Besides fish data, many different human (
anthropogenic) landscape factors were assembled and used to characterize habitat condition. These factors include: urban and agricultural land use; intensity of different types of mining activities; impervious surfaces; estimates of nutrient loading to streams; estimates of
water withdrawals; major point sources of water pollution; and measures describing fragmentation of rivers by dams (Table 1). To increase accuracy, the 2015 stream assessment incorporated 12 additional human disturbance variables into the fish analysis compared to the 2010 assessment. Associations between all human disturbance variables, summarized in both catchments as well as stream buffers, were tested against stream
fish metrics to develop assessment scores. Additional variables incorporated into the 2015 assessment and their summary within catchments and buffers allowed for more explicit characterization of the diverse set of disturbances to stream fish habitats occurring across the Nation than what occurred in 2010, and this was made possible due in part to advances in available GIS layers.
Some important threats to fish and fish habitat that could not be incorporated into the assessment due to data limitations include: historical land use,
hydrologic changes, legacy mining, oil and gas extraction, fragmentation by culverts and small dams, sedimentation and woody debris recruitment and transport, water temperature and dissolved oxygen, other water quality impairments such as contaminants and nutrients, animal feed lots, channel and bottom morphology, forestry practices, grazing intensity, and regional habitat stressors. All of these missing variables will be addressed in future assessments as resources and data become available.
Based on missing factors and variables, 2015 habitat condition scores may underestimate the true amount of disturbance in some systems and reaches. This limitation should be kept in mind as the reader interprets the information in this report.
