Estuarine Influence Research Articles

Fish assemblage structure in relation to macrophytes and filamentous epiphytes in shallow non-tidal rocky- and soft-bottom habitats

The fish assemblage in nineteen shallow water (0–3 m) areas on the Swedish west coast, including an estuarine zone, was assessed during spring and autumn 1989 and autumn 1990, using semi-quantitative survey nets. Samples of macrovegetation were collected concurrently for estimates of species composition and biomass. Nine stations had rocky-bottom substrata and ten had soft-bottom substrata all characterized by high coverage of macrovegetation and variously overgrown with epiphytic filamentous algae. Fish assemblage structures were compared and related to vegetation biomass, substrata and estuarine influences. At rocky-bottom stations total fish biomass was positively correlated with total vegetation biomass and negatively correlated with the proportion of filamentous algae during autumn samplings. In soft-bottom habitats variation in vegetation was small between stations, and no correlation existed between vegetation biomass and fish biomass. However, the number of fish species in soft-bottom habitats decreased significantly with increasing dominance of filamentous algae. The component species of the fish assemblage varied in their relation to the vegetation biomass and structure suggesting differences in degree of association with vegetation at the species level. Multivariate analysis based on fish species composition and on vegetation assemblages at the individual stations, yielded two major groups in accordance with division of the substrate into rocky- and soft-bottom habitats. Vegetation biomass superimposed on the fish assemblage ordination indicated a relationship between vegetation biomass and fish assemblage structure. Location of stations, in relation to the estuary was reflected in subgroups formed in the fish assemblage based cluster and ordination, suggesting a substantial estuarine influence on the fish assemblages. Thus, substrate type, vegetation biomass and structure, and estuarine influence are all potential structuring factors for the fish assemblages. In our study, vegetation structure seems to be of major importance and changes such as increased dominance of filamentous algae, like that observed in coastal areas in Sweden, might cause significant changes in fish assemblage structure.

The atmospheric input of nitrogen species to the North Sea

An assessment of atmospheric inputs of nitrogen to the southern North Sea (south of 56°N) has been made following a series of research cruises between August 1988 and October 1989, during which wet and dry sampling for aerosol and gaseous species was undertaken. Wet and dry deposition appear to contribute approximately equally to total deposition, yielding fluxes of 126 × 10 3 t N a -1 and 102 × 10 3 t N a -1 , respectively. A tentative assessment for the northern North Sea has been made based on extrapolation from data generated here and from coastal sites. When combined with fluxes calculated for the southern area, the total atmospheric deposition of nitrogen to the whole North Sea is estimated to be 412 × 10 3 t a -1 . In terms of gross nitrogen inputs to the North Sea, the contribution from the atmosphere is relatively minor, the budget being dominated by the influence of the North Atlantic inflow. However, it does represent at least 26% of the terrestrial input. Furthermore, the effects of both seasonality in inputs and remoteness from estuarine influence suggest that during the growing season, when primary production in the North Sea is often nutrient limited, the atmosphere may provide the dominant source of nitrogen in stratified areas away from the coast, and at a time when the long-term trend in European emissions of NH 3 and NO x to the atmosphere is upward. DOI: 10.1034/j.1600-0889.1993.00005.x

Tidal influence in Cretaceous fluvial strata from Utah, USA: a key to sequence stratigraphic interpretation

ABSTRACTDetailed models already exist that outline physical and temporal relationships in marine and marginal marine strata. Such models are still in their infancy in alluvial deposits. Recognition of tidal and estuarine influence in fluvial strata is critical to the development of high resolution sequence stratigraphic correlations between marine and non‐marine strata. Strata that have previously been interpreted as low energy meandering river deposits contain sedimentary and biogenic structures that suggest a tidal influence. These structures include sigmoidal bedding, paired mud/silt drapes, wavy and lenticular bedding, shrinkage cracks, multiple reactivation surfaces, inclined heterolithic strata, complex compound cross‐beds, bidirectional cross‐beds, and trace fossils including Teredolites, Arenicolites and Skolithos. Although none of these structures is unique to tidal processes, the preponderance of data suggests that fluvial systems have been affected by tidal processes well inland of coeval shoreline deposits. These deposits rarely form a significant proportion of a depositional sequence; however, their occurrence allows time significant surfaces to be extended for tens or even hundreds of kilometres inland from coeval shoreline deposits.In Turonian through Campanian strata exposed in the Kaiparowits Plateau of southern Utah, tidally influenced facies are recognized within at least two distinct stratigraphic levels that were deposited during periods of relatively rapid base level rise. These strata form part of an alluvial transgressive systems tract. Landward of each of the marine transgressive maxima, tidal facies are present in fluvial channels that are completely encased in non‐marine strata at distances up to 65 km inland from a coeval palaeoshoreline. Our work suggests that such deposits may have gone unrecognized in the past, but they form a significant component of alluvial strata in many depositional sequences. Although these tidally influenced fluvial deposits may be difficult to recognize, they are temporally equivalent to marine maximum flooding surfaces and provide a chronostratigraphic correlation between alluvial and nearshore marine deposits.

