Manure and Algal Blooms

In my first blog, I discussed how fertilizer run off is ending up in bodies of water and leading to algal blooms. Well in most cases, this fertilizer is manure; therefore, this is a problem that needs to be addressed by the animal agriculture industry.

Before we get into the nitty gritty of the solutions let me explain the problem a little more. Algal blooms are caused by a process called eutrophication. Eutrophication is the enrichment of a body of water with the nutrients of nitrogen and phosphorus. Normally these nutrients are in small enough concentrations to limit the growth of algae. Agricultural runoff and other sources of nutrient pollution raise the amount of these nutrients high enough to allow for rapid proliferation. Algal blooms are problematic because, not only do they deplete oxygen levels and create uninhabitable “dead zones,” some can be toxic. Blue-green algae or cyanobacteria can release toxins that can sicken or kill people and animals (Harmful).

In agriculture, manure is the largest source of this type of pollution. Nutrients fed to production animals either end up in the products sold from the farm or in the manure. The manure is then applied to crops as fertilizer where the nutrients are ideally taken up by plants. However, some of the nutrients are inevitably either lost through runoff or leeched into the groundwater where they can eventually wind up in local bodies of water.

For nutrient pollution to occur, there needs to be a source and a mode of transport. We can limit the source by adjusting manure application to correctly meet the nutritional needs of the crops it is being applied to. By knowing exactly how much plants can uptake, we can reduce the amount of excess nutrients that are being added to the environment. One caveat is that crops need each nutrient, nitrogen and phosphorus, in different concentrations. When this happens, fields can be tested to evaluate the risk of each application rate. The tests look at two factors that affect the risk of nutrient pollution: source and transport. Field evaluation for source largely looks at the current phosphorus content of the soil. Based on the results it may be determined to apply manure to balance these levels or even determined that manure can not be applied at all and that commercial fertilizer must be used to supplement nitrogen levels. Secondary field evaluations are then done to look at the likelihood of transport. If the risk for transport is found to be low then it may be determined that manure can be applied in excess of necessary phosphorus levels (Nutrient Management Planning). The case with nitrogen is slightly different. Due to its chemical properties, it is more likely to be transported than phosphorus. For this reason, some states, including Pennsylvania, have regulations in place that prohibit producers from applying nitrogen in excess (Nutrient Management Legislation).

Due to topography, some fields naturally have a low transport risk. However, producers can reduce the risk even more by adjusting application procedures. First, by applying manure when crops are ready to use it (close to the growing season) will reduce losses. Also, incorporating the manure into the soil can reduce the chance it will runoff (Nutrient Management Planning). This can be done by different machines and can include injecting liquid manure into the soil or cutting trenches into the soil.

All these solutions are focused on what crop producers can do to limit nutrient pollution. While some animal producers do grow feed crops, the specialization of the industry is reducing the number of producers that do. This is not to say these producers do not have a place in helping with the nutrient pollution problem. From the beginning it is important to limit the amount of nutrients lost in manure. These means producers can limit feed inefficiencies such as unconsumed or non-digestible portions of feed. By using feeders that limit lost food or by using feed that is more digestible, livestock producers can reduce the amount of nutrients that end up in manure. Also, manure storage is incredibly important because it can help to reduce the chance of run-off before application to fields. By storing manure under cover, in tanks, or far from water ways, producers can significantly reduce their contribution to nutrient pollution.






“Harmful Algal Blooms.” EPA, Environmental Protection Agency, 7 Apr. 2017,

“Nutrient Management Legislation in Pennsylvania.” Penn State Extension, .

“Nutrient Management Planning: An Overview (Pennsylvania Nutrient Management Program).” Penn State Extension,

5 thoughts on “Manure and Algal Blooms”

  1. In my Biology 110 class last semester we learned about algal blooms, and went slightly in depth into the concept, but definitely not as detailed as I would have like to hear about. Mostly because environmental issues and biology can be so intertwined, and I personally think it’s important to learn as much as we can. But alas, we were on a tight schedule that every “weed-out” introductory science course is known for. Thanks for giving me more to learn about the situation!

  2. It’s awesome that you explained several ways to minimize fertilizer runoff and the subsequent algal blooms, because I feel like everywhere I hear about this, there are no solutions proposed. But these solutions sound doable and definitely within reach, so I have hope that these problems can be dealt with in the near future!

  3. Wow i have never seen a picture like the first one that has algae spreading over the water. I never knew algae could spread that large as I thought it was mostly on ponds that had stagnant water. There are some great solutions in there that can really help save animal lives and stop the pollution of water.

  4. Every time I read your blog I’m so impressed with how knowledgeable you are on the subject. I think the agricultural field is oftentimes overlooked in this area because it is just generally overlooked in life (which I think is horrible considering how important the ag industry is). I also think it’s so interesting reading your blog because it highlights just how complex the problem, and more specifically industry, is even though the ag industry is often dismissed in terms of complexity. Although I definitely don’t know all the answers, your blog definitely helps me better understand all sides of the issue, particularly when this stuff isn’t what we learn about from the news.

  5. It is always nice to be informed on a very large problem that affects, if not everyone, than most people in the world. Eutrophication/algal blooms were something that I learned about in my Biology II and AP Biology classes in high school, and that they are a huge problem. I will always remember the story my teacher told me about her pond that she had going through this process and becoming a field, which can be very bad. I am glad you went through some proposed suggestions on fixing these problems, as that is something that is very much needed.

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