Terms of Reference

Validation of DO as MEQ measure of nutrient loading status of estuaries

Regional Advisory Meeting – Gulf Region

February 23 and 24, 2021
Virtual meeting

Chairperson: Rémi Sonier

Context

Under the Oceans Act, Fisheries and Oceans Canada (DFO) is responsible for managing estuarine, coastal and marine ecosystems through three principals: sustainable development, integrated management and the precautionary approach. Integrated management plans require objectives to protect ecosystems. These objectives may include enhanced protection of species considered important to maintain ecosystem structure and function which may be designated as Ecologically Significant Species (ESS). Within coastal systems of eastern Canada eelgrass, Zostera marina, has been designated an ESS due to its many ecosystem services.

Nutrient enrichment, eutrophication, is one of the leading causes of impaired water quality in coastal ecosystems. In the shallow estuaries and bays of the southern Gulf of St. Lawrence this process can lead to the displacement of eelgrass habitat by macroalgae which, in turn, can have deleterious impacts to biodiversity. Increased biomass from algal proliferation leads to swings in dissolved oxygen (DO), increasing during the day due to photosynthesis and declining at night in its absence. When algae begins to decompose in summer, this can lead to sustained hypoxia/anoxia resulting in severe impacts to fauna. These severe instances of sustained anoxia have become relatively common in Prince Edward Island (PEI) where nitrate loading is high and directly linked to intensive agricultural activity. For this reason, nutrient enrichment has been identified as one of the main pressures impacting eelgrass coverage in the Gulf Region.

The Oceans Act Marine Environmental Quality (MEQ) guidelines, objectives or criteria are management measures that can offer protection to ESS by limiting the amount of stressor permitted in an ecosystem. As such, current efforts in the Gulf Region on MEQ guideline development are focusing on nutrient enrichment. The objective is to develop an MEQ guideline to foster efforts to reduce nutrient loading in estuaries of the Northumberland Strait.

Development of the MEQ initiative has been supported by a significant body of research in the Northumberland Strait since 2005 to understand causes of deteriorating environmental conditions. Partnerships between federal and provincial government departments and academia, notably through the development of nitrogen criteria led by the province of PEI and the Northumberland Strait Environmental Monitoring Partnership (NorSt-EMP) have helped advance collective understanding of the issues. DFO’s Marine Protection and Conservation Program was an active participant in NorSt-EMP and identified the new MEQ initiative as an opportunity to implement recommendations of this collaborative research program.

Based on NorSt-EMP’s recommendations, the MEQ initiative is supporting DFO Science and partnering with provincial departments and environmental non-governmental organizations to implement a monitoring program throughout the Northumberland Strait, including all of PEI. The goal of the monitoring program is to evaluate the trophic status of estuaries and provide scientific basis for guideline development. Indicators being monitored include: DO, phytoplankton (via chlorophyll a), eelgrass distribution and fish communities.

Among the recommended indicators, DO was most effective for assessing the trophic status of shallow estuaries of the Northumberland Strait (Coffin et al., 2018). In eutrophic estuaries, DO levels undergo large spatial and temporal fluctuations, sometimes ranging from supersaturation to anoxia within a matter of hours. Coffin et al. (2018) monitored DO across a spatial and nutrient loading gradient within the Northumberland Strait, with sites ranging from oligotrophic to eutrophic, and developed DO metrics that were symptomatic of eutrophication. The two most important DO metrics for discriminating between sites, a metric for hypoxia and for supersaturation, were integrated to produce a composite variable termed eutrophic time. Eutrophic time was shown to significantly correlate with predictors of eutrophication, nitrate loading and estuarine water residence time and was well-correlated with habitat type, eelgrass or algae habitat (Coffin et al., 2018). Therefore, eutrophic time is suggested as the basis of the MEQ guideline to address nutrient enrichment in the Gulf Region.

Objectives

• The main advise requested is to define the DO threshold, or DO range, to be included in the Gulf’s MEQ guideline. The intent is to include DO as the main indicator in a regional monitoring program to assess the trophic status of estuaries and evaluate ecosystem recovery following the implementation of nutrient management measures on land. More precisely, advice is requested to:
• Validate the use of DO to characterize the trophic status of shallow estuaries of the Northumberland Strait.
• Define conditions under which this indicator can effectively assess the trophic status of estuaries, i.e. is it applicable in other regions of Canada or specific to the environmental conditions found in estuaries of the Northumberland Strait?;
• Recommend a DO threshold to be included in the Gulf’s MEQ guideline to minimize adverse effects of eutrophication such as loss of eelgrass, losses of biodiversity and abnormal DO signatures in estuaries. The DO threshold may be defined as a range rather than a specific value given that new data are being incorporated into the model developed by Coffin et al. (2018).    
• Based on the threshold recommended, identify first whether a management strategy is needed to reduce nitrate loading to the estuary and second, to estimate the degree of reduction required to remediate eutrophic estuaries. 
• Recommend a monitoring cycle for DO to effectively assess the trophic status of estuaries and evaluate ecosystem recovery following the implementation of management measures on land.
• Advice is also requested to assess the relationship between estuarine eelgrass coverage and nutrient loading. This information is requested to determine if nutrients can be considered among the main pressures on this ESS in the Gulf Region. The intent is to monitor estuarine eelgrass coverage as part of a regional monitoring program to understand the impacts of eutrophication on this valued ecosystem component and inform ecosystem recovery following the implementation of nutrient management measures on land.
• Summarize conditions under which this indicator can effectively assess the trophic status of estuaries, and highlight uncertainties regarding the broader applicability of this methodology to other regions of Canada.

Expected Publications

• Science Advisory Report
• Proceedings
• Research Document

Expected Participation

• Fisheries and Oceans Canada (Ecosystems and Oceans Science, and Aquatic Ecosystems Management)
• Academia
• Province of PEI, Departments of Environment, Water and Climate Change, and Agriculture and Land
• Province of NB, Departments of Agriculture, Aquaculture and Fisheries, and Environment and Local Government
• Non-governmental organizations
• Invited experts

References

• Coffin MRS, Courtenay SC, Pater CC, van den Heuvel MR. 2018. An empirical model using dissolved oxygen as an indicator for eutrophication at a regional scale. Marine Pollution Bulletin 133: 261-270.
• van den Heuvel MR, Hitchcock JK, Coffin MRS, Pater CC, Courtenay SC. 2018. Inorganic nitrogen has a dominant impact on estuarine eelgrass distribution in the Southern Gulf of St. Lawrence, Canada. Limnology and Oceanography 64: 2313-2327.