A review of uncertainties in the inputs to critical loads of acidity and nutrient nitrogen for woodland habitats

Abstract

Abstract Critical loads have been used at both the national and international scale in negotiations of protocols controlling the emissions of sulphur and nitrogen. Further, reductions in these pollutants have increasingly high costs; hence, quantifying the uncertainties in the calculation of critical loads and their exceedances has become increasingly important. The UK uses mass balance modelling techniques to calculate steady-state acidity and nutrient nitrogen critical loads for woodland habitats. The calculation uses data from a wide range of sources and the accuracy of the critical loads are influenced by the accuracy of the input data sets. This paper aims to quantify the uncertainties in the data used. A comparison of the uncertainties derived for UK data and those calculated by other European countries reveals a wide range in the estimates of uncertainty and in the methods used to derive them. Possible reasons for these differences are the different methods used to estimate the uncertainty, the scale at which the uncertainty was assessed and underlying methodological differences. Transparency in the way the uncertainties are derived are necessary for communication between scientists and decision makers.