Abstract. The coastal lagoon of Bahía-Magdalena, located on the west coast of the Peninsula of Baja-California, is a subtropical ecosystem with an arid climate and very little freshwater input. During the 2005-2011 period the thermohaline properties varied between cold and warm halfyearly periods. They were influenced by the Transitional Water mass transported by the South California Current from February to July and by the Subtropical Surface Water from August to January. The nutrient concentrations increased (viz up to 16 µM of nitrate) from March to June, when the upwelling index was the highest. Similarly, the inter-annual variation of chlorophyll-a showed a six-monthly pattern with the highest average monthly concentrations being found in June (5 mg·m -3 in situ or 8 mg·m -3 based on satellite information) and the lowest in DecemberJanuary. A spatial zoning was also observed in the lagoon with a shallow inner zone that is warmer and richer in chlorophyll-a than the deeper closed mouth area. In the Bahía-Magdalena lagoon a spatial-temporal division into two zones and two seasons was repeated year after year with only minor differences. During the first semester in the outer zone, years 2006 and 2007 were colder and nutrient rich while 2010 was warmer, according to the upwelling conditions in the Southern California Region. Hence, among the coastal lagoons that present a prevailing marine influence, the coastal system of Bahía-Magdalena corresponds to an unusual type of subtropical coastal lagoon where the nutrient input is mainly due to upwelling phenomena.Keywords: inter-annual, intra-annual, biogeochemistry, California Current, chocked lagoon, Bahía-Magdalena, Pacific coast, Mexico. -INTRODUCTIONContinental shelf waters represent 8% of the Earth's oceanic surface but it is where nearly 25% of the primary sea production occurs (Walsh, 1989) and where a variety of types of coastal systems, which determine the exchange between land and sea, are found. In these systems, coastal lagoons, making up 13% of the coastal areas worldwide, are predominant (Kjerve 1994). Coastal lagoons are inland water bodies, usually oriented parallel to the coast, separated from the sea by a barrier and connected to the ocean by one or more restricted inlets (Kjerfve and Magill 1989). In the subtropical climate region bordering, as delimited by Perillo et al. (1999), the Tropics of Cancer and Capricorn (23.5° latitude) and the temperate region (40° latitude), coastal lagoons are subject to a wide climatic diversity ranging from monsoons to desert-like conditions. In all of these climate types the availability of nutrients restricts biological richness (Salomons et al., 2005). Despite this fact, subtropical coastal lagoons have not been studied extensively from a biogeochemical viewpoint, rather it is the ecological aspects that have undergone a more indepth examination (Kjerfve, 1994).The wide variety of subtropical coastal lagoons have been classified according to the type of entrance channel into choked, restricted or leaky lago...

To know the environment impact on a harbor of the Santa Rosalía port on the Baja California peninsula, the concentrations of metals (Cd, Co, Cu, Mn, Pb, U and Zn) in harbor sediments were determined for 13 stations and compared with their average upper Earth´s crust abundance. The mean enrichment factors, calculated using Al as a normalizer, were higher than the unity for Ag, Ba, Bi, Cd, Co, Cu, Mn, Ni, Pb, Sb, U, V and Zn. Concentrations of slightly enriched Cd in the sediments are below the effect range low (ERL) sediment quality guidelines value only at three stations. The levels of Pb in the harbor sediments at four stations (1, 6, 9 and 11) are between the ERL (46.7 mg kg(-1)) and the effect range medium (ERM) (218 mg kg(-1)), and Pb content in the rest of the sediment samples is higher than the ERM, demonstrating the high extent of the anthropogenic impact of this metal on the sedimentary environment. The total concentrations of the potentially toxic elements Cu (3,390 ± 804 mg kg(-1)) and Zn (1,916 ± 749 mg kg(-1)) very strongly exceed their ERM, showing a high possibility of toxicological danger for marine biota, living inside or entering the harbor.

Relevancia de fuentes nitrogenadas nuevas y regeneradas en la columna de agua en Bahía Magdalena (SO Península de Baja California), MéxicoAbstract.-Six bimonthly surveys during 2007 were carried out in Magdalena Bay (Mexico) during spring tide conditions. Spatiotemporal variations of temperature, salinity, nitrite, nitrate, ammonium, phosphate and chlorophyll-a were analyzed in the Bay. During spring-early summer (April-June) seawaters were colder and richer in new nutrients and chlorophyll-a than autumn and winter (February and October-December). The coastal upwelling during spring-early summer contributes with new nutrients to the Bay, whereas bottom-recycled nutrients should be the main input during the autumn-winter period. Thus, nutrients availability, dissolved inorganic nitrogen and phosphate, promote a seasonal pattern of phytoplankton biomass in Magdalena Bay.

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.

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