The mass transport model TEOTIL was used to project nitrate (NO₃) fluxes from the Tovdal River basin, southernmost Norway, given four scenarios of climate change. Forests, uplands, and open water currently account for 90% of the NO₃ flux. Climate scenarios for 2071–2100 suggest increased temperature by 2–4°C and precipitation by 3–11%. Climate experiments and long-term monitoring were used to estimate future rates of nitrogen (N) leaching. More water will run through the terrestrial catchments during the winter but less will run in the spring. The annual NO₃ flux from the Tovdal River to the adjoining Topdalsfjord is projected to remain unchanged, but with more NO₃ delivered in the winter and less in the spring. Algal blooms in coastal waters can be expected to occur earlier in the year. Major sources of uncertainty are in the long-term fate of N stored in soil organic matter and the impacts of forest management.