Developing a Watershed Prioritization Index to Guide Restoration Initiatives in the Upper Little Tennessee River Basin

Abstract

Our research objectives were to: 1) analyze geospatial data across the Upper Little Tennessee River Basin (ULTRB) to 2) rank subwatersheds for risks to water quality at multiple spatial scales and 3) link land cover change over time to water quality and aquatic biota. We extracted land cover and landscape feature data at multiple spatial scales to categorize attributes and rank subwatersheds from least to most susceptible to impairment. Water quality and aquatic habitat were sampled in a subset of subwatersheds to verify and validate geospatially derived prioritization rankings. Historical fish and macroinvertebrate assemblage data were compiled and georeferenced to identify gaps in knowledge and target supplemental sampling efforts. Although the ULTRB is predominantly forested (>87%), ~8.5% is developed and ~2.5% is agricultural. Some subwatersheds exceeded 78% developed land use and others exceeded 34% agricultural land use within a 30m riparian zone. Altered land uses (i.e., agriculture and development) were negatively correlated to steep slopes and concentrated in areas of gentler slopes found in riparian zones. Soil erodibility was not strongly correlated to land use or slope steepness. Agricultural land uses had the strongest negative correlation to larger substrate sizes and stream reaches with more agriculture had higher percentages of finer substrates (i.e., sand and silt). Development was also positively correlated to the percentage of silt within stream reaches. Visual habitat assessments were negatively correlated to percentage of agriculture and development. Macroinvertebrate indices of biotic integrity scores were also negatively correlated with agriculture and development. However, fish indices were only negatively correlated to development. Macroinvertebrate indices were most correlated to physical habitat and positively correlated to bottom velocity and percent cobble. Macroinvertebrates were negatively correlated to percent silt and weakly correlated to turbidity. Fish indices were negatively correlated to bottom velocity and positively correlated to riffle embeddedness and chain roughness. Macroinvertebrate indices were positively correlated to visual habitat assessments, whereas fish indices did not have a strong correlation to visual habitat assessments. In general, sites with the highest percentage of agriculture had the lowest habitat quality and, consequently, the lowest biotic integrity. Sites within more developed watersheds generally had suboptimal habitat quality but had better ecological integrity compared to agricultural subwatersheds. Sites with intact riparian zones and forested headwaters had the highest habitat quality and ecological integrity. These results confirm the importance of healthy riparian zones for maintaining water quality and ecological integrity, especially in areas that are highly susceptible to erosion and intense rainfall. We recommend continued monitoring of water quality, biota, and land use changes throughout the region to further elucidate these relationships. We also recommend targeting watersheds with the greatest impairment or risk of impairment to provide the most ecological uplift during restoration efforts. Effective restoration and watershed management will require active participation from individual landowners. With regional partners, we will help to establish watershed coalitions to educate landowners, promote hydrologically connected communities, and enhance stewardship of our local watersheds. Additionally, the transferability of techniques we used could be tested in other regions of the state with inherently different landscape attributes.