Chlorophyll Overload: Can It Be Used for Irrigation?

Chlorophyll-*a* exceedance is not a direct irrigation criterion, but a signal of eutrophication. The current Chinese irrigation water standard (GB 5084-2021) does not set a chlorophyll limit; its control items include BOD, COD, suspended solids, nutrients, and heavy metals. Therefore, “chlorophyll” essentially means the water is moderately to heavily eutrophic.

The real risks come from algal metabolites. Cyanobacterial blooms can release microcystins, which are hepatotoxic, chemically stable, and can be taken up by crops, impairing photosynthesis and reducing yields. For sprinkler-irrigated leafy vegetables, dried algal cells may adhere to leaves and remain toxic for months, creating a food safety hazard. Eutrophic water also causes biological clogging in drip systems, as algae and their secretions accumulate in filters and emitters, reducing irrigation uniformity.

The appropriate use depends on severity. Mildly eutrophic water (<10 μg/L chlorophyll-*a*) may be used for general dryland irrigation after settling or filtration, provided other indicators meet standards. Moderately eutrophic water (10–26 μg/L) requires pretreatment such as sand filtration and activated carbon adsorption, and drip or furrow irrigation should be preferred over sprinkler systems. 

Severely eutrophic water (>26 μg/L), especially with visible blooms, is not recommended for vegetables or raw-eaten crops unless toxin testing confirms microcystin levels are safe. In short, chlorophyll itself is not the problem—the algae and toxins it represents are.