The Legacy of Conventional Oil and Gas Development Outweighs Shale Gas Impacts on Stream Biodiversity.

Unconventional oil and gas development (UOGD) has expanded rapidly across the Appalachian Basin, raising concerns about its ecological effects. Although UOGD has been linked to water quality changes that may affect stream biota, a generalized relationship with stream biota remains unresolved. We evaluated how UOGD and conventional oil and gas development (COGD) influence benthic macroinvertebrate (BMI) communities across the Marcellus Shale region of Pennsylvania using one of the most comprehensive statewide BMI datasets, integrating delineated catchments, oil-gas records, and more than 6800 BMI samples. Linear mixed-effect models and co-occurrence network analyses were used to quantify effects on BMI taxonomy, functionality, and network structure while controlling for confounding factors. We found no significant association between UOGD intensity and BMI diversity metrics, whereas COGD intensity was correlated with reduced richness, diversity, and biotic integritycomparable to the impact of developed land cover. Network analyses indicated altered community structures near both development types: COGD was linked to larger, more connected networks dominated by pollution-tolerant taxa, while UOGD was associated with larger but more fragmented networks. Both forms of development were tied to increases in generalist taxa and declines in specialists. Overall, UOGD exerted limited but detectable ecological effects, whereas COGD imposed broader stress on stream communities.