Fiber-optic distributed temperature sensing, seepage meter, vertical temperature profiler, water level, water quality, and streambed thermal property data collected to better understand groundwater and surface water connectivity at two sites in the Illinois River Basin

As part of the US Geological Survey's Next Generation Water Observing Systems Program (NGWOS) Research and Development efforts in the Illinois River Basin, two intensive technology 'testbed' locations were established for the purpose of conducting a detailed groundwater and surface water interaction study regarding the fate and transport of excess nutrients. Specifically, nitrate is commonly applied in agricultural settings to supplement crop growth and produce larger yields, but in some agricultural settings, high nitrate persists in groundwater. A detailed characterization of the shallow coupled stream-aquifer system is needed to better understand the fate of nitrate in groundwater and its potential loading to surface waters. One testbed site is in Mason County, IL close to the main channel of the Illinois River along the Mason-Tazewell Drainage Ditch (also known as Quiver Creek). Mason County is intensively irrigated and water-soluble nitrate is injected into center pivot irrigation systems in a practice referred to as fertigation. Biennial water quality sampling by the Illinois Department of Agriculture identified several wells in Mason County where nitrate concentrations in groundwater exceeded the EPA designated Maximum Contaminant Level of 10 mg/L. The second testbed site is in LaPorte County, IN in the far Northeastern part of the watershed along the Kankakee River which is a substantial tributary to the Illinois River. The topography is flat and characterized by intensive agriculture but is not heavily irrigated and there is no documentation of exceedingly high nitrate concentrations. There are numerous drainage ditches lining fields in the area, and there is a levee between the well cluster and the Kankakee River that was constructed to promote agriculture within the Kankakee floodplain. Both testbed sites consist of multiple wells at various depths within the hyporheic zone, stream stage adjacent to the wells, and nearby downstream surface water sites with stage and discharge. Routine real-time data at the sites includes nitrate and basic water quality parameters and groundwater levels, additionally; heatpulse flowmeters are deployed at both sites to collect high-frequency measurements of groundwater flow velocity and direction. To supplement the analysis of these data several different approaches were used to elucidate hydrologic processes controlling nutrient loading at each site. Fiber Optic Distributed Temperature Sensing (FO-DTS) surveys we