BIOECONOMIC MODELING TO ASSESS ECONOMIC AND WATER QUALITY IMPACTS OF LAND USE CHANGE

Changes in water quality and agricultural and forest revenues due to land use changes are compared. A biophysical model estimates the effect in nitrogen and phosphorus runoff and sediment deposition. The results are combined with farm enterprise budgets to estimate the economic returns resulting from land use changes.Land Economics/Use,

Modeling of first-flush reactor for stormwater treatment

Stormwater runoff is one of the most common sources of non-point source water pollution to lakes, rivers and estuaries. Nitrate-nitrogen in stormwater runoff is an important limiting factor to the eutrophication phenomenon. While most pollutants and nutrients, including nitrate-nitrogen, in stormwater are discharged into receiving waters during the first-flush period, no existing Best Management Practices (BMPs) are specifically designed to capture and treat the first-flush portion of urban stormwater runoff. In addition, nitrate-nitrogen removal rates of most existing BMPs are relatively low. This thesis presents results from both laboratory experiments and numerical modeling of nitrate-nitrogen removal in a designed first-flush reactor. A new numerical tool, called VART-DN model, for simulation of denitrification process in the designed first-flush reactor was developed using the Variable Residence Time (VART) model. The new model is capable of simulating various processes and mechanisms responsible for denitrification in the first-flush reactor, including (1) dispersion and transport, (2) mass exchange, (3) oxygen variation, (4) bacterial growth, and (5) nitrate-nitrogen consumption. The VART-DN model is intended to investigate the influence of oxygen, biomass, dissolved carbon, and temperature on denitrification process. The data used in the development of the VART-DN model were from laboratory experiments conducted using both highway stormwater and secondary wastewater. Based on sensitivity analysis results of model parameters, the dispersion coefficient, maximum nitrate utilization rate in mobile phase, biomass concentration, oxygen inhibition constant, biomass inhibition constant, temperature and temperature coefficient for denitrification have significant influence on the denitrification process, with percent change in root mean square error (RMSE) being 16.9%, 15.8%, -13.1%, -11.5%, 14.5%, -9.2% and -29.7%, respectively, when values of the parameters increase by 10%. The average removal rate of nitrate-nitrogen in natural stormwater was 92.05%. The average influent and effluent concentrations in the column experiment with wastewater were 1.189 mg/L and 0.260 mg/L, respectively, with a removal rate of 78.1% for nitrate-nitrogen. The VART-DN model results for the denitrification process of natural stormwater showed good agreements with observed data; the simulation error was lower than 9.0%. The RMSE for simulating denitrification process of wastewater was 0.8157, demonstrating the efficacy of the VART-DN model

Simulation of Daily Flow Pathways, Tile-Drain Nitrate Concentrations, and Soil-Nitrogen Dynamics Using SWAT

Tile drainage significantly alters flow and nutrient pathways and reliable simulation at this scale is needed for effective planning of nutrient reduction strategies. The Soil and Water Assessment Tool (SWAT) has been widely utilized for prediction of flow and nutrient loads, but few applications have evaluated the model\u27s ability to simulate pathway-specific flow components or nitrate-nitrogen (NO3-N) concentrations in tile-drained watersheds at the daily time step. The objectives of this study were to develop and calibrate SWAT models for small, tile-drained watersheds, evaluate model performance for simulation of flow components and NO3-N concentration at daily intervals, and evaluate simulated soil-nitrogen dynamics. Model evaluation revealed that it is possible to meet accepted performance criteria for simulation of monthly total flow, subsurface flow (SSF), and NO3-N loads while obtaining daily surface runoff (SURQ), SSF, and NO3-N concentrations that are not satisfactory. This limits model utility for simulating best management practices (BMPs) and compliance with water quality standards. Although SWAT simulates the soil N-cycle and most predicted fluxes were within ranges reported in agronomic studies, improvements to algorithms for soil-N processes are needed. Variability in N fluxes is extreme and better parameterization and constraint, through use of more detailed agronomic data, would also improve NO3-N simulation in SWAT. Editor\u27s note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series

Simulating hydrological and nonpoint source pollution processes in a karst watershed: A variable source area hydrology model evaluation

