Insights into the long-term physical controls on estuarine food webs and implications for future change

Freshwater discharge is an important driver of coastal ecosystem productivity. We use a variety of approaches from stable isotope assessmentof foodwens to trackinger coastal herring movements in rivers to understand the freshwater to saltwater linkages.

We observed a strong influence of freshwater residency time on the contribution of benthic and pelagic production sources in the food web and a significant reliance on high marsh prey items with increasing inundation times for benthic consumers in our module. We infer that long-term changes in flow regime and inundation time will likely compress the influence of the riverine sources of production and increase dependence on high marsh and upland production sources. In the short term this will likely result in an increase in secondary productivity and enhanced connectivity between estuarine and coastal ocean food webs. However, if saltmarsh plants are unable to keep up with sea level rise the system productivity will decrease as productive marsh habitats are converted to open water.

We are finding that small changes in average conditions are associated with large changes in the frequency and intensity of extreme events.  We are also finding large biases in the NARRCAP regional climate model simulations of historical conditions. Information from this project will allow managers and citizen groups to determine how much freshwater inflow is needed to sustain productive estuaries.