Nutrient and Sediment Production, Watershed Characterization, and Land Use in the Town Creek Watershed, Mississippi

摘要

Sediment and nutrient impairment of streams is a predominant condition for watersheds in the Tombigbee River basin, which drains through the Mobile River Basin into the Gulf of Mexico. Currently, a study is underway in Town Creek watershed (MS) as a pilot watershed physically representative in geology, physiographic, and climate of Ecoregion 65 watersheds into the Tombigbee River Basin. The study monitors surface water discharge and concentration of Dissolved Phosphorus (DP), Total Phosphorus (TP), Suspended Sediments (SSC), and associated physical parameters (pH, turbidity, Dissolved Oxygen, Electric Conductivity). Monitoring has been done in 7 grab sampling stations and two automated sampling stations along the approximated 45 miles principal channel, and 17 grab sampling stations on 10 tributaries into the 1769 km2 watershed. Analyses performed in the study area (which is composed by more than 50% for agriculture lands (cropland and pasture), 39 % for forest, and 10% for urban area), has shown that more than 40% of the water quality samples obtained since summer 2008 are above 0.1 mg TP/L (established nutrient criteria for streams). The highest TP concentrations (0.35 mg/l) in the principal channel were observed after the input of tributaries discharges from the urban area (TP-0.35). Highest SSC in the principal channel during the studied period were observed in areas influenced by structures in construction, tributaries from urban areas, and streams in agricultural areas with deficiencies orabsence of a riparian zone and evidence ofstreambank erosion processes. Tributaries located downstream of the urban area did not contribute significant concentrations of TP (<0.05mg/l), allowing a dilution effect observed in a 10% increase of the ratio DP/TP at the watershed outlet.