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Within the State of Maryland, the potential water quality benefits of beaver are not recognized as contributing to regulatory-mandated pollution reductions. Therefore, jurisdictions lack a regulatory incentive to either encourage beaver colonization or manage and protect existing beaver habitat. Such an incentive is important, as conflicts between human and beaver habitat regularly arise. While beaver habitat often increases the groundwater table and the wetted extent of a stream system, this is not always welcomed by homeowners and can result in beaver being trapped out, with beaver dams dismantled. If beaver ponds were a recognized BMP to improve water quality, it would assist local jurisdictions with the development of beaver habitat conservation programs via easements and adaptive management. Rather than living on top of nature and replicating nature’s original ecosystem engineers with significant amounts of tax dollars, citizens could live with nature allowing tax dollars to go further, and implement more ecological restoration.
The fluxes and concentrations of materials from two contiguous second-order watersheds in the Coastal Plain of Maryland, U.S.A. were measured for six years prior to and six years subsequent to the formation of a 1.25 ha beaver pond near the bottom of one of the watersheds. The watersheds have a clay aquiclude and were equipped with V-notch weirs and continuous volume-integrating water samplers. The beaver pond reduced annual discharge of water, total-N, total-P, dissolved silicate, TOC, and TSS by 8, 18, 21, 32, 28, and 27%, respectively. Most of the total-N reduction was due to increased retention of nitrate in the winter and spring and TON in the winter and summer. Most of the total-P reduction was the result of retention of both TPi and TOP in the winter and summer. Dissolved silicate retention peaked in the spring, while TOC and TSS retention peaked in the winter. Prior to the formation of the beaver pond, concentrations of TON, TPi, TOP, TOC, and TSS had highly significant correlations with stream discharge, especially in the winter, but subsequent to the pond there was little or no relationship between these concentrations and stream discharge. However, concentrations of nitrate in the spring and ammonium in the summer were highly correlated with stream discharge both before and after the formation of the beaver pond and regressions of discharge versus concentrations of these nutrients explained more of the variation in concentrations after the formation of the pond.