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Biological surveys can be implemented in several tiers, ranging
from a simple and inexpensive screening to detailed field sampling,
analysis, and assessment. Each integrated tier includes both biological
and habitat components. Higher tiers require successively more effort
and yield more reflect higher quality information and reduced uncertainty
in the final assessment. The tiered approach gives agencies flexibility
in planning and implementing biological surveys. A desktop screening
and three field survey tiers are described below.
Tier 0
Tier 0 is a desktop screening assessment that consists of compiling
documented information for the ecosystems of concern through a literature
search and sending survey questionnaires to local experts. No field
observations are made at this assessment level. Desktop screening
should precede any of the three subsequent tiers. Its purpose is
to support the planning for monitoring and more detailed assessments.
Information to be compiled in Tier 0 includes area and geomorphometric
classification; habitat type; watershed land use; population density;
NPDES discharges; water quality data (i.e., temperature, DO, pH,
turbidity); biological assemblage data; and water column and bottom
characteristics.
Tier 1
Tier 1 is the least complex of the survey approaches. It consists
of a one-time visit to sites during a suitable, predetermined index
period to collect biological and habitat data using standardized
methods. The focus of this tier is on developing screening or survey
information. These variables include a rudimentary identification
of organisms (i.e., benthos, fish, macrophytes, or phytoplankton),
water column characteristics (i.e., temperature, DO, pH, Secchi
depth and/or turbidity, water depth), and bottom characteristics
(i.e., grain size, total volatile solids, and sediment toxicity).
States may choose some variation of this list depending on regional
characteristics and resources. Evaluation of the data collected,
as well as historical data for the area, leads to an initial classification
of sites and identification of candidate reference sites.
Tier 2
Tier 2 is more complex. A higher level of detail is incorporated
into the standardized biological survey methods and multiple visits
to the site are made to address temporal variability and seasonality.
Another assemblage (epifauna) could be selected in addition to those
listed above. Water column nutrient measurements are added to the
Tier 1 water column characteristics. More detailed grain size measurements,
plus total organic carbon, are added to the bottom characteristics.
The data collected in this tier will allow the development of preliminary
biocriteria.
Tier 3
Tier 3 is the most rigorous survey tier. It includes multiple site
visits to account for seasonal variations in the selected ecosystem
biological assemblages and should incorporate supplemental studies
which might be necessary for diagnostic assessment of the potential
causes of observed impairments. This tier adds water column pesticides
and metals measurements, plus full grain size characterization,
and measurement of acid volatile sulfides and sediment contaminants.
This tier also allows the resource agency to develop a database
sufficient to support resource management activities to reduce the
identified impairments and to develop and refine biocriteria.
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