Adapting Edge-of-Field Monitoring for Water Quality and Soil Health Assessments in Sinkhole-Dominated Crop Fields, Homeplace Farm, Campbellsville, Kentucky

a. Project Background: Approximately 55-60% of Kentucky is underlain by soluble carbonate rocks prone to karst development, including much of the state’s prime agricultural cropland. The rolling topography at Homeplace Farm, near Campbellsville, KY, is typical of much of Kentucky’s agricultural karst areas, being characterized by numerous shallow sinkhole depressions that collect surface runoff and drain internally. Each sinkhole depression, in effect, acts as an isolated (zero-order) surface catchment. The nexus or integration of drainage contributed collectively by individual sinkhole catchments occurs in the subsurface by way of networks of integrated cave stream passages and karst conduits that typically increase in size and drainage capacity downstream and discharge to one or more karst springs. In this manner, surface runoff that drains directly into open sinkhole throats (called “swallets”) or that infiltrates through soil-covered sinkhole floors contributes to the loading of potential contaminants such as nutrients, pesticides, and bacteria to local area waters. Because of the relative lack of “normal” topographically integrated surface runoff and the predominance of subsurface drainage routes, conventional edge-of-field monitoring techniques used for assessing existing water-quality conditions and water-quality improvements due to implementation of agricultural best management practices are ineffective in sinkhole-dominated karst areas. In karst areas, water-quality assessments must be based in part on characterization of the hydrologic characteristics of sinkholes and karst conduits that drain cropped fields, as well as the solute-contaminant transport characteristics of the entire karst drainage system, which includes sinkholes, karst conduits, and springs. The Homeplace on Green River is a working farm that is owned and operated as a 501c3 non-profit organization, and in 2016 the Kentucky legislature formally recognized the Homeplace as “Kentucky’s Outdoor Classroom.” The Homeplace works with a lease farmer to grow crops, typically a corn-soybean rotation that is typical of many other farming operations. Recently, the Homeplace embraced cover cropping for soil health. There are approximately 90 croppable acres on the farm. One 30 acre field will be cover cropped for soil health every year, while the other fields on the farm will be cropped as no-till only, with no cover cropping. Homeplace Farm therefore provides an ideal setting in which to develop and employ innovative methods for assessment and protection of karst water resources typical of a working farm where the farm operators are committed to fully exploring and understanding the relationship between farming activities and karst drainage systems, and are also implementing farming practices with high conservation interest. Staff from both KGS and USGS have made visits to the site for the sole purpose of determining whether the Homeplace would provide a suitable venue for this innovative CIG project, and KGS and USGS are excited about this collaborative opportunity and the probability that a successful project can be undertaken here. b. Project Objectives: The proposed project is intended to lay the foundation needed for future more comprehensive assessments of the benefits of cover-cropped vs. non-cover-cropped fields relative to water quality and soil health at Homeplace Farm. The proposed tasks and scope of work are designed to develop techniques and information needed to fully characterize the karst drainage system present at the farm, help establish suitable water-quality monitoring stations, and improve the understanding of how the presence of karst and sinkhole drainage components potentially impact the water quality and 3. Project Description contaminant migration potential in agricultural areas dominated by karst topography and hydrology. The sinkhole drainage characterization, water-tracer testing, and karst water-quality sampling methods being proposed are unique to this project and somewhat experimental. The insight and findings that are anticipated as project outcomes will contribute to the development of a valuable new approach to assessing water-quality in karst agricultural areas in Kentucky, and elsewhere, and therefore we believe the project has a potentially high technological transfer value. c. Project Methods: The following specific project tasks are proposed: 1. Determine sinkhole drainage characteristics in the primary cover-cropped and non-cover-cropped fields at Homeplace Farm. 2. Delineate groundwater flow paths and approximate basin boundaries of Homeplace Farm cave spring. 3. Identify the natural range in variability in the cave spring’s discharge and field water-quality parameters and assess its rainfall-response characteristics. 4. Spring and sinkhole water-quality sampling. 5. Laboratory analysis. 