Possible ecological effects of continuous hydraulic sediment removal as an alternative to dredging at a small port entrance (Cervia, northern Adriatic Sea)

Siltation and sediment accumulation is a problem that affects many ports and harbours worldwide. Usually, dredging is the most common technique to handle this issue, but nowadays there is increasing concern about its several effects and impacts to the marine environment, especially referred to benthic communities, so that the need to find sustainable alternatives is becoming a topic of wide interest. One of these possible alternatives is represented by the so-called sand by-passing plants. In this study, the potential ecological effects of a new sand by-passing plant, called ejectors plant, have been investigated through a before-after control-impact design (beyond-BACI). The plant was installed in the proximity of the port inlet of Cervia, a small municipality situated in Emilia-Romagna, on the northern Adriatic coast. For the study, 3 different sampling periods (one before and two after plant installation) and 5 different sampling locations (one impact and four control locations) were established. The analysis has evaluated the sediments organic matter percentages and grain size classes composition, the shell debris weight, the structure of benthic communities and fish assemblages. PCO analysis and DistLM were performed to evaluate similarity between benthic communities and to find taxa and environmental variables most correlated with macrofaunal patterns. Moreover, a literature analysis about impacts of dredging on benthic communities have been performed. All results indicate that in last sampling period, 2nd after plant installation, the two possibly affected areas (sand pickup and deposit areas, respectively) values were more similar to control ones than before, suggesting that the ejectors plant could represent an eco-friendly solution alternative to dredging for harbour siltation problems. This work is part of the LIFE15 MARINAPLAN PLUS project, which had the aim of testing the efficiency and sustainability of the ejectors plant at industrial scale.