Tidal time-scale variation of inorganic nutrients and organic matter in Bahia Blanca mesotidal estuary, Argentina

Land-derived materials are regulated by coastal and shelf environmental conditions before being transported to the open sea. It is of great concern to understand the processes and to establish the extent in which they modify terrestrial compound fluxes, such as nutrients, that end up in the oceans. At present, one of the topics that arouses the highest interest within environmental coastal studies is the direction and magnitude of inorganic nutrients and the exchange fluxes of organic matter between the water column and the associated tidal plains during the daily tidal cycle. These processes, together with the local hydrographic conditions, define the key role of this type of environment: its function as a nutrient and organic matter reservoir and/or as a source. A research programme directed to understand this mechanism within mesotidal estuaries was developed in the Bahia Blanca estuary, on the coast of Buenos Aires (Argentina). On a tidal time-scale basis, levels of DIN (nitrate + nitrite + ammonium), DIP, DISi, and organic matter were measured in the estuarine water column and tidal plain porewater, for two years. Results showed no significant variations during the tidal cycle, even though the temporal variation of these compounds was clearly identified. In addition, the biological production of the estuary was considered and taken into account, so as to understand the organic matter cycle within the system. Particular conditions of the environment (sediment characteristics, porewater chemical environment, hydrodynamics, anthropogenic sources, etc.) were also considered to help fully understand the results.