Including function in river condition assessment: organic carbon processes in upland catchments

The need to include a whole-catchment perspective in river management and river condition assessment has been recognized for decades. Recently, the focus of river condition assessment has shifted from approaches using only structural components (e.g. water quality, biodiversity, etc.), to approaches that combine structural components with assessment of ecosystem processes. Here we introduce an innovative approach to investigate the relationship between land-­use and the condition of an upland river and its catchment. This holistic approach is based on organic carbon (Corg), the source of energy for biota, and uses a suite of ecosystem processes which reflect the direction of flow of Corg in the catchment. The flow of Corg in the catchment -­from vegetation through soil into the river can be quantified by measuring: 1, decomposition in soil and water as a measure of biological activity and nutrient cycling; 2, Corg­-leaching from soil and Corg-­transport in surface runoff as a measure of the soil's ability to retain resources and the delivery of essential resources from land to river; 3, riparian litter input to the river and periphyton production as a measure of Corg for heterotrophic aquatic biota; and 4, benthic respiration as a measure of Corg readily available for heterotrophic biota in the river. Preliminary data suggests that the differences between impaired and reference sites in Corg -­storage and processing within/between soil and streams may be able to be used to provide information about functional changes.