Holbox Island (with its coastal lagoon, Yalahau Lagoon) located in the littoral zone at the north-eastern tip of the Yucatan Peninsula, Gulf of Mexico, is a relatively undisturbed ecosystem that is currently under threat from unplanned and intensive urban development. Although other ecosystems in this littoral zone have been studied to determine the basic requirements for sustainable development, little information about Holbox Island exists. Thus far, no data concerning coastal pollution in Yalahau Lagoon have been published. As part of a larger, on-going study, this article reports the results of analyses to determine the temporal and spatial variations of standard physical and chemical parameters and to evaluate the relationships among these parameters. Water and sediment samples collected from 42 stations during two seasons of the year (rainy and dry seasons) were analyzed using standard methods. The results indicate that, in general, the area is relatively undisturbed by human influence. Dissolved oxygen content was lower than 4 ml l−1 and the percentage of oxygen saturation lower than 90%, suggesting that the site supports higher consumption than production of oxygen. Nitrogen is mostly present as ammonium and low concentrations of nitrate; nitrite, and phosphate indicate that eutrophication is not widespread in the area. Sediments are mostly sandy,containing less than 10% organic matter at most stations. The redox potential of sediments was negative for all samples. Water quality at stations in the proximity of boating and dumping activities shows higher degradation than at other stations within the lagoon. These preliminary results provide the opportunity to construct a baseline for coastal water quality,prior to impending urban development, and may serve to determine whether the future natural and development processes have impact on the conditions and health of coastal ecosystems around Holbox Island. In addition, because the area is, as yet, relatively undisturbed, the data reported here allow us to take stock of the extent to which other sites in the Yucatan littoral zone have already been degraded by human development activities.
Recibido en septiembre de 1993; aceptado en enero de 1994 RESUMENSe realizó un estudio en los sedimentos de la Laguna Chelem, situada en el litoral del Golfo de México, al norte de la Península de Yucatán (México), midiendo la concentración de nutrientes en el agua intersticial. El amonio tuvo un máximo de 1,045 PM, con valor medio de 459 k 281 PM; el nitrito alcanzó 5.3 PM, con valor medio de 1.8 f 1.8 PM; el nitrato se encontró en concentraciones de hasta 34.7 PM, con valor medio de 8.2 f 10.3 PM, y el fosfato presentó un máximo de 1 .l @vI, con valor medio de 0.4 f 0.4 PM. Usando la ecuación de la primera ley de Fick, se calculó el flujo de los nutrientes mencionados, a través de la interfase agua-sedimento. En todos ellos, el flujo promedio de las catorce muestras de la laguna fue del sedimento hacia el agua, siendo de 182 pmol/m*h para el amonio, 0.5 wol/m*h para el nitrito, 1.9 pmol/m* h para el nitrato y 0.03 pol/m*h para el fosfato. Con el fm de conocer las tasas de desnitrificación, se realizaron incubaciones de los sedimentos en condiciones anaeróbicas, con agua de la laguna enriquecida con nitrato. Este proceso se llevó a cabo activamente en cinco de las catorce estaciones muestreadas y la tasa mayor fue la de la estación 8, con 16.07 pmo l/m *h. La muestra de esta estación también presentó el contenido de materia orgánica más elevado (9.2%) y el mayor flujo de nitrato (del agua al sedimento). Las estimaciones de los flujos netos, con base en las áreas de cada una de las zonas de la Laguna Chelem, indicaron un importante aporte de los sedimentos hacia la columna de agua, de los cuatro nutrientes estudiados, sobre todo del amonio.Palabras clave: nutrientes, flujos, sedimento, laguna, desnitrificación. ABSTRACTThe sediments of Chelem Lagoon, on the coast of the Gulf of Mexico, north of the Yucatán Peninsula, were studied measuring the nutrient concentrations in the interstitial water. Ihe average values were: ammonium 459 f 281 PM, peaking up to 1,045 PM; nitrite 1.8 f 1.8 PM, with a maximum of 5.3 PM; nitrate 8.2 f 10.3 PM, reaching 34.7 PM, phosphate 0.4 f 0.4 PM, with a maximum of 1.1 PM. Fluxes were estimated with Fick's tirst law equation. In al1 cases, the mean flux of the 14 samples from the lagoon were from the sediment to the water column; these values were 183 umol/m'h for ammonium, 0.5 umoVm*h for nitrite, 1.9 umol/m*h for nitrate a.nd 0.03 umol/m*h for phosphate. In order to determine denitritication rates, incubations of the sedi-65 http://dx.doi. org/10.7773/cm.v20i1.953 Ciencias A4urinas, Vol. 20, No. 1, 1994 ments were carried out under anaerobic conditions with water from the lagoon enriched with nitrate; denitrification was found to be active in tive of the 14 samples, with the highest rate in sample No. 8 (16.07 umol/m*h), which had the greatest content of organic matter (9.2%) and the highest nitrate flux (from the water to the sediment). The calculation of the net flux in the Chelem area showed an important supply from the sediment to the water column of the four nutrients stu...
Se realizó el estudio hidrológico de la Laguna Celestún durante 1985, el cual mostró que este cuerpo de agua, comunicada permanentemente con el mar, tiene una gran influencia de manantiales de agua dulce, que además de bajar la salinidad, aportan silicatos, nitritos y nitratos, y aumentan la alcalinidad al elevar las concentraciones de bicarbonato y carbonato. El fósforo tuvo fluctuaciones, pero en términos generales se encontraron concentraciones altas y más aún en la parte interna de la laguna, el amonio también presentó un comportamiento similar es decir bajas concentraciones fuera de la laguna y concentraciones mayores dentro de ella.
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