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1.
The effect of the North Atlantic Oscillation (NAO) indices on climatic conditions and their subsequent influence on water temperature of two Basque estuaries (estuary of Bilbao and estuary of Urdaibai) were assessed by transfer function (TF) models for the period 1997–2006. Results showed that air temperature had an immediate (lag=0) and significant negative response to the NAO, whereas rainfall was not correlated with this climate index. The negative correlation between NAO and air temperature was found to be stronger with the seasonal indices derived from the differences in surface pressure between Iceland and Azores than with that derived from the principal component time-series of the leading eigenvector of the sea-level pressure in an Atlantic sector. The correlations between rainfall and river discharge, and between air temperature and water temperature were positive and highly significant in both estuaries. The response of water temperature to air temperature was immediate in both estuaries, whereas one-quarter lagged responses were also observed in the estuary of Bilbao, which is deeper and more stratified than the estuary of Urdaibai. Our study provides evidence that on the Basque coast the NAO plays an important role in climate variations, which in turn affect estuarine water temperature.  相似文献   

2.
The EC Water Framework Directive requires that ecological quality be assessed in transitional waters using the abundance and species composition of macroalgae. In estuaries, which form the majority of transitional waters, species composition is not a suitable measure. This arises from two features: (i) there is a continuous, natural change in species composition along the gradient of estuarine conditions which makes it difficult to know where within an estuary the species composition should be assessed, (ii) the inner estuarine macroalgal community of mat-forming species is very tolerant to both natural and anthropogenic stress and species poor which makes it insensitive to environmental variations in terms of species composition. An alternative feature is proposed based on the extent of upstream penetration of perennial fucoid algae. This proposal is founded on a series of case studies of the changes in fucoid limits, within a number of estuaries in the British Isles, consequent upon changes in pollution status over the last three decades. This also has to take into account variations of fucoid penetration owing to natural factors such as range of salinity variation and turbidity. The abundance criterion is taken to mean the absence of macroalgal blooms or "green tides", because general abundance of species is hard to quantify meaningfully in the upper estuarine mat-forming species and in the lower estuary is subject to great variation owing to the physical variability of estuary types.  相似文献   

3.
Different levels of eutrophication and pollution in the Baltic coastal waters in general, and in estuaries particularly define variations in the buffering capacity of ecosystems of these important filter zones between rivers and the adjacent Baltic Proper. Phyto- and zooplankton in the estuaries form important components of the pelagic food webs that participate in producing and structuring the matter, energy, and information fluxes in the ecosystems. Due to salinity gradients, estuaries provide a large variety of aquatic habitats for native populations of marine, brackish and fresh water plankton species. Non-indigenous planktonic species that expand their bio-geographical range and invade the Baltic coastal ecosystems also find favourable environments, establish permanent populations there, and impact aboriginal ecosystems. The dynamics of abundance, species diversity, population structure, productivity of planktonic communities, and peculiarities of trophic interactions in different Baltic estuaries are influenced by a number of common environmental factors. Being measured on the unified basis and monitored, changes (or stability) of structural and functional parameters of plankton communities can serve as indicators of alterations to the ecosystems. Comparative analyses and quantitative estimates of long-term changes in phyto- and zooplankton can contribute to evaluation of functional response of Baltic coastal ecosystems to anthropogenic stress. Both theoretical (modeling) and empirical studies of interactions within plankton communities aimed at the assessment of the role of planktonic organisms in water quality regulation, and applicability of these data for the evaluation of the status of ecosystems and their management can be considered as major goals for the future investigations in Baltic estuaries.  相似文献   

