Assessing the ecological responses of a shallow mesotrophic lake to multiple environmental stressors using paleolimnological techniques

Abstract Murphy MJJ, Sivarajah B, Grégoire DC, Vermaire JC. 2022. Assessing the ecological responses of a shallow mesotrophic lake to multiple environmental stressors using paleolimnological techniques. Lake Reserv Manage. 38:67–79. White Lake, located in southeastern Ontario, Canada is a long, shallow, multibasin lake that supports recreational activities year-round and has 1538 private and commercial dwelling units. The construction of a dam at Waba Creek in 1845 resulted in the minimum water level at White Lake increasing by ∼1.5 m, and several water-level management strategies have been implemented since the mid 20th century. The lake has also been impacted by land-clearance activities and shoreline development along the eastern shores and is presently mesotrophic. More recently, White Lake was colonized by zebra mussels (Dreissena polymorpha) in 2015, and annual algal blooms have also been observed. In this paleolimnological study, diatom-based approaches and loss on ignition were used to track past changes in water quality and sediment characteristics, respectively, to inform the White Lake Property Owners Association’s ongoing lake monitoring program. The diatom-inferred total phosphorus (DI-TP) reconstruction suggests that White Lake has been mesotrophic (DI-TP range 11.5 − 17 µg/L) over the past ∼200 years. Notable changes in the diatom assemblages and declines in sedimentary organic content were recorded around the 1890s in the sediment core retrieved near Hardwood Island. The decrease in sedimentary organic content was likely a response to early land-clearance activities around the lake as erosion often leads to greater inorganic export from the catchment to the lake. The switch among benthic fragilarioid diatom taxa suggests that the light conditions at this shallow lake may have changed in response to higher allochthonous inputs. Continuous monitoring of White Lake is needed to ensure that the cumulative impacts from emerging environmental stressors (e.g., climate-mediated changes, invasion by dreissenids) are considered when making management decisions.