Dr. Paerl proposes an intensive examination of nitrogen cycling in diverse marine benthic microbial mat systems. Microbial mats are extant relatives of stromatolites, the ancient life form on Earth, and are important not only from a paleobiological/evolutionary standpoint, but are ecologically as well, often making substantial contributions to the overall productivity of the ambient environment. Nitrogen fluxes attributable to nitrogen fixation, denitrification, and nitrification will be quantified. The spatial and temporal distribution of each process will be determined. Three field sites will be used on the basis of the dual criteria of representing areas of potentially great importance to shallow water nutrient fluxes and close resemblance to fossil stromatolites. This investigation represents the first comprehensive examination of nitrogen transformations in microbial mats, within which the spatial distribution of oxygen (and thus the distributions of many important geochemical transformations), changes dramatically on a diel basis. Changes of this type are characteristic not only of microbial mats but a large number of benthic photosynthetic communities occurring in areas of fundamental ecological importance, such as salt marshes, tidal flats, mangrove swamps, and barrier islands.
