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Biological Monitoring

Monitoring water quality in our environment is complicated—streams are constantly in flux and are affected by soil, air, ambient temperatures, man-made pollution, and seasonality. Biological communities such as aquatic insects, fish, and stream salamanders rely on clean water, normal stream flows, and adequate stream habitats to survive. These organisms are therefore very useful indicators of water quality.

Generally speaking, a biological community consisting of less diverse, more pollution-tolerant species indicates poor stream health, while a biological community consisting of diverse, sensitive species is characteristic of higher water quality. 

The County's biological monitoring program was developed over time based on the Department of Environmental Protection's evaluation of its own data and in partnership with state and federal scientists. The protocols used today have received extensive review from state and federal scientists. These protocols ensure that DEP's data are comparable with data from other ongoing monitoring efforts.


Index of Biotic Integrity (IBI)

Image of a northern red salamander.DEP worked with EPA's Biological Criteria Group to develop an Index of Biotic Integrity (IBI) locally adapted to the County's eco-regions. The IBI uses several metrics (measures) that constitute an overall score. This score describes stream health in terms of ecological structure and function.

DEP takes raw data collected from a waterbody and develops the data into the multimetric IBI score (a unitless score rating for a waterbody). This involves taking various data on the count and other variables about the species found in the waterbody and using a peer-reviewed methodology to "rate" the data variables with numeric indices. The indices are then combined for an overall IBI score for the individual species (e.g., fish IBI score, benthic macroinvertebrate IBI score). The metrics include:

  • The number of species, a measure of community structure of fish and benthic macroinvertebrates (bottom-dwelling organisms)

  • The functional feeding group, a measure of community function

  • Pollution sensitivity of populations (of fish, amphibians, and other organisms)

  • Proportion of introduced species

DEP biologists compare the IBI scores from the streams they monitor against the scores from the highest-quality, least-impaired streams in the same eco-region (reference streams). Reference streams, usually found in heavily forested and less-developed areas, provide a benchmark against which streams in more developed areas can be compared to determine their relative state of health.

The IBI scores are then classified into four narrative classes: Excellent, Good, Fair, and Poor. Streams that have IBI scores comparable to those in the reference streams are classified as "Excellent." Streams rated "Excellent" or "Good" are considered healthy. "Poor" streams are considered impaired or severely impacted.

Learn more about IBI scores on the County Monitoring webpage.


Image of a brown trout.Site Selection Process

Stream monitoring supports different water resource management needs of the County, such as assessment of water quality over time, assessment of stream restoration outcomes, or sampling of sediment and erosion control and stormwater control practices.

To select monitoring sites, Montgomery County uses both targeted (preselected) and probability-based (random) sampling to support different management needs. Monitoring sites are points along particular sections of stream, known as reaches.

  • Sites are selected in one of three ways:

  • Stream reaches (lengths of stream) are randomly selected, and sites are randomly chosen within each reach.

  • Stream reaches are targeted, and sites are randomly chosen along the reach.

  • Both reaches and sites are targeted.

For purposes of developing integrated estimates of stream condition, only the probability-based samples (selection methods 1 and 2) are used.

Targeted sites are useful for other purposes, particularly to diagnose causes of stream degradation at specific local sites; however, they don't support area estimates with known precision.


Comparability with Statewide Stream Monitoring

Image of a crayfishMontgomery County's monitoring protocols were peer-reviewed by state, local, and federal agencies and have been used for more than 14 years. During that time, the Maryland Department of Natural Resources developed the Maryland Biological Stream Survey (MBSS), which included standardized field methods to monitor fish and benthic macroinvertebrates. In 2000 DEP and the U.S. Environmental Protection Agency's Mid-Atlantic Integrated Assessment (MAIA) program executed a Memorandum of Understanding (MOU) to establish a working partnership. This MOU committed DEP and EPA to work together to share information and develop joint products addressing the County's work in biological monitoring, stream protection, retrofitting of urban stormwater controls, and restoration of degraded habitats. As a result of a comparative study funded by MAIA, in 2001 Montgomery County revised its field monitoring methods to directly compare to those of the MBSS.

The MBSS has the daunting task of monitoring over 15,000 miles of wadeable streams and rivers across the entire state of Maryland. Without the help of County monitoring efforts, it would be impossible to get a proper representation of stream health. One reason is that the state monitors on a less detailed scale than the County.  This is the spatial scale at which DEP assigns stream order and names monitoring stations.The MBSS uses the 1:100,000 scale stream coverage to select stations, and the County uses the 1:24,000 scale coverage. 

This means that many first-order streams (smaller streams) are not monitored by the state but are monitored by the County. Also, by monitoring additional stream miles, the County helps to add to the sampling size through the sharing of data. Montgomery County employs the same methods that the state uses to assess local water quality conditions and is therefore able to contribute finer-scale data to the state, which can be used to protect statewide water resources and the Chesapeake Bay.