Can't See the Forest for the Stream? In-stream Processing and Terrestrial Nitrogen Exports
This peer-reviewed article from BioScience investigates the decline in nitrate in New England watersheds. There has been a long-term decline in nitrate (NO3) concentration and export from several long-term monitoring watersheds in New England that cannot be explained by current terrestrial ecosystem models. A number of potential causes for this nitrogen (N) decline have been suggested, including changes in atmospheric chemistry, insect outbreaks, soil frost, and interannual climate fluctuations. In-stream removal of NO3 has not been included in current attempts to explain this regional decline in watershed NO3 export, yet streams may have high removal rates of NO3. We make use of 40 years of data on watershed N export and stream N biogeochemistry from the Hubbard Brook Experimental Forest (HBEF) to determine (a) whether there have been changes in HBEF stream N cycling over the last four decades and (b) whether these changes are of sufficient magnitude to help explain a substantial proportion of the unexplained regional decline in NO3 export. Examining how the tempos and modes of change are distinct for upland forest and stream ecosystems is a necessary step for improving predictions of watershed exports.