At all LTER sites we quantify phytoplankton biomass and productivity by coupling PAR measurements with pulse amplitude modulated fluorometry. In this technique, a rapid series of high frequency flashes permits measurement of the absorption cross section of Photosystem II (quantum yield), the rate of photosynthetic electron transport, the level of photochemical quenching, and the concentration of chlorophyll a. At these same sites we enumerate bacteria using DAPI epifluorescent microscopy and determine bacterial productivity using 3H-thymidine uptake experiments. We compare algal:bacterial biomass and productivity as well as grazing rates in an effort to characterize the microbial loop.
DOM Bioavailability Assays
We conduct biomass leaching experiments (abiotic) to characterize the DOM generated by specific sources. Results of such `end-member? experiments are then applied in the field. We conduct bioavailability assays on ambient and leached DOM using 16 day incubations. We quantified loss of the DOM (DOC, DON) fraction as well as the chemical characteristics. The assays are designed to quantify the effect of nutrient additions on DOM degradation and are conducted with an ambient control.
Shark River Surveys
Biannual sampling events of the Shark River estuary in the Everglades were performed in March 2001 and ended October 2002. Surveys were conducted at slack low and high tide along the salinity gradient. In addition samples were collected at a central station in the river over a 48 hour period. Variables measured included temperature, salinity, dissolved oxygen, ammonium, nitrate, nitrite, total organic nitrogen, soluble reactive phosphorus, total phosphorus, total organic carbon, chlorophyll a, alkaline phosphatase activity, turbidity, and light extinction. Algal energetics (as quantum yield) and chlorophyll a concentrations for major phytoplankton guilds (green algae, brown algae, and cyanobacteria) were quantified using a PhytoPAM fluorometer. Bacteria were quantified by direct counts using DAPI; 3H-thymidine uptake was used to measure bacterial production.