Journal
WATER RESEARCH
Volume 97, Issue -, Pages 83-95Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2015.11.034
Keywords
Lake restoration; Eutrophication control; Cyanobacteria; Sediment P release; Iron chloride; Phoslock (R)
Funding
- Water Framework Directive Innovation Grant of Agentschap NL of the Ministry of Economic Affairs
- Province of Noord-Brabant (The Netherlands)
- Wageningen University
- water authority Aa en Maas
- water authority Brabantse Delta
- water authority De Dommel
- Dutch Foundation for Applied Water Research
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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 mu g L-1 (1992-2008) to 6 mu g 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. (C) 2015 Elsevier Ltd. All rights reserved.
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