Small Estuary Research Articles

Conservation and restoration of endangered coastal areas: The case of small estuaries in Northern Spain

The extent of degraded estuarine and wetland zones on the north coast of Spain is discussed. A method for the analysis and diagnosis of such zones is proposed. The method is based on the identification and mapping of homogeneous environmental units and the definition of indicators for the assessment of these units in terms of attributes relevant for restoration and management. The specification of a set of criteria enables the diagnosis maps thus obtained to be transformed into maps with proposals for management actions, for which specific designs are proposed. The cost of the actions proposed is also estimated. The results obtained from the analysis in three small estuaries are extrapolated to determine the possible extent of different rehabilitation activities and to estimate the cost of recovery plans for the whole coastal sector analysed.

Heavy-metal accumulation by Fucus ceranoides in a small estuary in north-west Spain

Concentrations of Fe, Al, Mn, Cu, Ni, Co, and Zn were measured in Fucus ceranoides and F. vesiculosus from Pontedeume, a small estuary on the northwest coast of Spain, affected by mining activities upstream and by sewage discharge to the estuary itself. Plants were collected from two intertidal levels at each of six locations, each sample eventually consisting of the homogenized tissues of ten individuals. Tips and thalli were analysed separately. By using these methods, it was found that three or four samples were sufficient to detect differences between means for different sites of 50% for all the metals considered except Cu, the high variability of which made eight samples necessary in order to detect differences of 100%. It was demonstrated that the contribution of particulate matter not removed during washing prior to analysis is significant only in the cases of Fe, Al and Cr. Mn and Co, and, to a less but still considerable extent, Ni and Zn, were found to be greatly enriched in the algae studied. Concentrations in mature tissues were higher than in apices for all the metals studied except Cu, for which there were no significant differences between the two tissues. The vertical position on shore did not affect apical metal concentrations but showed correlations with Mn, Co, Ni, Zn and Cu in mature tissues. Possible reasons for these correlations are discussed.

Tidal Intrusion Fronts

A tidal intrusion front forms as a dense seawater inflow plunges (subducts) beneath ambient estuarine water during flood tide. The associated foam lines and color changes have been observed on many smaller estuaries with constricted mouths. Internal hydraulic theory and laboratory experiments are reviewed and expressions are obtained for the position of plunging and the amount of associated mixing. The existence of a tidal intrusion front and its structure are discussed in terms of densimetric Froude numbers. These fronts are particularly important in smaller estuaries in which the intrusion process may dominate wind and tidal mixing and thus determine the overall stratification of the estuary. Three classes of three-dimensional plunging flow are identified and discussed. In particular, it is suggested that the peculiar, cursive V-shape plunge line is characteristic of strongly plunging flow.

The Distribution of Estuarine Macrophytes in Relation to Freshwater

A continual flow of freshwater into estuaries was shown to create a salinity gradient along which different macrophyte communities were distributed. In systems with no freshwater inflow there was no spatial separation of macrophytes and salt marshes and the submerged macrophyte Zostera capensis, normally associated with the marine end of estuaries extended into the upper reaches. In small estuaries, salinities fluctuated because of the major influence of periodic small floods. During the study period the small estuaries studied were in a stable brackish condition (13-28 ppt.) and dominated by dense Ruppia cirrhosa communities which are normally associated with lower salinity regions (...)

European estuaries and lagoons: A personal overview of problems and possibilities for conservation and management

Abstract1. European estuaries and lagoons fall into three categories in respect of their conservation status and potential for ecological management. (i) Small lagoons, although greatly reduced by natural and man‐made changes to the coastal environment, are relatively easily recreated behind longshore shingle barriers, but natural colonization of such habitats may have ceased and successful artificial introduction of species or whole assemblages is hampered by lack of knowledge of the processes structuring natural lagoonal communities. (ii) Small estuaries require very little conservation management, only control of further human exploitation especially in respect of the siting of marinas and other recreational usage. (iii) Large estuaries are in many cases already altered beyond recognition, and such is their economic importance that it is unlikely that the pressures for further reclamation, impoundment, and development will be resisted. Nevertheless, it is may be possible to protect areas within each such estuarine system that could serve as staging posts for migratory birds.2. Integrated action is needed to assess the status and importance of the remaining European estuarine and lagoonal habitats, and to conserve and manage them in the future, if they are to continue to provide any significant habitats for organisms into the 21st Century and beyond.

