INCREASED AMMONIUM CONCENTRATIONS IN A TIDAL FRESH-WATER STREAM DURING RESIDENCE OF MIGRATORY CLUPEID FISHES

This study was done to test the hypothesis that dense aggregations of spawning, anadromous clupeid fishes (Alosa spp.) could substantially i ncrease ammonium concentrations in Wards Creek, Virginia, a tidal fres hwater stream in the mid-Atlantic coastal plain. In 1992 and 1993, we measured total ammonia nitrogen concentrations in the stream during Fe bruary-July, before, during, and after clupeid fish migration. Abundan ce of migrating fish was estimated by electrofishing. During the perio d of high clupeid abundance (catch greater than 20 fish/h) in 1992, st ream total ammonia was significantly higher (P < 0.01) than when clupe id fish were present in low abundance (catch 20 fish/h or fewer). A si milar pattern was observed in 1993. In addition, total ammonia concent rations in both years were strongly and positively correlated (r = 0.8 4) with migratory clupeid abundance. Our findings, although somewhat p reliminary, suggest that anadromous clupeid fishes could substantially alter the chemical environment of Wards Creek, and we speculate that ammonia inputs may affect biotic interactions and nutrient dynamics in other similar streams.