Benthic Macroinvertebrate samples
were taken at 15 sites in the Paxton Creek Watershed:
- 11 of the project’s ambient monitoring
sites
- 3 of the demonstration sites
- 1 site in the headwaters of Paxton Creek
Statistical
Methods
A number of different metrics are used to
analyze the macroinvertebrate data. These metrics evaluate
the overall number and diversity of macroinvertebrate taxa
present in each sample, the percentage of pollutant sensitive
and pollutant tolerant species, and the organic pollution
tolerance of each species. Three of the metrics are described
at the right:
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Taxonomic Richness:
Total number of taxa in the sample. Number decreases with
increasing stress.
- Values ranged from 40 taxa in the
Paxton headwaters to only 12 taxa at the mouth of
Paxton Creek
- The average for all sites was about
17
Shannon Diversity Index: A
measure of taxonomic diversity of the community. Number
decreases with increasing stress.
- Values ranged from 0.73 at the mouth
of Paxton Creek to 2.34 at the Asylum Run tributary
- The average for all sites was about
1.5
- An unimpaired reference site in Powell
Creek watershed (comparable to Paxton Creek in drainage
size, ecoregions, and subecoregions) had a value of
2.60
EPT Index: Total number
of Ephemeroptera (mayflies), Plecoptera (stoneflies),
and Tricoptera (caddisflies) taxa present in a sample
(Three pollutant sensitive taxa). Number decreases with
increasing stress.
- Values ranged from 0 at the mouth
of Paxton Creek to 15 at the Asylum Run tributary
site
- The average for all sites was about
6
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