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Example of a river, Tigris River near Hasankeyf, in Turkey. The Streeter–Phelps equation is used in the study of water pollution as a water quality modelling tool. The model describes how dissolved oxygen (DO) decreases in a river or stream along a certain distance by degradation of biochemical oxygen demand (BOD).
Decline of oxygen saturation to anoxia, measured during the night in Kiel Fjord, Germany. Depth = 5 m. 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
Decreased levels of dissolved oxygen (DO) is a major contributor to poor water quality. Not only do fish and most other aquatic animals need oxygen, aerobic bacteria help decompose organic matter. When oxygen concentrations become low, anoxic conditions may develop which can decrease the ability of the water body to support life.
The major zones in river ecosystems are determined by the river bed's gradient or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of dissolved oxygen , which supports greater biodiversity than the slow-moving water of pools.
BOD test bottles at the laboratory of a wastewater treatment plant. Biochemical oxygen demand (also known as BOD or biological oxygen demand) is an analytical parameter representing the amount of dissolved oxygen (DO) consumed by aerobic bacteria growing on the organic material present in a water sample at a specific temperature over a specific time period.
Red circles show the location and size of many dead zones (in 2008). Black dots show dead zones of unknown size. The size and number of marine dead zones—areas where the deep water is so low in dissolved oxygen that sea creatures cannot survive (except for some specialized bacteria)—have grown in the past half-century.
Riffles also serve to aerate the water, increasing the amount of dissolved oxygen in the body of water. [13] Water with high and relatively stable levels of dissolved oxygen is typically considered to be a healthy ecosystem because it can generally support greater biodiversity and total biomass.
They carry out part or all of their life cycle within the stream or river. Macro invertebrates limited mobility and extended presence in the water means that they are exposed on a continuous basis to water quality in that stream or river. In particular, many of these organisms breath dissolved oxygen that is in the water.