Stable, nutrient-rich surface water favours cyanobacterial blooms that produce toxins and the taste-and-odour compounds geosmin and 2-MIB. We assess the bloom-forming risk — nutrients, light, residence time and species — and design the mixing that removes the calm surface layer they depend on, documented against the cyanotoxin and aesthetic standards that apply to your supply.
We test whether mixing can actually control the dominant species — comparing the critical mixing depth against the euphotic depth and weighing nutrient supply and residence time — before committing to destratification. Where nutrients dominate, the assessment says so, and the design follows the diagnosis.
Explore Our ProcessBuoyancy regulation, light and nutrients give cyanobacteria the edge in a calm, warm surface layer
Many cyanobacteria carry gas vesicles that let them float to the light and sink to the nutrients — an advantage only a stable, unmixed column allows. Destratification removes that stability: cells are circulated below the euphotic zone and lose their competitive edge to faster-settling diatoms and green algae.
Phosphorus released from anoxic sediment (the internal load) and catchment inputs drive biomass. Holding the bed oxidised cuts the internal supply, while the nitrogen-to-phosphorus balance shapes which species, including nitrogen-fixers, are likely to dominate.
Blooms can release hepatotoxins (microcystins, cylindrospermopsin) and neurotoxins (anatoxin, saxitoxin), plus the earthy–musty compounds geosmin and 2-MIB detectable at single-figure nanograms per litre. Preventing the bloom is far cheaper and more reliable than treating its products downstream.
The decisive test is whether circulation can keep buoyant cells out of the light long enough to suppress them. We compare the mixed-layer (or induced circulation) depth Zmix with the euphotic depth Zeu ≈ 4.6/kd, where kd is the light-attenuation coefficient inferred from Secchi transparency. When the Zmix:Zeu ratio is driven well above unity, the average cell spends most of its time below the compensation depth and net growth collapses — the same critical-depth logic Sverdrup set out for phytoplankton. Destratification has to deliver enough circulation to push that ratio over the threshold, which is exactly what the bubble-plume sizing targets. Where the nutrient supply is so high that even a well-mixed column blooms, the assessment flags that mixing alone is insufficient and a nutrient-control lever is needed — an honest result the design depends on.
From bloom history and species to a sized mixing system — with a defined alert and response framework
Past bloom frequency, the dominant cyanobacteria and the toxins and taste-and-odour compounds they produce establish the specific risk to the supply.
Total phosphorus and nitrogen, the N:P balance, Secchi transparency and the euphotic depth quantify what is fuelling growth and how deeply light penetrates.
The achievable circulation depth is compared with the euphotic depth to confirm whether mixing can suppress the dominant species, or whether nutrient control is also required.
Destratification, surface circulation or a combined nutrient-and-mixing strategy is selected on the evidence — with internal-load control where sediment phosphorus dominates.
The mixing system is sized to hold the circulation depth that suppresses blooms across the season, integrated with the reservoir’s abstraction and treatment arrangement.
A tiered alert-level response (cell counts, toxins, geosmin/2-MIB) is defined and tracked against the pre-aeration baseline to verify the design is working.
Evidence mapped to the cyanotoxin and aesthetic standards that govern your supply
The species, nutrient, light and mixing analysis documenting the cyanobacteria risk and how the design controls it — ready for a drinking-water safety plan.
The euphotic-depth and circulation-depth analysis and bubble-plume sizing that demonstrate mixing can suppress the dominant species, fully reproducible.
Targets referenced to the applicable values — WHO and UK guideline levels for microcystin-LR, and the Australian Drinking Water Guidelines for microcystins, cylindrospermopsin and saxitoxins — alongside the “no abnormal taste or odour” requirement for geosmin and 2-MIB.
A documented tiered monitoring-and-response plan (cell counts, toxin and taste-and-odour thresholds) aligned with recognised cyanobacteria alert-level frameworks.
As-built records and the measured circulation and water-quality response confirming the mixing design is delivering bloom suppression.
The seasonal operating protocol and an annual report comparing bloom frequency, toxins and geosmin/2-MIB with the pre-aeration baseline.
The stable surface layer blooms depend on — assessed in full and designed out.
Read MoreGeosmin and 2-MIB thresholds, monitoring and the destratification-plus-GAC treatment chain.
Read MoreReversing eutrophic, bloom-prone conditions in lakes and amenity water bodies.
Read MoreReynolds & Bauhm assesses the bloom-forming risk, tests whether mixing can control it, and designs the destratification that removes the surface layer blooms rely on — documented against the cyanotoxin and aesthetic standards that apply.
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