What generally causes an increase in taste and odors when natural waters lack dissolved oxygen?

An increase in taste and odors in natural waters, particularly when there is a lack of dissolved oxygen, is primarily attributed to anaerobic decomposition. This process occurs in environments where oxygen is limited, leading to the breakdown of organic matter by bacteria that do not require oxygen. These anaerobic bacteria produce a range of byproducts, including hydrogen sulfide and other volatile compounds that can create unpleasant tastes and odors.

In contrast, aerobic decomposition typically involves bacteria that thrive in oxygen-rich conditions, which generally results in fewer odorous byproducts. Acidic runoff can alter water chemistry but is not a primary cause for increased taste and odors due to oxygen levels. Similarly, while pollution from industrial waste can affect water quality, the specific increase in taste and odors due to low dissolved oxygen is more directly related to the processes of anaerobic decomposition.