Sediment amendment with Phoslock® in Clatto Reservoir (Dundee, UK): Investigating changes in sediment elemental composition and phosphorus fractionation

Lanthanum-modified bentonite clay (Phoslock (R)) is a lake remediation tool designed to strip dissolved phosphorus (P) from the water column and increase the sediment P-sorption capacity. This study investigated short term alterations in sediment elemental composition and sediment P-fractions based on sediment cores taken 2 days before and 28 days following the application of 24 t of Phoslock (R) to a 9 ha, man-made reservoir. Following the application, sediment lanthanum (La) content increased significantly (p < 0.05; n = 4) in the top 8 cm of the sediment, thereby theoretically increasing sediment P-binding capacity on the whole reservoir scale by 250 kg. Mass balance calculations were used to estimate the theoretical binding of release-sensitive P (P-mobile; sum of 'labile P'. 'reductant-soluble P' and 'organic P fraction) by La across the top 4 cm and 10 cm depth of sediment. The amended mass of La in the sediment had the potential to bind 42% of P-mobile present in the top 4 cm or 17% of P-mobile present in the top 10 cm. However, with the exception of a significant increase (p < 0.05; n = 4) in the 'residual P' fraction in the top 2 cm, sediment P-fractions, including P-mobile, did not differ significantly following the Phoslock (R) application. Experimental P-adsorption studies indicated P-saturation values for Phoslock (R) of 21,670 mg P kg(-1) Phoslock (R). Sequential extraction of P from saturated Phoslock (R) under laboratory conditions indicated that around 21% of P bound by Phoslock (R) was release-sensitive, while around 79% of bound P was unlikely to be released under reducing or common pH (5-9) conditions in shallow lakes. Applying Phoslock (R) is, therefore, likely to increase the P-sorption capacity of sediments under reducing conditions. (C) 2011 Elsevier Ltd. All rights reserved.