Stream habitat is one of the primary factors that affect the aquatic biotic
in-stream habitat often results from uncontrolled storm water runoff
and uncontrolled runoff from intensively grazed or cultivated agricultural
In Montgomery County, which has relatively few industries, physical degradation of in-stream habitat is the most likely cause
of biological impairment. Chemical contamination from industrial
effluent discharges is also a factor but less common. Biological impairment of streams
in the County is tracked by monitoring benthic macroinvertebrate
and fish biological communities and analyzing the data.
Learn more about watershed conditions throughout the County based on our
monitoring data and assessments.
How does stream habitat affect biological organisms and the ecosystem?
Stream habitat affects the benthic macroinvertebrate (benthic) community in a variety of ways.
- Excessive sediment can smother benthic communities by filling in the interstitial spaces that the community would need for oxygen transport and habitat space.
- Lack of in-stream cover for fish could adversely affect the fish community.
- Lack of habitat essential for reproduction such as small pools
- Lack of riffles, pools and runs in the streamís longitudinal structure which each have characteristics important for different organisms lifecycles
- Murky, cloudy water prevents fish from seeing their food
- Abrasion of fish and other stream life from suspended sediment particles
In addition to in-stream habitat parameters, the adjacent riparian zone (stream
banks) have a significant influence on the nearby stream. Problems
in the riparian zone include:
- Direct access by agricultural animals in the stream causing siltation and muddy conditions
- Lack of trees on the bank to provide shade for cooler water conditions
- Stream bank erosion caused by mowing up to the edge of the stream
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Stream Habitat Assessment Activities
Training exercises on habitat assessment protocols held annually, helps to reduce subjective bias among field biologists.
Stream habitat is assessed in the field by trained biologists using a set of ten parameters that describe various physical habitat attributes (see Barbour and Stribling: Visual Based Habitat Assessment for Riffle/Run Prevalent Streams (PDF, 64 pp, 5.7Mb)). Each habitat parameter is scored by two biologists who work together as a team to assess each specific habitat attribute. However, prior to providing a score for each habitat parameter, the biologist rates the specific parameter and places it into a specific habitat category (i.e.: optimal, sub-optimal, marginal, or poor). Since there is some subjectivity and personal biases even among trained biologists, a calibration session is held at the beginning of each monitoring season to ensure reduction in the variability among raters.
Each habitat parameter is given a score from 0 to 20. For cases where each side of the stream is assessed separately (e.g., stream banks), each side is scored from 0 to 10. There are a total of ten habitat parameters, so the highest possible score is 200.
The ten habitat parameters are as follows:
- In-stream Fish Cover
This includes the relative
quantity and quality of a variety of stable in-stream structures
that provide cover for fish. Natural in-stream structures can
include root wads, undercut banks, deep pools, and boulder cover.
Generally, the greater variety of available cover, the better.
Artificial structures meant to enhance or replace natural cover
are also beneficial to fish populations.
- Epifaunal Substrate
This includes the relative quantity
and quality of a variety of in-stream structures that provide
living spaces for benthic macroinvertebrates. Natural structures
that increase the amount of dissolved oxygen (e.g.: riffles) are
beneficial to the benthic macroinvertebrate community. Greater
variety and availability of appropriate habitat structure is optimal
for the stream. Heterogeneous structures that offer more variety
of habitats (e.g.: various sizes of riffle substrate) are better
than homogeneous structures that offer less variety.
This refers to the extent that riffle substrate (e.g.: gravel, cobble, and boulders) are embedded with silt, sand, or sediments. The filling in with sediment of the interstitial spaces between the rocks within the riffle reduces the amount of available habitat and the amount of oxygen that is produced by the action of water flowing through the riffle.
- Channel Alteration
This is a measure of human-caused changes to the size and shape of the stream channel. For instance, many streams in urban areas were transformed into concrete to transport water or to restore banks. Such streams offer substantially less suitable habitat for benthic macroinvertebrates and fish, and also disrupt the aquatic communities with hydrologic impacts during high flows. Artificial support structures for the stream banks (e.g.: rip-rap or concrete sidewalls) indicate the need for unnatural repair processes to streams that have already been damaged from the effects of urbanization.
