Extremes in pH can make a river inhospitable to life.

• pH is the levels of Alkalinity/ Acid. 7 is neutral. 1-6 is acidic (with 1 being more acidic than 2, which is more acidic than 3 etc.) 8-14 is alkaline or base (with 14 being more alkaline than 8, which is more alkaline than 9 etc.)

• pH is a measure of how acidic or basic (alkaline) a solution is. It measures the hydrogen ion (H+) activity in a solution, and is expressed as a negative logarithm. The pH measurements are given on a scale of 0.0 to 14.0. Pure water has a pH of 7.0 and is neutral; water measuring under 7.0 is acidic; and that above 7.0 is alkaline or basic.

• Values of pH are based on the logarithmic scale, meaning that for each 1.0 change of pH, acidity or alkalinity changes by a factor of ten; that is, a pH of 5.0 is ten times more acidic than 6.0 and 100 times more acidic than 7.0

• Low pH is especially harmful to immature fish and insects

• Most estuarine organisms prefer conditions with pH values ranging from about 6.5 to 8.5 whilst the largest variety of freshwater aquatic organisms prefer a pH range 6.5 - 8.0.

• Unanticipated decreases in pH could be indications of acid rain, runoff from acidic soils, or contamination by agricultural chemicals.

• Values of pH outside the expected range of 5.0 to 10.0 should be considered as indications of industrial pollution or some cataclysmic event.

• Long-term database on alkalinity values provides researchers with the ability to detect trends in the chemical makeup of estuary waters

• Human activities that cause significant, short-term fluctuations in pH or long-term acidification of a waterbody are exceedingly harmful. For instance, algal blooms that are often initiated by an overload of nutrients can cause pH to fluctuate dramatically over a few hour period, greatly stressing local organisms. Acid precipitation in the upper freshwater reaches of an estuary can diminish the survival rate of eggs deposited there by spawning fish. Several other factors also determine the pH of the water, including:

• bacterial activity;

• water turbulence;

• chemical constituents in runoff flowing into the waterbody;

• sewage overflows; and

• impacts from other human activities both in and outside the drainage basin (e.g., acid drainage from coal mines, accidental spills, and acid precipitation).

• Estuarine pH levels generally average from 7.0 to 7.5 in the fresher sections, to between 8.0 and 8.6 in the more saline areas. The slightly alkaline pH of seawater is due to the natural buffering from carbonate and bicarbonate dissolved in the water.

• The pH of water is critical to the survival of most aquatic plants and animals. Many species have trouble surviving if pH levels drop under 5.0 or rise above 9.0. Changes in pH can alter other aspects of the water’s chemistry, usually to the detriment of native species. Even small shifts in the water’s pH can affect the solubility of some metals such as iron and copper. Such changes can influence aquatic life indirectly; if the pH levels are lowered, toxic metals in the estuary’s sediment can be re-suspended in the water column. This can have impacts on many aquatic species.

• For more information click this link

• https://www.epa.gov/sites/production/files/2015-09/documents/2009_03_13_estuaries_monitor_chap11.pdf