Nitrogen and Phosphorus Losses in Shallow Tile Drainage and Surface Water From an Agricultural Peatland: A Case Study of Extreme Summer Rainfall From Southeastern Massachusetts, United States

Tile drainage has been incorporated into many cranberry production operations. Given the potential water quality impacts of tile drainage, we quantified its contribution to surface water flows and nutrient loads for a 2 ha cranberry bed during the 2014 growing season. Our results revealed that tile drainage tracked surface water flow except during (1) two major daily storm events ( > 99th percentile and > 95th percentile based on local rainfall records), which caused enhanced overland and shallow subsurface flow, and (2) extended dry periods, when surface water was stored in ditches and/or recharged to groundwater. The combination of the two major storms contributed 44% of the total N (TN) export load in the growing season and 39% of the total P (TP) export load in the growing season. The TN load in tile drainage (4.3 kg ha(-1)) accounted for approximately half of that exported in surface water (7.5 kg ha(-1)), indicating a substantial release of N during major storm events in the form of runoff, shallow groundwater flow, and potentially from the release of ditch sediments. Conversely, the TP load in tile drainage (2.7 kg ha(-1)) was approximately twice that exported in surface water (1.5 kg ha(-1)), which was consistent with the retention of P in ditch sediments.