Peat-dominated upland ecosystems represent major stores of a number of nutrient elements, including nitrogen. It is anticipated that climatic warming in such environments will increase the rate of nitrogen cycling, potentially leading to the release of nitrogen into river waters. This could have negative effects on ecosystem function and downstream water quality. Thus, it is important to study the underlying hydrological and biogeochemical processes that control nitrogen flux and speciation in upland river waters. Currently, fieldwork aimed at improving understanding of these processes is being carried out at Moor House-Upper Teesdale National Nature Reserve, North Pennines, UK. The research focuses on two key areas: Hillslope hydrology, which is being examined using an EMMA (end-member mixing analysis) approach to identify the relative contributions of different source waters to overall channel flow under a range of conditions; and in-stream biochemical transformations of nitrogen species, which are being studied through chemical tracing experiments. The ultimate aim is to integrate these two pieces of research in order to improve understanding of how the hydrochemical signature of upland drainage waters is generated.