The Cycles of Nitrogen and Phosphorus
Both the salt marsh and the estuarine water at Sapelo Island are highly eutrophic (Figure 8.1). Nutrient limitations at some levels, or in certain microhabitats, do exist, but they are not a major concern in our efforts to understand how the elements, especially phosphorus and nitrogen, function within the system. The earliest ecological studies of essential elements focused on their role as limiting factors in the sense of Liebig. Nutrient-organism interaction was emphasized, but the fundamental unity or interconnectedness of nutrient pools in all forms of an element and in all parts of an ecosystem were not. We now recognize the value of analyzing nutrient flows as a descriptor of ecosystem function. In this way nutrient flows can be used in the same way energy flows are used to describe properties of the ecosystem, although flows of energy and nutrients will not be identical. Elements are of concern to ecologists not only as limits to system biomass and function, but also as indicators of formation, transformation, and degradation of organic matter, both living and nonliving. Our emphasis here is on a holistic perception of the flux of phosphorus and nitrogen through the salt-marsh ecosystem.
KeywordsSalt Marsh Nitrogen Fixation Dissolve Organic Nitrogen Tidal Creek Estuarine Water
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