Water Chemistry: pH

pH pH is the measure of hydrogen ions (H+) –Negative logarithm of the H+ concentration Higher the pH, the lower the H+ concentration (Base or Alkaline) Lower the pH, the Higher the H+ concentration (Acid) Logarithmic Scale: 10 times each step –Example: There are 10 times as many hydrogen ions available at pH 7 then pH 8 Range of 0-14

pH The pH of water determines solubility –Effects how much nutrients can be utilized How much and what form And if aquatic life can use it –Heavy metals affected as well Degree of solubility determines toxicity Generally more toxic at lower pH (acidic) because they are more soluble

pH Natural Variation –Photosynthesis uses up dissolved carbon dioxide Results in an increase of pH (more basic or alkaline) –Respiration produces Carbon Dioxide Results in a decrease of pH (more acidic)

pH So, would pH go up or down at night? Would pH go up or down with an increased depth?

pH Thankfully, aquatic environments can resist these changes –Buffering Capacity keeps the pH of Natural waters between 6.5 and 8.5

pH Impact of pollution –Increased Temperature or excess nutrients result in an increased pH (more acidic)

pH Remember: –More Acidic = lower pH value –More Basic/Alkaline = higher pH value