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Assessing the Holocene paleoenvironmental history of Lake Scugog

Assessing the Holocene paleoenvironmental history of Lake Scugog

by Randelle Adano

Randelle Adano

Lake Scugog is a large, shallow reservoir in southern Ontario that has faced multiple stressors like climate change, eutrophication, and invasive species over the post-industrial period. The arrival of the first, early settlers in ~1700 has brought significant infrastructure development in the area, most notably the building of the Lindsay Dam in the 1800s that flooded the Scugog basin to form the present-day Lake Scugog. Expansion of urban and agricultural development over the last several decades has contributed to nutrient enrichment (eutrophication), the effects of which are most pronounced in the west arm near the town of Port Perry.

Paleolimnology is the science that uses proxies preserved in lake sediments to reconstruct past environmental conditions. Figure created by J. Korosi using Biorender.

Anthropogenic climate change is an emerging stressor for Lake Scugog, which will have implications for lake water levels and water quality. As the effects of climate change are known to vary spatially, Holocene paleoenvironmental studies are needed to get insights into what climate change might look like for the Lake Scugog basin. The Holocene, is the current geological epoch, and encompasses the last ~10,000 years. Several climatic changes occurred over the Holocene. For my NSERC Undergraduate Student Research Award project, I worked under the supervision of EUC Professor Jennifer Korosi to use paleolimnology to reconstruct the Holocene paleoenvironmental history of the southwestern arm of Lake Scugog. Paleolimnology is the science of using biological, chemical, and physical remains preserved in sediments of inland water systems to assess lake ecological history.

Xenochironomus, a chironomid from the tribe Chironomini, under the microscope at 200x magnification.

I used a 2.5 metre long sediment core that was retrieved in 2020 and sectioned into 1-cm slices. Each sediment slice represents a different period of time in the lake’s history (new sediments deposit on top of older sediments – called stratigraphy). I isolated subfossil remains of Chironomidae (Diptera), a family of non-biting midges. Chironomids have an aquatic larval stage, and its head capsules fossilize well in the sediment due to the high presence of chitin, a polysaccharide naturally found in the exoskeleton of many organisms. Different species of chironomids live in different environmental conditions, which allows them to be used as paleoindicators for conditions like oxygen, temperature, pH, and trophic status.

Map of Lake Scugog and its watershed (blue hashed line). The inset on the left shows the location of Lake Scugog, northeast of Toronto, Ontario. Figure used with permission from P.Do (2021).

The isolated chironomid head capsules from the sediment matrix was observed under the microscope, and I identified which species they belonged to. The relative abundance of each taxa was then plotted in a stratigraphy to readily observe species changes over time and infer what this means for environmental change. The results from my preliminary findings show that chironomids first appeared in the sediments at a core depth of 95 cm, corresponding to about ~4000 years before present (mid-Holocene), when warm and dry conditions persisted in southern Ontario. No chironomids were recovered for the early Holocene. The climate returned to cool and wet conditions by ~3000 years before present. The taxa Ablabmesyia, Endochironomus, Procladius, and Tanytarsus were the most dominant in the core, and these taxa indicate mesotrophic to eutrophic aquatic conditions. The chironomid assemblage observed during the Mid-Late Holocene was broadly similar to the present-day assemblage that I previously analyzed in a short gravity core representing the last ~200 years of Lake Scugog’s history, even though water levels increased after the formation of the Lindsay Dam.

In the next steps of this research, additional work is needed to fill in the chironomid assemblage for the missing sediment intervals between 10-50 cm and 50-75 cm. My results will also be incorporated into a multi-indicator paleoenvironmental reconstruction of long-term ecological change in the Lake Scugog watershed being put together by several EUC faculty, graduate, and undergraduate students in partnership with the Scugog Lake Stewards.

Randelle Adano is an environmental science undergraduate student working alongside Professors Jennifer Korosi and Joshua Thienpont in the Limnology and Paleoenvironmental Research Group (LPRG) to assess long-term ecological change in lake ecosystems in Canada. Her research focuses on analyzing sub-fossilized Chironomidae (non-biting midges) head capsules in lake sediments to understand how their assemblage has changed throughout a lake’s ecological history. Her research sites include Lake Scugog (Southern Ontario) and Lake Nipigon (Northwestern Ontario). She is a recipient of the NSERC Undergraduate Student Research Award (USRA) for which she analyzed benthic macroinvertebrates as paleoecological indicators of long-term changes in trophic status in Lake Scugog.