Cyanotoxin Bloom Reactor | mysimulator.uk

Lake Conditions

Phosphorus loading 55 µg/L

Water temperature 26°C

Wind mixing / UV exposure 30%

Live Readouts

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Cyanobacteria density

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Growth rate μ

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Dissolved microcystin

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Toxin quota / cell

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WHO recreational-water guidance for microcystin-LR: <10 µg/L low probability of adverse health effects, 10–20 µg/L moderate, >20 µg/L high (advisory / closure). Provisional drinking-water guideline: 1 µg/L.

How it works

Cyanobacteria population N grows logistically toward a nutrient-set carrying capacity K, with a temperature response and a background loss (lysis) rate:

dN/dt = μ·N·(1 − N/K) − λ·N
μ  = μmax · P/(P+Ks) · exp(−((T−Topt)/σ)²)
K  = K0 + kP·P          (phosphorus sets the ceiling)
λ  = λ0 + kmix·mix       (mixing/turbulence raises background mortality)

Toxin quota (intracellular microcystin per cell) rises under nutrient/temperature stress — a real, well-documented effect. As cells die, their intracellular toxin dumps into the water; sunlight and microbial activity degrade it back out:

q   = q0 + qStress·stress(P,T)          (toxin per cell)
dCd/dt = λ·N·q  −  kdecay·Cd
kdecay = k0 + kUV·mix

The algaecide button is the pedagogically important part: killing the bloom chemically doesn't remove the toxin already inside the cells — it detonates it. A short spike in λ dumps the whole intracellular pool (λ·N·q) into the water almost at once, which is why copper-sulfate treatment of a cyanobacterial bloom can briefly push dissolved microcystin far above the pre-treatment level, even as the visible bloom collapses. This is exactly why water utilities monitor dissolved toxin — not cell counts — after any bloom-control intervention.

Phosphorus loading — raises both the bloom's ceiling (K) and its growth rate (Monod kinetics), mirroring agricultural/wastewater nutrient runoff.
Temperature — growth peaks near 25°C and falls off on both sides (Gaussian response), and stress away from the optimum raises the toxin quota.
Wind mixing / UV — higher values break up surface scum (raising background lysis) but also speed photolytic/microbial toxin decay, so its net effect on risk depends on the balance of both terms.

Algaecide applied — toxin spike incoming

Live cyanobacteria cells Water toxin haze (Cd)

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