SEDMET-IV Cruise, RV García del Cid

Abstract

The equipment was recovered and the bottom sediment sampling and the hydrographic profiles were performed to characterize the area at the end of the spring season which corresponded to the end of the study period.The proposed research project consists in the study of the sediments and associated heavy metals dynamics, and very specially in determining the effect that the floods and storms exert on them, in a coastal system affected by industrial and urban activities. The coastal system of Besòs is one of the most polluted areas known and presents a complex situation with different sources of pollution (river, outfall, collectors, pluvial) and with an important historical contamination (since the beginning of the 20th century) from some of the these sources, which now also constitutes a contaminating source in itself. Although the presence of high levels of contamination in the prodeltaic sediments of the Besòs River is well known, studies of the dynamic processes that affect them and their repercussions have still not been carried out. To advance in the knowledge of this subject, the present project foresees to register during the season of floods and storms temporary series of currents, temperature and salinity, concentration of sediment in suspension and vertical flows of particles through the anchoring of instrumented oceanographic tripods, as well as the periodic realization of hydrographic profiles and of sampling of matter in suspension and sediments. At the same time, it is proposed to monitor the surface plumes of river and stormwater discharges by means of time series of video images acquired by an Argus system, and water and particulate samples and to take sedimentary cores to study the recent evolution of the deposit and make measurements of the critical resuspension conditions. With all this, we intend to 1) characterize the discharges of solids and associated heavy metals and nutrients from the Besòs River and the pluvial waters of the Barcelona seafront and determine in which situations they occur. 2). Study the transport processes, and the resuspension processes that affect the contaminated sedimentary deposit. 3). Determine the critical conditions under which the erosion and remobilization of current and historical contaminated sediments occurs. 4). Quantify the associated sedimentary and heavy metal flows. 5). Determine if the corrective measures applied in the Besòs basin are contributing to reduce historical pollution levels in the marine system. 6) Characterize situations of maximum risk that can contribute to establishing actions to forecast and prevent adverse conditions for the development of activities in the coastal zone. All this, placing special emphasis during events of storms, fluvial avenues and heavy rains. The knowledge of this dynamic has an application for the definition of potential environmental risks that affect the coastal system, and can contribute to improve environmental management within the scope of the European Community Water Framework Directive.The concrete activities. Instrumented tripods. 2 tripods will be installed. The main tripod will have a coherent pulse Doppler profiler (PCADP) and an acoustic profiler to measure the suspended sediment (ABS). An RCM9 correntimeter will be added to the tripod with pressure sensors, turbulence, temperature and conductivity and a sequential sedimentary trap. The triopods will be installed at a depth of 30 meters, one in front of the mouth of the Besos River and the other in front of pluvial waters. The final position will be adjusted after making a reconnaissance bathymetric and bottom sediment. Hydrological stations. CTD / turbidity / fluorometry transects perpendicular to the continental shelf will be carried out. Samples of water will be taken with the rosette that will be filtered on board to obtain samples of matter in suspension. The water samples will also be used to analyze nutrients, chlorophyll and to account for phytoplankton. Sedimentary stations (dredge, HASP and Boxcores). The surface sediments will be sampled with the dredge where the hydrographic stations are made. Sediment core samples will be taken with HASP and Boxcore where the instrumented tripods will be installed. The sediment cores will be sub-sampled for later sedimentological and geochemical analysis (granulometry, radiographs, heavy metals, C, N, CaCO3, dating with Pb)