Freshwater-saltwater interface and estuarine sediment in situ assays based on post-exposure feeding of chironomids and polychaetes

An integrated approach for ecological and ecotoxicological sediment assessments along the freshwater saltwater interface (FSI) and estuarine areas in general was developed, through the adaptation of recently proposed methods for the midge larvaChironomus riparius (an in situ assay based on post-exposure feeding for sediment toxicity assessments in freshwater systems) and the development of new techniques for the polychaeteHediste (Nereis) diversicolor (an in situ post-exposure feeding assay). Based on the previously proposed methods, improvements were made to the feeding quantification ofC. riparius fourth instar larvae. A method to quantify the post-exposure feeding ofH. diversicolor was developed and optimized under laboratory conditions using newly hatchedArtemia franciscana nauplii as a food source. Assay chambers and procedures fromC. riparius assays were easily adapted forH. diversicolor in situ exposures. Sediment assays using this integrated approach were successfully performed at an uncontaminated river-estuarine system. They consisted of a 48-h exposure followed by a 1-h post-exposure feeding for chironomids and a 2-h post-exposure feeding for polychaetes. Good recovery rates were obtained after the 48-h field exposure. Fluctuations in various physicochemical variables at the FSI, due to the tidal regime, did not significantly influenceC. riparius larval post-exposure feeding rates, suggesting that uncontaminated freshwater sites located upstream of FSI areas can be used as reference sites forC. riparius in situ evaluations in estuaries. Adapted assay chambers and procedures were suitable forH. diversicolor in situ exposures.