performed to find out whether the RMG sectors in Bangladesh are practicing the right process of HR functions and whether this sector is considering HR as an integral part of its business. Simple Random Sampling Method is applied in this study. The study will have both practical and academic value. It will lead anyone to get a clear idea about Human Resource Management Practices, its procedure and present scenario of RMG sector in comparison with BGMEA rules and regulations. This study will also focus on the issues of fraud and forgery in Human Resource Management Practices, and their guidelines in prevention. On the other hand the findings of the study will direct to think about appropriate actions and steps for the betterment of the existing practices.&#x0D;

Environmental life-cycle assessment of rapeseed produced in Central Europe: addressing alternative fertilization and management practices

This article presents a life-cycle assessment (LCA) of rapeseed produced in Central Europe (France, Germany and Poland), addressing different fertilization and management practices. Two alternative fertilization scenarios were compared (on the basis of the most common fertilizer types used in Europe, namely nitrogen, phosphate P2O5, and potash K2O fertilizers) and two different scenarios of soil management practices were assessed (taking into account climate and soil type prevalent in each region). Six environmental impact categories were investigated: abiotic depletion; global warming; acidification; eutrophication; ozone layer depletion; and photochemical oxidation. Results showed that the choice of fertilizer type had significant implications in the environmental impacts. Calcium ammonium nitrate (CAN) manufacturing had considerably higher greenhouse gas emissions than urea production, due to the use of nitric acid in the former. In terms of field emissions, ammonia and nitrate released following the application of nitrogen fertilizers dominated the acidification and eutrophication impacts. Nitrogen–phosphorus–potassium (NPK) compounds showed particularly high impacts in terms of photochemical oxidation, as a result of sulfur dioxide emissions from manufacturing. The remaining fertilizers (P2O5 and K2O) hardly contributed to the impacts. Soil carbon change associated with different agricultural management practices significantly contributed to the greenhouse gas (GHG) intensity of rapeseed production, but important soil carbon stock variations were calculated: between 938 (release) and 271 kg CO2eq/1000 kg dry seeds (sequestration) due to different standard soil organic carbon contents in the three rapeseed production systems and alternative tillage methods in the reference scenarios of land management.

Impact of water management practice scenarios on wastewater flow and contaminant concentration

Due to frequent droughts and rapid population growth in urban areas, the adoption of practices to reduce the usage of fresh water is on the rise. Reduction in usage of fresh water can be achieved through various local water management practices (WMP) such as Water Demand Management (WDM) and use of alternative water sources such as Greywater Recycling (GR) and Rainwater Harvesting (RH). While the positive effects of WMPs have been widely acknowledged, the implementation of WMPs is also likely to lower the wastewater flow and increase the concentration of contaminants in sewage. These in turn can lead to increases in sewer problems such as odour and corrosion. This paper analyses impacts of various WMP scenarios on wastewater flow and contaminant load. The Urban Volume and Quality (UVQ) model was used to simulate wastewater flow and the associated wastewater contaminants from different WMP scenarios. The wastewater parameters investigated were those which influence odour and corrosion problems in sewerage networks due to the formation of hydrogen sulphide. These parameters are: chemical oxygen demand (COD), nitrate (NO3−), sulphate (SO42−), sulphide (S2−) and iron (Fe) that were contributed by the households (not including the biochemical process in sewer pipe). The results will help to quantify the impact of WMP scenarios on odour and corrosion in sewerage pipe networks. Results show that the implementation of a combination of WDM and GR had highly increased the concentration of all selected contaminant that triggered the formation of hydrogen sulphide, namely COD, sulphate and sulphide. On the other hand, the RH scenario had the least increase in the concentration of the contaminants, except iron concentrations. The increase in iron concentrations is actually beneficial because it inhibits the formation of hydrogen sulphide.

Potential carbon sequestration of European arable soils estimated by modelling a comprehensive set of management practices.

