Aquatic invertebrate abundance and biomass in Arkansas, Mississippi, and Missouri bottomland hardwood forests during winter
The Mississippi Alluvial Valley once had extensive bottomland hardwood forests, but less than 25% of the original area remains. Impounded bottomland hardwood forests, or greentree reservoirs, and naturally flooded forests are important sources of invertebrate or other prey for waterfowl, but no previous studies of invertebrate abundance and biomass have been at the scale of the Mississippi Alluvial Valley. Additionally, the Lower Mississippi Valley Joint Venture of the North American Waterfowl Management Plan requires precise, contemporary estimates of invertebrate biomass in hardwood bottomlands to determine potential foraging carrying capacity of these habitats for wintering ducks. We used sweep nets to collect aquatic invertebrates from four physiographically disjunct hardwood bottomlands in the Mississippi Alluvial Valley and Mississippi’s Interior Flatwoods region during winters 2008–2010. Invertebrate abundance varied inversely with water depth in both early and late winter, with greatest abundances in depths ranging from 10 to 20 cm. The estimate of invertebrate biomass in naturally flooded forests of the Mississippi Alluvial Valley for both years combined was 18.39 kg(dry)/ha (coefficient of variation [CV] = 15%). When we combined data across regions, sites, greentree reservoirs and naturally flooded forests, and years, the estimate of mean invertebrate biomass decreased to 6.6 kg/ha but precision increased to CV = 9%. We recommend the Lower Mississippi Valley Joint Venture adopt 18.39 kg(dry)/ha as a revised estimate for invertebrate biomass for naturally flooded forests, because this estimate is reasonably precise and less than 2% of remaining hardwood bottomland is impounded greentree reservoirs in the Mississippi Alluvial Valley. Additionally, we recommend managing to invoke dynamic flooding regimes in greentree reservoirs to mimic natural flood events and provide maximal coverage of depths less than 30 cm to facilitate foraging ducks’ access to nektonic and benthic invertebrates, acorns, and other natural seeds.