A survey of the fish fauna of Transkei estuaries Part Four: The Mntafufu and Mzamba River estuaries

The Mntafufu and Mzamba Rivers have small catchment areas (178 and 505 km2, respectively) in the forested coastal belt of Transkei and have relatively small estuaries (5 and 2 km long, respectively). Although the annual rainfall is in excess of 1000 mm in this area, the mean annual runoff was less than 70 Mm3 in both cases. Serious floods were not observed during the survey period, while turbidity and sediment loads were usually very low. Salinities were usually high (x = 30,0-38,0‰) in the bottom water and temperatures in the upper reaches were usually higher than in the lower reaches. The species composition, and seasonal and spatial abundance of the fish fauna of the two estuaries were determined by means of gill nets. A total of 1043 fish (385,8 kg) representing 42 species were caught in the Mntafufu estuary. The orangemouth glassnose Thryssa vitrirostris and V. cunnesius were the most abundant fish in the estuary. Numerically 42% of the catch (46% gravimetrically) belonged to the family Mugilidae (1...

Studies of dissolved carbohydrates (or carbohydrate-like substances) in an estuarine environment

Variations in concentrations of dissolved sugars were studied along the salinity gradient of a small estuary (Elorn, Bay of Brest, France) from February 1985 to January 1986. Total dissolved carbohydrate (TDCHO) and dissolved monosaccharides (MCHO) were measured by the methods of Burney and Sieburth and Johnson and Sieburth respectively. It must be noted that these methods cannot distinguish between carbohydrates and carbohydrate-like substances; consequently, these methods probably do not closely reflect biologically available pools of carbohydrates. In the river, TDCHO and MCHO values ranged from 230 to 970 μg C l −1 and from 75 to 450 μg C l −1 respectively. In the estuary, TDCHO and MCHO were usually lower; they varied respectively from 20 to 570 μg C l −1 and from 0 to 180 μg C l −1. In June, some TDCHO values were much higher, probably because some polysaccharide was produced at this time by phytoplankton excretion or lysis. The relationship between Cl%o and TDCHO was dependent on the seasons. TDCHO was conservative in autumn, winter and early spring. TDCHO and DOC concentrations were fairly well correlated during the same period. Similar results have been previously reported by various workers. MCHO and TDCHO concentrations were well correlated throughout this study except in June. From these results, it was concluded that most dissolved carbohydrates were linked to a conservative fraction of the organic matter in periods of low biological activity, whereas newly biosynthesised carbohydrates were responsible for non-conservative behaviour.

Kinetic and equilibrium approaches to estuarine chemistry

A one-box model is used to examine the relationship between freshwater residence time ( T) and the time constant (half-life, t 1 2 ) for a first-order chemical reaction in an estuary. Higher and lower limits of the ratio t 1 2 /T appropriate for conservative or chemical equilibrium modelling, respectively, are derived. These limits depend also on the equilibrium constant for the reaction and the initial reactant and product concentrations. For intermediate values of this ratio, the system can be described quantitatively only by using a kinetic model. Systematic inter-estuarine variability in the distributions of dissolved metals as a function of estuarine size (or hydrodynamic turnover time) is predicted by this model when the potential for sorptive particle-water exchanges is examined. However, this deduction, which is based on kinetic criteria alone, is not confirmed by evidence in the literature. Indeed, the model is contradicted in that dissolved metals appear to be most interactive in some, but not all, small estuaries and least interactive in large estuaries. It follows that the thermodynamic drive for metal interactions to occur is a necessary additional consideration. Gross thermodynamic disequilibrium with respect to particle-water metal exchange, which in turn generates highly non-conservative dissolved metal distributions, is most readily generated in small, highly dynamic systems through enhanced internal mobility of estuarine resuspendable sediment.