4.
Abundance and biochemical composition of organic materials in sediments of the estuaries of Mundaka and Bilbao (SE Bay of Biscay) were analysed to assess the effect of organic wastes released to these systems. Organic and labile contents were higher in the sediments of Bilbao, denoting organic enrichment with poorly decomposed materials by human dumping. Spatially, organic matter distribution skewed seaward in Bilbao and upward in Mundaka, in agreement with the location of major point sources of sewage. Labile material, proteins and protein:carbohydrate ratio showed upward increases in both estuaries, attributed to the oxygen restrictive conditions to decompose organic materials. Vertical distribution of organic components into sediments reflected the history of human activities. In Bilbao, the significant reduction of organic and labile compounds, and the decrease of protein:carbohydrate values in top layers seem a result of recent remedial actions to reduce urban sewage inputs and improve environmental conditions. Higher contributions of proteins and lipids were associated with anthropogenic materials, and higher contributions of carbohydrates with autochthonous materials. High protein:carbohydrate values indicate poorly decomposed materials of human origin. The close relationship of carbohydrates with chloropigments in Mundaka suggests that phytobenthic populations and derived detritus contributed to a greater extent to the organic fraction in this estuary.  相似文献   

5.
The Pearl River Estuary is among the largest estuaries in the subtropical areas of the world. Along the salinity and turbidity gradient between the freshwater reach of the Pearl River and the marine water of the South China Sea, the spatial and temporal composition and abundance of phytoplankton was examined in relation to physic-chemical variables during the dry and wet seasons of 2009. Water samples for phytoplankton and environmental parameters were collected from 18 stations during two seasons along a transect from upper estuary to estuarine and marine sectors. A total of 162 species belonging to 7 phyla were identified, with diatoms dominated in both seasons while dinoflagellates proliferated in autumn. Two main clusters and three sub-clades under each main cluster corresponding to seasons and water sectors were defined with multivariate analysis (cluster and nMDS). Based on the species composition and abundance of phytoplankton, both seasonal and spatial variability were observed at a significant level (ANOSIM: season effect, R=0.896, P<0.01; station effect, R=0.463, P<0.01). The correlation analysis between biotic and abiotic variables indicated that instead of the “proverbial” anthropogenic nutrients loading and salinity gradient, the best 2-variable combination (temperature and turbidity) showed a significant effect on the pattern of phytoplankton assemblages (ρw=0.49, BIOENV analysis) between wet and dry seasons in the Pearl River Estuary. This result suggests that physical disturbance either natural or manmade is a more important factor in regulating the phytoplankton community structure within the hydrologically distinct zone of estuaries.  相似文献   

6.
While recent studies have revealed that tidal fluctuations in an estuary significantly affect groundwater flows and salt transport in the riparian zone, only seawater salinity in the estuary has been considered. A numerical study is conducted to investigate the influence of estuarine salinity variations on the groundwater flow and salt dynamics in the adjacent aquifer to extend our understanding of these complex and dynamic systems. Tidal salinity fluctuations (synchronous with estuary stage) were found to alter the magnitude and distribution of groundwater discharge to the estuary, which subsequently impacted on groundwater salinity patterns and residence times, especially in the riparian zone. The effects of salinity fluctuations were not fully captured by adopting a constant, time-averaged estuarine salinity. The modelling analysis also included an assessment of the impact of a seasonal freshwater flush in the estuary, similar to that expected in tropical climates (e.g. mean estuary level during flood significantly greater than average), on adjacent groundwater flow and salinity conditions. The three-month freshwater flushing event temporarily disrupted the salt distribution and re-circulation patterns predicted to occur under conditions of constant salinity and tidal water level fluctuations in the estuary. The results indicate that the salinity variations in tidal estuaries impact significantly on estuary–aquifer interaction and need to be accounted for to properly assess salinity and flow dynamics and groundwater residence times of riparian zones.  相似文献   

7.
The distribution and abundance of benthic foraminifera and a range of elements have been analysed in six long cores (up to 10 m long) from the Bilbao estuary, N. Spain, to document environmental transformation of this estuarine ecosystem and to determine sediment contamination levels. Three different environmental zones could be distinguished in the recent sedimentary record based on its microfaunal and geochemical contents. Initially, a pre-industrial zone containing very abundant and diverse foraminiferal assemblages together with baseline metal levels. Secondly, an older industrial zone exhibiting co-existence of abundant and diverse foraminiferal assemblages with high concentrations of metals. Finally, a younger industrial zone with extreme concentrations of metals and barren of indigenous foraminifera. This environmental transformation has been caused by the discharge of untreated domestic and industrial effluents during the last 150 years. The occurrence of foraminifera in the two industrial zones and along the estuary is not related to defined levels of metals, and this seems to confirm oxygen limitation as the key factor to explain complete estuarine defaunation during deposition of the younger industrial zone (period 1950-2000). Effectiveness of current regeneration schemes could be assessed using microfaunal and geochemical proxies as environmental quality indicators.  相似文献   

