Describe the EPT index and how macroinvertebrate communities reflect water quality; what do high versus low EPT richness indicate?

• A. EPT stands for Ephemeroptera, Plecoptera, and Trichoptera; high richness indicates good water quality, cold, well-oxygenated conditions, and low pollution.
• B. EPT richness indicates higher salinity tolerance.
• C. EPT richness indicates nutrient level only.
• D. EPT richness is unrelated to oxygen levels.

Answer: (A)

EPT index uses the presence and diversity of Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) to gauge stream health. These aquatic insect larvae are generally sensitive to pollution and, importantly, to dissolved oxygen levels and habitat quality. In clean, cold streams with good oxygen, you typically find a richer assemblage of EPT taxa because the habitat supports these sensitive groups. When water quality declines—through pollution, higher temperatures, sedimentation, and lower oxygen—the sensitive EPT taxa drop out and the community becomes dominated by more tolerant organisms, leading to lower EPT richness. So, high EPT richness points to good water quality, cold temperatures, and well-oxygenated conditions with low pollution; low EPT richness signals degraded water quality, often with reduced oxygen and harsher conditions for these sensitive insects.