CARACTERÍSTICAS HIDROLÓGICAS DE BAHÍA MAGDALENA, B.C.S. MÉXICO, EN EL PERÍODO 2001-2003

En el período de noviembre de 2001 a febrero de 2003 se realizaron seis muestreos en una red de 23 estaciones hidrográficas en Bahía Magdalena B.C.S., México, bajo diferentes amplitudes de marea, con el propósito de analizar la variación espacio temporal de temperatura superficial del mar (TSM), material particulado suspendido (MPS), concentración de clorofila a (Cla) y nutrientes inorgánicos disueltos (NID) Los resultados mostraron, al menos, dos épocas contrastantes en sus características físicas y químicas: 1) noviembre, mayo, julio y 2) enero, febrero. Los primeros presentaron generalmente marcados gradientes de TSM, MPS y NID de la boca al interior de la bahía asociados a altos índices de surgencia y en julio debido al efecto de alta irradiación y marea muerta. En la segunda época las características físicas y químicas fueron relativamente más homogéneas, con diferencias menores de 1ºC de TSM y menores concentraciones de MPS y NID, asociadas a bajos índices de surgencia y posiblemente otros aportes externos, así como mayor consumo de autótrofos. Se analiza la importancia de las condiciones físicas y químicas por época y por zonas, así como su posible papel en la ecología de este sistema. Hydrological characteristics of Bahía Magdalena, B.C.S., Mexico, during the period 2001-2003 From November 2001 to February 2003 we carried out six sampling field trips in Bahía Magdalena, Baja California Sur, Mexico, over a sampling net consisting of 23 hydrographic stations. Samples were obtained at different tide ranges in order to analyze time-space variations. Parameters analyzed were sea surface temperature (SST) suspended particle matter (SPM), Chlorophyll a (Chla) and dissolved inorganic nutrients (DIN). Results suggest at least two contrasting seasons, with different physical and chemical characteristics. One was during November - May - July, and the other was January – February. in the first period there were marked gradients of SST, SPM, and DIN,that increased inward the mouth of the lagoon, which was related to the upwelling index. In July, variations were associated to the effect of high solar irradiation and neap tides. During the second period, the physical and chemical characteristics were more homogeneous, and presented SST differences lower than 1ºC, and lower concentrations of SPM and DIN.Such condition was associated to the low upwelling index and other possible runoffs of water supplies, but also a higher consumption from autotrophic organisms. We analyzed the importance of physical and chemical characteristics importance for each period and by zone. We also discuss the role of these characteristics on the ecology of this ecosystem.