Long-term Holocene groundwater fluctuations in a chalk catchment: evidence from Rock-Eval pyrolysis of riparian peats

Abstract

The depositional history of peat dominated wetlands can be used to understand palaeoclimate and paleohydrology, and also constrain the impacts of future climate change. However, in chalkland valleys seasonal water table fluctuations and a high alkalinity have decimated key environment indicators such as pollen and there is a need for alternative investigative techniques. The method of Rock-Eval pyrolysis can track changes in organic matter source and degradation, potentially relating to historic changes in vegetation cover. This was piloted on cores from a groundwater dependent riparian chalk valley wetland combined with radiocarbon dating. The dating showed that the cores represented approximately 4000 years of depositional history. Rock-Eval demonstrated significant changes in the normal alkane composition of the peat indicating shifts of around 500 to 1000 years between terrestrial and more aquatic species, relating to periods of climate wetness. These climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest Europe. However, the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically-driven factors relating to land-use and vegetation cover changes in the catchment. Nonetheless this study suggests that Rock-Eval pyrolysis is a useful and cost-effective tool that can provide evidence for long-term Holocene groundwater fluctuations.

The distribution and utility of sea‐level indicators in Eurasian sub‐Arctic salt marshes (White Sea, Russia)

“…; Newell et al . ). As far as we are aware, this study is the first to explicitly apply Rock‐Eval to salt‐marsh sediment and to expressly investigate its potential as a sea‐level indicator.…”

“…; Newell et al . ). Instrument performance was checked every 10 samples against the accepted values of an Institut Français du Pétrole standard (IFP 160 000, S/N1 5‐081840).…”

“…From these measurements, we calculated additional parameters following Newell et al . (). (vi) Hydrogen Index (HI; calculated as (S 2 ×100)/TOC) is a parameter that can help to characterize the origin of organic material.…”

“…2015a; Newell et al . ). Application of both salt‐marsh microfossils and bulk‐sedimentary geochemistry as sea‐level indicators is dependent upon the availability of a modern training set with which to interpret assemblages and geochemical signatures preserved in sedimentary archives.…”

Root oxygen mitigates methane fluxes in tropical peatlands

“…Peat organic matter properties were assessed by Rock-Eval 6 pyrolysis configured in standard mode [25]. Organic matter properties were assessed using the following selected parameters: (i) total organic carbon (TOC RE6 ); (ii) Hydrogen Index (HI), a measure of released hydrocarbons relative to TOC RE6 ; (iii) Oxygen Index (OI), corresponding to the oxygen released as CO and CO 2 relative to TOC RE6 ; (iv) the I index, describing thermally labile organic matter; (v) the R-index describing highly thermostable mature organic matter [26].…”