The pH of water in a watercourse determines the solubility and toxicity of chemicals.
Aquatic Life: Most aquatic organisms have a specific pH range within which they can survive. Deviations from this range can reduce their reproductive success, or outright kill them.
Chemical Solubility and Toxicity: Lower (acidic) pH levels can increase the solubility of toxic metals like aluminum and lead, making them more available and harmful to aquatic organisms.
Nutrients: pH influences the availability of nutrients such as phosphorus and nitrogen which are essential for plant growth. Extreme pH levels can limit the availability of these nutrients, affecting primary production and the entire food web.
Biological Processes: Photosynthesis and respiration are pH-dependent. Enzymes that facilitate these processes have optimal pH ranges, and deviations can impair their function.
Corrosion and Scaling: Low pH can lead to the corrosion of pipes and fixtures, releasing metals into the water. High pH can cause scaling, which can clog pipes and reduce the efficiency of water heaters and other equipment.
Factors Affecting pH Stability
The pH of a water sample should be measured as soon as possible after it's taken, since several factors can affect the value.
- CO₂ Absorption: If left exposed to air, water absorbs atmospheric CO₂, forming carbonic acid, which lowers pH within as little as 30 minutes.
- Biological Activity: Microbial growth or algal respiration can alter pH within a time dependent on temperature and nutrients.
- Chemical Reactions: Oxidation of dissolved metals (e.g., iron) or sulfide compounds can affect pH.
- Temperature Change: pH is temperature-dependent; cooling or warming a sample can shift its reading.
Immediate measurement (on-site) is ideal for the most accurate results.
If lab analysis is required, preserve and chill the sample (4°C) and measure as soon as possible, up to 2 hours if kept sealed and cold.
To stabilize pH for longer storage, seal samples tightly, minimize headspace to prevent CO₂ exchange, refrigerate (but do not freeze) to slow biological/chemical changes, and use chemical preservatives (e.g., HgCl₂) for biological inhibition