Late Holocene ecohydrological and carbon dynamics of a UK raised bog: impact of human activity and climate change

Abstract

Understanding the ecohydrological responses of peatlands to climate change is particularly challenging over the late Holocene owing to the confounding influence of anthropogenic activity. To address this, a core spanning the last~2400 years from a raised bog in northern England was analysed using a comprehensive suite of proxy methods in an attempt to elucidate the drivers of change. A testate amoebae-based transfer function was used to quantitatively reconstruct changes in water table depth, supported by humification analysis and a plant macrofossil-derived hydroclimatic index. Pollen and plant macrofossil data were used to examine regional and local vegetation change, and human impacts were inferred from charcoal and geochemistry. Chronological control was achieved through a Bayesian age-depth model based on AMS radiocarbon dates and spheroidal carbonaceous particles, from which peat and carbon accumulation rates were calculated. Phases of both increased and decreased bog surface wetness (inferred effective precipitation) are present, with dry phases at c. AD 320-830, AD 920-1190 and AD 1850-present, and a marked period of increased effective precipitation at c. AD 1460-1850. Coherence with other records from across Northern Europe suggests that these episodes are primarily driven by allogenic climatic change. Periods of high bog surface wetness correspond to the Wolf, Spörer and Maunder sunspot activity minima, suggesting solar forcing was a significant driver of climate change over the last~1000 years. Following the intensification of agriculture and industry over the last two centuries, the combined climatic and anthropogenic forcing effects become increasingly difficult to separate due to increases in atmospheric deposition of anthropogenically derived pollutants, fertilising compounds, and additions of wind-blown soil dust. We illustrate the need for multiproxy approaches based on high-resolution palaeoecology and geochemistry to examine the recent trajectories of peatlands.

Micro-XRF Core Scanning in Palaeolimnology: Recent Developments

“…Analysis of the Br flux in Lake Constance, where Br was found to be permanently removed to the lake sediment, supports the use of Br as a proxy for past biological productivity (Gilfedder et al 2011). It has also been suggested that excess Br in cores from sites exposed to maritime influences, may also be the result of enhanced storminess (Unkel et al 2010;Turner et al 2014). In a recent Holocene record from Mauritius, De Boer et al (2014) use increased (ln) Br/ Ti ratios to infer infiltration of saline groundwater into a low-lying coastal wetland.…”

Testing the cause of the Sphagnum austinii (Sull. ex Aust.) decline: Multiproxy evidence from a raised bog in Northern Ireland

“…Ti, Y and Rb suggesting soil dust loading of the bog surface (Turner et al, 2014) The pollen record at this site indicates a reduction in arboreal taxa, replaced by increasing proportions of Cyperaceae, Poaceae and Plantago sp. pollen.…”

Dirt road: A geomorphological and geochemical record of Late-Holocene human activity in the catchment of Lake Radacz (Central Pomerania, Poland)

“…In studies of human impact, indices that help to distinguish natural conditions from anthropogenic ones are especially valuable. This is particularly difficult for the Late Holocene, disturbed by human activity (Turner et al, 2014).…”

“…On the basis of the development of mountain glaciers, Grove (2004) distinguishes the Subboreal (3800 and 3100 cal BP) and Subatlantic (3000 and 2300 cal BP). For Turner et al (2014), the beginning of the Common Era is primarily the mark of climate changes and human activity that have transformed lakes and peatlands. At the start of the second millennium, evidence of a generally warm climate (reconstructed from wood macrofossils, upper tree limits, pollen, diatoms, ice-cores, and other proxy data) and reduced glacier activity (proglacial lake sediments) between 900 and 1240 AD can be found in various parts of the world (Bradley et al, 2003;Grove, 2004;Wanner et al, 2008).…”