Eutrophication

Definition

Eutrophication, is the process of excessive richness of growth limiting nutrients (Nitrogen or Phosphates) in a lake or other body of water that results in the dense growth of aquatic plants or algae that results in the depletion of dissolved oxygen in that body of water. This lack of dissolved oxygen often results in the death of many organisms that rely on higher concentrations of oxygen in the water. Eutrophication occurs naturally over the course of many years, but can be accelerated by human activities - a phenomenon known as cultural eutrophication. Of these anthropogenic activities, agricultural runoff from fertilizers and the dumping of waste water are some of the leading causes of cultural eutrophication.

Causes

Naturally occurring eutrophication is a geological process that takes place over the course of hundreds of years, it has been influenced and accelerated due to human activities. As a result of anthropocentric impacts, cultural eutrophication significantly alters millions of lakes and bodies of water across the planet. Cultural eutrophication occurs through either non-point source or point source pollution, at the hands of humans. [2] Examples of point-source or non-point source pollution that increase the rates of eutrophication can include, detergents, fertilizers, or sewage which can come from almost anywhere whether it be parking lots and roads or agricultural fields. [3][4] One of the most problematic of these tends to be the synthetic fertilizers that are used primarily in the cultivation of agricultural fields and grass lawns. Not to mention, clearing of land as well as the building of cities and towns leads to sediment runoff which worsens the rates at which phosphates and nitrates make their way into bodies of water. [5]

Consequences

Because of this sudden flux of nutrients, plant life, especially algae, are permitted to flourish. It is when these organisms die, though, that they will quickly begin to decompose. Oxygen is consumed during the decomposition process, reducing the overall oxygen concentration in the water. In turn, this lack of available oxygen within the water affects the ability of many fish as well as other aquatic animals and plants to survive or thrive within the ecosystem. Overall biodiversity is lowered as a result. Furthermore, the dead algae and other plant material will often settle at the bottom of the body of water where it will undergo anaerobic digestion. This anaerobic digestion releases greenhouse gases like that of methane and carbon dioxide which are incredibly harmful to the atmosphere and the Earth as a whole. [6] Because of the large scale displacement of sediment, cultural eutrophication is extremely detrimental to the integrity of terrestrial soil habitats as well.

Prevention & Reversal

Despite its ability to devastate marine habitats, cultural eutrophication can be slowed and potentially reversed. There have been phosphorus removal measures taken in Finland which have been said to have had a 90% success rate. [7] Others have proposed encouraging the growth of shellfish populations due to the fact that these organisms take nitrogen out of the water, acting as natural filters and reducing the likelihood of algal blooms.[8] Reducing the harmful effects of non-point source pollution are some of the most widely supported methods of slowing the rates of eutrophication. Some of these methods include riparian buffer zones and organic farming.

Buffer Zones

Buffer zones, specifically riparian buffer zones, are meant to act as a filter to prevent non-point source pollution from contaminating a water source in the first place. [9] Rather than being a man-made structure, a riparian buffer zone is an area of natural vegetation along the bank of the stream/river[10] like that of a mangrove forest in Southern Florida.

Organic Farming

Organic farming is said to be another very effective method of slowing the rates of anthropogenic eutrophication due the non-existent use of synthetic, nitrogen rich fertilizers. A study found that fields that were fertilized through organic means were not nearly as harmful as more conventional farming practices in terms of nitrate leaching.[11]

References

1. Eutrophication. (n.d.). . Merriam-Webster. https://www.merriam-webster.com/dictionary/eutrophication.

2. Chislock, M. F., Doster, E., Zitomer, R. A. & Wilson, A. E. (2013) Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems. Nature Education Knowledge 4(4):10

3. Callisto, Marcos; Molozzi, Joseline and Barbosa, José Lucena Etham (2014) "Eutrophication of Lakes" in A. A. Ansari, S. S. Gill (eds.), Eutrophication: Causes, Consequences and Control, Springer Science+Business Media Dordrecht. doi:10.1007/978-94-007-7814-6_5. ISBN 978-94-007-7814-6.

4. Muir, P., 2012. Eutrophication [WWW Document]. Oregon State University. URL http://people.oregonstate.edu/~muirp/eutrophi.htm

5. Schindler, David W., Vallentyne, John R. (2008). The Algal Bowl: Overfertilization of the World's Freshwaters and Estuaries, University of Alberta Press, ISBN 0-88864-484-1.

6. Tittmann, A., n.d. Climate gases from water bodies [WWW Document]. IGB. URL https://www.igb-berlin.de/en/news/climate-gases-water-bodies

7. Räike, A.; Pietiläinen, O. -P.; Rekolainen, S.; Kauppila, P.; Pitkänen, H.; Niemi, J.; Raateland, A.; Vuorenmaa, J. (2003). "Trends of phosphorus, nitrogen and chlorophyll a concentrations in Finnish rivers and lakes in 1975–2000". Science of the Total Environment. 310 (1–3): 47–59. Bibcode:2003ScTEn.310...47R. doi:10.1016/S0048-9697(02)00622-8. PMID 12812730.

8. Kroeger, Timm (2012) Dollars and Sense: Economic Benefits and Impacts from two Oyster Reef Restoration Projects in the Northern Gulf of Mexico Archived 2016-03-04 at the Wayback Machine. TNC Report.

9. Carpenter, S.R.; Caraco, N.F.; Smith, V.H. (1998). "Nonpoint pollution of surface waters with phosphorus and nitrogen". Ecological Applications. 8 (3): 559–568. doi:10.2307/2641247. hdl:1813/60811. JSTOR 2641247.

10. Importance of Riparian Buffers. 2019. . https://dep.wv.gov/WWE/getinvolved/sos/Pages/RiparianMagic.aspx.

11. Kramer, S. B. (2006). "Reduced nitrate leaching and enhanced denitrifier activity and efficiency in organically fertilized soils". Proceedings of the National Academy of Sciences. 103 (12): 4522–4527. Bibcode:2006PNAS..103.4522K. doi:10.1073/pnas.0600359103. PMC 1450204. PMID 16537377.