Benthic infauna abundances are driven by sediment organic content and impacted by benthic restoration via dredging

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Kevin Johnson

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Estuaries worldwide are plagued by the accumulation of organic sediments from eutrophication. High levels of organic sediments smother benthic life, foster anoxia, and flux nutrients into the water column. One mitigation approach is legacy organic sediment removal via ecologically-focused dredging. Dredging for navigational purposes is common, but environmental dredging impacts are not well known. This study reports on three years of benthic population data in association with environmental dredging, including a baseline, pre-dredging period and continuing for a year after the cessation of dredging. The study estuary is the Indian River Lagoon (Florida), a diverse shallow subtropical estuary. Organisms tracked include invertebrates collected in benthic grabs. Sites sampled include stations within dredging areas, immediately adjacent, and away. Sediment organic content had inverse correlations with species richness (R²=0.74), diversity (R²=0.80) and overall densities (R²=0.72). Considering major taxa separately, population densities of crustaceans (R²=0.55), molluscs (R²=0.64), and polychaetes (R²=0.60) had inverse correlations with sediment organic content. Organic content correlates closely with silt-clay (R²=0.93) and porosity (R²=0.88), and the dissolved oxygen of the water column immediately above the sediments (R²=0.54). All correlations had significance of p<0.001, except polychaetes, p<0.016. Organisms absent from muck prior to dredging, but appearing in dredged sites during or afterwards, included polychaetes (Glycera americana, Alitta succinea, Pectinaria gouldii, Paradiopatra hispanica, Ctenodrilus serratus, and Hypereteone heteropoda) and amphipods (Cymadusa compta, Cerapus tubularis, Corophium sp., andGrandidierella bonnieroides). Environmental dredging improves conditions for benthic infauna when muck is removed, but the benefits of removing intermediate organic sediments are less clear.

Resource Type:
Audio/Video, Conference Presentation, SER2019

Society for Ecological Restoration