H154-04
Building a mechanistic understanding of phosphorus retention on floodplains to inform restoration prioritization in the Lake Champlain Basin

Monday, 14 December 2020: 16:09
Virtual
Rebecca Manners Diehl1, Beverley Coghill Wemple1, Kristen Underwood2, Eric D. Roy3 and Donald S Ross4, (1)University of Vermont, Geography, Burlington, VT, United States, (2)University of Vermont, Department of Civil and Environmental Engineering, Burlington, VT, United States, (3)University of Vermont, Rubenstein School of Environment and Natural Resources, Burlington, VT, United States, (4)University of Vermont, Plant and Soil Science, Burlington, VT, United States
Abstract:
Because floodplains can slow flood waters and act as significant sinks for sediment and nutrients, watershed plans focused on improving water quality and enhancing flood resiliency are increasingly relying on such natural infrastructure. Yet, many floodplains are hydrologically disconnected and/or land-use history prevents them from properly functioning, requiring significant investment in floodplain improvements. To identify optimal places to restore, protect, or enhance floodplains, we are building a mechanistic understanding of the controls on the existing and potential capacity of floodplains to contribute to nutrient reduction targets within the Lake Champlain Basin (LCB).

In 2019, we established 184 monitoring plots on floodplains that represent the range of local and watershed environmental gradients present within the LCB, Vermont (i.e., watershed size, inundation frequency, valley characteristics, land use, etc). Each plot consists of four 15 cm x15 cm square artificial turf mats secured to the ground. Data collected at 140 plots, following four floods, were analyzed for total dry mass, percent organics, and total phosphorus (TP). Our results to date indicate that the surface’s inundation frequency exerts a strong control on deposition rates, which along with upstream land use and valley confinement and slope, determines a floodplain’s TP retention capacity.

Empirical relationships linking environmental variables and TP retention rates derived from this monitoring work will inform Vermont’s Functioning Floodplain Initiative, currently in development. The goal of this initiative is to highlight the importance of floodplains and provide stakeholders with tools to explore the numerous co-benefits of natural floodplains. Our work, when linked to complimentary work on the dynamics of soluble P, is likely to highlight the importance of hydrologically reconnecting floodplains, notably in moderately low-gradient settings.

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