Chapter 8 HYDROCHEMICAL AND BACTERIOLOGICAL STUDIES

Résumé -Abstract - Zusammenfassung -:

HYDROCHEMISTRY MAIN CHEMICAL FEATURES

* Calcium carbonate : Most of the waters show a classical karstic figure.
* Mg : Ca/Mg range from 4 to 7 in most of the samples ; this means that limestones are much more frequent than dolomites ( we sampled few waters coming from pure dolomite areas).
* Na - K - Cl : Very low contents (less than 10 % of total dissolved salts in  90 % of the samples, as usual in karstic areas, which are far from the sea. Similar concentrations of Na and K were found, which is quite scarce for a sedimentary area. A possible explanation is human pollution by fertilizers.
* CO2 and pH : All the waters contain very little dissolved CO2 and the pH is quite high (7.5 to 8.5), because the air itself in the big caves does not contain much CO2 (0.02 to 0.04 %). The caves are windy and the sampling was made in winter, when biological activity is very low.
* NO3 : The concentrations are relatively high for karstic areas (2 to 20 ppm), but lie below the maximum WHO standard for drinkable waters (45 ppm) and below the levels observed in European cultivated areas (20 to 80 ppm). Explanation : there is a pollution by fertilizers but it is reduced by their very efficient use.The main rivers are less polluted than the karstic springs.
* SO4 : The water coming from the coal mines, which are rich in sulphur, has a very high content of SO4 (200 to 900 ppm), which is related with iron. In the water originating from the karst, SO4 is not the dominant anion (between 5 and 15 % of anions in 75 % of the samples). This is usual in karstic areas, but the concentrations are far above what we expected. 50 % of the samples contained more than 20 ppm. Some possible explanations are: very high content of pyrite in the upper Permian series, which constitutes the upper basin of some rivers, quite pyritous limestones of some carbonate series (Trias), pollution by atmospheric SO2 linked to coal combustion.
* Mn-Fe : Very high concentration in the waters coming from the upper Permian, directly linked to the SO4 content ; that is a consequence of the dissolution of pyrite contained in the Permian clastic rocks near the coal levels ; the very low pH level (down to 2.8 !) explains the large amounts measured (up to 164 ppm), which are exceptional in natural waters. In karstic waters, the concentrations are higher than those  observed in Europe ; explanation : detritic outcrops in most river basins.
 The water coming from the coal mines is very acidic (pH ranges from 2.8 to 3.2). When it enters the karstic area, the pH increases very fast as a result of  dissolution of the bedrock and its mixing with karstic waters. The figure 95 shows that within a few meters pH is near to equilibrium.
 The chemical figure of the waters coming from Cambrian and Permian aquifers can be distinguished. The former contains very little SO4 and Mg. The latter is richer in SO4, Fe, Mn and Mg, which relates to detritic layers between the limestones.
 As far as calcium carbonate is concerned, all the rivers were oversaturated at the time of the expedition. It was the dry season and they  contained very little CO2. It should be different in summer, which is probably the time when most of the erosion takes place. We evaluated the specific ablation (from the discharge and the alcaline content of the water) to 40 mm/1000 years.

BACTERIOLOGICAL QUALITY OF KARSTIC WATERS

We took water samples in the big underground rivers explored during the expedition. These  represent the main water resources of these regions. Sampling was made all along the flow, to see how bacteriological pollution varied. We also tried to find drinkable waters in the little springs and the rimstone pools.
 In order to find out if the water was drinkable, we used a safe biological mark : coliform bacteria.Their presence is a proof of faecal contamination, which is the main cause of many diseases (dysentery, polio, hepatitis, cholera, typhus,...). A small water sample (1 ml) is filtrated through a porous film (0.5 micron). The coliforms stay on the filter and are breaded (35°C) in presence of a nutritious environment (TERGITOL TTC). Each bacteria of the sample generates a colony consisting of millions of bacteria and these colonies can be eye-counted. The whole device weighs only a pound.
 Two thirds of the samples show high levels of contamination varying between 1 to 22 coliform in 1 ml. These waters are not drinkable (reference : the WHO standard for drinkable water is a maximum of 3 coliform in a 100 ml sample). Pollution occurs in the big karstic rivers (this is quite common all over the world) and also in the small springs. In the main rivers, the high level of biological pollution does not decrease while the waters flow underground.
 This  method is convenient for speleological teams, who cannot carry heavy devices. The accuracy is limited by the size of the sample (1 ml) and the temperature variations during incubation. For these reasons, we intend to use bigger samples (10 ml) and a temperature regulator in future experiments. With such improvements the device should weigh 1.5 kg.
 The high contamination levels are related to the very high population density (300 hab/km2), which is uncommon for karstic areas. Despite the fact that a large part of the faecal materials is used on fields, the bacteriological input in the rivers extends the self-purification ability of the natural waters. During the underground flow, the waters are not purified for the following reasons: the stay time is too short (some hours or days) ; the waters are not exposed to solar UV ; big bats  colonies bring more organic and faecal matters.
 In China, because of the poor water quality, people mostly drink boiled water. Thus, it is possible to find drinkable hot water in almost every place and the members of the speleological team did not suffer the dysenteries so frequent during expeditions in tropical regions.

Keywords: karst, hydrochemistry, bacteriology, pollution, water quality, nitrate, sulfur, coal, China.