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Examining mutli-scale patterns in soil water DOC in the UK

Kasia Sawicka1, Joanna Clark1, Elena Vanguelova2, Don Monteith3, Andrew Wade1
1 Soil Research Centre, Geography and Environmental Science, University of Reading
2 Forest Research
3 Environmental Change Network, Centre for Ecology and Hydrology

P 7.17 in Controls of dissolved organic matter fluxes in ecosystems

Poster Session 1 on Monday, 16:30-18:30

Over the past two decades increasing concentrations of dissolved organic carbon (DOC) have been widely observed, in many, but not all surface waters across parts of Europe and North America.  Several hypotheses have been proposed to explain these trends: climate change, changes in land management, nutrient deposition, CO2 enrichment and declining acid deposition. However, none of these hypotheses are yet accepted universally.  DOC dynamics is influenced by many different factors that affect the production, mobility and transport of DOC across varying temporal and spatial scales.  One key challenge in explaining long-term change through statistical analysis of time series monitoring data is the correct attribution of drivers to different components of the time series that affect the level (overall mean or median concentration), seasonality and trend.  In this study, we explore the factors controlling the spatial distribution in time series level compared to seasonality and trend in soil waters across the UK.  Data are presented from nine Forest Research long term intensive monitoring plots, part of the EU ICP Forest Level II network, and six Environmental Change Network Sites from 1992-2010. Analysis showed that the variation between DOC trends follows the patterns in soil and soil water acidity indexes – such as Aluminium, Chloride and strong base cations such as Calcium and Magnesium trends. Vegetation cover (forest/no-forest) and hydrological regime also played an important role in explaining variation in DOC trends. The spatial pattern in median DOC concentrations could be attributed to the exposure to acid deposition and soil buffering. A relationship between spatial variability in long-term averaged DOC concentration and vegetation type was not detected. However, the strength of DOC trend was strongly linked to vegetation type. The greatest trends in DOC were observed under forested sites, whereas in grassland sites the rate of change oscillated around zero. Over the time period studied, DOC trends were non-linear and not monotonic.  Seasonal variation in both concentration and fluxes were mostly explained by climatic variables, rainfall and temperature.  Our analysis overall suggests that acid deposition was a dominant factor controlling the spatial variation in median DOC concentrations, whereas it had only a partial contribution to the trend because other ecosystem properties (i.e. vegetation cover) influence on the sensitivity to changes in acidification. This highlights the importance of understanding different sources of variation in a data set for each time series component and spatial site attributes in order to correctly identify drivers of change.

Letzte Änderung 05.04.2014