Abstract
Water quality in the Lower Little Bow River was monitored to determine if irrigation return flow streams had a significant impact on river water quality and to examine relationships between land use and water quality in this diverse agricultural watershed. Water samples were collected weekly or biweekly during the irrigation season and monthly in winter for three years. A comprehensive land use assessment was also completed. Significant differences in flows, and in nutrient and bacteria loads, were found along the mainstem of the river following the inflows of irrigation return water; however, differences in concentrations were only significant in a drought year when mainstem flows were reduced. Pearson correlations among land use, soil types, and water quality variables identified significant positive relationships between the proportion of cereals, irrigated land, and confined feeding operation (CFO) density and maximum concentrations of total nitrogen (TN), nitrate-nitrogen, and total phosphorus (TP) that were observed during runoff events. Most nutrient variables were inversely related to the proportion of native prairie. The variation in maximum TP and median dissolved P concentrations was largely explained by the proportion of cereals in the sub-basin, while the variation in maximum and median TN concentrations was explained by the proportions of irrigated land and native prairie, respectively. Microbiological variables were not related to any of the measured variables, suggesting that factors influencing bacteria populations operate at different scales.
Coupled control of land use and topography on nitrate-nitrogen dynamics in three adjacent watersheds