Macroinvertebrate diversity, particularly taxa within Ephemeroptera, Plecoptera, and Trichoptera (EPT), serves as a critical indicator of habitat quality and forms the base of the aquatic food web for native fish species, including Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi). As these trout are of ecological and cultural significance to the Kalispel Tribe, understanding the land use drivers of their food sources is vital for watershed management.
We sampled macroinvertebrates from tributaries in the Lake Pend Oreille basin to evaluate how land use influences community structure, biomass, and voltinism. Site-specific land use was classified by extracting pixel values from the USGS Annual National Land Cover Database (NLCD) Collection 1.1 using the 'Extract Multi Values to Points' tool in ArcGIS Pro. Sites were categorized as Evergreen Forest (NLCD 42), Woody Wetland (NLCD 90), or Developed (NLCD 21–24). We collected Surber samples (n = 22) across these gradients, targeting Evergreen Forest (n = 17), Woody Wetland (n = 3), and Developed (n = 2) reaches.
Our results revealed distinct productivity hierarchies. Woody Wetland sites consistently supported the highest biodiversity (Mean Shannon H’ = 2.21) and total biomass (>68 mg/sample), driven by large-bodied, univoltine shredders (e.g., Tipulidae). Evergreen Forest reference sites exhibited high variability (H’ range: 0.56–2.40), where mean diversity (H’ = 1.66) was frequently dampened by episodic blooms of multivoltine taxa. In contrast, Developed sites maintained high diversity (H’ ~1.97) comparable to reference reaches but supported the lowest standing crop biomass (~10 mg/sample), suggesting that urbanization may limit secondary production despite maintaining taxonomic richness.
These findings suggest that woody wetlands function as critical high-production habitats that may subsidize downstream food webs. Furthermore, the high variability in forest reference sites highlights the importance of distinguishing between natural disturbance regimes and anthropogenic degradation when establishing bioassessment criteria. This study provides a refined framework for identifying key habitats that maximize food web stability for native trout populations.