6. Project data analysis and reporting. Additional technical details for these tasks are provided as follows: Task 1: Sinkhole drainage characterization will be accomplished using a combination of (a) double ring infiltrometer tests, (b) soil boring and shallow piezometer installation, and (d) water-tracer tests. Double ring infiltrometer tests will be conducted at the lowest elevation in each of the two major sinkhole depressions that drain the cropped fields at Homeplace Farm (see map). Infiltrometer tests will be conducted to calculate soil saturated hydraulic conductivity values and water infiltration rates. Shallow piezometer (2-inch diameter) will be drilled near the lowest elevation in the two sinkholes to a completion depth of 1 foot into top of bedrock. Soil cores will be retrieved during the drilling process and sinkhole soil profiles will be described. Kentucky regulations require that boreholes, wells, or piezometers used for the collection of water-quality samples be drilled by a state certified water-well driller. The piezometers will be completed as screened monitoring wells and equipped with water-level and specific conductivity loggers to track deep soil saturation levels and fluctuations of a hypothesized seasonal or storm-induced perched water table at the farm site. Infiltrometer tests and a shallow piezometer installation will also be made at a location on the upland drainage divide that separates the two crop field sinkholes for comparison as an “upgradient” site. Water tracing tests of sinkhole drainage using non-toxic fluorescent dye and/or ionic tracers will be conducted to determine tracer time-of-travel and breakthrough characteristics through the soil column present in each sinkhole (from the land surface to the top of the limestone bedrock or karst aquifer), and from the point subsurface water enters the karst aquifer to its discharge at the cave spring. Information gained by the tracer test data should provide valuable insight into the migration and residence times of potential contaminants transported in surface runoff from the cropped fields into, and out of, the sinkholes, and through the karst aquifer. 3. Project Description Task 2: Additional water-tracing tests will be conducted using non-toxic fluorescent dye tracers injected at selected sinkhole locations on and off site to confirm the subsurface flow paths (groundwater flow directions) beneath the farm and help delineate the cave spring basin (or springshed) boundaries. Monitoring for resurgence of injected dye tracers will be accomplished using (1) automatic water sampling equipment deployed at the Homeplace Farm cave spring, and (2) passive charcoal dye detectors deployed at selected locations in nearby streams and springs. Methods of dye detection will include analysis of water samples and eluent from charcoal detectors at the KGS water analytical laboratory using scanning spectrofluorophotometer equipment. Based on topographic and bedrock structure considerations, approximately 5-6 tracer injections are anticipated to be needed to the north and east of the Homeplace Farm property. Discharge measurements made at the spring during summer low-flow conditions will also be used to calculate an estimated total drainage basin area and a unit-base flow value (discharge per unit area) for the karst aquifer. Task 3: A multi-parameter water-quality data sonde and logger will be purchased and installed in the spring channel near the mouth of the cave to collect high-frequency (15-minute) measurements of spring discharge (water level), temperature, specific conductivity, pH, and turbidity. Rainfall data will be collected using a digital tipping-bucket gage installed on-site near the geographic center of the Homeplace Farm property. These collected data will be used to track the range in natural variability in spring discharge characteristics during the project period, determine the rainfall-runoff response characteristics of the spring basin, and assess its potential sensitivity to suspended sediment, nutrients, and pesticides mobilized during and after storm events. Tasks 4 and 5: Relatively limited water-quality sampling will be conducted as part of this proposed project to help establish baseline (ambient) water quality in the springshed during a growing season. Water samples will be collected twice monthly from the spring and the three piezometers during February-October 2017. Water samples from the piezometers will be collected after purging three borehole volumes if practicable, depending on the static water levels and piezometer recharge rates. Water temperature, specific conductance, dissolved oxygen, and pH measurements will be collected at the time of sampling. Additional groundwater samples may be collected from the farm’s on-site domestic water well, or alternately, from a suitable off-site private water well (assuming accessibility and land owner cooperation) located elsewhere within the springshed. Collected water samples will be transported to the KGS Water Lab for analysis of major and minor ions, nitrogen, phosphorus, TDS, and TSS. Task 6: Results of all water sample analyses will be archived in the Kentucky Groundwater Data Repository and will be publically accessible through the Repository’s KGS webpage (http://kgs.uky.edu/kgsweb/DataSearching/watersearch.asp). Summaries of water quality data, as well as other project data including results of infiltometer and water-tracer tests, soil borings, site maps, and ancillary geological and hydrological information will be compiled digitally using ESRI Story Map software technology, and made accessible at the end of the project period as a webpage added to the KGS Water Research home webpage (http://www.uky.edu/KGS/water/index.htm). 3. Project Description d. Geographic location and size of project or project area: The Homeplace farm is located in Taylor County, Kentucky. The overall farm is approximately 220 acres in size, with approximately 90 of those acres in continuous row crop production. e. EQIP eligible producer participation: The Homeplace itself is an EQIP-eligible producer, as is the lease farmer who crops the Homeplace acreage. In addition, the Homeplace serves as a working farm to demonstrate various agricultural best management practices, and various field days and events are held at the farm each year. This setting, therefore, will provide many opportunities to reach hundreds of EQIP-eligible producers each year.