PEARL

Background - Dams and reservoirs are ubiquitous on the landscape of North America. The Duncan Dam, located near the headwaters of the Columbia River Drainage Basin (CRDB) in northeastern Canada, is one of several thousand dams in North America. Following the ratification of the Columbia River Treaty between Canada and the United States, Duncan Dam was completed in 1967. At this time, Duncan Lake, behind the dam, became a reservoir and increased in size to over 40 km long and over 140 m in depth. Water control structures, like Duncan Dam, provide several benefits associated with flood control, water conservation and downstream hydroelectricity generation. However, the creation of dams and reservoirs also results in changes in nutrient cycling and biological production, both above and below the dam. Changes above the dam, include nutrient releases from flooded vegetation, and retention of sediment; whereas changes below the dam can include decreases in nutrient flows, changes in the timing and intensity of water flows, and increases in light due to reduced turbidity, amongst other factors (Wang et al. 2022). As a result, reservoirs tend to exhibit initial increases in nutrients and production, followed by a decline as they age (Northcote et al. 2005, Paterson et al. 2019). Lakes below dams can decrease in nutrients, which may elicit changes in primary and secondary producers. Resultant changes in fish abundances and community structure can occur, due to changes in nutrients and light, which can impact overall aquatic production. However, nutrient dynamics in large lakes and reservoirs are complex, and have been impacted by many other drivers of ecosystem change since the early 1900s including: nutrient loadings and other pollutants from landscape disturbances (e.g., mining, agriculture, forestry, urbanization, and industry); degradation of nearshore habitats and spawning areas; changes in fish and invertebrate communities from other factors including fish hatcheries, and the introduction of non-native invertebrates and fish. Characteristic nutrient losses in downstream lakes, have necessitated large-scale lake fertilization programs to sustain aquatic production, fish, and even species at risk, such as in the north basin of Kootenay Lake, ongoing since 1992 (Schindler et al. 2020).

● Goals of the partnership, the potential outcomes, and impacts - There are pressing needs for innovative approaches to evaluate dynamic changes in aquatic nutrients associated with the operation of dams, which have traditionally been undertaken using mass balance models (e.g., Perrin and Kormann 1997). However, non-stationarity associated with climatic, landscape, and human influences, and a general lack of consistent long-term measurements of chemistry and/or primary and secondary production through time, require development of new approaches that can assess high-resolution changes over the past decades to understand and respond to such complex interactions. Fortunately, reconstructive proxy approaches, using paleolimnological techniques, can be used to reconstruct changes in nutrients over time (e.g., Cumming et al. 2015) based upon the physical, chemical, and biological information preserved in well-dated sediment cores from lakes and appropriate reference systems.

We propose to develop and apply two complementary approaches to provide a robust understanding of changes in the related topics of nutrients and biological production in a coupled reservoir-lake system using: i) a modelling approach based on the measurement of changes in different forms of phosphorus in dated lake sediment cores; and ii) a quantitative assessment of biological proxies that are highly associated with changes in primary (diatoms and sedimentary algal pigments) and secondary production (i.e., Cladocera, important and preferred invertebrates for many planktivorous fish). These approaches are interlinked as nutrients such are highly related to algal production (Paterson et al. 2019).

This project will provide information on changes in nutrients and primary and secondary producers before and following the implementation of the BC Hydro’s Water Use Plan (WUP) in 2007 and the construction of the Duncan Dam, both behind and downstream of the dam. These two timescales will provide data relevant to water managers to assess the changes associated with the Duncan Dam WUP, which commenced as an operational alternative in 2007 to mitigate excess nutrient retention within Duncan Reservoir, and before and after the establishment of the Duncan Dam in 1967 so that pre-dam nutrient dynamics and baseline levels of production can be understood. These approaches will be used in addition to the traditional numerical modelling approaches used by BC Hydro. As a result, this study will result in: new and complementary approaches to assess the efficacy of adaptive flow management of dams associated with mitigation efforts; an increased understanding of changes in nutrient dynamics and lake production both in reservoirs and in downstream lakes; a better understanding of the cumulative nature of drivers of production in large oligotrophic lakes; and an assessment of changes in ecosystem structure across trophic levels directly relevant to fish, and relative to the implementation of the 2007 WUP and pre-dam conditions. Understanding the impact of dams on nutrients and primary/secondary production is essential to characterize changes in energy flows to guide appropriate mitigation.

In collaboration with our Alliance Grant partners, BC Hydro and Fisheries and Oceans Canada, we will create and evaluate cost-effective approaches to assess changes in nutrient budgets and levels of primary and secondary production in reservoirs and downstream lakes, associated with dam operations. These approaches will be based upon chemical and biological evidence readily available from sedimentary cores retrieved from the impacted and reference lakes. This information will be used by our partners to verify the effectiveness of existing water management plans and in the creation of new aquatic ecosystem mitigation plans. Decadal and longer-term changes in nutrients, and primary and secondary production in both reservoirs, and downstream receiving lakes will be used to assess past management practices and inform future ones, including the creation of new mitigation approaches.

