Correll, D. L.. Smithsonian Environmental Research Center, correll@serc.si.edu
Weller, D. L.. Smithsonian Environmental Research Center, weller@serc.si.edu
Jordan, T. E.. Smithsonian Environmental Research Center, jordan@serc.si.edu

 
FLUXES OF DISSOLVED SI FROM THE CHESAPEAKE BAY WATERSHED: MORE LIMITING OVER TIME?
 
As N/P fluxes to Chesapeake Bay have increased, silicate has become a limiting nutrient for diatoms. The watershed has different geological formations so weathering rates and fluxes of silicate vary widely. Mean silicate concentrations from 26 geological areas (over 500 streams) ranged from 2.17 for sandstone/shale ridges to 12.5 mg Si/L for Coastal Plain on the Rhode River, where watershed fluxes over the last 13 years averaged 29.2 kg Si/ha. Yet at times the tidal Rhode River was silicate-limited. Silicate concentrations from 4 Rhode River subwatersheds were compared for 1971-1972 and 1995-1996, periods of similar rainfall. Mean silicate concentrations were 35% lower in 1995-1996 (P < 0.01). A large beaver pond was built on one subwatershed in 1990. Silicate concentrations were not significantly different from those of a contiguous unaltered watershed for 6 years prior to the dam, but during 6 years subsequent to the dam averaged 29.5% lower (P < 0.001). On the Patuxent River for 3 years we measured inputs/outputs of silicate for two reservoirs. Outputs from the upper and lower reservoir were reduced 33% and 45%. These data indicate that while N and P inputs to Chesapeake Bay have increased, dissolved silicate inputs have declined.
 
Day: Friday, Feb. 5
Time: 02:30 - 02:45pm
Location: Sweeney Center
 
Code: SS13FR0230S