Sources and ages of dissolved organic matter in peatland streams: evidence from chemistry mixture modelling and radiocarbon data

Citation

Tipping E, Billett M, Bryant CL, Buckingham S & Thacker SA (2010) Sources and ages of dissolved organic matter in peatland streams: evidence from chemistry mixture modelling and radiocarbon data. Biogeochemistry, 100 (1-3), pp. 121-137. https://doi.org/10.1007/s10533-010-9409-6

Abstract
Monitoring data over the period 1994-2007 were analysed for three streams (Cottage Hill Sike, CHS; Rough Sike, RS; Trout Beck, TB) draining blanket peat underlain by glacial clay and limestone-rich sub-strata at Moor House (Northern England). Dissolved organic carbon concentration, [DOC], showed complex relationships with both discharge and calcium concentration, [Ca]. A model based on [Ca] was constructed to simulate stream [DOC] by mixing dissolved organic matter (DOM) from shallow peat, quantified by measured [DOC] (15-30 mg l-1) in peat porewater, with DOM assumed to be present at a constant concentration (c. 5 mg l-1) in groundwater. A temperature-based adjustment to the measured porewater [DOC] was required to account for relatively low streamwater [DOC] during winter and spring. The fitted model reproduced short-term variation in streamwater [DOC] satisfactorily, in particular variability in RS and TB due to groundwater contributions. Streamwater DOM is largely derived from surface peat, which accounts for more than 96% of the total DOC flux in both RS and TB, and 100% in CHS. Model outputs were combined with streamwater and porewater DO14C data to estimate the 14C contents, and thereby the ages, of DOM from peat and groundwater. The peat-derived DOM is 5 years old on average, with most of it very recently formed. The derived age of groundwater DOM (8,500 years) is comparable to the 4,000-7,000 years estimated from the DO14C of water extracts of clay underlying the peat, suggesting that the clay is the source of groundwater DOM.

Keywords
Carbon isotopes; Discharge; Dissolved organic matter; Groundwater; Peat; Stream

Journal
Biogeochemistry: Volume 100, Issue 1-3