Collaborative Research: LTREB Renewal - River ecosystem responses to floodplain restoration

Floodplains are the areas alongside rivers that are affected by water movement. Floodplains provide many important benefits to people, yet they are also susceptible to changes such as flooding, pollution, and other disturbances. Understanding the effects of long-term changes in river ecosystems affected by metal pollution is extremely important. This project studies changes over ten years in the Upper Clark Fork River in Montana following a large project that restored vegetation and removed contaminated soil after damage from extensive mining in the river’s headwaters. Changes in land use and wastewater treatment are also altering nitrogen and phosphorus concentrations along the river. Since 2013, nearly 17 km of river has been restored and three core data sets have been collected, which were initiated decades before the restoration. The long-term measurements and the spatial scale of the study provides an opportunity to observe the ecological processes involved in restoration practices. Several undergraduate and graduate students are educated as part of this project, data are made available to the public, and results are shared with many stakeholders in this river system through the Clark Fork Science Forum. The study system of the Upper Clark Fork River in Montana, has several unique qualities that enable this project to make significant scientific advances. First, the system has received high inputs of metals that have since ceased. This enables investigation of the ecosystem dynamics over time in response to this cessation. Second, the investigators have closely observed ecological and biogeochemical responses over decadal timescales, which is the appropriate timeframe to study the types of slow processes involved in river ecosystem recovery. The project generates core data sets including: 1) influences on organic matter and sediment metals, 2) changes in upstream-downstream gradients in sediment metals, 3) metabolic responses to floodplain reconnection in restored reaches during the spring flood pulse vs. summer baseflow, 4) changes in metal bioavailability caused by interaction with dissolved organic matter, and 5) measurements of nitrogen, phosphorus, and dissolved organic carbon in restored and unrestored parts of the river. Ultimately, this project investigates river ecosystem responses over large spatial (>200 km) and temporal (> decadal) scales. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.