SOMFLOOD · Compositional Changes of Sedimentary Organic Matter from a 100-year Flood Deposit: Insights into Event-Driven Processes in the Coastal Ocean

Periodic Report Summary 1 - SOMFLOOD (Compositional changes of sedimentary organic matter from a 100-year flood deposit: insights into event-driven processes in the coastal ocean)

Description of the project objectives: The first applicant objective was to define and develop a land-ocean conceptual framework for explaining particulate organic carbon (OC) deposition in event-dominated margins. The second goal was to define and develop a diagenesis conceptual framework for explaining the temporal variability of sedimentary OC in event-dominated continental margins affected by post-depositional processes. Description of the work performed since the beginning of the project: The work carried out so far include both field work and laboratory analyses. Concerning the field research, an event-response sampling was carried out in the northern Adriatic Sea (Mediterranean Sea) when the Po river experienced a significant flood event in May 2009. Suspended sediments were collected in the Po prodelta during two periods of the May 2009 flood, including early in the event under conditions of moderate river flow (∼5,000 m3 s-1) and later during peak discharge (∼8,000 m3 s-1). In addition, sediment cores were collected after and before the peak discharge. The overall aim of this time-series analysis was to characterise the non-steady-state OC accumulation in event-dominated coastal margins and to asses the role of distributary channels in affecting the delivery and accumulation of OC in the Po prodelta region (#1 applicant objective). Samples collected in the Po prodelta prior the May 2009 event, were already available from previous projects and were used to investigate the effect of post-depositional processes on organic carbon diagenesis (#2 applicant objective). These samples include sediment cores collected during the Eurostratoform project in the Po prodelta when the Po river experienced a 100-year flood. Stations were samples to understand the initial distribution of the flood and subsequently targets were reoccupied to follow changes of the flood deposit in the following two years. In the lab, all aforementioned samples (about 400) were analysed for bulk analyses (organic carbon, total nitrogen, stable carbon isotopes, surface area and grain size) and biomarkers (lignin-phenols, benzoic acids, cutin-derived products, fatty acids, and dicarboxylic acids). Main results achieved so far: #1. Po river discharge exerts first-order control on both sediment concentration in the plume and sediment deposition in the subaqueous prodelta. During the May 2009 flood, significant plume intrusion and accumulation were only observed for river discharge higher than ∼8,000 m3 s-1. Therefore below ~8,000 m3 s-1 most of the sediment supply is trapped in shallow waters and/or within distributary channels because of the multi-channel setting that reduces the river flow. In addition, sediment cores collected in the Po prodelta after 8 flood events inferior to 7 000 m3 s-1 occurred between November 2008 and late April 2009, exhibited weak evidence of layering. Lack of preservation of these eight events suggested that sediment accumulation was too low to keep pace with post-depositional processes (e.g bioturbation and storm-induced waves). As a result, below a river discharge of 7 000 m3 s-1, event layers have weak chance to be preserved in the sedimentary record. #2. Ten year time-series analysis of a flood deposit allowed to characterise the preservation of event-strata and particulate OC with time since the flood emplacement. Over 10 years, the Po River experienced several flood events. However, evidence of preservation was observed only for extreme events (50-year return period). Conversely, moderate flood events have a low chance to be preserved in the sedimentary record. Preliminary biogeochemical analyses indicate selective preservation of biomolecules. Dicarboxylic acids and cutin-derived products were degraded faster than lignin-derived phenols. No selective preservation was observed for OC and TN. Some compounds, such as short chain fatty acids, increased with time. This maybe due to bacterial growth during OC diagenesis.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз