Phosphorus speciation in agricultural catchment soils and in fresh and dried sediments of five constructed wetlands

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http://hdl.handle.net/10138/173465

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Laakso , J M , Uusitalo , R & Yli-Halla , M J 2016 , ' Phosphorus speciation in agricultural catchment soils and in fresh and dried sediments of five constructed wetlands ' , Geoderma , vol. 271 , pp. 18-26 . https://doi.org/10.1016/j.geoderma.2016.02.007

Title: Phosphorus speciation in agricultural catchment soils and in fresh and dried sediments of five constructed wetlands
Author: Laakso, Johanna Marketta; Uusitalo, Risto; Yli-Halla, Markku Juhani
Contributor: University of Helsinki, Department of Food and Nutrition
University of Helsinki, Department of Food and Nutrition
Date: 2016
Language: eng
Number of pages: 9
Belongs to series: Geoderma
ISSN: 0016-7061
URI: http://hdl.handle.net/10138/173465
Abstract: Constructed wetlands and ponds (CWs) are installed to trap suspended material and particulate phosphorus (P) in agricultural runoff. This study investigated whether the P speciation and P sorption capacity of source soils differ from those of CW sediments and whether drying of dredged sediment changes its characteristics. Samples collected from five agricultural CW sites in south-west Finland, two with chemical-aided (aluminium chloride and ferric sulphate) P precipitation and all representing fine-textured mineral soils, were analysed for various P plant availability indices. Clay contents of the CW sediments were much higher than in catchment soils, likely because of selective erosion. All CW sediments were characterised by similar total P content but clearly higher content of anion exchange resin-extractable P in fresh sediments than the source soils. In general, sediment content of NH4F-extractable (aluminium (Al)-associated) P was significantly lower and NaOH-extractable (iron (Fe)-associated) significantly higher than in source soils. Reduced conditions, conducive to mobilisation of Fe-associated P, were observed in all CWs. Accumulation of sulphur (S) in sediments and a pH decline of up to two units upon drying suggested presence of Fe sulphides. Drying also increased oxalate-extractable Al and Fe (hydr)oxide content by 9–47%, resulting in lower degree of P saturation. These results indicate that dredged CW sediments differ greatly in their P retention characteristics from their parent soils. Returning CW sediments to fields is likely to decrease the amount of readily available P for crop uptake.
Subject: 1172 Environmental sciences
Soil science
Soil chemistry
Phosphorus
Erosion
Reducing conditions
Sediment
4111 Agronomy
Soil amendment
soil analysis
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