Investigation of Marine Sediments at the Esso Refinery Piers in Augusta Bay, Italy

As part of efforts to assess the benthic characteristics of the sediment around the Esso piers to determine if natural deposition has improved sediment health, scientists from INSPIRE Environmental performed a combined Sediment-Profile and Plan-View Imaging (SPI/PV) survey around the Esso Piers and at three reference locations (NREF-A, REF-B, REF-D) in Augusta Bay, Sicily.

To assess sediment characteristics and benthic community status around the Esso Piers (an area with historical sediment contamination), the project team designed a comprehensive grid of stations in and around the Piers, with three reference locations serving as an undisturbed control. Historical data on sediment contamination in Augusta Bay were used to determine placement of reference areas, such that locations with minimal sediment contamination were selected. A total of 148 stations were sampled (121 at the Esso Piers, 11 at NREF-A, 12 at REF-D, and 4 at REFB). Four replicate images were collected from each station with analysis of up to three images. Physically the sediment characteristics at the Esso Pier stations were approximately similar to the background reference stations. The predominant grain-size at the Esso Piers was composed of very fine sediments which was also observed at the background areas, and both locations were found to have low sediment shear strength coupled with a sediment-water interface that was shaped by biological activity. After salinity, sediment grain-size is the primary determinant of benthic community structure, so it is important that comparative reference locations are similar in grain-size to the area of focus.

Despite the history of contaminant disturbance in Augusta Bay, and the close proximity of the Esso Piers to an active urban industry, there were little to no indications of disturbance in the sediment profiles. The aRPD depths at the Esso Pier stations were moderately deep. This important boundary layer provides a visual indication of sediment health. The aRPD is the discernable layer between oxidized and reduced sediments with its depth related to both molecular oxygen diffusion and infaunal feeding and respiratory processes. Mature, deep burrowing benthic communities were prevalent at the Esso Pier stations, and the presence and burrowing activity of these communities was found to be equivalent to background reference stations in Augusta Bay. Mature Stage 3 organisms are considered to be equilibrium taxa, and are an indication that a benthic community has not experienced disturbance in its recent history; these sensitive taxa are the first to die during disturbance.

While deposition of fine particulates undoubtedly occurs in Augusta Bay, the rate of deposition and presence of mature Stage 3 taxa makes identification of distinct depositional contact boundaries impossible. As a result, no specific inference could be made about deposition of material as it relates to recovery of the Augusta Bay ecosystem. At the Esso Pier stations there was also an absence of adverse sediment characteristics that indicate an area is perturbed by organic loading (a common trait of marine systems adjacent urban areas). There was no documentation of sedimentary methane, thiophilic bacteria, or hypoxia. The presence of one or more of these deleterious conditions can have dire impacts to the health and maturity of benthic communities, often resulting in depauperate fauna.