The pH of a pond containing algae will increase during the day because algae remove carbon dioxide from the water during photosynthesis in the presence of sunlight. Carbon dioxide (CO₂) is acidic in water. Algae and microbes tend to drop pH in the pond during the night as they algae respire and add CO₂ back into the water.

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Sample Bottles: Bottles should be clean. Use a 16 oz. plastic water bottle.

Sampling Technique: Before filling, rinse the sample bottle out three times with the water being collected. Fill the bottles completely and cap tightly (Don’t leave air space at the top if possible).

Sampling Timing & Location: Water should be collected at the same depth (if pond, river, stream, etc.) or location (e.g. pump). Collect sample at the same time of day water is used to irrigate crops. If collected from the end of irrigation lines – let the line flush sufficiently before collecting the sample (wait 2 minutes or so after irrigation system turns on to collect from the bypass or at a sprinkler head).

Sample Handling and Storage: Avoid sample agitation and prolonged exposure to air. Identify each bottle by attaching an appropriate label (Date & time collected, location, your name/operation). Store the sample in cool/dark location (i.e. refrigerator (best) or in a cooler on ice) until submitting to lab for analysis. IF sending sample to a lab – ship overnight with samples kept cold in an insulated shipping container with ice-packs. Sample doesn’t need to be frozen – but needs to be kept cold in the dark to reduce changes in sample composition between sampling time and analysis by the lab.

Submit the sample(s) for analysis as soon after sampling as possible. Ideally the samples should be analyzed within 24 hours of sampling.  

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Eucalyptus leaf discs for baiting Phytophthora are placed onto a selective agar culture medium to test for the presence of the pathogen (the thread-like rings around the leaf discs). Photo by Dr. Robert Wick, University of Massachusetts.

Check whether your state university extension plant diagnostic lab can run the sample. For example, the University of Massachusetts Plant Diagnostic Clinic plates out water samples to test for Pythium and Phytophthora to the genus level.

You can also send a sample to the University of Guelph, which does a DNA fingerprint-type analysis for a range of pathogens down to the species level.

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