pH

What is pH?

pH is a measurement of the concentration of hydrogen ions in the water. pH is measured on a logarithmic scale (0-14 pH units), with lower values considered acidic (high levels of H+ ions) and higher values considered basic (lower levels of H+ ions). The carbonate system is a natural process that maintains pH equilibrium in waters impacted by the photosynthesis and respiration of aquatic plants and decomposition by bacteria. Pollution from sewage overflows, stormwater runoff, carbon dioxide emissions, chemical spills and acid precipitation can negatively impact healthy pH levels.

Why is pH important?

Consistent and moderate levels of pH are critical for the survival of aquatic life. pH affects the availability of essential nutrients and minerals, and the presence of toxic substances in the water. Acidic waters (low pH) impede the ability of freshwater invertebrates to build their calcium carbonate shells. Low pH levels also increase the availability of phosphorus, driving algal blooms that can ultimately result in harmful decreases of dissolved oxygen. Basic waters (high pH) increase the availability of ammonia, which is toxic to aquatic life.

How do we measure pH?

pH is measured at tidal sampling sites with an optical probe lowered from our Waterkeeper boat the R/V Muckraker, into the water at each station location. pH readings are automatically collected at 0.25, 0.5 or 1.00  meter intervals from the water’s surface to just above the river bottom. pH at nontidal stations is measured by placing a YSI Probe into the water, completely submerging the sensor. We assess pH data using a numeric pass/fail threshold of 6.5 – 8.5 (SU pH), which was established by the Mid-Atlantic Tributary Assessment Coalition (MTAC) Sampling and data analysis protocols for Mid-Atlantic tidal and nontidal tributary indictors.