Scenario analysis predicts context-dependent stream response to landuse change in a heavily mined central Appalachian watershed Eric R. Merriam 1,5 , J. Todd Petty 1,6 , Michael P. Strager 2,7 , Aaron E. Maxwell 3,8 , AND Paul F. Ziemkiewicz 4,9 1 Division of Forestry, Natural Resources, and Design, West Virginia University, Morgantown, West Virginia 26506-6125 USA 2 Division of Resource Management, West Virginia University, Morgantown, West Virginia 26506-6125 USA 3 Natural Resource Analysis Center, West Virginia University, Morgantown, West Virginia 26506-6108 USA 4 West Virginia Water Research Institute, West Virginia University, Morgantown, West Virginia 26506 USA Abstract. Scenario analysis has the potential to improve management of aquatic systems throughout the Mountaintop Removal–Valley Fill mining (MTR–VF) region of central Appalachia. However, the extent to which surface mining interacts with other landuse stressors (i.e., cumulative effects) is unclear, and this limits our ability to predict the effects of new mines on physical, chemical, and biological conditions downstream. We tested for additive and interactive effects of landuse change (surface mining, deep mining, and residential development) on water quality (specific conductance and Se), habitat quality, and benthic macroinvertebrates via a uniquely designed watershed-scale assessment of the Coal River, West Virginia (USA). We derived equations for predicting in-stream response to landscape changes and predicted the outcome of a realistic future scenario involving development of 15 permitted mines. Elevated Se concentrations were directly correlated with incremental increases in surface-mining extent. Surface mining, deep mining, and residential development had additive effects on elevated specific conductance and reduced biological condition. We found evidence of a positive interactive effect (stressor antagonism) of deep mining and residential development on biological condition, presumably caused by stream-flow augmentation from deep mines. Landscape context influenced predicted impacts from construction of 15 new mines because of additive and interactive effects of landuse change. New surface mines increased the number of receiving streams exceeding chemical and biological criteria, but a greater proportion of receiving streams exceeded chemical and biological criteria at equivalent levels of new mine development when pre-existing stressors were present. When surface mining was the only stressor, §30 or 40% increases in surface mining caused 100% of streams to exceed chemical or biological standards, respectively, whereas in streams stressed by deep mining and residential development, §10% additional surface mining caused 100% of streams to exceed chemical and biological standards. Continued progress in this area will require a better understanding of how landuse change affects aquatic systems in the rest of the MTR–VF mining region, where watershed-to-watershed variation in landuse patterns probably causes variability in ecological response. Key words: scenario analysis, additive vs interactive effects, coal mining, residential development, landscape indicators. Human alteration of natural landscapes is among the greatest threats to aquatic ecosystems (Allan 2004). Watershed characteristics are important deter- minants of aquatic ecosystem structure and function (Likens and Bormann 1974, Hynes 1975), and recent advances in geographic information systems (GIS) and enhanced resolution of spatial data sets have 5 E-mail addresses: emerriam@mix.wvu.edu 6 jtpetty@mail.wvu.edu 7 mstrager@wvu.edu 8 aaron.maxwell@mail.wvu.edu 9 pziemkie@wvu.edu Freshwater Science, 2013, 32(4):1246–1259 ’ 2013 by The Society for Freshwater Science DOI: 10.1899/13-003.1 Published online: 8 October 2013 1246