Tile Drainage Water Quality Assessment in Saline Soils in North Dakota

Over the last ten years there has been a significant increase in the acres of agricultural land tile drained in the Red River Valley in eastern North Dakota. There is not an official accounting of acres that are tiled, but the rough estimate would be between 75,000 and 100,000 acres, almost all in the Red River Valley. The recent tiling is primarily due to excessive precipitation received since the early 1990's, the resultant rise in water tables and movement of salt into the root zone. Tiling is being installed primarily to reduce the effects of soil salinity on crop production; therefore, the drain effluent may have a detriment to water quality in the Red River Basin and ultimately Lake Winnipeg in Canada. There has been little monitoring of the effect tile drainage has on surface water quality of receiving waters, and therefore, little is known about potential impacts to water quality in the Red River Basin. It is estimated that 1.5 million to 2.5 million acres of land in eastern North Dakota are saline soils; and it is likely salinity and acres tiled will increase with continued higher than normal precipitation. A monitoring project was initiated in the spring of 2008 to sample 17 sites in Cass county North Dakota on a weekly basis for total nitrogen, total Kjeldahl nitrogen, nitrate-nitrate, ammonia, total phosphorus, ICP metals, cations and anions, temperature, pH, and conductivity. Comparisons with past surface water quality data show increased nitrogen values and decreased phosphorus, along with increases in conductivity at lift stations and high mineral levels at various sites. With support from the local County Soil Conservation District and 319 nonpoint source funding, this baseline water quality assessment will be useful in assisting legislators and state and federal agencies in developing science-based rules and regulations where needed.