| The acid neutralizing capacity （ANC） of South Africa＇s freshwater ecosystems |
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| 作者姓名： | Stephanie de Villiers |
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| 作者单位： | Geology Department, University of Stellenbosch, Stellenbosch, South Africa |
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| 摘 要： | Acidification is considered the most important one of the primary chemical stress factors that impact on freshwater ecosystems. In unpolluted freshwater systems, the primary controls on the degree of acidification are factors such as the geological substrate of the catchment area, the presence of organic acids secreted by vegetation in the river system, and equilibrium exchange of carbon dioxide with the atmosphere. Anthropogenic factors that can impact on the degree of acidification of freshwater systems include agricultural, mining and industrial activities, either through direct runoff into river systems or through deposition of atmospheric pollutants from these sources. The capacity factors alkalinity and acidity, which represent the acid- and base-neutralizing capacity （ANC and BCN） of an aqueous system, have been used as more reliable measures of the acidic character of freshwater systems than pH. Unlike pH, ANC and BNC are not affected by parameters such as temperature and pressure. Therefore, ANC has been employed as a predictor of biological status in critical load assessments. Freshwater systems with ANC＇s eq/L isμeq/L are considered sensitive to acidification, ANC=0 μbelow 150 commonly used as the predictor for fish species such as trout in lakes, and an eq/L as more realistic for streams. Acid-neutralizing capacity μANC value of 40 （ANC） can be determined by titration with a strong acid to a preselected equivalence point. Alternatively, it can be calculated as the difference between base cations （BC]） and strong acid anions （SAA]）： ANC=BC]- SAA]=Ca^2＋]＋Mg^2＋]＋Na^＋]＋K^＋]-SO4^2-]-NO3^-]-Cl^-] To date, there has been no attempt to establish the ANC of South Africa＇s freshwater ecosystems or variability therein, despite the fact that long-term water quality monitoring data exist for all the parameters needed to calculate it according to the above equations. As a result, the relationship between the acid neutralizing capacity of freshwater ecosystems in South Africa and biodiversity factors, such as fish status, is unknown. Results of the first comprehensive （country-wide scale） evaluation of the acid neutralizing capacity of river systems in South Africa will be presented. Long-term monitoring data obtained from the Department of Water Affairs and Forestry （DWAF） from most of South Africa＇s river systems were used to establish geographic and temporal variabilities in ANC. The results show that the Berg and Breede River systems are most susceptible to acidification, and that geological substrate appears to explain most of the geographic variabilities observed.
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| 关 键 词： | 淡水 生态系统 河流 酸性压制 ANC |
The isotopic evidence of gas source of the cold mineral springs with high pCO2 in Wudalianchi |
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| Stephanie de Villiers.The isotopic evidence of gas source of the cold mineral springs with high pCO2 in Wudalianchi[J].Chinese Journal of Geochemistry,2006,25(B08):146-146. |
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| Abstract: | |
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| Keywords: | acid neutralizing capacity freshwater river ecosystem |
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