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1.
Estuaries exhibit a large range in their responses to nitrogen loadings determined in part by characteristics of the driver, such as magnitude and frequency, but also by such intrinsic characteristics as physical/chemical factors (e.g., depth, volume, hypsometry, salinity, turbidity) and biological factors (e.g., nature of ecological communities, trophic interactions). To address the richness of estuarine response to driver variables, the aim ultimately is to establish a simple estuarine classification scheme, beginning with a river-dominated subset of estuarine systems and focusing on the role of water residence time in the estuary. Residence time (or flushing time) is related to other drivers (streamflow, nutrient, and sediment loads) and drives much of the biological response of estuaries because of flushing effects on plankton, temperature, nutrients, and light. Toward this goal, nutrient–phytoplankton–zooplankton (NPZ) models have been used to examine a range of subjects including effects of nutrient limitation and zooplankton predation on phytoplankton dynamics and fish predation. This class of model can admit a wide range of behavior, including multiple steady-states and oscillatory behavior. The NPZ equations include terms for nutrient recycling, phytoplankton settling, benthic regeneration, and zooplankton mortality. Analysis of the equations suggests that both the nature of nitrogen loading (i.e., whether it is correlated with discharge or independent of it) and residence time are critical in determining the steady-state response of the system. 相似文献
2.
Thomas M. Church 《Marine Chemistry》1986,18(2-4)
Generally the large tidal estuaries of the eastern United States, such as Delaware Bay, are characterized by rather high suspended particle concentrations at the landward end and high biological activity at the seaward end. As such, these estuaries can be conceptualized as geochemical and biochemical “reactors” for those processes controlling the transmission of trace elements from fresh to the coastal shelf waters. The efficiency of these reaction processes relative to estuarine flushing will control the residence times of microconstituents in such estuaries.Evidence is drawn from the Delaware estuary to illustrate biogeochemical estuarine reaction processes using salinity distribution data and mass balance calculations. The Delaware retains some of its estuarine trace elements as sedimented estuarine particles, while others are more conservative and largely exported. Those retained by sedimenting processes include trace elements in primarily geochemical (particle reactive) chemistries, while those exported appear recycled by biochemical (nutrient reactive) chemistries. Often, the behavior of trace elements (e.g., Fe, Cd) and nutrients (e.g., PO4) appear biogeochemically linked. Other examples are drawn from mixing studies to illustrate particle interaction, and benthic flux measurements to illustrate limited diagenetic reflux.The residence time of estuarine microconstituents should depend seasonally on the relative turbidity, flushing rate, and primary production of tidally dominated estuaries such as the Delaware. Thus, residence times of the more biogeochemically reactive microconstituents must be substantially shorter (days to weeks) than the average flushing times of these larger estuaries, while the residence times of the less reactive ones should approach such flushing times (weeks to months). True estuarine residence times of microconstituents can only be modeled after using large data sets averaged over time (season, tides) and space (salinity). 相似文献
3.
Mysids form a large biomass and mediate the benthic–pelagic coupling of numerous estuaries in southern New Zealand. An intra-annual (2011–2012) field survey in the breeding seasons (i.e. austral spring followed by summer) of mysids Tenagomysis chiltoni and Tenagomysis novaezealandiae, examining the body and brood sizes, was conducted. Samples were collected from six open and eight intermittently open/closed estuaries along the Otago coastline. Brood size of gravid females of T. chiltoni was not significantly related to their body size. Brood size of gravid females of T. novaezealandiae showed a significantly positive relationship with body size in spring but not in summer. It appears that brood size of gravid mysids do not always necessarily depend on body size, but may be influenced by breeding season (e.g. spring) and estuarine typology (e.g. intermittently open/closed). 相似文献
4.
W.R. Geyer 《Estuarine, Coastal and Shelf Science》1997,44(6):713-722
Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events. 相似文献
5.
