Variability of Aquatic Chemistry in Central Guizhou Karst Region,China

It is necessary to understand the aquatic chemical characteristics of natural surfacefresh water for water quality assessment. The chemical data from different kinds of water inthe central Guizhou karst area showed that spring water from carbonate rock cracks (crack-water) is of neutrality or meta-alkalinity and [C] Ca Ⅱ type. The amounts of all ions and theconcentrations of HCO3 and Ca2+ were higher in the autumn than in the spring. the crack-water was influenced by the infiltration of surface water in the process of erosion and/or transportation with decreasing HCO3- and increasing PH, SO, Cl, K+ and Na+ during runningin a certain distance on the land suffice. In particular, the chemical compeitions of the watersat Tianxingqiao (upper-stream), Shuiliandong (mid-waterfall) and Luoshuitan (down-pool)near the Huangguoshu Waterfall were much different from those of the crack-water. The concentrations of , Na+, Fe3+ and NO3- varied closely with seasons. The CaCO3 depositedviolently with CO2 release in the spring. In Lake Hongfeng the HCO3- /So- equivalent ratioswere only 2. 1 - 2. 4, but Ca2 + /Md+ up tO 2. 4 - 4. 2. The CI- concentration increased by afactor Of 1 and Na+ by order of magnitude relative to the spring water. These indicated the in-crease in artificial pollutant discharge in the Lake Hongfeng watershed. In addition, porewater in the soils coveing carbonate rocks belongs to strongly mineralized water. The obvious differences in water quality were controlled by carbonate despition, sulphate mineralization and nitrogen fixation as well as ammonification. It is indicated that the chemical compeitions in thewaters from the karst region were unstable and changeable.