Vegetation and Waterfowl Response to a Drawdown on a Semi-Permanent Emergent Wetland

Semi-permanent emergent wetlands within the Lower Mississippi Alluvial Valley provide migratory stopover and wintering habitat resources for waterfowl. Monotypic stands of wetland obligate species (e.g., American lotus [ Nelumbo lutea ], giant cutgrass [ Zizaniopsis miliacea ]) can decrease habitat quality for wintering waterfowl in semi-permanent emergent wetlands without periodic disturbance to reset wetland succession cycles (e.g., managed drawdowns). We documented a drawdown event at Big Lake National Wildlife Refuge, a wetland complex in northeast Arkansas that provides habitat for more than 200,000 waterfowl during migration and winter. We developed deep learning models to estimate the monthly and yearly change (June–November 2021–2023) for 6 vegetation community classes before and following dewatering. Aerial survey and eBird data were used to build annual migration curves to estimate waterfowl use days and vegetation surveys were conducted to estimate energetic carrying capacity. Non-persistent emergent vegetation (i.e., moist-soil vegetation) increased 310% from fall 2021 (prior to the drawdown) to fall 2022 (following the drawdown). Other than non-persistent emergent vegetation replacing open water, there was little change in vegetation communities in fall 2022 or 2023 relative to pre-drawdown. Energetic carrying capacity more than doubled in the fall following the drawdown, but was similar the year following the drawdown relative to the pre-drawdown year. Importantly, the energetic carrying capacity still fell short of the objectives set for the refuge. To achieve waterfowl energy and use goals, Big Lake National Wildlife Refuge will require increased active management with periodic drawdowns to encourage non-persistent emergent vegetation growth.