Maintaining the proper PH level in our streams is important to enable the survival of all the aquatic species in the waterway. If the PH is too low the stream becomes too acidic to support life. One of the contributers to low PH levels in our streams has been acid rain. This is rain loaded with pollutants from our industrial society. Pollutants such as sulfur dioxide and nitrogen oxide from the burning of fossil fuels increases the acidity of our rainwater significantly. In some areas of our country the soil can counter these effects or act as a buffer against acid rain. However, the ANF has poor buffering capacity due to the type of bedrock and soil that does not contain good buffering qualities. This usually means that the PH of our streams in the ANF are roughly equal to the acidity of our rainwater.
The passage of the Clean Air Act in 1970 and subsequent amendments over the years has had a positive impact on the acidity of our rainwater in the ANF. The diagrams below show the improvement in the PH of our rainwater from 1986 to 2016.
These improvements are the result of higher emissions standards for power generating plants and other industrial plants that rely on fossil fuels such as coal and higher emission standards for automobiles.
The picture below shows the PH levels of various streams in the ANF that were measured during the spring 2018 snapshot day. The Pennsylvania Department of Environmental Protection deems a PH level of 6-9 as being optimum level to support cold water fish such as trout. In the northern half of the forest the PH levels are for the most part within the DEP’s standards which indicates these streams can support a robust aquatic ecosystem. However, in the lower portion of the forest there are many watersheds that suffer from low PH levels making it difficult for them to support aquatic life. Despite an improvement in the acidity of our rainwater there are many streams that still suffer from low PH levels. And, due to the monitoring of our streams in the ANF there have been additional streams found that appear to be impaired from acid deposition.
Measuring and identifying the PH level of our streams is a huge undertaking by all involved. There are hundreds of hours expended on the collection and compilation of all the data. Some progress has been made with the improvement in the PH of rainwater, but more work is needed. The next step is to identify and implement restoration opportunities that will improve the PH of our streams that are impaired. More testing and evaluation needs completed on the impaired watersheds and the best course of action will need to be determined to improve these streams.
I would like to thank Trout Unlimited for allowing me to share the diagrams included in this post. TU, the National Forest Service, and Penn State University are driving the study of the watersheds in the Allegheny National Forest.
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