Phosphorus Removal in a Wetland Constructed on Former Arable Land
- Anu Liikanena,
- Markku Puustinen *b,
- Jari Koskiahob,
- Tero Väisänenc,
- Pertti Martikainena and
- Helinä Hartikainend
- a Department of Environmental Sciences, Research and Development Unit of Environmental Health, University of Kuopio, P.O. Box 1627, FIN 70211, Kuopio, Finland
b Finnish Environment Institute, P.O. Box 140, FIN 00251, Helsinki, Finland
c North Ostrobothnia Regional Environment Centre, P.O. Box 124, FIN 90101, Oulu, Finland
d University of Helsinki, Department of Applied Chemistry and Microbiology, FIN 00014, University of Helsinki, Finland
Phosphorus in surface runoff water may cause eutrophication of recipient water. This study clarifies the mechanisms of P removal in the wetland of Hovi, Finland, constructed on arable land in 1998. Before the construction, the surface soil (removed in the construction) and subsoil (the current wetland bottom) were analyzed for Al and Fe oxides (Alox and Feox) reactive in P sorption, and for the distribution of P between various pools as well as for P exchange properties. Retention of P from runoff water within the wetland was studied from 1999 to 2001 in situ and factors affecting the P removal (O2 availability and P concentration in water) were investigated in a laboratory microcosm. The processes taking place in the wetland diminished by 68% the total P load and by 49% the dissolved reactive P load. Desorption–sorption tests indicated that without removal of the surface soil, there would have been a risk of the wetland being a source of P, since the equilibrium P concentration of the soil removed was high compared with the mean P concentration of the inflowing water. The subsoil contained less P and high amounts of reactive oxides, which could bind P. Evidently, the P sorption by Alox played an important role in a first phase removal of P, since the wetland retained P efficiently even under anoxic conditions, where Fe tends to be reduced. Fine-textured, mineral soil on the bottom of the wetland (subsoil of the former arable land) seemed to be very efficient in retaining P from agricultural runoff.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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