1a.Objectives (from AD-416):
Three specific research objectives are proposed: (1) to determine the magnitude of specific hydrologic pathways of streamflow under runoff and baseflow periods at various spatial and temporal scales in an agricultural claypan watershed, (2) to understand how the hydrologic pathways control the transport of nutrients and herbicides to streams at those temporal scales and quantify the contributions of nutrients and herbicides from various hydrologic pathways (i.e. source waters) to streamflow, and (3) to develop and test a quantitative model for evaluating the impact of changes in land use and catchment scales on nutrient and herbicide transport.
1b.Approach (from AD-416):
To achieve the research objectives, two field experiments are needed to characterize the hydrologic pathways and their impact on contaminant transport. One experiment supports Objective 1 through a combination of meteorological measurements and source water samples to characterize the chemical contents of stream water, soil water, groundwater and precipitation. A key outcome of Objective 1 will be the development of a mixing model that accurately captures the relative contribution of the different hydrologic pathways (runoff, interflow, and groundwater recharge). This model will be then be used in conjunction with the Soil Water Assessment Tool model to look at the impact of scale and changing land use on contaminant transport. The other field experiment supports Objective 2 by specifically investigating the role of interflow on contaminant transport by directly measuring the quantity and quality of interflow. For Objective 3, the results of mixing models will help to develop a conceptual framework for SWAT and calibrate some of its parameters. The sensitivity analysis of the Soil and Water Assessment Tool model (SWAT) helps validate the hydrologic controls of nutrients and pesticides in stream water. SWAT will then be used to simulate stream water quality (nutrients and herbicides) with changes in crops and catchment scales.
For Objective 1, numerous water samples representing rain, runoff, stream, and ground water sources were collected from within Goodwater Creek Experimental Watershed (GCEW) over the last year. These samples were analyzed for common cation and anion concentrations, and analyses for stable H and O isotopes are pending. These samples will be used to determine the variation in hydrogen and oxygen isotopes and common ion concentrations for each water source as a prerequisite for quantifying the source components comprising the stream flow of Goodwater Creek. For Objective 2, tentative spring sites for the interflow study have been identified and needed water sampling and soil moisture equipment has been purchased.