It has been established that freshwater ecosystems are limited by phosphorus availability while primary production in marine systems is limited by nitrogen instead. However, the reasons for such a shift are still not understood. I have shown that along a salinity gradient in an estuary there are intrinsic differences in physical and chemical characteristics of coastal wetland sediments that contribute to the observed increases in phosphorus availability seaward (Sundareshwar and Morris, 1999, L&O).  Through comparative ³¹P NMR study of sediments from coastal wetlands in impacted and unimpacted watersheds, I revealed heretofore-unreported occurrences of pyrophosphate (Ppi) in estuaries, and showed that the accumulation of Ppi in coastal environments was a function of degree of urbanization in the watershed. Importantly, Ppi cannot be detected using standard water quality techniques, but is bioavailable and can potentially alter trophic status and overall ecosystem productivity (Sundareshwar et al. 2001, L&O).  Similarly, I have further shown that phosphorus loading in the Cape Fear River (the largest river system in North Carolina) occurs in diverse chemical forms, including Glyphosate (a commonly used weedkiller), Aminomethylphosphonic Acid (a degradation product of Glyphosate), and pyrophosphate (the smallest chemical form of polyphosphate with wide industrial applications) (Sundareshwar and Richardson, 2002, WRRI).

Watershed land use characteristics alter the availability and abundance of these chemical forms of P. I have found that converting natural wetland forests to agricultural land leads to the loss of ‘chemical diversity’ in nutrient speciation, analogous to the loss of biological diversity upon habitat destruction. However, wetland restoration promotes the re-establishment of this diversity in chemical speciation of phosphorus.  Since chemical speciation of nutrients in ecosystems is a result of biological activity, restoration of these forms may indicate the restoration of ecosystem function – if not that of ecosystem structure. Furthermore, this study also suggests that ³¹P NMR spectrometry can be used as a tool to track the progress of wetland restoration actions, current guidelines for which are very subjective at best (Sundareshwar, Richardson and Bruland. Science. Submitted). A proposal to examine the links between ecosystem structure and function in restored agroecosystems is under review at the NSF.

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