The types of animals living in lake and stream bottom sediments, Benthic Macroinvertebrates, serve as an indicator of long-term conditions and are periodically examined and enumerated to assess overall water and sediment quality conditions. Seminole County Scientists use methods established by The Florida Department of Environmental Protection (FDEP) to determine if the lakes and streams within our county support a healthy, well-balanced aquatic animal community or if human disturbance has impacted a system.
What are benthic macroinvertebrates?
Benthic (meaning "bottom-dwelling") macroinvertebrates are small aquatic animals and the aquatic larval stages of insects. They include dragonfly and stonefly larvae, snails, worms, and beetles. They lack a backbone, are visible without the aid of a microscope and are found in and around water bodies during some period of their lives. Benthic macroinvertebrates are o~en found attached to rocks, vegetation, logs and sticks or burrowed into the bottom sand and sediments.
Why is it important to evaluate benthic macroinvertebrates?
Benthic macroinvertebrates are commonly used as indicators of the biological condition of waterbodies. They are reliable indicators because they spend all or most of their lives in water, are easy to collect and differ in their tolerance to pollution. Macroinvertebrates respond to human disturbance in fairly predictable ways, are relatively easy to identify in the laboratory, often live for more than a year and, unlike fish, have limited mobility. In fact, because they cannot escape pollution, macroinvertebrates have the capacity to integrate the effects of the stressors to which they are exposed, in combination and over time. Biologists have been studying the health and composition of benthic macroinvertebrate communities for decades.
What do benthic macroinvertebrates tell us about the condition of water?
Evaluating the abundance and variety of benthic macroinvertebrates in a waterbody gives us an indication of the biological condition of that waterbody. Generally, waterbodies in healthy biological condition support a wide variety and high number of macroinvertebrate taxa, including many that are intolerant of pollution. Samples yielding only pollution-tolerant species or very little diversity or abundance may indicate a less healthy waterbody. Biological condition is the most comprehensive indicator of waterbody health. When the biology of a waterbody is healthy, the chemical and physical components of the waterbody are also typically in good condition.
What methods are used by Seminole County Scientists?
For flowing waters (, the following methods are used in Seminole County to determine if the macroinvertebrate communities are healthy or imbalanced: rivers and streams)
Stream Condition Index (SCI)
The Stream Condition Index (SCI) is a multi-metric index that assesses the biological health of stream ecosystems' by the evaluation of the population and diversity of macroinvertebrates that are found in a 100 meter stream reach. The SCI method consists of collecting 20 D-frame dipnet sweeps (0.5 m in length) of the most productive habitats in a 100 meter reach of stream. The organisms are sub-sampled, sorted, and identified to the lowest practical taxonomic level. The resulting data is used to calculate the SCI which is based on ten biological metrics of invertebrate health. The points from each of these metrics are then summed to determine an overall score of biological health, with scores of 64-100 considered "exceptional", scores from 40-63 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. They differ 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 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 final BioRecon score is regionally adjusted and normalized to a range from Oto 10 points. Scores of 6 to 10 are "exceptional," scores from 4 to 6 are considered "healthy," while scores below 3 indicate impairment.
Stream Habitat Assessment
Overall habitat quality is determined by measuring eight attributes known to have potential effects on the stream biota. DEP bioassessment protocols require a habitat assessment at each stream site, which involves mapping the stream and conducting a series of observations. Using all the information collected, each of the eight habitat parameters are given a score (ranging from 1 to 20, with 20 being the highest quality).
The primary habitat parameters are:
Substrate Diversity - an indicator of the number of productive habitats (snags, roots, aquatic vegetation, leaf packs or mats, and rock) present in a stream
Substrate Availability - an indicator of what percentage of the area of the stream bed is composed of productive habitats (as listed above)
Water Velocity - a valuation based on the maximum observed velocity of the stream at a typical transect, where higher velocities typically receive higher scores
Habitat Smothering - an indicator of the percentage of the area of the stream bed which is covered or "smothered" by sand, silt, or algae accumulation
The secondary habitat parameters are:
Artificial Channelization - a visual interpretation of the anthropogenic channelization of a stream based on its physical alteration from natural stream patterns (sinuosity) and the presence of artificial bank structures
Bank Stability - a visual interpretation of the stability of a stream's banks based on evidence of or potential for erosion or bank failure
Riparian Buffer Zone Width - a valuation based on the estimated width of the riparian vegetative buffer on each side of the stream
Riparian Zone Vegetation Quality - a valuation based on: the percentage of riparian zone surfaces which are vegetated by native plant species; the presence of the expected vegetative classes (such as trees, understory shrubs, and groundcover); and evidence of community disruption (for example, bare soil, mowed areas, and vegetative harvesting)
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).
For , the following method is used in Seminole County to determine if the biological communities are healthy or imbalanced: lakes
Lake Condition Index (LCI)
The Lake Condition Index (LCI) is used to monitor and assess the biological condition of Florida Lakes by using benthic macroinvertebrate communities as indicators to identify trends within similar lake systems. This is achieved by sectioning off a lake into 12 equal pieces, and a "grab" is taken in each segment, between 2 and 4 meters deep, using an Ekman sampler. The 12 grabs are then combined into a single composite sample, and each sample is randomly subsampled to a count of at least 100 organisms, which are identified to the lowest practical taxonomic level. (Lakes greater than 1000 acres are divided into two or more basins and are retained as separate samples).
The LCI is calculated by combining six benthic macroinvertebrate measures which appear to be responsive to lake stressors (urban runoff, agricultural drainage, contamination, etc.). The LCI score is produced from the mean of those six measures. Scores greater or equal to 55 are considered "Very Good", 35-54 are considered "Good", 18-34 are considered "Poor", and anything less than 18 is considered "Very Poor".