Nitrogen and phosphorus are naturally occurring nutrients that every plant and animal needs to grow and survive, so how can they be bad? Well, in the normal natural cycle, the levels of nitrogen and phosphorus are minute, I’m talking like five parts per million (ppm). But, humans have found several ways to alter the nitrogen and phosphorus cycles. One study by S.R. Carpenter (professor of Limnology at the University of Wisconsin) and his research team states, “nutrient enrichment seriously degrades aquatic ecosystems and impairs the use of water for drinking, industry, agriculture, recreation, and other purposes.” That is a pretty inclusive list of all the things water is good for, so maybe we should look at our nitrogen and phosphorus manipulation.
The most prolific cause of nitrogen and phosphorus pollution is through fertilizers (mainly by industrial agriculture, but by our backyard gardens too). That is not the only way that nitrogen and phosphorus get added to the system. Human waste and animal manure are also large fluxes for nitrogen. Human waste finds its way into the system through our sewers and septic tanks that do not always operate properly. Animal manure finds its way into the water through runoff and groundwater seepage. Phosphorus can also be added through cleaning products such as laundry or dishwasher detergents that have phosphates in them that the water treatment facilities cannot remove. Lastly, cities overall can be a place of nitrogen and phosphorus addition.
Let’s start with the largest problem: industrial agriculture. A study conducted by R.W Howarth (professor of Ecology and Systematics at Cornell University), A.N. Sharpley (Pasture and Watershed Systems Management Research Lab) and D. Walker (on the Oceans Study Board at The National Academies in Washington D.C.) in 2002, illustrated that in industrial agriculture soil the nitrogen levels can be three times the norm and in heavily polluted areas up to eight times higher. In addition, the global flux of phosphorus prior to phosphorus fertilizer use was eight teragrams per year. With the addition of fertilizers by farming, that figure is up to 22 teragrams per year. A teragram is 1,000,000,000,000 grams (this increase is definitely something to be concerned about). This large of an addition to the natural cycle is worrisome because when the natural cycle is used to having such as small about of nitrogen and phosphorus it does not know how to adapt to the large amount except by making uncommon events such as algae blooms common.
To help put nutrient pollution in perspective, the study conducted by Howarth et al. (2002) looked at the increase of nitrogen fixation compared to CO2 fixation from 1900 to 1980. At the turn of the century, the human input of nitrogen was small compared to what it is now. This is because, before World War One, humans had not figured out how to artificially make nitrogen or ammonia, both of which are needed to make fertilizer, until the invention of the Haber-Bosh process (named after it’s creators). Even though the artificial nitrogen arrived on the scene almost 100 years after the industrial revolution, nitrogen fixation has skyrocketed past CO2 fixation. By 1960 nitrogen fixation would reach a 20 percent increase from pre-1900 values, a number that CO2 fixation would not reach until the end of the study at 1980. Nitrogen fixation continued to climb exponentially to a 95 percent increase by 1980 (Howarth et al. 2002). That is 60 teragrams of nitrogen fertilizer a year.
So those numbers were from 1980, let’s look at more recent data to better understand our current situation. A study done by S. Fields (2004) found that nitrogen fertilizer now adds 100 teragrams of nitrogen to the natural cycle every year and that that value will increases by 15 teragrams annually. The natural nitrogen cycle only produces 140 teragrams of reactive nitrogen a year. If we continued on that path of 15 teragrams a year since 2004 we are now adding 310 teragrams of fertilizer a year, more than doubling the natural cycles input. A change this drastic to such a fundamental cycle could send shock waves up the food web affecting all the cycles around it.
Phosphorus is a little different than nitrogen. In that phosphorus is usually rarer, so aquatic and terrestrial ecosystems have evolved to work with shortages. In addition to the fertilizer, phosphorus is added to the natural cycle in various ways. For example, many commercial laundry detergents used to have phosphates in them before countries started to ban their use because of pollution concerns, but most dishwashing detergents still have phosphates in them. Phosphorus-rich pet waste and garden fertilizers can also find their way into rivers, lakes, and streams through storm drains.
A major downfall of cities is that they are much more susceptible to runoff than undeveloped (natural) land because concrete does not absorb water, therefore any rain or snow that falls in a city finds its way to the nearest body of water or storm drain. The storm runoff carries all the pollutants from the yards and parking lots into the nearby rivers and streams. Some sewer and storm drains are actually designed to dump excess untreated sewage into nearby rivers, lakes, and streams in heavy storm events to avoid massive overflow. This system failsafe is known as “combined sewage overflow” (EPA). Dumping untreated sewage and waste into our rivers causes a massive influx of nitrogen and phosphorus because most of the nitrogen and phosphorus our body excretes it does so through urine and feces. In total the average human excretes 4 kilograms of nitrogen and .5 kilograms of phosphorus a year. Now that might not seem like a lot when we have been talking about teragrams, but when an entire city’s waste is not being cleaned, that can result in millions of kilograms of nitrogen and phosphorus getting dumped into the waterways (Del Porto D. & Steinfeld C. 1999).
