@article{c0066669e5214484ba608fe5c577b03b,
title = "Stream denitrification across biomes and its response to anthropogenic nitrate loading",
abstract = "Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated, causing more bioavailable nitrogen to enter groundwater and surface waters. Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins, indicating that substantial sinks for nitrogen must exist in the landscape. Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favour microbial denitrification. Here we present data from nitrogen stable isotope tracer experiments across 72 streams and 8 regions representing several biomes. We show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of in-stream nitrate that is removed from transport. Our data suggest that the total uptake of nitrate is related to ecosystem photosynthesis and that denitrification is related to ecosystem respiration. In addition, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks.",
author = "Mulholland, {Patrick J.} and Helton, {Ashley M.} and Poole, {Geoffrey C.} and Hall, {Robert O.} and Hamilton, {Stephen K.} and Peterson, {Bruce J.} and Tank, {Jennifer L.} and Ashkenas, {Linda R.} and Cooper, {Lee W.} and Dahm, {Clifford N.} and Dodds, {Walter K.} and Findlay, {Stuart E.G.} and Gregory, {Stanley V.} and Grimm, {Nancy B.} and Johnson, {Sherri L.} and McDowell, {William H.} and Meyer, {Judy L.} and Valett, {H. Maurice} and Webster, {Jackson R.} and Arango, {Clay P.} and Beaulieu, {Jake J.} and Bernot, {Melody J.} and Burgin, {Amy J.} and Crenshaw, {Chelsea L.} and Johnson, {Laura T.} and Niederlehner, {B. R.} and O'Brien, {Jonathan M.} and Potter, {Jody D.} and Sheibley, {Richard W.} and Sobota, {Daniel J.} and Thomas, {Suzanne M.}",
note = "Funding Information: Acknowledgements Funding for this research was provided by the National Science Foundation. We thank N. Ostrom for assistance with stable isotope measurements of N2 and N2O, and W. Wollheim for initial development of the model that we modified to estimate denitrification rates from field data. We thank M. Mitchell, B. Roberts and E. Bernhardt for their comments on earlier versions of the paper. We thank the NSF LTER network, US Forest Service, National Park Service and many private landowners for permission to conduct experiments on their lands. Partial support to P.J.M. during manuscript preparation was provided by the US Department of Energy, Office of Science, Biological and Environmental Research under contract with UT-Battelle.",
year = "2008",
month = mar,
day = "13",
doi = "10.1038/nature06686",
language = "English",
volume = "452",
pages = "202--205",
journal = "Nature",
issn = "0028-0836",
publisher = "Nature Research",
number = "7184",
}
