THE INFLUENCE OF MILL DAM PONDS ON THE BIOGEOCHEMISTRY OF SMALL STREAMS

The abundance of mill dam ponds on the eastern coast of the United States is thought to have physically impacted the evolution of streams, and so might have an affect on chemical processes within stream-pond systems. Previous studies have shown ponds to be nutrient sinks, even during the winter when uptake of nitrogen by microorganisms slows down and most removal is done through settling and gas exchange with the atmosphere. This study focuses on the water chemistry of the input and output of ponds within three representative steams in the Hudson River watershed (in Dutchess County, NY). These streams have a basic pH (~8) and variable nitrogen loads. The most polluted stream has nitrate levels above 75 μM, whereas the other two streams are usually below 50 μM. Sampling is ongoing, but preliminary data suggest that the ponds are nutrient sources rather than sinks. We will separate the chemical retention processes of these ponds from removal due to residence times of the water but consider retention time for total removal rates.