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The management of protected areas in karstic regions is a challenge because flooded cave systems form there and provide underground hydrological conducts that may link different zones. As a consequence, affectations to the protected areas can possibly occur as a consequence of human activities in remote areas and may therefore pass undetected. Thus, the monitoring of possible contaminants in these regions is becoming imperative. In this work, we analyze the concentration of essential (iron) and non-essential metals (cadmium and chromium) in the seagrass Thalassia testudinum that grows in Yalahau Lagoon, located in a near-to-pristine protected area of the Yucatán Peninsula, close to the rapidly developing touristic belt of the Mexican Caribbean. Salinity and silicate patterns show that Yalahau is an evaporation lagoon, where groundwater discharge is important. High iron (> 400 μg/g), cadmium (>4 μg/g), and chromium (≈ 1 μg/g) concentrations were found in the area of highest groundwater input of the lagoon. High levels (5.1 μg/g) were also found near the town dump. In the rest of the sampling sites, metal concentrations remained near to background levels as estimated from other works. Temporal changes of concentrations in the seagrass tissues show also a local input and an input from the groundwater that could provoke an environmental problem in the Yalahau Lagoon in the near future.

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A B S T R A C TIntratidal variability and flux of salt, chlorophyll-a and suspended materials were evaluated in a shallow tropical tidal channel linking a coastal lagoon to the western Gulf of Mexico. Velocity, temperature and conductivity were used to calculate the fluxes. Data were recorded during three tidal velocity cycles (tvc) under extreme river discharge conditions. Chlorophyll-a and suspended materials were determined below the surface. In both seasons (dry and rainy), the flow was ebbdominated and with longer duration than when in flood. Maximum current velocities were 0.30 m s -1 in May (dry season) and 0.60 m s -1 in September (rainy season). In the dry season the mean chlorophyll-a export was of 7.56 Kg over tvc while the import was of 3.32 Kg. In the rainy season mean export (47.3 Kg) was 6 times greater than the import (7.93 Kg over tvc). Phytoplankton was dominated by organisms of marine origin. The mean of exported, suspended materials in the rainy season (111.3 Kg) was 4.6 times greater (859 Kg) than that in the dry season (184.7 Kg over tvc). Tidal velocity asymmetry is an effective mechanism of exportation, introducing relatively warm and saltier water into the river through the tidal channel. R E S U M OA variabilidade intramaré, o fluxo de salinidade, a clorofila-a e material em suspensão foram avaliados em um canal superficial de maré tropical em uma lagoa costeira ao oeste do Golfo do México. Os dados de velocidade, temperatura e condutividade foram usados para cálculo dos fluxos durante três ciclos de velocidades das marés (tvc) sob condições extremas de descarga. A Clorofila-a e material em suspensão foram determinados abaixo em subsuperfície. Em ambas as estações (seca e chuvosa), o fluxo dominante foi durante o refluxo e com duração maior durante o fluxo de entrada. A máxima velocidade encontrada foi 0.30 m s -1 em maio (estação seca) e 0.60 m s -1 em setembro (estação chuvosa). Durante a época seca foram exportadas 7.56 Kg de clorofila-a, enquanto a importação foi de 3.32 Kg. Durante a temporada de chuva a média exportada (47.3 Kg) foi seis vezes maior que a importada (7.93 Kg). A concentração media de material em suspensão exportado durante a época de chuvas (111.3 Kg) foi 4.6 vezes maior (859 Kg) que durante estação de seca (184.7 Kg). A assimetria das marés é um mecanismo efetivo de transporte, introduzindo no rio águas relativamente quentes e mais salinas através do canal de maré.

En esta revisión se señalan los efectos del Cambio Climático Global (CCG) y cuáles de ellos podrían dañar al Sistema Lagunar Costero de Mandinga (SLCM), México. Mandinga está rodeado por bosque de mangle, y se realza la importancia de este bosque por los servicios ambientales que proporciona a la población, inclusive a los no pescadores. El CCG trae efectos que se manifiestan de diferente manera en diferentes latitudes, génesis y fisiografías de las lagunas costeras. A partir de información publicada se describen las variables ambientales y el estado actual del SLCM. A partir de los efectos del CCG y de las variables observadas en el SLCM se advierte que hay algunos efectos del calentamiento global que pueden afectar el sistema; el más obvio es la elevación del nivel del mar, el cual se suma a la subsidencia del terreno por compactación. Probablemente la modificación del régimen hidrológico y sedimentación afecten la calidad del agua y del bosque de mangle. Sin embargo, se observó que la naturaleza del riesgo al sistema costero va relacionado con la actividad humana; la contaminación es significativa, la tala de mangle agresiva y el cambio de uso de suelo acelerado (preferentemente a suelo urbano y comercial). Alrededor de Mandinga está el agravante del crecimiento poblacional, que contamina la fuente de riqueza de la zona, la producción de ostión, además de otros contaminantes no asociados a la densidad poblacional. Es difícil discernir los efectos del cambio climático global de los provocados por el desarrollo humano.