A Hydroinformatic Tool for Sustainable Estuarine Management

Abstract

Hydrodynamics and pollutant loads dispersion characteristics are determinant factors for an integrated river basin management, where different waters uses and aquatic ecosystems protection must be considered. Strategic Environmental Assessment (SEA) of river basin planning process is crucial to promote a sustainable development. Towards this purpose, the European Water Framework Directive (WFD) establishes a scheduled strategy to reach good ecological status and chemical quality for all European water bodies. As transitional aquatic environments, where fresh and marine waters meet, estuaries are generally characterized by complex interactions, with strong gradients and discontinuities, between physical, chemical and biological processes. This complexity is often increased by intensive anthropogenic inputs (nutrients and pollutants) from urban, agricultural and industrial effluents, leading to sensitive structural changes (Paerl, 2006) that modify both the trophic state and the health of the whole estuarine ecosystem. As a response to this, there has been an enormous increase in restoration plans for reversing habitat degradation, based on knowledge of the processes which led to the observed ecological changes (Valiela et. al., 1997). Estuaries are recognised worldwide for providing essential ecological functions (fish nursery, decomposition, nutrient cycling, and shoreline protection) and support multiple human activities (fisheries resources, harbours, and recreational purposes). Each estuary is unique, because of its specific geological structure, morphology, hydrodynamics, land use, and the inflowing freshwater s characteristics (amount and quality). Estuarine waters are generally characterized by intense biogeochemical processes that can renew the aquatic compartment, but their flushing capacity is mainly dependent on the hydrodynamic processes. The major driving forces of estuarine circulation are tides, wind, freshwater inflow, and general morphology (bathymetry, intertidal areas extension, roughness). The mixing and dispersion processes are critically dependent upon the salinity intrusion type (concerning it spatial distribution), which defines estuaries ranging from those with a highly stratified salt-wedge and a sharp halocline in the vertical structure to well-mixed systems. The description of the estuarine transport process can be expressed by the definition of a transport time scale. This time scale is generally shorter than the time scale of the biogeochemical renewal processes and gives an estimate of the water-mass retention within the river basin system. So, the influence of hydrodynamics must not be neglected on