The chemical, physical and biotic characteristics of sediment are important determinants in restoration of submerged macrophytes in eutrophic lakes. The chemical and physical properites of sediment in Yuehu Lake, a small eutrophic shallow lake, were investigated. The effects of point source pollution, sampling seasons and sediment depth on the contents of nutrient and organic carbon and redox condition of sediment were determined. Whilst the relationships between sediment characteristics and submerged macrophytes were analyzed. In addition, laboratory experiments were conducted to study the effects of light intensity and sediment anoxia on gorwth and physiology of submerged macrophytes. Finally, the impact of sediment drying and phytoremediation, as technologies of sediment amendation, on sediment characteristics and submerged macrophytes were studied. The main results were summarized as below:
1. The concerntrations of TN, TP and organic carbon in sediment of Yuehu Lake showed significant pollutants accumulated in surficial sediment. The concerntrations of TN and TP in sediment did not varied with season. However, the redox potension (Eh) of sediment in different sampling sites were different and were varied with season, the Eh values were low in the sediment near the sewage outlet, and reached the minimums in June.
2. The concentrations of N and P in submerged macrophyte were significantly affected by those nutrient and organic carbon in sediment. Compared with clay, the sediment from Yuehu Lake resulted in increased concentrations of chlorophyll, soluble carbonhydrate and soluble protein in submerged macrophytes growing on it, and antioxidative system of plants responsed differently to different sediment types.
3. Sucrose addition into sediment could be used as a method to simulate sediment anoxia within a period time (one month).
4. The biomass and germination of submerged macrophytes were significantly inhibited by sediment anoxia. Medium light intensity might alleviate this inhibition, but light had little effect when sediment anoxia was severe. Howerver, low level of sediment anoixa (0.1% sucrose addition) had favorable effects on root growth and metabolism of submerged macrophytes. Sediment anoxia and the porewater sulfide exposure were interpreted as important factors involving in the failure of macrophyte restorations in eutrophic lakes.
5. Sediment drying could inhibite the releases of ammonia and sulfide from sediment and improve the redox potentials of sediment within a period of time, thus benified the growth of submerged macrophytes. Drying benefited phytoremediation of sediment. Nutrient accumulations in plant were different in different plant species, season and plant organ, and the concentration of nutrient in leaf was higher than those in stem and root generally.
In conclusion, the inner loadings of nutrient and organic pollution are excessive in Yuehu Lake, probably hamper the restoration of submerged macrophytes. Sediment anoixa is one of important mechanisms by which sediment affect the macrophyte restoration.Sediment drying and phytoremedation can be used as effective technologies for in-situ remediation of polluted sediment and dredged sediment.