Maryland Department of NATURAL RESOURCES

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Maryland Biological Stream Survey

MBSS Statewide Sampling Round Five

The Maryland Biological Stream Survey (MBSS) was started by the Maryland Department of Natural Resources in 1993 as a pilot study in three watersheds. Four sampling rounds have focused on assessing the ecological condition of Maryland’s streams during discrete time periods, with specific sampling designs, stream maps, and watershed scales.

During ​Round One, 955 sites were selected from a 1:250,000 scale map for sampling over a three-year period (1995-1997) to assess the health of Maryland streams at a statewide and 18 major river basin scales. During Round Two, 1,099 sites were sampled from a 1:100,000 scale map over five years (2000-2004) with a focus on statewide and 84 Primary Sampling Unit (watershed) scales. During, and especially following Round Two, substantial targeted site sampling was added with locations selected to spatially and/or temporally coincide with a specific condition or action. This sampling is used to answer specific questions about the influence of the condition or action at that location (e.g., a steam restoration project, a dam removal, weather and climate influences). During Round Three, 252 sites with randomly selected locations were sampled between 2007 and 2009 on the same 1:100,000 scale stream map used for Round Two. The Round Three assessment focused on statewide and 12 major river basin scales.

Since some of the most frequently asked and important questions to be answered by the MBSS pertain to changes in stream conditions over time (e.g., are stream conditions improving?; are stream conditions degrading?), certain sites originally sampled during Round One and Two were re-sampled during Round Four. Round Four was conducted during 2014 – 2018 (20 years after Round One and 14 years after Round Two).

The Fifth Round of the MBSS utilizes a finer-scale (higher resolution) stream map (1:24,000) than has been used previously. This map provides a framework for more comprehensive assessments of Maryland’s more than 16,000 stream miles – including more small headwater streams - than assessed during previous rounds. As with some previous MBSS sampling rounds, sites are randomly selected for sampling. Unlike other MBSS rounds during which a subset of watersheds was sampled annually, the MBSS Round Five design includes sampling a site in each of the 84 primary sampling unit watersheds each year. Multiple years of sampling data will be combined to assess the condition of Maryland’s streams. As with previous rounds, targeted and fixed sampling will be combined with random sampling to help answer important management questions. Round Five began in 2021 and continues to the present day.​


​Round Five Objectives

  • Assess the ecological condition of the more than 16,000 Maryland’s streams and rivers on a 1:24,000 scale stream map
  • Assess the ecological condition of streams mapped at the 1:100,000 scale used during Rounds Two and Three for historical comparison
  • Identify indicators of potential stressors to stream ecological conditions such as climate change, atmospheric deposition, and other factors
  • Provide an inventory of biodiversity in streams mapped at the finer (1:24,000) scale
  • Estimate the distributions and abundances of rare and imperiled stream species to help inform conservation status

Check out the rest of the MBSS website for more information and to learn more about what MBSS will be doing in the coming years.

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