Geomorphological effects of catastrophic flooding on a small subtropical Estuary

AbstractThe Mgeni Estuary is situated on the east coast of South Africa. Tidal salinity changes commonly extend 2.5 km upstream from the mouth. The subtropical climatic regime causes seasonal flooding, the geomorphological effects of which are increased by a steep river gradient. A 120‐150 year flood event during September 1987, with an estimated peak discharge of 10800 cumecs, resulted in the erosion of 1.86 × 106 m3 of sediment from the estuary. The normal high tide volume of the estuary (0.35 × 106 m3) increased to 1.85 × 106 m3 after the flood. The post‐flood intertidal volume (tidal prism) of the estuary was 0.43 × 106 m3 compared to 0.19 × 106 m3 before the event.The nature and extent of erosion in the estuary was controlled by the composition of the estuary banks and bed material. Gravel and sand substrates were preferentially eroded from the estuary bed before the cohesive bank materials were undercut in sections of the estuary. Mud and fine sand were deposited on overbank areas when the flood waned and a lag of coarse sand and gravel was produced on the estuary bed. Approximately 46 per cent of the bedload sediment supplied to the estuary since 1917 was retained in the estuary until the 1987 flood. The remainder was transported through the system and into the Indian Ocean. Results show that catastrophic floods play an important role in sedimentation in small estuaries.

Seasonal changes in Ectoparasite infection of juvenile Yellowfin Bream, Acanthopagrus australis, (Gunther) (Pisces: Sparidae). from a small estuary in Northern NSW

Seven monogenean, 1 digenean and 9 copepod species of ectoparasite were found on 179 juvenile Acanthopagrus australis collected bimonthly over two 12-month periods from a small estuary at Red Rock in northern New South Wales. The monogenean Allomurraytrema spari and the copepod Alella macrotrachelus showed a consistent cycle of spring-summer high and late summer-autumn low in prevalence and intensity of infection, whereas the digenean Prototransversotrema steeri was present only in winter. The monogenean Haliotrema spariensis was highly prevalent year-round, but other monogeneans were inconsistent in seasonal prevalence and intensity. The copepods Paraergasilus acanthopagri and Dermoergasilus acanthopagri showed inconsistent annual cycles, but their fluctuations in prevalence and intensity were nearly identical. The other species of ectoparasite had no consistent cycles or were rarely found. Temperature does not appear to directly regulate the abundance of ectoparasites on juvenile Acanthopagrus australis in Red Rock estuary.

Decision Support for Estuarine Water Quality Management

Management of water quality in estuarine systems is a multistepped process, ranging from characterization of the hydrological and hydromechanical properties that govern water quality changes through identification of waste loads, regulatory constraints, and water quality attributes to identification of alternative candidate plans and selection by so‐called decision makers‐ of the best plan to be implemented. The ultimate step in this complex process is to operate the physical system within the stipulated performance goals. Recently, with the advent of everincreasing computer power, geographic information systems (GIS) and interactive graphics, supporting integrated user‐friendly data management and processing, have been added to the body of tools intended to support the decision process through its many steps. This paper focuses on implementation of a new generation microcomputer as the sole host of the decision support system, and seeks to demonstrate how it may be used at each step of the decision process. Special attention is given to features like: (1) Object‐oriented data and control handling; (2) the integration of simulation models into the decision support system; and (3) the water quality management process. The case of a small estuary in Southern California is presented as a demonstration of the approach.

Ria de Alvor as a spawning place and a nursery ground

Ria de Alvor is a small estuary between Lagos and Portimão on the south coast of Portugal, 37°7′–37°10′N, 8°35′–8°38′W.Samples were collected monthly in the period April 1985–March 1986 in an ichthyoplankton and ichthyofauna survey of the estuary. A WP‐2 plankton net was used for catching ichthyoplankton, and a beam trawl and a beach seine were used for catching ichthyofauna.Scaldfish, Arnoglossus laterna (Walbaum, 1792), even though the most abundant species in ichthyoplankton samples, was never found in ichthyofauna samples.From the results obtained, it is concluded that a great part of the fish species are temporary marine visitors using the Ria as a nursery ground, although this system appears to provide a spawning area for species with benthic eggs. No evidence was found of pelagic spawning.

Manganese and Suspended Matter in the Yaquina Estuary, Oregon

The longitudinal distribution of total suspended matter and total, dissolved, and particulate manganese in a small coastal plain estuary is described. The distribution of manganese is a consequence of estuarine circulation; a within-estuary maximum is inversely correlated with river flow, and is a function of residence time in the estuary, resuspension in the upper estuary, and desorption from particles introduced from within the estuary or from the river. The turbidity maximum is similarly most pronounced during low river flows. The upper estuary (salinity <15‰), comprising a small percentage of the total estuary volume during low flow, receives material from the river and along the bottom from the lower estuary; this material is returned to the water column by resuspension and desorption from estuarine and riverine particles. The lower estuary tends to damp out these processes because of the greater volume and (residence) time available for mixing.

