Have watershed disturbances over the past ∼200 years affected lakes in Algonquin Provincial Park (Ontario, Canada)?

Wilkins CAT, Rühland KM, Meyer-Jacob C, Paterson AM, Smol JP. 2026. Have watershed disturbances over the past ∼200 years affected lakes in Algonquin Provincial Park (Ontario, Canada)? Lake Reserv Manag. XXX–XXX.Algonquin Provincial Park (APP or the Park), located in south-central Ontario, spans an area of 7,635 km2 and is a destination for over 800,000 visitors annually. Although APP was established as a protected area in 1893, some of its lakes and catchments have experienced varying degrees of anthropogenic stress, including logging, private cottages, railways, roadways, and experimental manipulation. The effects of these stressors on lake ecosystems are not yet well understood. To address this knowledge gap, paleolimnological methods were used to assess whether anthropogenic stressors have affected APP lakes over the past ∼200 yr. Using diatom assemblage composition, alongside spectrally inferred chlorophyll a and lake-water dissolved organic carbon (DOC) concentrations from 210Pb-dated sediment cores collected from 5 lakes, we determined preindustrial (baseline) conditions and examined whether historical catchment disturbances, as well as regional climate change, have registered a response in the sedimentary records. To help distinguish the effect of local catchment disturbances from natural and climatic variability, comparisons were made between 3 lakes (Cache, Canoe, Smoke) that support cottages and commercial establishments, as well as 2 remote reference lakes (McIntosh, Welcome). In general, diatom assemblage changes were modest in all lakes, except for a clear response to a nutrient manipulation experiment in Cache Lake in the 1940s. In all lakes, mid-19th-century diatom compositional changes, together with trends in chlorophyll a and DOC, appear to be a response to logging in the region. Importantly, we found little evidence that cottages have had a discernible effect on these lakes.