LTREB: Collaborative research - River ecosystem responses to floodplain restoration

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The Upper Clark Fork River in western Montana has a legacy of mining pollution and flooding. A $200 million-dollar ecological restoration of the river was initiated in 2013 and will continue for 20 years. For over 20 years, state agencies and scientists have gathered data on the river's water chemistry, the algae that grow on the river bottom, and the abundance and distribution of metal contamination along 280 km of the river. These core data sets have captured the history of a highly impaired river, but most of the funding and personnel responsible for these data sets have been lost over time This research extends and capitalizes on these long-term monitoring data to address how the river's physical forms and biological processes will respond to the simultaneous influences of changing nutrient abundance and large-scale floodplain restoration. Comparisons of past and future dynamics of the river provide an opportunity for the researchers to address fundamental theories of ecology in response to a system manipulation that is rare in scope. The research will provide a framework for understanding effects of large-scale floodplain restoration that will be applicable to future river projects. Educational and outreach activities will include the establishment of a research training program for undergraduate interns, mentoring Native American undergraduate REU participants, working with a the Clark Fork Watershed Education Program, and developing a project with 5th grade science classes in rural communities along the Clark Fork River. Restoration will include removal of metal-laden floodplain soils, lowering of the floodplain to its original elevation where it will be more readily connected to the river during flooding, and re-vegetation of over 70 km of the river's floodplain closest to contaminant sources. This research will generate data to test the hypothesis that restoration will change the river ecosystem structure and function because restoration responses will reflect removal of floodplain tailings, reestablished floodplain connectivity, and reduced nutrient inputs to upstream reaches. Additionally, the research will measure how changes to upstream reaches within the drainage network will alter longitudinal gradients in energy and materials available to downstream river segments. The research will re-establish monitoring of inorganic phosphorus and nitrogen concentrations, benthic organic matter stocks, and total recoverable metals in depositional sediments. Longitudinal surveys of isotopic signatures for inorganic nitrogen will be used to track changing nutrient sources. Historical monitoring will be augmented with tracking of dissolved organic carbon concentration and composition using characterization by fluorescent spectroscopy, along with experiments to address how carbon composition influences metal bioavailability. Use of Submersible Autonomous Moored Instruments will provide high-resolution measures of pH, oxygen, and carbon dioxide that will be used to generate models of river metabolism (primary production and respiration) in order to link functional changes to altered chemical and biological environments. Together these efforts will provide opportunities to address the ecological changes in the Upper Clark Fork River over a temporal and spatial scale commensurate with landscape restoration.