Challenges in modelling the sediment retention ecosystem service for an ecosystem account, with examples from the Mitchell catchment

If soil resources and the benefits derived from water quality are to be maintained, the on- and off-site effects of soil erosion must be adequately represented and communicated to decision makers so that appropriate management responses can be identified. The System of Environmental-Economic Accounting - Ecosystem Accounting (SEEA-EA), is one approach to quantify both the contributions that ecosystems make to the economy, and the impacts of economic activity on ecosystems. However, due to the difficulty of obtaining empirical data on ecosystem service flows, in many cases such quantification is informed by ecosystem service models. Previous research on the Mitchell catchment, Queensland Australia allowed us to explore the implications of using a model of hillslope erosion and sediment delivery in isolation (as represented in one of the most frequently used ecosystem service models - InVEST) by comparing such estimates against multiple lines of local empirical data, and a more comprehensive representation of locally important erosion and deposition processes through a sediment budget model. Estimates of the magnitude of hillslope erosion modelled using an approach similar to InVEST and the calibrated sediment budget differed by an order of magnitude. If an uncalibrated InVEST-type model was used to inform the relative distribution of erosion magnitude, findings suggest the incorrect erosion process would be identified as the dominant contributor to suspended sediment loads. However, the sediment budget model could only be calibrated using data on sediment sources and sinks that had been collected in the catchment through a sustained research effort. A comparable level of research investment may not be available to inform ecosystem service assessments elsewhere. The results summarised here for the Mitchell catchment demonstrate that practitioners must exercise caution when using estimates of the sediment retention ecosystem service flow which have not been calibrated and validated against locally collected empirical data.