Edge-of-field practices such as denitrifying woodchip bioreactors can be used to improve the water quality of agricultural effluents. This study evaluated the effectiveness of four field-scale woodchip bioreactors in removing nitrate‑nitrogen (nitrate-N) from subsurface drainage in eastern South Dakota. Four woodchip bioreactors were installed and monitored between 2014 and 2016 near Arlington, Baltic, Hartford, and Montrose, South Dakota. Results showed that reduction in nitrate-N concentration for the four bioreactors ranged from 7 % to 100 %, corresponding to removal rates of 5 to 27 g N/m3/day for the four bioreactors during the study period. Average Nitrate-N load reduction in the four bioreactors studied ranged from 39 % to 89 % during the study period. Reduction of nitrate-N in the four bioreactors decreased, on average, by 30 % when temperature dropped below 12 °C during the study period. Flow rate and hydraulic retention time (HRT) also influenced nitrate-N removal in the bioreactors as samples collected immediately following rainfall events showed high nitrate-N load removal compared to samples collected later after the rainfall events during the study period.

Controlled drainage (CD), sometimes called drainage water management, is a practice whereby the drainage system outflow is managed during specific periods to retain more water in the field. Although CD has been shown to reduce downstream nitrate-N (NO3--N) load, seasonal patterns have been less consistent which can potentially impact the effectiveness of conservation practices. The main objective of this study was to assess the regional and seasonal impact of conventional free drainage (FD) and CD on drainage flow and nitrate-N load. Using experimental data from ongoing and historical CD experiments across the Corn Belt and in North Carolina, we evaluated subsurface drain flow, nitrate-N load, and performance of CD systems. Across the data set and regions, there was little difference in annual flow from FD conditions. Seasonally, more northern and western sites experienced a greater percentage of the annual flow occurring in the spring. There was no nitrate-N concentration reduction with CD. Flow and nitrate-N load reductions with CD did not vary by plant hardiness zone across the region, but the season with the greatest reduction did shift from winter to spring moving north and west in the study area. Absolute flow reductions (in mm) were similar regardless of precipitation category. Consequently, the percent reduction was lower as the amount of precipitation (category) increased. Overall, this analysis found CD to be an effective practice for reducing drain flow and nitrate-N loading directly delivered by the drains to downstream water bodies across the region.

Excess nutrients from agricultural settings contribute to surface water and groundwater impairment. Constructed wetlands have been widely used for water quality protection in various agricultural systems. We used a synthesis approach to document the performance of constructed wetlands for nutrient removal from a range of landscapes and geographic regions with the following objectives: (1) review the current use of constructed wetlands in agricultural applications, (2) summarize the nutrient removal efficiency of constructed wetlands, and (3) identify the geographic usage and costs associated with constructed wetlands. We reviewed over 130 publications and reports to characterize nutrient removal performance for the following types of agricultural effluents: cropland surface and subsurface drainage, and wastewater from livestock production, greenhouse, aquaculture, and hydroponic systems. Data from the reviewed studies indicate that constructed wetlands are efficient in protecting water quality in agricultural production settings. However, differences in constructed wetland characteristics reported by the studies suggest that standards are needed to ensure nutrient removal goals are met based on wetland design. Researchers should consider including basic performance parameters for constructed wetlands in published reports, including influent and effluent concentrations, hydraulic retention time, hydraulic loading rate, watershed to treatment wetland ratios, and plant species and relative cover. Future studies are needed to explore cost-benefit analyses to assess the feasibility and potential promotion of wetland incentive programs in various geographic regions and watershed nonpoint-source pollution goals for using these systems in agricultural settings.

Green infrastructure (GI) is a land development approach that uses a network of natural and built areas and waterways to create healthier urban environments. This study presents a synthesis of GI planning and adoption in 16 cities selected from around the world; 12 of these cities are located in the United States. The study highlights key socio-economic benefits associated with GI adoption and documents analytical procedures used to quantify the benefits linked to GI implementation. The benefits as identified and reported in this study are qualitative rather than quantitative.

