Fluxes of Nitrogen

The largest source of atmospheric ammonia is ammoniafication and volatilization from animal excreta (Freney et al., 1983). Direct anthropogenic 

The fixation/denitrification cycle (Fig. 12-7) is perhaps the most heavily perturbed by humans, but the effects of these perturbations are poorly understood. In the atmosphere, the principal components 

The data of Weiss (1981) suggest that the fixation-denitrification cycle is not balanced, which he attributes to anthropogenic influences. In his extensive data set of gaseous N2O concentrations, several facts are apparent First, mean N2O con- 

Stedman and Shelter (1983) claim that the magnitude of the northern-southern hemispheric difference in N2O concentrations is consistent with a major terrestrial source and a large oceanic sink, as suggested by McElroy et al. (1976), since the largest land masses are in the northern hemisphere. The N2O model presented by Stedman and Shelter (1983) includes large soil source and sink terms, and gives an N2O residence time of about 20 years. Their model is consistent with much of the soil data (presented in the earlier sections of this paper) which suggest that soils are both a major source and sink for N2O (see also Keller et al., 1983). However, Stedman and Shelter s model is inconsistent with the data and calculations of Weiss (1981), the data of Hahn and Crutzen (1982), the residence time for atmospheric 

The fluxes in Table 12-3 have been divided into the 

The inflow from the Changjiang River is the major source of nutrients to the Changjiang River Estuary and coastal waters. The nutrient concentrations as well as nutrient loads of the Changjiang River, notably DIN, increased exponentially and by a factor of seven from the 1960s to the end of the 1990s, mainly due to the increasing amount of fertilizer application and effluents 

The effect of atmospheric inputs of nutrients on biological cycles is particularly important for oligotrophic oceanic provinces, and episodic deposition may even induce algal blooms. The ECS adjacent to the East Asia mainland is influenced by a monsoon climate and strong emissions of natmal and anthropogenic compounds into the atmosphere. Soil-derived dust and anthropogenic compounds are transported over the ECS via atmospheric circulation, while aerosols from the ocean also play an important role in the chemical characteristics of precipitation. 

As aerosols in the atmosphere originate from multiple sources, the composition of nutrients changes considerably over the four seasons. Nitrate, NOJ, and NHJ are defined as secondary aerosol-associated species and are not associated with primary aerosols. The combustion of fossil fuels is a significant source of NO, whereas NHj may originate from anthropogenic emissions such as animal waste and the application of chemical fertilizers. 

3 Benthic Flux of Dissolved Nutrients at the Sediment Water Interface 

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The heat of permeation of chlorine in a silicone rubber membrane is —3 to — 5 kcal mol-1 while that of nitrogen is 1.0-1.5 kcal mol-1. Separation of these gases therefore is helped by low temperature. The flux of chlorine actually increases as temperature is lowered, reflecting the increased sorption. The flux of nitrogen decreases, reflecting the lower diffusivity. 

Table 24.8 Benthic Fluxes of Nitrogen Species and Their Relative Contribution to Local Primary Production. ... 

Table 4.5. Characteristics of the reservoirs and fluxes of nitrogen in the biosphere (Figure 4.6).

Howarth, R.W., Jaworski, N., Swaney, D., Townsend, A., and Billen, G (2000) Some approaches for assessing human influences on fluxes of nitrogen and organic carbon to estuaries. In Estuarine Science A Synthetic Approach to Research and Practice (Hobbie, J.E., ed.), pp. 17-42, Island Press, Washington, DC. 

Rivera-Monroy, V.H., Day, J.D., Twilley, R.R., Vera-Herrera, F., and Coronado-Molina, C. (1995) Flux of nitrogen and sediments in a fringe mangrove forest in terminus Lagoon, Mexico. Estuar. Coastal Shelf Sci. 40, 139-160. 

Fig. 13.3 Stocks and fluxes of nitrogen in the Varzea forest ecosystem (Furch 1997).

Goolsby, D. A., and Battaglin, W. A. (2001). Long-term changes in concentrations and flux of nitrogen in the Mississippi River Basin, USA. Hydrol. Process. 15, 1209-1226. 

Green, P. A., Vorosmarty, C. J., Meybeck, M., Galloway, J. N., Peterson, B. J., and Boyer, E. W. (2004). Pre-industrial and contemporary fluxes of nitrogen trough rivers A global assessment based on topology. Biogeochemistry 68, 71-105. 

Tyler, A. C., McGlathery, K. J., and Andersen, I. C. (2003). Benthic algae control sediment-water column fluxes of nitrogen in a temperate lagoon. Limnol. Oceanogr. 48, 2125—2137. 

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). 

There is a great deal of variation in nitrogen fluxes off the landscape in rivers at scales smaller than the continents (Fig. 36.9). For example, within North America contemporary fluxes of nitrogen in rivers per area of watershed are estimated as 76 kg km year in Labrador and the Hudson s Bay area, as 566 kg km year in the Mississippi River basin, and as 1070 kg km year in the northeastern United States from Maine southward through Virginia (Howarth et al., 1996 Fig. 36.10). At finer scales yet, more variation is observed within the major watersheds in the northeastern United States, the riverine nitrogen flux per area varies from a low of 317 kg km year in the Penobscot River basin to 1755 kg km year in the... 

Figure 36.9 Fluxes of nitrogen (kg per km of watershed area per year) from the landscape to coastal oceans in rivers for contrasting regions of the world in the temperate zone. The natural background flux is based on the intercept of plots of nitrogen export vs. NANI (such as shown in Figs. 36.2 and 36.4B). Data from Flowarth el al. (1996,2002) Bashkin et al. (2002).

Sano Y., Takahata N., Nishio Y., Fischer T. P., and Williams S. N. (2001) Volcanic flux of nitrogen from the Earth. Chem. Geol. 171, 263 -271. 

The flux of hydrogen (component 1) is not too different from the flux estimated using the linearized equations in Example 5.3.1. However, the effective diffusivity method predicts a very small flux of nitrogen (component 2), a result quite different from the predictions of the linearized theory. This, of course, is because the effective diffusivity method ignores the contribution due to the driving forces of the other components. We will investigate the consequences of this prediction in Example 6.4.1. ... 

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