Evaluation of phosphorus mobilization potential in rewetted fens by an improved sequential chemical extraction procedure

After rewetting of peatlands, phosphorus (P) pore-water concentrations were up to three orders of magnitude greater than under pristine conditions. It was hypothesized that different mobilization processes such as ion-exchange reactions, biotic/abiotic redox reactions, acidification and ongoing anaerobic decomposition of particulate organic matter by hydrolytic cleavage and fermentation might be responsible. To identify P pools in peat samples of varying degrees of decomposition, we modified and improved a sequential chemical extraction method that allowed conclusions on potential mobilization mechanisms in rewetted peatlands. The results indicated that the earlier drainage of rewetted fens strongly increased the P mobilization potential in the upper decomposed peat layers. Accordingly, the amount of P bound to redox-sensitive (bicarbonate/dithionite soluble) compounds (BD-P) was, on average, one order of magnitude greater in decomposed peat of rewetted fens (5.4-14.3 mu mol P g(-1) dry matter or DM) than in underlying less-decomposed peat layers (0.2-1.9 mu mol P g(-1) DM) or slightly decomposed peat derived from pristine fens (0.4-2.0 mu mol P g(-1) DM). The BD-P fraction found in the upper very decomposed peat layers appears to be most important for P mobilization in rewetted fens and accounted for 85% of the variability of P mobilization rates. Despite uncertainties regarding P diagenetic processes in peat, as well as the development of microbial decomposition processes, in the long-term, high pore-water P concentrations can be expected in rewetted fens for decades to come.