Influence of recovery from acidification on the dynamics of dissolved organic carbon (DOC) in organic soils

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Peaty soils, which dominate the uplands of the UK, represent a significant store of carbon, containing around a third of the global terrestrial carbon, which is equivalent to the total amount of carbon stored in the atmosphere. These soils slowly release carbon into rivers and lakes. It is this dissolved organic carbon that gives upland waters their brown colour. Over the last 15 years, the colour of these waters has become darker as the amount of dissolved organic carbon draining from peatlands has increased, by on average 91%. This increase in the loss of carbon from peatlands soils has promoted fears that we have disturbed the stability of the global carbon cycle. The increase in water colour is also a problem for water companies as the dissolved organic carbon can react with the chlorine in water-treatment processes to produce potentially carcinogenic chemicals. Some scientists have suggested that increasing temperatures or decreasing rainfall due to global warming is resulting in more carbon being released from peatlands, while others have suggested that increasing atmospheric carbon dioxide is itself the cause. If these climate change mechanisms are responsible for the increasing trend in dissolved organic carbon, it suggests that peatlands are becoming unstable, with major implications for the global carbon cycle (with feedback effects on climate), water quality and water treatment. We argue, however, that recent rises in temperature and carbon dioxide have been insufficient to cause the observed changes in dissolved organic carbon. We believe that the decline in acid rain over the past 20 years has been a more important influence on dissolved organic carbon concentrations, as the solubility of organic carbon is controlled by pH: the more acid the water, the less is dissolved. If correct, this has very different consequences for the global carbon cycle and long-term water quality, as the systems are simply returning to their pre-industrial conditions. Therefore, increased dissolved organic carbon in freshwaters may represent an environmental recovery to more 'natural' conditions, and not an environmental degradation in response to climate change. The overall aim of this research project is therefore, to determine whether the decline in acid rain can account for the majority of the observed increase in DOC concentration in freshwaters across the UK since 1988. The research will be conducted in two ways. We will use laboratory experiments to measure the changes in soils subjected to different levels of pollution. We will also study evidence for these changes in soils from different locations across the UK. The research will take three years to complete and involves collaboration between scientists at the University of Leeds, Centre for Ecology and Hydrology and University College London. Finally we will integrate the experimental results with analysis of long-term monitoring data for upland catchments dominated by organic soils.