Running-off with our Marine Biodiversity – The Impact of Agricultural Runoff Worldwide

Posted Jul 27, 2017 | Blog Post

Hello everyone and welcome back to the second installment of Turning a New Leaf, the new sustainability blog for TruLeaf!  For the next few months, I hope to take you on a journey across the world through the global state of agriculture as we examine the impacts that large-scale and greenhouse farming has had on our earth’s finite resources. This includes tackling topics from unsustainable global water use, to excessive deforestation for cropland, to even the impacts of global biodiversity loss. However, to start things off, today’s blog will focus on an issue that has all the aforementioned problems intertwined. It’s an issue that not only affects our marine life, but also the quality and health of our drinking water. That issue is agricultural runoff and subsequent ocean eutrophication caused by a combination of excessive fertilizer use and water irrigation.


Water irrigation is fundamental to all forms of farming. Irrigation is the artificial application of water to land for the purpose of agricultural production, and influences the entire crop growth cycle. Irrigation provides flexibility to farm operation systems since it allows farm land to produce higher crop yields, lengthens growing periods, and converts formerly unproductive dry land to crop-producing areas. However, heavy fertilizer use combined with excessive irrigation without proper water waste management leads to a process called agricultural runoff, which destroys many of our freshwater aquatic and marine ecosystems along with polluting the quality of our drinking water.


Agricultural runoff promotes and leads to eutrophication; a process whereby excessive plant and algae grow in lakes, rivers and other aquatic environments depleting oxygen levels and causing the death of many plant and animal species. This algal and plant growth is caused by excessive photosynthesis made possible by an increased nutrient availability from fertilizers, which enters these waters through cropland water runoff. While eutrophication occurs naturally over centuries in lakes and rivers as they age and fill with sediments, this unprecedented, rapid discharge of excessive nitrogen and phosphorus into marine environments (the largest components of farm fertilizer) is speeding up this process and having dramatic consequences on fisheries, aquatic life and human drinking sources.


Take for example the Gulf of Mexico “dead zone.” This water area has little to no oxygen within its borders and can kill fish and marine life that swim into its regions. In 2015, the ‘dead zone’ spanned 6,474 square miles of the Gulf and was above average in size than forecasted by various oceanic and atmospheric global agencies and watch-groups.

Map showing distribution of bottom-water dissolved oxygen from July 28 to August 3 2015. (Data: Nancy Rabalais, LUMCON; Eugene Turner LSU. Credit: NOAA)


The red to deep red areas in the figure above have very little to no dissolved oxygen in these aquatic ecosystems and have been created over years of agricultural and nutrient runoff from the Mississippi river. When there are heavy rains in the region, (like in 2015) there are higher rates of runoff and a larger than average dead zone. This dead zone is usually the size of the US states of Connecticut and Rhode Island combined, and is the second largest human-caused hypotoxic area in the world (out of more than 550 occurring annually worldwide). The largest dead zone is within the Baltic Sea and is comprised of seven out of ten of the world’s largest dead zones, and has too been caused by excessive agricultural fertilizer runoff and sewage-treatment waste pollution.


Normally, when issues such as this have such negative environmental impact, global preventative action is taken to halt its continuation. However, no substantial measures have been taken on this issue. Why? Well, the truth is in order to meet the food demands of a rapidly growing population, traditional farming and its associated fertilizers and irrigation systems are necessary. Between 1961 and 1999, land under irrigation has increased by 97 percent, nitrogen use in farming has increased by 638 percent, and phosphate fertilizer use has increased by 203 percent.  Nitrogen and phosphate are the two main nutrients that lead to algal blooms, low water oxygen, increased water acidity, and a loss in biodiversity. Furthermore, irrigation has been the largest contributor to increased food yield in the past half century; China, India and the US would all need two to three times more cropland for farming than at current rates if irrigation was not implemented.


So… what are we to do to then if our global food demand is destroying our marine habitats? Firstly, large-scale farms need to do more in ensuring proper water waste procedures in their irrigation systems and in employing more efficient systems to minimize water waste. Secondly, agricultural runoff can also occur through water waste runoff from animal waste from animal farming, and this must be effectively addressed moving forward. Lastly, new innovative technologies need to be harnessed and employed to reduce both the use of fertilizer, and the blind and broad use of irrigation.


Vertical farming, for example, leverages such technology through an irrigation system that combines water with the precise nutritional formula to feed the plant greens as they grow. This nutritional formula is optimized for plant growth and the water is reused and recycled at rates of 70 to 80 percent. Furthermore, the small amount of water that does go to waste has negligible amounts of nitrogen, phosphorus and other chemicals since the majority has been taken up by the plants. Through this technology, vertical farms produce no agricultural runoff and save our lakes and rivers from pollution and decay.


Have you ever encountered water bodies with dead-zones or seen the impacts of agricultural runoff in your local communities? Let me know where, and any other ways you believe we can put an end to this vicious cycle of run-offs and save our marine environments!


Author: Bojana Radan

Photo Credit: Creative Commons, Eutrophication&Hypoxia