Nutrient contamination from an agricultural non-point source and its mitigation: A case study of EKU Meadowbrook Farm, Madison County, Kentucky

Non-point sources are now responsible for most nutrient contamination in surface water and groundwater, leading to eutrophication and decreased water quality. Because of fertilizer use and animal husbandry, agricultural areas are prime sources for nutrient contamination. Consequently, it is advisable to mitigate entry of nutrients into watersheds from agricultural runoff and groundwater flow. Eastern Kentucky University (EKU) Meadowbrook Farm (Madison County, Kentucky) seeks to decrease its export of nutrients to Muddy Creek, which is tributary of the Kentucky River. To demonstrate the efficacy of any sequestration strategies, nutrient export must be measured both before and after sequestration efforts are implemented. Over the past two field seasons, we have investigated the sources and behavior of dissolved nutrients (phosphate, PO43-; ammonium, NH4+; nitrate, NO3-) and other dissolved ions, and their transport via hydrologic pathways at the Farm. Here, we present our findings in three parts: (1) background nutrient concentration in surface water and groundwater during fair-weather times and identification of likely nutrient sources (Borowski et al.); (2) details of cation and nutrient drainage from the Farm during rain events (Buskirk et al.); and (3) quantification of nutrient export from a representative sub-watershed on the Farm during a major rainfall event (Winter et al.). Meadowbrook Farm is a working farm raising crops (mainly corn and soybeans), and rearing dairy and beef cattle and other livestock. Livestock produce manure that is eventually applied to pasture and croplands; supplemental fertilizer is also used. These are the primary sources for excess nutrients that leave the Farm via overland and groundwater flow. We sampled water from several different water sources and measured their nutrient content. Water types include that from drainage tiles, springs (groundwater), and surface water within intermittent streams on the Farm, other adjacent streams, and Muddy Creek. Water samples were passed through a 0.4 mm syringe filter and then preserved at a pH of 2 with sulfuric acid (H2SO4). Nutrient concentration, expressed in terms of phosphorus (P) and nitrogen (N) content, was measured colorimetrically using an UV-VIS spectrophotometer and the ascorbic acid (orthophosphate; P-PO43-), sodium hypochlorite (ammonium, N-NH4+), and cadmium reduction (nitrate, N-NO3-) methods. Nitrate is the nutrient contaminant with highest median concentration (~1.1 mg/L N-NO3) in surface waters; median concentration for ammonium and phosphate are ~0.3 mg/L N-NH4+ and ~0.03 mg/L P-PO43-, respectively. Relative to national data, Farm groundwater is enriched in all nutrients with median concentrations of ~0.04 mg/L N-NH4+, ~7.3 mg/L N-NO3, and ~0.04 mg/L P-PO43-. Enrichment in ammonium is more significant compared to that of nitrate and phosphate. These data provide fair-weather, background estimates for comparison to nutrient export that occur during rain events

Modeling Seasonal Spring Development and Head Reversals in an Isolated Ridgetop Wetland in the Daniel Boone National Forest

The Daniel Boone National Forest has a number of isolated ridgetop wetlands that are connected to perched groundwater. In the spring and during storms, the hydraulic head in the groundwater rises above the surface water in one of these wetlands, creating a spring on the upslope side of the wetland. During the summer, groundwater storage is depleted and the head in the groundwater falls below the wetland pool, causing a head reversal and leakage from the wetland. Explaining this system with a numerical model is difficult as ridgetop isolation creates few discernable boundary conditions. Our objective was to use field investigations and LIDAR data to characterize the wetland system and to define boundary conditions in order to create a MODFLOW model that explains the development and depletion of the spring in an isolated ridgetop wetland. Field investigations included installing a well field in 2017, characterizing the geology, measuring monthly hydraulic head, and measuring hydraulic conductivity. Next, we analyzed LIDAR data for the wetland and characterized geomorphic features such as cliff boundaries and ephemeral channels. The final steady-state model incorporated cliff faces as no-flow boundaries, the wetland pool as a constant head, and ephemeral channels as drains. When the model was calibrated, we found that groundwater recharge and drain boundaries explained most of the monthly head values with RMS errors as low as 0.06. The model indicated that the groundwater spring develops due to seasonal changes between recharge and leakage through drain boundaries, while evapotranspiration was a secondary outflow

THE IMPACT OF AGRICULTURAL DEVELOPMENT ON NUTRIENT CONTAMINATION HOTSPOTS WITHIN A SMALL, INTERMITTENT WATERSHED AT EKU’S MEADOWBROOK FARM, MADISON COUNTY, KENTUCKY

Eastern Kentucky University’s (EKU) Meadowbrook Farm and many others in the Muddy Creek watershed are located within small, intermittent subwatersheds with thin, impermeable soils and little riparian cover. Hence, these locations tend to have flashy hydrographs and quickly funnel water into larger order streams without many opportunities for nutrient attenuation. These combined factors make intermittent watersheds potential nutrient contamination hotspots that may disproportionately impact larger water bodies. However, the impacts of surface-groundwater interactions on baseflow nutrient behavior in these small intermittent watersheds and potential ramifications for large-scale watershed contamination is not well understood. Hence, we characterized spatial and temporal sources and controls on nutrients and their baseflow transport behaviors. Seventeen sampling sites were established at different water types in one of these watersheds at EKU’s Meadwobrook Farm. Electrical conductivity(EC), temperature, and pH were measured with a YSI Pro-DSS probe. Dissolved major ions (Ca2+, Mg2+, Na+, K+, Cl-, and SO42-) and nutrients (NO3-, NH4+, PO43-) were measured with ion chromatography and UV-Vis spectrometry. Principal component analysis (PCA) shows incomplete dilution of contaminated farm complex water by local groundwater-soil-surface waters. Furthermore, PCA results show that this contamination slowly diminishes after the end of the growing season and renews with agricultural activities. GIS analysis shows that similar intermittent watersheds comprise ~10% of the Muddy Creek watershed. Despite being a minor water flow contributor to higher order streams, the presence of intensive agriculture in these specific regions could have a disproportionate impact on nutrient loading

Nutrient export from a proximal intermittent stream draining EKU Meadowbrook Farm, Madison County, Kentucky

Agricultural activities contribute significant amounts of nutrients that contaminate surface and subsurface water. Eastern Kentucky University Meadowbrook Farm seeks to decrease its export of nutrients into Muddy Creek. The first step in this process is to determine nutrient export at present, before sequestration efforts take place. Here we estimate the export of phosphate, nitrate, and ammonium during three rain events in summer 2017 from a proximal, intermittent stream (the BRC). This stream drains a representative portion the Farm, receiving water from a dairy complex, pasture, and cropland. To estimate nutrient export, both discharge and nutrient concentration must be determined. We measure discharge over an instrumented dam during rain events. Nutrient concentration is measured in water samples using established colorimetric methods: ascorbic acid (phosphate), cadmium reduction (nitrate), and sodium hypochlorite (ammonium). Discharge and concentration data were parsed into 30-second time steps, and we used a cubic spline application (grafted into MS Excel) to produce a continuous function for each parameter. The integrated area under the discharge and concentration curves yielded total solute mass for the events. Total discharge volume and nutrient export are somewhat proportional but results vary over several orders of magnitude. The largest rain event, Tropical Storm Cindy, exported 3.1 kg phosphorus was (P) as dissolved orthophosphate, and 6.3 kg nitrogen (N) as dissolved nitrate (5.3 kg) and ammonium (1.0 kg). In order to better determine the relationship between total discharge and nutrient export, we intend to capture many more rain events during the field season of 2018