Urban development, Shanghai, China
When land is covered with concrete and rooftops, water runs off quickly and pollutants are not filtered out.

Hills and valleys in the earth’s surface form drainage basins, also called catchments and watersheds, where the water from a given area collects. If poorly managed, different forms of land use can change the way that water flows across the land, and increase pollution of waterbodies. Changing where and how much water flows is also a big problem which can change ecosystems, affecting plant and animal life dramatically. It can cause flooding and drought through re-routing water supplies.

Making changes to the land can also increase turbidity in local waterbodies. This is because the reshaping of the earth can expose new areas of ground or soil to be eroded away, and because water can pick up speed on impermeable surfaces, causing faster and more dramatic erosion. For a better idea of why land use and runoff are such a big issue, watch this video from the US Department of Agriculture which explains watersheds, and how contamination in one small area can end up causing a big problem somewhere else.
 

 

Sometimes, high levels of turbidity are an indicator of a past algae bloom, or poor water quality. It can also have a damaging effect on aquatic biodiversity, as plants are starved of the light they need to produce the energy they need to survive. Movement of land and erosion of exposed earth can cause increased turbidity, leading lakes to fill in faster, and particles in the water can provide attachment areas for other pollutants such as metals and bacteria.
 

Activity

Activity: To gain a better understanding of catchment health, how water is important for an ecosystem - and to have some fun! - play this game: Catchment Detox

Catchment Detox, click to play

 

Further Reading

PDF

U.S. EPA Watershed Academy - read more about the natural and human-made changes in catchments and waterbodies.

 

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