Origin and history of nitrate in confined groundwater in the western Kalahari

Regional Patterns in the Isotopic Composition of Natural and Anthropogenic Nitrate in Groundwater, High Plains, U.S.A.

“…For the transect wells, denitrification in the saturated zone was estimated from analyses of Ne-Ar recharge temperatures and N2 concentrations (21). Both the initial concentration and the initial isotopic composition of NO3 -in recharge were reconstructed by combining data for reactant NO3 -and product excess N2 gas in denitrified groundwater samples (12,29). Samples from the agricultural water-table wells contained >60 µM (>2 mg/L) O2, so they are not expected to have undergone substantial denitrification (21,29,30).…”

Noble Gases in Lakes and Ground Waters

“…In confined aquifers in the Western Kalahari, Heaton et al (1983) found even larger concentrations of excess air than in South Africa, in particular in the Nossob aquifer. Their most important finding, however, were systematic variations of excess air with ground-water age in the Stampriet Auob aquifer.…”

“…Vogel, Heaton and colleagues provide convincing evidence for Nz excess (.6.N z ) due to N03 reduction in old anoxic ground waters in Southern Africa Heaton et al 1983). The authors show that the observed excess of molecular nitrogen consists of at least two components similar in magnitude: (1) .6.N2 due to excess air fonnation, and (2) excess Nz as the product of nitrate reduction.…”

“…1986). Of course, Nz is not a noble gas and can be affected by biogeochemical processes (e.g., denitrification, Heaton et al 1983). A better choice of gases would be Ne and Xe, because their solubilities differ strongly (compare Fig.…”

Techniques isotopiques (15N 18O) appliquees a l etude des nappes des alterites et du socle fracture de l ouest africain

“…Elle n'a pas permis de trancher entre les deux hypothèses retenues par l'auteur, pollution d'origine domestique ou pollution liée à la deforestation, mais apporte toutefois des arguments en faveur de la seconde. En Afrique australe, Heaton et al [1983], Heaton [1984] et Heaton et Collet [1985] établissent, à l'aide de la composition isotopique des nitrates, que les sols et les excréments d'animaux sont responsables de la pollution nitratée dans des nappes profondes et dans des nappes plus superficielles. Le socle altéré sur lequel reposent ces formations pédologiques peut atteindre, dans le Liptako, plus de 27 mètres [Ousmane, 1989].…”