Dissolved Oxygen web-research nugget 01 (collected on 09052021)
https://www.sciencedirect.com/topics/engineering/dissolved-oxygen

Fundamentals of Quorum Sensing, Analytical Methods and Applications in Membrane Bioreactors
Reham M. Abu Shmeis, in Comprehensive Analytical Chemistry, 2018

1.7.2 Dissolved Oxygen
Dissolved oxygen (DO) refers to the level of free, non-compound oxygen (O2) dissolved in water or other liquids. The bonded oxygen in water (H2O) is in a compound and does not count toward dissolved oxygen levels. DO is an important parameter in assessing water quality because of its influence on the organisms living within a body of water. Oxygen gets into water by diffusion from the surrounding air, by aeration, or as a waste product of photosynthesis. DO is essential to the survival of organisms in a stream. The presence of oxygen is a positive sign and the absence of oxygen is a sign of severe pollution. Waters with consistently high dissolved oxygen are considered to be stable aquatic systems capable of supporting many different kinds of aquatic life (Davis and Cornwell, 2012; Weiner and Matthews, 2003).