мÓÆÂÁùºÏ²Ê¿ª½±Ö±²¥

Powell Lake on the Sunshine Coast of British Columbia may look like an outlier among the many marine research sites studied by CERC.OCEAN - and it may well be regarded as that. However, if you dig deeper, about 300 meters deeper, you find saltwater at the bottom of Powell Lake. This is because the southern basin of the now landlocked lake used to be a fjord connected to the Pacific Ocean until the end of the last ice age about 11,000 years ago, when retreating ice masses allowed the landmass around the lake to lift and isolate it from the ocean. Over millennia, much of the seawater closer to the surface got washed out and replaced by freshwater, but isolated, ancient seawater remains at the bottom of the lake. The density of the saltier deep water also prevents the water in the bottom 200 meters of the lake from ever mixing with the surface, which allows oxygen and other chemical gradients to establish; Powell Lake’s water is completely depleted of oxygen below about 130 meters.

A team of CERC.OCEAN researchers (Shona MacDonald, Anna Haverstock, Sebastian Haas), together with collaborators from the Earth and Ocean Sciences Department at the University of British Columbia (UBC), went back to Powell Lake this June, following up on the first sampling campaign from 2016. The PhD project of CERC.OCEAN’s Sebastian Haas is focused on the biogeochemical cycling of nitrogen over the oxygen gradient and in the isolated, ancient seawater. Using a research boat rented from UBC, Niskin samples were taken for the analyses of a variety of compounds contained in the lake water: gasses, such as the greenhouse gases nitrous oxide and methane that are produced in the lake, microbial DNA, as well as various chemical forms of carbon, nitrogen, and sulfur. The team also used oxygen sensors to accurately document the depth of oxygen depletion, a task that was vitally supported by a 170 meter long communication cable prepared by CERC.OCEAN engineer Mike Vining, allowing for live observation of the sensors’ output while they were measuring about 150 meters beneath the surface. Moreover, incubations for the quantification of microbial activity were prepared in the CERC.OCEAN container lab, which had been moved to a parking lot by the lake.

The results from the two sampling campaigns undertaken by CERC.OCEAN may eventually lead to a better understanding of how nitrogen compounds are cycled and transformed under low or no oxygen, and how under these circumstances the nitrogen cycle is connected to other biogeochemical cycles by microbes that may use substances such as sulfide or methane to reduce nitrogen oxides. Insights into these processes may be applied to our understanding of marine oxygen depleted zones or improved treatment of wastewater. The study of biogeochemical cycling under the extreme, oxygen-free conditions of Powell Lake may even be helpful to understand by analogy the cycling of chemical elements in ancient oceans during Earth’s history or to identify biogeochemical processes that could potentially occur on other planets.

We thank our collaborators at UBC, Prof. Rich Pawlowicz and the UBC technicians Chris Payne and Larysa Pakhomova who navigated us to and across Powell Lake. Support and use of lab infrastructure was also graciously provided by Prof. Maite Maldonado and Ross McCulloch at UBC. We also thank the owners of The Shinglemill restaurant for providing their premises for parking of the container lab.

To read the report about the latest research paper published in the journal ‘Environmental Microbiology’, click HERE.