One heavily polluted lake near Atlanta, Georgia is the result of the city’s poorly treated water and combined sewage overflows. West Point Lake is a 40 square mile lake and located 60 miles downstream of Atlanta, Georgia. A study conducted by P.P. Emmerth, and D.R. Bayne (1996), both professors at the University of Alabama studying fisheries and aquacultures, found that 97 percent of the total phosphorus in the lake came from the study designated “upper sub-basin area”- from Franklin, Georgia to the headwaters of the Chattanooga River, and only three percent came from the “lower sub-basin” (from the headwaters to the lake). Of the 97 percent, 91 percent was from the Atlanta area.
The ninety-one percent of the pollution that was coming from Atlanta was mostly the result of the major city’s outdated and breaking sewage system, and the refusal by the city to update it. Instead of paying for the updates the city of Atlanta decided they would just pay the fined slapped on them by the EPA every year, shelling out millions of dollars in fines and dumping billions of gallons of untreated sewage into the waterways over the several year period of protest. Each year from 1900 until 1998 (when the Chattanooga River-keeper won the lawsuit against the city) the dilapidated sewage system dumped 400 million gallons of untreated sewage a year into the river, and within that yearly sewage was also 4 million tons of phosphorus (Inglis et al., 2014). Now, 16 years after the lawsuit, the city of Atlanta’s untreated sewage spills are down by 99 percent, but how is the lake? Luckily after the lawsuit, the city kicked it into high gear fixing almost all the leaky pipes and the lake as returned to safe swimming and fishing levels and is now under strict monitoring in several different locations along the river and in the lake to ensure the levels stay low and to be on top of any changes (Inglis et al., 2014). West Point Lake, even though it saw massive pollution with tons of phosphorus, the conditions were no right to create algae bloom because of the vast amounts of raw sewage and other pollutants in the water.
However, there is one lake has been seeing massive algae blooms over the past three decades: Lake Erie. Lake Erie is unfortunately surrounded by large-scale industrial farming operations and towns. This means that most of the fertilizer runoff and seepage makes its way to the Lake, resulting in high levels of nitrogen and phosphorus. The nitrogen and phosphorus that gets dumped into our rivers and lakes and the resulting algae blooms can result in toxic water condition for both the animals living in and around the water and the people surrounding the river and lake trying to swim or fish in the water. A bloom becomes toxic when it consists of Blue-green algae. Blue-green algae can be made up of cyanobacteria that produce a neurotoxin called microcystins that dissolves nervous tissue in mammals (F.S. Chapin et al., 2011). When the concentration is too high the water treatment facilities cannot remove all the toxins, and cities might have to tell residents to stop drinking the water for several days.
This happened during the summer of 2011 when Lake Erie experienced one of the largest and most toxic blooms the lake has ever seen. This bloom was almost entirely made up of microcystins. At the blooms peak, it was four times larger than the average bloom and two and a half time larger than the previous largest bloom. A study done by Anna M. Michalak and her research team (2013) found that the bloom was way more toxic than the normal blooms. This bloom in 2011 had a microcystin surface toxin concentration of 4,500 micrograms per liter. The world health organization has a guideline for average microcystin concentration of 20 micrograms per liter. This increase in toxicity and size is becoming the trend for the algae blooms in Lake Erie because of the warming temperature and the constantly increasing levels of nitrogen and phosphorus (Michalak et al., 2013). If the blooms continue to become more toxic, the harmful health effects caused by the microcystins will become more prevalent. Greater measures will have to be taken just to keep the blooms where they are.
Fortunately, blooms usually do not create toxic water conditions, typically the algae bloom uses up all the available oxygen (mainly when the algae dies) killing all the fish in the surrounding waters known as a “fish kill.” This might seem like the better form of algae blooms, but these types of blooms still create dead zones, also known as hypoxia, hundreds of square miles wide. Dead zones are the area underneath and around the bloom that becomes unlivable for anything but the algae and continues to be unlivable after the algae die. This might seem confusing if you know how photosynthesis works because plants like algae are supposed to use carbon dioxide to create energy and then respire oxygen. However, Tim Seastedt, professor of Ecology at the University of Colorado Boulder, explains the process like this. At the beginning of the bloom when the algae are still alive, there are niches within the bloom that instead of using CO2 they use oxygen to create energy. They do this because, with the massive spread of algae, the group is bound to use up all the available CO2, so some have to switch to oxygen (basally reversing the traditional respiration cycle) a process know as anaerobic respiration. Then when the bloom dies after a week or so the algae begin decomposing. During the decomposition process, the microbes in charge of decomposing gather up all the oxygen for themselves before it has a chance to diffuse into the organic compounds needed by fish and plants to grow. Lake Erie has and there is evidence it will continue to experience both toxic and non-toxic algae blooms for the foreseeable future.
