Macroinvertebrate and organic matter export from headwater tributaries of a Central Appalachian stream

Headwater streams export organisms and other materials to receiving streams, and macroinvertebrate drift can shape colonization dynamics in downstream reaches while providing food for downstream consumers. Spring-time drift and organic matter export was measured once monthly (February-May) over a 24-h period near the outlets of 12 eastern Kentucky (USA) streams to document and explore factors governing downstream transport. We compared drift measures as loads (day(-1)) and concentrations (volume(-1)) including drift density, biomass, richness, composition, and particulate organic matter across catchment area, month, reach scale factors, and network proximity. Aquatic invertebrate drift densities were roughly 10 times greater than terrestrial invertebrate densities; aquatic richness ranged from 18 to 45 taxa with Ephemeroptera, Plecoptera, Trichoptera, and Diptera genera dominating drift sample richness and abundance. Ordination revealed that assemblages clustered by month and catchment area; organic matter exports (loads or concentrations) also varied by month and catchment area factors. While drift measures were correlated with catchment area and sample date, local factors (e.g., substrate composition, riffle length, channel slope, and network proximity) were generally non-influential. The findings can be used to inform preservation and restoration strategies where headwater streams serve as sources of colonizers and provide food subsidies to receiving streams.