title: Management of eutrophication in Lake De Kuil (The Netherlands) using combined flocculant - Lanthanum modified bentonite treatment.
abstract: Eutrophication of Lake De Kuil (The Netherlands, 6.7 ha, maximum depth 9 m) has frequently caused cyanobacterial blooms resulting in swimming bans or the issue of water quality warnings during summer. The eutrophication was mainly driven by sediment phosphorus (P)-release. The external P-loading was in the range of the critical loading for phytoplankton blooms. Hence, the reduction of the internal P-loading provided a promising way to reduce cyanobacterial blooms. To mitigate the cyanobacterial blooms, the combination of a low dose flocculant (iron(III)chloride; Flock) and a solid phase phosphate fixative (lanthanum modified bentonite; Lock) was applied in May 2009. This combined approach both removed cyanobacterial biomass from the water column and also intercepted P released from the bottom sediments. Immediately after treatment, the Secchi depth increased from 1.5 m up to 5 m. Sediment P-release decreased from 5.2 mg P m(-2) d(-1) (2009) to 0.4 mg P m(-2) d(-1) (2010) but increased in later years. Mean summer concentrations of total P decreased from 0.05 mg L(-1) (1992-2008) to 0.02 mg L(-1) (2009-2014) and chlorophyll-a from 16 μg L(-1) (1992-2008) to 6 μg L(-1) (2009-2014). Mean summer Secchi depth increased from 2.31 m (1992-2008) to 3.12 m (2009-2014). The coverage of macrophytes tripled from 2009 to 2011. In the winter of 2010/2011 Planktothrix rubescens bloomed, but cyanobacterial biomass decreased during the summers after the Flock and Lock treatment in comparison to prior years. After the Flock & Lock the bathing water requirements have been fulfilled for six consecutive summers. As the sediment P-release has gradually increased in recent years, there is a risk of a reversion from the present mesotrophic state to a eutrophic state.
authors.affiliation: Water Authority Brabantse Delta, P.O. Box 5520, 4801 DZ, Breda, The Netherlands; Aquatic Ecology & Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 47, 6700 AA, Wageningen, The Netherlands. Electronic address: g.waajen@brabantsedelta.nl.
authors.forename: Guido
authors.initials: G
authors.lastname: Waajen
authors.affiliation: Aquatic Ecology & Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 47, 6700 AA, Wageningen, The Netherlands. Electronic address: jean.vanoosterhout@wur.nl.
authors.forename: Frank
authors.initials: F
authors.lastname: van Oosterhout
authors.affiliation: CSIRO, Land and Water, Centre for Environment and Life Sciences, Private Bag 5, Wembley, WA 6913, Australia. Electronic address: Grant.Douglas@csiro.au.
authors.forename: Grant
authors.initials: G
authors.lastname: Douglas
authors.affiliation: Aquatic Ecology & Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 47, 6700 AA, Wageningen, The Netherlands; Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), P.O. Box 50, 6700 AB, Wageningen, The Netherlands. Electronic address: miquel.lurling@wur.nl.
authors.forename: Miquel
authors.initials: M
authors.lastname: Lürling
mesh_terms: D001546:Bentonite; D005068:Eutrophication; D060106:Lakes; D007811:Lanthanum; D009426:Netherlands; D010758:Phosphorus
chemical_list: D001546:Bentonite; D010758:Phosphorus; D007811:Lanthanum
keywords: Cyanobacteria; Eutrophication control; Iron chloride; Lake restoration; Phoslock(®); Sediment P release