The following is in response to the watershed management issue in the Gulf of Mexico, where the water’s quality is greatly affected by eutrophication.
Buffering is an excellent method of reducing hypoxia levels in the Gulf and is certainly less harmful than the use of cheap fertilizers, but there are many problems contributing to hypoxia in the Gulf and removing these factors may not be enough to fix what has already been done. The government has been using buffering since the 1960s, yet not only has hypoxia subsisted, but the dead zones have grown larger over time. This is because buffering prevents point source pollution, when watersheds like the Gulf are affected by nonpoint source pollution. A much larger issue is the excess nutrient loading in the Gulf, a problem systemic of human interaction with the watershed. Sewage and wastewater treatment plants pump excess nutrients into our rivers. Fertilizer, cheap or not, grows crops that provide nutrients to rivers that flow to the Gulf. The excess nutrients cause algae to form. When too much algae forms, blooms occur, which sink to the bottom of the river and produce bacteria. The new bacteria eat away at the oxygen levels in the water, and forms hypoxia. On top of that, the addition of fresh water from the Mississippi river causes stratification, which is described by the director of the Competitive Research Program for the NCCOS, Alan Lewitus in the article, Dealing with Dead Zones: Hypoxia in the Ocean. Here Alan states,
“Stratification often occurs when fresh water is loaded into a system which creates a barrier for mixing, so the fresh water sits on top of the more saline water. So bottom waters are restricted from mixing from high-oxygenated surface waters. That combination of high stratification and high nutrient loading are the factors that, in combination, can lead to your most problematic hypoxic zones.”
Nutrient loading and stratification are not only affected by human intervention (sort of). As climate change increases, storms and precipitation can carry fresh water and nutrients into river waters. So how can we go about reducing nutrients in the Gulf? Well, an answer has already been provided by The Wetland Initiative. According to their article, Nutrient Removal, the TWI team successfully constructed a wetland in the Big Bureau Creek watershed, a “huge contributor” to the Gulf, which reduced nutrients off of farmlands, “through a combination of physical, chemical, and biological processes”. Plants, bacteria, and algae in these wetlands all subsist off of the phosphorus and nitrogen brought in by the rivers. The biota intake these compounds via their roots, using them during the spring and summer to stimulate growth. During the fall and winter, many of the nutrients absorbed by plants are released back into the wetlands, but some are contained in litter piles, which eventually is returned to the soil. The nutrients absorbed by bacteria go through a series of chemical reactions, transforming into nitrogen gas, ammonia, and nitrate. Nitrogen gas is created through denitrification, where bacteria absorb nutrients from the river, and feed off of the plants in the wetlands.
This process occurs during the summer, and the wetlands are regulated by humans, installing plants into the soil to maintain equilibrium if algae or bacteria grow too vast. Phosphorus particles, which enter the wetlands typically from waste management locations, are broken down by physical and chemical processes. Particles may also enter through a process known as sedimentation. Particles fall as the streams passing through wetlands slow down, becoming phosphate. This phosphate can be stockpiled by sorption, a process that adheres or absorbs nutrients into the environment, either by adhering the nutrients to other compounds, forming physical objects, or allowing liquids to absorb the nutrients. The phosphate may also be removed by precipitation. To maintain the levels of phosphate in these wetlands, new soils made from vegetation, debris, algae, bacteria, and invertebrates must replace the old soil.
What's more, TWI's wetlands have been successfully placed in farmland, providing an immediate alleviation to the farm’s nutrient supply, while also not imposing crop production. Two of these wetlands have already been created, and seven more are on the way. If done right, strategic wetlands can be placed along the Mississippi river, creating more space for nitrogen and phosphorus to deposit, reducing hypoxia further in the Gulf, and creating new habitats for wildlife.
Citations
US Department of Commerce, and Troy Kitch. “NOAA Ocean Podcast: Hypoxia.” NOAA's National Ocean Service, National Oceanic and Atmospheric Administration, 22 Feb. 2018, oceanservice.noaa.gov/podcast/feb18/nop13-hypoxia.html.
Kostel, Jill. “Nutrient Removal.” The Wetlands Initiative, 2015, www.wetlands-initiative.org/nutrient-removal.