Data: Existing wetland conservation programs miss nutrient reduction targets

By Shan Zuidema1, Chris Kucharik2, Richard Lammers1, Wilfred Wollheim1

1. University of New Hampshire 2. University of Wisconsin

Estimated fluxes of nitrate (as nitrogen) across the Mississippi River Basin under scenarios of wetland restoration following two existing conservation programs. At full adoption, neither program achieves needed nitrate reduction to the Gulf of...

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Version 1.0 - published on 14 Dec 2022 doi:10.13019/1N4Q-0X09 - cite this

Licensed under CC0 - Creative Commons


Manuscript abstract: Increasing coastal hypoxia results largely from riverine export of excess nutrients used for fertilization of row crops and has the potential to fundamentally change marine habitats over the next millennium.  Nutrient-rich runoff from agricultural lands in the Mississippi/Atchafalaya River Basin must decline by about half to begin reducing hypoxia in the Gulf of Mexico.  Nutrient mitigation measures should target hot-spots of excess fertilizer application or manure production and numerous studies identify wetland restoration as a critical intervention.  Here, process-based Earth system models evaluated the efficacy of existing wetland conservation programs to reduce nutrient export to the Gulf of Mexico.  We show that full adoption of two programs meet only half the nutrient reduction targets for agriculture, primarily due to subsurface storage and geographic separation between restorable lands and heavily fertilized croplands.   Daily model resolution captured the seasonal and stormflow dynamics inhibiting wetland nutrient removal due to mismatches in the timing of peak wetland effectiveness and nutrient inputs.  Considering these limitations, and large legacy pools of nitrate in the groundwater, restoration efforts should balance measures that limit new inputs and maximize treatment across all hydrologic flowpaths from field margins, through groundwater, and ultimately to rivers.

We coupled macro-scale process models of agroecology  (Agro-IBIS) and hydro-biogeochemistry (WBM), and introduced new functionality to WBM that represented water flow and nitrate transport from local croplands through field-margin treatment wetlands.   Briefly, our model of wetland denitrification assumes a well-mixed system with denitrification occurring in benthic sediments parameterized as a temperature-dependent process (Q10 = 2), with flow and nitrate mass bypassing wetland processing when wetland water storage exceeds a maximum depth.  The overall WBM framework applied here represents nitrate throughout the Mississippi River Basin considering remaining natural wetlands and scenarios of wetland restoration under the two national US programs that focus on highly optimized treatment wetlands on subsurface-drained crops (Farmable Wetlands Program), and opportunistic restoration of wetland systems where ecologically feasible (Wetland Reserve Program).

Each NetCDF file in this dataset represents the interannual mean of annual total fluxes from 1998 to 2007 across 11 different variables relating to nitrate flux throughout the Mississippi River watershed.  More detail regarding the data files are provided in the accompanying readme file.

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