Baseline aquatic monitoring on Santa Rosa Island shows widespread reach‑scale impairment, high salinity and watershed clustering of communities

Researchers from CSU Chico and collaborators presented baseline aquatic monitoring from Santa Rosa Island (Channel Islands National Park), comparing CRAM, CSCI and habitat data across multiple sampling rounds.

The study established monitoring sites across the island and used a modified CRAM (reach‑scale components), SWAMP bioassessment protocols and CSCI calculations at resampled sites. Overall CRAM scores averaged in the mid‑70s, but the reach‑scale (bio‑phys) metrics indicated impairment at roughly half of sites. CSCI scores ranged from 0.58 to 0.93 with many sites below the common 0.79 threshold for ‘good’ condition. Specific habitat measures showed extensive bank vulnerability, low flow‑type diversity, sand‑dominated substrata and large accumulations of coarse particulate organic matter (largely Typha stands), consistent with legacy grazing impacts and the island’s harsh environment.

“Sites in Water Canyon scored highest for CSCI, most likely due to perennial flow,” the presenter said, noting that other island sites often resemble mainland developed sites in their macroinvertebrate metrics because of altered channel structure and persistent groundwater/salinity influences.

Field probes measured specific conductance commonly near 2,000 µS/cm at many sites—substantially higher than typical mainland freshwater streams—and about 55% of sites exceeded impairment thresholds for salinity. Ordination of benthic macroinvertebrate communities showed clustering by watershed (e.g., Water Canyon sites grouped together), suggesting hydrologic context drives community composition.

Presenters concluded that observed impairments are likely the product of legacy grazing combined with the island’s natural conditions; they recommended future comparisons with mainland sites having similar CSCI scores and environmental profiles, and continued monitoring to track trajectories over time.