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Environmental oxygenation can be important to the
sustainability Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livi ...
of a particular
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
. Insufficient oxygen ( environmental hypoxia) may occur in bodies of water such as
pond A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from tha ...
s and
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...
s, tending to suppress the presence of
aerobic organism Aerobic means "requiring air," in which "air" usually means oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, ...
s such as
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
. Deoxygenation increases the relative population of anaerobic organisms such as plants and some
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
, resulting in
fish kill The term fish kill, known also as fish die-off, refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (2005) ''Plant Management in Fl ...
s and other adverse events. The net effect is to alter the
balance of nature The balance of nature, also known as ecological balance, is a theory that proposes that ecological systems are usually in a stable equilibrium or homeostasis, which is to say that a small change (the size of a particular population, for example) w ...
by increasing the concentration of anaerobic over aerobic
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
. Oxygenation by water aeration can be part of the
environmental remediation Environmental remediation deals with the removal of pollution or contaminants from environmental media such as soil, groundwater, sediment, or surface water. Remedial action is generally subject to an array of regulatory requirements, and may al ...
of a usually stagnant body of water. For example,
Bubbly Creek Bubbly Creek is the nickname given to the South Fork of the South Branch of the Chicago River. It runs entirely within the city of Chicago, Illinois, U.S. It marks the boundary between the Bridgeport and McKinley Park community areas of the c ...
in
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = List of sovereign states, Count ...
,
Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rock ...
, was hypoxic (deficient in oxygen) due to its use as an open sewer by Chicago's meat packing industry but has been oxygenated by introducing compressed air into its waters, increasing the fish population. A similar technique has previously been used in the
Thames The River Thames ( ), known alternatively in parts as the River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the second-longest in the United Kingdom, after the R ...
. Dissolved oxygen (DO) is measured in standard solution units such as millilitres O2 per litre (mL/L), millimoles O2 per litre (mmol/L), milligrams O2 per litre (mg/L) and moles O2 per cubic meter (mol/m3). For example, in freshwater under atmospheric pressure at 20 °C, O2 saturation is 9.1 mg/L. In aquatic environments, oxygen saturation is a relative measure of the amount of
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
(O2) dissolved in the water compared to equilibrium conditions.
Supersaturation In physical chemistry, supersaturation occurs with a solution (chemistry), solution when the concentration of a solute exceeds the concentration specified by the value of solubility at Solubility equilibrium, equilibrium. Most commonly the term ...
of oxygen (i.e. saturation levels above 100%) can occur naturally. The most common cause is oxygen production by photosynthetically active species such as plants and algae. According to Henry's law, the equilibrium oxygen concentration is proportional to the partial pressure of oxygen gas. As air contains about 21% oxygen the equilibrium concentration of pure oxygen gas corresponds to nearly 500% air saturation. The other reason is that the oxygen concentration can be slow to adjust to changes in the environment. A rapid increase in temperature can reduce the equilibrium concentration of oxygen to a value below the actual concentration in the water, giving raise to more than 100% saturation until the system has had time to equilibrate through
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...
. Supersaturation can sometimes be harmful for organisms and cause decompression sickness. Solubility tables (based upon temperature) and corrections for different salinities and pressures can be found at the USGS web site. Tables such as these of ''DO'' in millilitres per litre (mL/L) are based upon empirical equations that have been worked out and tested: :\ln(DO) = A_1 + A_2*100/T + A_3*\ln(T/100) + A_4*T/100 + S\left(B_1 + B_2*T/100 + B_3*(T/100)^2\right) where ln is the symbol for natural logarithm and the coefficients take the following values: To convert the calculated ''DO'' above from mL/L to mg/L, multiply the answer by (P/T)*0.55130, P=mmHg, T=Kelvin


Measurement

DO levels are typically measured using "rugged dissolved oxygen" (RDO) equipment which measures luminescence quenching ability of a sample. Increased oxygen levels result in increased quenching which is well characterised and allows accurate measurements to be made with a probe which requires minimal maintenance. Prior to the development of RDO technology membrane redox technology was used which measured oxygen levels using a clark electrode. Electrochemical equipment requires considerable maintenance to remove fouling and prevent degradation of the membrane. Redox methods may also display some cross-sensitivity to other gases such as . For small or low concentration (less than 2 ppm) samples RDO equipment is significantly better as it does not consume oxygen in the sample (and therefore does not require stirring) or struggle to measure zero-levels. Wet chemistry methods such as the
Winkler test for dissolved oxygen The Winkler test is used to determine the concentration of dissolved oxygen in water samples. Dissolved oxygen (D.O.) is widely used in water quality studies and routine operation of water reclamation facilities to analyze its level of oxygen satur ...
can also be used for DO measurement but as with all wet chemistry measurements these require a skilled technician to obtain accurate results.


See also

* Oxygenate * Streeter-Phelps equation


References

{{reflist


External links


Dissolved Oxygen Explained
Hydrology ca:Oxigenació