8.
Bacterial counts for total coliforms and E. coli in estuaries are normally orders of magnitude greater at the freshwater end than at the seaward end and tidal movements and variations in freshwater flows produce continual change in the freshwater/seawater mix--this causes the bacterial counts to vary greatly throughout the estuary and the complexity creates difficulty in appraising or assessing the bacterial counts (i.e. difficulties arise when deciding if the bacterial counts for estuarine water samples are within an acceptable range--relative to their corresponding salinities). The situation is further complicated in estuaries where sewage is discharged directly. Microbiological criteria and indices that can be used in a practical way to overcome these difficulties were developed. The procedure is summarised as follows: 1. Primary criteria are proposed for total coliform and for E. coli bacteria in the freshwater at the head of the estuary and in full seawater at the mouth of the estuary. 2. For estuarine or transitional waters (i.e. waters with salinity ranging from 0 per thousand to 35 per thousand), distinct criteria are calculated for each individual sample--with a separate criterion for total coliforms and for E. coli--the individual criteria are founded on the primary criteria and vary with salinity on a pro-rata or linear basis. 3. Finally, the Microbiological Index for each result is obtained by dividing the actual bacterial count by the corresponding criterion--the acceptable Index is then equal to 1--at any salinity (i.e. where the Index is <1 then the bacterial count complies with the criterion, and where the Index is >1 then the count breaches the criterion). The Index also indicates the extent of the compliance or non-compliance with the corresponding criteria. An example of the application of the Microbiological Index is also presented--including examples of graphs that demonstrate how microbiological data for estuarine waters can be summarised and presented.  相似文献   

9.
This study quantitatively characterizes annual, interannual, and decadal variability of Middle Atlantic Bight (MAB) river discharges, MAB surface salinities, Long Island Sound (LIS) surface salinities, and LIS salinity stratification via wavelet analysis. Links among rivers, salinities, and standard climate indices are investigated through correlation analysis of the complete data records and low-pass time series (including periods greater than 1.5 years). All rivers and salinities analyzed have strong annual cycles that are distinguishable from random noise. All records have interannual power, but this variability is indistinguishable from the noise background. Some MAB rivers have significant multi-decadal power (near either 18-year or 26-year periods). Correlations are strong among MAB rivers, salinities at different shelf sections, and salinities at LIS stations. Negative correlations between MAB rivers and surface salinities account for a significant part of the observed variance: up to 29% for shelf salinities and 46% for LIS salinities. Shelf and estuary salinities are positively correlated; accounting for at most 61% of the variance. LIS salinity stratification is positively correlated with river discharge (up to 36% of the variance). Interannual variability exhibits similar statistical relationships with higher correlations. Average annual cycles indicate a 1–2-month sequential lag between peak river discharge, minimum estuary salinity, and minimum shelf salinity. Weak but significant correlations indicate a tendency for high discharge, low LIS salinity, and high LIS stratification to coincide with positive intervals of the North Atlantic Oscillation Index.  相似文献   

