Scaling up: site-specific measurements to global-scale estimates of denitrification
Seitzinger, S. (2000). Scaling up: site-specific measurements to global-scale estimates of denitrification, in: Hobbie, J.E. (Ed.) Estuarine science: a synthetic approach to research and practice. pp. 211-240 In: Hobbie, J.E. (Ed.) (2000). Estuarine science: A synthetic approach to research and practice. Island Press: Washington D.C.ISBN 1-55963-700-5. XI, 539 pp., more |
| Abstract | Site-specific process studies of denitrification are used in correlation analyses and in existing regional and global models to explore controlling factors and the spatial pattern of denitrification at a number of scales. Initial studies of denitrification in four estuaries had suggested that, at the ecosystem scale, external dissolved inorganic nitrogen (DIN) loading was an important factor controlling denitrification, with approximately 40-60% of the DIN loading removed by denitrification. More recent analyses using data from 14 coastal marine systems demonstrate that the relationship between denitrification and DIN loading is much more variable (3-100%) than earlier studies suggested. Expanding that analyses to include loading of organic-N as well as DIN results in two relatively good relationships; one between total N (TN) loading and denitrification rates (r²= 0.7) and another between the percentage of TN loading that is removed by denitrification and water residence time (r²= 0.75). The combination of water residence time and N loading also provides a good prediction of the percentage of N inputs removed by denitrification in rivers (r² = 0.8). Estimates of the regional distribution of denitrificaiton in estuaries of the North Atlantic suggest that while the amount of TN transport by rivers is highest in the tropics and lowest in the high latitudes, denitrification in tropical estuaries is predicted to show the opposite pattern. That is, denitrification in tropical estuaries will be low because almost 70% of the TN export by rivers in tropical latitudes is discharged directly onto the shelf by large rivers, thus bypassing estuaries. Estimates of denitrification for the continental shelf of the North Atlantic suggest that ~80% Occurs in the mid to high latitude areas, with only 20% in tropical shelf sediments. Results of a global model of DIN transport by world rivers indicate that almost 90% of the denitrification in rivers and estuaries is in the northern hemisphere, with almost half of this occurring in China, India, and southeast Asia. While there have been considerable advances in our understanding of denitrification rates and controlling factors in the last 20 years, there are still large uncertainties in estimating current ( future patterns of denitrification in rivers, estuaries, and continental shelves at ecosystem, regional, or global scales. |
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