Maryland Biological Stream Survey

MBSS Statewide Sampling Round Four

The Maryland Biological Stream Survey (MBSS) was started by the Maryland Department of Natural Resources in 1993 as a pilot study in three watersheds. It is now a statewide program that has sampled nearly 4000 sites. The third round of statewide random sampling concluded in the summer of 2009. The Fourth Statewide Round of the MBSS will run from 2014 to 2018. Check out the rest of the MBSS web site for more information and to learn more about what MBSS will be doing in the coming years.

Sampling design summary of Round Four


The Fourth Round of the MBSS will optimize our ability to detect changes in Maryland’s stream conditions. This will help us to inform management decisions in the future.


Stream ecosystems are incredibly complex and variable. There is a need to know how they are responding to management efforts in the face of continued impacts. Over the last 20 years the population of Maryland has increased, putting stress on our streams. At the same time, stream restoration activities and conservation (including additional state and local regulations and policies) have increased. Round Four will provide an assessment of how stream ecological conditions have changed which could lead to recommendations on the success of these activities and whether management actions should be adapted to become more effective.


The MBSS uses randomly selected sites to provide a statistically rigorous representation of Maryland's stream conditions. Round Four involves re-sampling a subset of randomly-selected stream sites that were sampled previously, a widely accepted design. This process will take five years. Sites that were sampled in 1995, 1996, and 1997 will be re-sampled 20 years later (in 2015, 2016, and 2017). A separate set of sites that were sampled in 2000, 2001, 2002, 2003, and 2004 will be sampled beginning in 2014 — 14 years later.

Expected Results and Applicability

By 2018 we will have collected sufficient information to compare statewide and river basin estimates of stream condition over 20 and 14 year intervals. We will also have collected sufficient information to compare conditions within select sub-watersheds. For example, Mattawoman Creek will be the first 8-digit watershed where changes will be investigated — all sites that were sampled during 2000 in this watershed will be re-sampled in 2014, thus providing sufficient information to describe stream conditions in 2014 for comparison to conditions in 2000.

Maps of Watersheds Sampled in Each Year

Round Four sampling will include revists of Round One and Round Two random sites. Because each round used random sampling to characterize the condition of disimilar size watersheds differently, there are two maps needed to describe the sampling schedule. The first map shows when watersheds from Round One will be sampled, and the second shows Round Two. Note that the watersheds are much bigger in the first map. These are considered "Basins" when used by MBSS biologists, but other groups may refer to them as 6-digit watersheds. The watersheds sampled in Round Two are called PSUs (Primary Sampling Units). They are Maryland 8-digit watersheds, with very small ones combined to make the sampling units more uniform in size.

Round One BasinsSampled in Round Four

Round Two Watersheds Sampled in Round Four

Management Questions

A list of questions that potentially can be answered by the MBSS Round 4 data is given below.


  • Did the general ecological condition of Maryland’s streams change?
  • Did the status of sensitive indicators of high quality streams change?
  • Did the status of stressor-specific indicators change?
  • Did the estimated abundance of any fish species change?
  • Are any species of fish, mussels, crayfish, or stream salamanders conspicuously absent from areas where they were collected previously?
  • Were new species of fish, mussels, crayfish, or stream salamanders added to Maryland’s stream fauna?
  • Did the distribution of any invasive stream species change?
  • Did the number of gamefish species change?
  • Did the size of gamefish species change?
  • Did the proportion of sites with rare species change?
  • Did fish biomass change?
  • Did the occurrence of anomalies change?
  • Did the occurrence of sensitive benthic macroinvertebrates change?
  • What proportion of sites (sampled at least twice) exhibit 1) improved ecological condition; 2) reduced ecological condition; 3) no change in ecological condition?
  • How many benthic macroinvertebrate taxa were added to the MBSS database?


  • Were weather conditions different?
  • Could any observed ecological changes be explained by concomitant changes in physical, chemical, or landscape?
  • Could any improvements in conditions be (at least in part) attributable to state environmental regulations, policies, or initiatives?
  • Are there detectable changes that could be attributed to climate change?
  • Did the proportion of landowners granting permission for sampling change?
  • If the proportion of landowners granting permission decline, why?
  • Do Stream Waders data collected at or near Round 4 sites support those from the respective MBSS sites?


  • Did the chemical condition of Maryland’s streams change?
  • Were nutrient concentrations different?
  • Were acidic conditions different?
  • Were conductivity levels different?
  • Were chloride concentrations different?
  • Did the proportion of streams affected by AMD, acidic deposition, and other sources of acidity change?


  • Did the physical habitat of Maryland’s streams change?
  • Did erosion change?
  • Did the temperature change?
  • Did riffle embeddedness change?
  • Did fish or benthic macroinvertebrate habitat change?
  • Did riparian buffer condition change?
  • Did riffle quality change?
  • Did riffle pool quality change?


  • Did the land cover change in site catchments?
  • Did stream restoration projects in site catchments increase?
  • If restoration was attempted, did indicators of stream condition respond?
  • Did the amount of protected land in catchments increase?
  • Did BMPs in site catchments increase?
  • If BMPs were implemented, were they successful in protecting stream conditions?

For All Sections...

  • Did conditions improve?
  • Did conditions become worse?
  • What are likely reasons for any observed changes?