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

摘要

Lanthanum-modified bentonite clay (Phoslock~®) 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 241 of Phoslock~® 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 (Pmobiie; sum of 'labile F, 'reductant-soluble F and 'organic F 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 F fraction in the top 2 cm, sediment P-fractions, including P_(mobile). did not differ significantly following the Phoslock~® application. Experimental P-adsorption studies indicated P-saturation values for Phoslock~® of 21,670 mgP kg ' Phoslock~®. Sequential extraction of P from saturated Phoslock~® under laboratory conditions indicated that around 21% of P bound by Phoslock~® 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~® is, therefore, likely to increase the P-sorption capacity of sediments under reducing conditions.