AbstractAn ecohydrological watershed model can be used to develop an efficient watershed management plan for improving water quality. However, karst geology poses unique challenges in accurately simulating management impacts to both surface and groundwater hydrology. Two versions of the Soil and Water Assessment Tool (SWAT), Regular-SWAT and Topo-SWAT (which incorporates variable source area hydrology), were assessed for their robustness in simulating hydrology of the karstic Spring Creek watershed of Centre County, Pennsylvania, USA. Appropriate representations of surface water – groundwater interactions and of spring recharge – discharge areas were critical for simulating this karst watershed. Both Regular-SWAT and Topo-SWAT described the watershed discharge adequately with daily Nash-Sutcliffe efficiencies (NSE) ranging from 0.77 to 0.79 for calibration and 0.68–0.73 for validation, respectively. Because Topo-SWAT more accurately represented measured daily streamflow, with statistically significant improvement of NSE over Regular-SWAT during validation (p-value=0.05) and, unlike Regular-SWAT, had the capability of spatially mapping recharge/infiltration and runoff generation areas within the watershed, Topo-SWAT was selected to predict nutrient and sediment loads. Total watershed load estimates (518t nitrogen/year, 45t phosphorus/year, and 13600t sediment/year) were within 10% of observed values (−9.2% percent bias for nitrogen, 6.6% for phosphorous, and 5.4% for sediment). Nutrient distributions among transport pathways, such as leaching and overland flow, corresponded with observed values. This study demonstrates that Topo-SWAT can be a valuable tool in future studies of agricultural land management change in karst regions

CLIMATE CHANGE IMPACTS ON THE SOIL EROSION AND NUTRIENT LOSSES IN THE GREAT LAKES REGION

Pollutants from non-point sources (NPS) have become the primary reason for water quality degradation in the Great Lakes region after great progress has been made in reducing point source pollution through the enforcement of total maximum daily loads (TMDL). Climate change may impact NPS pollutant transportation processes through influencing runof

Improved assessment of nitrogen and phosphorus fate and transport for intensively managed irrigated stream-aquifer systems

2019 Fall.Includes bibliographical references.Nitrogen (N) and Phosphorus (P) are essential elements for animal nutrition and plant growth. However, over the previous decades, excessive loading of fertilizers in agricultural activities has led to elevated concentrations of N and P contaminations in surface waters and groundwater worldwide and associated eutrophication. Therefore, precisely understanding and representation of water movement and fate and transport of N and P within a complex dynamic groundwater-surface water system affected by agricultural practices is of essential importance for sustaining ecological health of the stream-aquifer environment while maintaining high agricultural productivity. Modeling tools often are used to assess N and P contamination and evaluate the impact of management practices. Such models include land surface-based watershed models such SWAT, and aquifer-based models that simulate spatially-distributed groundwater flow. However, SWAT simulates groundwater flow in a simplistic fashion and therefore is not suited for watersheds with complex groundwater flow patterns and groundwater-surface interactions, whereas groundwater models do not simulate land surface processes. This dissertation establishes the modeling capacity for assessing the movement, transformation, and storage of nitrate (NO₃) and soluble P in intensively managed irrigated stream-aquifer systems. This is accomplished by (1) developing a method to apply the SWAT model to such a system, and includes: designating each cultivated field as an individual hydrologic response unit (HRU), crop rotations to simulate the impact of changing crop types for each cultivated field, including N and P mass in irrigation water, and seepage from earthen irrigation canals into the aquifer; (2) simulating land surface hydrology, groundwater flow, and groundwater-surface water interactions in the system using the coupled flow model SWAT-MODFLOW, with the enhanced capability of linkage between SWAT groundwater irrigation HRUs and MODFLOW pumping cells, and the use of MODFLOW's EVT package to simulate groundwater evapotranspiration; and (3) linking RT3D, a widely used groundwater reactive solute transport model, to SWAT-MODFLOW to credibly represent of NO₃-N and soluble P fate and transport processes in irrigated agroecosystems to evaluate best management practices for nutrient contamination. This last phase will also address the uncertainty in system output (in-stream nutrient loads and concentrations, groundwater nutrient concentrations model predictions). Each modeling phase is applied to a 734 km² study region in the Lower Arkansas River Valley (LARV), an alluvial valley in Colorado, USA, which has been intensively irrigated for over 130 years and is threatened by shallow water tables and nutrient contamination. Multiple best management practices (BMPs) are investigated to analyze the effectiveness in reducing NO₃-N and soluble P contamination in the LARV. These strategies are related to irrigation management, nutrient management, water conveyance efficiency, and tillage operations. The most effective individual BMP in most areas is to decrease fertilizer by 30%, resulting in average NO₃-N and soluble P concentrations within the region could be reduced by 14% and 9%, respectively. This individual BMP could lower the average NO₃-N concentrations by 19% and soluble P concentrations by 2%. Combinations of using 30% irrigation reduction, 30% fertilization reduction, 60% canal seepage, and conservation tillage are predicted to have the greatest overall impact that can not only provide a decrease of groundwater concentration in NO₃-N up to 41% and soluble P concentration up to 8%, but also reduce the median of the in-stream NO₃-N and soluble P to meet the Colorado interim standard. As nutrient conditions within the Lower Arkansas River Valley are typical of those in many other intensively irrigated regions, the results of this dissertation and the developed modeling tools can be applied to other watersheds worldwide

