The Distribution Characteristics And Transformation Mechanism Of Phosphorus Research On Water/Sediments Wet-Dry Alternation In Water Level Fluctuating Zone Of Three Gorges Reservoir Area

The water level fluctuating zone in Three Gorges Reservoir Area (TGRA) is considered to be the most fragile ecological zones along the Yangtze River belt, different from the any other existing fluctuating zone or artificial wetlands. Based on Phosphorus Research of TGRA and opportunity when water level reaches 172.5m for the very first time in 2008, this paper studies 13 newly typical fluctuating zones according to anti-seasonal wet-dry alternation. Furthermore, combined with entire cycle of "storing the clean and dredging the muddy", this research shows existing forms and distribution features of endogenesis phosphorous in the upper layer of soil /sediments of the first wet-dry alternation. This reveals source-sink law of phosphorous in water soil/sediment, complemented with mechanism of adsorption, release, transformation and accumulation, which accumulates reference data for continual research on phosphorous transformation and transfer and endogenesis phosphorous control during the gradual formation of TGRA eco-system. Finally, this article provides reference scientific basis for pollution control of eutrophication in TGRA. The results showed that:①The total phosphorus (TP) in overlying water in TGRA presents a climbing trend following as: November<May<August. Also, the higher the water level is, the fluctuation of TP in lower and upper reaches is smaller. During exposed period, TP in overlying water shows a declining trend from upper reaches (Tanlao to Wanzhou section) to lower reaches (Yunyang to Zigui section), as does the TP fluctuation. Therefore, anti-seasonal wet-dry alternation has little impact on TP in overlying water of TGRA during the initial phase of reservoir formation.②In exposed period, TP in sediments in TGRA presents the following patterns: TP (716.40mg/kg) sediment in May > TP (658.65mg/kg) sediment in August and TP in submerged sediment > TP in exposed sediment. It indicates the upper layer of exposed sediments were eroded because of abundant rainfall and water and sand discharge in summer, which presents anti-seasonal wet-dry alternation cycle is conductive to releasing endogenesis phosphorous. Compared with soils (TP 1006.26mg/kg), this reduces TP potential release risk on the next submerging and has a promoting effect on controlling endogenesis phosphorous and preventing and curing eutrophication.③Anti-seasonal wet-dry alternation is helpful to discharging relatively stable occlude phosphorus (O-P) and calcium bounded phosphorus (Ca-P) and promotes the accumulation of active phosphorus (Ac-P) and organic phosphorus (Or-P) in sediments which is close to Ac-P, Or-P in soils respectively. It increases the potential release risk in sediments on second submerging.④During 2008 fall, the first submerging, soils in TGRA presents a dominant release trend, whereas till November, this trend switches to absorbing, revealing soils transformed from source to sink in the initial phase.⑤The max adsorption quantity of phosphorus (Qm) in sediments, sediments with light fraction organic matter removal and sediments minerals all drop gradually with the removing of organic matter. Besides Qm (338.81mg/kg) in sediments minerals and soils minerals during wet-dry alternation stay in the same level, suggesting organic matter particularly light fraction organic matter controls the phosphorus release in the upper layer of sediments. After removing light fraction organic matter, Qm in submerged sediments, exposed sediments and soils all present a decreasing mode, especially obvious in sediments, which indicates the phosphorus stabilizing in upper layer in sediments were more affected by light fraction organic matter than that in soils. Readily desorbed phosphorus (RDP) in the same soils sample increases with the removal of light fraction organic matter, signifying light fraction organic matter removal stimulates the release of phosphorous.⑥Lab simulation experiment reveals that the wet-dry cycle can accelerate the phosphorus release on second submerging due to the accumulation of Or-P and Ac-P, additionally, release in soils are more in sediments.