Effects of landuse change of coastal tidal flat on the bio-available phosphorus in soils

To explore the effects of landuse change of coastal tidal flat on the bio-available phosphorus (BAP) in soils, total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus, and several BAPs (Olsen-P, M3-P, WSP, and Lo-P) were analyzed in the process of transformation from the pristine salt marsh to reclaimed farmlands. Results showed that concentrations of TP, IP and OP in soils increased significantly (by 19%, 12%, and 55%, respectively) after transformation from the pristine salt marsh to reclaimed farmlands. The ratio of IP/TP decreased significantly, and the ratios of OP/TP and OP/IP increased significantly, which suggested the cumulative rate of OP was clearly higher than TP and IP in the process of landuse change of tidal flat. The concentrations and ratios of BAPs in tidal flat soils increased significantly after transformation to reclaimed farmlands. The concentrations of Olsen-P, M3-P, WSP, and Lo-P increased by 282%, 379%, 275%, and 192%, respectively, and the ratios increased by 205%, 267%, 217%, and 142%, respectively. The increase of BAPs was far higher than TP, IP and OP. BAPs had significantly positive correlations with TP, IP, and organic carbon (TOC), and significantly negative correlation with soil salinity. The above results showed that the landuse change of tidal flat from the pristine salt marsh to reclaimed farmlands could raise greatly the BAP levels in soils,and the environmental consequences of which were worthy of attention.