Modeling Water Quality in Southern Saskatchewan Watersheds

The presence of accumulated nutrients in surface waters is a great concern for water quality. In Saskatchewan, for many streams, data on water quality is limited both spatially and temporally. An eco-hydrological model is a relatively low-cost method to help assess water quality where there are limited measurements. The study area is located in the Canadian prairie region where potholes are the dominant landscape feature and farming is an extensive activity. Potholes are closed-surface depressions that have a significant role in the prairie hydrologic cycle, flood mitigation, and water quality. The current modelling study was conducted in three southern Saskatchewan watersheds: Pipestone Creek above Moosomin Lake, Swift Current Creek below Rock Creek, and Lightning Creek near Carnduff. The hydrological model SWAT (the Soil and Water Assessment Tool) with the Probability Distributed Landscape Depressions module (SWAT-PDLD) (with seasonally variable soil erodibility) used in simulating flow and water quality results were compared to SWAT with its in-built pond routine (SWAT-lumped). Model results were then used to determine pond spilling and non-spilling period to examine whether any relationships between observed nutrient loading and streamflow differed during spilling and non-spilling periods. Both the SWAT-PDLD and SWAT-lumped models showed “good” performance for calibration period and “satisfactory” performance for validation period respectively for streamflow simulation based on statistical metrics for Pipestone Creek and Lightning Creek watershed. However, the SWAT-PDLD performed “good” for sediment export, total phosphorus export and total nitrogen export simulation whereas the SWAT-lumped model performed “satisfactory” for the same cases. Simulation results were improved using SWAT-PDLD over SWAT-lumped model. Spilling and non-spilling events were identified and categorized based on pond outflow contribution to streamflow. Both models could not satisfactorily simulate the streamflow for the Swift Current Creek watershed. It has been noticed that the observed total nitrogen load was significantly higher during model-predicted spilling periods than non-spilling periods in the Lightning Creek watershed. However, observed sediment export and total phosphorus export did not appear any different between spilling and non-spilling events. In the Pipestone Creek watershed, the relationship between loadings and streamflow did not appear to be different during spilling and non-spillling periods for sediment export, nitrogen, and phosphorus

Assessment of the spatial and temporal variations of water quality for agricultural lands with crop rotation in China by using a HYPE model

