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Subsurface Tile Drainage is an essential water management practice on many agricultural fields, allowing timely equipment access, reduced soil compaction, and increased crop yields in fields otherwise too wet to efficiently farm. The combined effects of drawing down the water table and providing rapid conveyance of subsurface water to an outlet can significantly change the hydrologic behavior of a field, reducing surface runoff by enhancing infiltration and groundwater transmission. It was long believed that, despite hydrologic changes caused by the implementation of subsurface drainage, phosphorus (P) losses from agricultural lands occurred primarily via surface runoff and that very little P was lost through subsurface drainage.

In Vermont and across the Lake Champlain Basin, little is known about the extent of tile drainage systems, and the potential impacts of tile drainage systems on water quality have not been assessed with adequate rigor. To address certain knowledge gaps in our understanding of the impacts of tile drainage systems on water quality in Vermont, the Lake Champlain Basin Program (LCBP) engaged Stone to perform an intensive study in the Jewett Brook watershed (JBW) in St. Albans, Vermont. The main components of this ongoing study are a literature review (completed), an automated water quality and flow monitoring program of 12 selected tile drainage systems, and analyses to quantify: 1) the degree of association between the water quality data and agronomic variables, and 2) the proportion of all phosphorus exported from the watershed that is contributed by tile drains.