Can the spatial distribution of dissolved organic carbon concentration in upland waters inform our understanding of processes and long term trends.

Don Monteith1, Peter Henrys1, Chris Evans1, Iain Malcolm2
1 NERC Centre for Ecology & Hydrology
2 Marine Scotland

O 7.6 in Controls of dissolved organic matter fluxes in ecosystems

14.07.2014, 15:35-15:55, H19

Space for time substitution, where spatial environmental relationships are used to infer or predict temporal environmental change, is often criticised on the grounds that individual sites tend to be tightly biogeographically constrained, and modelling tends to achieve mixed levels of success. We developed a simple linear multivariate logistic regression model to infer long-term (20 year) mean dissolved organic concentration in upland waters across the UK. Leave-one-out cross validation demonstrated that the model, comprising five terms, representing both geographical parameters and variables representing sulphate concentration and non-marine divalent base cation concentration,  was highly effective at predicting concentrations across wide gradients of altitude, precipitation, soil type and sulphur deposition (R2 = 0.92; Root Mean Standard Error of Prediction = 1.06 mg DOC L-1). We then applied the coefficients from the spatial model in a site-specific temporal context, to predict the impact of changing sulphate concentration (representing changing sulphur deposition) on DOC concentration at individual sites when all other predictors were held constant. For most sites the predicted change in DOC concentration corresponded well with the observed relationship between DOC concentration and sulphate concentration observed in individual samples, suggesting space for time substitution in this case was defensible and providing further support for the hypothesis that recent DOC trends have been dominated by the effects of changes in acid deposition on soil biogeochemistry in this region. We consider further possible implications of the spatial model structure for future DOC behaviour, particularly in the context of the negative effect of site altitude in the spatial model and its relevance for the potential impact of regional warming.     

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last modified 2014-04-03