What can excessive herbicide runoff lead to in aquatic environments?

Excessive herbicide runoff can lead to decreased oxygen levels in aquatic environments, which is a critical concern for the health of these ecosystems. When herbicides enter water bodies, they can kill not only targeted aquatic plants but also non-target species, disrupting the food chain and altering the natural balance of the ecosystem. As plants die off, the decomposition process consumes dissolved oxygen, reducing its availability for fish and other aquatic organisms. This depletion of oxygen can lead to hypoxic conditions, where oxygen levels drop too low to support most marine life, ultimately harming fish populations and other wildlife dependent on oxygen-rich water.

The other potential options, like increased biodiversity and better fish habitats, would typically require a healthy, balanced ecosystem. Excessive herbicide runoff usually does the opposite, harming the diversity and natural habitats within aquatic environments, leading to a less harmonious ecosystem.