VI.  Stream Response

The Maryland Biological Stream Survey

The Maryland Biological Stream Survey (MBSS ) is a statewide assessment that provides information on biological, chemical, and physical conditions in non-tidal streams.  One of the survey's primary objectives is to quantify the extent to which acid deposition is affecting Maryland streams, fish, and other aquatic life.

Acid neutralizing capacity (ANC) was used as an overall measure of stream acidification and acid sensitivity.  Among the 954 sites sampled by the Survey during the March-to-May index period during the years 1995-97:

• 24% of the sites were acidic  (ANC < 0  ueq/l) or acid-sensitive (0 < ANC < 200  ueq/l). 

• Although the majority are affected by acid deposition, these estimates include a small number of sites affected by acid mine drainage (in western Maryland) and natural organic acids.

• Acidification can have adverse affects on stream communities.  For example,  1996 MBSS sampling showed a dramatic decrease in fish abundance and species richness at low ANC sites (Figure 7).

Figure 7.  Fish Abundance and Species Richness by Acid Neutralizing Capacity Class, 1996 MBSS.

• The greatest densities of acidic stream sites in the MBSS monitoring occurred in the Appalachian Plateau and Southern Coastal Plain, with a few sites in the Northern Coastal Plain.

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This page was updated on 4/7/2004