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Investigating Turbidity

After a heavy rainfall, will your local stream be more clear or more turbid?

Water clarity is heavily influenced by weather events such as droughts and rain storms. As a result, it fluctuates a great deal from one year to the next. When rains fall in the Bay's watershed, it runs off the ground carrying sediments into local rivers that eventually lead to the Bay. This sediment laden combines with other materials such as decaying plant and animal matter, industrial wastes, and sewage to form suspended solids in the water. Suspended solids cause the water to be more turbid because the very small particles scatter light. Clear waters are a reflection a healthier Bay, with acceptable levels of sediments, nutrients and algae in the water column. So if you said more turbid, YOU ARE RIGHT!

Some other factors that influence water clarity include:

  • CDOM (Colored Dissolved Organic Material): CDOM is essentially tiny particles of plant or animal matter-leaves, wood, grass-and comes primarily from the land. For example, forests are a source of CDOM and contribute to the dark colored water Chesapeake Bay tributaries. When CDOM is present in the water it can absorb certain light wavelengths
  • Phytoplankton: Phytoplankton reduces the intensity of light by scattering light particles and by absorption of light at certain wavelengths. In addition, phytoplankton in excessive amounts has the nasty habit of falling to the bottom, decomposing, and removing precious dissolved oxygen from the bottom waters.

Turbidity Facts:

Low Turbidity High Turbidity
Relatively clear water Cloudy or opaque water
Little to no algae blooms Dense algae blooms
Low amounts of sediment and runoff Events that stir up sediments or cause runoff such as storms or dredging

Percent of sunlight reaching SAV leaves:

  • 13% in low salinity waters
  • 22% in high salinity waters
Very low percentage of sunlight reaching SAV leaves - Bay grasses grow poorly or die