PARENT SESSION
Oral Session #76: Ecosystem Ecology: Larger scale processes, geomorphology, soils.
Presiding: W. Straw
Thursday, August 8. 9:00 AM to 11:30 AM. Gila Meeting Room, TCC.

Isolating biogeochemical and hydrologic effects of increasing freshwater inputs to Everglades wetlands using long-term sawgrass productivity data.

CHILDERS, DANIEL^*,1, IWANIEC, DAVID¹, MADDEN, CHRIS², NOE, GREGORY¹, RONDEAU, DAMON¹, RUBIO, GUSTAVO¹, VERDON, EMILIE¹, ¹ Florida International University, Miami, FL² South Florida Water Management District, West Palm Beach, FL

ABSTRACT- Several recent restoration projects have increased freshwater inputs to the Southern Everglades, with potential impacts of changes in both water quantity and quality. We used long-term sawgrass productivity data from 16 Southern Everglades sites to separate these two effects and predict restoration outcome. Sawgrass mortality showed little intra-annual variation at most sites, averaging about 10% mo^-1. Sawgrass annual production (AP) was quite low across this oligotrophic landscape (100-500 gdw m^-2 y^-1). Surface water rarely showed elevated phosphorus concentrations (>0.3 M TP) at canal-side sites, and sawgrass productivity did not increase at these sites. At the estuarine ecotone, we found dramatic inter-annual differences in sawgrass AP related to salinity stress. Our longest dataset (1998-2001) showed a long-term decline in net annual productivity (NAP) at many sites across the landscape (up to −175 gdw m^-2 y^-1) following increased freshwater inputs. Because sawgrass is perennial and grows year-round in the Everglades, we argue that a negative NAP represents a net loss of biomass capital for future production. Thus, long-term measures of NAP actually track the ecological capital of this species. This negative NAP response was expected because sawgrass typically grows in relatively short hydroperiod conditions. As hydroperiod increases, a more slough-like community should replace the sawgrass community. This long-term decline in sawgrass ecological capital is the first step in this process, demonstrating the importance of such long-term data to Everglades restoration efforts.

KEY WORDS: wetlands, Everglades, productivity, sawgrass