Evaluating Water and Nutrient Losses in Surface and Subsurface Agricultural Runoff: An Edge-of-Field Approach.

Quantifying effectiveness of soil management practices on surface and subsurface water quality at the field scale is becoming increasingly important in the Lake Champlain Basin and other agricultural watersheds.  During 2012 and 2013, we established field plots (25 x 75 m) at the Lake Alice Wildlife Area in Chazy, NY to begin a long-term water quality monitoring study.  Plots were established in a cool season grass field (1 ha) leased and managed by the William H. Miner Agricultural Research Institute in Chazy, NY.  The upslope area transitions from well-drained outwash soils to poorly drained silty clay at the toeslope.   Three artificial tile drainage lines were installed in the center of each plot (7.5 m lateral spacing) and outlet to individual concrete manholes (1.2 m i.d.) where water is sampled and measured.  Surface runoff water is collected at the lower boundary of each plot by shallow PVC-lined trenches which outlet to the manholes.  Continuous water flow is measured in buckets with v-notch weirs and pressure transducers.  In the laboratory, flow curves were generated by relating measured flow to pressure head (transformed to water height) and showed very good agreement between measured and predicted values.  Preliminary flow curves generated from field runoff show good agreement between bucket water height and measured flow.  Water quality samples are collected weekly during low flow and more frequently during storm events.  For this study, plots were randomly assigned to either a tile-drained or undrained treatment (e.g., tiles are plugged).  Total phosphorus, soluble reactive phosphorus, total nitrogen, nitrate-N, ammonium-N and sediment loads will be estimated by multiplying runoff volume by event mean concentrations. Nutrient loads will be analyzed using repeated measures ANOVA.  In addition, water and nutrient losses from each plot will be simulated using HYDRUS-2D/3D and compared to measured losses.