Mitchell, Edward

2011, van der Knaap, W.O., Mariusz Lamentowicz, van Leeuwen, J.F.N, Hangartner, S., Leuenberger, M., Dmitri Mauquoy, Golslar, T., Mitchell, Edward, Kamenikg, C.

We present a record of peatland development during the last 1000 years from Mauntschas mire in the eastern Swiss Alps (Upper Engadine valley; 1818 m a.s.l.) inferred from testate amoebae (pH and depth to the water table (DWT) reconstructions), stable oxygen isotopes in Sphagnum (δ¹⁸O; proxy for water vapour pressure) and carbon isotopes in Sphagnum (δ¹³C; proxy for mire surface wetness), peat accumulation rates, charcoal (indicating local burning), pollen and spores (proxies for human impact), and plant macrofossils (reflecting local vegetation and trophic state). Past human impact on the local mire conditions was strong but fluctuating during AD 1000–1570 (±50 yr; depth–age model based on 29 ¹⁴C AMS dates) with local irrigation of nutrient-enriched water and grazing. Human impact was minor AD 1570–1830 (±30 yr) with partial recovery of the local mire vegetation, and it was absent AD 1830 (±30 yr)–present when hummock formation took place. Correlations among DWT, pH, δ¹³C, and δ¹⁸O, carried out both with the raw data and with linear trends removed, suggest that the factors driving peatland development changed over time, since only testate amoeba-based pH and DWT co-varied during all the three aforementioned periods. δ¹⁸O correlates with δ¹³C only in the period AD 1830–present and with DWT only during AD 1570–1830, δ¹³C correlates with DWT only during AD 1000–1570. Part of this apparent instability among the four time series might be attributed to shifts in the local mire conditions which potentially formed very different (non-analogue) habitats. Lack of analogues, caused, for example, by pre-industrial human impact, might have introduced artefacts in the reconstructions, since those habitats are not well represented in some proxy transfer functions. Human impact was probably the main factor for peatland development, distorting most of the climate signals.

, Payne, Richard J., Mitchell, Edward, Nguyen-Viet, Hung, Gilbert, Daniel

Peatland testate amoebae are widely used to reconstruct paleohydrological/climatic changes, but many species are also known to respond to pollutants. Peatlands around the world have been exposed to anthropogenic and intermittent natural pollution through the late Holocene. This raises the question: can pollution lead to changes in the testate amoeba paleoecological record that could be erroneously interpreted as a climatic change? To address this issue we applied testate amoeba transfer functions to the results of experiments adding pollutants (N, P, S, Pb, O₃) to peatlands and similar ecosystems. We found a significant effect in only one case, an experiment in which N and P were added, suggesting that pollution-induced biases are limited. However, we caution researchers to be aware of this possibility when interpreting paleoecological records. Studies characterising the paleoecological response to pollution allow pollution impacts to be tracked and distinguished from climate change.