Because chlorophyll-a is an indicator of algae counts, these high levels show that Thunderbird is “at risk of potentially dangerous algae levels that could render the water body unusable as a drinking water source,” according to staff reports.
If the city can reduce the amount of phosphorus in Lake Thunderbird, algae will decrease. Phosphorus levels in Thunderbird were documented in the Storm Water Master Plan completed in November 2009 and adopted by the city council in June 2011.
While there is no single solution to the problem of contaminant nutrients in the lake, fertilizer control and education have been identified as key components.
The ordinance prohibits phosphorus or phosphate being applied to “general turf within the city,” with some important exceptions. Phosphorus fertilizer will be allowed during the first six months that turf is established from seed or sod. It also is allowed if a soil test indicates a phosphorus deficiency.
In addition, naturally occurring phosphate — such as that found in unadulterated natural or organic fertilizers — is allowed. When applied, phosphorus fertilizers must be watered into the soil within 14 hours to avoid runoff.
The ordinance also outlines rules limiting application when rainfall is imminent, from running on driveways and other impervious services and using it near a wetland.
An educational pamphlet will be made available to commercial applicators and businesses that sell fertilizer annually. Businesses will be required to identify phosphorus fertilizers and notify buyers of the city’s regulations.
The ordinance also requires phosphorus fertilizers to be stored safely to avoid runoff. Commercial businesses that apply fertilizers will be required to register annually.