Algal blooms: Investigating causes & consequences in the Wolastoq watershed
Authored by: ECAB Lab students Brenell, Catherine, Marissa, and William
The #1 issue facing freshwaters
Algal blooms have increased in frequency and severity in many lakes across the world. Some algae produce toxins that can harm living organisms and so present a threat to human health. Algae thrive when they have lots of nutrients—such as from applications of fertilizers that can move into lakes after heavy rains. Once algae populations become large and begin to die, the breakdown process of algal biomass via microbes lowers the level of dissolved oxygen (DO) in the water. This process is called eutrophication, where excess nutrients cause rapid algae growth to occur in aquatic ecosystems and reduce DO levels. DO is needed for aquatic organisms to breathe, with varying levels required across species. Eutrophication negatively impacts the health of a lake where it can reduce preferred habitat and in extreme cases lead to the deaths of organisms such as fish. Eutrophication can also reduce property values of waterfront residences.
The Geography-specific issue
The Wolastoq (or Saint John River) Watershed is located within New Brunswick, Quebec, and Maine. It is among the largest watersheds east of the Mississippi River (USA) and consists primarily of forested watershed, few residential areas, limited agriculture, and many low-nutrient lakes. Algal blooms are typically seen in high-nutrient systems, which makes their confirmed presence throughout the Wolastoq Watershed unusual. Algal blooms have been confirmed in 25% of 40 seemingly healthy lakes surveyed from 2005 to 2016 in New Brunswick, nine of which are in the Wolastoq Watershed. So, the question is: why are low-nutrient lakes in New Brunswick experiencing algal blooms without environmental characteristics traditionally associated with blooms?
Introduction to the project (2024-2027)
The way that we understand lakes is often through observations and collecting measurements of physical, chemical, and biological variables. We can measure DO levels in lakes by taking direct measures of the water at various depths and during different seasons. We can also compare these measures between lakes. But what if we want to understand DO levels from five, ten or even hundreds of years ago? Unless someone was taking measurements back then (which they likely weren’t), we’d have no way of knowing what typical or “baseline” levels of DO are for a given waterbody. So instead, we can use bioindicators like chironomids (non-biting midges) whose larval head capsules are preserved in the sediment of lakes. Using sediments, we can build a better understanding of how lakes have changed over long periods of time and what is happening in the environment to push these changes. Sediments act as nature’s archivists and capture “signals” from the watershed, airshed, and lake itself at the time of sediment deposition. Lake sediments accumulate in order and can thus be used to track environmental changes through time. Most sediment cores from lakes in eastern North America that contain 20+ cm of undisturbed sediment reflect several hundred years of inputted materials. This scientific discipline is known as paleolimnology and requires a range of knowledge from related fields, such as aquatic science, ecology, geology, environmental science, geography, and climatology.
Image: ECAB Lab researcher measuring a lake sediment core before sectioning the core into layers to study bioindicators.
Chironomids and their use as a proxy
As chironomids spend most of their lives at the bottom of lake systems, they are especially sensitive to aquatic environmental conditions. Adult chironomids have brief lifespans and lay their eggs on or near lake surfaces. As many chironomid species are particular about DO levels, any shifts in this variable may cause changes to relative abundances of chironomid species and their overall diversity. The head capsules of chironomids are made of chitinous material which is resistant to breaking down, allowing them to preserve nicely in lake sediments for thousands of years. Thus, chironomids can be used to infer past DO conditions throughout a lake’s history. This will help us determine if the eutrophication we’re observing in some lakes from the Wolastoq Watershed is a recent phenomenon or can be linked with other environmental changes that the lake or region may experience. Additional environmental measures, combined with the timing of changes in lake health provided by the chironomids, can help us determine the cause of ecological shifts in the lake. Often, land-use and climatic changes are part of the reason that eutrophication occurs. That said, some lakes are more sensitive (or resilient) than others to environmental changes and so we may not expect all lakes to behave in the same way even if they are exposed to the same stressors.
Image: ECAB Lab student observing chironomids preserved in lake sediment with a microscope.
In the course of this multi-year project (2024-2027) funded by Canada Water Agency’s Freshwater Ecosystems Initiatives, we plan to take sediment cores and water quality measurements from 40 New Brunswick lakes in the Wolastoq Watershed and analyze them to better understand baseline and contemporary lake conditions. In addition, six lakes have been chosen with our partners to focus concerted efforts on and these include dating of the sediment cores and various measures we can make through time. This project represents a collaboration between researchers at Mount Allison University (Drs. Kurek and Liefer), UNB, and Queen’s University, along with additional partnerships with NGOs (Nashwaak Watershed Association, New Brunswick Alliance of Lake Associations, and the Société d’aménagement de la rivière Madawaska Inc) and government (including the Department of Fisheries and Oceans, and the New Brunswick Department of Environment and Local Government). Supported by a diverse team of scientists at different career stages and with some shared and novel expertise, we are hopeful for a successful project that yields results that can continue to develop our understanding of lakes and environmental change. Healthy lakes provide many benefits to people, society, and biota. Overall, our goal is to improve management, policy, and understanding of lakes in the Wolastoq Watershed.