Seasonal Variation in Nutrient Export Along Streams in the Northern Great Plains

摘要

Spatial and temporal trends in nutrient concentrations and loads were analyzed for three rivers in the Red River watershed, Manitoba, Canada to determine changes in nutrient export across hydrologic seasons and along river continua in the Great Plains. Annual patterns in all three rivers were strongly influenced by the snowmelt period: 25-89 % of the total annual river volume, 42-92 % of the total annual TP load, and 41-81 % of the total annual TN load were delivered during snowmelt. Concentrations of TP and TN varied among the hydrologic seasons (snowmelt, summer, fall, and winter), but showed more variability and larger values during winter and snowmelt, with peak values reaching 1.960 mg TP L~(-1) and 16.07 mg TN L~(-1). Although the flat topography and semi-arid climate of the Red River watershed results in hydrolog-ical disconnects along river continua, discharge and nutrient export increased along the three river gradients. In contrast, TP or TN concentrations showed no significant longitudinal change for the two agriculturally dominated watersheds yet increased along the forested stream. Our finding that TP and TN exports from northern Great Plains rivers are strongly influenced by seasonal hydrology, with snowmelt being a critical period for nutrient export has implications for design and implementation of appropriate management practices to minimize nutrient export to proximal and downstream aquatic ecosystems.