Riparian wetlands have a demonstrated ability to filter and control nitrogen (N) and phosphorus (P) movement into streams and other bodies of water; few studies, however, have examined the roles that individual plant species serve in sequestering N and P pollutants. We evaluated the potential for growth and consequent N and P accumulation by five species of wetland perennials. We planted blocks consisting of 900-cm2 plots of each species at 11 sites within a riparian wetland that receives large inputs of agricultural runoff. Plant shoots and roots were collected at the time of peak standing crop to determine net accumulation of biomass, N, and P for one growing season. A portion of the plant shoots was placed in decomposition litterbags in the field to determine biomass, N, and P losses for 60, 120, and 150 days. Of the five species, bur reed (Sparganium americanum) had the greatest aboveground accumulation of N and P but had the lowest belowground accumulation values. In contrast, woolgrass (Scirpus cyperinus) had the lowest aboveground values for N and P accumulation but had the highest belowground value for P. Soft rush (Juncus effusus) and reed canary grass (Phalaris arundinacea) showed high values for both aboveground and belowground N and P accumulation, while blue joint grass (Calamagrostis canadensis) showed low values for aboveground N and P. The five species also showed wide variations in the retention of N and P in decomposing shoots. Juncus effusus had the highest percentages of N and P remaining in litter after five months (87% N and 69% P), while P. arundinacea retained only 28% N and 18% P. Sparganium americanum had high retention rate for N in litter (74% N) but showed low P retention values (35%). Scirpus cyperinus and C canadensis also showed high retention rates of litter N but lower values for P retention. Our study suggests that species show differential accumulation and release of N and P and may influence the overall potential of a wetland to retain agricultural nutrients. © 2003, The Society of Wetland Scientists.
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