9403292 Rosemond Although nutrients in aquatic food webs may control growth rates of primary producers (which are consumed by higher trophic levels), few investigations have directly probed the role of nutrients in detrital systems. Landscape - scale volcanic activity in Central America results in prominent changes to surface water chemistry, including dramatic increases in soluble reactive phosphorus (P) concentrations, with appreciable localized effects on stream biota. This research will examine whether geothermal P inputs enhance microbial biomass, nutrient content, and leaf litter decomposition rates. Effects of P variation on higher trophic levels will be assessed by comparing drift and trap densities, and size of detritivorous shrimp. High and low P site comparisons of leaf litter quality will be performed using measures of detritivore growth and fat content. The relative importance of microbial versus macroconsumer processes in leaf decomposition will be determined using in situ manipulations of nutrient levels. Both bottom - up (nutrient) control and top - down (detritivory) control will be examined. %%% The role of detritus in trophic dynamics hasn't been well studied, particularly in lotic (flowing water) ecosystems. But beyond fundamental research aspects, this project's importance derives our need to know how aquatic systems operate, as human population pressures place increasing burdens on the natural environment, in the United States, Latin America, and around the world. ***
