On the impact of wastewater effluent on phytoplankton in the Arctic coastal zone: A case study in the Kitikmeot Sea of the Canadian Arctic

We present a case study on the impact of effluent from a wastewater lagoon-wetland system on phytoplankton and local primary production near a coastal Arctic community (Cambridge Bay) over spring to fall 2018. Results are also placed within an interannual and regional context for the surrounding Kitikmeot Sea. We find the shallow, relatively fresh Kitikmeot Sea is one of the most nutrient-deplete regions of the Arctic Ocean with NO3− + NO2− concentrations below the surface mixed layer rarely exceeding 2 μmol L−1 and a N:Si:P ratio of 1:6:1. The fjordal-type bathymetry of the main study site and a persistent pycnocline below the bay's exit sill led to slightly elevated N:Si:P of 3:11:1 through trapping of wastewater-sourced N at depth via sinking and remineralization of primary production. Total production in Cambridge Bay over the 3-month open water period was 12.1 g C m−2 with 70% of this production occurring during the 1-month discharge of wastewater into the system. Local primary production responded rapidly to high NO3− + NO2−, NH4+ and PON concentrations provided by wastewater effluent, comprising up to 20% of the production during the discharge period. Remaining production was mostly explained by the deep nutrient pool in the bay, which was only accessed towards the end of the discharge period as the diatom-dominated deep chlorophyll maximum settled below the pycnocline. Although not yet eutrophic, caution is raised at the rapid response of the marine system to wastewater release with a strong recommendation to develop a research and monitoring plan for the bay. [Display omitted] •The Kitikmeot Sea is among the most N-deplete systems in the Arctic Ocean.•Wastewater effluent significantly increased local primary production.•Wastewater-influenced diatom bloom was critical for transporting fixed N to depth.•Fjordal-type basin and stratification trap wastewater N at depth in Cambridge Bay.•Interannual ventilation of Cambridge Bay moderates build-up of N at depth.