Seasonal cycle of nutrients, temperature, salinity and chlorophyll a in Bahía Magdalena, BCS, Mexico (2006-2007).

Abstract

Durante el periodo de febrero de 2006 a diciembre de 2007 se midieron en la superficie del mar de 14 estaciones de muestreo en Bahía Magdalena (Baja California Sur, México), con una frecuencia bimestral y bajo condiciones de mareas vivas, las concentraciones de nitrógeno inorgánico disuelto (NID): nitrito (NO2), nitrato (NO3), amonio (NH4), fosfato (PO4), temperatura (T), salinidad (S) y concentración de clorofila a (Cla). La relación T-S mostró que las aguas más frías y menos salinas generalmente se encuentran en regiones con profundidades > 10 m asociadas a las aguas provenientes de la plataforma continental y las aguas más cálidas y salinas se localizan en la zona de canales donde prevalecen condiciones con características antiestuarinas. La asociación de T vs. NO2 +NO3 mostró un patrón similar al detectado en zonas de divergencia de California y Baja California. La composición del NID mostró que la concentración de nitritos es baja durante todo el año, mientras que los nitratos y el amonio son las especies químicas dominantes. La relación NID vs. PO4 mostró que la utilización de nutrientes en Bahía Magdalena N/P fue en la mayoría de los casos menor a la razón propuesta para aguas oceánicas. Se proponen dos épocas que mejoran la comprensión de la ecología del fitoplancton de la bahía. Una época fría en la que se desarrollan especies con mayores requerimientos de nutrientes, particularmente nitratos y fosfatos, menor temperatura y posiblemente limitadas por una zona eufótica más somera. En cambio, las especies con requerimientos menores de nutrientes o con oportunidad de aprovechar fuentes esporádicas de amonio, temperatura cálida y una zona eufótica más profunda, podrán desarrollarse en la época cálida. Los resultados obtenidos en este estudio muestran un avance en el conocimiento de algunos factores ambientales que determinan la alta productividad en Bahía Magdalena. Seasonal cycle of nutrients, temperature, salinity and chlorophyll a in Bahía Magdalena, BCS, Mexico (2006-2007) From February 2006 to December 2007, 14 oceanographic stations located in the Bahía Magdalena, Baja California Sur, Mexico, were sampled every two months exclusively during spring tides. Surface concentration of dissolved inorganic nitrogen (DIN): nitrite (NO2), nitrate (NO3), and ammonia (NH4), phosphate (PO4), temperature (T), salinity (S) and chlorophyll a (Cla). were determined. The TS diagram showed that colder waters with lower salinity generally were located in regions with depth > 10 m where water from the continental shelf penetrates into the bay, while warmer and more saline waters were located in the “Zona de Canales” region, which has more estuarine characteristics. The T vs. (NO2 +NO3) analysis showed a similar pattern to those reported for upwelling areas off the coast of California and Baja California. The nitrite concentration in the area is considerably low throughout the year, while nitrates and ammonium were the dominant chemical species. The DIN vs. PO4 (N/P) ratio showed that nutrient uptake in Bahía Magdalena was 6.7/1, which is about half of the ratio known for oceanic waters. Our results show that there are two separate seawater conditions in the bay. During the cold season here is a growth of species with a higher requirement for nutrients, especially nitrates and phosphates, associated to low temperatures and a shallow euphotic zone. On the other hand, opportunistic species or species with a lower nutrient demand associated with warmer water and a deeper euphotic zone, grow during the warmer season. The results from this study give insight into the factors controlling primary production in Bahía Magdalena.

Impact of “The Blob” and “El Niño” in the SW Baja California Peninsula: Plankton and Environmental Variability of Bahia Magdalena

“…This lagoon is an anti-estuary because it is in a semi-arid zone and lacks permanent continental drainages. The lagoon area covers 565 km 2 , and two zones can be identified according to depth and thermohaline structure: the inner zone is shallow (<20 m) and occupies approximately half of the lagoon's surface, it is characterized by a homogeneous vertical distribution of salinity, temperature, nutrients and Chl-a (Cervantes-Duarte et al, 2010;Zaitsev et al, 2010). The deeper zone (>20 m) is connected to the ocean through a mouth, and the influence of the sea can be identified there due to the thermohaline stratification modulated by the coastal upwelling activity (Zaitsev et al, 2010).…”

“…Coastal upwellings are the primary source of BM nutrient supply, and the tidal currents advect cold nutrient-rich water from the ocean to the lagoon (Zaytsev et al, 2003;Cervantes-Duarte et al, 2010). The temperature diminish, and nitrate and phosphate concentrations increase from March to June, the period of considerable upwelling strength; ammonium is also higher in this period and is associated to high biological activity.…”

“…Species richness, diversity and abundance of phytoplankton in BM decreased during the 1982-1983 El Niño and had a slow recovery process starting in 1985and completed in 1986(Gárate-Lizárraga and Siqueiros-Beltrones, 1998. In contrast, the seasonal pattern of Chl-a, an indicator of phytoplankton biomass, was recovered in 1998 when the El Niño ended (Palomares-García et al, 2003) but the highest Chl-a concentration was approximately 25% smaller than in 2006 under ENSO-neutral conditions, andthe weak 2007 El Niño (Palomares-García et al, 2003;Cervantes-Duarte et al, 2010). Zooplankton biomass (ZB) decreased in BM during both strong the El Niño (Palomares-García et al, 2003;Hernández-Trujillo et al, 2010).…”

Environmental Considerations for the Management of the Bivalve Fisheries of Bahía Magdalena (Mexico), a Coastal Lagoon at the Southern End of the California Current

“…temperature, nutrients, and chl-a is homogeneous (Cervantes-Duarte et al, 2010;Zaitsev et al, 2010). The deeper zone (>20 m) communicates with the ocean through an inlet and receives the influence of marine processes as the coastal upwelling (Zaitsev et al, 2010).…”

“…Coastal upwellings are the primary source of BM nutrients, and tidal currents advect the cold, nutrient-rich water from the ocean into the lagoon (Zaytsev et al, 2003;Cervantes-Duarte et al, 2010). During spring, upwellings are stronger, so temperature diminishes, and nutrient concentrations (nitrate and phosphate, mainly) increase; ammonium is also higher in this period because of high biological activity.…”