Nitrogen in Aquatic Ecosystems

In the oceans, nitrates, nitrites and ammonium compounds are utilized as nutritive salts for plankton. As a result the surface layers of the seas are often lacking in nitrogen compounds. At depth the contents of these compounds are higher, maybe 0.3-0.5 ppm. If the nitrogen content of the surface layer increases, the production of 

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Berman, T., Bechemin, C., and Maestrini, S. Y. (1999). Release of ammonium and urea from dissolved organic nitrogen in aquatic ecosystems. Aquat. Microb. Ecol. 16, 295—302. 

Camargo JA, Alonso A (2006) Ecological and toxicological effects of inorganic nitrogen pollution in aquatic ecosystems a global assessment. Environ Int 32 831-849... 

Historically, nitrogen deposition has not been considered a serious threat to the integrity of aquatic systems. Most terrestrial systems have been assumed to retain N strongly. In such cases there is a small probability that deposited N would make its way to the surface waters that drain these terrestrial systems. Nitrogen within aquatic ecosystems can arise from a... 

Different roles in aquatic ecosystems, from acting as nutrients for living organisms (nitrogen and phosphorus compounds) to exerting toxic effects on such organisms (arsenic and mercury). 

Nutrients—these are elements essential to the metabolism of living organisms. Nitrogen, phosphorus, and silicon are the most important and commonly studied nutrients in aquatic ecosystems. 

Caraco, N.F., and Cole, J.J. (2003) The importance of organic nitrogen production in aquatic systems a landscape perspective. In Aquatic Ecosystems Interactivity of Dissolved Organic Matter (Findlay, S.E.G, and Sinsabaugh, R.L., eds.), pp. 263-283, Academic Press, New York. 

Element-based approaches are commonly used to estimate reservoirs and fluxes of organic carbon, nitrogen, and phosphorous in aquatic systems, mainly because the measurements can be conducted directly on water samples without isolation of the DOM. Such approaches provide insight into the processing of carbon, nitrogen, and phosphorous in aquatic ecosystems however, the real power of element-based approaches is only realized when an elemental analysis that includes hydrogen and oxygen is performed. Such an elemental analysis can be conducted with acceptable accuracy only on dry, low-ash samples (Huffman and Stuber, 1985). 

The denitrification is still insufficiently quantitatively understood in aquatic ecosystems, especially by comparison to terrestrial ecosystems. There are different views on whether the oceans are a source or sink of nitrous oxide. Various data indicate that the ocean is, on average, supersaturated with respect to N2O, and that N2O supersaturations are positively correlated with N03 and negatively correlated with O2. A number of studies have suggested that denitrification is a major sink for fixed nitrogen in the oceans. Recent studies suggests that denitrification losses in the oceans are on the order of 0.13 x 10 tons/yr (9.2 x 10 mol N per year) that exceed known oceanic N inputs. More than half of this denitrification (0.067 x 10 tons/yr (4.8 x lO mol N per year) takes place in sediments, with the remainder in pelagic oxygen minimum zones (see Box 3 for more details). 

Our same research group used tracer to measure the rate of inorganic N-uptake by phytoplankton to evaluate the relative importance of nitrogen cycling mechanisms for phytoplankton productivity in aquatic ecosystems (17), We measured nitrate uptake rates of 54.2 it 14.6 ftg-N/h in an oligotrophic lake. The precision of these measurements as well as the wide range over which they have been effectively used demonstrate the advantages of short-lived radioisotopes for tracer biochemistry. 

The most recent review of the epidemiological evidence merely extends the inconclusive verdict although no firm links have been found between dietary intakes of nitrate and stomach, brain, esophageal, and nasopharyngeal cancers, an association caimot be ruled out. In contrast to these continuing epidemiological uncertainties, the undesirable impacts of water-borne reactive nitrogen on aquatic ecosystems have... 

Acid rain and air pollution are very important problems that must be solved in the future because such pollution has major effects on terrestrial and aquatic ecosystems. At present, one of the most significant problems is removal of NOx, which are produced during high-temperature combustion and are an important group of air contaminants. In particular the decomposition or reduction of nitrogen monoxide (NO) is a major target to be achieved. 

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