Controls on Soil Carbon Export revealed by Novel Tracers on multiple timescales (SCENT)

Dissolved organic carbon (DOC) occurs naturally in all aquatic environments but in recent decades, riverine DOC levels have dramatically increased, causing problems both for organisms living in those waters and the water treatment industry. Some believe this is an effect of climate change, with increasing CO2 and rising temperatures leading to destabilisation of our soils, and the release of excess carbon to the environment. Others have suggested that a decrease in acid rain has altered the solubility of soil carbon. In the recent past, pollutant sulphur emissions led to acid rain, and this acidity may have suppressed carbon release from soils. With sulphur emissions and acid rain now in decline in western Europe, soils are recovering, potentially returning carbon to pre-industrial levels. This may be an oversimplification. We already know that soil microbes that use sulphur in their metabolism can be stimulated by the additional sulphur inputs from acid rain. This anaerobic respiration consumes acidity, and may naturally reduce the chemical effects of acidity on DOC. Progress in this area of research has been hampered by a lack of reliable data from the past. We do not know exactly when DOC starting increasing, or whether the type of carbon being released from soils changed. This information is crucial to understanding whether the carbon cycle is responding to climate or acid rain, and whether this is a biological or chemical problem.
Recent work suggests we are now able to tackle the DOC problem from a new perspective. There have been exciting advances in the analysis of cave deposits (speleothems) as records of the past environment. These cave deposits form from water percolating from the overlying soil, and importantly, preserve chemical signals in the annual growth layers. Elemental analysis of the stalagmites can provide detailed information about the overlying soil, and the processes that took place in the past, including seasonal responses, and even individual flooding events. Pioneering methods using trace element signatures in Scottish stalagmites have identified a change in the type of carbon released from soil over the past 150 years which appears to be driven by an increase in temperature and enhanced microbial processing. This breakthrough demonstrates the potential for stalagmites to inform DOC research.
Our project aims to address the causes of DOC increases by a combination of laboratory soil experiments and stalagmite analysis, together with information from river archives, some unpublished, of recent decades. In order to understand the causes of change, we will recreate the atmosphere-soil-cave system in the lab, using artificial acid rain treatments and temperature controls to simulate past conditions. This will allow us to determine the effect of acidity, temperature and soil microbial processes on DOC release. Importantly, by measuring trace elements and other chemical signals at the same time, we can compare the experimental results to the chemical signals preserved in stalagmites, and interpret the full historical record. In the first instance, this allows us to make a rigorous test of the hypothesis that trace element signatures in Scottish speleothems directly reflect temperature-controlled organic processing. By carrying out analogous experiments on soils from other sites we will end up with a set of predictions for different sites with varying acidification and thermal histories. We will use sophisticated new stalagmite techniques to examine the record of carbon (both directly in terms of the organic matter properties, and indirectly from the trace element characteristics) to establish the timing and nature of change in carbon cycling over the last 200 years. This combined approach will tell us the precise timing and type of DOC change, and whether this was driven by changes in acid rain or climate, resolving our understanding of a key part of the modern carbon cycle.

This research is aimed at elucidating fundamental mechanisms of response to environmental change. Because of the link to water quality there is a clear relevance to the water industry as well as the educational and public interest. The relevance to the water industry is in terms of their long-term planning as to what to expect in terms of dissolved organic matter levels in relation to known trends in environmental drivers such as decreasing acidification and rise in mean temperatures.

There will be a particularly strong awareness among the public living and visiting northern Britain who will have observed at first-hand the strongly coloured discharges from peatland catchments. The public is interested in the varied consequences of environmental change and there is an opportunity to send the message that we need to be aware of both the first-order atmospheric drivers and also the response of land systems

The PDRA will participate in the dissemination activities as part of their general and further training in communicating science to the public and will be trained appropriately, but all the investigators will also contribute through public lectures in addition to the following activities.

A major arm of outreach will be the Lapworth Museum at Birmingham which it is intended will be extensively redeveloped and enlarged during the first half of the grant period. Here we plan a permanent exhibits on speleothems and a mobile Discovery Lab related to water fluorescence. Water industry outreach will be via an industrial forum facilitated through the University of Lancaster and a themed British Hydrological Society meeting to be held at Birmingham.

The timetable for our plans can be summarized as:
by December 2013: Speleothem Discovery Lab planned in outline
by June 2015: Fluorescence-related activity developed
by December 2015: Speleothem Discovery Lab implemented
by January 2016: Outreach forum arranged with delivery event later in the year in Lancaster
by June 2016: At least two Lapworth lectures and a minimum of six other public lectures by members of the team delivered
September 2016: BHS Conference on dissolved organic matter at Birmingham