Abstract:

To rationally develope, utilize and protect the water resources in lakes of lower reaches of the Yellow River, hydro-chemical composition of natural water in Dongping Lake, Daotunwa Lake, Mata Lake and Baiyun Lake was analyzed, hydro-chemical types and fundamental characteristics were determined and nutritional types of the water were also comprehensively evaluated. To determine the nutritional type standards of these four lakes, five indexes [chla (chlorophyll), TN, TN, CODmn and SD (transparency)] were selected as evaluation parameters. Compared with the eutrophic criteria of lakes in China and referd to the method that dividing the Tai Lake nutrient in percentage terms, individual grading and comprehensive grading methods were adopted. The results of water quality monitoring data showed that: the type of water of Dongping Lake and Baiyun Lake was CIINa, Mata Lake and Daotunwa Lake was CIIINa, and they were alkaline lakes. Organic oxygen consumption in Daotunwa Lake and Mata Lake was very high, with an average of 9.58 mg/L and 21.47 mg/L, respectively, which indicated water here had been polluted. Organic oxygen consumption in Dongping Lake and Baiyun Lake was low, with 5.06 mg/L and 4.02 mg/L on average, respectively. The N:P ratio in Dongping Lake and Baiyun Lake was 61 and 45, respectively. The higher N:P ratio demonstrated that nitrogen was fully supplied in these two lakes and growths of plants and algae were limited by phosphorus. The results of nutritional types of the water data showed that: Dongping Lake, Daotunwa Lake, Mata Lake and Baiyun Lake were in mesoeutrophic-eutrophic state, eutrophic state, high eutrophic state and mesotrophic state, respectively. On the whole, most of the lakes at the Lower Reaches of the Yellow River had been suffering from varying degrees of pollution, water quality is deteriorating in recent years, and nutritional types of water had reached the eutrophication level. However, water quality in Baiyun Lake remained stable in good condition, and needed to strengthen the protection.