Sanders, J. G.. Academy of Natural Sciences, jsanders@acnatsci.org
Weinstein, M. G.. Academy of Natural Sciences, weinstei@acnatsci.org
Breitburg, D. L.. Academy of Natural Sciences, breit@acnatsci.org

 
THE EFFECTS OF MULTIPLE STRESSORS ON ESTUARINE ECOSYSTEMS: SEASONAL VARIABILITY IN RESPONSE OF PHYTOPLANKTON COMMUNITIES TO TRACE ELEMENTS
 
As part of a larger program (COASTES), we have examined the response of natural phytoplankton communities from the Patuxent River (a subestuary of Chesapeake Bay) to multiple stressors (nutrients and the trace elements As, Cu, and Cd). A number of replicate runs were performed during 1996 and 1997 in 1000 liter mesocosms in which phytoplankton were exposed to either ambient or elevated levels of nutrients and trace elements, separately and in combination, over a 5 week period. Response to trace elements was more variable both temporally and among phytoplankton taxa than was the response to nutrients. Integrative measures of response (biomass, productivity) tended to be reduced by trace elements. Individual taxa, however, responded both positively and negatively. The most dominant species, a large centric diatom, Rhizosolenia fragilissima, was greatly stimulated by elevated nutrients, and often inhibited by trace elements. Interactions between the stressors were important in regulating phytoplankton response. In particular, seasonal shifts in the nutrient that limited phytoplankton growth in the Patuxent River (P in spring, N in mid-late summer and fall) greatly affected the toxicity of trace elements, presumably by either facilitating (when P was limiting) or impeding (when P was abundant) As uptake, incorporation and subsequent toxicity.
 
Day: Friday, Feb. 5
Time: 04:30 - 04:45pm
Location: Sweeney Center
 
Code: SS28FR0430S