Bottom-up estimates from long-term field experiments and modelling are the most commonly used approaches to estimate the carbon (C) sequestration potential of the agricultural sector. However, when data are required at European level, important margins of uncertainty still exist due to the representativeness of local data at large scale or different assumptions and information utilized for running models. In this context, a pan-European (EU + Serbia, Bosnia and Herzegovina, Montenegro, Albania, Former Yugoslav Republic of Macedonia and Norway) simulation platform with high spatial resolution and harmonized data sets was developed to provide consistent scenarios in support of possible carbon sequestration policies. Using the CENTURY agroecosystem model, six alternative management practices (AMP) scenarios were assessed as alternatives to the business as usual situation (BAU). These consisted of the conversion of arable land to grassland (and vice versa), straw incorporation, reduced tillage, straw incorporation combined with reduced tillage, ley cropping system and cover crops. The conversion into grassland showed the highest soil organic carbon (SOC) sequestration rates, ranging between 0.4 and 0.8 t Cha(-1) yr(-1) , while the opposite extreme scenario (100% of grassland conversion into arable) gave cumulated losses of up to 2 Gt of C by 2100. Among the other practices, ley cropping systems and cover crops gave better performances than straw incorporation and reduced tillage. The allocation of 12 to 28% of the European arable land to different AMP combinations resulted in a potential SOC sequestration of 101-336 Mt CO2 eq. by 2020 and 549-2141 Mt CO2 eq. by 2100. Modelled carbon sequestration rates compared with values from an ad hoc meta-analysis confirmed the robustness of these estimates.

Assessing biogeochemical effects and best management practice for a wheat–maize cropping system using the DNDC model

Abstract. Contemporary agriculture is shifting from a single-goal to a multi-goal strategy, which in turn requires choosing best management practice (BMP) based on an assessment of the biogeochemical effects of management alternatives. The bottleneck is the capacity of predicting the simultaneous effects of different management practice scenarios on multiple goals and choosing BMP among scenarios. The denitrification–decomposition (DNDC) model may provide an opportunity to solve this problem. We validated the DNDC model (version 95) using the observations of soil moisture and temperature, crop yields, aboveground biomass and fluxes of net ecosystem exchange of carbon dioxide, methane, nitrous oxide (N2O), nitric oxide (NO) and ammonia (NH3) from a wheat–maize cropping site in northern China. The model performed well for these variables. Then we used this model to simulate the effects of management practices on the goal variables of crop yields, NO emission, nitrate leaching, NH3 volatilization and net emission of greenhouse gases in the ecosystem (NEGE). Results showed that no-till and straw-incorporated practices had beneficial effects on crop yields and NEGE. Use of nitrification inhibitors decreased nitrate leaching and N2O and NO emissions, but they significantly increased NH3 volatilization. Irrigation based on crop demand significantly increased crop yield and decreased nitrate leaching and NH3 volatilization. Crop yields were hardly decreased if nitrogen dose was reduced by 15% or irrigation water amount was reduced by 25%. Two methods were used to identify BMP and resulted in the same BMP, which adopted the current crop cultivar, field operation schedules and full straw incorporation and applied nitrogen and irrigation water at 15 and 25% lower rates, respectively, than the current use. Our study indicates that the DNDC model can be used as a tool to assess biogeochemical effects of management alternatives and identify BMP.

Modeling water quality to improve agricultural practices and land management in a tunisian catchment using the soil and water assessment tool.

Agriculture intensification has impaired water quality. In this study, the risk of pollution by nitrates was assessed by experimental monitoring, spatial integration of farm census, and modeling of water quality using the Soil and Water Assessment Tool (SWAT), version 2009, over the period of 1990 to 2006 for a catchment located northern Tunisia. Under a semiarid climate, the water quality is influenced by the predominating agriculture activities. The hydrological results are compared with the observed flows derived from measurements at the outlet of the Joumine watershed. Model performance showed good statistical agreements, with a Nash-Sutcliffe efficiency of 0.9 and a value of 0.92 after monthly calibration. The model predicted the timing of monthly peak flow values reasonably well. During the validation period, SWAT simulations were nearly as accurate, with Nash-Sutcliffe efficiency and values of 0.89 and 0.92, respectively. The model was used to simulate NO concentrations. The predicted NO concentration values were compared with in situ measured concentrations. The simulated and measured NO-N concentrations varied in the same range of 0 to 5 mg L at the E3 and E5 locations. The calibrated model was then used for simulating the impact of the best management practice scenarios to reduce NO loads to the river. The first set-up consisted of reducing the N fertilizer application by 20 and 100% from the current state. These two scenarios induced a reduction in NO loads by 22 and 72%, respectively. The second set-up consisted of using vegetation filter strips. The last scenario combined filter strips and a reduction of 20% in N fertilizer application. Results showed NO reduction rates of 20 and 36%, respectively. The SWAT model allowed managers to have several options to improve the water quality in the Joumine watershed.

