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Using stable isotopes and models to explore estuarine linkages at multiple scales
Citation:
KALDY, III, J. E., C. A. BROWN, AND P. M. ELDRIDGE. Using stable isotopes and models to explore estuarine linkages at multiple scales. Presented at Texas Academy of Sciences, 111th Annual Meeting, Corpus Christi, TX, March 06 - 08, 2008.
Impact/Purpose:
Estuarine managers need tools to respond to dynamic stressors that occur in three linked environments – coastal ocean, estuaries and watersheds.
Description:
Estuarine managers need tools to respond to dynamic stressors that occur in three linked environments – coastal ocean, estuaries and watersheds. Models have been the tool of choice for examining these dynamic systems because they simplify processes and integrate over multiple scales. Similarly, stable isotopes integrate over a variety of biogeochemical processes and provide a sensitive and robust tracer. We use empirical measurements of 15N in green macroalgae to document switching of the N loading from a watershed source to an oceanic source in estuaries. By incorporating 15N into a hydrodynamic model, we can quantify the contributions from the various sources in the system. Ocean upwelling supplies N during the summer, while watershed inputs from N fixing red alder trees dominates loading during the winter. We have used these findings to classify estuaries. As another example, we have used a similar empirical/model/isotope approach to evaluate seagrass protective criteria. Using empirical data we have developed a stress response model for Zostera marina (eelgrass) including detailed measurements of growth, biomass, carbohydrates, photosynthetic parameters and DOC exudation. Model validation efforts include in-situ stable isotope enrichment experiments, short-term transplanting efforts and mesocosm studies. Using the model we evaluated the potential effectiveness of water clarity criteria on Zostera marina and found that values similar to those used in Chesapeake Bay would be protective of eelgrass. These examples demonstrate how simple models coupled with critical empirical data and stable isotope measurements can be a very powerful tool to address linkages across temporal and spatial scales.