Using Multiple Lines of Evidence to Assess Aquatic Resource Condition for Western Public Lands: A Case Study from the Northern Great Basin, USA

TL;DRAbstract

Macroinvertebrate bioassessment tools are used to determine the biological condition of streams, but they do not identify the stressors responsible for degraded conditions nor the source of a given stressor. To address these issues, we selected sites on BLM land in Northeast California and Northwest Nevada using a spatially explicit random sample. At each site we measured biological, chemical, and physical attributes to make condition determinations. Using a multimetric index, we found 51.5% of stream km within the study area have degraded biological condition. Of the chemical and physical indicators, total nitrogen, total phosphorus, and canopy cover were the most pervasive stressors. We found that 68.0% of stream km have excessive total nitrogen, 41.7% have canopy cover below expected conditions, and 36.9% have excessive total phosphorus. Using random forest models, 27.8% of the variability in biological condition was explained by total nitrogen and phosphorus concentrations, riparia

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