Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 59

Report summarising analyses of wetland sediment cores

This report summarises progress on the three activities planned for the first twelve months In Work Package 3, Task 3.2, Wetland palaeoecology: 1− Selection of wetland site, 2 − Reconnaissance and collection of cores, and 3 − Sampling and processing of cores. This task aims to study a single key site to develop a new palaeoecological method for exploring long−term, nutrient−climate change interactions from sediment records and long−term data−sets in wetlands.

The report focuses on presentation of the preliminary data from the first phase of analyses of sediment cores collected from Boxford Water Meadows. Boxford Water Meadows (UK grid reference SU 428719) is a Site of Special Scientific Interest (SSSI) which comprises a series of flood pastures and disused water meadows along the River Lambourn, Berkshire, UK. The site overlies alluvium and the soils consist of calcareous alluvial gleys. A total of eight gouge cores were taken along a south to north transect on the west side of the river on 27th April 2005. At each coring location, the sediment depth was recorded, the material briefly described and local vegetation and other relevant landscape features were noted.

Coring site 8 at the northern−most end of the transect (UK grid reference SU 42880, 72213) was selected as the main coring site for further study owing to it?s location on the site of an old channel, the depth of sediment accumulation and the interesting stratigraphic changes observed. Two overlapping drives with a standard Russian corer were taken and the core was coded BOXF1. In the laboratory, drive 1 was subsampled at 0.5 cm contiguous intervals from 0−50 cm and drive 2 was subsampled at 1 cm contiguous intervals from 50−90 cm. The main characteristics of the sediment and any stratigraphic changes were noted. The upper 25 cm is a dark brown, sedge peat with abundant root linings. The uppermost 16 cm has a very high organic content of ~80%, gradually decreasing to ~30% over the section 16−25 cm. The section from ~25−70 cm is a light brown sedge peat with an organic matter content of ~30% from 25−57 cm declining to ~10−15% coincident with the presence of mineral fragments and chalk particles in the section 58−70 cm. From 70−80 cm, the sediment is comprised of a chalky mud matrix. The carbonate content fluctuates between ~10−20% over the section 40−80 cm. At 80 cm there is a marked change to a coarse chalk aggregate which is white in colour with a high carbonate content of ~30−35%. The lowermost 10 cm are comprised of a fine grained calcareous mud with chalk clasts.

Ten sub−samples at 10 cm intervals throughout the core were prepared and screened for diatoms. Diatoms are present in all of the screened samples although at varying degrees of preservation. Subsamples from the core have been sent to NERI for screening of cladocera. Further processing of the core BOXF1 will be undertaken over the next 12 months. Priority will be given to the analysis of spheroidal carbonaceous particles (SCPs) to establish an approximate chronology, and screening for ostracods and molluscs. A more detailed work plan will be produced on completion of these tasks. The availability of instrumental records will be explored and colleagues in the LOCAR programme will be contacted to assess the potential for linking this study with ongoing projects based at the site.

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