10.
An experimental study using mesocosms was conducted in the main shallow lake of a temperate wetland (Otamendi Natural Reserve, Argentina) to analyse the impact of zooplankton on phytoplankton and the microbial assemblages. The lake is characterised by the presence of a fluctuating cover of floating macrophytes, whose shading effects shape the phytoplakton community and the ecosystem functioning, which was absent during the study period. The experiment was run in situ using polyethylene bags, comparing treatments with and without zooplankton. The cascade effect of zooplankton on phytoplankton and the lower levels of the microbial food web (ciliates, heterotrophic nanoflagellates (HNF) and picoplankton) were analysed.A significant zooplankton grazing on the nano-phytoplankton fraction (3–30 μm) was observed. Conversely, large algae (filamentous cyanobacteria, colonial chlorophytes and large diatoms) increased in all mesocosms until day 10, suggesting that they were not actively grazed by zooplankton during this period. However, from day 10 until day 17 this fraction decreased in the enclosures with mesozooplankton, probably due to an increase in the abundance of large herbivores.The results of the experiment would also indicate a trophic cascade effect on the lower levels of the microbial community. In the treatment where zooplankton was removed, the abundance of ciliates followed the same increasing pattern as the abundance of HNF, but with a time lag in its response. In the enclosures without zooplankton, HNF remained relatively constant throughout the experiment, whereas ciliates strongly decrease during the last week. Total picoplankton abundance increased in the enclosures with mesozooplankton, thus supporting the existence of a four-link trophic cascade (copepods–microzooplankton–HNF–picoplankton). Zooplankton composition changed significantly from the beginning until the end of the experiment; cyclopoid nauplii and rotifers were notoriously dominant at t0, whereas 10 days later the community showed a more equitable proportion of cyclopoids, calanoids, nauplii, cladocerans and rotifers.  相似文献   

11.
Silver sorbs readily at low salinities to both phytoplankton and suspended sediments. As salinity increases, the degree of sorption decreases. Nearly 80% of silver sorbed to suspended sediments at low salinities will desorb at higher salinities, but desorption does not occur when silver is associated with phytoplankton. Thus, silver incorporation onto/into cellular material will increase the retention of silver within the estuary, reducing its rate of transport.  相似文献   

12.
The main regularities of hydrological and hydrological-environmental processes occurring within the complex estuary, the Chesapeake Bay and the mouths of its tributaries, are discussed. The peculiarities of the estuary morphological structure, including the structures of tidal and net currents, salinity and water turbidity fields and their variability, the environmental conditions, and their human-induced changes. Using the Chesapeake Bay as an example, it became possible to reveal the basic features of classical estuaries subject to a considerable impact of river runoff and featuring mixing of river and sea water and moderate stratification of the water mass. It is shown that the regularities of hydrological processes in the Chesapeake Bay are typical of many mouth water bodies of estuarine type (inlets, drowned river valleys, lagoons, and tidal estuaries proper).  相似文献   

13.
Increases in nitrate loading to the Mississippi River watershed during the last 50 years are considered responsible for the increase in hypoxic zone size in Louisiana-Texas shelf bottom waters. There is currently a national mandate to decrease the size of the hypoxic zone to 5000 km2 by 2015, mostly by a 30% reduction in annual nitrogen discharge into the Gulf of Mexico. We developed an ecosystem model for the Mississippi River plume to investigate the response of organic matter production and sedimentation to variable nitrate loading. The nitrogen-based model consisted of nine compartments (nitrate, ammonium, labile dissolved organic nitrogen, bacteria, small phytoplankton, diatoms, micro- and mesozooplankton, and detritus), and was developed for the spring season, when sedimentation of organic matter from plume surface waters is considered important in the development of shelf hypoxia. The model was forced by physical parameters specified along the river-ocean salinity gradient, including residence time, light attenuation by dissolved and particulate matter, mixed layer depth, and dilution. The model was developed using measurements of biological biomasses and nutrient concentrations across the salinity gradient, and model validation was performed with an independent dataset of primary production measurements for different riverine NO3 loads. Based on simulations over the range of observed springtime NO3 loads, small phytoplankton contributed on average 80% to primary production for intermediate to high salinities (>15), and the main contributors to modeled sedimentation at these salinities were diatom sinking, microzooplankton egestion, and small phytoplankton mortality. We investigated the impact of limiting factors on the relationship between NO3 loading and ecosystem rates. Model results showed that primary production was primarily limited by physical dilution of NO3, followed by abiotic light attenuation, light attenuation due to mixing, and diatom sinking. Sedimentation was mainly limited by the first three of these factors. Neither zooplankton grazing or plume residence times acted as limiting factors of ecosystem rates. Regarding nutrient reductions to the watershed, simulations showed that about half of the percent decrease in NO3 load was reflected in decreased plume sedimentation. For example, a 30% decrease in NO3 load resulted in a 19% decrease in average plume primary production and a 14% decrease in sedimentation. Finally, our model results indicated that the fraction of primary production exported from surface waters is highly variable with salinity (7–87%), a finding which has important implications for predictive models of hypoxic zone size that assume a constant value for this ratio.  相似文献   

