While the Chesapeake Bay is a well-known example, similar losses are occurring in the coastal waters of Cape Cod. The sources of nitrogen include septic discharge and lawn fertilizer associated with development, and acidic deposition. Some of this nitrogen is transmitted to the coastal waters via groundwater flow. In this project, we seek to determine the efficiency with which transmission of nitrogen via groundwater occurs, and in particular the extent to which denitrification lessens the nitrogen burden of groundwater as it moves shoreward. M any streams in New England and elsewhere are acidic, particularly during spring runoff, when nitrate levels may be elevated.
Early results suggest a major role for nitrification.
Driveable probes based on LIF may overcome these problems to a degree, but are hindered by the use of large above-ground lasers and the associated problem of propagating ultraviolet excitation to the subsurface via optical fiber, which is lossy in the UV range. In this project we developed a probe based on a Q-switched microlaser developed at MIT's Lincoln Labs. In addition, the probe has been characterized with respect to the effects of different soil types and textures, and a model that predicts correction factors for different soils has been developed. This toxicity is due to the formation of methylmercury by natural microbial populations, especially sulfate-reducing bacteria. However, the extent of mercury methylation varies greatly from lake to lake, and no satisfactory explanation is yet available.