Tesoriero,A.J., Saad,D.A., Burow,K.R., Frick,E.A., Puckett,L.J. and Barbash,J.E.(2007): Linking ground-water age and chemistry data along flow paths: Implications for trends and transformations of nitrate and pesticides. Journal of Contaminant Hydrology, 94, 139-155.

『流路に沿って地下水の年代と化学データを結びつける:硝酸塩と殺虫剤の動向と変化との関連』


Abstract
 Tracer-based ground-water ages, along with the concentrations of pesticides, nitrogen species, and other redox-active constituents, were used to evaluate the trends and transformations of agricultural chemicals along flow paths in diverse hydrogeologic settings. A range of conditions affecting the transformation of nitrate and pesticides (e.g., thickness of unsaturated zone, redox conditions) was examined at study sites in Georgia, North Carolina, Wisconsin, and California. Deethylatrazine (DEA), a transformation product of atrazine, was typically present at concentrations higher than those of atrazine at study sites with thick unsaturated zones but not at sites with thin unsaturated zones. Furthermore, the fraction of atrazine plus DEA that was present as DEA did not increase as a function of ground-water age. These findings suggest that atrazine degradation occurs primarily in the unsaturated zone with little or no degradation in the saturated zone. Similar observations were also made for metolachlor and alachlor. The friction of the initial nitrate concentration found as excess N2 (N2 derived from denitrification) increased with ground-water age only at the North Carolina site, where oxic conditions were generally limited to the top 5 m of saturated thickness. Historical trends in fluxes to ground water were evaluated by relating the times of recharge of ground-water samples, estimated using chlorofluorocarbon concentrations, with concentrations of the parent compound at the time of recharge, estimated by summing the molar concentrations of the parent compound and its transformation products in the age-dated sample. Using this approach, nitrate concentrations were estimated to have increased markedly from 1960 to the present at all study sites. Trends in concentrations of atrazine, metolachlor, alachlor, and their degradates were related to the timing of introduction and use of these compounds。Degradates, and to a lesser extent parent compounds, were detected in ground water dating back to the time these compounds were introduced.

Keywords: Agriculture; Trends; Atrazine; Metolachlor; Alachlor; Fertilizer; Pesticides; Dissolved oxygen; Ground water』

1. Introduction
2. Site descriptions
 2.1. Lizzie, North Carolina
 2.2. Portage County, Wisconsin
 2.3. Eastern San Joaquin Valley, California
 2.4. Sumter County, Georgia
3. Methods
4. Results and discussion
 4.1. Chemical transformations: implications for the fate of nitrate and pesticides
  4.1.1. Dissolved oxygen loss
  4.1.2. Nitrate reduction and excess N2 fraction
  4.1.3. Pesticide transformations and degradate fractions
   4.1.3.1. Atrazine
   4.1.3.2. Metolachlor and alachlor
 4.2. Trends in nitrate and pesticide concentrations
  4.2.1. Nitrate
  4.2.2. Atrazine, metolachlor and alachlor
5. Conclusions
Acknowledgements
References


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