Land use from water quality: development of a water quality index across Pennsylvania streams

Anthropogenic stressors to lotic environments are diverse and often act in complex and synergistic ways through space and time. The need to adequately quantify and communicate these stressors in lotic environments is important for assessing stream health and informing management decisions. We used 21 physicochemical parameters from water quality samples and weighted each parameter by relationships with land use to develop a water quality index (WQI) across lotic environments in Pennsylvania. Four dominant land use categories were identified from water quality analysis: forested, urban, agriculture, and land disturbance. These categories were indexed (0-100) with low scores representing disturbed and high scores representing least-disturbed conditions for each land use category. We propose an interpretation and validation schema for establishing an overall measure of stress, while providing insight into both expected and unexpected sources of stress. The WQI was highly correlated with land use at a coarse scale, where scores decreased in response to non-forested landscapes. We then present two case studies that serve as examples of stressor quantification and communication. In addition to outperforming static measures of land use/cover, the resulting WQI serves multiple functions by communicating stream health to policy makers and citizens in an easily understood form, providing a stressor gradient for biological assessments and measuring stream condition across Pennsylvania's diverse water resources.