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Degradation of Phytoplankton & Zooplankton Populations (BUI # 13)

A recent scientific assessment indicates that there are no issues with the condition of phytoplankton and zooplankton populations in the Niagara River. The biomass and productivity of the Niagara River are consistent with the oligotrophic conditions in eastern Lake Erie. A BUI Status Assessment Report, which compiles all supporting information for changing the status of the Degradation of Phytoplankton & Zooplankton Populations BUI to ‘Not Impaired’, was prepared and submitted to the Canada-Ontario Agreement (COA) Annex 4 Co-Leads for formal review. In 2019, the COA Annex 4 Co-Leads formally confirmed and supported the recommendation to change the BUI’s status.

The Degradation of Phytoplankton & Zooplankton Populations BUI is no longer considered impaired for the Niagara River.


Why is plankton an indicator?

Plankton are important indicators of ecosystem health because they form the base of the food chain and they are sensitive to changes in water quality. Phytoplankton are primary producers (i.e., organisms that form the base of the food web and make energy from sunlight) and are an important food source for zooplankton and other organisms. In turn, zooplankton become food for fish and other organisms, some of which are consumed by people. There must be enough phytoplankton in the water to form the base of the food web. If there is not enough phytoplankton, the web is broken and the rest of the organisms in the food web may suffer.

According to information on the International Joint Commission website, this beneficial use impairment applies “when the plankton (microscopic plants and animals) community structure significantly diverges from unaffected comparison sites of similar physical and chemical characteristics” (source: IJC).


Status of BUI Over Time

Since the inception of the Remedial Action Plan (RAP) initiative in the late 1980s, there has been uncertainty about the condition of phytoplankton and zooplankton populations in the Niagara River Area of Concern (AOC). The BUI was listed as ‘Requires Further Assessment’ from 1993-2018. Below is a summary of BUI status in major RAP reports over time.


Science & Monitoring

Scientists from the Department of Fisheries and Oceans conducted a comprehensive scientific study examining water chemistry and phytoplankton and zooplankton composition at six different monitoring sites along the Niagara River. The sites were sampled monthly (from June to October 2014). The results of the technical assessment show that there are no issues related to populations of phytoplankton and zooplankton in the Niagara River Area of Concern, and that the status of the Degradation of Phytoplankton and Zooplankton Populations BUI be changed from ‘Requires Further Assessment’ to ‘Not Impaired’.

Key findings of the study are:

  • Plankton population levels were low but consistent with expectations for a large river, sourced from a Great Lake with low nutrient levels (oligotrophic) and a high flow rate.
  • The most prominent plankton in the Niagara River were rotifers, water fleas, copepods, mussel veligers, and filamentous diatom algae, which tolerates high-flow environments.
  • Due to the high flow rates of the river, plankton would only be in the river for a day before exiting into Lake Ontario.
  • The amount of zooplankton decreased downstream with the lowest zooplankton levels found in the lower river below Niagara Falls, which was expected because zooplankton experience high mortality when entering high flow river systems.
  • A small increase in plankton populations was found downstream of the hydroelectric reservoirs, which likely act as a source of plankton for the river. The reservoirs provide refuge from the fast-flowing river and give plankton time to recover.
  • Minor diatom and cyanobacteria peaks occurred in August and September, respectively, but were still very low biomass and not expected to negatively impact the environment.
  • Bacteria growth and biomass was elevated in the river compared to Lake Erie, but the highest peaks followed heavy rainfall events.
  • Phytoplankton levels were very low—similar to oligotrophic eastern Lake Erie, which is consistent with the findings that the Niagara River is not impaired with respect to eutrophication and algae.
  • There were no dramatic changes in zooplankton species composition down river.
  • A reduction in zooplankton densities in the upper river (closest to Lake Erie) is most likely due to plankton-eating fishes such as Emerald Shiner and Yellow Perch.


What is left to do?

No further studies/remedial actions are required.


The Bi-National Connection

This BUI is listed as ‘Not Impaired’ on the New York, USA side of the Niagara River. Learn more about the restoration efforts on the U.S. side of the Niagara River: https://www.epa.gov/great-lakes-aocs/about-niagara-river-aoc

About Us

Efforts from many key partners in the RAP Team continue to help complete priority actions for the restoration, protection, and enhancement of the Niagara River ecosystem. This initiative is made possible through the financial support of the Government of Canada and Ontario, in partnership with the Niagara Peninsula Conservation Authority.

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