Riparian Wetlands as River Modulators Across Landscapes

Abstract

In the context of a river, riparian wetlands appear as discontinuities in the typically gradual changes of riverine hydrology, biology and chemistry with drainage area. Most broadly defined, riparian wetlands include dynamically inundated wetlands within the floodplain such as wet prairie and bottomland hardwood forest, as well as flow-through wetlands such as beaver ponds, farm ponds and constructed treatment wetlands. In comparison to rivers, wetland residence time is longer, productivity is greater and biogeochemistry is often more dynamic. Riparian wetland connectivity varies with river stage, making the dynamics of the river network especially important to consider when evaluating the river-wetland complex. This talk will provide examples highlighting wetlands as river modulators in mountainous and agricultural landscapes.

In the first part of this talk, Dr. Wang will discuss how beaver-induced riparian wetlands regulate groundwater recharge and groundwater-surface water interactions in mountainous regions of the western U.S. She will present research showing that at their site, groundwater recharge from beaver ponds can increase by an order of magnitude relative to dry conditions, though much of this recharged water moves laterally through gravel bed layers and exits downstream as fast underflow. She will also show that thick soil layers can increase water residence time, allowing more water to be lost to evapotranspiration (ET) and offsetting recharge gains. Assessing how the water balance benefits of beaver ponds therefore requires considering both groundwater recharge and ET together to determine their net effect on downstream streamflow. She will conclude by discussing her group's ongoing work on beaver wetlands in northeast forests and beaver dam analog sites in the western U.S.

In the second part of this talk, Dr. Hansen will discuss how wetlands modulate riverine water quality in agricultural watersheds. She will present research indicating that wetland effect on river nitrogen concentrations does not scale linearly with area and can be limited by resource supply or hydraulic residence time. Justifying the conceptualization of rivers as river-wetland complexes, or wetlandscapes, she will share optimization results indicating that small, connected, wetlands located on headwater streams were most cost-effective at reducing nitrate concentration and synergistically reducing load. She will conclude by discussing some remaining complexities that should be addressed before implementing these results into practice or policy.

Bios

Lijing Wang is an Assistant Professor in the Department of Earth Sciences at the University of Connecticut. Her research integrates hydrologic modeling, machine learning, and hydrologic and geophysical field observations to advance understanding of groundwater-surface water interactions under climate variability and natural disturbances. She received her Ph.D. in Geological Sciences with a minor in Computer Science from Stanford University in 2023 and then worked as a postdoctoral researcher at Lawrence Berkeley National Laboratory. She is also committed to teaching data science to geoscientists, as reflected in her first-authored textbook Data Science for the Geosciences, published by Cambridge University Press in 2023. Dr. Wang’s research has been funded by the U.S. National Science Foundation and the U.S. Geological Survey.

Amy Hansen is an Associate Professor in the Civil, Environmental and Architectural Engineering Department at the University of Kansas. She received her Ph.D. in Civil Engineering with a minor in Ecology from the University of Minnesota. Amy’s research investigates ecological and hydrological controls on water quality in wetlands, streams and river networks. She uses a combination of field observations, watershed modeling and laboratory experiments to determine how land use and climate change alter ecohydrology and hydro-biogeochemistry from mechanistic to regional scales. Dr. Hansen’s research has been funded by state and federal agencies including the U.S. National Science Foundation, the U.S. Department of Agriculture, the U.S. Environmental Protection Agency, and others. She received an NSF CAREER award in 2024 and a Fulbright U.S. Scholar award in 2026 which she will complete in Chile.