Final answer:
The pH of streams and rivers is influenced by both human activities like acid rain and natural factors such as minerals and biological processes in the water. Human-induced acidification is a major concern for aquatic ecosystems, but natural elements also significantly contribute to the overall pH.
Step-by-step explanation:
Variations in the pH of streams and rivers can be caused by both human and natural factors. While human activities like acid rain significantly influence the pH levels, leading to acidification of water bodies, natural processes also play a key role.
Acid rain, a result of emissions from the burning of fossil fuels, lowers the pH of aquatic environments, causing harm to ecosystems. In addition, natural elements such as minerals in the river bed or the presence of certain ions in rainwater also affect the pH.
It is not just industrial and vehicular emissions that lead to changes in pH but also natural occurrences like the dissolution of minerals and organic matter, as well as biological activities in water bodies. Elements such as Ca2+, Mg2+, and HCO3- found naturally in rainwater and in geological formations contribute to the hardness and pH balance of stream or river water.