Cecilia Enriquez

Effects of drought and subtidal sea-level variability on salt intrusion in a coastal karst aquifer

In many coastal regions, groundwater is the main water source for humans. However, because of population growth and sea-level rise, many coastal aquifers increasingly suffer from salt intrusion, especially in karstic areas where the high permeability and porosity of the rock favours salt penetration. We collected field data from a Mexican karst system to show that sea-level variability at low frequencies (subtidal) may induce salt penetration further inland and generate larger oscillations than those observed at tidal frequencies. Measurements of conductivity and pressure from inland wells (5 and 10 km) and from substantial (~1 m3 s–1) submarine groundwater discharge (SGD) at ~2-m depth entering a shallow ocean were analysed. We found that sea and piezometric levels co-oscillated at subtidal frequencies, with a correlation of 0.6 and a differential lag. Conductivity of the SGD resembled that of the aquifer. Intense droughts driven by the 2009 ‘El Nino’ event markedly increased the conductivity of the aquifer and its discharge. Our findings indicated that coastal land use and the consequences of climate change (i.e. sea-level rise and the alteration of rain patterns) on the Yucatan Penisula threaten water availability.

Morphodynamic Evolution and Sediment Transport Processes of Cancun Beach

ABSTRACT González-Leija, M.; Mariño-Tapia, I.; Silva, R.; Enriquez, C.; Mendoza, E.; Escalante-Mancera, E.; Ruíz-Rentería, F., and Uc-Sánchez, E., 2013. Morphodynamic evolution and sediment transport processes of Cancun Beach. Large-scale construction of tourist infrastructure on beaches around the world is consistently linked to unwanted morphological changes that lead to coastal erosion. Dune destruction, alteration of sediment sources, and the rigidisation of the coastal system are known to be the main causes of erosive behaviour on many tourist beaches. To plan sound shoreline management strategies, detailed understanding of the sediment transport processes is necessary. The present contribution focuses on the main sediment transport processes that take place at Cancun, Mexico, a large (12 km) and highly developed tourist beach. High-resolution quarterly beach profile monitoring from September 2007 to June 2009 is used to calculate volumetric changes that are reasonably well explained by the spatial patterns of modelled sediment transport potential. This parameter was calculated using the wave propagation model WAPO of Universidad Nacional Autonoma de Mexico, which explicitly solves diffraction and reflection processes that are particularly important in systems with pronounced rocky headlands, such as the northern and southern ends of Cancun beach. Results show a dominance of northward longshore transport in most of the system, and an important transport divergence with consistent southward transport at the southern end. Cross-shore transport seems to dominate the middle-north section of the beach. This behaviour is consistent with recent advances in the understanding of wave circulation in embayed beaches. The method used here is considered a good approximation of sediment transport patterns when local (surf zone) morpho- and hydrodynamic data are absent or difficult to acquire.

Salt intrusion at a submarine spring in a fringing reef lagoon

Variations in discharge and turbulent kinetic energy (TKE) were studied at a point-source submarine groundwater discharge (SGD), within a fringing reef lagoon, from quadrature (neap) to syzygy (spring) tides. The principal factors affecting discharge and TKE variations were tides and waves. Field data indicated discharge, and TKE varied with high and low tides, and with quadrature and syzygy. Maximum discharge and TKE values were observed during low tides when the hydrostatic pressure over the jet was minimal, while the lowest discharge and TKE values were found at high tides. Syzygy tides produced consistent saltwater intrusion during high tides, while quadrature tides produced the greatest TKE values. In general, as the discharge intensified during low tides, jet temperatures decreased suggesting that waters originated further within the aquifer. At the same time jet salinities increased, suggesting a mixing of aquifer and seawater. To reconcile these two seemingly opposing views, it is proposed that the jet conduit is connected to a stratified chamber with seawater below brackish water. The greatest subtidal discharge occurred during quadrature tides. Syzygy produced low subtidal discharge driven by flow reversals (flow into the aquifer) observed throughout syzygy high tides in conjunction with the peak wave setup (>5 cm) observed during a storm. While tides were the primary driving force of the discharge, waves played a nonnegligible role. Wave effects on the discharge were most evident during syzygy high tides combined with a storm, when the subtidal spring discharge was weakest and salt intrusion developed.

The Effects of Wind on Upwelling off Cabo Catoche

ABSTRACT Reyes-Mendoza, O.; Mariño-Tapia, I.; Herrera-Silveira, J.; Ruiz-Martínez, G.; Enriquez, C., and Largier, J.L., 2016. The effects of wind on upwelling off Cabo Catoche. Upwelling of cold, nutrient-rich waters at the NE corner of the Yucatan Peninsula is known to enhance productivity over the Yucatan Shelf, fueling fisheries and harboring the largest global aggregation of whale sharks. Nevertheless, the physical processes that control this upwelling and the spreading of upwelled waters onto the Yucatan Shelf are not well known, particularly near the coast. In this study, upwelling behavior close to the coast was characterized, and the contribution of wind was assessed. Time series of wind, air and ocean temperatures, sea level, and current velocities from two moorings were analyzed. Wavelet transforms showed cold-water pulses with timescales that vary across the seasons and also between the shallower site (8 m) and the deeper site (12 m), with a broader range of periodicities observed further offshore. These upwelling pulses do not correlate simply with wind-driven Ekman transport, suggesting that the process is not locally controlled. Temperature covaried with horizontal currents, suggesting an advective mechanism, which is related to the wind. Although local winds may at times enhance the nearshore intrusion of upwelled waters along the northern shore of the Yucatan Peninsula, more important in these data was the disappearance of cold waters during northerly winds. This appears as an interruption of upwelling, which was highly coherent at periods of 7 to 16 days. These northerly winds are typical from October to February, but can occur at other times as well, for example during an intensive field campaign in April 2012.