Eutrophication assessment and management methodology of multiple pollution sources of a landscape lake in North China

Landscape lakes in the city suffer high eutrophication risk because of their special characters and functions in the water circulation system. Using a landscape lake HMLA located in Tianjin City, North China, with a mixture of point source (PS) pollution and non-point source (NPS) pollution, we explored the methodology of Fluent and AQUATOX to simulate and predict the state of HMLA, and trophic index was used to assess the eutrophication state. Then, we use water compensation optimization and three scenarios to determine the optimal management methodology. Three scenarios include ecological restoration scenario, best management practices (BMPs) scenario, and a scenario combining both. Our results suggest that the maintenance of a healthy ecosystem with ecoremediation is necessary and the BMPs have a far-reaching effect on water reusing and NPS pollution control. This study has implications for eutrophication control and management under development for urbanization in China.

Development of Best Management Practices for Controlling the Non-Point Sources of Pollution Around Lake Victoria Using SWAT Model: A Case of Simiyu Catchment Tanzania

Recent studies carried out in Lake Victoria Basin have identified major sources of Non-Point Source (NPS) of pollution in the Simiyu catchment of Lake Victoria using land-uses of 1975 and 2006 and compared the relative impact of land-use change on sediment and nutrient load (P and N) into the Lake. The main aim of this study was to identify and develop Best Management Practices to control NPS pollution in the Simiyu Catchment. The SWAT model was used to stimulate and assess the Best Management Practices Scenario for the catchment. The catchment was divided into seven (7) sub-basins. The results show that there was no intensive use of artifical fertilisers in the catchment and manure is the major type of fertiliser in use. Simulation was done for the period 2000 to 2005. High nutrient concentration was observed in Sub-basin 6; 0.558-0.779 kgN/ha/yr than in Sub-basin 7; 0.018-0.115 kgN/ha/yr, despite the larger area of coverage by the latter. This is also irrespective of the fact that Sub-basin 7 covers a larger area, 3,426.52 km 2 compared to Sub-basin 6 (72.97 km 2 ) and Sub-basin 4 (618.16 km 2 ). Relatively, considering their size, Sub-basin 6 produces higher pollution than Sub-basin 7. It was also observed that the sediment yield from the whole catchment reduced from 81,222 ton/yr to 98,400ton/yr.It was observed that to control the NPS pollution problem, Best Management Practices like reduced manure application rate, tillage and contour yielded a decrease of 1.4% in N load and 1.57% in sediment load. As a result, it was concluded that the SWAT modelling tool can be used in developing Best Management Practices because pollutant proc- esses per sub-catchment had been fully understood. With good model performance, developing management strategies to control NPS pollution around Lake Victoria can be achieved using the SWAT model. The BMPs have been devised de- pending on the sub-basin, which has a big collective reduction and control in NPS pollution in the whole catchment.

Ecosystem approach to water resources management using the MIKE 11 modeling system in the Strymonas River and Lake Kerkini

