Eutrophication
As is generally the case, too much of a good thing can actually be bad. This is true for nitrogen and phosphorous as well. Most plants and animals cannot survive in environments with excessive amounts of either chemical. Normally, this is rarely a problem. In fact, most habitats don’t have enough nitrogen or phosphorous, and plants will compete fiercely for them. However, extensive use of fertilizers, which are composed of mainly nitrogen and phosphorous, by humans has led to a buildup of these essential chemicals in aquatic environments near areas of intense fertilization. This nutrient buildup is called eutrophication, and when it occurs, bacteria and algae experience intense exponential growth and quickly use all of the available oxygen, killing off all other species in the ecosystem. Sounds bad, and it is. Eutrophication has occurred in small ponds on tiny farms and in huge bodies of water, like the Baltic Sea. No matter the scale, it’s bad news for the ecosystem involved.