Presented by Beau Bauer - Email: firstname.lastname@example.orgWidgeongrass (Ruppia maritima) and other native SAV are propagated in brackish managed tidal impoundments (MTIs) in coastal South Carolina to provide forage for waterfowl and other waterbirds and habitat for aquatic invertebrates. We conducted a field study to test effects of complete drawdown (CD) to dried substrates versus partial, shallow water (0-10 cm) drawdowns (PD) on widgeongrass and other SAV biomass and aquatic invertebrate biomass in MTIs in southern coastal South Carolina. This information was lacking to estimate foraging carrying capacity and inform managers of best practices to promote waterfowl and other waterbird forage. We sampled sediments and SAV in 20 MTIs (CD n = 8, PD n = 12) and 3 non-impounded natural tidal marsh sites (control) during August 2016, November 2016, January 2017, and April 2017. We used mixed model analysis of variance to test effects of drawdown on SAV and benthic invertebrate biomasses and mixed model analysis of covariance to test effects of drawdown and SAV biomass (covariate) on total invertebrate biomass (benthic and epifaunal combined). Partially drawndown MTIs contained greater SAV and invertebrate biomasses for sampling periods with detected drawdown effects with the exception of benthic invertebrate biomasses in both CD and PD being greater than unmanaged marsh in January 2017. We also detected a positive effect of SAV biomass on total and benthic invertebrate biomass for most sampling periods. Additionally, we determined that PD MTIs had about 3 times greater potential foraging capacity for dabbling ducks than completely drawndown impoundments. We recommend partial drawdowns to maximize invertebrate and SAV biomasses and foraging carrying capacities for ducks and other waterbirds in South Carolina MTIs and similar wetlands. Additionally, we encourage complete drawdowns when deemed necessary (e.g., 23 year cycle) to regulate predatory aquatic invertebrates and fish and consolidate flocculent soils detrimental to SAV rooting and retention.