黄河水质地球化学

在对1958—2000年期间黄河水系100个站点水质监测资料进行统计分析的基础上,研究了黄河主要离子的地球化学。结果表明,黄河流域各区河水总溶解性固体(TDS)含量的差异达2~3个数量级,TDS的总平均值为452mg/L,是全球河流均值的4倍。Na+、K+、SO42-和Cl-的含量是世界河流均值的10~20倍。相比之下,河水TDS含量的季节差异却不大,远不及与此呈反比关系的流量的季节差异。黄河洪水期的水量通常是枯水期的4~5倍,但枯水期河水的TDS通常只是洪水期的2倍,完全不同于世界其他大河。黄河的离子化学主要受沉积岩(尤其是富含碳酸盐矿物的黄土)化学风化作用和在干旱气候影响下水中溶解盐的蒸发浓缩和结晶作用的控制。近半个世纪来黄河河道径流量有显著减少的趋势,这与新修建的众多水库的蓄水有关,与此相适应,近半个世纪来黄河水质表现出明显的盐渍化过程,这一过程主要由含盐量高的农田灌溉回水所引起。

Geochemistry of water quality of the Yellow River basin

The geochemistry of major dissolved ions and silica in the Yellow River water was studied from historical records at 100 stations in the drainage basin for the period of 1958—2000. This river system with an area of 750 000 km~2 presents an exceptional temporal and spatial water chemistry variability compared to other major world rivers. The total dissolved solid (TDS) concentration in the Yellow River varied over 2～3 orders of magnitude throughout the basin with a median TDS concentration of 452 mg/L, which is about 4 times the world spatial median value. In particular, the concentrations of Na~+, K~+, SO~2-4 and Cl~- in the Yellow River were 10～20 times higher than in other major world rivers. The TDS at a given station is seasonally variable and inversely related to river runoff with a variation factor less than 2.0, despite the water being diluted fourfold to fivefold in the summer flood season. The chemical weathering of sedimentary rocks, evaporation, and fractional crystallization were found to be the major water process controlling the major ion chemistry of the Yellow River, owing to the abundance of loess and clastic rocks under arid and semiarid climates. A persistently increasing annual trend has been observed in the concentrations of TDS and all the salts except for HCO~-3 at all main-channel stations, except for the uppermost Lanzhou city. The rate of increase in the TDS concentration was the highest in the middle reaches. The increasing trend coincides with a significant decrease in water discharge at most of the main-channel stations for the last 40 years. This is attributed to increasing regulation of reservoirs and intensive water withdrawal for irrigation and diversions, as well as several other anthropogenic processes.