Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 19, 2007
Publication Date: May 1, 2008
Citation: Clark, P., Johnson, D.E., Hardegree, S.P. 2008. A direct approach for quantifying stream shading. Rangeland Ecology and Management.61:339-345. Interpretive Summary: Existing field and analysis tools are inadequate for assessing stream shading within extensive rangeland and forest stream systems. Management and regulatory standards for stream shading have been established to mitigate excessive stream temperature which may impact threatened and endangered salmonid species as well as other aquatic animals and plants. We developed and evaluated new, effective, and low-cost field and image analysis techniques for assessing stream surface shading from digital images. These research products will allow researchers, natural resource managers, and environmental quality regulators to more efficiently and effectively monitor stream shading and investigate its relationship with stream temperature variability
Technical Abstract: Excessive stream water temperature causes thermal stress in fish and invertebrates, decreases dissolved oxygen, and encourages bacterial and algal growth. Solar radiation affects stream temperature. Shade cast by riparian vegetation reduces thermal inputs to stream water. Stream shading standards have been established to mitigate excessive stream temperature. Existing shade assessment tools, however, are inadequate for extensive stream networks. Our objectives were to develop and evaluate new, effective, and low-cost field and image analysis techniques for assessing stream surface shading from digital images. We developed inexpensive field equipment and a quadrat-based technique for directly imaging stream surface shading. Random point sampling techniques were found to be the most accurate, efficient, and robust image analysis techniques. Pairing the field technique and random point-sampling image analysis techniques will enable managers to conduct ground-based, extensive assessments of stream shading or to collect ground-truth samples for even broader-scale, remote sensing-based stream shade assessments. Likely enhancements to this stream shade assessment approach include solar path modeling and use of a thermal imaging camera.