Eutrophication

Definition

Eutrophication is the process of excessive nutrients building up in a body of water and resulting in the dense growth of aquatic plants and algae. This leads to the depletion of dissolved oxygen in that body of water. The most common nutrients involved in eutrophication are nitrogen and phosphates. A lack of dissolved oxygen often results in the death of many organisms that rely on higher concentrations of oxygen in the water. [1]

Causes

Eutrophication occurs naturally over 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 wastewater are some of the leading causes of cultural eutrophication. Normally, phosphorus or nitrogen concentrations in the water are low enough to prevent aquatic plants or algae from growing out of control. However, fertilizers are designed to be rich in phosphates or nitrogen (plant specific) to aid in the growth of crops and produce higher yields. Natural events, such as rain, can carry these chemicals via runoff to ponds or lakes which effectively removes the limiting growth factor of the local plant and algae population allowing exponential growth. [13]

Consequences

This rapid increase in plant and algae population produce harmful algal blooms that pose serious threats to more than just the quality of water. Some algal blooms release toxins that can kill fish, birds, and mammals that drink the effected water causing detriment to the entire ecosystem. In extreme cases, these toxins may even cause severe human illness or death. [12] While not all algal species are toxic, algae reduce the levels of dissolved oxygen when they die and enter through the decomposition process. 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 within the ecosystem. Overall biodiversity can be lowered as a result and significantly modify the local food chain. 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 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 because 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 is one of the most widely supported strategies for 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 for slowing the rates of anthropogenic eutrophication due to 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 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.

12. Morris, J. G. Harmful algal blooms: an emerging public health problem with possible links to human stress on the environment. Annual review of Energy and the Environment 24, 367-390 (1990)

13. Michael F. Chislock (2013) Eutrophication Causes, Consequences, and Controls in Aquatic Ecosystems - Nature Education