14.
A total of 92,934 fish larvae representing 19 families were sampled monthly from the Sangga Kecil estuary (Matang Mangrove Forest Reserve) and adjacent coastal waters from May 2002 to October 2003. Larval fish assemblages were numerically dominated by Gobiidae (50.1%) and Engraulidae (38.4%). Canonical Correspondence Analysis (CCA) revealed that the larval fish assemblages, including their ontogenetic stages, differed between the mangrove estuary and adjacent offshore waters, and that salinity, turbidity and zooplankton food are the major environmental factors structuring the larval fish assemblages. Estuarine preflexion gobiid larvae were ubiquitous in the coastal and estuarine waters. Larval stages of euryhaline species that were spawned in offshore waters, such as Engraulidae and Clupeidae, were largely advected into mangrove areas at the postflexion stages. Larvae of other euryhaline fishes (Sciaenidae, Blenniidae and Cynoglossidae) that may have been spawned inside the estuary were, however, exported to offshore waters. Given that the collective number of juvenile and adult fish families in the Matang estuary was 53, while the number of larval families was only 17, the former is quite disconnected from the existing larval fish population in the estuary.  相似文献   

15.
A method, utilising overlaid graphs for nutrients vs salinity, was developed in order to determine which nutrient is limiting for plant growth in estuarine waters-at any salinity. Dissolved inorganic nitrogen (DIN=NO(3)(-)+NO(2)(-)+NH(4)(+)) and o-phosphate (PO(4)(-)) are the main forms of N and P that are readily bio-available for plant growth in waters and these have a Redfield atomic ratio of N:P=16:1 (i.e. aquatic plants absorb N and P in the average ratio of 16 atoms of N to 1 atom of P). Graphs are prepared for (i) DIN vs salinity and (ii) o-phosphate vs salinity with the vertical scales for DIN and o-phosphate set at a ratio of N:P=16:1; when these graphs are overlaid on each other then the lowermost trendline denotes the limiting nutrient for plant/algal growth-at any salinity. The graphs also indicate the extent by which one or other of the nutrients is limiting--at any salinity. Furthermore, if there is a transition from P to N limitation somewhere along the salinity gradient, then this occurs at the salinity where the trendlines intersect. The concept was applied to three estuaries in the southeast of Ireland and the results show that, in all of these circumstances, P is the limiting nutrient throughout--except for the higher salinities (i.e. salinities 30 per thousand), where either (i) N and P may become equally limiting at salinity approximately 35 per thousand or (ii) N may become limiting at salinity 30 per thousand. Overlaid nutrients vs salinity graphs were also used to demonstrate that, in the estuaries in southeast Ireland, carbon (as dissolved inorganic carbon, DIC=CO(2)+H(2)CO(3)+HCO(3)(-)+CO(3)(2-)) is not the limiting nutrient--at any salinity.  相似文献   

16.
The hydrodynamics associated with the Mundaka Sandbar are described. The sandbar (ebb tidal delta) is responsible for the formation and the quality of a “world famous” surfing wave, at the mouth of the Oka Estuary in the Urdaibai Biosphere Reserve. The primary factor controlling the shape of the sandbar is the shoreline configuration. In turn the size of the sandbar is controlled by the volume of the tidal outflow and the wave energy. Periods of tidal dominance occur during summer (associated with sandbar accretion); with mixed energy conditions during winter and wave dominance under storms (sandbar erosion).The surfing wave lost its characteristics following, intensive dredging along the estuary, combined with beach nourishment, in May 2003. Between May 2005 and April 2006, the outer part of the estuary was monitored, to understand the processes controlling recent morphological changes over the area.Recent studies undertaken in the mouths of estuaries, together with the results of the monitoring are described; these are complemented by the numerical modelling of wave hydrodynamics under medium and extreme sea states. Analyses of the wave and current survey data, combined with the modelling outputs, have demonstrated that the changes were not irreversible. As such, the natural shape of the sandbar has recovered gradually, as has the quality of the Mundaka surfing wave.  相似文献   

