title: Geo-engineering experiments in two urban ponds to control eutrophication.
abstract: Many urban ponds experience detrimental algal blooms as the result of eutrophication. During a two year field experiment, the efficacy of five in situ treatments to mitigate eutrophication effects in urban ponds was studied. The treatments targeted the sediment phosphorus release and were intended to switch the ponds from a turbid phytoplankton-dominated state to a clear-water state with a low phytoplankton biomass. Two eutrophic urban ponds were each divided into six compartments (300-400 m(2); 210-700 m(3)). In each pond the following treatments were tested: dredging in combination with biomanipulation (involving fish biomass control and the introduction of macrophytes) with and without the addition of the flocculant polyaluminiumchloride, interception and reduction of sediment phosphorus release with lanthanum-modified bentonite (Phoslock(®)) in combination with biomanipulation with and without polyaluminiumchloride; biomanipulation alone; and a control. Trial results support the hypothesis that the combination of biomanipulation and measures targeting the sediment phosphorus release can be effective in reducing the phytoplankton biomass and establishing and maintaining a clear-water state, provided the external phosphorus loading is limited. During the experimental period dredging combined with biomanipulation showed mean chlorophyll-a concentrations of 5.3 and 6.2 μg L(-1), compared to 268.9 and 52.4 μg L(-1) in the control compartments. Lanthanum-modified bentonite can be an effective alternative to dredging and in combination with biomanipulation it showed mean chlorophyll-a concentrations of 5.9 and 7.6 μg L(-1). Biomanipulation alone did not establish a clear-water state or only during a limited period. As the two experimental sites differed in their reaction to the treatments, it is important to choose the most promising treatment depending on site specific characteristics. In recovering the water quality status of urban ponds, continuing attention is required to the concurrent reduction of external phosphorus loading and to maintaining an appropriate fish community.
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: Water Authority Brabantse Delta, P.O. Box 5520, 4801 DZ Breda, 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: D000818:Animals; D005068:Eutrophication; D010758:Phosphorus; D010839:Phytoplankton; D061005:Ponds; D060753:Water Quality
chemical_list: D010758:Phosphorus
keywords: Biomanipulation; Dredging; Lake restoration; Lanthanum-modified bentonite; Phoslock(®); Polyaluminiumchloride