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EPA/600/R08/055
Effectiveness of Restored Wetlands for the Treatment of Agricultural Runoff
(39 pp, 1.0MB, About PDF)Abstract
Throughout the Delmarva Peninsula drainage activities that commenced during colonial times and intensified during the 20th century have resulted in the creation of extensive ditch systems through the generally flat, alluvial soils for the purpose of rapidly removing water in order to support agriculture and human habitation. Ditching frequently involved extending surface water systems (ditches) into areas that were naturally perennial or seasonal wetlands, resulting in the drainage of these forested wetlands and the lowering of the local water table. The straight configuration of the ditches and the straightening, widening, and deepening of some perennial nontidal stream channels expedited flow downstream and accommodated the larger volumes of storm flow coming from the watershed which were no longer being retained by wetlands. The large decrease in storm water residence time on the land and the larger volumes resulted in greatly elevated loadings of sediments and nutrients to downstream lower energy waters (i.e., lakes/ponds, tidal rivers, estuaries). The ensuing shallowing and occurrences of algal blooms triggered by nutrient enrichment in these low energy "receiving" waters have impacted both human economic activities and ecological health to varying extent which in some cases has been catastrophic.
In Delaware since the 1990’s there has been substantial and increasing effort to reestablish some of the wetland acreage that has been lost over the past 300 years. Such restoration is part of a broader strategy to develop comprehensive watershed management plans as part of TMDL driven Pollution Control Strategies. The objective of this work has been to enhance the sediment/nutrient retention capability within watersheds, with an ultimate goal of achieving improvement in economic and ecological condition in areas that have been impacted by the reduction or elimination of the buffering functions afforded by wetlands. This exploratory project represents the first concerted effort by the State of Delaware to obtain some water quality data from a restored wetland and adjacent riparian corridor in order to examine the interception and retention of sediments and nutrients transported in overland runoff from agricultural fields.