Alexander,R.B., Bohlke（oの頭に¨）,J.K., Boyer,E.W., David,M.B., Harvey,J.W., Mulholland,P.J., Seitzinger,S.P., Tobias,C.R., Tonitto,C. and Wollheim,W.M.(2009): Dynamic modeling of nitrogen losses in river networks unravels the coupled effects of hydrological and biogeochemical processes. Biogeochemistry, 93, 91-116.

『河川ネットワークにおける窒素損失の動的モデル化は水文と生物地球化学過程の複合した影響を解き明かす』

『Abstract
　The importance of lotic systems as sinks for nitrogen inputs is well recognized. A fraction of nitrogen in streamflow is removed to the atmosphere via denitrification with the remainder exported in streamflow as nitrogen loads. At the watershed scale, there is a keen interest in understanding the factors that control the fate of nitrogen throughout the stream channel network, with particular attention to the processes that deliver large nitrogen loads to sensitive coastal ecosystems. We use a dynamic stream transport model to assess biogeochemical (nitrate loadings, concentration, temperature) and hydrological (discharge, depth, velocity) effects on reach-scale denitrification and nitrate removal in the river networks of two watersheds having widely differing levels of nitrate enrichment but nearly identical discharges. Stream denitrification is estimated by regression as a nonlinear function of nitrate concentration, streamflow, and temperature, using more than 300 published measurements from a variety of US streams. These relations are used in the stream transport model to characterize nitrate dynamics related to denitrification at a monthly time scale in the stream reaches of the two watersheds. Results indicate that the nitrate removal efficiency of streams, as measured by the percentage of the stream nitrate flux removed via denitrification per unit length of channel, is appreciably reduced during months with high discharge and nitrate flux and increases during months of low-discharge and flux. Biogeochemical factors, including land use, nitrate inputs, and stream concentrations, are a major control on reach-scale denitrification, evidenced by the disproportionately lower nitrate removal efficiency in streams of the highly nitrate-enriched watershed as compared with that in similarly sized streams in the less nitrate-enriched watershed. Sensitivity analyses reveal that these important biogeochemical factors and physical hydrological factors contribute nearly equally to seasonal and stream-size related variation in the percentage of the stream nitrate flux removed in each watershed.

Keywords: Denitrification; Seasonal; Nitrate model; LINX; NHD river network; Nitrate loss; Nitrate removal efficiency; anthropogenic nitrogen』

Introduction
Methods: estimating stream nitrate transport
　The dynamic nitrate transport model
　Case study watersheds for applying the nitrate transport model
　Field denitrification data and regression models
　Application of the nitrate transport model to the river networks
Results and discussion
　Field denitrification data and regression models
　Application of the nitrate-transport model to Sugar Creek and Nashua watersheds
　　Nitrate loading to streams, discharge and predicted nitrate concentration
　　Relative nitrate removal by denitrification in streams
　　Mass removal of nitrate by denitrification in streams
　　Implications for the downstream fate of nitrate
Conclusions
Acknowledgments
Open Access
Appendix
　A1. Predicting reaction rate constants for Sugar Creek and Nashua streams
　A2. Stream hydrological estimates
　A3. Lateral loadings of nitrate to streams
　A4. Stream nitrate removal metrics
References

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