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Cyanobacteria are commonly found in aquatic ecosystems and generally are only a problem when conditions favor cyanobacteria over other aquatic organisms.
So, what indicators may help determine if a cyanobacteria bloom may be forming near a source water intake? EPA’s Water Treatment Optimization for Cyanotoxins, Version 1.0, Table 2-2, Source Water Quality Indicators has a list of parameters that may help warn operators that a bloom is forming when recorded and reviewed regularly.
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Increase in Treatment Difficulties: If the operator starts seeing an increase in problems with the treatment results, such as decreased filter run times, increased usage of chemicals, difficulty in meeting turbidity goals, or struggling to maintain a disinfectant residual, further investigation in the source water quality would be warranted.
- Changes in water clarity:
- Pigments – There are sensors available that can be placed in water bodies to send readings of phycocyanin (blue photosynthetic pigments found in cyanobacteria) to your computer.
- Turbidity – While there are multiple reasons to see changes in turbidity, unexplained increases may indicate an increase in cyanobacteria populations.
- Secchi Depth – Secchi disks are 8-inch disks with alternating black and white sections. Lowering the disk into the water until the markings “disappear” and recording the depth this occurred each day can warn when visibility is decreasing. When the “disappearance” level becomes shallower, the higher the probability that cyanobacteria concentrations are increasing. Secchi depth does have some of the same limitation as turbidity, such as rain runoff or other watershed events.
- Changes in water chemistry:
- pH – Cyanobacteria are photosynthetic (meaning they use light to create nutrients) and they multiply best when exposed to long periods of sunlight. Due to the photosynthesis process, operators may see an increase in pH during the day and a decrease at night in their raw water monitoring when a bloom is occurring. Another possibility is a prolonged increase in pH from their normal readings.
- Temperature – Cyanobacteria thrive in warm water and rising temperatures may indicate that a bloom could happen soon.
- Nutrients – Recording and watching for increasing phosphorus and nitrogen levels in the source water over time may help the operator recognize the conditions most favorable for a bloom to occur.
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Taste, Odor, or Color: Some species of cyanobacteria will cause unpleasant taste and odor issues in the water. A color change can also take place (usually a green tint).
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Natural Organic Matter (NOM): Increases in NOM, including total organic carbon (TOC), in the source water without a recent rainfall or other upstream event (wildfire, construction) can also be a bloom indication.
Indicators, such as turbidity, TOC, and pH, are regularly recorded as part of the treatment process. It does require regular review of these levels to see if trends can be recognized. Other parameters are abnormal drinking water operations. However, government agencies, companies, and citizen science projects may already be doing these measurements as part of an effort to protect the overall water body. Check to see if these other groups are willing to share their data can help the public water system personnel plan for a cyanobacteria event.
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