Historic Wetland Loss The Indicator Wetlands can be lost through lowering the local water table by ditching, by excessive pumping of the surface water table, or by blocking the flow of recharge water from its source. Soils which must be drained at least part of the year in order to support agriculture are considered historic wetlands now converted to other uses. The indicator maps non-wetland hydric soils--soils which are or at one time were saturated with water much of the year. Saturated soils frequently show accumulations of organic matter in excess of similar unsaturated soils because the anaerobic bacteria are less efficient at breaking down organic material than are aerobic bacteria. The presence of the excess organic material and the absence of free oxygen causes these soils to become highly acidic, which in turn changes their color, permitting detection of hydric soils after they cease to be saturated with water. The chemical environment of saturated soils favors the reduction of nitrates to gaseous nitrogen, thus reducing the nitrate loadings of the water which passes through the saturated zone of the wetland soils. The longer a soil remains unsaturated the more the organic material is oxidized, the lower its fertility becomes and the less identifiable the hydric soil characteristics become. To calculate the indicator, all the soils classified as hydric on maps prepared for the Maryland Office of Planning were combined with National Wetland Inventory (NWI) maps. Hydric soils coinciding with areas identified by NWI as wetlands, or which are permanently flooded by standing water--ponds, rivers or the bottom of bays or estuaries--were subtracted; the resulting map comprises non-wetland hydric soils. Interpretation A high acreage of non-wetland hydric soils points to a history of hydrologic modifications in that watershed, including agricultural ditching or tiling for improving soil tillage. These practices have been widespread and of long standing in the Lower Eastern Shore Tributary Basin. Only the Honga River, Monie Bay and Big Annemessex River watersheds did not score in the highest quartile statewide for this indicator when the Unified Watershed Assessment was prepared. As the map shows, the Upper Pocomoke River watershed includes the largest acreage of converted wetlands in the State. Indicator Use A high acreage of non-wetland hydric soils helps to identify potential for the restoration of wetlands for flood amelioration, wildlife habitat and water quality improvement functions. It will be easier and less expensive to restore the hydrology to a place where it formerly existed than to alter a site to provide surface saturation where it has not existed. Go to metadata for this indicator

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