Manuel R. Reyes

The Worldwide Use of the SWAT Model: Technological Drivers, Networking Impacts, and Simulation Trends

The Soil and Water Assessment Tool (SWAT) is one of the most widely used watershed-scale water quality models in the world. Nearly 600 peer-reviewed SWAT-related journal articles have been published and hundreds more have been published in conference proceedings and other formats. The SWAT model has proven to be a very flexible tool for investigating a range of hydrologic and water quality problems at different watershed scales, as well as very adaptable for applications requiring improved hydrologic and other enhanced simulation needs. We investigate here the various technological, networking, and other factors that have supported expanded use of SWAT, and also highlight current worldwide simulation trends. Examples of technological advances include easy access to web-based documentation, user-support groups, and SWAT literature, a variety of Geographic Information System (GIS) interface tools, pre- and post-processing calibration, statistical evaluation, and other software, and an open source code which has proven to be a model development catalyst for multiple user groups. Extensive networking regarding the use of SWAT has also developed, via internet-based user support groups, model training workshops, regional working groups, regional and international conferences, and targeted development workshops. The use of SWAT has expanded dramatically, not only in North America and Europe but also in Africa, Southeast Asia and countries such as China, India, and Iran. Several important trends have also emerged regarding improved hydrologic, best management practice (BMP), and pollutant transport methods, which will be further highlighted.

Dynamics of Soil Carbon, Nitrogen and Soil Respiration in Famer’s Field with Conservation Agriculture, Siem Reap, Cambodia

The years of intensive tillage in many countries, including Cambodia have caused significant decline in agriculture’s natural resources that could threaten the future of agricultural production and sustainability worldwide. Long-term tillage system and site-specific crop management can affect changes in soil properties and processes, so there is a critical need for a better and comprehensive process-level understanding of differential effects of tillage systems and crop management on the direction and magnitude of changes in soil carbon storage and other soil properties. A study was conducted in farmer’s field to evaluate the effect of conservation agriculture (CA) and conventional tillage (CT) on soil carbon, nitrogen and soil respiration in three villages of Siem Reap, Cambodia. Soil organic carbon (p≤0.01), soil total nitrogen (p≤0.01) and soil respiration Original Research Article Edralin et al.; IJPSS, 11(1): 1-13, 2016; Article no.IJPSS.25339 2 (p≤0.10) for at least in two villages were significantly affected by tillage management. The soil quality was improved in villages with CA compared with villages with CT by increasing soil organic carbon (10.2 to 13.3 Mg ha) and soil nitrogen (0.87 to 1.11 Mg ha) because of much higher soil moisture (15.7±8.6 to 20.0±11.9%) retained in CA and with reduced soil temperature (30.4±2.0 to 32.4±2.3°C) during the dry period. Additionally, fi eld soil respiration was higher in CA (55.9±4.8 kg CO2-C ha -1 day) than in CT (36.2±13.5 kg CO2-C ha -1 day), which indicates more microbial activity and increased mineralization of soil organic carbon for nutrient release. The soil’s functions of supporting plant growth and sink of carbon and recycler of nutrients was likely improved in agroecosystem with CA than in system with CT. Our results have suggested that CA may have had enhanced soils’ carbon and nitrogen contents, nutrient supplying capacity and microclimate for soil microorganisms in three villages with vegetable production.

Water Quality Assessment on Organic Plots under Conventional and Tillage Systems in Upper French Broad Watershed with APEX Model

The Upper French Broad is impacted by the sediment from agriculture and urban sources. Research is ongoing at the Mountain Horticultural Crops Research Station in Mills River, N.C. to evaluate surface water and groundwater quality from organic (managed organically for 15 years and undergoing organic certification) and conventional systems that have the same crop (continuous sweet corn with winter cover crops_ wheat and crimson clover) system and the same amount of N fertilizer applied from different sources. The Agricultural Policy Environmental Extender (APEX) is used to assess the long term impact of organic plots on surface water (nutrients and sediment) and groundwater quality (nutrients) under conventional and conservation tillage systems. APEX predictions on the control and four treatments will be shown: organic vegetable in conventional tillage system, organic vegetable in conservation tillage system, non-organic vegetable in conventional tillage system, and non-organic vegetable in conservation tillage system. There will be no comparisons of predictions with mean measured observed values. Data collection in the plots just started. This research may extend the application of APEX for simulating organic systems and may confirm its applicability for use in the Piedmont.

Modeling Streamflow with SWAT in the Upper Haw River of North Carolina

SWAT (Soil and Water Assessment Tool) has been used widely in the United States to develop total maximum daily load (TMDL) programs. As far as we know, there are no previously published studies modeling a North Carolina river with SWAT. North Carolina has 658 water bodies on the EPA’s 303(d) list of impaired waters including several branches of the Haw River. The Haw River has its headwaters in the upper Piedmont physiographic region of the state and stretches 110 miles through agricultural, residential, urban and forested land, before eventually becoming part of the Cape Fear River. The objective of this project is to simulate streamflow for the upper Haw River using SWAT and the curve number technique. The chosen section of the Haw watershed covers about 1150 km2 from the headwaters to just upstream of Burlington, NC, and includes the urban sub-basin of Greensboro, NC, and the predominantly rural sub-basin to its north. Data for soils and elevation will be obtained from USDA-Natural Resources Conservation Service, for land use from USDA-National Agricultural Statistics Service, for weather from USGS-National Water Information System, NOAA-National Climatic Data Center, and the NC State Climate Office, and for reservoirs from NC Department of Natural Resources. Results of the simulation will be compared against twenty years of observed data from USGS streamflow gauges to see if SWAT could be used for watershed modeling in the North Carolina Piedmont.