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, field plots (22.9 x 45.7 m) were established 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 soil type transitions from an excessively drained outwash soil on the upslope to a very poorly drained silty clay series at the toeslope. Tile drainage lines were installed in each plot and drained to concrete manholes at the corner of each plot where water was sampled and measured. Plots were randomly assigned to a tile-drained (TD) or naturally-drained treatment (UD). Tile outlets were plugged in the UD treatment to enable natural drainage conditions. Surface runoff water was collected at the lower boundary of each plot by shallow PVC-lined trenches that outlet to the manholes. Continuous water flow from each hydrologic pathway was measured in 5-gallon buckets with v-notch weirs and pressure transducers. Total phosphorus (TP), soluble reactive phosphorus SRP), unreactive phosphorus (UP) and sediment (TSS) loads were estimated by multiplying the mean hourly runoff volume by the respective sample concentration for each hydrologic pathway.
Data were collected April 21, 2014 through June 30, 2015. Loading rates were unable to be calculated from February 22, 2015 through April 9, 2015 due to freeze/thaw cycles preventing accurate water flow data collection. Event-based loading for TP, SRP, UP, TSS, and water yield were calculated in addition to cumulative losses over the study duration. No significant differences in cumulative TP exports were found between treatments (UD = 230.9 g ha-1; TD = 233.9 g ha-1). Approximately 55% more SRP and 158% more TSS was exported by UD (130.8 g ha-1; 168.8 kg ha-1) than TD (84.2 g ha-1; 65.5 kg ha-1). Unreactive P exports from TD (149.7 g ha-1) were 50% greater than UD (100.1 g ha-1). Two runoff events dominated the treatment response. An intense rain storm on May 16, 2014 generated the greatest sediment losses in both treatments during an individual event, contributing 65 and 67% of the cumulative losses from TD and UD, respectively. This event was also responsible for 40% of UP losses from TD. A 3 d rain/snowmelt event beginning on December 24, 2014 resulted in 61 and 84% of all SRP losses for TD and UD, respectively. The results of this study indicate that tile drainage may not have a negative impact on water quality relative to a naturally drained field. However, additional years of data are needed to develop more robust conclusions as different management strategies and weather conditions could result in different outcomes