Jessica L. McKenzie Gerry P. QuinnTy G. Matthews Jan BartonAlecia Bellgrove 《Estuarine, Coastal and Shelf Science》2011
Outflows from estuaries potentially contribute to the productivity of adjacent coastal waters, although most previous work has been on estuaries with considerable river discharge. We investigated the influence of estuary outflow on aspects of coastal sediments adjacent to two seasonally intermittent estuaries, the Curdies and Anglesea Rivers, in southwest Victoria, Australia. For each estuary, we measured sediment organic matter, microphytobenthic chlorophyll a and microbial utilization of carbon sources at three locations associated with each estuary: (1) inside estuary mouth, (2) estuary swash and (3) control swash (an open beach distant from any estuarine influences). Sampling occurred one week before and at one and nine weeks after both an artificial mouth opening and a separate natural flood at both estuaries. Significant temporal changes were detected for all three variables at the estuary mouth and estuary swash but the direction of change was inconsistent across the two estuaries and between the artificial mouth opening and natural flood. Organic matter in both estuaries showed no difference after the artificial mouth openings. Only Anglesea showed an increase in organic matter in the estuary mouth and estuary swash after the floods. Microphytobenthic chlorophyll a concentrations were highest when the estuary mouths were closed. Concentrations decreased at all locations at Curdies after the mouth was artificially opened. The estuary mouth at Anglesea sustained high chlorophyll concentrations and the estuary swash increased one week post artificial opening. The flood event resulted in an increase in chlorophyll a at the estuary mouth and swash at both estuaries, one week post flood. At Curdies, the microbial utilization of different carbon sources changed after both mouth events; estuary mouth and estuary swash showed similar patterns at one and nine weeks post opening. At Anglesea, the bacteria utilized different carbon sources between locations and the only significant interaction between location and time was post flood with change in carbon sources utilized by bacteria in the estuary mouth and estuary swash for one and nine weeks post flood. The southern coastline of Australia is characterized by estuaries with small catchments. This study highlights the spatial and temporal variability in the effects of the output of relatively small, intermittent estuaries on coastal sediment of adjacent beaches, particularly during prolonged periods of drought. 相似文献
6.
Freshwater inflow has a strong impact on the biological, chemical and physical characteristics of estuaries, which in turn affect the distribution and abundance of estuarine organisms. Increased climatic variability associated with climate change is predicated to modify precipitation patterns, which will likely intensify floods in estuaries. The demersal fish assemblage of the freshwater-dominated Great Fish Estuary, South Africa, was sampled using beam trawls, monthly, from December 2013 to November 2014. The first six months of the study were characterised by river flooding and high flow, with estuarine conditions found only in the mouth region; this was followed by six months of intermediate flow, with estuarine conditions recorded up to 10 km from the mouth. River flooding and subsequent reduced salinity resulted in a decrease in species richness and abundances of fishes in the estuary, with only two estuarine species (Glossogobius callidus and Psammogobius knysnaensis) and one marine migrant (Solea turbynei) recorded following river flooding (201 m3 s?1), in January 2014. The greatest species richness and abundances among both marine and estuarine fishes were recorded during intermediate flow conditions. We conclude that although freshwater inflow into estuaries is important for the nursery function of these systems, flooding—especially in freshwater-dominated estuaries—may cause a temporary decline in the abundance of most marine and estuarine fish species, including important bentho-pelagic marine migrant fishery species, such as Argyrosomus japonicus and Pomadasys commersonnii. 相似文献
7.
This study investigated whether the current lateral boundary for estuaries in South Africa, i.e. the estuarine functional zone (EFZ), includes all estuarine habitats. The EFZ covers 173 930 ha in 304 estuaries/outlets nationally. Field surveys and analysis of available aerial images showed that 82 (12 956.70 ha) of these estuaries (26%) had estuarine habitats occurring outside of this boundary. As a result of mapping scale, the National Vegetation Map does not represent habitats that are associated with small estuaries (approximately 50% of South Africa's estuaries). For estuaries in the Western and Eastern Cape provinces, most habitats have been lost due to urban development, whereas in subtropical areas (northern Eastern Cape and KwaZulu-Natal), cultivation has removed estuarine habitat. Although delineation of boundaries can be complicated by landcover changes, the estuarine lateral boundary in Cape estuaries could be identified based on sediment characteristics (moisture content, organic content, electrical conductivity), groundwater characteristics (salinity, conductivity and depth) and plant species. The delineation of the EFZ needs to be consistent, inclusive of all estuarine physical and biological processes, and cost-effective to identify so that it can protect estuarine habitats. 相似文献
8.
