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Development and Application of DEP Bioassessment Methods
Biological assessment provides a direct measure of designated use attainment for the vast majority of Florida’s surface waters, where the goal is propagation and maintenance of a healthy, well balanced aquatic community. Because accurate assessment requires that the methods be customized for specific system types, Florida DEP has developed biomonitoring tools for streams, lakes, and wetlands. The methods for streams (Stream Condition Index and BioRecon) and lakes (Lake Vegetation Index) have been comprehensively validated and calibrated using the process described below. While standardized sampling and interpretation methods for wetlands have been developed, they have not yet been fully calibrated. There exists a “biological integrity” determination in marine waters (measured as a 25% reduction in Shannon diversity); however, development of more sophisticated marine bioassessment methods is still in its infancy. Check this site periodically for updates on the development of these tools.
In 1993, the Regionalization Project for Florida delineated 13 sub-ecoregions from the 3 ecoregions originally determined in the Ecoregions of the Conterminous United States (1987) mapping project. Within 9 of the regions, stream reference sites were identified to establish biological expectations. The southernmost ecoregion, and its 4 sub-ecoregions, was not included in stream biocriteria development because of its unique ecological characteristics (typical streams are extremely rare; generally only canals and occasionally flowing wetland sloughs or strands are found in this area).
Using the recently developed 20 dip net sweep technique, data was collected and analyzed from the ecoregions north of Lake Okeechobee. After examining data from five years of twice-yearly sampling, the 9 ecoregions were collapsed into 3 relatively homogeneous bioregions, consisting of the panhandle, the peninsula (excluding the Everglades Ecoregion) and northeast Florida.
The final products of Florida’s stream bioassessment development include the current ten-metric Stream Condition Index (SCI) and the six metric Bioreconnaissance (or BioRecon). The SCI is the primary indicator of stream ecosystem health, identifying impairment with respect to minimally disturbed condition. The BioRecon is used as an initial watershed screening method to determine whether or not additional resources should be allocated to the area, such as sampling using the SCI method. A major recalibration of the SCI, using the Human Disturbance Gradient (HDG) and Biological Condition Gradient (BCG) approaches, occurred in 2007. To provide information for interpreting bioassessment results, a standardized evaluation of habitat conditions is performed concurrently with SCI and BioRecon sampling. For additional technical information about the development of the modern SCI and BioRecon tools, see Bioassessment Publications page.
The SCI is a composite macroinvertebrate index for use in flowing streams. Sampling consists of 20 dipnet sweeps of the most productive habitats found in a 100-meter stretch of a stream. DEP SOP FS 7420 outlines the protocol to be used in calculating an SCI for a watercourse. Organisms collected in these sweeps are preserved and brought back to the laboratory for processing in accordance with the DEP SOP LT 7200. Data generated on the taxonomy and abundance of these organisms is used to calculate ten biological metrics, each of which has been shown to respond predictably to human disturbance. The metrics are:
The majority of these metrics decrease in response to adverse human influences, while two of the metrics (% dominant taxon and % very tolerant taxa) increase in response to human disturbance. Once the metrics are calculated, points are assigned for each metric based on criteria which have been regionally calibrated and are contained in DEP SOP LT7200. The points from each of these 10 biological metrics are then summed to determine an overall score of biological health, with scores of 64-100 considered “exceptional,” scores from 40 to 63 considered “healthy,” and scores of 0-39 considered “impaired.”
BioRecon is the initial screening tool for streams, intended to rapidly assess a site to prioritize it for more intensive sampling. The SOP for Performing BioRecons (DEP SOP FS 7410) differs from that for an SCI sample in that only four dipnet sweeps of the most productive habitats are performed. A Biorecon also differs from SCI sampling in that the organisms are sorted in the field using the BioRecon Field Sheet (FD 9000-01) to target specific numbers of individuals for subsequent laboratory identification. Regionally based thresholds specific to this method have been established for each of 6 calculated metrics (a subset of the 10 metrics used in the SCI). The metrics in the BioRecon assessment, all of which decrease in response to human disturbance, include:
The final Biorecon score is regionally adjusted and normalized to a range from 0 to 10 points. Scores of 6 to 10 are “exceptional,” scores from 4 to 6 are considered “healthy,” while scores below 3 indicate impairment.
Overall habitat quality is determined by measuring eight attributes known to have potential effects on the stream biota. FDEP bioassessment protocols require a field habitat assessment at each stream site using DEP SOP FT 3100, which involves a mapping exercise (using FD 9000-04, see sample) and conducting a series of observations as specified in the Physical/chemical characterization SOP (DEP SOP FT 3001). Using all the information collected, each of the eight habitat parameters on the Field Habitat Assessment Form (FD 9000-05) is given a score (ranging from 1 to 20, with 20 being the highest quality).
The primary habitat parameters are:
The secondary habitat parameters are:
The values assigned for each of these parameters are then averaged and assigned a rating corresponding to one of four categories (“optimal”: 120-160 points, “suboptimal”: 80 to 119 points, “marginal”: 40 to 79 points, and “poor”: 8 to 39 points).
Incorporation of Stream Assessment Tools into Program Areas
Several program areas use these bioassessment tools. Regulatory applications include:
Non-regulatory applications include:
Florida DEP has developed two methods to assess periphyton communities, one for species composition and the other to estimate attached algal coverage. Algae respond to a number of stressors, making them potential early indicators of adverse aquatic change.
