The anthropogenic use of waterways leading to and from ports entails intensive maintenance measures of the shipping channels. These activities include removal of sedimented materials which is either relocated to other parts of the waters or to land. Together with colleagues from the TU Delft, TU Delft, Netherlands (Prof. Dr. Julia Gebert, Dept. Geoscience & Engineering) we address the role that microbes and their catalyzed biochemical reactions have in relation to different maintenance strategies of the nautical depth by example of the Port of Hamburg and the Seaport Emden.
Due to the presence of degradable organic matter and reduced inorganic compounds (such as NH4+, Mn2+, Fe2+) and limited oxygen diffusion rates, reducing conditions quickly develop in fine-grained sediments settled in low-flow areas at the river bottom. Under these reducing conditions, microbially mediated degradation of sediment organic matter (SOM) results in gas production (e.g., methane, carbon dioxide). Due to the variability of SOM composition and thus its degradability, the degree of gas production varies in space and time. SOM degradation and respective gas generation may pose a series of problems, including changes sediment density, viscosity, shear strength and rheology. This in turn is reflected in delayed sediment consolidation, susceptibility of sediment constructions towards erosion and subsidence. Gas bubble production can hinder sonic depth finding. Further, methane is known to be a strong contributor to global warming. The resuspension of potential sediment-bound contaminations may also pose a further problem. In this study we address the link between microbial community composition and SOM degradability and turnover rates. These insights provide the basis for targeted changes specific maintenance procedures. The microbiology study is a subproject of BIOMUD (lead by Prof. Dr. Julia Gebert, TU Delft) within the sediment research network MUDNET.
The Seaport Emden avoids the cost-intensive post-dredging relocation of mud in the waterways. Instead, the sediments are circulated through the trailing suction hopper dredger (TSHD) and released back into the water. This causes a well-ventilated fluid mud layer in which ships can navigate, sail, and maneuver. However, possible increases in the discharge of hinterland freshwater, forecasted to result from climate change, may alter this well working system. In this project, TU Delft (lead Prof. Dr. Julia Gebert), Deltares, GEOMAR and the University of Hamburg will conduct mesocosm experiments to investigate whether and how the microbial community and its activity as well as sediment rheological parameters and organic matter degradability in the Seaport will be affected by envisioned changes in hinterland water discharge to the port. At the end of the project a recommendation to Niedersachsen Ports will be given on future sediment and water management strategies as these are at the core of the running EU INTERREG project NON-STOP in Emden harbor.