Long-term phosphorus assimilative capacity in freshwater wetlands: A new paradigm for sustaining ecosystem structure and function

Statistical analysis of a North American Wetland Database (NAWDB) allowed u s to develop a mass loading model that was used to separate P assimilative capacity (defined as P absorption with no significant ecosystem change and no elevated P output) from storage capacity (maximum storage) in wetlands. Our analysis indicates that, given ample supplies of other nutrients, avera ge P assimilative capacity (PAC) in North American wetlands is near 1 g m(- 2) yr(-1). From this analysis, we proposed a "One Gram Assimilative Capacit y Rule" for P loadings within natural freshwater wetlands if long-term stor age of P, maintenance of community structure and function, and low P efflue nt concentrations are required. An Everglades test site supports our hypoth esis that natural wetlands will lose native species, become P saturated in a few years, and export unacceptable amounts of phosphate when phosphorus l oading exceeds PAC. Moreover, our findings clearly demonstrate that even P- limited wetlands have the capacity to assimilate low levels of P loadings w ithout significant changes in ecosystem structure and function.