Predicting Barrier Beach Breaching due to Extreme Water Levels at San Quntín, Baja California, Mexico

ABSTRACT Vidal-Juárez, T.; Ruiz de Alegría-Arzaburu, A.; Mejía-Trejo, A.; García-Nava, H., and Enriquez, C., 2014. Predicting barrier beach breaching due to extreme water levels at San Quintín, Baja California, México. This study comprises a first approach to numerically determine the hydrodynamic conditions leading to barrier breaching at San Quintín, located in the northwestern coast of the Baja California peninsula in Mexico. The barrier is backed by a large coastal lagoon, fronted by a field of submerged volcanoes located several kilometers off the coast and is exposed to large incoming wave energy dominated by the Pacific swell. The narrowest barrier beach sections are vulnerable to flooding due to overwash events that take place during concurrent high spring tides, energetic storm waves and a range of storm surge levels. Here, the conditions to barrier overwash and breaching occurrence are identified, and the extent of the floods is numerically quantified. For that purpose, the Delft3D hydrodynamic model is applied coupling waves and flows to simulate a series of scenarios, which comprise storm waves of different magnitudes and periods approaching from typical directions, and coupled to spring tides and several storm surge levels. As a consequence of the presence of submerged volcanoes off the coast, the incoming wave energy is mostly concentrated at two specific locations along the barrier beach, which correspond to the lowest and narrowest barrier locations. Due the large distance between both sites, longshore variations are not expected to be as strong as the cross-shore. Numerical results suggest that the barrier is susceptible to flooding during spring tides combined with extreme waves of significant wave heights larger than 3.5 m and a peak period of 7.5 s, and storm surge levels exceeding 0.9 m, which may lead to breaching.

A Retrospective Analysis of Water Quality in an Open Bay on the Mexican Pacific

ABSTRACT de la Lanza-Espino, G.; Silva, R.; Hernández-Pulido, S.; Mariño-Tapia, I., and Enríquez, C., 2017. A retrospective analysis of water quality in an open bay on the Mexican Pacific. In: Martinez, M.L.; Taramelli, A., and Silva, R. (eds.), Coastal Resilience: Exploring the Many Challenges from Different Viewpoints. Journal of Coastal Research, Special Issue, No. 77, pp. 39–50. Coconut Creek (Florida), ISSN 0749-0208. Lack of knowledge about the complex interactions between the dynamics of natural systems (physical, chemical and biological) and the need for the resources found in coastal environments has led to the unplanned and disorganized development of several anthropogenic activities in the study area. It is important to revert this tendency and promote medium term studies that can help to foresee the unwanted effects, sometimes irreversible, of human activities on the environment. This paper includes results from hydrodynamic and water quality studies carried out in Petacalco Bay, Guerrero (Mexican Pacific) in order to present elements for future appropriate management of industrial outflows in the region. Around this bay there are important rivers and small villages, a major port, chemical and thermoelectric plants, all discharging their (generally untreated) effluents directly into the sea. The results of this study show that the overall water quality is similar to natural concentrations found in the ocean. Nevertheless, eutrophization was found, associated with the fertilizer industry, and the hot water discharge from the thermoelectric plant generates hot plumes, which dissipate in the environment, despite the intense and variable hydrodynamic characteristics of the region.

Pacific Coast of Mexico

Abstract The Pacific coast of Mexico has 68% of the country’s coastline. It comprises several distinct ecoregions and a wide variety of habitats, a great diversity of coastal types and marine diversity, and several endemic or flagship species that live there permanently or transiently. This natural richness offers many opportunities for development and also provides a great challenge for conservation, since the influence of events acting at different scales, including global warming, urban population growth, industrial development, contamination, and overfishing, is evident clearly. The increasing economic activities enhance population growth in some coastal municipalities. Growing urban areas require new resources, magnifying pressures on the environment that manifest themselves through habitat destruction, greater waste production, and soaring pollution. The coasts of the Mexican Pacific are environments vulnerable not only to a variety of natural phenomena but to human activities whose catastrophic effects on natural communities are unequivocally obvious. This review shows that the Mexican Pacific is a region with serious sustainability challenges. A prominent need is to prioritize factors promoting wellness; previously economic growth has been the main and almost only driver without taking into consideration environmental conservations. The need is for diversifying activities that trigger economic growth, reduce socioeconomic inequality, modernize the infrastructure, and improve public security. At the same time, actions to protect critical socio-ecosystems, with the services that they provide, and to conserve the unique biological diversity they support, must be implemented to address the complex challenges that this region of the world is experiencing.