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Chang-song ZHOU, Sheng-zhang ZOU, Hao XIE, Dan-ni ZHU, Hong-feng CHEN, Jian-guo YU. The Effect of Testing Lag on Chemical Indexes of Karst Water[J]. Rock and Mineral Analysis, 2019, 38(1): 92-101. DOI: 10.15898/j.cnki.11-2131/td.201711040175
Citation: Chang-song ZHOU, Sheng-zhang ZOU, Hao XIE, Dan-ni ZHU, Hong-feng CHEN, Jian-guo YU. The Effect of Testing Lag on Chemical Indexes of Karst Water[J]. Rock and Mineral Analysis, 2019, 38(1): 92-101. DOI: 10.15898/j.cnki.11-2131/td.201711040175
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The Effect of Testing Lag on Chemical Indexes of Karst Water

    Abstract
  • BACKGROUNDSample testing is important for studying hydrogeology, engineering geology and environmental geology in Karst areas. The inconvenience of transportation, the difficulty of sample shipping and the delayed sample analyses by testing laboratory in Karst areas lead to the lag of sample testing in varying degrees. However, existing research cannot effectively explain the impact of test lag on the properties of Karst water samples.OBJECTIVESTo make progress on this scientific problem, a typical Karst spring in Xuanwei City, Yunnan Province was selected as research object.METHODSTen indicators of K+, Na+, Ca2+, Mg2+, Cl-, SO42-, HCO3-, pH, NO3- and CO2(fs) of spring water samples were determined by Ion Chromatography and Atomic Emission Spectrometry. These samples were collected at the same time and the same place according to the time series of 1d, 3d, 5d, 7d, 9d, 11d, 13d, 15d, 17d, 35d, 50d, 75d. The effect of test lag on the properties of Karst water samples was discussed.RESULTSThe results show that test lag had certain influence on analytical results. During 75 days Karst water sample placement, the uncertainty values of type A standard of the indicators were 0.02-1.83, and uncertainty values of HCO3- and Ca2+ were significantly higher than other indicators. Shapiro-Wilk normality test results showed that the pH, K+, Mg2+, Cl-, and NO3- follow normal distribution. As time elapsed, the relative deviation ranged from 0% to 57.38%. The relative deviation of pH, Ca2+, SO42- and NO3- was within the allowable error range. Overall, the mean content and coefficient of variation of ten indicators showed significant negative correlation (Spearman correlation coefficient is -0.709, P < 0.05), and the variation coefficient decreased as follows:Na+, K+, CO2(fs), Mg2+, Cl-, SO42-, Ca2+, HCO3-, pH, NO3-. These results revealed that the influence of test lag on different indicators was different, especially on the indicators with low mass fraction. The analysis of indicators changing over time showed that the change process of water quality of the water sample could be divided into five stages:stationary stage (0-3 day), preliminary change stage (3-5 day), mixed change stage (5-17 day), potential impact stage of bacteria (17-35 day) and relative equilibrium stage (35-75 day). Among them, bacterial action and carbonic acid balance were the two most important mechanisms during Karst water sample placement.CONCLUSIONSThe research results can provide technical support for improving the testing precision of water samples in Karst regions.

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