Eutrophication & Hypoxia

Eutrophication is the over enrichment of water by increasing amounts of nutrients, largely consisting of nitrogen and phosphorus, being put into it. The main contributor is industrial size agriculture, which uses large amounts of fertilizer. When it rains, the water washes fertilizer away with it, back into a river most likely headed for the ocean. Urban runoff is also a factor contributing to over enrichment of our water. The phosphorus and nitrogen from industrial farming going through a river ecosystem can cause other environmental problems such as freshwater quality impairments, acid rain, changes in local food webs, and a decrease in biodiversity. The Millenium Ecosystem Assessment (MA) found that human activities have resulted in the near doubling of nitrogen and tripling of phosphorus flows to the environment when compared to natural values. 

Once reaching the coast, the initial reaction of nutrient rich water is the excessive growth of phytoplankton, and both micro and macro algae. There are a range of problems that arise with this increase of phytoplankton, such as damage to coral reefs and a decrease in sub aquatic vegetation. The most severe consequence from eutrophication comes in the form of hypoxia. The algae and phytoplankton cause the dissolved oxygen levels to decrease to a point in which aquatic life cannot survive. Creatures that are stationary or are to slow to get out of the dead zone will suffocate. Hypoxia does occur naturally at times due to less dense fresh water failing to mix with more saline ocean water, therefore not sufficiently circulating the oxygen from higher to lower depths. Pictured left: This body of water shows the difference between moderately enriched (top) and eutrophic water (bottom).

This is a problem caused by more developed, industrialized countries like the US and China but the problem affects multiple countries. Under developed coastal countries whose economy as well as ones own livelihood may depend on the abundance of sea life is becoming at risk at no fault of their own. A loss and potentially collapse of aquatic ecosystems is the main concern in this bloggers mind. So what can we do to reverse the effects? Restoring natural environments like marshes and bogs is a way to reduce the amount of nutrients reaching the ocean. One of the most obvious way would be to decrease the amount of fertilizer we use on our farms, and also to use better drainage systems to reduce urban runoff. Technological advancements can play a huge role, as seen in 2001 at the Manchester Ship Canal in England, when a compressed air injection system was able to raise oxygen levels by up to 300%. 

Article found at: http://www.wri.org/project/eutrophication/about