| Summary: | Degradation of streams in urban-rural fringe regions occurs through complex interactions between hydrological, physical, chemical and biological mechanisms of the stream environment and surrounding landscape. Biological monitoring using macroinvertebrates may capture the complex and cumulative influences of land activity on the stream environment. The Salmon River catchment in the township of Langley, British Columbia, Canada straddles urban and rural environments in the Lower Fraser Valley. To date the Salmon River catchment has been subject to several environmental surveys. Following these earlier investigations, this study quantified relationships between the stream environment and changing land activity, across multiple scales, from 1975 to 2005, using macroinvertebrates as environmental integrators.
Current and historical water, sediment, and macroinvertebrate information along with land use and land-cover evaluations were used to quantify relationships between the macroinvertebrate community and land activity in the catchment.
Spatial and seasonal results for specific conductivity (a total dissolved ion indicator) and NO₃⁻-N and PO₄³ (nutrient indicators) traced groundwater and overland inputs to the stream environment. Nitrate guideline exceedances occurred at groundwater-influenced sites. Elevated sediment trace metal concentrations and Zn guideline exceedances occurred mid-reach in the catchment. Peak total macroinvertebrate and sensitive taxa abundance occurred mid-reach in the catchment in 2005, while richness and proportional sensitive abundance peaks were seen at groundwater-influenced sites. The dominance of tolerant to moderately pollution tolerant taxa occurred throughout. Despite historical water quality concerns at groundwater-influenced sites, greater shifts in community composition occurred in headwaters regions. Patterns of land use and land cover changed in sensitive areas (i.e. above aquifer and in the headwaters). A greater number of correlations between land activity and macroinvertebrate measures occurred at streams sites with 100 m buffers. The abundance of sensitive taxa positively correlated with the amount of agricultural land use, while rarefaction declined. Several Macroinvertebrate functional feeding groups correlated positively to forest cover, while sensitive taxa abundance and Zn concentrations declined. Results suggest continued water quality and sediment trace metal concerns, while macroinvertebrate results point to nutrient enrichment and greater historical variability in headwaters regions. Agricultural activity appears to have a stronger influence on aspects of the stream environment despite the presence of urban-rural land activity.
|
|---|
