Habitat assessment

The habitat evaluation process involves rating many different habitat conditions as optimal, suboptimal, marginal or poor based upon criteria (descriptions and a rating scale) included on the survey data sheets. The optimal category is a description of conditions that meet natural expectations; suboptimal includes descriptions of criteria that are less than desirable, but satisfies expectations under most circumstances; marginal is a description of moderate levels of degradation with severity at frequent intervals throughout the reach; and poor are descriptions of criteria for streams that have been substantially altered with severe degradation characteristics.  Descriptions of the habitat conditions are provided below.  For additional information go to Chapter 5 of the US EPA’s Rapid Bioassessment Protocols Manual.  The conditions here should be applied when describing the habitats of rocky-bottom streams and rivers.
Embeddedness refers to the extent to which rocks (gravel, cobble, and boulders) are surrounded by, covered, or sunken into the silt, sand, or mud of the stream bottom. Generally, as rocks become embedded, fewer living spaces are available to macroinvertebrates and fish for shelter, spawning and egg incubation. To estimate the percent of embeddedness, observe the amount of silt and sand sediments overlying and surrounding the larger gavel and cobble size particles.  You should base your embeddedness assessment on the composition of the materials that you observe.  Embeddedness is always evaluated in the riffles used for your macroinvertebrate collections.  In most cases the best person(s) to comment about this condition is the person(s) collecting macroinvertebrates.  If cobble and gravel are easy to remove from the riffle and there is little sand or silt either in the net or suspended during collections, embeddedness is minimal.  In some cases chemicals can cement (armoring) the substrate together and cause severe embeddedness. 

Sediment deposition is an estimate of the amount of sediment that has accumulated and the changes that have occurred to the stream channel as a result of deposition. Deposition occurs from large-scale movement of sediment. Sediment deposition may cause the formation of islands, point bars (areas of increased deposition usually at the beginning of a meander that increase in size as the channel is diverted toward the outer bank) or shoals, or result in the filling of runs and pools. Usually deposition is evident in areas that are obstructed by natural or manmade debris and areas where the stream flow decreases, such as bends. High levels of sediment deposition are symptoms of an unstable and continually changing environment that becomes unsuitable for many organisms. Sediment deposition should be rated throughout your reach and should not be confused with embeddedness.  Sediment deposition is probably the most difficult condition to assess.  It is a natural process and bars often form in streams that are very stable and have little sediment from the surrounding land or few problems with erosion.  When assessing this condition look for indicators that are unusual or beyond what is expected to be normal for the stream.  The most effective way to learn is to view many different stream types representing both degraded and natural conditions.  In most cases island formation, especially in small streams (1st through 3rd order), is an indication of excessive deposition.  The most common cause for unusual or un-natural deposition in most streams is human encroachment (i.e. structures such as bridges, roads, culverts etc. to close to the stream or built so that the stream is narrowed) and bank erosion. Steep sloping banks with exposed surfaces are more likely to erode.  Undercut banks can often erode but are sometimes very stable if covered with vegetation, tree roots and rocks.  Look for deposition around eroding banks, especially if they show bare soils consisting mostly of fine materials (fine gravel, sand and silt).  Hard surfaces no matter how steep or undercut are less likely to erode

The next two conditions are assessed on both the right and left side of the stream.  Note: Right and left are determined by facing downstream. 

The bank stability condition evaluates whether the stream banks are eroded (or have the potential for erosion). Steep banks are more likely to collapse and suffer from erosion than are gently sloping banks, and are therefore considered to be unstable. Signs of erosion include crumbling, un-vegetated banks, exposed tree roots, and exposed soil. Eroded banks indicate a problem of sediment movement and deposition, and suggest a scarcity of cover and organic input to streams. 

Riparian buffer width is an estimate of the width of natural vegetation from the edge of the stream bank out through the riparian zone. The vegetative zone serves as a buffer to pollutants entering a stream from runoff, controls erosion, and provides habitat and nutrient input into the stream. A relatively undisturbed riparian zone supports a robust stream system; narrow riparian zones occur when roads, parking lots, fields, lawns, bare soil, rocks, or buildings are near the stream bank. Residential developments, urban centers, golf courses, and rangeland are the common causes of anthropogenic degradation of the riparian zone. Conversely, the presence of old fields, paths and walkways in an otherwise undisturbed riparian zone may be judged to be inconsequential to altering the riparian zone and may be given relatively high scores. 


Riparian buffers are the most valuable protection a stream system has against outside influences.  In most cases healthy riparian directly reflects upon the condition of the stream unless the source of the insult is a specific pollutant.  Enhancement of the riparian buffer by re-planting native grasses, forbs, shrubs and trees is the first step in the recovery of the stream back to a more natural condition.  Some of the benefits of a healthy riparian buffer include: 
  • Provides organic material as food for invertebrate, fish and wildlife;
  • Supplies large and small pieces of woody debris that provide habitat for fish, invertebrates and amphibians;
  • Alters how sunlight reaches the stream and is an important temperature moderator;
  • Stabilizes stream banks and reduces erosion;
  • Filters sediment and materials from overland runoff and roots of many plants traps and holds the sediments;
  • Absorbs nutrients from overland and sub-surface flows; and
  • Reduces the impacts of flooding through temporary storage, interception/diversion and slow releases (especially wetlands) from heavy rain.

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