Hypoxia (environmental) meters below the surface. Oxygen depletion can result from a number of natural factors, but is most often a concern as a consequence of pollution and eutrophication in which plant nutrients enter a river, lake, or ocean, and phytoplankton blooms are encouraged. While phytoplankton, through photosynthesis, will raise DO saturation during daylight hours, the dense population of a bloom reduces DO saturation during the night by respiration. When phytoplankton cells die, they sink towards the bottom and are decomposed by bacteria, a process that further reduces DO in the water column. If oxygen depletion progresses to hypoxia, fish kills can
The Limits to Growth over "The Limits to Growth" concluded in 1978 that optimistic attitudes had won out, causing a general loss of momentum in the environmental movement. While summarizing a large number of opposing arguments, the article concluded that "scientific arguments for and against each position ... have, it would seem, played only a small part in the general acceptance of alternative perspectives." In 1989, a symposium was held in Hanover, Lower Saxony, entitled "Beyond the Limits to Growth: Global Industrial Society, Vision or Nightmare?" In 1993, "Beyond the Limits" was published as a 20-year update on the original material. "Limits to Growth: