Salinity In Estuary Research Articles

Seasonal colonisation and effects of salinity and temperature on species richness and abundance of fish of some brackish and estuarine shallow waters in Sweden

In this study two questions concerning the structure and organisation of shallow brackish and estuarine fish assemblages are: (1) Does the species number decline with lower salinity as found for the macrofauna invertebrates? (2) Does the water temperature during the year influence the abundance of fishes along the Swedish coast?In a west coast estuary salinities were higher but fluctuated more than in the Bothnian Sea. Days with temperatures exceeding 15°C were up to twice as many in the west coast estuary as in the Bothnian Sea. In spring the species number increased, but later on in summer it declined to increase again in autumn, but declined once again as winter approached. Fish density in the west coast estuary increased gradually to a maximum in late summer and then declined, while in the Bothnian Sea there was often a decline during summer. Positive correlations were found between observed minimum salinities and average species number, and between number of days with temperatures exceeding +15°C and both yearly average and maximum fish densities. Juveniles (0+) were present for longer periods in the west coast estuary than in the Bothnian Sea and reproduction of the common species started earlier in the former area. In winter the shallow areas are devoid of fish because of ice and so are re‐colonised each spring. The study demonstrates that water salinity limited the species number, and water temperature the abundance of fish.

Na-K-ATPase generates an active transport potential in the gills of the hyperregulating shore crab Carcinus maenas

Perfusing and bathing isolated gills of shore crabs Carcinus maenas with artificial saline or sea (brackish) water enabled us to determine potential differences (PDs) between ambient bathing medium and perfusion solution. Establishment of diffusional PDs was avoided by employment of the same solution on the internal and external side. The PDs measured were therefore of an active nature. We compared the properties of the PDs with the well-known properties of the Na-K-ATPase: dependence on biological energy (ATP), on salinity and sodium concentration, susceptibility of PD to depletion of internal K and to the addition of 5 mM internal ouabain. Considering also the magnitude of the PDs measured, the results obtained indicate that it is the Na-K-ATPase that generates an active transport potential for Na in the gills of shore crabs. This PD represents the driving force for the active uptake of Na in crabs that hyperregulate their body fluids when they inhabit environments of reduced salinity regimes or fluctuating salinities in tidal estuaries. This process counteracts diffusional losses of Na in crabs exposed to dilute media.

Optimization of the indophenol blue method for the automated determination of ammonia in estuarine waters

Existing automated methods for the determination of ammonia in natural waters suffer from serious ‘salt error’ in estuaries because of changes in pH, ionic strength and optical properties with salinity. A modified automated indophenol blue method is described which minimizes the ‘salt error’ to less than 8% over the entire salinity of estuaries.

Seasonal Abundance of Atlantic Croaker (Micropogonias undulatus) in Relation to Bottom Salinity and Temperature in South Carolina Estuaries

During 1973 and 1974 seasonal abundance and mean total length of Atlantic croaker,Micropogonias undulatus, were investigated by otter trawl at 33 stations in South Carolina estuaries in relation to bottom salinity and temperature. Relative abundance of Atlantic croaker was measured by catch per unit effort at 3°C temperature intervals and 3‰ salinity intervals. Croaker occurred over a bottom temperature range of 9.0–31.4°C while occurring most abundantly in waters above 24.0°C. No significant correlation between size and temperature was found. Croaker were collected in salinities from 0.4 to 34.4‰. High correlations of size and salinity were evident in 1973 during winter (r=0.79), summer (r=0.82), and fall (r=0.94). In 1974, correlations were significant only during fall (r=0.76).

Variations in benthic community structure in a sub-tropical estuary

A one year study was carried out to investigate the variations in benthic community structure along an environmental gradient of salinity and bottom substratum in a sub-tropical estuary in Hong Kong. The community was dominated by the gastropod Turritella terebra, and to a lesser extent, by the gastropod Murex trapa and the crab Portunus hastatoides. The total number of animals, biomass as well as the domanance of T. terebra in the community decreased, while species diversity increased along a gradient of increasing salinity and decreasing siltclay fraction of the sediment.

Bathymetry as an indicator of net circulation in well mixed estuaries 1

In well mixed, high salinity estuaries of the southeastern U.S. the net circulation is mirrored in the bathymetry. Measurements in North Inlet, South Carolina, indicate a net current reversal across the estuary. The cross section bathymetry is usually bimodal with two channels separated by a shallow area. The deeper channel experiences ebb‐directed net flow with ebb‐oriented sand waves as the predominant bedform. In the shallower channel, the net current is flood directed. In well mixed estuaries similar to North Inlet, it may be possible to determine qualitative circulation features from a few lateral and longitudinal bathymetric traces without measurements of current velocity and salinity.

Distribuição de Invertebrados Marinhos na Planície Costeira do Rio São João, eEtado do Rio de Janeiro

A study of the distribution of macrofauna and the ecological factors affecting their distribution in the São João coastal plain, State of Rio de Janeiro, has made it possible to formulate a series of criteria for interpreting modern and ancient depositional environments. In all the extension of the area there are uncontestable records of ancient sea - levels higher than the present. During the Flandrean transgression the sea reached the foot of the Precambrian crystalline rocks along the entire coastline of the studied area. Different assemblages were recognized in the São João coastal plain such as shallow hypersaline, open lagoon, closed lagoon and river influenced low salinity estuary.

Factors affecting the seasonal abundance, composition and diversity of fishes in a Southeastern New England estuary

Fish communities in the Slocum River, Buzzards Bay, Massachusetts were sampled over a 2-year period. Physical variables were measured when each of the 221 seine hauls were taken. A total of 54 species representing 36 families and comprising 18 913 individuals was collected. The measures of species diversity were computed for each month and the physical and biological data were subjected to factor analysis. The Slocum River estuary is dominated by a few resident species that are common in similar habitats along the northern mid-Atlantic states. The number of individuals increased with seasonal increase of temperature but this relationship was only approximate. The mean number of species per seine haul per month was more closely associated with temperature. The reciprocal of Simpson's index, SI′, peaked during the spring and fall. The low diversity during the summer was probably due to the invasion of large numbers of a few anadromous species. The high autumn diversity is caused by invasion of a small number of several expatriate tropical species. Within the estuary salinity influences the composition and diversity of the fishes. Station 1, which was an essentially freshwater habitat, produced all of the freshwater species and station 4, which was an essentially saltwater habitat, produced mostly stenohaline saltwater species. The diversity indices were lowest at these two stations. In contrast, stations 2 and 3 varied most in salinity and tended to be the most diverse. Factor analysis further reduced the large quantity of data and somewhat simplified the handling and the interpretation of the information. The loadings per year were reasonable associations of physical and biological parameters. Temperature was overall the most important physical factor while salinity was most important within seasons. The other physical variables measured were generally intercorrelated with temperature or with salinity and had by themselves no discernible effect on the abundance, composition, or diversity of the fishes.

Predicting Estuarine Salinity from River Inflows

An analysis system is described that enables the second-order and higher nonlinear interactive effects to be estimated in the relationship between the input and output of nonlinear systems. No data are, in principle, required other than an input and output time history over a sufficient period. The method is compared with the functional approach of Weiner and shown to have advantages in practical application. An application to the prediction of salinity in estuaries from river inflows is described. An error analysis for the prediction of salinity at Benicia, Calif., shows that systematic errors in the data and the influence of unaccounted-for variables contribute the bulk of the error in making the predictions and that the error attributable to the analysis leading to the construction of the predictor contributes a smaller error, which is estimated to be on the order of 8% in this application.

Mixing and Dispersion in Estuaries

Prior to 1950, studies of estuaries were primarily observational. Rhodes ( 1950), for instance, described velocities and salinities in several estuaries along the eastern coast of the United States. Stommel & Farmer (1952) compiled data from 20 world­ wide estuaries, ranging in size from the Moros in France (2.3 km long and a few meters deep) to the Straits of Juan de Fuca (100 km long and 350 m deep). Their report, although more than 20 years old, remains one of the more extensive compilations of salinity and velocity data in existence and, in addition, shows the wide range of water bqdies we call estuaries. Since the appearance in the early 1950s of Ketchum's work (1951a,b, 1955), of the unpublished manuscript On the Nature of Estuarine Circulation by Stommel & Farmer (1952), and of Pritchard's analyses of the salt balance in the James (1952 and later), researchers have used more analytic techniques to try to understand the process of mixing in estuaries and to quantify such aspects as residence times and pollutant concentrations. It is not easy to agree on what an estuary is. Schubel (1971) listed 10 earlier definitions each of which he found unacceptable for some reason and settled on an eleventh definition by Pritchard (1967): An estuary is a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage. Even this definition is inadequate for our purpose, because it excludes such estuaries as San Diego Bay where the fresh-water flow is less than the evaporation, but which can be treated like other estuaries with respect to mixing problems. For our purposes it may be more appropriate to say that estuaries are something like pornography­ hard to define exactly, but we know one when we see one. A number of writers (Stommel & Farmer 1952, Bowden 1967, Pritchard 1967, Schubel 1971, Dyer 1973) have given classification schemes for estuaries. In hydro­ dynamic terms all the schemes distinguish three major categories: sharply stratified estuaries, such as fjords and salt-wedge estuaries; partially stratified estuaries, in which there is a significant vertical-density gradient and vertical mixing is inhibited;

Influence of Tidal Inlets on Salinity in Estuaries

The paper outlines mathematical hydrodynamic and salinity transport models applicable to the analysis of the effects of tidal inlets on shallow irregularly shaped estuaries typical of the Gulf Coast of the United States of America. The practical utility of these models has been developed and demonstrated for the simulation of salinity distributions under well-mixed water conditions for two estuaries on the Gulf Coast. Specifically, Matagorda Bay, Texas, is used to verify the salinity distribution model. Comparison between the computed concentrations and ground truth data is found to be excellent. Galveston Bay, Texas, is used to demonstrate the effects of a tidal inlet on salinity distribution. Comparison with the existing data indicate good qualitative agreement. The effects of tidal inlet are found to be mainly localized for the case considered.

Impact of Drought on New Jersey's Water Resources

New Jersey, together with other northeastern states, in 1966 began to recover from its 5th consecutive year of severe drought. The environmental effects of this drought upon the state's surface water resources were manifold. Among them were deterioration of stream quality, severe decreases in streamflows, critical depletion of storage in reservoirs used for public-water supply, increased chemical-treatment costs for potable-water supplies, record high intrusion of salinity in estuaries, changing fish-migration patterns, and upstream movement of a major oyster predator onto seed beds. Residual effects of this drought on streamflow and water quality were evident for up to 2 years after the meteorological drought had ended.

Salt-water intrusion in Prince Edward Island

The numerous saline estuaries situated throughout Prince Edward Island permit high tides to carry salt water a long way inland and to penetrate the bedrock aquifer. Very little groundwater consumption occurs around the banks of the Eliot River estuary, yet salt water has moved into the bedrock and created a large zone of diffusion. This salty water extends as far as 1200 ft inland and has penetrated to a depth of 185 ft. Beneath this salty water is fresh groundwater, which extends down to about 600 ft where it is underlain by salty water.The salty water in the upper 185 ft of the aquifer is not separated from the fresh groundwater by a confining stratum, but is kept in this position by the higher head of the fresh groundwater. This head maintains a dynamic equilibrium with the heavier salty water. The effect of density in maintaining the position of a fresh and salt water front is not as important as has been previously thought.

