Fertilizers increasing nitrate concentration

Vegetables are also a prime source of nitrate, and variations in their nitrate levels occur due to conditions employed during the cultivation and storage processes. The nitrate concentration in surface water has increased due to increased use of artificial fertilizers, changes in land use and disposal of waste from intensive fanning. Nitrate is readily converted in mammalian systems through bacterial and mammalian enzymes to nitrite which can react with amines, amides and amino acids to form NOC. 

Denitrification causes the 6 N of the residual nitrate to increase exponentially as nitrate concentrations decrease, and causes the acidity of the system to decrease. For example, denitrification of fertilizer nitrate that originally had a distinctive 6 N value of A-0%c can yield residual nitrate with much higher 6 N values (e.g., -K5%o to - -30%o) that are within the range of compositions expected for nitrate from a manure or septic-tank source. Measured enrichment factors (apparent fractionations) associated with denitrification range from —40%o to —5%o hence, the fi N of the N2 is lower than that of the nitrate by about these values. The N2 produced by denitrification results in excess N2 contents in groundwater the fi N of this N2 can provide useful information about sources and processes (Vogel et al., 1981 Bohlke and Denver, 1995). 

The concentration of nitrous oxide (N20) in the atmosphere is only about 0.30 ppm but it increases by about 0.2% per year and so is at least partly of anthropogenic origin. Nitrous oxide is a product of the degradation of nitrate fertilizers, but some 7 x 105 tonnes of N2O are released annually to the atmosphere during production of nylon.20 The residence time of N20 in the atmosphere is about 150 years, and it could in the future contribute up to 10% of the anticipated greenhouse warming. 

An increase of C02 concentration in the atmosphere does not determine substantial fertilization of marine bioproductivity—but does lead to pH decrease. As temperature grows, C02 assimilation by the ocean decreases, but C02 emissions due to upwellings are reduced and the transport of excess carbon to deep layers of the ocean diminishes. The anthropogenically induced input of nutrients to the oceans through river run-off and deposition of atmospheric aerosols (especially nitrate and iron as elements of atmospheric aerosols) can affect bioproductivity. 

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