Impacts of Droughts and Acidic Deposition on Long-Term Surface Water Dissolved Organic Carbon Concentrations in Upland Catchments in Wales

Jaeyoung Lee,Jim W. Hall,Paul G. Whitehead,Martyn N. Futter

doi:10.3389/fenvs.2020.578611

Abstract

Concerns have been raised about rising trends in surface water dissolved organic carbon (DOC) concentrations in UK upland catchments over the past decades. Several mechanisms have been proposed to explain these trends, including changes in climate and declines in sulphate deposition across Europe. Drier summers and wetter winters are projected in the UK, and there is an increasing interest in whether the rising trends of DOC would be continued or stabilised. In this paper, the INCA (INtegrated CAtchment) water quality model was applied to the upland catchment of the River Severn at Plynlimon in Wales and used to simulate the effects of both climate and sulphate deposition on surface water DOC concentrations. We introduced new parameter sets of INCA to explain enzymatic latch effect in peatlands during droughts. The model was able to simulate recent past (1995-2013) rising trends in DOC in Plynlimon. Climatic projections were employed to estimate the future trends on DOC in the uplands and to consider potential impacts on catchment management. The model was run with climatic scenarios generated using the weather@home2 climate modelling platform and with sulphate deposition scenarios from the European Monitoring and Evaluation Programme (EMEP) for 1975-2100. The modelling results show that the rising DOC trends are likely to continue in the near future (2020-2049) and the level of DOC concentrations is projected to stabilise in the far future (2070-2099). However, in the far future, the seasonal patterns of DOC concentrations will change, with a post-drought DOC surge in autumn months.

Highlights

While the peatlands cover a relatively small amount of the Earth’s terrestrial area, they contain approximately one-third of the world’s soil carbon pool (Gorham, 1991; Pastor et al, 2003) and about 40% of the UK’s total soil carbon storage (UK National Ecosystem Assessment, 2011)
The Monte Carlo simulation produced an ensemble of 10,000 model runs and those results were assessed based on observed values of flow and water quality (DOC) at reach two for both the Hore and Hafren catchments (Lower Hore and Lower Hafren)
The impact of climate change and acidic deposition on flow and water quality was analyzed for an uplands catchment, Plynlimon in Wales, UK

Summary

Introduction

While the peatlands cover a relatively small amount of the Earth’s terrestrial area, they contain approximately one-third of the world’s soil carbon pool (Gorham, 1991; Pastor et al, 2003) and about 40% of the UK’s total soil carbon storage (UK National Ecosystem Assessment, 2011). Several mechanisms have been proposed to explain these trends including changes in climate and declines in sulfate deposition across Europe (Evans et al, 2005; Monteith et al, 2007). Fluvial DOC export determines a significant proportion of the peatland carbon balance, and widespread increases in DOC fluxes suggest that this carbon balance may be altering, with major implications for terrestrial carbon budgets. These increases appear to be driven by regional or global-scale environmental changes, the key driving mechanisms have yet to be conclusively identified

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