Salt marsh nitrogen analysis : fertilization and the allocation of biological productivity

Abstract

A five compartment schematic model of the flow of nitrogen through Great Sippewissett Marsh is presented. Flows are described in terms of annual inputs, outputs and intercompartmental transfers of nitrogen. The nitrogen in all forms occurring in the marsh is considered, though dissolved organic nitrogen is disaggregated from the total flow. A computer aided input - output analysis is performed on the model to assess the degree to which nitrogen inputs to the marsh surface are linked to nitrogen outputs in the form of net growth in marsh shellfish. In this way the effects of both direct and indirect flows linking the two compartments involved are considered. The analysis is done to assess the likelihood that a large scale application of fertilizer to the marsh surface will signjficantly enhance shellfish growth in marsh tidal creeks. While no definitive answer to this question can be given, it is argued that the present level of understanding of the marsh nitrogen cycle does not support an expectation that shellfish growth will be enhanced. This argument is supported by a comparative analysis which shows a strong likelihood that Spartina growth is enhanced by fertilization, an effect which has already been observed.