Phosphorus status, disposition and seasonal dynamics in the Swedish Kristianstad Riparian Histosol Wetlands

The Kristianstad wetlands in southern Sweden are officially classified as Wetlands of International Importance. They are located in intensively cultivated areas and were previously used for wastewater treatment, making them a potential source of environmental contamination. Little is known about phosphorus (P) status, disposition and dynamics in the wetlands. Total P (TP) content determined by fusion with Na2CO3 in successive 20 cm layers of undisturbed Histosols to 100 cm depth determined in samples taken in June and September 2000 and April 2001 ranged between 1510 and 3938 mg kg-1 dry soil and decreased with depth. Sequential extraction of TP with a chloride anion (ResP) → 0.5 M (pH 8.5) NaHCO3 (BicTP) → 0.1 M NaOH (HydTP) → 1.0 M HCl (HClP) → residual P (ResidP) revealed an increasing order (% of mean TP) of 1.14% ResP<2.35% HClP<29.26% ResidP<31% BicTP<36.21% HydTP. Speciation of BicTP and HydTP pools into inorganic P (IP) and organic P (OP) did not reveal difference between BicIP and BicOP, while HydOP constituted 70-90% of HydTP. Seasonal P dynamics based on P contents of the entire profile revealed marked declines in TP, BicTP, HydTP and ResidP with time, whereas ResP and HClP increased. Conclusions were that: (1) TP content at the site investigated was declining, apparently due to leaching and retention in vegetation and dead plant debris; (2) summation of P contents in layers gave a clearer trend of seasonal P dynamics than data determined in separate layers; (3) some re-distribution of P among the P compartments had occurred.