Spatial and temporal dynamics of suspended load at-a-cross-section: the lowermost Ebro River (Catalonia, Spain)

Suspended load dynamics were analyzed for the period 2007-2009 in a semi-meandering cross-section under different hydrological conditions. Samples were collected at four different points of the cross-section. During "low discharges" (≤ 600 m³/s) suspended load samples were collected at-a-monthly basis, whereas at "high discharges" (> 600 m³/s) sampling was conducted intensively (at-a-daily basis during the first stages of the flood event). Results indicated that during low discharges, both organic and inorganic suspended load concentrations tended to be uniformly distributed across the fluvial section; but during high discharges, two distinct areas were found: an area extending from the "Inner-bank" to the "Channel centre" (Area-I) with higher suspended concentrations (organic and inorganic) than those recorded in the "Outer bank" (Area-II). This phenomenon was likely related to the formation of secondary flow velocity cells and the activation of new sources of sediment. In addition, a non-significant relationship between organic suspended load and water flow was observed in the outer-bank. At-a-monthly basis, the analysis of the suspended load showed the existence of an intra-annual cycle of the inorganic concentrations, with a progressive increase from October to March followed by a decrease from March to September. Nevertheless, the organic suspended load did not show any trend, being equally distributed along the year, suggesting that other sources of organic matter besides phytoplankton are predominant.