#oxygenislife

Who would have thought having too many nutrients could be a bad thing? We hear the word “nutrients” and assume that the being or the body of water is healthy! However, the dumping of excess nutrients can result in Dead Zones, which are regions with very low levels of dissolved oxygen (2 mg oxygen / L water or less), also called hypoxia. These low oxygen levels prevent many organisms from living in these regions, and therefore causes a decrease in biodiversity. Sometimes these Dead Zones are created naturally, however, in recent years, these zones can often be attributed to anthropogenic causes. 

Today, I will tell you the four steps in creating a Dead Zone. 

Step 1: 

Nutrients, such as Phosphorous and Nitrogen, are carried in moving water to the coastal waters. They can be transported from both point and non-point sources. If you don’t know already, point sources are those sources of pollution that are localized and confined. That is, you know exactly where the pollutants and nutrients are coming from. Examples of this can include runoff from sewage treatment plants and other industries. Non-point nutrient pollution, on the other hand, are those sources of pollution that are widespread, and diffuse sources without a single location at fault. Examples include agricultural runoff of pesticides and herbicides, and urban runoff from residential and commercial areas. 

Step 2:

These nutrients are then used by primary producers and autotrophs, and their population increases very quickly, creating an “algal bloom.”  As the plankton bloom, so do the zooplankton as they consume these primary producers. This may seem all fine and dandy right now, however, as the zooplankton increase their consumption, and reproduce rapidly, the population of plankton decreases, which causes death of zooplankton as well. 

Step 3:

As these plankton and zooplankton die, this organic matter (biomass) sinks to the bottom of the water. Decomposers love to eat this biomass, as they are heterotrophs just like the consumers. This means they consume oxygen as they gain energy and carbon sources from the organic matter. Since there was an unusually high amount of deaths, more biomass is created, and therefore leads to decomposers consuming an unusually high amount of oxygen.

Step 4:

As these decomposers continue to break down the biomass and consume this oxygen, it begins to get depleted from the water. As the amount of oxygen decreases, the organisms that rely on it to live either flee the area to somewhere with more oxygen, or die. What is left behind is a body of water that has 2 mg of dissolved oxygen per 1 L of water or less, which is a Dead Zone. 

It is very important to control and prevent this hypoxia from occurring, especially by anthropogenic causes. Without oxygen in the water, many organisms die and cannot reproduce. In order to increase biodiversity, there needs to be a healthy amount of oxygen and therefore, less nutrient pollution runoff from agricultural and urban areas. If we decrease nutrient loading, fish  and other marine life will thrive, creating healthy ecosystems.