The Qualitative Periphyton Sampling SOP (DEP SOP FS 7220) is a method for the collection of algal community composition information from natural substrates. A total of 10 sample aliquots are apportioned across available habitats (snags, roots, leaf packs, vegetation and rock, excluding sediments) in a 100 m stream reach. To perform the method, a seasoned substrate is chosen, and algae is removed from a 9 cm diameter area and placed into a wide-mouth jar that was been filled with 100 mL of site water. Water and algae are mixed and a 4 mL aliquot is removed and placed into a centrifuge tube. Nine additional aliquots are sampled in this manner for a final volume of 40 mL. FDEP used periphyton data collected using this SOP to attempt to develop the Stream Diatom Index.
Stream Diatom Index Development
In a process similar to that described for the SCI and LVI, DEP attempted to develop a periphyton assessment tool, the Stream Diatom Index (SDI), using a combination of the Human Disturbance Gradient (HDG) and Biological Condition Gradient (BCG) approaches. Unfortunately, the diatoms appear to be very strongly influenced by pH (as well as conductivity and color), which confounds the periphyton community response to human disturbance, including nutrient enrichment effects. The SDI does not appear to clearly or predictably respond to objective measures of human disturbance, currently making it an unreliable tool for assessing adverse human effects on stream systems. FDEP has much additional work before periphyton community composition may be used as a reliable bioassessment tool. (Final SDI Report)
Rapid Periphyton Survey
The Rapid Periphyton Survey (RPS) (conducted per DEP SOP FS 7230) quantifies the extent and abundance of algae in a 100 m stream segment. Nine observations are made every 10 m for a total of 99 observations (11 transects, including 0 and 100 m marks). A canopy measurement is made at the mid-point of each transect using a spherical densiometer. A small handful of substrate is haphazardly collected at each transect point and is visually examined for the presence/absence and for the type of algae (filamentous, diatom, or other). The average thickness is measured perpendicular to the substrate and this noted on the Rapid Periphyton Survey field sheet (FD 9000-25). When sufficient data are collected using the RPS method, DEP intends to establish an RPS threshold that indicates where the algae interfere with the designated use of a waterbody.
Florida DEP has developed lake bioassessment protocols to monitor and assess the biological integrity of Florida lakes. Initial geographic regionalization resulted in the delineation of 47 lake regions within Florida (Griffth et al. 1996. Florida Lake Regions Report. US EPA, Corvallis, OR). Although an early Lake Condition Index (LCI) was developed by comparing reference lakes to non-reference lakes, subsequent efforts in 2007 to recalibrate the LCI using the Human Disturbance Gradient (HDG) concluded that the LCI was not well correlated with adverse human effects because macroinvertebrate response was overwhelmed by natural factors (see Evaluation of Benthic Macroinvertebrates Assemblages as Indicators of Lake Condition.
Lake Vegetation Index
Because of the complications in assessing human disturbance in lakes using the invertebrate community, DEP developed methods involving the lake aquatic macrophyte community resulting in the Lake Vegetation Index (LVI), a multi-metric tool which assesses lake health based on the plant community structure. Four LVI metrics were chosen based on an HDG evaluation, and the LVI was subsequently calibrated via the BCG process. DEP currently uses the LVI as the primary method to assess biological health in Florida lakes. The LVI is sampled per DEP SOP FS 7320 and calculated per DEP SOP LT 7500. The LVI method involves dividing a lake into 12 units and identifying plants to the lowest possible taxonomic level in 4 of the 12 units. Plants are identified in each unit by a visual boat “drive by” and also via a transect approach. A frodus is deployed a minimum of five times during the transect to assess the presence of submersed aquatic plants. All plants for a unit are recorded in a single column on the Lake Vegetation Index Data Sheet (FD 9000-27) and a dominant or co-dominant is assigned based on areal extent. Unknown plants are brought back for expert identification and verification. The sampling season for the LVI is May through October. Data generated on the presence of species is used to calculate four biological metrics - each of which has been shown to respond to human disturbance. The metrics are:
Florida DEP has concluded the initial development of biological monitoring tools for wetland ecosystems. A research team, led by Dr. Mark Brown of the University of Florida's Center for Wetlands, investigated attributes from multiple biological assemblages in wetlands for use in the development of biocriteria for these systems. The wetland biological assessment tools consists of vegetation transects, 20 dipnet sweeps for macroinvertebrates, and a qualitative periphyton sample collection. The University of Florida research team developed a classification scheme for Florida’s wetland types and also completed a wetlands regionalization map. The Wetland Condition Index has three components: a Wetland Vegetative Index, a Wetland Macroinvertebrate Index and a Wetland Diatom Index. All three indices are strongly correlated with the LDI. Wetland indices were developed for isolated herbaceous wetlands, isolated forested wetlands, and forested strands and floodplain wetlands (see documents on Bioassessment Publications page). DEP ultimately plans to calibrate these indices using the BCG approach.
FDEP has conducted exploratory studies and workshops for the development of estuarine and marine bioassesment tools (see history of marine bioassessment activities). While the previous attempts have not yielded practical results, DEP is currently planning studies for further development, potentially including an evaluation of epi-benthic taxa and fish in a variety of habitat types.
For more information please email Nia Wellendorf, or call 850/245-8190.
Last updated: June 30, 2015
2600 Blair Stone Road M.S. 3500
Tallahassee, Florida 32399
850-245-8336 (phone) / 850-245-8356 (fax)