Rates of Change in the Numbers of Dunlin, Calidris alpina, Wintering in British Estuaries in Relation to the Spread of Spartina anglica

SUMMARY (1) The number of dunlin, Calidris alpina alpina (L.), wintering in the British Isles has decreased by almost half since 1973-74, much of the decrease occurring before 1977-78. A similar decrease seems to have occurred in the other main wintering areas in Holland and France between 1973-74 and 1977-78. But since then, numbers in these two countries have not decreased whereas in Britain numbers declined by a further 77 000 by 1985-86. (2) The rate of decline since 1977-78 has varied between British estuaries, many showing no change in numbers. Dunlin numbers declined at the greatest rates in estuaries where cord grass, Spartina anglica C. E. Hubbard, has spread most over the intertidal flats where the birds feed. In estuaries where the extent of Spartina has not changed, numbers of dunlin have not declined significantly, except in some small estuaries in south Devon and in north Scotland. (3) The results suggest that most birds displaced from estuaries where Spartina has spread have not yet been able to re-establish themselves elsewhere in Britain or in some other countries within the wintering range of Calidris alpina. Nor have dunlin numbers' increased in estuaries where Spartina has declined through natural die-back. The reasons for this, and the implications of the results as a whole for the conservation of dunlin, are discussed.

The nutrient status of the Kromme River estuary, South Africa

The Kromme is a small estuary in rural eastern Cape, South Africa with a relatively unpopulated and undisturbed catchment. Physical and chemical variables including the major nutrients and E. coli were examined. It was found to be a well oxygenated, well mixed estuary with some stratification in its upper reaches. Nutrient levels were generally low with nitrate values higher in winter than during summer. While no overt seasonality was detected for phosphorus, levels were comparatively high. Faecal E. coli levels were low with a mean count of 26 per 100 ml for the estuary. Along the Kromme, nutrients were highest at the confluence of the Geelhoutboom tributary suggesting it was a major nutrient contributor. At the head of the Kromme, silicate and E. coli were significantly linked to riverflow, while nitrate was correlated with rainfall. In the Geelhoutboom, only nitrate was correlated with riverflow and rainfall. When nutrient gradients (total inorganic nitrogen, total phosphorus and silicate) were correlated against salinity, significant relationships were observed for nitrogen and silicate (Kromme and Geelhoutboom) and for phosphorus along the Geelhoutboom, but not the Kromme, reflecting differences in sub-catchments. An overall N:P atomic ratio of 0.89:1 was found for the system, with more nitrogen relative to phosphorus at the head of the Kromme and vice versa for the Geelhoutboom and mouth. The Kromme is low in nitrogen, conservative in silicate and low in phosphorus while the Geelhoutboom supplies nitrogen, phosphorus and silicate to the system. Although there may be nutrient absorption by sediments in the upper estuary, and by macrophytes in the lower estuary, the Kromme may be classified as a non-conservative mesotrophic marine-dominated estuary which probably exhibits some nutrient recycling.

Flow-carried and active swimming migration of the glass eel(Anguilla anguilla) in the tidal area of a small estuary on the French Atlantic coast

The study of the migration dynamics of glass eels(Anguilla anguilla) in a small estuary of the French Atlantic coast shows a two-stage sequence: (1) From November to March, the glass eels migrate upstream by using the tidal currents. The estuarine hydrology leads to a natural trapping of migrants in a typical area where the current speed slows down. The location of this zone depends on hydraulic conditions. The greater the tide is the farther upstream this area will be. This phenomenon leads to an increasing catchability of elvers. (2) From April onwards, when the water temperature reaches 10–12 °C, the glass eels swim actively upstream in the estuary. Then, fish concentrate just below the first dam. This behaviour shift shows the beginning of the colonization process of the whole riverine system.

Impacts from Mosquito Control-induced Sulphur Mobilization in a Cape Cod Estuary

Insect control programmes sometimes include environmental modification techniques such as diking and drainage. The impacts of such techniques are not often known or assessed. As a telling example having wide implications, we present an analysis of impacts in a small estuary which has been subjected to both diking and ditching—primarily for mosquito control.The major impacts stem from katteklei formation. Desiccated salt-marsh sediments produce acidified leachates which result from oxidation of pyrites. Lowered pH and high (acid-mobilized) aluminium concentrations both surpass levels that are known to be toxic to aquatic fauna. Fish and invertebrate communities in the basin are impoverished, and important commercial species such as American Eels and Alewives are heavily decimated. The acid-tolerant mosquito Aedes cantator thrives, however. Thus a natural system of substantial economic and aesthetic value has been inadvertently devastated through application of unnecessarily harsh as well as, in this case, ineffective mosquito control methods. Their use should be re-evaluated for similar impacts wherever such application has been carried out or is being contemplated.

Raptor predation on wintering waders in southeast Scotland

Predation on waders was investigated over the winters of 1982‐83 and 1983‐84 at a rocky shore and a small estuary in southeast Scotland. Probably all the waders which were found after being eaten were killed by raptors; mammalian predation and death due to severe weather were of minimal importance in comparison to the effects of raptor predation. Sparrowhawks were probably the major predators of waders at both sites, but owls also took some. Differences were found between the rocky shore and the estuary in the species of raptors which were seen (more Peregrines and Merlins seen on the estuary) and in the numbers of wader kills which had been plucked and eaten on open ground (more open ground pluckings, indicative of Peregrines and Merlins, found on the estuary). It is suggested that Peregrines and Merlins took more waders at the estuary due to their preference for hunting over large open expanses. Winter mortality rates due to predation varied in different species of waders: at the rocky shore the Redshank suffered the heaviest winter mortality (20% and 16%) whilst on the estuary the Ringed Plover had the highest winter mortality (19%). At both sites no large waders such as Curlews and Oystercatchers died as a result of predators and for these species other factors, such as severe weather or starvation, appeared to be a greater source of mortality. Significantly more juvenile Redshanks, Turnstones and, probably, Dunlin and Ringed Plovers were found eaten than was expected from the age‐composition of their respective populations. In the Redshank and Turnstone several differences in the behaviour of juveniles and adults were discovered which may have made juveniles more vulnerable to predation.

Evidence for the presence of a viral non‐lymphocystis type disease in winter flounder, Pseudopleuronectes americanus (Walbaum), from the north‐west Atlantic

Abstract. A non‐lymphocystis type disease associated with virus particles has been documented in winter flounder, Pseudopleuronectes americanus (Walbaum), taken from a small estuary in Conception Bay, Newfoundland. The papillomatosis‐type lesions found on the dorsal surface of the fish contained numerous electron‐dense particles, approximately 30 nm in diameter. A number of lines of evidence, including cytochemical studies, indicated that the particles were not glycogen but virions. Sensitivity to deoxyribonuclease enzyme treatment and the presence of crystalline viral‘factories’ in the nuclei of infected cells further suggested that the particles were small DNA virions. Characteristics including nucleic acid composition, particle size, site of multiplication and the lack of an envelope indicate that this fish virus is similar to the Papovaviridae and Parvoviridae families of mammalian viruses. Lymphocystis is common in flatfish populations along the Newfoundland and Labrador coasts of the N.W. Atlantic, but this is the first record of flatfish infection with a small DNA virus.

Evidence for the presence of a viral non‐lymphocystis type disease in winter flounder, Pseudopleuronectes americanus (Walbaum), from the north‐west Atlantic

Abstract. A non‐lymphocystis type disease associated with virus particles has been documented in winter flounder, Pseudopleuronectes americanus (Walbaum), taken from a small estuary in Conception Bay, Newfoundland. The papillomatosis‐type lesions found on the dorsal surface of the fish contained numerous electron‐dense particles, approximately 30 nm in diameter. A number of lines of evidence, including cytochemical studies, indicated that the particles were not glycogen but virions. Sensitivity to deoxyribonuclease enzyme treatment and the presence of crystalline viral‘factories’in the nuclei of infected cells further suggested that the particles were small DNA virions. Characteristics including nucleic acid composition, particle size, site of multiplication and the lack of an envelope indicate that this fish virus is similar to the Papovaviridae and Parvoviridae families of mammalian viruses. Lymphocystis is common in flatfish populations along the Newfoundland and Labrador coasts of the N.W. Atlantic, but this is the first record of flatfish infection with a small DNA virus.