Biodiversity in dead zones of freshwater and marine ecosystems is primarily caused by what?

The primary cause of biodiversity loss in dead zones within freshwater and marine ecosystems is the influx of nitrogen and phosphorus nutrients, primarily stemming from agricultural runoff. When fertilizers rich in these nutrients are applied to crops, they can wash into nearby waterways during rain events. This leads to nutrient enrichment, which promotes algal blooms.

These blooms can consume significant amounts of oxygen in the water when they decompose, resulting in hypoxic conditions, or areas with low oxygen levels. Many aquatic organisms, including fish and invertebrates, cannot survive in such environments, leading to a decline in biodiversity. The overabundance of nutrients disrupts the natural balance of ecosystems, making it difficult for various species to thrive.

While DDT, untreated sewage, and endocrine disruptors can also impact ecosystems, their roles are often less direct in the specific context of creating dead zones. DDT is a pesticide that can lead to bioaccumulation and long-term ecological impacts but does not specifically create low-oxygen environments. Untreated sewage can contribute to nutrient loading but usually affects localized areas rather than leading to widespread dead zones in the same way agricultural runoff does. Endocrine disruptors may affect reproductive health in species but are not directly related to hypoxia and biodiversity loss in dead