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1.
Fresh water, a fundamental element of all estuarine ecosystems, is South Africa’s most limited natural resource. Recent projections
indicate that by the year 2020 the country will be utilizing all its exploitable freshwater sources. Steeply increasing demands
by a rapidly growing population on this limited commodity have already resulted in a severe reduction of water supplies to
natural users such as estuaries — this trend is predicted to increase in the future. Concurrent with excessive water abstraction,
poor land husbandry (e.g. soil erosion) in many catchment basins and pollution (e.g. salinization) in return flows have led
to a serious deterioration in water quality. In contrast, a review of estuarine responses to varying flow regimes stresses
the strong dependence of local systems on riverine fresh water inputs of adequate quantity and quality. Freshwater dependence
is i.a. expressed in: flooding events that scour accumulated sediments, riverine nutrient input to drive estuarine phyto-
and zooplankton production, axial salinity gradients that increase habitat and species diversity, and maintenance of open
tidal inlets that prevent salinity and temperature extremes and facilitate larval exchange, fish migrations and tidal flushing
of salt marshes. Thus, estuarine conservation will have to encompass management of rivers and watersheds and play an increasingly
political role in decision processes concerning water allocations among ‘human’ and ‘natural’ users. 相似文献
2.
Ojeda J. Sanchez E. Fernandez-Palacios A. Moreira J. M. 《Journal of Coastal Conservation》1995,1(1):109-118
This paper deals with the application of satellite images to characterize some aspects of the circulation dynamics of the
Tinto-Odiel estuary using turbidity patterns as ‘natural tracers’. 15 images (Landsat TM and Spot HRV) were processed to provide
synoptic, instantaneous views of the circulation patterns under different environmental conditions. In addition, a comparison
was made between results of oceanographic field work, using biplanes and fluorescent tracers, and satellite image turbidity
patterns used as ‘ground truth’ data for specific hydroclimatic situations. This approach allowed (1) the identification and
mapping of dynamic processes of interest during a theoretical tidal cycle, (2) the elaboration of additional information on
the ‘flow schemes’ at the mouth of the estuary with improved spatial and temporal resolution, and (3) the supply of basic
data to improve the knowledge of exchange processes between estuarine and coastal waters. The results of this study are considered
to be useful for the management of the estuarine system. 相似文献
3.
J. Ojeda E. Sanchez A. Fernandez-Palacios J. M. Moreira 《Journal of Coastal Conservation》1995,1(2):109-118
This paper deals with the application of satellite images to characterize some aspects of the circulation dynamics of the
Tinto-Odiel estuary using turbidity patterns as ‘natural tracers’. 15 images (Landsat TM and Spot HRV) were processed to provide
synoptic, instantaneous views of the circulation patterns under different environmental conditions. In addition, a comparison
was made between results of oceanographic field work, using biplanes and fluorescent tracers, and satellite image turbidity
patterns used as ‘ground truth’ data for specific hydroclimatic situations. This approach allowed (1) the identification and
mapping of dynamic processes of interest during a theoretical tidal cycle, (2) the elaboration of additional information on
the ‘flow schemes’ at the mouth of the estuary with improved spatial and temporal resolution, and (3) the supply of basic
data to improve the knowledge of exchange processes between estuarine and coastal waters. The results of this study are considered
to be useful for the management of the estuarine system. 相似文献
4.
Interactions between water and land in The Netherlands 总被引:1,自引:0,他引:1
The Netherlands are one of the most densely populated coastal countries in the world and there is only limited space for living,
working, transport and recreation, while there is also the need to preserve and expand valuable natural habitats. In order
to solve many existing and future conflicts of interest, and in order to create ‘added value’, strategies are developed to
optimize the use of water-land systems.
The principle of ‘building with nature’ is applied in order to integrate land in sea and water in land in such a way that
future generations will be able to use coastal resources in a sustainable way, including a minimal effort to maintain the
coastline and the promotion of a multiple-use system.
