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Why was this BUI originally listed as not impaired?
- The BUI status was deemed not impaired based on the density, diversity, and species composition of phytoplankton and zooplankton in the Detroit River. However, the composition of permanent, nearshore zooplankton populations was not examined at the time, thus it was noted that further assessment of the nearshore zooplankton communities was needed (MDNR and OMOE 1991).
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This BUI will be considered to be ‘not impaired’ when….
The composition and relative abundance of phytoplankton and zooplankton of the Detroit River reflect that of Lake Huron, and therefore represent primarily oligotrophic/mesotrophic conditions.
What was done?
- 2007 Great Lakes Institute for Environmental Research (GLIER): The study was conducted between August and November 2007 to determine if the composition and relative abundance of species of phytoplankton and zooplankton in the waters of the Detroit River changed from upstream to downstream. Overall, phytoplankton abundance in the Detroit River was low; however, this result is not surprising considering waters in the Detroit River is replaced in approximately 21 hours and is representative of Lake Huron waters. The phytoplankton and zooplankton community assemblages were shown to be indicative of oligotrophic-mesotrophic conditions that are representative of the upstream waters of Lake Huron. There were no obvious signs of deformities in zooplankton from the Detroit River.
- 2015 GLIER: A survey was conducted between June and November 2015 to cover spatial and seasonal changes in the zooplankton community structure in both nearshore and offshore waters of the Detroit River AOC and in Lake St. Clair (reference site). It was concluded that the overall quality of zooplankton communities in the Canadian waters of the Detroit River AOC does not differ from its nearest upstream water body, Lake St. Clair.
- 2019 Study by the Department of Fisheries and Oceans: Sampling at eight Detroit River sites found low but healthy phytoplankton and zooplankton populations, consistent with a fast-flowing river. Zooplankton abundance declined downstream and was dominated by smaller organisms, likely due to fish predation, while Lake Huron was determined to be an unsuitable reference site because plankton communities are altered before reaching the Detroit River.
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