Understanding Impacts of Oyster Aquaculture on Sediment Nitrogen Cycling - Toward Meeting Community Water Quality Management Objectives

Ginny Edgcomb, Geology & Geophysics
Hauke Kite-Powell, Marine Policy Center


2014 COI Funded Project


Anthropogenic impacts on coastal estuaries have been building for decades, with eutrophication from inputs of non-point source nitrogen (N) having the severest impact.  Excessive N loading in coastal systems has been linked to toxic algal blooms, coastal anoxia, and destruction of habitats critical to commercial fisheries and enjoyed by coastal communities.  Nutrient bio-extraction via oyster aquaculture is one potentially transformative alternative to costly sewering, and offers additional benefits including job creation and food.  Bio-extraction is an environmental management strategy by which nutrients are removed from an aquatic ecosystem through the harvest of enhanced biological production.  While it is straightforward to measure the nutrients extracted in oyster biomass (principally nitrogen) via harvesting, there is much debate about how much N is also lost from the ecosystem as a result of environmental alteration.  Oyster biodeposits export carbon and N to the underlying sediments and thereby may stimulate associated microbial communities, leading to enhanced denitrification.  Denitrification is a nitrogen removal process that occurs in marine sediments and portions of the water column with oxygen levels below ~5 ppm, and are thought to be performed primarily by prokaryotes (eubacteria and archaea).  Denitrification may be significantly increased in areas of oyster aquaculture.  This project aims to measure N removal in sediments under oyster aquaculture in Little Pond, Falmouth, Massachusetts, the site of a 3-year pilot study of bio-extraction via the culture and harvest of millions of oysters in a local estuary.  Results of this study will be incorporated into a multi-variant planning tool (WatershedMVP) that will provide the Town of Falmouth and other Cape Cod communities valuable data to assist decision making about the appropriate role of bioextraction in future water quality management plans.

This investigation involves interdisciplinary collaboration between scientists in the fields of microbiology, biogeochemistry, and marine policy (economics).  We will carry out a set of complementary measurements and experiments to understand impacts of oyster farming on microbial N removal.  We will measure total organic carbon, nutrients, and denitrification activity in core samples collected in Little Pond (below oyster cages and a nearby control site) in summer of 2014.  Additionally, we will establish whether levels of gene expression of several key genes involved in denitrification correlate with measured denitrification rates.  Aside from providing much needed proof of concept data for a future NSF submission, results of this interdisciplinary project will provide the first field-verified sediment N-removal rates via DNF in the presence of shellfish aquaculture, and will provide critical data for current local efforts to understand the potential of aquaculture solutions to coastal N loading.  Two to three local high school students will assist with fieldwork in order for them to gain experience in locally-based, but globally relevant coastal ocean science.