Mid-Holocene hemlock decline and diatom communities in van Nostrand Lake, Ontario, Canada

Terrestrial ecosystem disturbances inferred from the fossil hemlock pollen decline (ca. 4,800 BP) and recovery (ca. 3,800 BP) affected van Nostrand La ke, including the diatom communities. Ecological models suggest the lake re sponded by eutrophying, reflecting higher nutrient influx resulting from in creased erosion. A decline in lake productivity followed as the forest vege tation recovered and erosion slowed. Lastly, as the forest switched from ea rly and middle successional species to mature species, lake productivity in creased as erosion increased nutrient inflow, especially phosphorus. Howeve r, this eutrophication response was delayed or buffered, perhaps due to wet land development surrounding the lake. The lake never fully returned to its initial, pre-hemlock decline state, but oscillated between more eutrophic and more mesotrophic or oligotrophic stages, possibly reflecting other dist urbances in the catchment and climatic change.