recognized as one of the most important mitigation options in obeying the quality goals of the European Water Framework Directive. While the nitrogen removal efficiency of restored wetlands is well accepted, the impact of wetland restoration on phosphorus (P) is less obvious. An increasing number of studies have called to the attention that wetland restoration on former agricultural soils may result in P release. Despite the high priority of wetland restoration there is a serious lack in understanding the fate of P following wetland restoration, and predictive model tools are highly needed. Prediction of P dynamics in restored wetlands is extremely challenging because of the complex interactions and feedbacks between hydrology, hydrochemistry and sediment geochemistry. In the Danish Strategic Research project MONITECH, one of the major objectives was to investigate the possibility of developing a P risk assessment tool to predict the potential risk of P release following restoration of wetlands on former agricultural lowlands. Batch incubation experiments investigating changes in soil-water concentrations of PO4-P, total P and total dissolved Fe as a function of time after rewetting in 31 riparian peat and minerogenic lowlands, demonstrated significantly different responses to rewetting in terms of Fe-reduction and P mobilization. Statistical analysis to identify key controlling geochemical parameters included content, form (oxalate, bicarbonate- dithionite, citrate-bicarbonate-dithionite extractable) and ratios of P, Fe, Al, as well as carbon content, C:N-ratio, C:Fe-ratio, Fe crystallinity, pH and bulk density. Soil analysis demonstrated very large variations in all key parameters e.g. carbon contents varied from <1 to >40%, oxalate extractable P (Pox) from 20-5.000 mg/kg, oxalate extractable Fe (Feox) from 80-75.000 mg/kg and variation in bulk density from 150-1400 kg m-3. Statistical analysis revealed that the soil FeBD:PBD-molar ratio (BD – bicarbonate-dithionite extractable), and bulk density (indicator of soil type, carbon content) turned out to be the best parameters in describing P mobilization in rewetted lowland sediments. Based on the experimental results a statistical model was developed describing potential P mobilization as a function of time with soil FeBD:PBD-molar ratio and bulk density as key predictive variables. The model has further been operationalized as a risk assessment tool to predict the potential risk of P losses following wetland restoration. Based on new experiments simulating the continuous upward percolation of groundwater in selected intact soil cores we investigated the hydrobiogeochemical mobilization of phosphorus during variable flow conditions. Soil redox conditions and hydrology turned out as major factors controlling 109 phosphorus release. The presentation will focus on an evaluation of the P risk assessment tool based on data form the continuous flow experiment.
Proceedings From the 7th Sws 2012 European Chapter Meeting, 2012
Main Research Area:
Society of Wetland Scientists meeting European, 2012