Evidence for abiotic DOC losses in a peatland stream Sheila M. Palmer, Mark Crowther and Pippa Chapman School of Geography, University of Leeds, Leeds, LS2 9JT, UK. firstname.lastname@example.org. Background
Evidence for abiotic DOC losses in a peatland streamSheila M. Palmer, Mark Crowther and Pippa ChapmanSchool of Geography, University of Leeds, Leeds, LS2 9JT, UK. email@example.com
All peatlands are sources of DOC and there is growing interest in understanding the potential for in-stream processing and in particular the fate of fluvial C lost from peatlands. Previous studies have shown decreased DOC concentrations and fluxes downstream of peatlands, but it is not clear whether this was due to dilution by incoming low-DOC waters, or to biotic/abiotic in-stream processing. Processes which remove DOC include: i) microbial degradation; ii) photoreduction; iii) adsorption onto mineral particles, particularly Fe- or Al-oxides; iv) co-precipitation and/or flocculation with Fe and Al.
Objective: To assess the downstream patterns in DOC and POC in an upland stream with relatively high concentrations of Fe (0.5-1.0 mg L-1) and which receives sediment from eroding stream banks in its lower section (Fig. 1).
Fig. 1 Catchment map of Little Blowing Gill Beck
Fig. 4 Sub-catchment contributions to DOC, POC, Fe and Al at key sampling points (y-axis, LHS), and metal/carbon rations (Y-axis, RHS).
Fig.3 Downstream changes in DOC, POC, pH, total dissolved Fe and Al concentrations. Circles=main stem; diamonds=tributary. Closed symbols=11 June; open symbols=17 June; grey symbols=15 July.
Little Blowing Gill Beck (LBB) catchment has a drainage area of 0.8 km2 and the stream has a flowing length of approximately 1.8 km. The stream has one major tributary which has a similar drainage area to the main channel above the point of confluence (Fig. 1). Our approach was a longitudinal study conducted on three separate occasions including conditions typical of summer baseflow and high flow (Fig. 2).
Loss or dilution of DOC and POC?
Downstream sampling sites drain progressively larger catchments and are influenced by the chemistry of waters upstream. To estimate the contribution of sub-catchments to stream DOC & POC independent of the waters upstream, the following equation was used (Billett et al., 2006):
Cd-u = QdCd – QuCu
Qd – Qu
Where Cu and Cd = concentration at two successive sampling points, upstream and downstream of a stream reach; Qu and Qd = discharge at two successive sampling points. Cd-u therefore represents the contribution of the catchment draining to point d, but not point the area draining to the upstream point.
Negative values indicate removal (rather than dilution) of stream DOC and POC.
Fig. 2 Stream discharge at the outlet of LBB on the three sampling dates
Billett et al. (2006), J. Geophys. Res-Biogeosciences G02010, doi:10.1029/2005JG000065
Nierop et al. (2002), Sci.Tot.Environ. 300: 201-211.