The spring-time abundance and feeding ofEurytemora affinis (Poppe) in Volkerak-Zoommeer, a newly-created freshwater lake system in the Rhine delta (The Netherlands)

Eurytemora affinis, a calanoid copepod, has been encountered in Volkerak-Zoommeer (Rhine delta region, S.W. Netherlands) both before this lake system was isolated in 1987 from the estuarine influence, and after. It was the main particle-feeding crustacean at all the 3 sampling stations in March–April 1990 when it reached densities of up to 215 ind.l−1. Its decline from mid April onwards, and low densities through summer, coincided with increase in cladocerans, especiallyDaphnia spp. (D. pulex andD. galeata), a decrease in seston (<33μm) and chlorophyll concentrations and in primary production rates. The clearance rates (CR) ofEurytemora measured in the spring period varied enormously (0.6–24 ml.ind−1.d−1) depending mainly on size (0.44–1.06 mm), food concentration (0.8–2.2 mg C.l−1), and the water temperature which varied only narrowly (8.0–9.0°C). Mean ingestion rates of the animals measuring 0.68±0.02 mm during the study was 6.7±3.2 μgC.ind−1.d−1; and assimilation efficiency varied between 27 and 53% (mean: 41±9%). The weight specific CR (SCR) varied between 0.96 and 6.4 litre.mg−1 body C.d−1. Pooled regression of SCR on the animal's body weight at the 3 study stations revealed a significant inverse relationship. Also daily ration and specific assimilation ofE. affinis varied greatly and inversely with the body weight. This calanoid contributed from about 50 to 100% to the zooplankton community grazing rates and assimilation rates, the former often exceeding the phytoplankton primary production.

The attached algal flora of the estuary and Firth of Forth, Scotland

SynopsisA current intensive mapping scheme for Forth seaweeds shows the normal attenuation gradient of species going upstream in the estuary with the existence of two areas of species depletion in the firth, around Kirkcaldy and Edinburgh. Ordination of species presence data suggests the continuation of estuarine influence into the firth and the possibility of slight differences in composition of the flora between the north and south banks in the mid and inner firth. Impoverishment of the flora around Edinburgh since the 19th century can be ascribed to increased pollution, but possibly also, to a lesser degree, to shore reclamation. Following abatement of sewage pollution, differences in the recovery of the algal flora on different shores may be related to the nature of the pollution-induced animal community. Recent work on the upper estuarine flora of the many small, highly-stratified sub-estuaries of the Forth system has revealed a marked shore zonation pattern of smaller mat-forming species.

Aspectos bio y cronoestratigráficos del Mioceno de Berá (Tarragona)

Se estudian los Moluscos, Foraminíferos, Palinología y Nanoplancton calcáreo de unos nuevos niveles arcilloso-limosos descubiertos en la excavación de un pozo en las proximidades de la Ermita de Berá (Tarragona); la excelente conservación de los restos paleontológicos permite un estudio más exhaustivo. En conjunto, la mayoría de las características indican que se trataría de una sedimentación en condiciones neríticas alrededor de los 30 metros de profundidad con ciertas influencias de carácter estuarino. La presencia de abundantes Orbulina, T. mayeri, junto con G. praemenardii y ausencia de G. fohsi peripheroronda (presente en otras secciones próximas) permite atribuir los niveles a la biozona de G. mayeri, de edad Serravalliense; los datos de Nanoplancton son acordes con dicha edad.

