Fine-scale temporal characterization of trends in soil water dissolved organic carbon and potential drivers
Thisis relevant to the following issues:
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Pollution and subsequent climate change have led to unprecedented environmental changes across the globe, including decreases in air, soil and water quality. Among many indicators, levels of dissolved organic carbon (DOC) concentrations (primarily derived from soil organic matter) in soils and surface waters inform us about water and soil quality.
In recent decades, concentrations of DOC have tended to increase in soils and surface waters in many northern hemisphere regions. This has raised concerns for public health and the fate of our soil carbon stocks, since DOC plays several important roles in the environment:
It is therefore important to understand what controls long-term changes in DOC concentrations and if these concentrations may be subject to further change in the future. Climate change, land use change, and nitrogen deposition have all been offered as explanations for rising DOC concentrations. An alternative hypothesis, rapidly gaining acceptance, is that the DOC trends are linked to recovery from human-caused acidification ('acid rain' from the burning of fossil fuels).
Long-term monitoring of soil water chemistry provided by the Environmental Change Network and the UK's Forest Monitoring Level II programme provide unique opportunities to explore linkages between different DOC drivers and ecosystem properties and management.
In this study, scientists collated up to 18 years of data on soil water DOC concentrations, and corresponding soil water chemistry, atmospheric deposition and weather indicators from nine different ecosystems with varying soil types, vegetation types and land management. They applied state-of-the-art statistical techniques to identify periods of significant changes in DOC and corresponding candidate drivers.
The study confirmed that grassland and forest soils in the UK are in the process of recovering from acidification. Large reductions in sulphur deposition correlated with soils becoming less acidic and DOC concentrations increasing in surface organic layers. Although long-term DOC trend patterns varied between sites, the strongest increases in DOC were seen in acidic forest soils and were most clearly linked to declining acid deposition.
The analysis also suggested that increases of DOC in upper soil horizons due to declining acid deposition are the most likely sources of increased DOC in stream waters. This has important implications for how recent trends are perceived and the extent to which they might be managed or mitigated.