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Impact of changing hydrology on lake water quality

Impact of changing hydrology on lake water quality

Kristen Coleman on research fieldwork in Northern Territory

Kristen Coleman, a PhD candidate in Professor Jennifer Korosi’s lab and a Weston Family Northern Scientist, studies impacts to lake water quality as a result of permafrost thaw near the southern extent of permafrost in the Northwest Territories (NT), Canada. Here permafrost is sporadic, occurring beneath 10-50% of the landscape. She focuses on the impacts that changing hydrology has on lake water quality, with a specific focus on dissolved organic carbon (DOC), as current landscape alterations due to thawing permafrost has the potential to deposit large amounts of carbon into water bodies.

Permafrost thaw can alter how water flows through the landscape, primarily by increasing the number of flow paths, and how deep into the ground water can flow. In combination with the release of previously frozen organic material, that is material that is produced from living things such as plants and animals, these changing flow paths have increased the amount of carbon entering lakes, contributing to a phenomenon called “lake browning”. This occurs because of the highly coloured nature of terrestrial carbon, and works in the same way that tea colours water. Importantly, lake browning has the potential to drastically impact lake ecology.

As a result of increasing air temperatures, the Scotty Creek basin, located in the Deh Cho region, NT, is undergoing large scale landscape changes as permafrost rapidly disappears. The Scotty Creek Research Station has been a key research site, gathering data on landscape changes for over three decades. This research has allowed us to understand how the landscape here is changing, and how it alters the movement of water through the landscape. However, we currently don’t understand how landscape and water movement changes are impacting lakes in these regions of sporadic permafrost. Kristen is conducting environmental assessments on several lakes in this region to understand how they have changed, and when these changes began.

Getting water sample in fen wetlands

Lakes fill up over of time with materials both from the surrounding landscape, and materials produced within the lake. The materials that are deposited in the bottom of lakes form the lake’s sediments and act as a record of the environmental conditions at the time they were deposited. These lake sediments build up over time, where the oldest deposits are at the bottom and the surface of the record represents the present (at the time of collection). By retrieving a sediment core from lakes, the field of paleolimnology uses the information stored in lake sediments to reconstruct past environmental changes.

Kristen is reconstructing past environmental changes in lakes in the Scotty Creek basin using diatoms, which are a type of algae that preserve well in sediments because they have cell walls made of silica (like glass), and are ideal indicators of lake water conditions due to species-specific habitat preferences. Using diatoms we can track how lake colour has changed in these lakes, and get a better understanding of how these lakes will change with future climate warming and continued permafrost thaw. Being able to predict how environments will change is an important first step in mitigating the impacts of our changing climate.