Climate changes impacts affecting a tidal marsh estuarine ecosystem: futures perspectives

ANDRÉS H. ARIAS; M. CINTIA PICCOLO; CARLA V. SPETTER; RUBÉN H. FREIJE; JORGE E. MARCOVECCHIO

Estuaries, Types, Movement and Climatical Impacts

Nova Science Publishers

Año: 2009;

Climatic change will generate an increase in temperature around the globe, a sea level rise, an increase in precipitation in the global mean, among other alterations of the environment. While the expected consequences of climate change are global, the occurrence of extreme events and specific environmental problems are usually local or regional phenomenon. In particular, coastal ecosystems are vulnerable zones to early climate impacts. The Bahia Blanca estuary, Argentina, is located at 38º 40´ S and 62º 09´ W with an area of 2300 km2. Along the northern shore of the estuary it is found the most important deepwater harbor of the country, where most of the agricultural and many industrial products are exported. Based on historical oceanographic and meteorological data of the Bahia Blanca estuary, an outline of present and future climatic impacts is presented.  Water temperature shows, on average, a consistent warming with an increase in the values of maximum temperature and strong interannual variations in the last four decades. In addition, the water pH trend, which represents the CO2 air-CO2water – Bicarbonate – Carbonate equilibrium, shows the globally observed acidification trend. This trend was climatically altered due to ENSO events at the early 00’s. On the other hand, a great variability of the precipitation was found in the study region. In the last two decades the area presented extreme droughts (i.e., 1995) and extreme precipitation amount such the one that occurred in 2001. This fact leaded to higher freshwater inputs and as a consequence, a decrease in the mean salinity of the estuary water, achieving the minimum values during 2007.  The long term variation at water temperature, salinity, pH and dissolved oxygen are correlated with documented effects on the ecosystem, namely, phytoplankton and zooplankton community’s changes and commercial crustaceans and fisheries decrement. In 2003, the climate effects restricted the phytoplankton growth, leading to other factors (i.e., grazing) the size control of the bloom’s assemblage, resulting in the dominance of small cells (<20 um) for the first time in 20 years. In 2007, the combination of low temperatures and high salinities leaded to significant changes in the zooplankton communities, registering for the first time the dominance of the invasive Eurytemora Americana. During the 1998-2000 periods, a strong decrement in shrimp and prawn catches correlated with water dissolved oxygen drop and strong interannual temperature variations. Documented fisheries decrements were linked to temperature, dissolved oxygen, pH and salinity variations. Water alkalinization and oxygenation correlated with augmented catch, on the contrary, acidification and deoxygenation with diminished amounts.  Finally, the analysis of the impact of a 1 m increase of the sea level on the estuary revealed a probable flooding of an area of approximately 1463 km2, covering all the existing islands and therefore changing the ecosystem functioning conditions.