Variation in the sensitivity of DOC release between different organic soils following H2SO4 and sea‐salt additions |
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| Authors: | J M Clark G M F
Van Der Heijden S M Palmer P J Chapman S H Bottrell |
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| Institution: | 1. School of Earth and Environment and School of Geography, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK;2. Wolfson Carbon Capture Laboratory, School of Biological Sciences, Bangor University, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK;3. Grantham Institute for Climate Change Fellow, Civil and Environmental Engineering, Imperial College London, South Kensington, London SW7 2AZ, UK;4. Soils Research Centre, Department of Geography and Environmental Science, School of Human and Environmental Sciences, University of Reading, Whiteknights, PO Box 233, Reading RG6 6DW, UK;5. Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK |
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| Abstract: | Long‐term monitoring data from eastern North America and Europe indicate a link between increased dissolved organic carbon (DOC) concentrations in surface waters over the last two decades and decreased atmospheric pollutant and marine sulphur (S) deposition. The hypothesis is that decreased acidity and ionic strength associated with declining S deposition has increased the solubility of DOC. However, the sign and magnitude of DOC trends have varied between sites, and in some cases at sites where S deposition has declined, no significant increase in DOC has been observed, creating uncertainty about the causal mechanisms driving the observed trends. In this paper, we demonstrate chemical regulation of DOC release from organic soils in batch experiments caused by changes in acidity and conductivity (measured as a proxy for ionic strength) associated with controlled SO42? additions. DOC release from the top 10 cm of the O‐horizon of organo‐mineral soils and peats decreased by 21–60% in response to additions of 0–437 µeq SO42? l?1 sulphuric acid (H2SO4) and neutral sea‐salt solutions (containing Na+, Mg2+, Cl?, SO42?) over a 20‐hour extraction period. A significant decrease in the proportion of the acid‐sensitive coloured aromatic humic acids (measured by specific ultra‐violet absorbance (SUVA) at 254 nm) was also found with increasing acidity (P < 0.05) in most, but not all, soils, confirming that DOC quality, as well as quantity, changed with SO42? additions. DOC release appeared to be more sensitive to increased acidity than to increased conductivity. By comparing the change in DOC release with bulk soil properties, we found that DOC release from the O‐horizon of organo‐mineral soils and semi‐confined peats, which contained greater exchangeable aluminium (Al) and had lower base saturation (BS), were more sensitive to SO42? additions than DOC release from blanket peats with low concentrations of exchangeable Al and greater BS. Therefore, variation in soil type and acid/base status between sites may partly explain the difference in the magnitude of DOC changes seen at different sites where declines in S deposition have been similar. |
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