Abstract
The filamentous green alga Cladophora grows to nuisance proportions in Lake Ontario. Stimulated by high phosphorus concentrations, nuisance growth results in the degradation of beaches and clogging of industrial water intakes with attendant loss of beneficial uses. We develop a multi-module bioavailable phosphorus model to examine the efficacy of phosphorus management strategies in mitigating nuisance algal growth. The model platform includes modules simulating hydrodynamics (FVCOM), phosphorus-phytoplankton dynamics (GEM) and Cladophora growth (GLCMv3). The model is applied along a 25 km stretch of the Lake Ontario nearshore, extending east from Toronto, ON and receiving effluent from three wastewater treatment plants. Simulation results identify the Duffin Creek wastewater treatment plant effluent as a driving force for nuisance conditions of Cladophora growth, as reflected in effluent bioavailable phosphorus concentrations and the dimensions of the plant’s phosphorus footprint. Simulation results demonstrate that phosphorus removal by chemically enhanced secondary treatment is insufficient to provide relief from nuisance conditions. Tertiary treatment (chemically enhanced secondary treatment with ballasted flocculation) is shown to eliminate phosphorus-saturated conditions associated with the Duffin Creek wastewater treatment plant effluent, providing local relief from nuisance conditions. Management guidance presented here has wider application at sites along the highly urbanized Canadian nearshore of Lake Ontario.
Highlights
IntroductionFilamentous green algae of the genus Cladophora are found in freshwater and marine ecosystems worldwide, favoring environments with unidirectional flow (rivers) or periodic wave action (lakes and estuaries [1])
Filamentous green algae of the genus Cladophora are found in freshwater and marine ecosystems worldwide, favoring environments with unidirectional flow or periodic wave action
The analysis presented here simulates nearshore SRP concentrations and nutritional status of Cladophora (P-limited or P-saturated growth) across the matrix of flows and treatment options specified in the Duffin Creek WWTP Phosphorus Reduction Action Plan (PRAP)
Summary
Filamentous green algae of the genus Cladophora are found in freshwater and marine ecosystems worldwide, favoring environments with unidirectional flow (rivers) or periodic wave action (lakes and estuaries [1]). A binational call for action in controlling nuisance growth of Cladophora [15]), contributed support for implementation of phosphorus management programs on the Great Lakes in the late 1970s and early 1980s. These efforts achieved a marked reduction in both the phosphorus nutrition and areal biomass density of the alga [16]. This reprieve was, short lived, as clearing of the water column by invasive dreissenid mussels, beginning in the 1990s, extended the depth of colonization by Cladophora, increasing production by up to a factor of six and leading to a resurgence in beach fouling despite a continued reduction in P nutrition through phosphorus management [17]
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