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

Utilizing agricultural drainage tiles to extend the growing season and allow for cultivation in poorly-drained, glacially influenced soils has been a common practice for decades in the Midwestern United States, however the effects of drainage tiles on erosion are not fully understood. The link between drainage tiles—perforated tubes that facilitate drainage of agricultural land when the water table rises above the tiles—and increased nutrient inputs is well documented, and artificial drainage systems have been implicated in channel widening, yet 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, ²¹⁰Pb_ex, and ⁷Be gamma spectrometry to track movement of sediments. Agriculture accounts for 73% of land use in the Vermilion watershed, and 28-72% of the upstream area in sampled subwatersheds is drained artificially.

This study analyzes 28 fluvial bed sediment samples collected from the Vermilion watershed upstream of a major knickpoint. Using GIS, we identified watersheds of approximately equal sizes and slopes with differing percentages of upstream land with drainage tiles and collected samples at the outlets of these subwatersheds. Tile distribution was estimated based on land use and soil drainage properties. Detrital samples were sieved to <63μm, dried, and leached in HCl to remove grain coatings, allowing ²¹⁰Pb_exto be measured more accurately. Samples were counted for 24-96 hours in a high purity germanium detector to measure fallout radionuclides.

Understanding the sources and magnitude of sediment pollution is of critical importance in the Great Lakes, as sediment and the contaminants it may carry can have a detrimental impact on ecosystem services, including drinking water and aquatic animal habitat. 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.