Prolonged and frequent droughts in Southern California present hazards and uncertainty for the region’s increasing population, resulting in proactive and aggressive water management strategies. The goal of this study is to present a case study of the San Diego region’s rainfall and temperature time series analysis in order to determine annual and seasonal trends and their significance. Rainfall and temperature data from 20 rain-gauged stations were analyzed for the period 1985–2017. A project database was set up for data compilation and quality control, and a Mann-Kendall test for trend analysis was used. Results indicated that rainfall in the region decreased both annually and during the rainy season (November–April) by up to 0.14 mm between 1985 and 2017, although not in a statistically significant manner, except at two rainfall observation stations. Rainfall appears to have increased in many of the stations examined during the dry season (May–October), with an average magnitude of 0.09 mm. Analysis of daily minimum and maximum temperature reveals overall average annual and seasonal increases of 0.07 °C and 0.04 °C, respectively, with statistically significant increases at 10 of 17 for minimum temperature, and 0.27 °C and −0.25 °C with statistically significant increases at 9 of 16 for maximum temperature. Temperature tends to have increased more during the dry season compared to the rainy season. This study reveals an overall decreasing tendency in rainfall and an increasing tendency in minimum and maximum temperatures (although not statistically significant) in the San Diego region between 1985 and 2017, which likely contributed to important management implications for the region’s water resources.

Understanding groundwater recharge processes is important for development of water resources in arid and semi-arid regions. This study sought to build a regional-scale surface water-groundwater model with SWAT-MODFLOW for assessing the spatial distribution of annual and seasonal groundwater recharge and interactions with surface water in the Limpopo River Basin (LRB), Africa. The model was calibrated and evaluated for monthly streamflow from 1984 to 2013 in the basin. Due to the lack of reliable measured water table data, water table elevation was compared to estimates of water table depth reported in the literature for the basin. Simulation results from this study suggest an annual average recharge of almost 0-530mm over the basin while simulations show a range of 1300m in summer to 1400m in autumn for groundwater table elevation. Annual and seasonal analysis show high spatial variability in both water table and recharge. Annual recharge along the Limpopo main river and at the outlet of the basin was high compared to other locations in the basin. Groundwater table appears generally shallow in the rainy east region and along the Limpopo River network. Summer months have the highest groundwater recharge with an average of 147 mm/year over the basin, followed by autumn with an average of 27 mm/year, spring with 3.2 mm/year, and winter having the lowest seasonal recharge of 0.3 mm/year during the 30-year study period. The simulations also suggest high spatial variability in groundwater-surface water interactions in the basin's rivers. Rivers in the southern region show input from groundwater discharge while west river channels appeared to seep to the underlying aquifer. The results can assist with groundwater management by providing insights into areas of high recharge and problematic areas susceptible for water quality pollution, especially where groundwater discharge is experienced.

Conversion of grassland to cultivated cropland has been linked to downstream alteration of flow regimes. This study used the Soil and Water Assessment Tool (SWAT) to construct seven “what if” scenarios for quantifying the impacts of grassland to cropland and vice versa conversion (i.e., replacement of grassland with selected agricultural crops) on river flow regimes in Skunk Creek watershed. The Cropland Data Layer for the year 2011 in conjunction with historical climate data was used to create SWAT models for scenario simulations over 19 years, from 1996 to 2014. The model developed for the historical climate records (baseline) was compared with the scenarios examined using stream flow metrics for a range of flow regimes, including magnitude, duration, frequency, and timing of annual low‐ and high‐flow conditions. The simulation results suggest that grassland conversion to cultivated cropland would generally increase river flows compared with conversion of cultivated cropland to grassland, which may reduce flows in the watershed. Low and moderate flows increased by 2–8% from the baseline scenario with conversion of grass crop and by 1–20% decreases with crop–grass conversion. High flows increased by 3–7% and decreased by 1–18% when grass is converted to crop and crop to grass, respectively. The analysis also suggests that grassland establishment may attenuate the peaks of prolonged small floods and shorter but earlier large floods.

