Aquatic ecosystems are undeniably vital to society. The food, energy, and medicinal sources that oceans, rivers, and lakes provide humanity are essential to survival, and the services they provide must be protected at all costs. While Earth’s water is seemingly bountiful, it is undoubtedly under threat - increased human activities and industry are ruining the quality of water supplies. Pollution can ruin the physical, biological, and chemical integrity of water, making it harder for biodiversity, economies, and humans to thrive. Water pollution can take many different forms. Environmental contaminants like heavy metals, oils, and plastics can poison wildlife, pose human health risks, and ruin water reserves. Another major example of these contaminants comes not from an industrial plant or an oil tanker, but from farms. While water bodies provide farms with irrigation for food, an essential ecosystem service, they also produce agricultural runoff that results in a massive issue threatening marine ecosystems today - Dead Zones, or areas of aquatic habitats that kill biodiversity and ruin water quality.
To understand the severity of Dead Zones, it is important to understand how they form. Because of the booming human population, more and more fertilizers are needed to feed 8 billion people and counting. Synthetic fertilizer use has increased by 400% in the past 60 years according to Our World in Data. While this massive increase in fertilizer use may allow for the worlds’ dietary needs to be met, it comes at a tremendous environmental cost. In many cases, fertilizers are heavily applied on agricultural land to maximize crop yields. Because of this overapplication, many of these fertilizers aren’t actually absorbed by the plant, leaving an excess of nutrients on soil. During rainfall events, these nutrients get washed away in surface runoff and drain into a major river, where they get deposited into the ocean. Once in the ocean, photosynthetic algae, who use these very chemicals as a catalyst for growth, boom in population size. When these available nutrients eventually lower, algal populations respond dramatically - populations decline and tons of dead algae float in the ocean. Decomposing bacteria capitalize on this massive plume of dead biomass by feeding on them, and in doing so, their populations now increase drastically. These bacteria are aerobic organisms, meaning when they feed on the algae, they consume the surrounding dissolved oxygen in the water. In the natural world, the depleted oxygen from decomposers is restored by producers, but in a case where all the producers are dead and the decomposers populations are massive, this isn’t the case. The bacteria siphon all the available dissolved oxygen from the water to break down the algae, leaving little to none for surrounding aquatic life. The lack of dissolved oxygen causes hypoxia in fish, crustaceans, coral, and other aquatic plants. The result is an aquatic area full of dead organisms, rightfully coined Dead Zones. Dead Zones can have devastating effects on the world. The hypoxic conditions can decimate aquatic life, which threatens biodiversity and ruins the livelihoods of fishers who rely on the water and the seafood it provides. The large presence of dead algae and bacteria can also lower water clarity, preventing photosynthesis in the ocean from occurring and decreasing tourism in the local area. Algal blooms can also pose human health risks by contaminating drinking water and releasing toxins into water bodies that humans use.
Large Dead Zones can usually be found at the mouth of a major river basin that's used for agriculture. In the United States, an extremely large Dead Zone can be found in the Gulf of Mexico, which serves as the draining point for the Mississippi River Basin. The Mississippi River Basin is one of the largest freshwater drainage basins in the world and the largest in the United States. The size and importance of this river can't be overstated - it drains almost 40% of the United States runoff and is responsible for 90% of the county’s agricultural exports. It’s because of this importance, however, that the Gulf of Mexico is struggling. It is estimated that over 1.6 million metric tons of nutrient pollution gets deposited into the Gulf of Mexico each year by the Mississippi River Basin. Once there, the excess nutrients cause a Dead Zone the size of Connecticut to form and wreak havoc on the ecosystem, economy, and people living there. The Gulf of Mexico Dead Zone kills tons of fish everyday, leading to massive species declines and hurting the region’s 1.8 billion dollar fishing industry. The dead algae present can increase water murkiness, ruining the clear waters the Gulf of Mexico is known for and negatively impacting the vital tourist industry there. In addition, Cyanobacteria blooms produce toxins that ruin water quality and contaminate drinking water sources for the gulf’s residents. These are just a few of the ways in which the gulf suffers as a result of heavy fertilizer application.
Cases like the Gulf of Mexico aren’t unique - scientists report that over 400 Dead Zones exist throughout the world creating similar issues, with notable ones being found along the Baltic coast and the Korean Peninsula. Because the problem is so widespread and dire, substantial research and movements have been underway to neutralize these Dead Zones. One such method involves tackling the algae itself. Large scale clean up efforts involve physically collecting algal blooms via netting or flocculants (molecules that cause particles to clump together, making them easier to collect) and placing them in landfills or anaerobic digesters for biogas generation. While these clean ups may temporarily remove the algae, blooms soon return because the excess nutrients themselves haven’t been removed from the water. To effectively combat Dead Zones, a more proactive approach must be taken - the source of the nutrient pollution must be targeted. Preventing agricultural runoff from reaching a river and contributing to Dead Zones has been proven to decrease nutrient concentrations in water, lowering zone size and preventing zones from regrowing. The best solutions often involve utilizing nature’s ability to act as a pollutant filter. Nature based solutions also offer other benefits, such as low construction and maintenance costs, increases in biodiversity, and aesthetic appeal to humans. Environments like wetlands, riparian zones (vegetation along a water body), and reservoirs can trap excess nutrients and store them in plant life or sediment, ultimately ridding the water of these nutrients. Building these biosystems next to major drainage points of agricultural runoff could neutralize Dead Zones in a sustainable and simple way. Dead Zones are serious environmental disasters that can ruin ecological health, lower biodiversity, destroy industries and jobs, and threaten public health. While they are a result of society’s essential need for sustenance, there are methods to prevent them from occurring, and these methods are being implemented right now to achieve balance between feeding the world and promoting environmental stewardship.
