Land use change

As populations increase there is a greater need for food and clean water. These factors are intricately linked with land use. Watersheds are developed and changed into urban, industrial, and agricultural areas. These land use changes may be more useful in terms of food production and provide extra space for human population growth, however, they do put the water supply under pressure as the natural water filter, the watershed, is no longer present.

Watersheds are the drainage area over which sediments, nutrients, pesticides and other chemical additions to the land are collected in a waterbody such as a lake, river, or ocean. Watersheds occur over different scales. A field could be considered a minor watershed in the same way that the huge Mississippi drainage area, USA, is a watershed. A key factor in watershed dynamics is the speed of rainfall runoff. A vegetated area will have a slower runoff movement than a cleared area. This is an important fact to consider when initiating practises such as forest clearing, mining, and changing land to agriculture or urban areas etc. Faster water flow washes much more sediment into water bodies. Sedimentation itself, if dire, becomes a water quality issue and could ultimately effect drinking water supply to local communities.

Runoff from agricultural land can mean excessive nutrients, such as nitrogen and phosphorus, flow down to ocean waters causing eutrophication. Consequences of this are hypoxia (very low levels of oxygen in water) and fish kills, the disappearance of seagrassses, macroalgae and coral reefs and harmful algal blooms. Many seas are effected by eutrophication: the northern Gulf of Mexico, Baltic, North, Adriatic and Black seas to name a few. With world populations increasing food demand shall rise and hence more fertiliser use is predicted, so eutrophication of coastal waters will get progressively worse.