THE EFFECTS OF AGRICULTURAL DRAINAGE TILES ON EROSION IN THE VERMILLION RIVER WATERSHED, NORTHEASTERN OHIO

While utilizing agricultural drainage tiles to extend the growing season and allow for cultivation in poorly-drained soils has been a common practice for decades in the Midwestern United States, the effects of drainage tiles on erosion are not fully understood. The link between drainage tiles and increased nutrient inputs is well documented, and artificial drainage systems have been implicated in channel widening, however there is little information concerning the effects of drainage tiles on erosion. This study aims to characterize the relationship between agricultural land use, drainage tiles, and depth of erosion in the Vermilion River watershed in Northeastern Ohio, using ¹³⁷Cs gamma spectrometry and powder X-Ray Diffraction to track the movement and weathering of sediments. Agriculture accounts for 73% of land use in the Vermilion watershed. Drainage tiles are installed 3-6 feet below ground and facilitate drainage when the water table rises above the tiles. 28-72% of the upstream area in sampled watersheds is drained artificially.

This study analyzes sediment samples collected from the Vermilion watershed upstream of a major knickpoint. Using GIS, we identified watersheds of approximately equal sizes and slopes, but differing percentages of upstream land with drainage tiles. Tile distribution was estimated based on land use and soil drainage properties. Detrital samples were sieved to <63μm, dried, and counted for 24-96 hours in a high purity germanium detector to measure ¹³⁷Cs. Preliminary results show a weak correlation between the percentage of upstream area with drainage tiles and concentration of ¹³⁷Cs, however the knickpoint complicates analysis.

pXRF is also used to examine the effects of drainage tiles on the composition of minerals in sediments and to distinguish between surface and subsurface erosion, under the hypothesis that surface erosion will be correlated with more weathered minerals.

Understanding the sources and magnitude of sediment pollution is of critical importance in the Great Lakes, as sediment and the contaminants it may carry have a detrimental impact on ecosystems and drinking water. Greater knowledge of drainage tiles and their contribution to erosion could provide information on topsoil loss, and help increase our knowledge about the impacts of agriculture on water quality.