Estimating changes in Scottish soil carbon stocks using ECOSSE. I. Model description and uncertainties

To predict the response of C-rich soils to external change, models are needed that accurately \nreflect the conditions of these soils. Estimation of Carbon in Organic Soils—Sequestration and \nEmissions (ECOSSE) is a model that allows simulations of soil C and N turnover in both mineral and \norganic soils using only the limited meteorological, land-use and soil data that is available at the \nnational scale. Because it is able to function at field as well as national scales if appropriate input data \nare used, field-scale evaluations can be used to determine uncertainty in national simulations. Here \nwe present an evaluation of the uncertainty expected in national-scale simulations of Scotland, using \ndata from the National Soil Inventory of Scotland. This data set provides measurements of C change \nfor the range of soils, climates and land-use types found across Scotland. The simulated values show \na high degree of association with the measurements in both total C and change in C content of the \nsoil. Over all sites where land-use change occurred, the average deviation between the simulated \nand measured values of percentage change in soil C was less than the experimental error (11% simulation \nerror, 53% measurement error). This suggests that the uncertainty in the national-scale simulations \nwill be ~11%. Only a small bias in the simulations was observed compared to the measured \nvalues, suggesting that a small underestimate of the change in soil C should be expected at the \nnational scale (–4%)