Phosphorus release from acid sulfate wetland soils in response to pH and dissolved oxygen alteration

Phosphorus (P) release from wetland soils is an important process for its widespread ecological impacts. The availability of soil P is determined by the type of sediments and their complex interaction with environmental drivers. This study investigated the potential of net P release in acid sulfate wetland soils of Tram Chim National Park (Vietnam). The lab-scale experiments were conducted on intact soil cores (to the 20 cm depth) at three sites with different dominant vegetation communities (Eleocharis dulcis (S1), mixed lotus and Eleochris dulcis (S2), and Melaleuca Cajuputi (S3)) to quantify soil P fractions and measure P release fluxes from the acid soils in response to changes in water pH and dissolved oxygen (DO). The results showed that labile P fraction, or the most available P in soils, accounted for less than 23% of measured P. Non-labile P was the most abundant fraction, either in the surface (0-10 cm) or deeper (10-20 cm) layers, and accounted for more than 47% of measured P species. P release rates increased significantly with increasing pH and DO availability. pH is the primary factor driving P release in acid sulfate wetland soils. The highest release rates of P were recorded at pH 11.0 under the oxic condition. This study suggests that P pools in acid sulfate wetland soils are highly sensitive to changes in the water column that could occur during the regulated flooding for water-level management.