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RESEARCH PRODUCT

Environmental Constraints on Pathways of Organic Detritus in a Semi-enclosed Marine System (W-Mediterranean)

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In order to assess seasonal and spatial changes in water-sediment interaction processes in a semi-enclosed marine system of Western Sicily (Marsala lagoon; W-Mediterranean), the biochemical composition of suspended and sediment organic matter was studied, during a one-year sampling period. The observed dynamic balance of resuspension vs. sedimentation processes and the macroalgal and vascular plant coverage appear major factors in affecting both amounts and biochemical composition of suspended and sedimentary organic matter and allowed us to identify two different sub-systems. The northern area, characterised by frequent wind-induced sediment resuspension events and by a scant vegetation, displayed higher amounts of high quality (i.e. protein) sedimentary organic matter and higher amounts of particulate organic matter. By contrast, the southern area, characterised by less wind exposure and a deeper water column, displayed lower particulate organic matter concentrations and increasing sedimentary organic matter concentrations. The oligotrophy of the system (phytoplankton biomass < 0.1 μg Chl-a l−1) and the relatively low concentrations of photosynthetic pigments in the sediments (on annual average 3.1 μg g−1) suggest that this system is largely dominated by organic material of detrital and/or heterotrophic origin. The overall picture of the study area suggests that the Marsala lagoon is a “pulsing” environment characterised by no clear seasonal change of the primary production processes and by the accumulation of large amounts of organic detritus in the sediments. Such uncoupling between amounts and nutritional value of suspended and sediment organic detritus suggests that this particular environment behaves probably as a detrital “trap”.