Water quality research
Water quality
Hydrologic optics

Components of water quality
  Colored dissolved   organic matter
  Suspended   particulate matter
  Water itself

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Components of water that affect
color and clarity
    Water bodies differ in the types and amounts of material they contain that affect their opitical properties. The differences among water bodies in amounts of optically important materials are related to the type of water body (i.e., lake, river, estuary, ocean), its locations (i.e., altitude, latituted, size and geology of its watershed), and human activity in the watershed and airshed.

    For example, estuaries tend to have higher concentrations of suspended solids than lakes, due to inputs to estuaries from rivers, and tidal currents that erode shorelines and resuspend bottom sediments. In contrast, the clearest natural waters tend to be crater lakes of extinct volcanoes (due to the fact that their watersheds are small, relatively inerodible, and chemically inert), or the central oceanic regions (due to their great distance from land.)

    The composition of a water body varies naturally over time, and also responds to human activity. Phytoplankton populations undergo seasonal changes in abundance with variations in temperature and sunlight, and also can proliferate to nuisance levels in response to nutrient inputs from agricultural application and sewage processing. Though the particular processes differ, similar statementes could be made for colored dissolved organic matter and suspended solids--the other two factors that affect the optical properties of water. Each of these three components--colored dissolved organic matter, phytoplankton, and suspended solids--as well as water itself, has characteristic optical properties, summarized in the table below.


Optical Result
Water itself Absorbs mainly red light, in the longer wavelengths. Weakly scattering
Colored Dissolved Organic Matter Strongly absorbs light, mostly shorter wavelengths, especially blues. Scatter is negligible.
Phytoplankton Strongly absorbing and scattering. Absorption is selective with peaks in the blue and red regions. Scatter is mainly directed forward.
Suspended Particulate Matter Strongly scattering. Absorption characteristics depend upon composition of the particulate material.

    These three components, colored dissolved organic matter, phytoplankton and suspended particulate matter, which influence water quality and have effects on the optical properties of water are the target components of water quality management programs across the globe. Increases in one or more of these components causes a decrease in water quality, which is affecting not only how humans can use the water, but also how marine flora and fauna live and survive in the water. Watershed management strategies that result in reductions in any or all of the components are a crucial and necessary undertaking.

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