Assessing long-term hydrological and ecological responses to drainage in a raised bog using paleoecology and a hydrosequence

Abstract

Question: We studied vegetation succession after drainage in a bog, as an analogue for potential persistent water table drawdown due to climate change. We asked: (1) how does bog vegetation change following a long-term water table lowering and (2) how are effects of drainage on hydrology and vegetation distributed temporally and spatially? Location: Mer Bleue peatland, Ontario, Canada (45.41°N, 75.48°W). Methods: Analyses of changes in vegetation and hydrology associated with drainage were examined spatially along a hydrosequence and temporally using paleoecological reconstructions from peat cores (testate amoebae, pollen) in a drained portion of a peatland untouched for 85 years following drainage. Relationships between modern vegetation and water table were assessed through clustering and ordination analyses of vegetation releves. Results: Post-drainage increases in tree cover, especially Betula and Larix, decreases in Sphagnum cover and shifts in species composition of dominant shrubs were observed. Present-day vegetation patterns along the hydrosequence were primarily related to seasonal variability of water table depth. Paleoecological records reveal that where the present-day vegetation has been impacted by drainage, persistent water table lowering occurred in response to drainage. However, in an area with relatively natural vegetation, a transient drop in water table depth occurred at the time of drainage. Conclusions: Temporal and spatial patterns revealed that the bog response to drainage was spatially and temporally heterogeneous, and probably mediated by feedbacks among vegetation, peat structure and hydrology. Spatial patterns along the hydrosequence were similar to those observed in paleoecological reconstructions, but the use of the two complementary techniques provides additional insights.