Studies On Application And Effect Of Sediment Restoration By Submerged Plants In Wetlands

In recent years, wetland eutrophication is continuous, various types of wetland sustained by different levels of pollution water. Sewage containing a lot of nitrogen phosphorus nutrients, as well as heavy metals discharges into wetland constantly, not only causing water quality deterioration, but also makes the sediment polluted and becomes the repository of pollutants by deposition. At present, the sediment control methods mainly are the physical chemistry repair and bioremediation restoration. They have certain effects, but when it comes to the waters which have a relatively complex ecological environment and large area open wetland waters, there is still a lot space of research and exploring. Though the submerged plant has been widely applied in the water ecological restoration, but researchers focus on the overlying water repair by submerged plants. The research on application and effect of sediment repair by submerged plants.In this paper, the submerged plant properties of sediment repair and pollutants cycle in water-sediment interface of different wetland were system researched, the experimental method was optimized. The similarities and differences between the submerged plant repair of landscape and aquaculture water were analyzed and compared. The deposition and release of pollutants during the submerged plant repair process were defined, discusses the interrelation between sediment pollutants releasing and water quality. It provided the theory basis and the application foundation for wetland eco-restoration projects and researches, and also provided researchers new access and ideas for the control technologies of sediment pollution releasing by submerged plants, water pollutants transport and transformation, researches on inner beneficial circulation of water ecological environment. The main conclusions are as follows:（1） The comparison experiments of sample-detection methods were did. The test of sediment organic matter used potassium dichromate oxidation; digestion furnace method was more secure, efficient and easy operation than oil bath heating. Phosphorus grading extraction process combined with its experimental features and our needs, synthesized the advantages of various methods in recent years. A developed extraction method is as follows: LP>RSP>Ca-P>Al-P>Fe-P>OP>Org-P, the experimental results verified the feasibility and effectiveness of the method.（2） The nitrogen and phosphorus absorption kinetics of 9 types submerged plants （Potamogeton crispus, Potamogeton maackianus, Elodea nuttallii, Potamogeton lucens, Myriophyllum spicatum, Ceratophyllum demersum, Hydrilla verticillata, Vallisneria spiralis, Potamogeton malaianus） were studied. The results showed that except the Ceratophyllum demersum, other eight submerged plants play a significant role on nitrogen and phosphorus release and control; they all have certain repair effects on two types of wetland water sediment （landscape and aquaculture water）. The results of the study show the amount of nitrogen and phosphorus release decreased with the increase of submerged plants biomass. The repair and control effect of nitrogen and phosphorus in sediment by Elodea nuttallii, Vallisneria spiralis and Potamogeton maackianus were better.（3） The repair experiments of landscape and aquaculture water were performed severally using the combinations of different submerged plants. The results demonstrate that with the repair process of submerged plants deepening, in four divisions of landscape water, sediment organic matter content decreased obviously. From the beginning of 1.73% descend to 0.74%. In 0-30cm depth of sediment, organic matter content of each layer dropped in the repair process, the repairing effect of submerged plant is obvious. Organic matter content in aquaculture water sediment was not significantly less.After repair of submerged plants, sediment TN contents of landscape water were reduced to the 78.7%, 78.9%, 79.2%, 81.9% and 83.9% of the background values. The sediment TN contents were slightly lower in winter, maintained at about 1.2 g·kg-1 before and after the experiment.Sediment TP contents landscape water were significantly reduced at the end of repair process. The organophosphorus （Org-P） was the highest proportion of 40% at the beginning. The soluble phosphate proportion （LP = 46%） was the highest one in the end. The TP, Org-P, Fe-P contents of aquaculture water increased with the repair process, the rise ratio is about 30%,others are decreasing.（4） There were coordinated variations between Sediment indexes. Among 10 monitoring indexes of landscape water, There were 9 pairs significant positive correlations, the maximum was the Org-P and OP (r_xy=0.696**), the minimum was TP and LP (r_xy=0.488**). There was a certain degree of correlation between some two of 7 sediment indexes of aquaculture water. RSP was correlative with the LP and OM respectively (r_xy=0.965**, r_xy=0.782**), Fe-P was correlative with the Org-P and TP respectively (r_xy=0.905**, r_xy=0.893**).（5） An organic index evaluation of the experiment water was made. The results was that the landscape water organic pollution （levelⅡ^Ⅳ） was more serious than aquaculture water （levelⅠ^Ⅱ）, but all evaluation indexes were decreased with the repair process, landscape water rose to levelⅡ, water aquaculture rose to levelⅠ.（6） Statistical analysis results by SPSS 17.0 showed that the relationship between overlying water and sediment was closely. Among the 110 groups of correlations of 11 kinds of water quality indexes and 10 groups of sediment indicators of landscape water, 35 pairs were correlated, account for 1/3. With regard to aquaculture water, 36 correlations of 6 water quality indexes and 6 sediment indicators were calculated, 3 pairs were correlative. The correlations in different period of the TP in water and sediment of were analyzed, and found that the temperature and season influenced the pollutants cycle of aquaculture water considerably.（7） Sediment heavy metal content were dynamic monitored during the repair process, using geoaccumulation index and potential ecological risk methods to evaluate the heavy metal pollution degree of sediment, two evaluation results show that the heavy metal pollution level of landscape water was moderate pollution, with the repair process, was gradually improving to slight pollution or no pollution. The heavy metal contents of aquaculture water were far below the standard of farmland soil environmental standards.