Roadside ditches play an important role in the quantity and quality of receiving waters. Very little, however, is known about the fate and transport of nutrients and trace metals in roadside ditches, especially their leaching to shallow groundwater. This study sought to document selected water quality constituent levels in infiltrated water (i.e., leachate) in roadside ditches maintained with permanent vegetation. Leachate sampling wells were installed in four roadside ditches, and water samples were collected from the wells following major rainfall events during the years 2016 and 2017. The samples were analyzed for nutrient and metal concentrations. Results indicated that nutrient concentrations in the water samples range from 0.00600 to 0.0107 mg/L for orthophosphate (PO4–P), 0.00500 to 6.80 mg/L for nitrate (NO3–N), 0 to 0.007 mg/L for nitrite (NO2–N), and 0.0100 to 314 mg/L for chloride (Cl−). Concentrations of the metals examined varied between 0.0100 and 104 mg/L in water samples. While there was no specific pattern in both nutrient and metal concentrations when roadside ditches maintained with cool season grass were compared to those of warm season grass ditches, results suggest that grass types will likely affect differently uptake of nutrients and metals in the ditches.

Water is vital for human survival and ecosystem health. In arid and semi-arid areas like the Limpopo River Basin (LRB) in Southern Africa, water is a precious commodity. The study of spatial and temporal distribution of freshwater components is an important step toward sustainable planning and management of water resources. This case study applied the Soil and Water Assessment Tool (SWAT) to characterize freshwater availability and scarcity in the LRB. SWAT predictions of hydrologic fluxes in the basin are generally satisfactory when compared to measured streamflow records, although uncertainties persist in model estimates. Estimates of streamflow, herein referred to as blue water, varied from 0.2 to 570mm/year between 1984 and 2013 over the basin. The analysis revealed alternating cycles of one to two years of water surplus periods and three to five years of dry periods during the study period. The results also indicated that, considering the natural water yield, 20% of the basin (mostly east) has enough water, while the remaining 80% continues to experience dryness and water stress.

Irrigation water is limited and scarce in many areas of the world, including Comarca Lagunera, Mexico. Thus better estimations of irrigation water requirements are essential to conserve water. The general objective was to estimate crop water demands or crop evapotranspiration (ETc) at different scales using satellite remote sensing-based vegetation index. The study was carried out in northern Mexico (Comarca Lagunera) during four growing seasons. Six, eleven, three, and seven clear Landsat images were acquired for 2013, 2014, 2015, and 2016, respectively, for the analysis. The results showed that ETc was low at initial and early development stages, while ETc was high during mid-season and harvest stages. These results are not new but give us confidence in the rest of our ETc results. Daily ETc maps helped to explain the variability of crop water use during the growing season. Based on the results we can conclude that ETc maps developed from remotely sensed multispectral vegetation indices are a useful tool for quantifying crop water consumption at regional and field scales. Using ETc maps at the field scale, farmers can supply appropriate amounts of irrigation water corresponding to each growth stage, leading to water conservation.

Water leaving roadside ditches has the potential to affect the quality of downstream waters. Vegetated filter strips (VFS's) and grassed swales (GS's) are often used to manage roadside ditches for water quality protection. This paper summarized field data from relevant studies to determine the efficiency of these two best management practices (BMPs) in removing nutrients and trace metals from roadside ditches, and discussed implications for downstream water quality, as well as driving factors that influence the performance of roadside VFS's and GS's. The literature examined shows that roadside VFS's and GS's are quite effective at reducing total suspended solids (TSS), while a mixed performance was reported for metal and nutrient removal. Based on the data, VFS's and GS's appear to be more effective at removing particulate-bound than dissolved pollutants.

