CAREER: Nitrogen exchange and removal in riparian wetlands - the role of vegetation

Excessive biologically available nitrogen has severely degraded water quality in streams and rivers of the agriculturally managed midwestern United States. Most nitrogen loading in this region occurs during high streamflow, flooded conditions when rivers are hydrologically connected to riparian wetlands. Despite clear evidence of wetland nitrogen removal, a mechanistic understanding of removal efficiency is lacking. Using a combination of field experiments, in situ and remote sensing observations, this project investigates how wetland vegetation regulates the interplay between water transport and nitrogen removal rates in physically and biologically distinct regions of riparian wetlands. This knowledge is required to harness the potential of wetlands to mitigate surface water quality degradation. In addition, a central challenge in managing water quality is the reliance on voluntary adoption of conservation actions to reduce nitrogen inputs. The education and outreach components of this project will provide opportunities to share science relevant to water quality stewardship with community members in an engaging setting and format. Overall, this project responds to a scientific and societal demand to generalize our understanding of wetlands system performance and identifies pathways to address impaired water quality under the expanding local, national and global footprint of agriculture. The overarching goal of this proposal is to advance scientific and student understanding of the role of riparian wetland vegetation in facilitating nitrogen removal during high streamflow, flooded conditions when most reactive nitrogen loading occurs. Specifically, this project will investigate the effect of riparian wetland vegetation distribution and structure on nitrogen removal at two spatial scales. At the reach scale, observational data along the study reach will quantify wetland inundation depth and extent, hydraulic exchange rate with the channel, vegetation structure and net nitrogen removal along the reach. At the vegetated canopy scale, field experiments will be used to measure nitrogen transformation and removal rates as a function of flow rate and in-canopy vegetation structure. Net nitrogen removal rates at canopy and reach scales will be compared via a modeling approach to determine whether local-scale interactions can explain net patterns in nitrogen removal. This project additionally seeks to promote water quality stewardship through an experiential, communication focused educational initiative and student led outreach activities. Educational activities will be structured to first build university student expertise via active learning in courses then have the students teach what they have learned through a local science center and its successful existing outreach program. 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.