17.
The community structure of zooplankton was studied in relation to physico-chemical characteristics of the river Chambal polluted by industrial effluents and domestic sewage near Nagda. Thirtytwo species of zooplankton of five main groups, viz. Protozoa, Rotifera, Cladocera, Copepoda and Ostracoda were observed at pre-pollution sampling stations. The abundance, distribution, total population, group percentage and species diversity were studied and correlated with pollution-indicating parameters. Species diversity values indicated a decrease from the sampling station near a pre-effluent point to an effluent discharge channel and an increase at a post-effluent discharge point revealing a slight recovery zone. Keratella tropica and Kellicottia sp. were identified as pollution tolerant taxa.  相似文献   

18.
Zinc, copper and cadmium were determined by atomic absorption spectrophotometry in zooplankton from the N. W. Mediterranean. Seasonal variations of metal concentrations in zooplankton as well as the dry weight of the samples and the salinities of surface seawaters were taken into consideration over two periods of 1 year each (1976 and 1978). Zooplankton samples, collected near the estuary of the River Var and near the sewage outfall of the town of Cannes, present higher values than those collected near Villefranche Bay. However, the range of our results appears to be in good agreement with the values reported in the literature for Mediterranean plankton.  相似文献   

19.
Imposex and organotin (OT) tissue contamination of the netted whelk Nassarius reticulatus (L.) were assessed in the continental shelves around the main estuaries of the central coast of Portugal (Lisbon: Tagus estuary; Setúbal: Sado estuary) and the main coastal lagoon in the Southern of Portugal (Faro: Ria Formosa). Pollution levels were higher in areas of more intense boat traffic and shipyard activities and imposex showed a clear decreasing gradient from the estuaries to the offshore, in relation to a similar gradient of tissue contamination by tributyltin. Remarkably, imposex was extensively spread over the adjacent continental shelves of Tagus and Sado estuaries. The current work shows that TBT pollution is undoubtedly a matter of concern not only for the above estuaries where harbours are implanted but also for the adjacent continental shelves, regardless the massive dilution of contaminants that may occur in these deeper areas.  相似文献   

20.
Nutrient and suspended sediment concentrations were measured in the dry season and during the rising and falling stages of flood events in the Annan and Daintree rivers to estimate catchment exports. These flood events were also sampled along the salinity gradient in the estuary and nearshore shelf to quantify the modification of terrestrial sediment and nutrient loads as they pass through estuaries into the Great Barrier Reef lagoon. In the Daintree River TSS concentrations were found to increase between the catchment and the estuary plume. The source of TSS may have been scour of the estuarine channel or from land use in the catchment of the lower estuary. In the dry season nitrogen enters the Annan and Daintree estuaries predominantly in the form of PON and DON in roughly equal proportions. Nitrogen exports to the GBR are mostly in the form of DON. In the wet season the majority of nitrogen enters the estuaries as DON and leaves as PON. Nitrogen removal in the estuaries and plumes appears to be biologically mediated once suspended sediment concentrations decrease to a point where phytoplankton growth is not light limited. In the dry season phosphorus enters and leaves the estuaries primarily in organic form. PIP is the dominant form of phosphorus in river water, but leaves the estuary more evenly distributed between all forms. These estuarine processes result in less nitrogen and phosphorus being delivered to the GBR lagoon than is exported from the catchment. The differences between these estuaries highlights the need for further work to explore modifications in estuaries that drain into the Great Barrier Reef lagoon.  相似文献   

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