Velocity variability in a cross-section of a well-mixed estuary

North Inlet, South Carolina, is a well-mixed, tidally driven, high-salinity, shallow type IA estuary consisting of winding creeks that intersect a 30 km2 Spartina alterniflora salt marsh. An intensive spring tide field sampling in a 320 m wide cross-section during three consecutive tidal cycles in November 1977 resulted in detailed information on the cross-sectional net and rootmean-square (r.m.s.) velocity distributions...

Construction of net isopleth plots in cross-sections of tidal estuaries

Construction of isopleth plots of net velocity, material concentration, or material flux in cross-sections of tidal estuaries is not a trivial matter. To construct a flux-preserving isopleth plot requires that each instantaneous measure is weighted by the subarea for which the measure is representative. This area-weighted averaging procedure is outlined. Without area-weighting, net isopleth plots typically yield misleading results in tidal estuaries. In our example, net fluxes of total nitrogen are over-estimated without area-weighting

Hindcasting of hurricane characteristics and observed storm damage on a fringing reef, Jamaica, West Indies

Hurricane Allen is one of the most severe hurricanes on record and caused extensive damage throughout the Caribbean in early August 1980. Coral reefs along the north coast of Jamaica were devastated by the hurricane-induced waves. As in the case of most hurricanes, no wave measurements were made. We have computed the wind field and hindcast the deep water wave characteristics as the storm impacted the fringing reef at Discovery Bay on the north central coast of Jamaica. The deep water waves propagated into shallow water on the forereef and transformed as a result of shoaling and refraction. We found that significant wave height at a given time varied by a factor of 2.6 and that incident wave power for the duration of the storm varied by a factor of 7 along a 3 km section of the Discovery Bay forereef due to variations in local bathymetry. Maximum hindcast breakers reached a height of 11.5 m with a significant wave period of 10.5 s. Observations of the most intense reef damage coincided with areas on the eastern forereef experiencing the highest breakers. We speculate that the degree of reef damage is a function of how much time has elapsed since the previous storm rather than frequency of hurricanes at a locality

Hydrodynamic Variability in a Microtidal Coastal Bay Geographically Susceptible to North East Trade Winds

The ecological integrity and overall health conditions of natural coastal systems are largely based upon the balance among physical processes. The objective of this study was to assess the effects of tides and winds on the water level variability, circulation patterns, and turnover time in Bahia de la Ascension (BA), a shallow, tropical coastal bay in the Mexican Caribbean prone to the influence of Trade winds due to its geographical location. The analysis of the hydrodynamics of BA using a 2D numerical model indicates that the tidal flow in the inlets and central basin of the bay vary by tidal phase. An averaged seawater inflow through the south inlet and outflow through the north inlet is observed for every simulated case, while peak instantaneous current velocities are evident in the northern entrance. Winds play a dominant role in the water turnover from the system’s interior to the main bay. The model shows an average turnover time of 45 days for the whole bay, with shorter turnover when Trade winds impart stress along the main northeast–southwest axis in the bay. Since the tidal signal is attenuated in the southwest endpoint of the bay, the relevance of winds in the transport phenomena was considered fundamental to preserve the ecological heterogeneity of BA

Impacts of brine disposal from water desalination plants on the physical environment in the Persian/Arabian Gulf.

Around the Persian (Arabian) Gulf, a considerable volume of freshwater is obtained by desalination of seawater with the residual brine dumped back into the Gulf. This discharge of saltier waters impacts the marine ecosystem and may also affect dynamic and thermodynamic processes. Here, a fully non-linear, high-resolution numerical model is used to investigate the physical impacts of brine discharge into the Gulf. Twin runs were executed. One with and another without brine discharge at specific points. The results show that, when brine is injected, surface gravity waves irradiate from the locations and induce perturbations in other thermodynamic variables in the far field. Instead of attenuating, the anomalies have long term impact. The differences between the two experiments show marked seasonal and spatial variability. The largest differences occur during the summer and are located mainly along the axis of the Gulf's deeper channel. After 5 years of run, a budget calculation shows basin wide saline increase of about 0.2 g/kg, in agreement with previous studies. This might appear small when compared with the present Gulf mean salinity. However, the small change seems to be associated with significant variability in the spatial distribution and in the seasonal variability at different locations. It is found that there are regions in the Gulf where the standard deviation may represent serious consequences for living organisms in the marine environment

