3 Methods
3.1 Field Sampling
Benthic invertebrate sampling was conducted between September 28 and October 3, 2025 by Al Irvine, R.P.Bio. (New Graph Environment Ltd.) and Tieasha Pierre (Wet’suwet’en Treaty Society), following the Canadian Aquatic Biomonitoring Network (CABIN) wadeable streams protocol (Environment Canada 2012). Samples were collected using the traveling kick-net method with a 400 μm mesh net. At each site, a 3-minute timed sample was collected by traversing a zigzag pattern in an upstream direction within the erosional zone (riffle, rapid, or fast-flowing run habitat).
Concurrent with benthic sampling, standardized habitat and water quality data were collected. Substrate composition was characterized using a 100-pebble count, measuring the intermediate axis of randomly selected particles along transects. Embeddedness—the degree to which particles are buried in fine sediments—was assessed for every 10th particle. Channel slope was measured using a lazer level.
Water quality parameters recorded at each site included temperature, pH, and conductivity. Instream habitat features documented included macrophyte coverage (percent cover in categories: 0%, 1–25%, 26–50%, 51–75%, 76–100%), periphyton coverage (5-category scale based on slipperiness and thickness), and canopy cover. Channel dimensions including bankfull width, wetted width, and depths were also recorded.
Three sites were sampled on the Neexdzii Kwa mainstem within known high-value Chinook spawning and rearing habitat (Figure 2.1). Site locations were selected to assess aquatic health upstream and downstream of potential point-source impacts, allowing comparison of species composition and community health metrics across the watershed:
- BUL-01 — the most downstream site, located just downstream of Houston and immediately upstream of the North Road overpass (Morice River FSR turnoff), adjacent to a public rest area. This reach is approximately 500 m downstream of the Houston wastewater treatment plant outfall and corresponds to CABIN historical site MOR37 (“Upper Bulkley @ Morice”), sampled in 2004 and 2018.
- BUL-04 — a mid-reach site approximately 11 km upstream of BUL-01, located just downstream of the Knockholt Bridge on McKilligan Road leading to the Knockholt Landfill.
- BUL-05 — the most upstream site, approximately 21 km upstream of BUL-01, located just downstream of the McQuarrie Creek confluence. McQuarrie Creek is a recognized cold-water tributary — Westcott (2022) placed paired temperature loggers on the Neexdzii Kwa mainstem above and below the confluence specifically to quantify its thermal influence.
All sites are accessible from public land. Triplicate kick samples were collected at each site to quantify within-site variability and enable statistical distinction between true site differences and natural spatial heterogeneity.
3.2 Laboratory Processing
Samples were preserved in 10% formalin and submitted to Cordillera Consulting Inc. (Summerland, BC) for sorting and taxonomic identification following CABIN protocols (Environment Canada 2012). Subsampling was performed using a Marchant Box to achieve a target count of 300 organisms per sample. Organisms were sorted from debris in gridded Petri dishes under a dissecting microscope, randomly selecting grids until the count target was met. Specimens were identified to genus or species level where possible, with Chironomidae identified using slide-mounted head capsules. Taxonomic determinations followed the CABIN taxonomic manual, SAFIT standard taxonomic effort, and PNAMP protocols. All taxonomists held Society for Freshwater Science (SFS) Level 2 certification.
Quality assurance procedures included both sorting and taxonomic quality control. Sorting efficiency was evaluated by re-sorting 10% of processed samples, with a 95% efficiency target required by CABIN. Taxonomic quality control involved blind re-identification of 10% or more of samples by an independent taxonomist. All samples met CABIN quality thresholds, with a total misidentification rate of 0.16% and mean sorting efficiency of 96.4%.
3.3 Data Analysis
Hilsenhoff Biotic Index (HBI), Shannon-Wiener diversity (H’, log base 2), and Simpson’s diversity (1 − D) values reported by Cordillera were independently verified by recalculating each metric from raw counts using tolerance values from the EPA Barbour et al. Appendix B [Northwest column; Barbour et al. (1999)] with SAFIT as a secondary source, and family-level fallback where genus-level values were unavailable. Independent and lab-reported values agreed closely (HBI mean absolute difference 0.09, Shannon 0.01, Simpson < 0.01), confirming the reliability of the lab-calculated metrics used throughout this report. The verification script is archived in the project repository (scripts/metrics_safit-barbour.R).
3.4 Historical Water Quality
Historical water quality data were compiled from the BC Environmental Monitoring System (EMS) for stations within the Neexdzii Kwa watershed. Stations were identified via a spatial query of BC Data Catalogue EMS monitoring locations intersected with the watershed boundary (1 km buffer), and records were retrieved from the EMS historic database via the rems R package (BC Ministry of Environment and Climate Change Strategy 2016). Nutrient and general water quality parameters were extracted and grouped by station context: Houston STP (upstream/downstream), Knockholt Landfill, Neexdzii Kwa mainstem gradient, and Buck Creek. BC Water Quality Guidelines were applied as reference thresholds — CCME trigger value (10 µg/L) for total phosphorus, 3 mg/L for nitrate, and 6.5–9.0 for pH. Ammonia guidelines were calculated per sample using the BC WQG formula conditional on concurrent pH and water temperature; where EMS temperature data were unavailable, monthly mean temperatures from ECCC hydrometric station 08EE003 (Bulkley River near Houston, 2017–2025) compiled via Allan Irvine ([2025] 2025) were substituted.
Additional water quality datasets exist for the watershed outside EMS — notably Oliver (2020) collected data that may reside in Skeena Knowledge Trust or other regional databases, and Remington and Donas (2000) generated periphyton and nutrient data not captured in the provincial system. EMS was selected as the sole data source for this analysis because it provides a standardized, publicly accessible, and programmatically reproducible pipeline via the rems package. Incorporating additional datasets would require case-by-case wrangling with no guarantee of consistent metadata, parameter codes, or quality assurance standards. Should additional data be loaded to EMS or consolidated into a comparable format, the analysis pipeline developed here can readily incorporate it.
3.5 Data Reproducibility and Reporting Framework
This report is produced using open-source tools (R, bookdown) with full version control via git. All code, data processing scripts, and revision history are accessible in the project repository, with ongoing tasks tracked via GitHub issues and version history maintained in the project changelog.