Question Keegan Science
Dissolved Oxygen and Turbidity – An Inverse Relationship
What is the relationship between Dissolved Oxygen and Turbidity?
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Turbidity describes the degree of haziness or cloudiness of a fluid, caused by particles suspended within it (Park, 2007). In bodies of water, turbidity can be used as a measure of quality; with higher turbidity indicating lower quality, and less turbidity (and therefore higher clarity) indicating higher quality (EPA, 2003). Dissolved oxygen (DO) describes the amount of gaseous oxygen (O2) dissolved in water and held in solution (Allaby, 2015). Highly turbid water contains less DO, whilst less turbidity correlates with more DO. Oxygen is among the most vital environmental factors in supporting life (Environmental Protection Agency (EPA), 2003), and water quality and DO levels are key determinants of survival, growth and reproduction of aquatic organisms. Generally, levels of DO decline with increasing pollution (Allaby, 2015). As such, conditions of high turbidity and low levels of DO negatively impact aquatic species. Low DO concentrations cause reduced growth rates, altered distributions and behaviours, and increased mortalities of aquatic organisms; which in turn lead to significant alterations in aquatic ecosystems (Breitburg 2002). DO concentrations of 5 parts per million (ppm) are recommended for healthy aquatic vegetation and fish, (Francis-Floyd, 1992). When DO concentrations drop to 2 ppm or below, aquatic organisms become stressed; below 1 ppm can be fatal (Francis-Floyd, 1992).
Rising water turbidity limits light penetration through water, limiting aquatic photosynthetic potential (Skidaway Institute of Oceanography, 2016) and reducing oxygen content. This again illustrates the negative relationship between DO and turbidity. It also means that gross primary production (GPP) decreases with increasing turbidity (Hall et al, 2015; Figure 1). This negative correlation is paralleled by the concomitant negative correlation between decreasing DO and increasing turbidity. In conclusion, there is an inverse relationship between turbidity and DO, and this relationship can be observed and measured readily in aquatic ecosystems.
Figure 1. Graph illustrating the declines in gross primary production (GPP) observed with increasing turbidity in the Colorado River, Grand Canyon. Taken from Hall et al, 2015.
ReferencesAllaby, M., 2015. A Dictionary of Ecology, 5th Edition. Oxford University Press: http://www.oxfordreference.com.ezproxy.library.qmul.ac.uk/view/10.1093/acref/9780191793158.001.0001/acref-9780191793158-e-1647?rskey=2G2Vff&result=3 [Accessed 15th November 2016]
Breitburg, D. L. 2002. Effects of hypoxia, and the balance between hypoxia and enrichment, on coastal fishes and fisheries. Estuaries: 25; 767-781.
Environmental Protection Agency (EPA), 2003. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
http://www.chesapeakebay.net/content/publications/cbp_13142.pdf [Accessed 15th November 2016]
Francis-Floyd, R., 1992. Fisheries and Aquatic Series. University of Florida: http://edis.ifas.ufl.edu/fa002 [Accessed 15th November 2016]
Hall, R. O., Yackulic, C. B., Kennedy, T. A., Yard, M. D., Rosi-Marshall, E. J., Voichick, N., Behn. K. E., 2015. Turbidity, light, temperature, and hydropeaking control primary productivity in the Colorado River, Grand Canyon. Limnology and Oceanology: 60 (2); 512–526
Park, C., 2007. A Dictionary of Environment and Conservation, 1st Edition. Oxford University Press: http://www.oxfordreference.com.ezproxy.library.qmul.ac.uk/view/10.1093/acref/9780198609957.001.0001/acref-9780198609957-e-8468 [Accessed 15th November 2016]
Skidaway Institute of Oceanography, 2016. Dissolved Oxygen (DO) Tutorials: http://ossabaw.skio.usg.edu/content/tutorial_DO.php [Accessed 15th November 2016]