Time-dependence of salinity in monsoonal estuaries 总被引：1，自引：0，他引：1
The theories and classification schemes commonly used for understanding estuarine dynamics often refer to a steady state of the estuary in which the salinity field is time-independent. In this state salinity-ingress into the estuary due to different processes (diffusion, gravity current formation, impact of tidal asymmetries, etc.) is balanced by salinity-egress induced by runoff. Here we point out that the salinity field of the estuaries that are located on the coasts of the Indian subcontinent and come under the influence of the Indian Summer Monsoon (ISM) is never in a steady state. We refer to such estuaries as “monsoonal estuaries”, an example of which is the Mandovi estuary located on the west coast of India. We describe the annual cycle of the salinity field in this estuary and conclude that the essential unsteadiness of the salinity field arises from two features of the runoff into it. First, most of the runoff occurs as a series of episodes of highs and lulls spread over about 4 months of the wet summer monsoon. Second, the total runoff is large, well over an order of magnitude larger than the estuarine volume. We define two parameters to represent these two features, and show that they can be used to distinguish the monsoonal estuaries from others. 相似文献
9.
10.
《Journal of Sea Research》2007,57(2-3):209-217
The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but their occurrence differed among the estuaries. P. flesus only occurred in estuaries north of the Tejo estuary (39°N), S. solea was quite rare along the southern Portuguese coast (south of 37°30′N), S. senegalensis occurred in estuaries throughout the coast, but its abundance varied considerably, and the occurrence of M. hispidus was limited to the Sado estuary and Ria Formosa. A Correspondence Analysis was performed to evaluate the relationships between flatfish species abundance and geomorphologic and hydrologic characteristics of estuaries (latitude, freshwater flow, estuarine area, intertidal area, mean depth and residence time). Abiotic characteristics (depth, temperature, salinity, sediment type) of nursery grounds of each flatfish species were also evaluated. Results showed that some estuaries along the Portuguese coast have nursery grounds used by several flatfish species (e.g. Ria de Aveiro, Sado estuary), while in other systems a segregation was noticed, with juveniles of different species occurring in distinct estuarine areas (e.g. Minho and Mondego estuaries). This emphasizes the relevance of niche overlap, but the potential for competition may be considerably minimized by differences in resource use patterns and by an extremely high abundance of resources. Peak densities of flatfishes recorded in nurseries areas along the Portuguese coast were within the range of values reported for other geographical areas. Inter-annual abundance variability of all the species in the Tejo and Sado estuaries was extremely high, with a drastic decrease in P. flesus in the Tejo estuary, probably related to higher water temperature in recent years due to global climate change. 相似文献
11.
中国河口研究五十年:回顾与展望 总被引：3，自引：0，他引：3
提要过去50年中国的河口研究取得了巨大的成就。在理论研究方面,一个显著的特征是动力、沉积和地貌研究相结合,取得了一系列的成果,如河口冲淡水、河口锋、最大浑浊带、泥沙运动、拦门沙的形成、河口不连续现象、河口发育等。在应用方面,如钱塘江河口和长江河口等有许多成功的范例。然而,河口是复杂的,随着人类活动和人工控制的增强,当前河口研究面临着许多新的挑战,人类活动已成为第三驱动力,河口的自然适应与人工控制协调问题将是河口未来理论研究和应用实践的重要问题。 相似文献
12.
