Nitrogen river fluxes

During the second part of the 20th century, river flux of organic matter, nutrients and pollutants markedly increased. For example, increase in concentration of ammonia nitrogen is 2.5 times, of nitrites and nitrates 4 and 5 times respectively, of phosphate 2 times. Since the beginning of 1970s, the concentration of heavy metals and oil in river water has also increased [9]. Over the period 1996-2000, the input of the contaminants to the Black Sea with the Danube waters comprises oil 53 x 1012 t, Cu 1.2 x 1012 t, and Zn 3.3 x 1012t [9],... 

At regional scales, there are also examples in which SGD of nitrogen equals or exceeds river fluxes. For example, DIN fluxes in groundwater discharges through salt marshes along the South Carolina coast are estimated to be equivalent to input from major rivers in this region ( 60 X 10 mol yr ) (Krest et ai, 2000) (Table 9.5). 

Fig. 10-13. The links between the cycling of C, N, and O2 are indicated. Total primary production is composed of two parts. The production driven by new nutrient input to the euphotic zone is called new production (Dugdale and Goering, 1967). New production is mainly in the form of the upward flux of nitrate from below but river and atmospheric input and nitrogen fixation (Karl et al, 1997) are other possible sources. Other forms of nitrogen such as nitrite, ammonia, and urea may also be important under certain situations. The "new" nitrate is used to produce plankton protoplasm and oxygen according to the RKR equation. Some of the plant material produced is respired in the euphotic zone due to the combined efforts...

The nitrogen supplies on land consist of the assimilable nitrogen in the soil VS2 0.19-104tkm-2, in plants (12 1091), and living organisms (0.2 1091). A diversity of nitrogen fluxes is formed here of the processes of nitrification, denitrification, ammonification, fixation, and river run-off. The intensities of these fluxes depend on climatic conditions, temperature regime, moisture, as well as the chemical and physical properties of soil. Many qualitative and quantitative characteristics of these dependences have been described in the literature (Hellebrandt et al., 2003). Let us consider some of them. 

Gardner, W.S., Escobar-Broines, E., Cruz-Kaegi, E., and Rowe, G.T. (1993) Ammonium excretion by benthic invertebrates and sediment-water nitrogen flux in the Gulf of Mexico near the Mississippi River outflow. Estuaries 16, 799-808. 

External nutrient supply is defined as the supply of dissolved nutrient that is biologically available for shelf plankton. The sources of these nutrients are from the river and upwelled offshore waters, nitrogen fixation regenerated terrestrial organic niatter, and absorbed material. The flux of P from desorption is considered part of this external supply, whereas the recycling of estuarine biogenic material (via microbial degradation or dissolution) is not. 

The fluxes illustrated in Fig. 17.3 reveal several important aspects of N cycling in the Amazon River/ocean mixing zone. First, the external supply of biologically available dissolved nitrogen (totalling 10-12 x 10 mol d, including N fixation) is considerably... 

Eyre and Pont, 2003 Jordan et ai, 2003 Nixon et al., 1995 Wollast, 1983 Table Al). In addition, a number of relatively complex, deterministic models of river nitrogen flux have been developed and applied to individual rivers (e.g., GWLF, Haith and Shoemaker, 1987 Lee et al., 1999 HSPF, BickneU et al., 1997 Fdoso et al., 2004 SWAT, Srinivasan et al., 1993). Several of these, as well as other models, have been described recently in Alexander et al. (2002). 

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. 

Nitrogen Fluxes from Rivers to the Coastal Oceans... 

Distribution of Nitrogen Fluxes in Rivers by Continent and Ocean Basin i577... 

There are many compHmentary approaches presented in the recent literature for considering fluxes of total nitrogen in rivers at regional and global scales, aU of which... 

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). 

---