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.
- Publication:
-
Water Research
- Pub Date:
- June 2016
- DOI:
- 10.1016/j.watres.2015.11.034
- Bibcode:
- 2016WatRe..97...83W
- Keywords:
-
- Lake restoration;
- Eutrophication control;
- Cyanobacteria;
- Sediment P release;
- Iron chloride;
- Phoslock<SUP>®</SUP>