Sedimentology of Paleochannels on Foreland Coastal Plain, Judith River Formation (Upper Cretaceous), Southeast Alberta: ABSTRACT

The upper 90 m (295 ft) of the sub-Bearpaw Judith River Formation, continuously exposed in the badlands along the Red Deer River 185 km (115 mi) east of Calgary, is famous for the unrivaled assemblage of dinosaur fossils. Dinosaur Provincial Park presents a rare opportunity to view the architecture of a foreland coastal-plain sequence as well as to clarify the origin and distribution of subbituminous coal zones and gas reservoirs associated with this formation across southeast Alberta. The distal reaches of paleodrainage from the developing Cordillera to the Western Interior seaway are being examined by north-south traverses across the badlands. Sharp-based paleochannel units, enclosed by rooted, olive-gray mudstone sequences that are commonly 4-6 m (13-20 ft) thick, vary between 2 end members. The first contains laterally accreted sand-mud couplets with abundant macrofloral debris, and represents cyclical, low-energy growth of point bars, possibly with an estuarine influence. The second, mainly comprising cosets of large trough cross-beds with mudstone intraclasts, was formed by episodic aggradation of high-energy systems. An intermediate composite type displays evidence for an energy increase as channel sinuosity decreased. This variation in paleochannel type is a tributed to alternating alluviation/rejuvenation associated with an unstable base level. Coal zones and potential reservoirs appear to be associated with the transgressive and regressive phases, respectively, of the Bearpaw coast. Amalgamation of paleochannels--marked by laterally extensive horizons of bone fragments, lithic and intraclastic gravel--is more common seaward over the axial region of the Sweetgrass arch. End_of_Article - Last_Page 496------------

Estuarine and Fluvial Systems, Lower Mesaverde Group (Campanian), Northwestern Colorado: ABSTRACT

Stacked shoreline sandstones near the base of the Mesaverde Group are well exposed along the southern flank of Rangely dome, northwestern Colorado. Overlying these marine deposits is a thick sequence of carbonaceous siltstones that encase elongate lenticular sandstones. This sequence records the evolution from estuarine to fluvial channels formed along the western margin of the Cretaceous Western Interior seaway. Sections 180 to 250 m (590 to 820 ft) long, were measured along a trend perpendicular to paleoshoreline. Several individual sandstones were studied in detail to develop depositional models. Data from over 300 well logs provided information regarding regional distribution and stratigraphic relationships of the systems. Two major stratigraphic successions were reco nized. Thin (0.5 to 2 m, 20 in. to 6.6 ft) bioturbated and root-mottled fine sandstones, interbedded with pervasive siltstones occur immediately over the marine shoreline deposits in both sequences. The sandstones are interpreted as storm washover deposits. At Gillam Draw in the eastern portion of the outcrop study area, the washover sandstones are overlain by 50 to 60 m (165 to 195 ft) of bioturbated shales and siltstones. Ripplestratified, upward-fining, fine to very fine sandstone lenses occur in this interval. These lenses are 4 to 8 m (13 to 26 ft) thick, have erosional bases, and have well-developed lateral-accretion bounding surfaces. Ophiomorpha and other trace fossils suggest an estuarine influence. The sandstone lenses are point bar deposits formed along meandering tidal creeks. Si tstones, coals, and 8 to 12 m (26 to 39 ft) thick lenticular sandstones overlie the tidally influenced interval. The sandstone lenses change significantly in geometry, bounding surface relationships, and textural trends within this succession. Stratigraphically lower sandstones form broad (100 to 200 m, 330 to 660 ft wide) belts. Individual sandstone bodies within the lenses have erosional bases and prominent lateral-accretion surfaces. Trough cross-bedding near the base is overlain by ripple stratification. These broad, lenticular sandstones represent fluvial meander-belt deposits. Sandstone lenses become narrower and lack accretionary surfaces higher in the section. These younger sandstones are multi-storied, rather than multilateral, channel deposits and are flanked by extensive crevasse splay facies. They are interpreted as confined anastomosing fluvial channels. West of Gillam Draw, the anastomosing fluvial system directly overlies shoreface and storm washover deposits. The multistoried lenticular sandstones are thicker (20 to 30 m, 66 to 100 ft). Sedimentation kept pace with subsidence in the eastern, basinward sections. Lower reaches of streams were tidally influenced even though the area was not inundated by marine waters. The western succession represents aggraded fluvial systems formed inland from the coast. Both sequences are characteristic of areas of rapid subsidence. End_of_Article - Last_Page 525------------

Some records of sea temperatures in the English Channel in February 1963

In mid-February 1963, a survey of sea temperatures in the western English Channel was made by means of a thermistor towed continuously behind the ship, also by water-bottle samples in a limited area between Plymouth and the Lizard. Evidence is given that surface temperatures, as measured by the thermistor, were representative of the whole water column. Sea temperature records from Torquay indicate that at this time temperatures were near their minimum for this exceptionally cold winter; at Plymouth where sea temperatures are usually more erratic because of estuarine influences the minimum had already been passed. A comparison with data for previous years at Plymouth shows that during January, February and March mean temperatures were lower than in any corresponding month since records were started in 1898.