The artificial Palm Islands in Dubai were designed to minimize sediment buildup along their channels.
Mud is a very fine sediment formed by the erosion process. It is usually found in or near bodies of water or where bodies of water once existed. It is often extremely fertile and an aid to human agriculture. However, changes in an ecosystem can cause a rapid change in the presence or absence of mud in a given location. These changes are particularly noticeable at the mouths of major rivers such as the Nile and the Mississippi.
Geological processes, such as erosion, break down rock fragments over time into tiny particles. Classification systems such as the one used by the US Department of Agriculture define sludge as particles less than one thousandth of an inch (0.05 mm) in size, even smaller than ordinary sand. The small size and weight of these particles means that bodies of water, such as rivers, can carry them long distances. All rivers carry some amount of sludge, although the presence of solid surfaces in the water can impede this process. When this happens, the particles will fall out of the water and accumulate on the surface, be it a shore, a natural body, or a foreign object.
This process had a profound impact on the development of human culture. Many of the earliest civilizations grew up around river mouths, or deltas, which provided fertile land for agriculture. In Egypt, for example, the Nile River regularly overflows its banks and then recedes, leaving vast deposits of silt on its banks. The society of ancient Egypt, one of the first empires in the world, prospered for thousands of years thanks to this agricultural benefit. Other ancient cultures such as Mesopotamia, China, and India also benefited from this process.
Sludge accumulation, or lack thereof, can be affected by human activity. On North America’s Mississippi River, for example, levees and dams built to regulate river flooding can also cause sediment buildup. This prevents sediment from being deposited in the river delta in the Gulf of Mexico. As a result, natural barrier islands and sandbars deteriorated. Unfortunately, these structures are home to many creatures that have consequently been displaced and threatened with extinction.
Human activity on land can have an opposite but equally damaging effect. Expanding populations often clear vegetation for housing developments or agriculture. As a result, rain and erosion carry silt and other forms of soil into nearby bodies of water. In regions like Madagascar and the Amazon rainforest, this reduces the fertility of the remaining soil, making it less useful for food production. Meanwhile, the resulting change in the ecosystem of nearby rivers and swamps could reduce fish populations, which in turn would affect creatures, including humans, that depend on fish supplies to survive.