nondeposition or even erosion. An undesired increased transport and sedimentation of suspended material is called siltation, and it is a major source of pollution in waterways in some parts of the world. High sedimentation rates can be a result of poor land management and a high frequency of flooding events. If not managed properly, it can be detrimental to fragile ecosystems on the receiving end, such as coral reefs. Climate change also affects siltation rates. In estuarine environments, settling can be influenced by the presence or absence of vegetation. Trees such as mangroves are crucial to the attenuation of waves or currents, promoting the settlement of suspended particles. Human-enhanced sedimentation Chemistry In chemistry, sedimentation has been used to measure the size of large molecules (macromolecule), where the force of gravity is augmented with centrifugal force in an ultracentrifuge. Sedimentation equilibrium When particles settling from a suspension reach a hard boundary, the concentration of particles at the boundary is opposed by the diffusion of the particles. The distribution of sediment near the boundary comes into sedimentation equilibrium. Measurements of the distribution yields information on the nature of the particles. Classification Classification of sedimentation: Type 1 sedimentation is characterized by particles that settle discretely at a constant settling velocity, or by the deposition of Iron-Rich minerals to streamlines down to the point source. They settle as individual particles and do not flocculate (stick to each other) during settling. Example: sand and grit material Type 2 sedimentation is characterized by particles that flocculate during sedimentation and because of this their size is constantly changing and therefore their settling velocity is changing. Example: alum or iron coagulation Type 3 sedimentation is also known as zone sedimentation. In this process the particles are at a high concentration (greater than 1000 mg/L) such that the particles tend to settle as a mass and a distinct clear zone and sludge zone are present. Zone settling occurs in lime-softening, sedimentation, active sludge sedimentation and sludge thickeners. See also Notes Earth sciences Laboratory techniques Liquid-solid separation