pages 17-18 of the UWP Educator’s Guide to Teaching Students About the Upper Uncompahgre River Watershed (also see contents, introduction & pdf link)
pH: What is It?
Most North American rivers, lakes and streams fall within the range of pH 6.5 to 8.2. National guidelines recommend pH of 6.5-9.0 for the protection of aquatic life in freshwaters.
pH measures the degree to which water is acidic (like lemon juice) or basic (like bleach or soap). pH is measured on a scale that ranges from 0 (strongly acidic) to 14 (strongly basic). In the middle is 7, where the pH is neutral (like in pure water).
Why Does it Matter?
pH in freshwater systems is affected by naturally occurring organic acids or by impacts from human activities, such as acid rock drainage (naturally occurring runoff over iron-laden rock) or acid rain and acid rock drainage (such as abandoned mines).When water is more acidic (has a lower pH) it can make certain chemicals and metals more toxic than normal. This is because acid waters make these elements more soluble – that is, they become more easily dissolved in the water and in this way become more biologically available to fish and other organisms.
Acid rain occurs when certain pollutants in the air (sulfur dioxide and nitrogen oxides) react with water to form acids. These acids are then deposited to the land, lakes, and rivers by rain and snow. A riverway can be impaired by both pH and iron.
Acid rock drainage is a common problem in and around mines that have not been remediated (see above) or areas that are naturally rich in iron (like Red Mountain pass). A riverway can be impaired by both pH and iron.
Acid mine drainage is a common problem in and around mines. Acidic conditions arise when tailings and waste rock piles are exposed to air and water. The acid often dissolves minerals, including metals, from the rock and both the acid and the metals can drain into waterways. A riverway can be impaired by both pH and iron.
Most fish prefer to live in water that ranges in pH from around 6.4 to 8.4. Fish eggs grow and survive best at a narrower range of pH; from 6.0-7.2.
How is It Measured?
pH can be assessed using pH strips that change color based on how acidic or basic the water is. The color is evaluated against a guide to determine the approximate pH range of the water. pH can also be measured directly in a lake or river using a water quality meter with a pH sensor. Before use, this sensor is calibrated using standard solutions of known pH (typically pH 4, 7 and 10).
Teachers: Students will each use a pH strip or groups of two students can use one pH strip.
pH is influenced by: background water chemistry – especially carbonate, bicarbonate and naturally-occurring acids.
pH influences: dissolved concentrations of many metals and metalloids in water.
Leading question: Do we have metals in Ouray County water?
NOTE FROM RIVER WATCH:
Unc River segment COGUUN03b_A, just above the confluence with Cascade Creek in Ouray to just above the confluence with Dexter Creek, is impaired for pH and total iron.
The short segment COGUUN03d_A that extends from below the confluence with Dallas Cr to the inlet of the reservoir is still listed as impaired for dissolved cadmium and copper, and total iron. It hasn’t been sampled recently, and was not assessed for the 2022 303(d) list.
Source: https://datastream.org/en-ca/guidebook/ph