Excessive phosphorus loading from anthropogenic sources is a major cause of eutrophication of natural waters. Phosphorus is also a non-renewable natural resource that cannot be substituted with other sources. The objective of this study was to determine the feasibility of using recycled steel byproducts to remove and recover phosphate from aqueous solutions. Laboratory fixed bed column experiments were conducted with recycled steel chips of different sizes to evaluate phosphate adsorption characteristics and phosphate recovery efficiencies using alkaline solutions. The results showed that phosphate adsorption onto steel chip filters was characterized by an initial fast breakthrough followed by a stable removal phase. The cumulative phosphate adsorption capacities of the steel chips were 8.43-10.4 mg P/g following 4800 empty bed volumes with a 3 min contact time and an initial concentration of 10 mg P/L. The phosphate adsorption onto steel chips was favored at low flow rates, low pH values, and low organic carbon concentrations. Sodium hydroxide solutions effectively desorbed phosphate from the steel chips. The total phosphate desorption percentages were 58.9%, 64.2%, and 83.4% after 120 empty bed volumes using 0.05 M, 0.10 M, and 0.20 M NaOH solutions, respectively. Steel chips also exhibited high phosphate adsorption and desorption capacities when treating agricultural subsurface drainage water, municipal wastewater, and stormwater runoff. Overall, the results of this study suggest that recycled steel byproducts are efficient and promising low-cost phosphate capturing materials for sustainable phosphorus management.

Understanding temporal and spatial characteristics of regional climate is essential for decision making in water resource management. Established statistical and GIS techniques were used to evaluate annual and seasonal variations of rainfall and temperature in time and space from 1979 to 2013 in the Limpopo River Basin (LRB). Annual means of rainfall in the LRB varied between 160 and 1109 mm, generally from west to east of the basin during the study period. Annual minimum and maximum temperature ranged from 8 °C in the south to 20 °C in the east of the basin, and 23 °C in the south of the basin to 32 °C in the east. The respective coefficients of variation (CVs) of these variables showed an inverse pattern to the annual values, with rainfall having high CV values (28% to 70% from east to west of the basin) compared to temperature CV values. Seasonal variations followed similar patterns as annual variations for the individual variables examined. Trend analysis showed upward trends for both annual and seasonal rainfall in most parts of the basin, except for the winter season which showed a decreasing trend. Analysis of minimum temperature on an annual basis and for the winter season and spring season shows upward trends during the study period over the whole basin while minimum temperature for summer and autumn showed decreasing trends. Maximum temperature, by contrast, showed decreasing trends on an annual, summer, autumn, and spring basis but an increasing trend for winter during the study period in most parts of the basin.

Highways are major source of stormwater runoff due to their large foot print of paved areas. The runoff can lead to many environmental problems such as non-point source pollution, soil erosion, and flooding. The low impact development (LID) practice, through incorporating best management practice (BMP) elements in linear infrastructure projects such as highways, can provide a cost-effective and environmentally sound solution for on-site control and management of stormwater runoff. Because of the diversity and variety of site conditions across the country, an extensive number of factors have to be considered. For a given project, factors can include soil characteristics such as soil type and infiltration rate; site conditions such as surface vegetation cover, drainage area and pathway, slopes, imperviousness; meteorological conditions such as rainfall; available land space for BMPs, and costs associated with the installation and maintenance of BMPs. To develop a most cost-effective engineering solution for a given site, a large number of scenarios need to be analyzed to evaluate the impact of essential factors aforementioned on the performance of BMPs, which is to be linked to the cost analysis of a given scenario. For practical application, an approach that can be readily deployed for efficient evaluation of many scenarios in relatively short time is needed. Such an approach should be integrated with considerations for cost analysis. Information and reporting in the currently available LID design manuals and related technical documents about such an integrated approach linking extensive performance evaluation with cost analysis is limited. This paper discussed results from our study that takes a modeling approach to evaluate the impact of many aforementioned factors on performance of several BMPs for control of stormwater from highways, as well as the linkage with cost analysis. This study used an idealized catchment and Personal Computer Stormwater Management Model (PCSWMM) for analysis. The modeled BMPs included bioswale, infiltration trench and vegetated filter strip. The analysis results on newly constructed BMPs indicated an average runoff reduction of up to 100% from the infiltration trench, of 70-83% and 68-78% for bioswale and vegetated filter strip, respectively. The linkage between the performance and the costs of BMP installation and maintenance for linear projects were discussed. Findings from this study provides valuable information to support decision-making for selecting and placing cost-effective stormwater BMP for controlling stormwater runoff from highways and beyond.