The ability to apply an ecosystem approach to the Strymonas River catchment was investigated using the MIKE 11 modeling system for the simulation of surface water. The Strymonas River catchment is shared mainly between Bulgaria and Greece. The river feeds the artificial Lake Kerkini, a significant wetland ecosystem, and further downstream it outflows to the Gulf of Strymonikos, whose estuary ecosystem is very important for fisheries, biodiversity and tourism. MIKE 11-NAM was used for the simulation of rainfall-runoff process in the Strymonas River catchment and MIKE 11-HD was used to simulate the unsteady flow of the Strymonas River and to apply management rules based on the water level of Lake Kerkini. Two water level management scenarios were investigated. The first scenario referred to the mean daily-observed water level of Lake Kerkini between 1986 and 2006, and the second scenario represented adjustments necessary to fulfill the lake's ecosystem requirements. Under the current water level management practices (Scenario 1), the Strymonas River-Lake Kerkini system has enough water to fulfill its Irrigation Water Requirements (IWR) in normal and wet years while a slight deficit is appeared in dry years; however, both Lake Kerkini and the Strymonas River estuary ecosystems are subject to pressures, since reduction of the forest area has been recorded. Applying the ecosystem approach (Scenario 2), the protection of the riparian forest of Lake Kerkini is achieved while in normal and wet years the IWR are fulfilled and the deficit of the IWR is increased in dry years. Compared to Scenario 1, the pressure of the Strymonas River estuary ecosystem is slightly increased.

Environmental and economic impacts of reducing total phosphorous runoff in an agricultural watershed

The economy of northwest Arkansas relies greatly upon livestock and poultry production. The supply of production by-products is increasingly coming under scrutiny as an important source of water pollution in the region. This study uses stochastic dominance techniques to evaluate, environmentally and economically, a range of ten best management practice scenarios to lessen water pollution in the Lincoln Lake watershed. The goal is to generate rankings that could be useful for supporting producers’ and watershed managers’ selection of management practices to reduce total phosphorous losses in runoff. Specifically, this study compares scenarios in terms of net return risk reduction for bermudagrass hay producers. The results showed that environmental and economic rankings differ from each other. Although all scenarios analyzed were effective in reducing total phosphorous losses when compared to a baseline, six of them also decreased net returns. This suggests that including some best management practices may lead to increased net return risk. However, some scenarios were identified that may increase net returns, reduce total phosphorous losses and do not differ considerably from producers’ current management practices. The previous results suggested that the joint environmental-economic impact was important when considering scenarios and that producers’ risk attitudes and best management practices’ economic impacts should be accounted for when selecting scenarios. Producers and watershed managers can weigh trade-offs between total phosphorous losses reduction and net returns variability when making water conservation decisions.

Sediment management modelling in the Blue Nile Basin using SWAT model

Abstract. Soil erosion/sedimentation is an immense problem that has threatened water resources development in the Nile river basin, particularly in the Eastern Nile (Ethiopia, Sudan and Egypt). An insight into soil erosion/sedimentation mechanisms and mitigation methods plays an imperative role for the sustainable water resources development in the region. This paper presents daily sediment yield simulations in the Upper Blue Nile under different Best Management Practice (BMP) scenarios. Scenarios applied in this paper are (i) maintaining existing conditions, (ii) introducing filter strips, (iii) applying stone bunds (parallel terraces), and (iv) reforestation. The Soil and Water Assessment Tool (SWAT) was used to model soil erosion, identify soil erosion prone areas and assess the impact of BMPs on sediment reduction. For the existing conditions scenario, the model results showed a satisfactory agreement between daily observed and simulated sediment concentrations as indicated by Nash-Sutcliffe efficiency greater than 0.83. The simulation results showed that applying filter strips, stone bunds and reforestation scenarios reduced the current sediment yields both at the subbasins and the basin outlets. However, a precise interpretation of the quantitative results may not be appropriate because some physical processes are not well represented in the SWAT model.

Reductions in non-point source pollution through different management practices for an agricultural watershed in the Three Gorges Reservoir Area

Non-point source water pollution generated by agricultural production is considered a major environmental issue in the Three Gorges Reservoir Area (TGRA) of China. The Annualised Agricultural Non-Point Source Pollution (AnnAGNPS) model was selected to assess the impact of the application of various management treats, including seven crops, five fertilizer levels and three-group management practice scenarios, on water quality from Heigou River Watershed in TGRA. The scenario subsets include conservation tillage practice (CTP), conservation reserve program (CRP) and conversion of cropland into forestland program (CCFP). Results indicated that tea can not be replaced by other crops because comparatively tea resulted in a higher sediment yield. CTP with no-tillage was more effective to reduce sediment yield, but could increased nutrient loss. CRP reduced sediment yield significantly, but slightly benefited on nutrient loss. CCFP reduced not only sediment yield but also the nutrient loss significantly. The conversion of cropland with a slope greater than 10° into forestland was found to be the best scenario as the sediment yield export is less than 5 tons/ha and nutrient loss is within the permissible limit.

