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

• Published in: Biogeochemistry Vol. 100; no. 1-3; pp. 121 - 137
• Main Authors: Tipping, E, Billett, M. F, Bryant, C. L, Buckingham, S, Thacker, S. A
• Format: Journal Article
• Language: English
• Published: Dordrecht Dordrecht : Springer Netherlands 01.09.2010; Springer; Springer Netherlands; Springer Nature B.V
• Subjects: Average age; Biochemistry; Biogeochemistry; Biogeosciences; Carbon; Clay; Creeks & streams; Discharge; Dissolved organic carbon; Dissolved organic matter; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Ecosystems; Environmental Chemistry; Exact sciences and technology; Freshwater; Geochemistry; Groundwater; Hydrology; Hydrology. Hydrogeology; Isotope geochemistry; Isotope geochemistry. Geochronology; Isotopes; Life Sciences; Limestone; Mineralogy; Peat; Peatlands; Pore water; Radiocarbon; Silicates; Stream; Streams; Water geochemistry; Watersheds; Wetlands; Central Alps; Alps; Great Britain; Europe; England; United Kingdom; Pennine Alps; Western Europe; British Isles, England; Stream; Dissolved organic matter; Groundwater; Peat; Carbon isotopes; Discharge; carbonate rocks; mixing; ground water; clay; aquifers; hydrochemistry; limestone; peat bogs; pore water; discharge; temperature; dating; dissolved materials; peat; clastic rocks; stable isotopes; models; calcium; C-13/C-12; streams; concentration; sedimentary rocks; C-14; organic materials; dissolved organic carbon
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-010-9409-6

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.