Population persistence in flowing-water habitats: Conditions where flow-based management of harmful algal blooms works, and where it does not

- Hydraulic flushing was examined as a way to mitigate harmful algal blooms.
- An advection-diffusion-reaction model with a hydraulic storage zone was applied.
- Steady state and time variable simulations were conducted.
- Clearance of algae from substantial portions of a small water body was predicted.
- Flushing can also produce unintended blooms under some conditions.

Control of harmful algae in the coves or bays of larger water bodies could be accomplished by hydraulic flushing with algae-free water. This suggestion is examined with a mathematical model of a harmful algal population, parameterized to represent the toxic haptophyte Prymnesium parvum, and its limiting nutrient. A small cove with a hydraulic storage zone and longitudinal advection and dispersion is coupled to a larger lake where ongoing or transient blooms serve as a source for the algal population. This population is transported upstream by dispersion and flushed downstream by advection. Morphometry and hydraulics represent a lake in Texas where blooms of P. parvum have been problematic. When dispersion and hydraulic storage are low to moderate, available pumping technology is predicted to be capable of suppressing the algal population within a variable portion of the cove, under both steady state and transient conditions. This suppression occurs when temperature-dependent algal growth is low. At temperatures high enough to support more rapid growth, flow augmentation carries a risk of stimulating a bloom under some hydraulic conditions. The model presented here complements similar models without population sources, and contributes to theoretical understanding of population persistence in reservoirs and other flowing-water habitats.

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