Factors affecting surface-water and ground-water quality within tribal lands of eastern Nebraska

Recent surveys indicate that water quality is a concern within tribal lands across the U.S., yet few studies document the occurrence of specific contaminants. This study reported results of baseline assessments within the Omaha and Santee Sioux Nations of eastern Nebraska and explored various factors affecting surface-water and ground-water quality. Land-use and stream-water quality data were utilized to determine impacts on streams in selected watersheds within both reservations. Within the Santee Sioux Reservation, nitrate-nitrogen (NO₃-N) and pesticide loads were highest in watersheds with the most land in row-crop production, whereas per hectare yield estimates were similar for all watersheds. A significant proportion of non-point source contamination entering the Santee Sioux Reservation appeared to originate from land in row-crop production outside the exterior boundary. Both reservations had high percentages of domestic wells containing coliform bacteria and exceeding the U.S. Environmental Protection Agency maximum contaminant level (MCL) for NO₃-N. In comparison to results from several regional, state, and national studies, both reservations had significantly higher percentages of domestic wells with these contaminants. Site-specific data as well as statistical and spatial analyses were used to examine the association between NO₃-N and coliform bacteria and various factors with the potential to influence the occurrence of these contaminants in domestic wells. Within the Santee Sioux Reservation, residences with livestock and land in row-crop production had a significantly higher percentage of wells in excess of the MCL for NO ₃-N, suggesting both point and nonpoint contamination as the source. All wells in excess of the MCL for NO₃-N were associated with Quaternary deposits, indicating that these shallow alluvial aquifers were more prone to contaminants than the deeper Dakota Formation. Within Nebraska, county median income and educational levels were related to the proportion of wells with NO₃-N and bacterial contamination. As the percentage of adults with no high school diploma increased, the proportion of wells with coliform bacteria and exceeding the MCL for NO₃-N increased. As median income increased, the percentage of wells exceeding the MCL for NO₃-N also increased. Development of effective water-quality management strategies will require cooperation between tribal, state, and federal entities.