News

The Bras d’Or Lakes in Cape Breton are Nova Scotia’s “Inland Sea” and constitute a widely ramified network of basins and channels connected to the Atlantic Ocean and protected as a UNESCO Biosphere Reserve. They cover a total area of about 1,100 km², their water has an intermediate, “brackish” salinity, and their many basins differ not only in depth but also in many other interesting ways. One of these basins is Whycocomagh Bay, which was the main destination of a field campaign in which two of our CERC.OCEAN Graduate Students, Lin Cheng (MSc) and Sebastian Haas (PhD), participated in June 2017. They were accompanied by researchers from the Bedford Institute of Oceanography and the Dalhousie Biology Department. The group was led by Professor Dr. Bruce Hatcher (Cape Breton University), whose expertise on the Bras d’Or system owes to decades of oceanographic studies and field work in the area. 

Whycocomagh Bay features a deep limestone sinkhole in its centre, which is approximately 50 meters deep. Water from outside the bay can only enter it via a relatively shallow, 15 m deep sill, which leads to very low water mixing in the bay. Since the water is also high in nutrients, the oxygen in the largely undisturbed deep water is completely used up by microbial activity. Under these oxygen-free conditions, so-called sulfate reducing bacteria create toxic hydrogen sulfide as part of their metabolism. Additionally, many other chemical and microbiological processes within the nitrogen and carbon cycles behave in unusual ways under these conditions, affecting the recycling of nutrients as well as the production of the green-house gases carbon dioxide, methane and nitrous oxide. 

Aquaculture sites around the native reserve of Whycocomagh are directly affected by this lack of oxygen in the deep water. Periodically, this oxygen-free water containing toxic hydrogen sulfide from bacterial activity makes its way up to the farm cages situated near the oxygen-free hole, decimating their fish populations. 

The aim of the field campaign and the associated research programs is to understand the chemistry and biogeochemical processes mediated by microbial activity in the water column of Whycocomagh Bay. Beyond local aquaculture and fisheries, this line of research has more global implications: so-called “Dead Zones”, vast zones of low-oxygen water in the open ocean, are predicted to expand with global warming. Our understanding of biogeochemical processes under these conditions will be crucial in mitigating the loss of ecological diversity, economic damage of global fisheries as well as greenhouse-gas emissions from these “Dead Zones”. 

Our special gratitude goes to Bruce Hatcher, whose enthusiasm for the Bras d’Or Lakes and hospitality has made our work there not only possible but very enjoyable. The work is partly funded by CERC.OCEAN and a MEOPAR research grant.