title: Controlling eutrophication by combined bloom precipitation and sediment phosphorus inactivation.
abstract: The hypothesis that the combination of the flocculent polyaluminium chloride (PAC) with the lanthanum-modified bentonite Phoslock(®) (Flock & Lock) could sink effectively a water bloom of cyanobacteria and could shift a turbid, cyanobacteria infested lake to a clear water lake was tested in a controlled laboratory experiment and a whole lake experiment. In the laboratory, a relatively low dose of the flocculent PAC (2.2 and 4.4 mg Al l(-1)) was insufficient to sediment positively buoyant cyanobacteria (Microcystis aeruginosa). Similarly, the lanthanum modified clay (dosed at 390 mg l(-1)) was insufficient to sediment the positively buoyant cyanobacteria. However, the combination of PAC and Phoslock(®) effectively sedimented cyanobacteria flocks. Likewise, a combined treatment of 2 tons PAC and 18 tons Phoslock(®) in Lake Rauwbraken in April 2008 effectively sedimented a developing cyanobacteria bloom of Aphanizomenon flos-aquae. The average chlorophyll-a concentration in the two years prior to this Flock & Lock treatment was 19.5 (±36.5) μg l(-1), while it was as low as 3.7 (±4.5) μg l(-1) in the years following the treatment. The combined treatment effectively reduced the amount of total phosphorus (TP) in the water column from on average 169 (±126) μg P l(-1) before the application to 14 (±15) μg P l(-1) after the treatment. Based on mean summer chlorophyll-a and TP concentrations, the lake was shifted from a eutrophic/hypertrophic state to an oligo/mesotrophic state. From directly after treatment in April 2008 until and including 2013, Lake Rauwbraken remained in an oligo-mesotrophic clear water state with TP reduced to less than 10% of the pre-treatment. This result shows that eutrophication in relatively small, isolated, stratifying lakes can be restored by targeting both water column and sediment P using a combination of flocculent and solid phase P-sorbent.
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
authors.forename: Frank
authors.initials: F
authors.lastname: van Oosterhout
mesh_terms: D000704:Analysis of Variance; D011232:Chemical Precipitation; D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000378:metabolism; D005068:Eutrophication; D005843:Geography; D019015:Geologic Sediments / Q000737:chemistry*; D060106:Lakes; D009391:Nephelometry and Turbidimetry; D009426:Netherlands; D010758:Phosphorus / Q000302:isolation & purification*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D012722:Sewage / Q000382:microbiology
chemical_list: D045332:Photosystem II Protein Complex; D012722:Sewage; D002734:Chlorophyll; D010758:Phosphorus; D000077194:Chlorophyll A
keywords: Eutrophication control; Lake management; Lake restoration; Lanthanum modified clay; Phoslock(®); Polyaluminium chloride