Distribution And Influence Between Phosphorous And Organic Matter In Soil/sediment Of Fluctuating Zone In Three Gorges Reservior Area

The fluctuating zone in Three Gorges Reservior Area(TGRA) is a special wetland region with anti-seasonal water level which is the higheset in winter and lowest in summer. This fluctuating zone is taken as the most ecologically vulnerable zone along the Yangtze river.Based on characteristics of fluctuating zone in TGRA and current studies on phosphorous migration and transformation in water-sediment/soil interface at home and abroad,analysis has been done on existing forms and distribution characteristics of phosphorous and organic content in water-sediment/soil interface.All the analysis are based on changing features in the wet-dry cycle of soil/sediment in newly typical fluctuating zone.Combined with lab simulation experiment,source-sink alternation law of phosphorous in water-sediment/soil interface,release law of phosphorous and organic matter in the wet-dry cycle and the contribution of organic matter to the phosphorous migration and transformation in water-sediment/soil interface have been revealed.The results show:1) In the initial phase of anti-seasonal regulation mode and wet-dry cycle in fluctuating zone in TGRA,internal phosphorous in soil/sediment has little impact on the overlying water and the water quality is within the standard.2) It is easier for phosphorous to migrate in submerged sediment than in exposed soil.Compared to sediment,phosphorous release's potential risk in higher in soil.Moreover,the phosphorous content in soil is more,the potential risk of phosphorous migrating and transforming to the overlying water is higher.Both wet-dry cycle and continous submerging is good to phosphorous'adsorption.3) The original use of fluctuating zone has more impact on the organic matter content in sediment in the beginning operation of TGRA.Organic matter release in soil has higher risk than that in sediment.Organic phosphorous release is the main way when TGRA is submerged for the first time.Organic phosphorous in soil also has higher risk than that in sediment.The study shows that both wet-dry cycle and coutinous submerging is apt to accumulation of organic matter and organic phosphorous.Moreover,source to sink alternation happens in the intial phase ,which does not alter the distribution of both organic matter and organic phosphorous.4) Distribution law of phosphorous forms in soil/sediment in fluctuating zone in TGRA presents in the following way: Ca-P>Organic-P>O-P>Al-P>Ex-P.Active phosphorous is released in the beginning of submerging and then the release turns into adsorption with the longer time of being submerged.Organic phosphorous content gradually diminishes with the longer time of being submerged.O-P and Ca-P contents are always stable.Compared to sediment,phosphorous release potential risk is higher.5) The results of simulation experiment show:The second submerging after wet-dry cycle is easier to release phosphorous in soil/sediment than that in continous submerging.Organic matter release has large impact on organic phosphorous release.Soil is easier to release organic matter than that in sediment whereas organic phosphorous in soil is more difficult to release than in sediment.Organic matter and organic phosphorous show a strong changing similarity in both wet-dry cycle and continous submerging.All the results above present the same law as in on-site monitoring experiment.