Study On Phosphorus Retention Capacities And The Impact Factors By Emergent Plants In Yeyahu Wetland

Phosphorus is a limited nutrient in most waters; therefore phosphorus controlling is the key to the prevention of eutrophication. Wetlands system has a variety of phosphorus interception mechanisms, including the vegetation mechanism, which is becoming a research hot spot. Located upstream of Guanting reservoir, the Yeyahu wetland plays important roles in nutrient retention and reservoir water eutrophication prevention. In this article the Yeyahu wetland was studied as the carrier, the phosphorus exchange quantities between emergent plants and environment were analyzed, then total seasonal phosphorus storage in emergent plants in this area were determined. At the same time, artificial simulation wetlands were built to study the phosphorus circulation and accumulation under controlled conditions, and then the influence of each factor to phosphorus absorption and release were investigated. Through the tracking field experiments and artificial simulation experiments, the following results were concluded:Phosphorus contents in vegetations distributed from the bank to the river center show gradually increasing; phosphorus contents in both water and plants presents a descend trend along the river; In the various forms of water phosphorus, particle phosphorus shows significant relevance with plants phosphorus, because of that particles phosphorus is easy to be captured and absorbed by vegetation system. The accumulation capacities of4plants in unit area are different. Zizania aquatica. and Typha latifolia. have higher accumulation capacity,followed by Scirpus planiculmis, then the Phragmites australis. lowest. Total phosphorus accumulation sum of4plants in the study area ranks as Typha latifolia.> Zizania aquatica>> Phragmites australis.>> Scirpus planiculmis.. In2010, Total phosphorus accumulation in the4plants comes to a maximum value of2210.8kg in summer, and a minimum value of1263.5kg in winter; in2011the maximum value of2595.1kg in summer and minimum value of375.7kg in winter. In general,the phosphorus accumulates from the environment to plants during winter to summer period, and release from plants to environment during summer to winter period. The decomposition dynamics of plant litter are affected by following factors:(1) water flooded condition can obviously accelerate the reduction of biomass, but at the same time it improves the growth of litter phosphorus content.(2) Summer is season with strongest decomposition intensity, followed by spring and autumn, and winter slowest; but to phosphorus, its content goes up rapidly during spring and summer, which are seasons with high litter decomposition velocity, and goes down slowly during autumn and winter.(3) Plants like Zizania aquatica. and Typha latifolia. with higher initial litter phosphorus contents show the trend of phosphorus release during the study period, while plants like Scirpus planiculmi. and Phragmites australis. with lower initial litter phosphorus contents show the trend of phosphorus enrichment during the study period.To all the simulation wetlands experimental groups, net phosphorus supply raised and then declined, the net soil phosphorus allocation present a dynamic of progressively reduce first and then gradually enlarge, Peak value of the net phosphorus supply and minimum value of the net soil phosphorus allocation both appeared in T3to T5. The utilization rates of phosphorus in nutrient solution of different plants were different, Zizania aquatica. and Typha latifolia. are higher, at about92%, while Scirpus planiculmi. and Phragmites australis. are lower at about85%; in normal phosphorus supply conditions (0.05g/d), net phosphours accumulation in plants Zizania aquatica. and Typha latifolia. are about lg, almost two times of Scirpus planiculmi. and Phragmites australis..; when phosphorus supply level is lower, phosphorus is mainly used for plant growth, while accumulation in soil can be neglected; when the phosphorus level rising, accumulation in plants and soil obviously raised; when the phosphorus level raised to10times, plant accumulation ability goes up rapidly, but the soil accumulation ability tend to decline.