The Missouri River system has a large water storage capacity, where baseflow plays an important role. Understanding historical baseflow characteristics with respect to climate and land use impacts is essential for effective planning and management of water resources in the Missouri River Basin (MORB). This study evaluated statistical trends in baseflow and precipitation for 99 MORB minimally disturbed watersheds during 1950-2014. Elasticity of baseflow to climate variability and agricultural land use change were quantified for the 99 studied watersheds. Baseflow was derived from daily streamflow records with a recursive digital filter method. The results showed that baseflow varied between 38 and 80% (0 and 331 mm/year) of total streamflow with an average of 60%, indicating that more than half of streamflow in the MORB is derived from baseflow. The trend analysis revealed that precipitation increased during the study period in 78 out of 99 watersheds, leading to 1-3.9% noticeable increase in baseflow for 68 of 99 watersheds. Although the changes in baseflow obtained in this study were a result of the combined effects of climate and land use change across the basin, upward trends in baseflow generally coincide with increased precipitation and agricultural land use trends in the basin. Agricultural land use increase mostly led to a 0-5.7% decrease in annual baseflow in the basin, except toward east of the basin where baseflow mostly increased with agricultural land use increase (0.1-2.0%). In general, a 1% increase in precipitation and a 1% increase in agricultural land use resulted in 1.5% increase and 0.2% decrease in base flow, respectively, during the study period. These results are entirely dependent on the quality of data used; however, they provide useful insight into the relative influence of climate and land use change on baseflow conditions in the Great Plains region of the USA. (C) 2017 Elsevier B.V. All rights reserved.

Manure application on frozen soil, which is a common practice in the upper Midwest of USA, results in degraded soil and water quality. During snowmelt or precipitation events, water runoff carries nutrients into nearby streams and impairs the water quality. There is a need, therefore, to identify improved management of manure application in the soils. This study was conducted to assess water quality impacts associated following manure application during winter months when soil is completely covered with snow. The study site included three watersheds, named south (SW), east (CW), and north (NW) managed with a corn ( Zea mays L.)-soybean ( Glycine max L.) rotation located in South Dakota. The SW and NW were used as treatment, and CW as the control watershed. The treatments included manure application on the upper half of the SW and lower half of the NW, and CW received no manure application. This study showed that manure improved soil properties including infiltration rate and organic matter. Nitrogen and phosphorus losses in the surface runoff were higher from NW compared to that of SW. The CW had similar nutrient losses compared to the NW with slight differences. It can be concluded that maintaining a setback distance can help in improving the environmental quality as well as managing the agricultural wastes during the winter months.

Study region: North and South Dakotas, United States Study focus: Changes in watershed hydrology are mainly driven by changes in land use and climate. This study evaluated the impacts of climate and land use changes on streamflow in an agricultural watershed in the Upper Midwest. Three projected climate change scenarios (A1B, A2 and B1) of three general circulation models (CGCM3.1, GFDL-CM2.1, and HADCM3) were developed for mid (2046-2065) and end (2080-2099) of the 21st century. Corresponding land use maps for years 2055 and 2090 were obtained from the FOREcasting SCEnarios of Land-Cover (FORE-SCE) model. The scenarios were designed in a way that land use was changed while climate conditions remain constant, land use was then held constant under a changing climate, and finally both land use and climate were changed simultaneously to reflect possible future land use and climate conditions. New hydrological insights for the region: Potential land use and climate changes would result in 12-18% % and 17-41% increases in annual streamflow, respectively, by end of the century. The combined effects of land use and climate changes would intensify future streamflow responses with 13-60% increases in the region. This study provides a broad perspective on plausible hydrologic alterations in the region, prompting individual and collective opportunities to engage with this topic for sustainable planning and management of watersheds.

