Attempted management of cyanobacteria by Phoslock (lanthanum-modified clay) in Canadian lakes: water quality results and predictions

Nurnberg GK. 2017. Attempted management of cyanobacteria by Phoslock (lanthanum-modified clay) in Canadian lakes: water quality results and predictions. Lake Reserv Manage. 33:163-170.When internal phosphorus (P) loading from the bottom sediments outweighs external P inputs to lakes, lake water quality and cyanobacteria blooms will not respond to external measures alone and therefore require an in-lake restoration treatment. Lake characteristics and governmental regulations do not permit a random choice of such methods. A treatment developed by an Australian research institute (CSIRO) more than 15years ago has recently been introduced to Canada and is licensed in Ontario. The lake water treatment consists of the application of a phosphate adsorbing and sediment capping agent called Phoslock in North America, a clay (bentonite) that has been systematically amended by the phosphate adsorbing element lanthanum. When applied, Phoslock sinks to the lake bottom where it intercepts the upward flux of internal load from sediment P release. Although the number of monitored Canadian applications is still small, suggestions to optimize restoration effects can be made, including the avoidance of high flushing during application, system isolation, and timing to coincide with high levels of inorganic P in the lake water. Initial results in at least 2 cases (Swan Lake, City of Markham, Greater Toronto Area; and Henderson Lake, Lethbridge, Alberta) were promising despite the unexpected external P input from waterfowl and possibly other external sources. Other applications are planned in a Quebec lake and are being discussed in several other provinces.