Characteristics of and Influencing Factors of Hydrochemistry and Carbon/Nitrogen Variation in the Huangzhouhe River Basin, a World Natural Heritage Site

In karst areas, the characteristics of water chemistry and carbon and nitrogen are of great significance to basic research. The contents of Ca(2+), Mg(2+), K(+), Na(+), HCO(3)(−), SO(4)(2−), NO(3)(−), Cl(−), dissolved organic carbon (DOC), and total nitrogen (TN) in water samples from 18 rivers and 14 springs in the Huangzhouhe River Basin were determined. The results showed that the water chemistry type in the Huangzhouhe River Basin is HCO(3)-Ca-Mg. The chemical composition is mainly affected by dolomite weathering and also by ion exchange and other human activities. The river and spring DIC remain at the same level in the upper and middle reaches and decrease in the lower reaches. The NO(3)-N and TN of river water and TN of spring water increase in the middle reaches, while NO(3)-N of spring water decreases in the lower reaches. The DOC in the basin increases with the increase of SO(4)(2−) and Cl(−), mainly due to the human influence of agricultural and domestic sewage. In the basin, the NO(3)-N and TN in spring water are larger, and the DOC in river water is larger, mainly because there are more phytoplankton and human activities in the river water. The carbon and nitrogen in the Huangzhouhe River Basin are mainly HCO(3)(−) and NO(3)(−) ions. The evaluation of pH, Cl(−), NO(3)-N, SO(4)(2)(−), and TDS shows that the water quality is good and the ecological environment is good.