Alistair Becker Laurie J.B. Laurenson Kylie Bishop 《Estuarine, Coastal and Shelf Science》2009,82(4):566-572
Fish kills are not uncommon within estuaries in many regions of the world. In seasonally open systems, which are common in temperate areas, they are often associated with mouth openings. Such a kill occurred in July 2005 in the Surrey Estuary following a closed mouth period of seven months resulting in the loss of many thousands of fish. At the time the fish community within the estuary was under investigation which provided comprehensive data of this population prior to the kill. Monthly water quality monitoring was also being conducted prior to the kill and also carried out on a daily basis following the mouth opening. The Surrey was stratified during the closed mouth phase, isolated waters below the halocline had stagnated and become anoxic. As a result only waters above the halocline contained oxygen concentrations capable of sustaining most fish. It appears that if a mouth opening happens under low flow conditions, a shearing effect occurs within the water column where surface waters flow out to sea leaving deeper waters behind. This resulted in only anoxic waters being present for in excess of six days and was responsible for the fish kill. Fish sampling of the Surrey Estuary was conducted three and six months following the kill and those data were compared to that collected in the 12 months prior to the event. Three months after the kill few fish were collected within the estuary and included marine opportunists near the mouth and estuarine resident species in the far upper reaches of the system. However six months following the kill large numbers of estuarine resident species were collected throughout the Surrey Estuary. As many species were euryhaline, it is believed that some individuals migrated into freshwater reaches of the Surrey to escape the anoxic conditions within the estuary. As conditions improved they recolonised the Surrey Estuary. The high fecundity and rapid growth of these small, short lived species probably aided in their re-establishing populations within the estuary. It is clear from this research that artificial openings of estuaries should be avoided during low flow periods when oxygen concentrations are low. It also appears that many of the small estuarine resident species common in seasonally open estuaries are capable of recolonising estuaries following fish kills. The effects on larger, longer lived resident species are not known but likely to be more detrimental due to longer time required for them to reach sexual maturity. 相似文献
13.
Nicola C. James Alan K. Whitfield Paul D. Cowley 《Estuarine, Coastal and Shelf Science》2008,76(4):723-738
Little is known about long-term changes in estuarine fish populations and related environmental variations. Fishes in the temporarily open/closed East Kleinemonde Estuary were sampled bi-annually, in summer and winter, using seine and gill nets between December 1994 and July 2005. A total of 18 families, represented by 33 species, were recorded. The 10 most abundant species caught were consistently recorded in catches each year, but CPUE of individual species varied on an annual basis and this can often be related to mouth state. Multivariate analyses of the annual marine fish community identified two distinct groups, with more species recorded during years that succeeded spring (September to November) mouth-opening events than in years following no mouth-opening events in spring. Interannual community stability (IMD) and seriation (IMS) also increased from the years following no opening events in spring to the years that succeeded spring opening events. These results highlight the importance of the timing of mouth opening to the marine fish community in a temporarily open/closed estuary. This study reinforces the importance of long-term studies to understanding community changes in estuaries caused by environmental variations over different time scales. 相似文献
14.
This study has compared the environmental characteristics of the basins and saline lower reaches of the tributaries of eight estuaries on the south coast of Western Australia, which differ in their degree of connectivity with the ocean. Although four estuaries between 115.1° and 121.8° E along that coast remain permanently open to the ocean, the others only become open when the volume of river discharge is sufficient to breach the prominent sand bars at their mouths, which occurs annually following heavy winter and early spring rainfall in some estuaries (seasonally open) and infrequently in others (normally closed). Estuaries to the west of 118.5° E are predominantly permanently open, e.g. Oyster Harbour, or seasonally open, e.g. Broke, Irwin and Wilson inlets, whereas those further east, e.g. Wellstead Estuary and Hamersley, Culham and Stokes inlets, where annual rainfall and thus discharge are much lower, only become open after exceptionally heavy discharge. In permanently and seasonally-open estuaries, pronounced haloclines and oxyclines are present in the narrow rivers but not the wide basins where the waters are subjected to wind-driven mixing. The extent of cyclical seasonal fluctuations in environmental conditions differed markedly among the three seasonally-open estuaries and between years in one of those systems. These differences reflected variations in the relationship between the volume of fluvial discharge, which is determined by a combination of the amount of local rainfall, catchment size and extent of clearing of native vegetation, and the amount of intrusion by marine waters, which is largely controlled by the size and duration of the opening of the estuary mouth. The mean seasonal salinities in the basins of the three normally-closed estuaries increased over three years of very low rainfall to 64 in the deepest of these estuaries (Stokes Inlet) to 145 in Hamersley Inlet and to 296 in the shallowest estuary (Culham Inlet). These results demonstrate that the environmental characteristics of estuaries on the south coast of Western Australia differ markedly, even among those of the same type, e.g. seasonally-open estuaries or normally-closed estuaries. 相似文献
15.
