Final answer:
Chemical and fertilizer runoff is most likely the cause or contributing factor to the environmental issue described in the headline, leading to eutrophication and dead zones in bodies of water such as the Gulf of Mexico.
Step-by-step explanation:
If we look at the news headline provided, which refers to an environmental issue, D. Chemical and fertilizer runoff is most likely the cause or contributing factor. This is because the use of fertilizers in agriculture has been linked to eutrophication, where excessive nutrients in bodies of water lead to algal blooms that ultimately create dead zones. Fertilizer runoff is considered a major source of water pollution and can drastically affect aquatic ecosystems, as seen in the Gulf of Mexico's dead zone. Additionally, land misuse, including poor irrigation and lack of crop rotation, are also significant contributors to soil degradation and desertification, demonstrating the negative impact of modern agricultural practices.
Pesticides and chemicals from agricultural practices can leach into soil and ground water, causing soil pollution and diminishing soil quality, which can lead to desertification. Overgrazing can also contribute to land degradation, but it is not the top contender based on the provided context which aligns more with agricultural runoff problems.