One goal of the FCE LTER is to investigate how long and short-term variation in water flow, quality, timing, and disturbance influence patterns of primary production along the freshwater to marine hydrologic/salinity gradient. Primary production is measured at all sites using methods and schedules that are pertain to the dominant plant or algal group present at each site. In the freshwater marsh, primary productivity of sawgrass is measured in three quadrats at each site on a bimonthly schedule using a non-destructive allometric technique. Productivity of periphyton is measured at the same sites during the wet season using triplicate artificial substrates and light-dark bottle incubations to determine oxygen production. Mangrove productivity is estimated at estuary sites in replicate 0.04 ha plots by quantifying litterfall (monthly), stem/wood production (annually) and belowground production (semi-annually). Marine sites are visited on a bimonthly schedule where productivity of benthic seagrass is measured by leaf-marking, macroalgae using vital staining, and microalgae using artificial substrates. At both the estuary and marine sites, phytoplankton productivity is quantified monthly by coupling PAR measurements with pulse amplitude modulated flourometry.
Research to date has shown that annual net primary productivity (ANPP) of many ecosystem components is enhanced in the ecotone sites of the TS/Ph transect, while ANPP by the dominant macrophytes showed a "wedge" of increasing productivity towards the marine endmember of the SRS transect (Ewe et al. 2006). The same marine-directed increase in ANPP occurs in Florida Bay (Fourqurean et al. 1992). Water column P concentrations followed a similar pattern, with unexpectedly high P in the TS/Ph ecotone during the dry season (Childers et al. 2006a). FCE reseachers are determining the relative contribution of marine and groundwater discharge of P to these productivity patterns, and determining how natural climatic and management-driven changes in downstream freshwater flow impact the location and timing of productivity peaks. Researchers also expect that the source of P (surface or ground) would affect biomass allocation in plants, so in FCE II they are measuring both above- and below-ground biomass in the FCE ecotone sites and determining changes in that allocation resulting from experimental P supplements.
Sharon Ewe and Edward Castaneda measuring mangrove seedlings
along transects at SRS-6 in Shark River Slough
Divers sampling seagrass in Florida Bay
Measuring sawgrass at TS/Ph-1 in Taylor Slough
Periphyton productivity is measured by determining growth
on substrates placed in the marsh for a set period of time
Measuring periphyton productivity using light-dark bottle
biological oxygen demand (BOD)