《African Journal of Marine Science》2013,35(2):163-180
Research in South African temporarily open/closed estuaries that includes studies on the hydrodynamics, sediment dynamics, macronutrients, microalgae, macrophytes, zoobenthos, hyperbenthos, zooplankton, ichthyoplankton, fishes and birds is used as a basis to review the ecology and management of this estuary type on the subcontinent. Particular attention is given to the responses of the different ecosystem components to the opening and closing of the estuary mouth and how this is driven by riverine and marine events, as well as anthropogenic influences. In addition, the wider implications of these research findings for the management of temporarily open/closed estuaries in terms of freshwater supply are explored, together with the role of government legislation in maintaining the ecological integrity of these important wetland systems. 相似文献
16.
In Australia, a large majority of small subtropical estuaries are narrow, elongated and meandering channels with large width to depth ratio and cross-sections which deepen and widen towards the mouth. Up to date, episodic rainstorm events in such small systems were rarely documented, and this study presents a field data set collected during and immediately after a rainstorm. A number of hydrodynamic and physio-chemical parameters were recorded simultaneously at several longitudinal locations for 12 h. The field measurements demonstrated a significant flushing of the estuarine zone, caused primarily by the rainfall runoff from the nearby shopping malls and roadways. Some strong vertical stratification of the water column was observed at all sampling locations, and the depth-averaged salinity data exhibited a dome-shaped intrusion curve. A solution of the salt dispersion equation provided some agreement with the freshwater flushing conditions during the wet weather. 相似文献
17.
Inês Cardoso Susana França Miguel Pessanha Pais Sofia Henriques Luis Cancela da Fonseca Henrique N. Cabral 《Estuarine, Coastal and Shelf Science》2011
The importance of estuaries for coastal environments is widely acknowledged but their role, structure and ecological status have been the focus of recent scientific efforts mainly concerning large estuarine areas. In this work we used fish assemblages to establish, for the first time, the functional and ecological role of five small estuarine systems along the Portuguese south and southwest coasts. Our results showed that, at a functional approach, fish communities did not differ between estuaries, and that all systems presented a seasonal pattern in diversity values, ecological and feeding guilds. These small estuaries contribute to the support of coastal fish populations by providing temporary habitats to the critical life stages of marine species, shelter and feeding grounds, and should be considered in an ecological and conservation perspective. 相似文献
18.
Human encroachment on the coastal zone has led to concern about the impact of anthropogenic nitrogen (N) on estuarine and continental shelf waters. Western North Atlantic watershed budgets suggest that the export of human-derived N from estuaries to shelf waters off the east coast of the US may be significant; however, models based on water inputs and estimates of upwelling of deepwater nutrients to surface waters of the mid-Atlantic bight indicate that estuarine N may be a relatively minor component of the overall shelf N budget. Stable N isotope ratios could provide a means to assess the relative input of anthropogenic N to shelf waters, particularly since dissolved N from human sources has elevated δ15N values (range: 7–30‰). We collected particulate material from surface shelf waters off the US east coast from 2000 to 2005 at near-shore sample sites proximal to the mouth of six estuaries and corresponding sites farther offshore. Near-shore (mean 33.7 km from estuary mouth) δ15N values ranged from 5.5 to 7.7‰ Offshore values (mean 92.4 km from estuary mouth) were consistently lower than near-shore sites (average 4.7 ± 1.0‰ versus 6.8 ± 1.1‰), suggesting different N sources to near and offshore stations. Near-shore regions are often more productive, as mean monthly chlorophyll-a concentrations from the sea-viewing wide field-of-view sensor (SeaWiFS) were significantly higher at near-shore sites near the mouth of three of the six estuaries. A mass balance using a concentration-dependent mixing model with chlorophyll-a concentrations as a surrogate for dissolved inorganic nitrogen can account for all of the nitrogen at near-shore sites south of Cape Cod with estuarine nitrogen estimated to contribute 45–85% of the nitrogen to the near-shore surface particulate material. Our results support the hypothesis that estuarine nitrogen is influencing continental shelf ecosystems, and also provide preliminary evidence of the spatial extent of its influence on shelf waters in the mid-Atlantic bight. 相似文献
19.
