Biological-physical interactions in estuaries

PERILLO, G.M.E.; PRATOLONGO, P.; CARBONE, M.E.; PICCOLO, M.C.

ESTUARINE COASTAL AND SHELF SCIENCE

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Año: 2009 vol. 85 p. 5 - 6

0272-7714

Estuaries are an excellent example of the complex interactions that normally occur in coastal environments. A large number of  factors (Perillo, 1995) interact simultaneously in a non-linear fashion, making rather difficult the exact prediction of even the simplest processes. The difference with other types of coastal settings is that this interaction occurs within the restricted space provided by the estuarine valley. Therefore, the local geomorphology becomes a dominant player. Tidal propagation, for instance, is affected by the geomorphology and wind action resulting in modifications of the symmetry of the tidal curve, duration and direction of the tidal currents and mixing of the waters. As these occur, sediment, nutrient and pollutant distribution are continuously changing, developing concentration zones (e.g., turbidity maxima) or modifying the residence time of the substances. All of these processes also control the living conditions and evolution of the biota that employs the estuary for a part or totality of their life. Although the flora and fauna participating in an estuary are well adapted to such strong variability (e.g., changes in salinity, dry/wet periods, directionality of tidal currents, etc.), they suffer from artificial changes that are induced by the ever increasing human activities at and around estuaries, or even at hundreds or thousands of km inland. Artificial structures (i.e., harbors, jetties), dredging of navigation channels (including material disposal) or damming of the river are only examples of the physical conditions that have a large impact on the biological community. Further impact is produced by input of pollutants and loads of nutrients and fertilizers. Although estuarine and coastal environments throughout Although estuarine and coastal environments throughout the globe share these similar driving forces, substantial differences arise among major geographic regions. Climatic var iations, different geomorphologic settings, particular past trends in relative sea level, and the biogeographic distribution of species can shape a wide diversity of ecosystem types, in terms of their structure and functions. In addition, the concentration of human activities near shorelines has also exerted profound changes, and a large number of natural coastal environments throughout the world have been radically modified over the past century.