Many water quality models have been successfully used worldwide to predict nutrient losses from anthropogenically impacted catchments, but hydrological and nutrient simulations with little data are difficult considering the transfer of model parameters and complication of model calibration and validation. This study aims (i) to assess the performance capabilities of a new and relatively more advantageous model-hydrological predictions for the environment (HYPE) to simulate stream flow and nutrient load in ungauged agricultural areas by using a multi-site and multi-objective parameter calibration method and (ii) to investigate the temporal and spatial variations of total nitrogen (TN) and total phosphorous (TP) concentrations and loads with crop rotation using the model for the first time. A parameter estimation tool (PEST) was used to calibrate parameters, which shows that the parameters related to the effective soil porosity were most sensitive to hydrological modeling. N balance was largely controlled by soil denitrification processes, whereas P balance was influenced by the sedimentation rate and production/decay of P in rivers and lakes. The model reproduced the temporal and spatial variations of discharge and TN/TP relatively well in both calibration (2006–2008) and validation (2009–2010) periods. The lowest NSEs (Nash-Suttclife Efficiency) of discharge, daily TN load, and daily TP load were 0.74, 0.51, and 0.54, respectively. The seasonal variations of daily TN concentrations in the entire simulation period were insufficient, indicated that crop rotation changed the timing and amount of N output. Monthly TN and TP simulation yields revealed that nutrient outputs were abundant in summer in terms of the corresponding discharge. The area-weighted TN and TP load annual yields in five years showed that nutrient loads were extremely high along Hong and Ru rivers, especially in agricultural lands

Evaluation of subsurface drainage on phosphorus losses and application of the SoilIceDB model in the Black Hawk Lake Watershed, Iowa

The Upper Midwestern United States is extensively tile drained and drainage provides a preferential pathway for nutrient losses from cropland. Phosphorus (P) in subsurface drainage is the focus of current research on agricultural nutrient losses, however, the effects of best management practice (BMP) implementation on drainage phosphorus losses is unclear. Phosphorus and suspended solids losses were monitored at five sites — two streams, two tile drain outlets, and a grassed waterway — located in three paired subwatersheds of Iowa’s Black Hawk Lake watershed. Subwatersheds ranged in size from 221.23-822.49 hectares and BMP implementation ranged from 22.5-87.5% of the subwatershed area. Specific water quality analytes examined include total phosphorus (TP), dissolved reactive phosphorus (DRP), total suspended solids (TSS), and volatile suspended solids (VSS). The results from the study reveal that drainage analyte losses can equal or exceed those of surface waters. Precipitation events accounted for the majority of analyte losses at each of the subwatersheds. An analysis of intra-event samples from the five monitoring sites showed that flow is the driving factor of event analyte concentrations. Results from the paired watersheds indicate that BMP implementation has a positive impact on P and suspended solids losses in both surface and drainage waters. This study also evaluated the performance of the new drainage phosphorus and sediment loss model, SoilIceDB, at the small catchment scale as well as its applicability to cropland outside of Scandinavia. Preliminary results suggest that with more extensive calibration, the model will be able to acceptably simulate drainage flow and DRP losses. Establishing relationships between BMP implementation and P losses and a successful model will assist water quality improvement projects and could identify areas for remediation and BMP implementation

Effects of local land-use policies and anthropogenic activities on water quality in the upstream Sesan River Basin, Vietnam

Study region: This study focuses on the upstream Sesan River Basin in the Central Highlands of Vietnam. Study focus: Local land-use policies and human activities can significantly affect hydrology and increase the magnitude of erosion and nutrients in downstream areas. The effects in terrestrial regions on water quality of the target area were evaluated during the 2000-2018 period using the SWAT (Soil and Water Assessment Tool) with updated land-use conditions following the local policy decisions and agricultural practices in different periods. New hydrological insights for the regions: This study indicates that the implementation of the local land-use policies, along with extensive anthropogenic activities, has had significant effects on the downstream aquatic environment as compared with the period before the implementation of the land-use policies. Higher annual sediment, total nitrogen (TN), and total phosphorus (TP) load-ings were found upstream from the Poko Watershed, where range land predominated, and in southern and southwestern Dakbla Watershed, where arable land and permanent cropland pre-dominated. Arable land had the highest proportion of sediment and nutrient loadings into the reach, especially in the 2005-2009 period (conducting afforestation, agricultural expansion, and urbanization) and in the 2010-2014 period (applying crop conversion policy involving a shift from mixed forests to rubber forests). Understanding the watershed characteristics along with the combination of spatial land use, local land-use policies, and agricultural practices will support the implementation of regional land use and water resources management strategies more comprehensively