- Sediment Deposition
This habitat parameter measures the accumulation of sediments within the stream channel from a variety of sources either within the stream channel (i.e.: bank erosion) or from outside of the stream channel (e.g.: uncontrolled runoff from construction sites). High levels of sediment create an unstable environment that is continuously changing, making the environment unsuitable for aquatic organisms, especially benthic macroinvertebrates.
- Riffle Frequency
This parameter measures the relative frequency of riffles within a stream compared with the width of the stream channel. Riffles are a high quality habitat for benthic macroinvertebrates. A greater number of riffles means more available benthic macroinvertebrate habitat, which ultimately leads to a greater amount of food for fish.
- Channel Flow Status
This parameter is the degree to which the stream channel is filled with water. This parameter is most closely affected by sediment deposition. The more sediment there is in the stream, the more channel bars are formed, and the less the channel is filled with water. This parameter is assessed by observing whether the water reaches from bank to bank or whether there are parts of the channel exposed. This parameter is most influenced by natural factors such as drought or flooding. When there is less water in the channel, there are also fewer habitats available for aquatic organisms.
- Bank Vegetative Protection
This parameter measures the amount of the stream bank (on the top and along the sides) that is covered by rooted (as opposed to overhanging) vegetation. The root systems of bank side vegetation help to stabilize the banks. The greater the variety (i.e., trees, shrubs, herbaceous) of bank side vegetation the greater the stability of the bank. Native vegetation is much more desirable, because invasive exotic vegetation typically have shallow root systems that are poorly suited to stabilizing the soil and tend to crowd out more desirable native vegetation. Furthermore, some exotic vegetation (e.g., multiflora rose) that grows on top of the banks overhangs over the sides of the bank and shades out vegetation that could become established along the sides which helps to keep the banks stable. Soil that is colonized by exotic vegetation is more prone to erosion than solids with a mixture of native vegetation. Exotic vegetation tends to establish itself as a single dominant species crowding out a more desirable mixture of native vegetation which also is less stable.
- Bank Stability
This parameter is closely related to bank vegetative protection. The better the quality of bank side vegetation, the more stable the banks, and vice versa. Unstable banks are also a source of sediment for the streams. Signs of an unstable bank include dewatered and exposed tree roots, crumbling, sloughing, and exposed soil.
- Riparian Vegetative zone and width
This is the only parameter that does not assess the condition of the stream itself, but rather the land immediately adjacent to the stream. It is generally defined as the transitional zone between terrestrial and aquatic habitats, and usually corresponds to the flood plain area. The riparian zone serves as a buffer between the stream and the uplands. The better the quality of the riparian zone, the better it serves its buffer roles of shading the stream from thermal impacts, slowing down runoff to the stream to control erosion, and trapping nutrient runoff that would otherwise end up in the stream. The wider the riparian zone and the more diverse the vegetation within the riparian zone, the better the condition of the stream. Again, a variety of predominately native vegetation within the riparian zone is of higher quality than a riparian zone dominated by a few species of mostly invasive exotic vegetation.
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Habitat Assessments Combined with Biological Monitoring
In-stream aquatic biological communities that are found to be impaired often
are a result of degraded habitat. Table 1 describes four possible
simplified scenarios relating biological condition to habitat condition.
For example, if habitat is degraded, the biological community would
be expected to be impaired. However, if the habitat is not degraded,
but the biological community is impaired, then chemical contamination
Table 1. Generalized summary table to assist with explaining causes of biological impairment.
||Possible Chemical Contamination
||Habitat probably primary cause
For more detailed examination of the correlation between biological and habitat condition, a graphic representation of percent biological condition versus percent reference condition is plotted. A generalized trend line among these two variables is fitted to the graph, with habitat condition being the independent variable and biological condition the dependent variable. Biological and habitat condition of various monitoring points are referred to as a percentage of reference condition; that is, the all points are referenced to the best attainable conditions.
Improving Habitat Quality with Stream Restoration
DEP restores streams with damaged habitat. For stream restoration to be most effective and remain in place, uncontrolled stormwater flows to the stream must be controlled which often involves retrofitting stormwater management ponds in sequence with the stream.
