Effects of acidity on dissolved organic carbon in organic soil extracts, pore water and surface litters

Catharine M Pschenyckyj; Joanna M Clark; Liz J Shaw; Robert I Griffiths; Chris D Evans

doi:10.1016/j.scitotenv.2019.135585

Effects of acidity on dissolved organic carbon in organic soil extracts, pore water and surface litters

Sci Total Environ. 2020 Feb 10:703:135585. doi: 10.1016/j.scitotenv.2019.135585. Epub 2019 Nov 18.

Authors

Catharine M Pschenyckyj¹, Joanna M Clark², Liz J Shaw², Robert I Griffiths³, Chris D Evans³

Affiliations

¹ Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne NE1 8ST, UK. Electronic address: catharine.pschenyckyj@northumbria.ac.uk.
² Soil Research Centre, Department of Geography and Environmental Science, School of Archaeology, Geography and Environmental Science, The University of Reading, Whiteknights, PO Box 227, Reading RG6 6AB, UK.
³ Centre for Ecology and Hydrology, Deiniol Rd, Bangor LL57 2UP, UK.

PMID: 31767326
DOI: 10.1016/j.scitotenv.2019.135585

Abstract

Over the past 30-40 years, dissolved organic carbon (DOC) concentrations have increased in soil solutions and surface waters in many acid-sensitive areas of Europe and North America. This has been linked to recovery from acidification in response to decreasing levels of atmospheric pollution. Evidence from radiocarbon dating suggests that DOC in surface waters is typically derived from recently photosynthesised organic matter such as plant litter and exudates, yet there is little information on the pH-sensitivity of organic matter solubility, or its decomposition, in litter layers and in different organic soils. Therefore the purpose of this study was to determine a) the sensitivity of DOC to acidity in different surface layers and soil types, in order to b) improve understanding of the key sources contributing to the increasing DOC trend. Such information is vital for understanding site specific characteristics contributing to inconsistencies in DOC release between catchments, and for improving predictions of carbon fluxes and budgets. Based on data collected at four established field pH-manipulation experiments in upland areas of the United Kingdom, we examined the sources, composition and acid-sensitivity of DOC export from the litter and organic soils. We found that litter generated nearly three times more DOC than the organic soils, consistent with radiocarbon evidence that recent plant inputs are a major source of DOC. Furthermore, litter derived DOC had lower specific ultraviolet light absorbance (SUVA) than organic soil DOC, suggesting greater biodegradability, and was not acid sensitive. In contrast, organic soil DOC concentrations were more strongly related to experimentally manipulated pH, implying that the mobility of this DOC may be subject to physicochemical rather than biotic controls. Our results suggest that physicochemically mediated controls on organic matter solubility may be a key driver behind the widely observed increases in surface water DOC in areas undergoing recovery from acidification.

Keywords: Acid deposition; DOC; Litter; Peat; Podzol; Solubility.