Partnerships:

BC Hydro is a Crown Corporation owned by the government of British Columbia. The mission of BC Hydro is to provide safe, reliable, and affordable clean electricity throughout British Columbia, with a vision of contributing to a more sustainable future. BC Hydro is committed to improving the standard of living of the people of British Columbia, supporting true and lasting reconciliation with Indigenous Peoples, protecting the air, land, and water of BC, and promoting equity in all aspects of its operations. BC Hydro has agreed to provide a cash contribution of $125,000 (which includes 25% overhead to Queen’s) to this project. Results from this project will initially be used by BC Hydro in a formal operational review of the existing Duncan Dam Water Use Plan (WUP) that was initiated in 2007. This review is being undertaken to ensure the values and objectives outlined in the original process were recognized and the expected outcomes realized. WUPs are technical documents that develop recommendations for dam operating strategies using a formal consultative process. The main objective of the process is to allow Regulators, First Nations, and other stakeholders to have an opportunity to contribute to dam management decisions (Province of British Columbia 1998). Following the review of the Duncan Dam WUP, the insights gained will inform subsequent WUP Operational Reviews throughout BC that are scheduled to occur through 2030.

Fisheries and Oceans Canada Canada (DFO) is a federal Ministry, responsible for sustainable management of fisheries and aquaculture in Canada. Dr. Daniel Selbie (Head, Lakes Research Program, Science Branch) has expertise in limnology and paleoecology, and understanding the trophic ecology of lakes to produce pelagic fish and fisheries. Dr. Selbie will provide in-kind analyses of sedimentary pigments for this project, using a high-pressure liquid chromatography (HPLC) system at the Cultus Lake Lab. These in-kind analyses involve technician expertise, time, and disposable costs. The generated data will be used to understand the cumulative impacts of anthropogenic influences (e.g., climate change, lake fertilization mitigations) on the trophic structure of large BC lakes, relevant to fish, fish habitat and fisheries.

Fisheries and Oceans Canada also has delegated responsibility for fish species at risk under Canada’s Species at Risk Act. The study area contains West-slope Cutthroat Trout (Oncorhynchus clarkia lewisi, SARA - Special Concern), and the iconic White Sturgeon (Ancipenser transmontanus; Kootenay River population, SARA - Endangered). Nutrients are foundational to productive ecosystems, this project will directly inform long-term, ongoing federal management of species at risk and their critical habitats within the Kootenay drainage, and develops mechanistic knowledge, portable and complementary to other impounded Canadian tributaries to the Columbia River. The study region is within a focal area for Canada-US Indigenous-led efforts to restore Pacific salmon to the Canadian portions of the Columbia River, an initiative that Dr. Selbie has advised on since 2011 and will provide invaluable data and environmental context to this important initiative, which seeks to directly support salmon restoration, indigenous reconciliation, and food security. Moreover, these data will be informative to ongoing renegotiation of the Columbia River Treaty (CRT) between Canada and the United States.

This proposal was co-developed largely between R. Whitehouse of BC Hydro and B. Cumming from Queen’s University, based on meetings with decision makers and planners at BC Hydro, and input from D. Selbie at DFO. BC Hydro requires a more comprehensive understanding of the effects of water management of Duncan Reservoir and the downstream receiving basin, Kootenay Lake. Interest in this project from BC Hydro comes from their desire to understand and assess the effectiveness of the Duncan Dam Project Water Use Plan (WUP, S73) initiated in 2007, and to increase BC Hydro’s understanding of nutrient retention in Duncan Reservoir because of dam operations. BC Hydro provides an annual subsidy to the ongoing Kootenay Lake Fertilization program (Schindler et al. 2020) for nutrients maintained in Duncan Lake by the dam, based upon estimates of phosphorus retention by Duncan Dam based derived from mass balance models (Perrin and Korman 1997). Nutrient cycling and production in reservoirs and lakes are dynamic processes (Stockner et al. 2001, Paterson et al. 2019, Wang et al. 2022). Estimates of nutrient cycling for Duncan Reservoir are based on models from seasonally collected water chemistry and flow data from a single year in the 1990s (e.g., Perrin and Korman 1997), with data currently being collected for 2023/24. However, inter-annual variability can be complex and subject to several factors including changes in water balance and human disturbances (Jones et al. 2008), and changes associated with reservoir aging or ontogeny (Paterson et al., 2019). In reservoirs, nutrient cycling normally increases following impoundment because of the decomposition of newly flooded vegetation, which then decreases over time as the organic matter is depleted (e.g., Paterson et al. 2019, Wang et al. 2020).

This project merges the interests of BC Hydro in providing environmental stewardship of dams and water flow, with academic and management interests in understanding long-term environmental change in production in large inland lakes and fisheries that are subject to multiple environmental drivers. The proposed project is complementary to the annual nutrient models but uses an alternative way to measure sediment burial of phosphorus and changes in nutrient concentrations in the surface waters (Moyle and Boyle 2021). Additionally, we will use proxies of primary production using diatoms and pigments (e.g., Cumming et al. 2015, Laird et al. 2021) and secondary production from Cladocera (e.g., Barouillet et al. 2019) to assess changes in production. To develop the best possible data to understand water flow management, BC Hydro is currently developing a new nutrient balance model for Duncan Reservoir in 2023-24, and in this project with Queen’s will use sediment cores collected from Duncan Reservoir, Kootenay Lake, and regional reference lakes to directly measure and characterize nutrient dynamics via estimates of phosphorus burial rates (Moyle and Boyle 2021) and production from biological proxies (Cumming et al. 2015) at a bi-yearly resolution since the early 1900s.

For details on the project, see the Diatom and Sedimentary Phosphorus Analyses report and the Long-term Cladocera Dynamics report.