2-YEAR GRAIN SIZE MONITORING OF THE RIVERBED SEDIMENTS FROM DANUBE DELTA

Abstract

The Danube Delta was studied following the Geo-Eco-Mar expeditions in the summer and autumn of 2019 and 2020, respectively, from a sedimentological, faunal and environmental quality point of view. The grain size analyses of the sediments from the bed of the Chilia, Tulcea, Sulina, St. George Branches, as well as the meanders of the Dunărea Veche and Tătaru identified two types of sediments: sediments in which the sand fraction predominates, consisting, in general, of fine sand, and the fractions silt and clay have, in most cases, very low cumulative percentages, often below 1%; clay-silty sediments (muds), consisting predominantly of silt and clay, present in areas where the water velocity has low values. The presence of gravel is also noted, but subordinate to the sandy fractions. Gravel elements are an indicator of human impact in the area. In general, sediments also contain organogenic material, consisting of shells, fragments and plant remains. The interpretation of the data resulting from the granulometric analyzes (the percentages of clay, silt, sand, gravel and textural parameters) highlighted the dynamic conditions in which these sediments specific to the deltaic environment were deposited. In general, the amount of sand varies from one season to another and from one year to another, especially near the banks, with an increase in the sand content in the autumn season. Sandy sediments illustrate a faster flow regime, are well sorted, and are generally present in the central part of the Danube Branches bed.