PARENT SESSION

MP6 Mercury in Stream Ecosystems
202 Oregon Ballroom
1:20 PM - 4:40 PM, Monday

() Long-term and large-scale trends in mercury bioaccumulation in the Suwannee River Basin, FL.

Chasar, L¹, Lange, T², Grubbs, J¹, Chanton, J³, ¹ United States Geological Survey, Tallahassee, FL, USA² Florida Fish and Wildlife Conservation Commission, Eustis, FL, USA³ Florida State University, Tallhassee, FL, USA

ABSTRACT- The Suwannee River exhibits strong gradients in land use and water chemistry along its 245 mile course, providing a unique opportunity for the study of mercury bioaccumulation in lotic systems. To evaluate temporal trends in mercury burden of largemouth bass (Micropterus salmoides), muscle tissue was analyzed for total mercury concentration in fish collected from the lower Suwannee River basin annually from 1987 to present. As a preferred prey item crayfish (Procambarus sp.) were collected in 1993 and 2001, and muscle tissue was analyzed for methylmercury. Spatial trends in bioaccumulation were evaluated by analyzing mercury burden, ¹³C, and ¹⁵N in crayfish, sunfish (Lepomis auritis) and largemouth bass collected in 2001 from stations 15 to170 miles upstream of the river mouth. Mercury levels in largemouth bass (age standardized, EHg₃) decreased from 0.80 (1989) to 0.25 g/g (2001), although values peaked in 1992 and 1999. Mercury levels in crayfish also decreased by approximately 60% from 1989 to 2001. Mercury body burden is apparently related to river stage; regression models indicate that mercury in largemouth bass is significantly correlated to the number of days at or exceeding flood stage (days overbank, i.e., streamflow exceeding 75% duration flow) during the life of the fish. Mercury concentration in the muscle tissue of sunfish and largemouth bass increased with increasing river miles upstream. Preliminary analysis of stable isotope data indicates little difference in trophic position for largemouth bass among all stations (¹⁵N_lmb − ¹⁵N_cray ranged from 4 to 6 ‰), suggesting that bioaccumulation rates are more tightly controlled by mercury source/transport, and local biogeochemical processes.

Key words: Lepomis auritis, Micropterus salmoides, Procambarus, Mercury