CHARACTERIZATION OF RIPARIAN SPECIES AND STREAM DETRITUS USING MULTIPLE STABLE ISOTOPES

Multiple stable isotopes were used to determine the effectiveness of d istinguishing among several dominant riparian species and aquatic macr ophytes both spatially (three sites) and temporally (three seasons) al ong an 8-km reach of a blackwater stream. The differences in isotopic composition were used to assess contributions of various organic matte r sources to the detrital pool of the stream. Samples of riparian and aquatic macrophyte vegetation and detritus were collected at three tim es to represent early leaf-out (April), mid-summer (August), and just prior to abscission (October). Each sample was analyzed for stable iso topes of carbon (delta(13)C), nitrogen (delta(15)N), and sulfur (delta (34)S) Within a site and sampling date, delta(13)C-values were signifi cantly different among certain riparian species and detritus samples. Species differences persisted between seasons. delta(34)S values were the most variable of the three elements examined although they remaine d fairly constant through time within each species and site. The resul ts suggest that temporal changes in isotopic composition of riparian s pecies and aquatic macrophytes are site-specific. Discriminant analysi s dissimilarity plots (based on all three isotopes) demonstrated that the contribution of species to the detrital pool depended on the site and season. At the upper site, detritus was isotopically most similar to Quercus laurifolia and Sparganium americanum in April, and the aqua tic macrophytes (S. americanum and Potamogeton spp.) in August and Oct ober. At the middle site, detritus was most similar to Carpinus caroli niana and Q. nigra in April but no single source was similar to detrit us in August or October. At the lower site, detritus was most similar to Taxodium distichum for all three seasons.