Beaver pond biogeochemical effects in the Maryland Coastal Plain

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. Beaver (Castor canadensis) were an abundant and important part of the landscape in eastern North America at the time of European settlement in the 15th and 16th centuries, but were extirpated over much of their range for their fur (Naiman et al. 1988). The Coastal Plain of Maryland was among the many regions where beaver populations were extirpated. In the 1970’s the U.S. Fish & Wildlife Service reintroduced beaver to the Coastal Plain of southern Maryland and beaver populations have subsequently increased rapidly. What are the biogeochemical effects of this beaver reintroduction on the streams of the Coastal Plain? While the landscape effects of beaver populations on the biogeochemistry of the Minnesota region have been explored in considerable