Context:
National Oceanic and Atmospheric Administration (NOAA) is forecasting an above-average summer “dead zone” in the Gulf of Mexico covering approximately 5,827 square miles.
Relevance:
GS I: Geography
Dimensions of the Article:
- About Dead Zones
- How are Dead Zones Formed?
About Dead Zones
- Definition:
- The term “dead zone” or “hypoxia” refers to low-oxygen areas in the world’s lakes and oceans.
- Because most organisms need oxygen to live, few organisms can survive in hypoxic conditions, leading to these areas being termed dead zones.
- Hypoxic zones can occur naturally, but human activities can also lead to the creation of new dead zones or the worsening of existing ones.
How are Dead Zones Formed?
- Eutrophication Process:
- Dead zones occur due to eutrophication, which happens when a body of water is overloaded with nutrients like phosphorus and nitrogen.
- Normally, cyanobacteria (blue-green algae) feed on these nutrients.
- Excessive nutrients cause a rapid overgrowth of algae, known as algae blooms.
- Dead zones form when these algae die, sink to the bottom, and are decomposed by bacteria, a process that depletes dissolved oxygen from the surrounding water.
- Dense algae blooms block sunlight, preventing underwater grasses from growing, which negatively impacts animals that rely on these grasses for food and shelter.
- Human activities often cause these nutrient excesses, leading to dead zones frequently being located near populated coastlines.
- Influencing Factors:
- Wind can mix oxygen from the surface into deeper water, helping to break up dead zones.
- High temperatures can worsen dead zones by creating a layer of warm surface water that traps colder, oxygen-poor water below.
- Heavy rainfall can increase the amount of pollution washed into waterways.
- Water Depth and Mixing:
- Shallow waters are less likely to stratify compared to deep waters, making them less prone to developing hypoxic conditions due to better mixing by winds and tides.
- Shallow and clear waters that allow light to reach the bottom can support primary producers such as phytoplankton, algae, and seagrasses, which release oxygen during photosynthesis.
-Source: Down To Earth
