Maryland Critical Loads and the Maryland Biological Stream Survey

Raymond P. Morgan II
University of Maryland Center for Environmental Science
Appalachian Laboratory
301 Braddock Road,
Frostburg, Maryland 21532-2307

The State of Maryland initiated a number of studies in the 1980s as a response to the potential effects of acidic deposition on water quality and biotic resources. A brief history of these early studies on acidic deposition is described, as well as results from the Maryland Critical Loads Study (1992). Following the critical loads analyses, a number of other statewide programs were initiated including the Maryland Biological Stream Survey (MBSS) in 1993. Initially, the MBSS focused on an assessment of acidic deposition on biological resources in non-tidal wadeable streams (1st, 2nd and 3rd order), as well as determining the condition of stream biotic resources. In addition, the MBSS program (with three multi-year rounds) eventually expanded to analyzing stressors, to compiling biodiversity inventories, to prioritizing areas for protection and restoration, and to documenting changes in biological resources (temporal component). Based on the first MBSS round (1995-1997), an estimated 28% of Maryland stream km are acidic or acid-sensitive, including about 2% acidic, 4% highly sensitive, and 22% sensitive to acidification. An estimated 38% of stream km are acidic or acid-sensitive (3% acidic, 8% highly sensitive and 27% sensitive) based on results from the second MBSS round (2000-2004). The presence of acidic or acid-sensitive streams correlated with poor watershed buffering capacity; stream biotic resources responded to acidic stressors. With the addition of state-wide sentinel sites in acid sensitive regions, especially western Maryland, long term biotic responses to acidic deposition will be monitored in the MBSS program.