SALINITY AND WATER CIRCULATION IN THE VELLAR ESTUARY

This paper reports a series of measurements of salinity, temperature, and current velocity in the Vellar estuary. This typical bar‐built estuary is shown, by comparison with dimensionless stratification parameters, to be a salt wedge at high river discharge and well stratified at low river discharge. During the tidal cycle, the salt wedge near the bottom became isolated in a series of basins during ebb tide; short period diffusion along the intense halocline seems to have been an important process in the salt balance of the water column. The water circulation at high river discharge was dominated by a meander system of alternating scour holes, with the high seaward flow in the deepest areas. Superimposed on this was a secondary lateral circulation system that broke down and reversed its sense at low river flows when the saline inflow developed.

Freshening of Deer Point Lake, Bay County, Florida

This article discusses a water resources study in Florida conducted by the U.S. Geological Survey (USGS) in cooperation with the Florida Geological Survey. It describes the construction of a saltwater barrier across the inland extension of North Bay, a saline estuary of the Econfina Creek drainage basin. The barrier consists of a sheet piling dam and extends across the estuary at Deer Point. A 24‐in. siphon extending from the bottom of the lake through the dam provides a means for the removal of saline water from the bottom of the lake. The filling of the reservoir provided an opportunity to observe the freshening of the lake and the effect of the higher lake levels on the local groundwater supplies.

An instrument for the measurement of salinity in estuaries

The instrument described was designed for salinity measurements in estuaries. It is carried in a boat, water being pumped through it from an intake which is lowered into the estuary. Electrical conductivity and temperature are measured and the salinity is computed readily from a nomogram. Radio-frequency circuits are employed for the measurements, the indicator being a milliammeter operated from a d.c. amplifier. The accuracy is better than ± 1/3 parts per thousand over a salinity range of from 0.2 to 50 p.p.t.

The Movements and Migrations of Mullet (Mugil cephalus L.)

The mullet school (Mugil cephalus L.) has a real entity. The same fish remain associated in a group for a considerable period. Some emigration from (and inferentially immigration to) the school takes place. Some schools remain in one locality (within a river system) for some months. Others appear to move more or less continually. A sojourn in fresh water does not appear to be essential though many fish are found there. It is impossible to generalize about age preferences for salinity. Fish of all age groups can be found at all times of year from fresh water to the lower saline estuaries. Some seasonal difference in the direction of movement is evident in Moreton Bay, Qld.; but this movement lacks the persistence of the seaward spawning migration of adult fish in late summer and autumn. There is some evidence to support the hypothesis that the majority of mature fish do not migrate every spawning season, but at greater intervals.

Growth and Habits of the Sea Mullet, Mugil dobula Gnnther, in Western Australia

Morphologically and physiologically, the sea mullet of Western Australia seems to be identical with that of the eastern Australian coast. No raciation can be detected either within Western Australian waters or between the stocks of eastern and Western Australia. However, the mean growth rate varies from one estuary to another and from year to year within any particular river system. Growth is isometric and shows considerable individual variation though tending to a mean rate. Increase in length is seasonal, practically stopping in midwinter and reaching a peak in midsummer. The seasons of fish and scale growth are contemporaneons. The annuli form at the end of September or the beginning of October, when growth recommences after the winter cessation. Mullet mature at a size of 31–35 cm. (12 1/2-13 3/4 in. length to caudal fin) at the end of their third year. The movement of mullet from the fishing grounds as they increase in size leads to an incomplete sampling of the population so that Petersen's method of age determination is inappIicable owing to the apparent nonprogression of the modes. Of 7110 mullet tagged, only 97 or 1.35 per cent. were returned. The return for separate tagging operations varied from nil to 25 per cent. and according to localities from nil to 16 per cent. Only three fish were retaken outside the rivers in which they were tagged. These showed a northerly movement. Inside the rivers the young fish spread out over the estuary and into the fresh water; but the older age-groups remain in the slightly brackish or fresh water except during the migration season, when they pass through the saline estuaries on the way to the sea.