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 were conducted within stream reaches adjacent to well clusters to pinpoint areas of discrete groundwater discharge to the streams. These DTS data were used to identify locations where longer- term deployments of vertical temperature profilers (VTP's) were conducted to estimate vertical groundwater discharge (L/T) at the shallow streambed interface over time. Additionally, point measurements of the thermal properties of the streambed sediments were made using a Tempos thermal property analyzer in the field to support the modeling of groundwater discharge rates. Seepage meter measurements were made at select locations on the streambed to better understand flux occurring at the streambed interface using direct measurements of discharge. When these meters were emplaced piezometers were installed next to them for determining vertical hydraulic gradients. This information was used to determine estimates of vertical hydraulic conductivity when combined with measured discharge flux rates from emplaced seepage meters. Additionally, these piezometers were pumped and instantaneous water quality information was collected using water quality sondes (YSI EXO2's) in the field. Continuous water level information (In-Situ Level Troll) was also collected in some piezometers to assess for any diurnal or other changes that might occur during the deployment period. In Mason County two piezometers were left in place at 80 cm and 160 cm below the stream bed to look at hydrologic dynamics over time and under different hydrologic conditions. This data release contains two child items, one for each testbed site. Contents of child items are explained locally.

美国地质调查局（US Geological Survey）下一代水资源观测系统计划（Next Generation Water Observing Systems Program, NGWOS）在伊利诺伊河流域的研发工作中，为开展针对过量养分归趋与运移的地下水与地表水相互作用的详细研究，设立了两个高强度技术“试验台（testbed）”点位。具体而言，硝酸盐常被应用于农业生产以补充作物生长所需养分、提升产量，但部分农业区域的地下水中常存在高浓度硝酸盐。为更深入理解地下水中硝酸盐的归趋及其向地表水的潜在负荷量，需要对浅层河流-含水层耦合系统进行详细表征。

第一个试验台点位位于伊利诺伊州梅森县（Mason County, IL），毗邻伊利诺伊河主河道，沿梅森-塔泽韦尔排水渠（亦被称为箭溪（Quiver Creek）。该县农业灌溉强度极高，当地采用的施肥灌溉（fertigation）技术，即将水溶性硝酸盐注入中心枢轴灌溉系统中。伊利诺伊州农业部（Illinois Department of Agriculture）开展的两年一次水质采样发现，梅森县多口井的地下水中硝酸盐浓度超过了美国环境保护署（EPA）规定的10mg/L最大污染物浓度限值。

第二个试验台点位位于印第安纳州拉波特县（LaPorte County, IN）流域最东北部的坎卡基河沿岸——坎卡基河是伊利诺伊河的重要支流。该区域地形平坦，以高强度农业开发为主，但灌溉程度不高，目前无超高浓度硝酸盐的相关记录。区域内农田周边分布有大量排水渠，且井群与坎卡基河之间建有防洪堤，旨在促进坎卡基河漫滩内的农业生产。

两个试验台点位均包含：分布于潜流带（hyporheic zone）不同深度的多口监测井、井群附近的河道水位监测点，以及邻近的下游地表水监测站点，用于监测水位与流量。点位的常规实时监测数据涵盖硝酸盐、基础水质参数与地下水位；此外，两处点位均部署了热脉冲流量计（heatpulse flowmeters），以采集地下水流速与流向的高频监测数据。

为辅助数据分析，研究团队采用了多种方法以阐明各点位控制养分负荷的水文过程：其一，在井群邻近的河道河段开展了光纤分布式温度传感（Fiber Optic Distributed Temperature Sensing, FO-DTS）调查，以精准定位地下水向河道的离散补给区域。基于DTS数据可识别需长期部署垂向温度剖面仪（vertical temperature profilers, VTPs）的点位，用于随时间估算浅河床界面处的垂向地下水补给量（单位：L/T）。其二，现场采用Tempos热特性分析仪对河床沉积物的热特性进行点测，以辅助地下水补给速率的模拟。其三，在选定的河床点位开展渗流计（seepage meter）测量，通过直接测量流量以更好地理解河床界面处的通量；安装渗流计时，会在其旁增设测压管（piezometers）以测定垂向水力梯度，结合渗流计测得的流量通量，可估算垂向水力传导率。其四，对这些测压管进行抽水作业，并使用YSI EXO2水质探头（YSI EXO2）采集瞬时水质数据。部分测压管中还部署了In-Situ Level Troll水位监测仪（In-Situ Level Troll），以采集连续水位数据，评估部署期间可能出现的日变化或其他动态变化。

在梅森县点位，还保留了两口分别位于河床下方80cm与160cm处的测压管，用于长期监测不同水文条件下的水文动态。

本数据集发布包含两个子项，分别对应两个试验台点位，子项的具体内容将在各子项中详细说明。