Influence Of Cadmium Input On The Nutritional Properties Of Eutrophic Lakes In Different Hydraulic Conditions

With the development of economic and the improvement of people's living standards, a large number of production wastewater and domestic sewage was discharged into the lake, causing eutrophication and heavy metal pollution in lakes and many other environmental problems. The environmental problem destroyed the ecological environment, affected people's health, survival and the socio-economic sustainable development.This paper studied the influence of cadmium (Cd) input on the nutritional properties of eutrophic lakes in different hydraulic conditions. Water and sediment of two different eutrophication degree lakes (Lake Donhu and Lake Nanhu) in Wuhan City were studied as tested overlying water and tested sediment in the reaction columns, and the Cd concentrations in overlying water were set 0mg/L, 5mg/L and 50mg/L three levels, expressed by Cd-0, Cd-5 and Cd-50, then the study was run in static and dynamic hydraulic conditons respectively. This paper discussed the relationships between Cd and nutrients in overlying water and total phosphorus, total nitrogen, urease activity, alkaline phosphatase activity in sediments. The main conclusions of this paper were listed below:1. After Cd was added into overlying water, Cd was adsorbed by sediments gradually, and Cd concentrations in the overlying water became low gradually. The Cd adsorption rates by sediment were different between Lake Donghu and Lake Nanhu, and the Cd adsorption rate by Lake Nanhu sediment in static condition was larger than that in dynamic conditon.2. Cd could inhibit the release of total phosphorus from sediment and the inhibition which was in relation to the hydraulic condition and the nutrient characteristics of lakes. In static hydraulic conditon, Cd in the Cd-5 and Cd-50 treatments of higher eutrophication degree Lake Nanhu inhibited the release of total phosphorus obviously. In dynamic hydraulic condition, Cd in the Cd-50 treatment of Lake Donghu inhibited the release of total phosphorus obviously, but did not in the Cd-5 treatment; Cd in the Cd-5 and Cd-50 treatments of Lake Nanhu could inhibit the release of total phosphorus, and the higher the Cd concentration, the more obvious inhibition.3. In static hydraulic condition, Cd in the Cd-5 and Cd-50 treatments of Lake Donghu and Lake Nanhu inhibited the release of soluble phosphate from sediments obviously. In dynamic hydraulic conditon, because of the factors caused by dynamic hydraulic conditon, the inhibition in the Cd-50 treatment was more obvious than that in the Cd-5 treatments.4. The effects of Cd to total nitrogen in the overlying water were not obviously in the treatments of Lake Donghu and Lake Nanhu. 5. In static hydraulic condition, the effects of Cd to ammonia-nitrogen concentrations in the treatments of Lake Donghu were not obviously. But to the higher eutrophication degree Lake Nanhu, Cd of Cd-5 and Cd-50 treatments could inhibited the release of ammonia-nitrogen. In dynamic hydraulic conditon, Cd in the Cd-50 treatments of Lake Donghu and Lake Nanhu promoted the release of ammonia-nitrogen in the later period of the test.6. In static hydraulic conditon, the changes of alkaline phosphatase activity in sediments of Lake Donghu and Lake Nanhu treatments were different in different phases. In dynamic hydraulic conditon, the changes of alkaline phosphatase activity in sediments of Lake Donghu treatments were complicated; the alkaline phosphatase activity of Cd-50 treatment in sediments of Lake Nanhu was inhibited obviously.7. The urease activity in sediments of Lake Donghu and Lake Nanhu treatments did not change obviously, and the inhibition of Cd to urease activity was not obviously.