Accurate estimation of crop evapotranspiration (ET) is a key factor in agricultural water management including irrigated agriculture. The objective of this study was to compare ET estimated from the satellite-based remote sensing METRIC model to in situ atmometer readings. Atmometer readings were recorded from three sites in eastern South Dakota every morning between 8:15 and 8:30 AM for the duration of the 2016 growing season. Seven corresponding clear sky images from Landsat 7 and Landsat 8 (Path 29, Row 29) were processed and used for comparison. Three corn fields in three sites were used to compare actual evapotranspiration (ETa). The results showed a good relationship between ETa estimated by the METRIC model (ETa-METRIC) and ETa estimated with atmometer (ETa-atm) (r2 = 0.87, index of agreement of 0.84, and RMSE = 0.65 mm day −1 ). However, ETa-atm values were consistently lower than ETa-METRIC values. The differences in daily ETa between the two methods increase with high wind speed values (>4 m s −1 ). Results from this study are useful for improving irrigation water management at local and field scales.

This study analyzed changes in hydrology between two recent decades (1980s and 2010s) with the Soil and Water Assessment Tool (SWAT) in three representative watersheds in South Dakota: Bad River, Skunk Creek, and Upper Big Sioux River watersheds. Two SWAT models were created over two discrete time periods (1981-1990 and 2005-2014) for each watershed. National Land Cover Datasets 1992 and 2011 were, respectively, ingested into 1981-1990 and 2005-2014 models, along with corresponding weather data, to enable comparison of annual and seasonal runoff, soil water content, evapotranspiration (ET), water yield, and percolation between these two decades. Simulation results based on the calibrated models showed that surface runoff, soil water content, water yield, and percolation increased in all three watersheds. Elevated ET was also apparent, except in Skunk Creek watershed. Differences in annual water balance components appeared to follow changes in land use more closely than variation in precipitation amounts, although seasonal variation in precipitation was reflected in seasonal surface runoff. Subbasin-scale spatial analyses revealed noticeable increases in water balance components mostly in downstream parts of Bad River and Skunk Creek watersheds, and the western part of Upper Big Sioux River watershed. Results presented in this study provide some insight into recent changes in hydrological processes in South Dakota watersheds. Editor's 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.

Agricultural subsurface drainage has been recognized as an important pathway for phosphorus transport from soils to surface waters. Reactive permeable filters are a promising technology to remove phosphate from subsurface drainage. Three natural minerals (limestone, zeolite, and calcite) and five industrial by-products (steel slag, iron filings, and three recycled steel by-products) were evaluated for phosphate removal from subsurface drainage using batch adsorption experiments. Phosphate adsorption onto these materials was characterized by Langmuir isotherm and second-order kinetic models. The adsorption capacities increased by factors of 1.2-2.5 when temperature was increased from 5 degrees C to 30 degrees C. Industrial by-products exhibited phosphate adsorption capacities that were one order of magnitude higher than natural minerals. Medium-sized steel chips exhibited high phosphate adsorption capacities (1.64-3.38 mg/g) across different temperatures, pH values, organic matter concentrations, and real drainage water matrixes. The strong chemical bonds between phosphate and steel by-products prevented the release of adsorbed phosphate back to the solution. The steel by-product filter can be paired with a woodchip bioreactor for nitrate and phosphate removal. It is suggested that the phosphate filter be connected to a woodchip bioreactor after the startup phase to minimize the impact of dissolved organic matter on phosphate adsorption. The results of this study suggest that the low-cost steel by-products examined could be used as effective adsorption media for phosphate removal from subsurface drainage.