Natural denitrification in the saturated zone: A review

Abstract

Denitrification is increasingly recognized for its ability to eliminate or reduce nitrate concentrations in groundwater. With this awareness comes a desire to predict the rate and extent of denitrification in aquifers. The limiting factor in making predictive models, however, is our limited knowledge of the physical characteristics of this process. This review synthesizes the published literature on natural aquifer denitrification. A background section discusses denitrification requirements and dissimilatory nitrate reduction to ammonium, which occurs in environments similar to those where denitrification occurs, and gives a historical perspective on denitrification. Other sections discuss denitrification with organic carbon serving as the electron donor (heterotrophic denitrification) and with reduced inorganic compounds serving as the electron donor (autotrophic denitrification). The section on heterotrophic denitrification is structured around two tables that summarize natural aquifer denitrification rates reported by laboratory studies and natural aquifer denitrification rates reported by field studies. The section on autotrophic denitrification discusses denitrification with reduced iron and reduced sulfur. Thus far, most studies only consider a single electron donor or donor type, whether heterotrophic or autotrophic. This review demonstrates, however, that multiple electron donors may be present in a given aquifer. Future research efforts are recommended to determine the factors affecting the availability of electron donors and their denitrification rates. Additional research is also suggested on how dissolved oxygen affects denitrification rates and on the factors influencing the partitioning of nitrate reduction products to nitrous oxide, a potential contributor to the destruction of the ozone layer, and to ammonium.

Nitrogen transport and transformations in a shallow aquifer receiving wastewater discharge: A mass balance approach

“…Consistent with the low levels of respiration, DIC concentrations did not greatly increase in the plume from denitrification or organic carbon oxidation. The maximum DIC contribution from denitrification, about 2-3 mg N/L (based on the N 2 data and a stoichiometric relation of 1.1 mg of carbon oxidized per milligram of nitrogen reduced [Korom, 1992]), was small relative to the DIC contribution from organic carbon oxidation in the unsaturated zone.…”

Natural Protection Against Groundwater Pollution by Nitrates in the Central Valley of Chile/Protection Naturelle Contre la Pollution des Eaux Souterraines par les Nitrates Dans la Vallée Centrale du Chili

“…Donoso et al (1999) made an analysis of available information about quality of groundwater used for drinking in 45 locations distributed throughout Chile. Only one location, in the Metropolitan Region, presented a nitrate-nitrogen concentration in drinking water slightly above the Chilean water-quality standard of 10 mg l -1 of NO 3 -N (INN, 1984), which is similar to the standard used by the United States Environmental Protection Agency (USEPA) (Korom, 1992;Jacinthe et al, 1999). Claret et al (2001) analysed levels of chemical and biological contamination of groundwater in a rural zone of Region VII (35-36ºS).…”

“…Four conditions are necessary for the denitrification process to take place: (a) the presence of nitrates; (b) the presence of biodegradable organic carbon, which can be supplied by the geological formation of the aquifer or can be leached from the topsoil; (c) the presence of denitrifying bacteria, which are usually found in natural systems, and (d) reducing conditions (Lowrance & Pionke, 1989;Korom, 1992;Starr & Gillham, 1993;Desimones & Howes, 1996;Brye et al, 2001). The amount of denitrification is also related to the characteristics of the aquifer and to the depth of the phreatic zone (Starr & Gillham, 1993).…”

“…Agriculture has been recognized as the main anthropogenic source responsible for high nitrate-nitrogen content in groundwater (Korom, 1992;Spalding & Exner, 1993). Given the possible negative effects of nitrate ingestion on human health, such as methaemoglobinaemia in infants or the occurrence of gastric cancer (Spalding & Exner, 1993;Canter, 1997;Rao & Putanna, 2000), there is a need for better understanding and mitigation of nitrate pollution in groundwater worldwide.…”

Kansas Case Study Applications of Nitrogen-15 Natural Abundance Method for Identification of Nitrate Sources

“…Measurements of 15 N abundances have been used for over 30 years to identify both point and non-point sources of nitrate. Work by Kreitler ( , 1979, Kreitler and Jones (1975), Shearer et al (1978), Kohl et al (1971), Heaton (1986), Mariotti et al (1988), Korom (1992), and Kendall (1998), and others, has contributed to development and use of the method. Examples of a few studies that illustrate the usefulness of the method include Gormly and Spalding (1979) in Nebraska, Mariotti et al (1988) in France, Mitchell et al (2003) in Canada, and Townsend et al (1994) in Kansas.…”