Cities and their suburbs take the place of both wild land and agricultural areas. More and more land is paved over as roads or covered with buildings, etc. Burning of fossil fuel, and other activities in cities change the local climate. Usually, things like tornados do not occur as frequently in big cities as in rural areas, probably also due to the difference in air temperature. Dams are constructed to cause major changes in the watercourse of a given river-system.
Pollution is a major human-induced problem.
Pesticides, herbicides, and fertilizers are washed into local water systems. Litter, landfills, and improperly-treated sewage may potentially leach a variety of chemicals and pathogenic bacteria into the surrounding environment. Also, burning of coal, and other fossil fuels releases sulfur and nitrogen compounds into the air. The sulfur compounds form sulfuric acid, and the nitrogen forms nitric acid. Acid rain, when absorbed into the soil, can alter the pH of the soil, therefore the solubility of various chemical ions used as nutrients.