The data has been used to improve our understanding of water and nitrate dynamics in this tropical montane region: where does nitrate come from, how and when does it enter the stream, and are there differences between the three land use types? Nitrate concentration and export were found to be strongly related to fertilizer inputs: the more fertilizer is applied, the higher the concentration and annual export of nitrate. In all land use types nitrate is transported to the stream through sub-surface flow. However, differences were observed in the response of nitrate concentrations during storm events and to changes in discharge in general in the two agricultural sub-catchments compared to the forested sub-catchments. These differences suggest that land use change could also result in changes in magnitude and timing of nitrate export, which could affect ecology of rivers and lakes in the area as well as downstream.