Seasonal variations of total phosphorus in marsh soils from open and closed wetlands.

The Fulaowenpao and Erbaifangzi wetlands were chosen as typical sites in which to study characteristics of the seasona1 dynamics of total phosphorus (TP) in marsh soils from closed and open wetlands and to discuss the relationship between TP and other physical and chemical properties.TP content in the 0-100 cm depth of Fulaowenpao wetland soil ranged from 48.77 to 377.19 mg/kg,and in the Erbaifangzi wetland,from 45.65 to 574.17 mg/kg.On a seasonal basis,soil TP content in the two wetlands decreased first and then increased.From December 2008 to May 2009,soil TP content remained high,then decreased slowly from May to August.It remained very low during September and October,and finally gradually increased between October and December.Soil TP was mainly distributed in the 0-40 cm top soils in both wetlands,with a low content that was little different below.Soil TP content of the two wetlands did not reach a level that caused eco-toxic effects.There was an obvious positive correlation between plant TP and soil TP.However,the vegetation of Fulaowenpao wetland was restricted by nitrogen and phosphorus while there was limitation to Erbaifangzi vegetation only from nitrogen.There were remarkable positive correlations between soil TP and total nitrogen,organic matter and soil clay,and but no significant correlation between soil TP and soil C/N in the two wetlands.pH negatively correlated with soil TP in Erbaifangzi wetland,but not in Fulaowenpao wetland.