Fresh‐Water/Sea‐Water Relationship Within a Ground‐Water Flow System, Northeastern Coast of the Yucatan Peninsula

Abstract

Ground‐water velocities within fractures and boreholes, hydraulic heads, and depth profiles of conductivity were measured along a 70 km section of the northeastern coast of the Yucatan Peninsula, Mexico. Hydraulic heads ranged from 40 to 60 cm above mean sea level between 2 and 4 km from the coast. Fluid velocities estimated from point‐dilution tests, in the dual‐porosity rock in a borehole several kilometers from the coast, were 0.021 cm/sec in the fresh‐water lens and 0.082 cm/sec near a fracture in the underlying sea‐water zone. Velocities in large fractures increased from 1 cm/sec 10 kilometers inland to 12 cm/sec near discharge points along the coast. This increase is attributed to the decrease in thickness of the fresh‐water lens. The thickness of the fresh‐water lens is approximately 40% less than the Ghyben‐Herzberg relation predicts for a static system, providing the potential to drive fresh water through fractures into the sea‐water zone below the halocline. Overall, the halocline appears to be in a steady‐state position due to the rapid flow of fresh water and brackish water towards the coast combined with rising sea water in corivectional flow.

Composition and fluxes of submarine groundwater along the Caribbean coast of the Yucatan Peninsula

“…Many studies have documented the impact of SGD in different environments (Burnett et al, 2003;Moore, 2010;Taniguchi et al, 2006), however SGD in karst environments may be particularly important due to rapid recharge and channelized flow pathways through fractures and cave systems. Specifically two types of flows may be present in karst systems: (1) focused fracture flow (conduits), and (2) diffuse flow through porous medium (Fleury et al, 2007;Moore et al, 1993;Perry et al, 2002). Conduit flow from deeper aquifers may discharge as submarine springs offshore.…”

Foraminifera and testate amoebae (thecamoebians) in an anchialine cave: Surface distributions from Aktun Ha (Carwash) cave system, Mexico

“…A foraminiferan community dominated by Bolivina and Elphidium is consistent with these interpreted environmental conditions in the cave based on their modern ecology (Culver and Buzas 1981;Murray 2007). We hypothesize that foraminifera are transported into the flooded marine cave as propagules (Alve and Goldstein 2003) on coastal upwelling currents and are subsequently incorporated into the subsurface hydrologic circulation patterns (Moore et al 1992;Beddows et al 2007), as there are currently no known physical conduits connecting the cave to the ocean. Rare testate amoebae and freshwater ostracods found with the MA are either transported by water currents or physically move into the deep cave and die (e.g., A. vulgaris in S75).…”

“…Hydrologic flow transports aquatic and terrestrial organic matter and nutrients from the cenotes and adjacent terrestrial surface into the cave (1 cm s 21 ; Moore et al 1992), and ambient light penetrates less than 20 m into the cave. Cave sediment is organic-rich gyttja near the cenotes, but it becomes increasingly patchy and sparse in the deep cave, where calcite crystals (.250 mm in diameter), limestone fragments (.1 cm in diameter), and marl with goethite are more common.…”

Identification of Phytoplankton Blooms under the Index of Inherent Optical Properties (IOP Index)

“…These areas are as follows: Area 1 is three coastal areas in the Yucatán Peninsula: Dzilam de Bravo (Dzilam for short) in the Yucatan state (Figure 1a), Holbox in the Quintana Roo state (Figure 1b), and Campeche Bay in the Campeche state (Figure 1c). This Peninsula is a karstic region, characterized by minimal soil cover and rapid infiltration of rain water, with the consequent high vulnerability of aquifer pollution [21,22]. The rainy season occurs from June through December with minimal rainfall occurring during the rest of the year.…”

“…The rainy season occurs from June through December with minimal rainfall occurring during the rest of the year. The unconfined Yucatán aquifer has submarine groundwater discharges (SGD) that can threat coastal ecosystems [22,23]. SGD has been linked to eutrophication and harmful algal blooms [23].…”