本文利用高分辨率数值模型,以2001年秋季为例,详细分析了影响坦帕湾水交换的三种因素:潮汐、河流和风。论文共设置了三组实验,驱动力分别为潮汐,潮汐和河流,潮汐、河流和风。模拟结果显示:只有潮汐作用时,由于坦帕湾潮汐较弱,潮程较短,坦帕湾与其临近海域的水交换主要发生在湾口附近;当潮汐和河流共同作用时,由于河流和湾口海水盐度的不同形成了水平密度梯度,在其产生的水平密度梯度力的作用下,坦帕湾形成了表层流向湾外、底层流向湾内的重力环流,从而加强了坦帕湾跟其临近海域的水交换;由湾内指向湾外方向(2001年秋季平均)的风应力加强了流向湾外的表层流,同时水位梯度力发生了反转,变成了由湾口指向湾顶,这加强了流向湾内的底层流,表层流和底层流的加强最终促进了坦帕湾跟其临近海域的水交换;在航道处,水深较深瑞利数较大,该处的重力环流较强,这使得相对于两侧的浅水区,航道处的水交换能力较强。此外,文章还分析了坦帕湾水交换的空间差异,在Old Tampa Bay的西侧和北侧,滞留时间最长,水交换能力最弱。为减少海洋生态灾害发生,今后应重点加强对该地区的生态环境保护。 相似文献
20.
Jonathan Selleslagh Rachid Amara Pascal Laffargue Sandric Lesourd Mario Lepage Michel Girardin 《Estuarine, Coastal and Shelf Science》2009
This study has analysed for the first time fish composition and assemblage structures of three small macrotidal estuaries of the Eastern English Channel (EEC) and has explored the influences of 19 biotic and abiotic variables on the fish assemblages. Fish from Canche, Authie and Somme estuaries were collected during spring (June 2006 and May 2007) and autumn (September 2006) along the estuarine gradients using a 1.5 m beam trawl. Using identical sampling protocols, the study also analysed and compared for the first time taxonomic and functional aspects of the fish assemblages in 15 estuaries located along the Atlantic and English Channel coasts. SIMPER analysis showed high similarities in fish assemblages in the three EEC estuaries and during either spring or autumn periods. However, intra-estuary similarities were relatively low, indicating that fish assemblage structures (species richnesses or abundances) were more variable within the estuary (salinity gradient) than between estuaries and/or seasons (spring vs autumn). Although numerous environmental variables were included in the study, only 47% of the variability observed in the fish distribution was explained. Fish spatial variations in the EEC estuaries are mostly driven by abiotic variables as opposed to biological interactions. As indicated by CCA, salinity and muddy sediments were the two most important factors structuring the fish assemblages. The macrobenthos being very abundant in the EEC estuaries (580–1121 ind. m−2), the availability of potential prey is probably not a limiting factor in the utilization of estuaries by fish. Contrary to the majority of French estuaries dominated by estuarine species (ES), the fish assemblages of the EEC estuaries are clearly dominated by marine migrant (MM) species (65% on average) with high abundance of juveniles (mostly young-of-the-year). Cluster and SIMPROF's analyses distinguished the functional structure of the 15 estuarine fish assemblages into different clusters. The three EEC estuaries form a similar group with the largest French estuaries (Seine, Loire and Gironde). The latters were characterized by higher MM/ES ratio compared to the other French estuaries. Freshwater flow and tidal range were the main factors associated with this group of estuaries. The results of the present study do not indicate that anthropogenic impacts (chemical contamination) on estuaries affect their ecological functioning as described by the fish ecological guilds. It is suggested that the guild approach may not be useful to provide valuable information on the ecological status of estuaries. 相似文献