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How can P runoff lead to a drinking water crisis? The case of Toledo, Ohio

August 20, 2014

Around 400,000 people in Toledo, Ohio are currently facing a drinking water crisis due to high levels of a dangerous toxin in their drinking water (1,2). The toxin is microcystin, released from a cyanobacterium Microcystis. A chain reaction following the blooming of the cyanobacteria exacerbates the water deterioration–the decomposition of the dead Microcystis consumes most of the oxygen in the water. This kills of almost all higher organisms since their lives depend on oxygen. The scientific term for this phenomenon is “eutrophication”.

A group of scientists in the Southern Extension and Research Activity – 17 (SERA-17) stated that the main cause of this algae bloom is P runoff from farmlands. Farming practices are particularly important in contributing to the P lost from the farm. Changing agricultural practices related to how and when to apply P fertilizer is crucial to solve the drinking water crisis in Toledo. In this article, I list some farming practices that could potentially be a source of P pollution and were discussed in SERA-17.

In the Maumee River watershed (as elsewhere), most of the P application is through chemical fertilizers. A common practice of applying chemical fertilizer is surface broadcast—a uniform application of P fertilizer on the soil surface. Surface application of P is prone to leaching by rainfall. When P fertilizer is applied in the fall combined with no-till practice, it becomes vulnerable to runoff through all winter. This could be prevented by occasional tillage to help with stratification and by less frequent but larger P applications.

Fertilizer application recommendations are set up in order to maintain agricultural productivity. However, these recommendations are often higher than what the crop actually needs. This has generally be done so as to keep farmers from coming back to the universities, extension offices, or fertilizer suppliers and complaining that their yield is lower due to low fertilization application recommendations.

Another potential source of P input to drinking water in Toledo is from decomposing vegetation during snowmelt or winter storm runoff either from no-till crop residue or the potentially large contribution from perennial, winter cereal, and cover crops. Besides the readily solubilized P released from the crop residues, organic P is another source that is converted by zebra mussels into inorganic P in Lake Erie.

The problem of toxic algae blooms is not just confined to the U.S., but has also been reported in several other parts of the world including China, Japan, Brazil, and Australia. Global climate change is also another potential threat for exacerbating such blooms, as increased temperatures and lake stratification also favor cyanobacteria. Identifying the hot spots of P runoff and reducing the amount of P in runoff are critical for improving water quality and preventing toxic algae blooms. Further improvements in farming practices can not only help us reduce P pollution but also help farmers save money by buying less P fertilizer without compromising marketable yield.


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