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Aquatic Life Use Support (ALUS)
Biocriteria Links
Additional Information
Appropriate Number of Sampling Sites
The spatial array of sampling sites in any given watershed or region and the extrapolation of biological condition and water quality to areas beyond the exact sampling point must be established in any type of assessment. Two primary guidelines can be identified for extrapolating biological assessment data to whole watersheds.
- First, the structure of aquatic communities in lotic (flowing water) systems changes naturally with an increase in size of the stream. Thresholds in this continuum of change can be established through an analysis of regional databases. The biological condition at any particular site can only be used to represent upstream and downstream areas of the same physical dimensions and flow characteristics. Likewise, lake size will influence the number of sites needed to adequately characterize a lake or area of a lake. In small lakes, one site will generally be sufficient. In large lakes with multiple basins or in reservoirs with various zones (inflow, midsection, outflow), a site representative of each basin or zone may be needed.
- Second, the change in land use patterns along a stream gradient or lake shoreline must be considered. Changes from agricultural land use to urban centers, forested parkland, etc., would warrant different representative sampling sites. A waterbody with multiple dischargers may also require numerous sampling sites to characterize the overall biological condition of the waterbody.