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High surface water-groundwater connectivity characterizes watersheds underlain by karsts, increasing contaminant transport risks. However, karsts are highly complex, making research necessary to understand the transport of contaminants from the surface, through the aquifer, to discharge areas. In Yucatan, the lack of waste water treatment raises the risk of groundwater contamination. We monitored stable isotopes (δ18O-NO3 and δ15N-NO3), cadmium, and lead to document waste water contamination and transport during the rainy and dry seasons, using water samples collected along the Ring of Cenotes during each season. Specific conductance and pH showed no consistent seasonality, with conductance ranging from 0.5 to 55 mS/cm and pH ranging from 6.6 to 8.6 for most samples. Nitrate concentrations in the cenotes averaged 205 ± 260 μM and no seasonal pattern was observed. Cd and Pb concentrations were 0.1 to 37.9 μg/L and 0.2 to 243.2 μg/L, respectively. Nitrate stable isotope values were 2.6 to 27.2‰ for δ18O and 1.2 to 20.7‰ for δ15N. The statistical relationship between δ15N and δ18O, in dry season samples, indicated that denitrification was occurring. A scale measure for waste water recognition showed: (1) high variability among sites probably related with dry/rainy seasons and/or diverse anthropogenic activities; and (2) specific water quality variables that contribute to contamination at each site during each season. Importantly, our analyses indicate that in the area surrounding the Ring of Cenotes, waste water exhibits spatial and temporal patterns related to complex transport and dilution processes, as is the case in karsts in general.  相似文献   
2.
The mechanisms governing dispersion processes in the northern Yucatan coast are investigated using a barotropic numerical model of coastal circulation, which includes wind-generated and large scale currents (i.e. Yucatan Current). This work provides the foundations for studying the dispersion of harmful algal blooms (HABs) in the area. Modelling experiments include effects of climatic wind (from long term monthly mean NCEP reanalysis), short term wind events (from in situ point measurements), and Yucatan Current (YC) characteristics. Its magnitude was approximated from published reports, and its trajectory from geostrophic current fields derived from altimeter data. These provided a range of real and climatic conditions to study the routes in which phytoplankton blooms may travel. The 2-D model results show that a synthetic and conservative bloom seeded in the Cabo Catoche (CC) region (where it usually grows), moves along the coast to the west up to San Felipe (SF), where it can either move offshore, or carry on travelling westwards. The transport to the west up to SF is greatly influenced by the trajectory, intensity and proximity of the YC jet to the peninsula, which enhances the westward circulation in the Yucatan Shelf. Numerical experiments show that patch dispersion is consistently to the west even under the influence of northerly winds. When the YC flows westward towards the Campeche Bank, momentum transfer caused by the YC jet dominates the dispersion processes over wind stress. On the other hand, when it flows closer to Cuba, the local processes (i.e. wind and bathymetry) become dominant. Coastal orientation and the Coriolis force may be responsible for driving the patch offshore at SF if external forcing decreases.  相似文献   
3.
Journal of Paleolimnology - Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence...  相似文献   
4.
The discharge of nutrients, phytoplankton and pathogenic bacteria through ballast water may threaten the Cayo Arcas reef system. To assess this threat, the quality of ballast water and presence of coral reef pathogenic bacteria in 30 oil tankers loaded at the PEMEX Cayo Arcas crude oil terminal were determined. The water transported in the ships originated from coastal, oceanic or riverine regions. Statistical associations among quality parameters and bacteria were tested using redundancy analysis (RDA). In contrast with coastal or oceanic water, the riverine water had high concentrations of coliforms, including Vibrio cholerae 01 and, Serratia marcescens and Sphingomona spp., which are frequently associated with “white pox” and “white plague type II” coral diseases. There were also high nutrient concentrations and low water quality index values (WQI and TRIX). The presence of V. cholerae 01 highlights the need for testing ballast water coming from endemic regions into Mexican ports.  相似文献   
5.
Bahia de la Ascension (BA) is a shallow, mangrove-fringed coastal bay connected to the Caribbean through two inlets, outlined by the Mesoamerican Barrier Reef System. This work represents an initial investigation of the relative contribution of hydrometeorological and hydrodynamic forcing on salinity variation in this lagoon. Our objective is to assess the sensitivity of the salinity in BA to fluctuations in freshwater inflow and coastal oceanography. Two field trips were undertaken during rainy and dry seasons in 2007. Surface salinity was mapped across the system and CTD deployments carried out within BA and in the sea end-member to characterize temperature, conductivity, and water level. Also, cross-sectional CTD profiles were implemented to examine vertical stratification. The water balance indicated that 16 % of rainfall over the drainage basin (DB) becomes groundwater discharge plus surface runoff into BA during dry season, while 68 % of the precipitation input to the DB is supplied through groundwater–surface runoff to the bay during rainfalls. This combined inflow showed larger fluctuations than direct rainfall and, thus, has a greater potential to alter the seasonal salinity variations within BA. The tidal signal is selectively attenuated within BA, as diurnal frequencies are more readily filtered out than semidiurnal frequencies. Mesohaline conditions in the southwest bay are associated with freshwater sources, while saline water masses in the inlet are influenced by prevalent SE winds in the region and tidal phase, establishing a strong horizontal SW-NE estuarine salinity gradient.  相似文献   
6.