A study conducted by Jeff Ho and Anna Michalak (2017), both Stanford professors specializing in Environmental Engineering and Global Ecology respectively, looked at the relationship between algae blooms caused by both long-term and springtime phosphorus loading. They found that the long-term loading of the yearly phosphorus might be accumulating in the water for up to ten years. This means that the susceptibility of the Lake to larger and more intense algae blooms is increasing as we keep adding more and more phosphorus to the system. Ho and Michalak (2017) after discovering this pattern state, “in order to achieve mild bloom conditions the total dissolved phosphorus in the lake would have to drop 58 percent from its 2001-2015 average.” Mild bloom conditions are defined as blooms smaller than 600 square kilometers nine out of ten years (to me this seems more than mild, but we’ll trust the experts).
Ho’s and Michalak’s (2017) discovery is important to the overall knowledge of phosphorus pollution because before this study it was thought that most of the phosphorus loading — the time when most of the phosphorus is added — occurred during the spring when industrial farming is in full bloom as well. But what they discovered is that it is not just this year’s springtime influx that matters, but that the fluxes from the past ten years could still be loading up in the system adding to the current intensity of algae blooms. This discovery will affect the way environmental agencies think about phosphorus management and bloom prevention because this adds to evidence that nutrient-polluted lakes are tipping-point ecosystems. Tipping-point systems are ecosystems that will load and load and seem to be functioning normally, but then something will set them off and they will shoot up in nitrogen fixation causing algae blooms. After the bloom, the ecosystem never returns to normal and operates in an elevated nitrogen state which makes them very susceptible to future algae blooms (F.S. Chapin et al., 2011).
Nitrogen and phosphorus are necessary building blocks for life but when we let them get out of hand they can also be the wrecking ball that brings down a whole ecosystem. As industrial farming grows to feed our the growing population, stricter fertilization laws will need to be put in place to ensure we don’t lose the water ecosystems. In my opinion, we need to take a closer look at natural ways in increasing crop yields. For example, we can have fallow fields, a practice that used to be popular before artificial fertilizers, in which the farmer sections off a portion of their land that they will not grow on for a season to replenish the nutrients. Another option is to get away from monocultures. It is proven that we can mix in nitrogen and phosphorus-depleting plants with plants that actually add nitrogen and phosphorus back to the soil and see similar grow yields. The steps needed to change the course of nutrient pollution are within our grasp. We need to rally together to save our global waterways.
Carpenter, S.R., Caraco, N.F., Correll, D.L., Howarth, R.W., Sharpley, A.N, & Smith, V.H. (1998) Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen. Ecological Society of America, 8, 559-568.
Chapin, F.S., Matson P.A., & Vitousek P.M. Principles of Terrestrial Ecosystem Ecology: second edition. Springer-Verlag, NY. 2001.
Del Porto, D., Steinfeld, C. 1(999). The Composting Toilet System Book. Ecological sanitation, Balingsholm, Sweden. Workshop.
Emmerth, P.P. & Bayne, D.R. (1996). Urban Influence on Phosphorus and Sediment Loading of West Point Lake, Georgia1. Journal of the American Water Resources Association, 32, 145-154.
Ho, J.C. & Michalak, A.M. (2017). Phytoplankton Blooms in Lake Erie Impacted by Both Long-term and Springtime Phosphorus loading. Journal of Great Lakes Research, 43, 221-228
Howarth, R.W., Sharpley, A., & Walker, D. (2002). Sources of Nutrient Pollution to Coastal Waters in the United States: Implications for Achieving Coastal Water Quality Goals. Estuaries and Coasts, 25, 656-676.
Inglis, J., Van Heeke, T., Weissman, G., & Hallock, L., Rumpler, J. (2014). Waterways Restored: the clean water act’s impact on 15 American lakes, rivers, and bays. Environment America Research and Policy Center,
Michalak, A.M., Anderson, E.J., Beletsky, D., Boland, S., Bosch, N.S., Bridgeman, T.B., Chaffin, J.D., Cho, K., Confesor, R., Daloğlu, I., DePinto, J.V., Evans, M.A., Fahnenstiel, G.L., He, L., Ho, J.C., Jenkins, L., Johengen, T.H., Kuo, K.C., LaPorte, E., Liu, X., McWilliams, M.R., Moore, M.R., Posselt, D.J., Richards, R.P., Scavia, D., Steiner, A.L., Verhamme, E., Wright, D.M., & Zagorski, M.A. (2013). Record-setting Algal Bloom in Lake Erie caused by Agricultural and Meteorological Trends Consistent with Expected Future Conditions. Proceedings of the National Academy of Sciences of the United State of America, 110, 6448-645.
The EPA family of sites. The nutrient pollution discharge elimination systems site (NPDES). The combined Sewage overflow site (CSO). 2018. https://www.epa.gov/npdes/combined-sewer-overflows-csos
Timothy Seasedt. Ecosystem Ecology: 4155, 2 April 2018, University of Colorado Boulder, Boulder, CO. Lecture.