Economic and Environmental Impacts of LSNT and Cover Crops for Nitrate-Nitrogen Reduction in Walnut Creek Watershed, Iowa, Using FEM and Enhanced SWAT Models

Nitrate nitrogen (NO 3 -N) enriched water originates from subsurface drains or tiles that underlay many fields in the Corn Belt and is the primary source of NO 3 -N to surface waters in this region. To better assess the fate and transport of nutrients, such as NO 3 -N, the tile drain and pothole components of SWAT (Soil and Water Assessment Tool) were enhanced and modified in the previous component of this study. In this study, the environmental and economic impacts of various best management practice (BMP) scenarios often adopted by local farmers to reduce sediment and nutrient loadings (in particular NO 3 -N) were evaluated using the modified SWAT (SWAT-M) and FEM (Farm-level Economic Model) models. Measured values of water quality indicators from the Walnut Creek watershed (WCW) located in central Iowa were used to verify the capability of SWAT-M to predict the impact of late-spring nitrate test (LSNT) and rye cover crop management on NO 3 -N reduction at the subbasin level. The results obtained from SWAT-M simulation results, similar to field measurement data, indicated a 25% reduction in NO 3 -N under the LSNT scenario. FEM results indicated a corresponding increased annual cost of $6/ha across all farms in the watershed. Simulation of other scenarios, including winter cover cropping and a combination of LSNT and cover cropping at different adoption rates within WCW, resulted in a progressive reduction in sediment and nutrient losses as adoption rates increased. Use of the rye cover crop added about $25/ha to $35/ha to the annual cost of the average farm, indicating that some cost-share support may be necessary to encourage farmers to use winter cover crops.

Uncertainty Analysis for Coupled Watershed and Water Quality Modeling Systems

A series of uncertainty analysis methods was applied to investigate the propagation of parameter uncertainty within a coupled model system and to evaluate the effects of uncertainty on model outputs and decision-making processes. First-order error analysis showed that among a large number of model parameters, only a few significantly affected the variation in pollutant loads at the watershed outlets and concentrations in the receiving body of water, and the variation in pollutant concentrations is greater than the variation in pollutant loads. The uncertainty analysis regarding the loads and concentrations showed different patterns, underscoring the importance of a complete uncertainty analysis and the need for an explicit quantification of the errors associated with the predicted loads. Monte Carlo simulation showed that best management practice scenarios considered as a safe scheme based on a deterministic model could actually lead to a significant risk of violating the water quality standards when model uncertainty is considered. With a modeling framework that considers uncertainty, feasible alternatives can be evaluated and ranked based on their risks of exceeding the target water quality criteria.

Watershed-Scale Impacts of Forest Buffers on Water Quality and Runoff in Urbanizing Environment

Forestry practices that are applied to buffer regions can be used as a strategy to improve water quality and flow regime in urbanizing watersheds. This study evaluates watershed-wide impacts of buffering urban forestry practices. Watershed simulation modeling is used to study the effectiveness of best management practices (BMPs) scenarios representing riparian and street buffers on water quality, quantity, and open space in rural, suburban, and urbanized environments. Results indicate that the watershed health can be improved through location-specific application of urban forestry practices. The proportion of urban forest cover reduced sediment and nutrient loading, decreased stormwater runoff, and increased groundwater recharge in urbanizing watersheds. Reduction in variability of watershed processes indicate that forest BMPs make the watershed more adaptive to handling adverse conditions, such as large storms, nonpoint source pollution, flooding, and high winds. Watersheds that are starting to get urbanized responded well to the BMP scenarios compared to more urbanized subbasins. General strategies include a focus on increasing pervious cover of the watershed with a higher priority in riparian and street buffers. Specific tree species and practical issues in forest buffering are also discussed. Policies like financial incentives and encouraging voluntary participation can be used to improve urban watersheds.