Oxygen isotopes and strontium concentrations were used as geochemical tracers to discern the sources of water to Celestún Lagoon, a small subtropical estuary on the western side of the Yucatán Peninsula of Mexico. Celestún Lagoon is underlain by karstified limestone with numerous locations where groundwater is observed discharging directly to the lagoon. In this study, samples of groundwater, lagoon surface water, and seawater (SW) were collected in April 2008 and June 2009 and analyzed for salinity, stable isotopes of oxygen, and strontium (Sr2+) concentrations. These geochemical tracers were used in two tertiary mixing models to calculate the relative ratio inputs of fresh groundwater, brackish groundwater, and SW to the lagoon. Two sources of groundwater were found to contribute to the surface water in the lagoon; one fresh and the other brackish with an average salinity of 19 psu. The fresh groundwater had an oxygen isotopic signature (δ18O) and strontium concentration (Sr2+) of δ18O?=?-3.30‰ and Sr2+?=?0.03 mmol/l, respectively. The brackish groundwater observed in the northern end of the lagoon add a dissimilar oxygen isotopic signature and Sr2+ concentration of δ18O?=?3.01‰ and Sr2+?=?0.12 mmol/l, respectively. Local SW had an isotopic oxygen signature and Sr2+ concentration between the two fresher sources (δ18O?=?1.40‰, Sr2+?=?0.09 mmol/l). The lagoonwide results of the two tracer mixing models (δ18O and Sr2+) agreed well (within 5 %) and indicated a ratio of brackish groundwater–fresh groundwater– SW of 31 %–26 %–43 % (±5 %) for the Sr2+ model and 35 %–25 %–40 % (± 5 %) for the δ18O model. Brackish groundwater is dominant in the northern portion of the lagoon, while SW dominates the southern portion. Fresh groundwater discharge is a significant contributor of water along the entire eastern boundary of the lagoon where mangrove forests are the dominant vegetation.  相似文献   
7.
Phytoplankton community structure in coastal areas is a result of various environmental factors such as nutrients, light, grazing, temperature, and salinity. The Yucatan Peninsula is a karstic tropical region that is strongly influenced by submerged groundwater discharge (SGD) into the coastal zone. Phytoplankton community structure and its relationship with regional and local water quality variables were studied in four ports of the northwestern Yucatan Peninsula. Water quality was strongly related to SGD, and variations in phytoplankton community structure were related to local nutrient loading and hydrographic conditions, turbulence, and human impacts. Our study provides an ecological baseline for the Yucatan Peninsula and serves as a basis for establishing monitoring programs to predict changes at sites with high hydrological variation and in developing an early alert system for harmful toxic algal blooms.  相似文献   
8.
This work is the beginning of a coastal water quality monitoring program to establish the baseline for the implementation of an integrated coastal management of the Yucatán Peninsula tropical ecosystem. Coastal water quality is affected by the increasing economic development. This area has no rivers because of its karst geomorphology, and the coastal freshwater comes from springs or seeps. Coastal water quality was studied in four towns from January to December 2000. Statistically significant differences among water quality variables and processes are discussed. Along with groundwater discharge, domestic and shrimp farming sewage are the main sources of nutrients, predominantly of nitrogen and silica. Salinity dilution is used to estimate the groundwater fraction that influences each area in northwestern Yucatán.  相似文献   
9.
Radium isotopes (223Ra, 224Ra, 226Ra, and 228Ra) and water chemistry were used to identify two chemically distinct sources of submarine groundwater discharge (SGD) in Celestún Lagoon, Yucatán, Mexico. Low salinity groundwater discharging from springs within the lagoon has previously been identified and extensively sampled for nutrient concentrations. However, a second type of groundwater discharging into the lagoon was detected during this study using radium isotope activity measurements. This second type of groundwater is characterized by moderate salinities (within the range of lagoon salinities) and very elevated radium activities in comparison to the low salinity groundwater, mixed lagoon water, and seawater. Further analysis showed that the two types of groundwater also have distinct chloride, strontium, and sulfate ratios, along with slightly different nutrient concentrations. Groundwater discharge occurs through large and small springs scattered throughout the lagoon, and both types of groundwater were detected discharging from one of the larger springs. The relative proportions of low salinity groundwater and brackish high radium groundwater varied over the tidal cycle. In order to better understand the relative contributions of each type of groundwater to the lagoon, a three end-member mixing model based on the distinct chemical and isotopic compositions of both types of groundwater and of seawater was used to estimate the distribution of each water type throughout the lagoon in different seasons. This study suggests that substantial groundwater discharge to the lagoon can occur during both dry and rainy seasons. The presence of two groundwater sources has implications for monitoring and protection of the Celestún Lagoon Biosphere Reserve, since the two sources may have different susceptibilities to anthropogenic contamination depending on their respective recharge area and recharge rates.  相似文献   
10.
The influence of subterranean water discharge on phytoplankton was studied at two localities (Progreso and Dzilam) on the northern coast of the Yucatan Peninsula. Hydrographic and phytoplankton samples were taken monthly between September 1998 and August 1999. High concentration of silicate (>65 μmol L−1) and nitrate (>80 μmol L−1) and low salinity showed the influence of submerged groundwater discharge (SGD) in the area. In Dzilam, hydrological conditions shows low salinity and high concentration of nitrate and silicate favored from the SGD. Meanwhile, high concentrations of ammonium, nitrite, and phosphate at Progreso (>150 000 inhabitants) suggest mixing of SGD and domestic waste waters. Thick-valve pennate diatoms dominated at Dzilam while dinoflagellates dominated in Progreso. Hydrological differences in both study zones suggest that local forcings, and interaction between coastal water masses and SGD plays an important role in hydrological conditions and primary productivity in the coastal zone of Yucatan. The anthropogenic modified SGD in Progreso may affect the nutrient regime and phytoplankton community structure, and may be used as indicator of eutrophication.  相似文献   
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