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Ecological Intelligence / Subject

macroinvertebrates

Peer-reviewed North America

The Elwha's insects returned in number before their river community recovered

Evidence
Peer-reviewed
Geography
Elwha River, Washington, United States
System
River / dam removal / sediment disturbance

WHAT THE EVIDENCE SAYS

Following removal of the Elwha and Glines Canyon dams, more than 20 million tonnes of reservoir sediment moved downstream as passage reopened to more than 90% of the watershed. Across five river reaches and nine years of observations, benthic invertebrate density fell as much as 95% during active removal, then returned near baseline within roughly three years of peak sediment transport. Taxa richness and community composition, notably some caddisflies and longer-lived groups, remained altered after that interval.

WHY IT MATTERS / OUR READ

The ecological signature of a restoration project can contain immediate disturbance, recovery in one metric and prolonged change in another. Restoration success criteria should distinguish connectivity, organism numbers, sensitive taxa and community composition; the years after construction are part of the intervention, not an optional follow-up.

CAVEATS / UNCERTAINTY

Observational before-during-after monitoring was conducted in one very large dam-removal system, with fish recolonization, sediment and habitat succession interacting. A numerical rebound does not prove all functions or populations are restored; these outcomes do not imply dams should remain.

SOURCE

Frontiers in Ecology and Evolution — Morley et al. (2026)
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Nine years of monitoring after two large dam removals show that the rebound in insect abundance and the recovery of community composition are not the same milestone.

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Peer-reviewed Europe

Hydropower lakes looked less different by richness than by what kinds of invertebrates remained

Evidence
Peer-reviewed
Geography
Trøndelag, central Norway
System
Regulated and unregulated lakes; littoral macroinvertebrate communities

WHAT THE EVIDENCE SAYS

Researchers compared littoral macroinvertebrates in three hydropower-regulated lakes and three nearby unregulated lakes across eight sampling events in 2023–2024. Regulated lakes tended to have lower abundance and richness, but those headline differences were not statistically decisive; functional-trait composition showed clearer separation, with temporarily attached taxa and taxa using vegetation or silk cases much more strongly represented in controls.

WHY IT MATTERS / OUR READ

The management signal is methodological: a community can be reorganized without a large or statistically clear change in simple richness. Where hydropower operations are assessed ecologically, trait composition and littoral function can reveal filtering that species counts alone may miss.

CAVEATS / UNCERTAINTY

The study covered only six lakes and used a space-for-time comparison rather than before–after experimental regulation. Lakes differed in physical characteristics, sampling was concentrated at one littoral area per lake, and operational data were partly proprietary; the richness and abundance results should therefore remain explicitly uncertain.

SOURCE

Aquatic Sciences
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In six central-Norway lakes, abundance and richness differences were uncertain, while functional traits exposed consistent filtering under 4–6 metres of water-level regulation.

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