title: Modelling impacts of atmospheric deposition and temperature on long-term DOC trends.
abstract: It is increasingly recognised that widespread and substantial increases in Dissolved organic carbon (DOC) concentrations in remote surface, and soil, waters in recent decades are linked to declining acid deposition. Effects of rising pH and declining ionic strength on DOC solubility have been proposed as potential dominant mechanisms. However, since DOC in these systems is derived mainly from recently-fixed carbon, and since organic matter decomposition rates are considered sensitive to temperature, uncertainty persists over the extent to which other drivers that could influence DOC production. Such potential drivers include fertilisation by nitrogen (N) and global warming. We therefore ran the dynamic soil chemistry model MADOC for a range of UK soils, for which time series data are available, to consider the likely relative importance of decreased deposition of sulphate and chloride, accumulation of reactive N, and higher temperatures, on soil DOC production in different soils. Modelled patterns of DOC change generally agreed favourably with measurements collated over 10-20years, but differed markedly between sites. While the acidifying effect of sulphur deposition appeared to be the predominant control on the observed soil water DOC trends in all the soils considered other than a blanket peat, the model suggested that over the long term, the effects of nitrogen deposition on N-limited soils may have been sufficient to raise the "acid recovery DOC baseline" significantly. In contrast, reductions in non-marine chloride deposition and effects of long term warming appeared to have been relatively unimportant. The suggestion that future DOC concentrations might exceed preindustrial levels as a consequence of nitrogen pollution has important implications for drinking water catchment management and the setting and pursuit of appropriate restoration targets, but findings still require validation from reliable centennial-scale proxy records, such as those being developed using palaeolimnological techniques.
authors.affiliation: Soil Research Centre, Department of Geography and Environmental Science, University of Reading, Reading RG6 6DW, UK; Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK. Electronic address: kasia.sawicka@wur.nl.
authors.forename: K
authors.initials: K
authors.lastname: Sawicka
authors.affiliation: Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK.
authors.forename: E C
authors.initials: EC
authors.lastname: Rowe
authors.affiliation: Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK.
authors.forename: C D
authors.initials: CD
authors.lastname: Evans
authors.affiliation: Environmental Change Network, Centre for Ecology and Hydrology, Lancaster Environment Centre, Bailrigg, Lancaster LA1 4AP, UK.
authors.forename: D T
authors.initials: DT
authors.lastname: Monteith
authors.affiliation: Centre for Ecology, Society and Biosecurity, Forest Research, Alice Holt Lodge, Farnham, Surrey GU10 4LH, UK.
authors.lastname: E I Vanguelova
authors.affiliation: Soil Research Centre, Department of Geography and Environmental Science, University of Reading, Reading RG6 6DW, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Wade
authors.affiliation: Soil Research Centre, Department of Geography and Environmental Science, University of Reading, Reading RG6 6DW, UK.
authors.lastname: J M Clark
keywords: Doc; Dynamic modelling; Nitrogen deposition; Sulphur deposition; Trend; Warming