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Data and Data Requests
Montgomery County has collected habitat data from 1994 to the present. Most monitoring stations have Rapid Habitat Assessment data for both the spring benthic and summer fish collections.
Habitat Data Table
||Two letter stream code + two letter stream reach code + order (1-4) + reach number (01-99).
||The date that the station was sampled.
||A three character code that designates whether the habitat information was collected during a fish sample (BIF) or a benthic sample (BIB).
||In-stream cover graded according to the scheme 16-20 = optimal; 11-15
= suboptimal; 6-10 = marginal; 0-5 = poor.
||Epifaunal substrate graded according to the scheme 16-20 = optimal; 11-15 = suboptimal; 6-10 = marginal; 0-5 = poor.
||Embeddedness of gravel, cobble, and boulders by sediment load graded according to the scheme 16-20 = optimal; 11-15 = suboptimal; 6-10 = marginal; 0-5 = poor.
||Channel alteration (channelization or dredging) graded according to the scheme 16-20 = optimal; 11-15 = suboptimal; 6-10 = marginal; 0-5 = poor.
||Sediment deposition outside of the water column graded according to the scheme 16-20 = optimal; 11-15 = suboptimal; 6-10 = marginal; 0-5 = poor.
||Frequency of riffles in the 75 meter section of the stream being sampled. Graded according to the scheme 16-20 = optimal; 11-15 = suboptimal; 6-10 = marginal; 0-5 = poor.
||Channel flow status. This measurement ranges from full at normal stream flow to very little water in the channel. Graded according to the scheme 16-20 = optimal; 11-15 = suboptimal; 6-10 = marginal; 0-5 = poor.
||Vegetative bank protection on the left bank when facing downstream. Graded according to the scheme 9 -10 = optimal; 6-8 = suboptimal; 3-5 = marginal; 0-2 = poor.
||Vegetative bank protection on the right bank when facing downstream. Graded according to the scheme 9 -10 = optimal; 6-8 = suboptimal; 3-5 = marginal; 0-2 = poor.
||Bank stability on the left bank when facing downstream. Graded according to the scheme 9-10 = optimal; 6-8 = suboptimal; 3-5 = marginal; 0-2 = poor.
||Bank stability on the right bank when facing downstream. Graded according to the scheme 9-10 = optimal; 6-8 = suboptimal; 3-5 = marginal; 0-2 = poor.
||Width of the riparian zone on the left bank as distance to the nearest human activities (i.e. parking lots, roads, mowed lawns, etc.) Graded according to the scheme 9-10 = optimal; 6-8 = suboptimal; 3-5 = marginal; 0-2 = poor.
||Width of the riparian zone on the right bank as distance to the nearest human activities (i.e. parking lots, roads, mowed lawns, etc.) Graded according to the scheme 9-10 = optimal; 6-8 = suboptimal; 3-5 = marginal; 0-2 = poor.
||Short text field for any habitat comments not covered by the above attributes.
Habitat Narrative Data Table
||The station field is a nine character code that identifies the station name. The stations are a combination of the two letter code for the watershed+ the two letter code for the subwatershed + the single digit stream order code+ the sequential reach number.
||Designates whether the sample was for Benthics or Fish.
||The year in which the station was sampled.
||The date the station was sampled.
||The final habitat summary score (0-200).
||Descriptive word to describe the condition of the stream in relation to reference streams. Narratives are either Excellent (166-200), Excellent/Good (154-165), Good (113-153), Good/Fair (101-112), Fair (60-100), Fair/Poor (48-59) or Poor (0-47).
Habitat scores are scored by a team of at least two biologists, and are somewhat subjective. Ideally, the scores from spring to summer should be somewhat similar.
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Submitting a Data Request
If you are interested in obtaining data or protocols, please contact DEP at email@example.com. In your request, please provide the following information:
Name, organization (if applicable), phone number, and/or email address
Type of data requested
Time frame requested
Explanation for use of data (helps to personalize the data request)
Preferred method of data retrieval (email, CD by mail, FTP, pick up CD or materials from DEP offices)
EPA's Rapid Bioassessment Protocols (RBP)
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