The Effect of Hypoxia on Greenhouse Gas Fluxes in Coastal Marine Ecosystems

Sarah Foster, Ph.D. research

Summary:

Over the past 150 years humans have dramatically increased the amount of reactive nitrogen (N) put into the environment.  In fact, humans have more than doubled the amount to the biosphere through the intensive production and use of fertilizers, agricultural practices, burning of fossil fuels, urban runoff and wastewater discharge.  At the convergence point of coastal drainage basins, estuaries receive a disproportionately large amount of this N pollution.  In many coastal ecosystems, N can cause a progression of conditions where the enhancement of primary production (algae growth) leads to the accumulation of organic matter, which encourages microbial consumption of dissolved oxygen in bottom waters.  Areas of low dissolved oxygen (hypoxia, concentrations less than 3 mg/L threshold) or no oxygen (anoxia) are increasing across the globe. The effect of hypoxia on macrofauna species such as invertebrates, crustaceans, fish, is well documented but what is less understood is how hypoxia impacts benthic biogeochemistry and microbial communities.
 

In my dissertation research I am using Waquoit Bay (Cape Cod, Massachusetts) as a natural laboratory to investigate the impact of low oxygen conditions on crucial ecosystem functions.  Nutrient regeneration, the removal of reactive N through denitrification and the regulation of greenhouse gases (e.g. nitrous oxide and methane), all have the potential to be dramatically changed under hypoxic conditions.  Over the past century changes in watershed land use have doubled the rate of land-derived N loading to the Waquoit Bay ecosystem.  As a result, the bay has seen dramatic ecological changes.  Most critically, in many regions of the bay, limited mixing of surface and bottom waters in addition to pervasive macroalgae mats creates large fluctuations in dissolved oxygen concentrations.  Using synergistic field observations and experimental manipulations I evaluate the biogeochemical and microbial response to low oxygen conditions by measuring changes in dissolved nutrient, di-nitrogen and greenhouse gas fluxes across the sediment-water interface.  It is my hope that findings from this work will further our understanding of the impacts of N pollution and eutrophication on coastal marine processes and provide crucial information to develop strategies to reduce, mitigate and control hypoxia.


Project Funding:
 
Woods Hole Sea Grant
 
National Defense Science and Engineering Graduate Fellowship
 
 
Acknowledgements:  Boat support & Outreach/Education
 
Waquoit Bay National Estuarine Research Reserve
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