Supplemental Water Quality Analysis - St. Johns Bayou and New Madrid Floodway

摘要

A supplemental assessment of water quality data was conducted to describe potential impacts on water quality in the St. Johns Bayou and New Madrid Floodway as a result of the proposed flood control project. Existing water quality data from Federal and state resource agencies and literature-based information on land use effects on water quality were compiled for evaluation. Results of this evaluation were used to describe water quality conditions and, in conjunction with land cover and hydrology information, the relative transport/retention of selected materials associated with various hydrologic events based on selected surface water elevations. Specific issues addressed included evaluation of: (1) the effects of hydrologic changes on water quality for both the area impacted by the proposed project and in relationship to the overall water quality of the Mississippi River, (2) the effects on water quality associated with potential changes in pesticide use, and (3) the effects of proposed groundwater supplement on Big Oak Tree State Park. Water quality in the area reflects conditions typical for basins where agriculture is the dominant land use. In general, nutrient concentrations (with the exception of phosphorus) were not excessively high except during periods of elevated flow, and basin concentrations were not substantially different than observations for the Mississippi River. Sediment concentrations were generally lower than concentrations in the Mississippi River and increase with runoff as expected. With the exception of a few occasional high concentrations of nitrates, groundwater quality is acceptable although phosphorus concentrations in groundwater were generally higher than in surface waters, Point sources were the most notable sources of extremes (high nutrients or low dissolved oxygen concentrations).