| Abstrakt: |
Sampling and analyses in Vietnam’s Phong Nha–Kẻ Bàng/Tu Lan Karst Areas and the Hin Nam No Karst area of Laos document hydrogeology, geomorphology, geochemistry, and petrology/mineralogy in one of the world’s largest protected karst area. Hydrogeologic mapping recorded spectacular caves with large speleothems and huge volumes of water flow. A total of ten rock and 34 water samples were collected. Water samples from rivers, sinking streams, caves, and springs had pH ranging from 6.15 to 8.48, specific conductance (SC) from 65 to 421 μS/cm, and total dissolved solids (TDS) from 32 to 209 mg per liter (mg/L). Temperature varied from 17.6 to 28.1 °C, oxidation reduction potential (ORP), measured in Vietnam only, ranged from 69 to 194. Alkalinity ranged from 34 to 230 mg/L (as CaCO3) and total hardness from 28 to 248 mg/L CaCO3. Calcium, magnesium, and bicarbonate dominated water chemistry, with low chloride, nitrate, and sulfate. All samples except one had trace metals below USEPA drinking water standards, though all samples from Vietnam had zinc and nitrate above USEPA Aquatic Life Criteria, and one exceeded the phosphate standard. Isotopic data indicate a meteoric origin of all waters, though with distinct isotopic signatures in Laos and Vietnam. The relatively pure limestone in these areas combined with a well-developed secondary porosity and a tropical climate, has developed the spectacular karst landscapes of Phong Nha-Kẻ Bàng and Tulan in Vietnam and Hin Nam No in Laos. Allogenic water from non-carbonate rocks flowing into these karst areas has formed some of the largest caves by volume in the world. This study will guide future research and conservation efforts of this unique and spectacular karst region. [ABSTRACT FROM AUTHOR] |
