Nitrogen deposition estimation

Nitrogen fluxes (in Tg N year ) are reported for contemporary conditions, with estimates under pristine conditions indicated in parentheses. Flux of nitrogen delivered from rivers and estuaries is the direct input of rivers that discharge onto the continental shelf plus the riverine input into estuaries, minus nitrogen consumed in estuaries. Atmospheric nitrogen deposition estimates in this table are those directly onto the waters of the continental shelf and do not include deposition onto the landscape (which is part of the flux from rivers and estuaries). The flux from the deep ocean represents the advection of nitrate-rich deep Atlantic water onto the continental shelf Data in this table are from Howarth (1998). 

Figure 5.5. Carbon to nitrogen ratios (C N) in the forest floor in relation to nitrogen deposition estimates in hardwood (R =0.19, P<0.001) and conifer (R =0.27, P<0.001) forests, showing different trends for hardwood and conifer stands (hardwood stands, R =0.19, P<0.001 conifer stands). From Aber et al. (2003), reprinted with permission, copyright American Institute of Biological Sciences...

Schindler, D. W. and Bayley, S. E. (1993). The biosphere as an increasing sink for atmospheric carbon Estimates from increased nitrogen deposition. Global Biogeochem. Cycles 7,717-733. 

Dore AJ, Kryza M, Hall JR, Hallsworth S, Keller VJD, Vieno M, Sutton MA (2012) The influence of model grid resolution on estimation of national scale nitrogen deposition and exceedance of critical loads. Biogeosciences 9 1597-1609... 

The calculated values of deposition of atmospheric nitrogen to each region are described in detail for the global scale and for individual domains in various papers (Prospero et al, 1996 Dentener et al, 2000). The authors presented modeled estimates of wet and dry deposition of oxidized (NOy) and reduced (NH ) forms of nitrogen. The resolutions vary from 2.5° x 3.25° LoLa (Latitute-Longitude) for oxidized nitrogen to 10° X 10° FoFa for ammonia species. These deposition estimates are based on a complex model of nitrogen emissions, transformation in atmosphere, transport and deposition. 

Two Approaches for Estimating Total Nitrogen Deposition in the Northeastern United States... 

The estimation of total nitrogen deposition from throughfall measurements often yields much higher rates than those inferred from wet deposi-... 

The Chesapeake Bay Program model relies on an estimate of total nitrogen deposition of 1,210 kg N km yr" (calculated from Figure A-4 Environmental Protection Agency 2003). The approach to derive this estimate is... 

National Research Council 2000 Howarth et al. 2002b). These areas of the watershed are therefore not monitored for their nutrient inputs to the Bay. While the fluxes of nitrogen from the watersheds above gaging stations in the Chesapeake Basin are reasonably well known, the fluxes from the watershed in the more urbanized areas on the coastal plain near Chesapeake Bay—where nitrogen deposition may be much greater, and retention of nitrogen in the landscape much less—are estimated only from models and not from empirical monitoring data. 

Table 1. Estimated 1987-88 growing season (April 15 - October 15) mean sulfur and nitrogen deposition at Mountain Cloud Chemistry Program sites (kg S or N/ha-mo). (Source Mohnen et al. 1990).

The degree of acidity production (N ) due to nitrogen depositions (l.e. the amount of nitrogen leaching) may be estimated fn>m ... 

The amount of acidify produced by nitrogen depositions can then be summed with that due to sulphur depositions to give a value of total deposition of acidifying substemces from anthropogenic sources. The total acid load should include ammonium depositions, estimates of which can now be derived (EUassen et oL, 1988 Saltbones, Sandnes and EUassen, 1989). 

Data from European sources (Popovie, 1985 Buldgen and Remack, 1984) suggest that observed leaching rates range from 0.1 to 20 kg N ha yr. Nitrogen deposition rates of 2 to 50 N ha yr have been measured. The leaching rates estimated by the method outlined above are in the range of 0-38 kg N ha yr. ... 

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