Field Manipulations

For each lake, three transects will be established along the desiccation gradients. For Salt Pond, 10-meter transects will be established, and for Storr's lake, 25 to 35-meter transects. Transects will encompass the full desiccation gradient. Mat samples will be collected every five meters. Environmental conditions, community structure, desiccation stress indicators, and EPS characteristics will be determined for mats along the gradient. Samples will be rehydrated with water characterized by two different salinities for 72 hours: ambient lake water, seawater, and freshwater.

After 72 hours, physiological rates (photosynthesis, nitrogenase activity, and EPS cycling) will be measured at two to four hour intervals for 27 hours in order to encompass a diel cycle. After 144 hours from the time of collection, the diel experiments will be repeated. For Storr's Lake, only 'Lyngbya Crust', 'Pie Mound", and 'calcareous mat' samples will be collected for rate measurements. The primary purpose of these experiments will be to establish relative rates of recovery from water stress for mats exposed to a gradient of desiccation. Conducting these experiments during rainy and dry seasons, over multiple years, will allow us to compare the responses of the same communities under different water stress conditions. These experiments also will allow us to characterize how different anhydrophilic communities respond to and recover from desiccation stress.

Determining short-term controls on primary production, nitrogenase activity, EPS cycling, and EPS content will be undertaken by conducting bioassay-type experiments. Mat samples will be collected and returned to the BFS. Small sub-samples will be removed and placed in freezer pans. Manipulations will consist of different salinity levels, UV filters, and nutrients. Nitrate (NaNO3, 5 mM), orthoposphate (H2PO4, 2 mM), trace metal mix (1 mM Fe and 0.5 each mM Mn, Cu, Zn, Mo, Co, and B), and organic carbon mix (10 mM each mannitol, acetate, glycollate) will comprise nutrient additions. Water and nutrients in the pans will be replaced each day. The freezer pans will be kept in circulating water baths to regulate water temperature in the freezer pans. Mat samples will be allowed to incubate for 7 to 10 days before sampling for physiological rate measurements (photosynthesis, nitrogenase activity, and EPS production). The purpose of these experiments is to assess the short-term controls on production, growth carbon and nitrogen cycling, and how their potential interactions might affect mechanisms of desiccation recovery (e.g. EPS production).

Additional experiments will be conducted at the IMS, Texas A&M, and U.S.C involving cultured organisms (Fig. 4). These will involve screening cultured organisms for desiccation tolerance, EPS production, and taxonomic molecular characterization. These studies will serve as topics for graduate student research and will require training in each laboratory, fostering interdisciplinary investigations and further ensuring collaborative efforts.