Mottled soils can be a sign of which environmental issue?

Mottled soils are characterized by spots or blotches of different colors, often indicating variations in moisture content and air presence in the soil profile. The presence of mottling typically suggests that the soil experiences fluctuations in saturation levels, which can occur in areas that are periodically flooded or waterlogged.

This seasonal saturation occurs when water levels rise and fall, causing the soil to remain saturated for parts of the year while becoming drier at other times. During the periods of saturation, anaerobic conditions can lead to changes in soil color—hence the mottling. These color changes are the result of chemical reactions occurring within the soil due to the presence or absence of oxygen, which is why mottled soils are often associated with wetland areas or regions with high water tables.

While other environmental issues like excessive salinity, pollution, or soil depletion can affect soil quality, they do not typically manifest in the specific pattern of coloration seen in mottled soils. Each of the other choices reflects different soil or environmental problems, but they do not specifically correlate with the appearance of mottled soils like seasonal saturation does.