Estuarine Primary Production from the Triple Isotopic Composition of Oxygen
|Benthic flux chambers in a nutrient-enriched creek in the Plum Island Ecosystem Long-Term Ecological Research site are being used to quantitatively examine the effects of eutrophication on benthic microalgal production. (Photo by R. Stanley)|
Amanda Spivak (WHOI), Linda Deegan (MBL), and Chuck Hopkinson (UGA)
More than 50% of the American population lives near the coast. Coastal regions provide valuable economic resources including fisheries and tourism, making coastal zones of great societal importance. Humans have heavily impacted coastal zones in general – and estuaries in particular – through water runoff and nutrient loading, which can lead to very low levels of oxygen in the bottom waters, harmful algal blooms, and fish kills. In addition, climate change will affect estuaries through sea level rise and the changing hydrologic cycle. Estuaries are regions of intense cycling of nutrients and carbon. There is a great need to better understand carbon cycling in estuaries in order to predict how biological production in these valuable habitats will respond to a changing environment.
Gross primary production forms the base of the food chain and thus is a key parameter for understanding estuarine carbon cycle dynamics. Two contrasting estuaries in Massachusetts offer the ideal locations to investigate gross production in estuarine systems. In Waquoit Bay, high nutrient loading has lead to macroalgae blooms which destroy seagrass habitats and occasionally result in anoxic water conditions and periodic fish kills. What is the variability of gross production? How does production respond to external factors? When macroalgae abundance decreases, does gross production in the estuary decrease or does the gross production shift from a macroalgal to a phytoplankton or microalgal based system? In the Plum Island Ecosystem estuaries, benthic microalgal mats are extensive and yet benthic microalgal production has rarely been quantified. What is the contribution of gross production from benthic microalgae? Additionally, a large-scale decade-long nutrient enrichment experiment allows us to examine the effect of eutrophication on primary production in tidal creeks. We will be making measurements of an innovative geochemical gas tracer – the triple isotopic composition of oxygen – in estuarine systems in order to quantify gross production in these two contrasting Massachusetts estuaries. The techniques developed through this work will yield key information on the carbon cycle in local estuaries and in the future could be applied to other estuarine systems.