Regional Estuarine and Coastal Systems of the Americas: An Introduction

Coasts in general and estuaries in particular are the most dramatically variable environments in the world ocean realm. Interactions between physical processes, geomorphology, and biology are closely linked and gradients in most variables are very large. Although research on coasts and estuaries has grown steadily during the past 40 years, our understanding of the processes and linkages still requires refinements and further detailed knowledge that new available technologies hopefully will be able to provide. Most of the knowledge about estuaries has been derived from environments in North America and Europe with more than 87% of all papers published in international scientific journals based on estuaries located there. In comparison, less than 1% of published papers derive from estuaries located in Latin America (PERILLO and PICCOLO , 1998; PERILLO et al., 1999). However, the Americas, both North and South, include more than 40% of the estuaries of the world, and only a small fraction of these have been treated scientifically with findings reported in the international scientific literature. Exception are the recent surveys and synthesis of a number of estuarine and coastal environments in Latin America (PERILLO et al., 1999; SEELIGER and KJERFVE, 2001).Fil: Perillo, Gerardo Miguel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; ArgentinaFil: Kjerfve, Björn. Universidad Nacional del Sur; Argentin

Effects of Tidal Range Variability and Local Morphology on Hydrodynamic Behavior and Salinity Structure in the Caeté River Estuary, North Brazil

Tidal influence and local morphology on circulation and salt transport are investigated in the Caeté river estuary, a well-mixed estuary along the north coast of Brazil. Velocity, temperature, and salinity data were collected in three different locations along the estuary’s main channel, over three single, 13 h tidal cycles. The aim of this study was to investigate the relationship between tidal distortion and salinity by using classical methods of comparison of three cross-channel circulation characteristics, as well as computation of salt flux and vertical mixing. Findings indicate a flood-ebb asymmetry in currents, due to the distinct funneling morphology of the estuary, with shallow marginal areas being dominant towards the estuary head, while both stratification and shear dominate near the estuary mouth. The tidal currents enhanced vertical diffusion in the mid- and lower reaches, explaining the prevailing weakly stratified conditions, while the dominant well-mixed conditions in the upper estuary are a result of a combination of stronger flood currents and negligible vertical saline gradient. The predominant downstream salt transport supports the conclusion that there is little accumulation of salt in the Caeté river estuary. In addition, findings indicate that tidal correlation and Stokes drift are important components in the upper estuary, while tidal correlation played an important role in the middle estuary, with fluvial discharge most important in the lower estuary

Response of Thalassia Testudinum Morphometry and Distribution to Environmental Drivers in a Pristine Tropical Lagoon.

This study was undertaken to determine the relationships between the biomass, morphometry, and density of short shoots (SS) of the tropical seagrass Thalassia testudinum and the physical-environmental forcing in the region. Seasonal sampling surveys were undertaken four times in Bahia de la Ascension, a shallow estuary in the western Mexican Caribbean, to measure plant morphology and environmental variables. The estuary has a fresh water-influenced inner bay, a large central basin and a marine zone featuring a barrier reef at the seaward margin. Leaf size was positively correlated with increasing salinity, but total biomass was not, being similar across most of the sites. Aboveground biomass exhibited seasonal differences in dry and rainy seasons along the bay, most markedly in the brackish inner bay where an abrupt decline in biomass coincided with the rainy season. The relationship between nutrients and biomass indicates that the aboveground/belowground biomass ratio increases as nutrient availability increases. Areal cover was inversely correlated with SS density during both dry and rainy seasons. Maximum SS recruitment coincided with the rainy season. Peaks in SS density were recorded in the freshwater-influenced inner bay during an ENSO cold phase in 2007 ("La Niña") which is associated with a wetter dry season and following a strong storm (Hurricane Dean). The onset of the rainy season influences both shoot density and T. testudinum biomass by controlling the freshwater input to the bay and thus, the system's salinity gradient and external nutrients supply from the coastal wetland