| Popis: |
Developing reference criteria for nutrient conditions on streams can be difficult especially in heavily farmed or urbanized regions where most of the landscape has been impacted by human development. SWAT (soil water assessment tool) simulations permit the removal of the anthropogenic impacted land use, allowing the simulation of natural conditions and a prediction of reference conditions. A Genesee River watershed simulation was developed to determine the nutrient and sediment contributions of subbasins of the Genesee River under the current human-impacted conditions and contrasted against natural conditions. Nutrient boundary values estimated for Genesee basin small wadeable streams (34.3 μg P/L) were nearly identical to those calculated by others for small, wadeable streams (30.7 μg P/L). For large streams, the simulation-based boundary total phosphorus (TP) value (75.8 μg P/L) of the Genesee River was high compared to other observations in New York State (30 μg P/L). Causes in the variability in large stream reference values include inappropriate use of regional reference conditions, stream bank erosion, basin geology, soil type, and catchment area. When river bank stabilization was added to the simulation, a 34.3% reduction in phosphorus loading was observed, resulting in a boundary value of ~ 54 μg P/L. This reduction in the simulated sediment load suggested that the Genesee River has a higher natural sediment and TP load than most streams in NYS. SWAT is an effective tool for simulations of small streams and may be an effective method in determining reference conditions for large rivers. |
