Can Human Activity Create Dead Zones?

Check out this answer from Consensus:

Human activities, particularly those related to agriculture and fossil fuel emissions, play a significant role in the creation and expansion of dead zones. The nutrient runoff from these activities fuels eutrophication, leading to hypoxia and the formation of dead zones. As these zones continue to increase in number and severity, it is crucial to address the underlying causes to protect marine ecosystems and the services they provide.

Dead zones, or hypoxic areas in coastal waters, are regions where oxygen levels are so low that marine life cannot survive. These zones have been increasing in both frequency and size, raising concerns about their impact on marine ecosystems and human activities. This article explores the role of human activity in the creation and expansion of dead zones.

The Role of Nutrient Runoff

One of the primary human activities contributing to the formation of dead zones is nutrient runoff from agriculture. For instance, the hypoxic zone in the Gulf of Mexico, which expanded significantly after the Mississippi River flood of 1993, is largely attributed to nutrient runoff from the Mississippi River basin. These nutrients, primarily nitrogen and phosphorus, fuel eutrophication, leading to large algal blooms. When these algae die and decompose, the process consumes oxygen, resulting in hypoxia1.

Impact of Eutrophication

Eutrophication, driven by anthropogenic nutrient loading, is a significant factor in the creation of dead zones. The decomposition of organic material from algal blooms increases microbial respiration, which depletes oxygen levels in the water. This process is exacerbated by water-column stratification and limited reoxygenation, making it difficult for oxygen to replenish in these areas2. The result is a largely lifeless zone where only a few species can survive, altering the community structure and ecosystem function2.

Global Trends and Consequences

Reports of hypoxic events have been increasing globally since the mid-1960s. These events have led to the mortality of bottom-dwelling life in numerous marine ecosystems and have stressed fisheries worldwide1. The increasing frequency, size, and duration of dead zones are linked to various anthropogenic factors, including nutrient runoff from agriculture, fossil fuel emissions, and climate change1 2. The consequences are far-reaching, affecting not only marine life but also human health and economic activities related to fisheries and tourism.

Can human activity create dead zones?

Martine Lizotte has answered Near Certain

An expert from Université Laval in Oceanography

Yes. The expression “dead zone” refers to an area of the ocean that is undergoing hypoxia, a condition of extreme reduction in levels of oxygen in the water. Hypoxic levels of dissolved oxygen, typically below 2 mg/L, may lead to the mortality of marine life that is stationary, such as fixed organisms on the seafloor, or to the avoidance of the hypoxic area by mobile organisms, such as fish. When this happens, habitats that would typically be brimming with life essentially become deserts, biologically speaking. This phenomenon can occur naturally, but recent increases in human activities, particularly agriculture and the use of nutrients (mostly nitrogen and phosphorus) to stimulate the growth of crops, has been of particular concern. While there are several physical, chemical and biological conditions that combine to drive the creation of dead zones, the supplemental supply of nutrients that runoff from agricultural lands and into rivers and coasts, the burning of fossil fuels and wastewater treatment discharges all have downstream impacts to aquatic ecosystems by stimulating the overgrowth of algae, the first step in a process called eutrophication. The overabundance of algae leads to an increase in the decomposition of this biomass by microorganisms. It is this decomposition of organic matter by bacteria that consumes oxygens and depletes its supply for the maintenance of marine life.

Can human activity create dead zones?

Robert  Steneck has answered Near Certain

An expert from University of Maine in Oceanography, Marine Biology

Yes, both directly via dumping of organics or fertilizers that stimulate organic production that consumes oxygen. Also indirectly by warming the ocean that results in lower oxygen saturation. The two can work synergestically.

Can human activity create dead zones?

Megan Cook has answered Likely

An expert from Ocean Exploration Trust in Oceanography

Human activity can create dead zones. Nutrients from development, landscaping, and agriculture running off to waterways fuels population explosions in plankton. When these blooms die and sink they are broken down by bacteria in the water which consume dissolved oxygen in this process, similar to how humans need oxygen for their own digestion. This massive scale aerobic (oxygen-using) breakdown depletes the oxygen in surrounding water. 

Can human activity create dead zones?

Can human activity create dead zones?

Jessica Meeuwig has answered Near Certain

An expert from University of Western Australia in Ecology, Marine Science

Yes. As oceans warm, we are seeing the expansion of what are called “oxygen minimum zones” – areas that have very low concentrations of oxygen, so called “dead zones”. In places like the Gulf of Mexico, the dead zone is a result of nutrient loading from the Mississippi river. Nitrogen and phosphorus from agriculture causes blooms of one cell plants, called phytoplankton. When the cells decompose, they suck up oxygen, resulting in the dead zone. Dead zones are also present in the Baltic Sea and the Gulf of Oman.