|
|||||
|
|
Distribution, source and evolution of nitrate in a glacial till of southern Alberta, Canada |
|
| Authors: | MJ Hendry RGL McCready WD Gould |
| Institution: | 1 Alberta Department of Agriculture, Agriculture Centre, Lethbridge, Alta. T1J 4C7, Canada 2 Biology Department, Dalhousie University, Halifax, N.S. B3J 4H1, Canada 3 Agriculture Canada Research Station, Lethbridge, Alta. T1J 4B1, Canada |
| Abstract: | This paper addresses the distribution, origin and controls upon nitrate in a 30-km2 area of the Interior Great Plains Region of southern Alberta, Canada. High concentrations of nitrate (> 100 mg l?1 NO?3-N) occurred in several isolated enclaves below the water table in brown weathered till. Nitrate concentrations of over 300 mg l?1-N were encountered in groundwater samples collected from these enclaves. Low nitrate concentrations (< 1.1 mg l?1 NO?3-N) were also encountered in the weathered till upgradient and downgradient of the nitrate enclaves. Groundwater samples collected from the underlying grey nonweathered till and bedrock had NO?3-N concentrations of < 1.1 mg l?1. Through the application of geochemical (NO?3-N and NH+4-N) studies, environmental isotope studies (tritium), microbial analyses (nitrifiers) and laboratory experiments, it was shown that the high nitrates found in the weathered till are the result of the oxidation of ammonium present within the tills. It is postulated that this oxidation occurred during the Holocene epoch when water tables were much lower than present-day levels (5–18 m, and 2 m below ground, respectively). Through the use of Eh measurements, the enumeration of denitrifying bacteria and laboratory experiments, the potential for denitrification was shown to exist below the present-day water table in the weathered till as well as in the nonweathered till and bedrock. Isotopic data showed that less denitrification may be occurring within the nitrate enclaves than in adjacent downgradient areas. |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ | |