High-frequency monitoring of ferry-induced sediment resuspension in coastal zones

Among various human activities in densely populated coastal areas, intense ferry traffic plays an essential role in coastal processes. Several studies of fast ferry traffic have shown that wake-induced mechanical sediment disturbance harms coastal environments in several ways. These include suppression of coastal vegetation, promotion of eutrophication through nutrient resuspension, sediment erosion, and enhanced coastal methane emissions. According to a recently published review on marine biodiversity loss, physical disturbance of the seabed is among the most common causes of biodiversity loss in Finnish coastal waters.

In our research, we aim to assess the rate of physical sediment disturbance caused by frequent ferry traffic near the Turku–Stockholm ferry lane in the Archipelago Sea, Finland. To capture evidence of nearshore disturbance, we use a prototype of an innovative online sediment trap. The online sediment trap is a prominent Finnish invention equipped with a computed tomography function. It performs tomographic scans of the trap tube interior, producing volumetric images of structures within it. This feature enables direct quantification of sediment flux induced by a single ferry passage, with measurements performed at an hourly timescale. These high-resolution monitoring data, combined with ferry passage data from the marine Automatic Identification System (AIS) and meteorological data, are analysed using statistical methods to uncover hidden patterns and drivers. The insights from our research are then interpreted in the context of sedimentological processes in the coastal environment to support sustainable maritime management and the protection of the fragile shallow and coastal environments of the Archipelago Sea.