The concept of Integrated multifunctional sustainable coastal zone development is introduced. This concept deals with a balanced
approach to the lack of space for present and future coastal uses in relation to each other, to the hinterland, and to the
sea. Flexible master plans are developed, taking into account many functions of the coastal zone, and facilitating adaptation
to future developments—e.g. impacts of climate change and relative sea level rise. In this regard increasing the flexibility
of the coastal zone is of vital importance.
Large-scale coastal land reclamations in The Netherlands are dealt with, based on two different principles: (1) polder systems
(low lying land reclamations surrounded and protected by dikes), (2) systems of ‘building with nature’—land reclamation protected
by man-made foreshores, beaches and dunes. In the latter type new flexible dynamic-equilibrium coasts are created for many
functions, while coastal vulnerability is reduced and a flexible coast is developed. 相似文献
5.
Coastal zones in Portugal, as interface areas between land and sea, have problems related to the growing human pressure in
terms of changes in land use associated with urban and industrial occupation, new accessibility (ports, motorways) and traffic
flows, intensification of recreational use (beaches, water sports) and excessive fishing. Impacts include deterioration of
water quality and sediments; alteration and degradation of natural habitats; new hydrodynamic situations; major landscape
changes: and rapid changes in habits and way of life of the local populations and increased exposure of populations and assets
to natural and induced risks (storms, accidents, spills, explosions).
Plans for the Management of the Coastal Zone (POOC) have been developed and seven of them have been approved, while two similar
plans are at a final stage of preparation. Together they cover the entire coast of Portugal. Their implementation and assessment
could be a first step towards an integrated management of the Portuguese coastal zones. River Basin Management Plans (PBH)
have been concluded and recently approved for the whole country. However, these plans do not consider estuarine systems and
some other issues related to coastal systems. The National Water Plan (PNA) is under public presentation and discussion. Several
‘key messages’ are presented in this paper as a contribution for assessment of the proposals of this plan on issues related
with coastal waters. 相似文献
6.
Christian Butzeck Uwe Schröder J. Oldeland S. Nolte K. Jensen 《Journal of Coastal Conservation》2016,20(3):221-236
Climate change and engineering activities have modified the hydrology and morphology of estuaries. However, the potential effects of these modifications on vegetation succession in estuarine marshes are still poorly understood. Therefore, we studied temporal changes in tidal habitats of the Elbe estuary over a period of 30 years. We compared vegetation maps from 1980 to 2010 and calculated the change in area of habitats with respect to three salinity and three elevational zones. To analyze the direction of the temporal change, we differentiated between progressive and regressive succession. By using regression tree models (conditional inference trees), we identified the most influential factors determining progressive or regressive succession of low marshes. The total area of the estuarine tidal marshes at the Elbe increased by 2 % from 1980 to 2010, but changes were unequal among the salinity zones. In the salt and brackish zones, the area covered by high marshes increased substantially but decreased in the tidal freshwater zone, while that covered by low marshes decreased in all the salinity zones. Additionally, we determined high persistence of tidal flats and high marshes, whereas only 19 to 28 % of the low marshes found in 1980 remained in 2010. In salt and brackish marshes, more than two-thirds of the area that had been identified as low marshes in 1980 had progressively developed into high marshes. In contrast, 44 % of the area of low marshes in tidal freshwater marshes showed regressive succession back into tidal flats. The distance to the navigation channel was the main factor determining successional direction in salt and brackish marshes. Here, greater proximity to the channel was correlated with higher risk of regressive succession. In tidal freshwater marshes, we identified both the distance to the navigation channel and the situation on the river shore (i.e. inner bank, outer bank or straight bank) as the main factors for marsh succession. Here, considerable engineering activities in the channel had simultaneously decreased the mean low water level and increased the mean high water level between 1980 and 2010, which led to an increase in tidal amplitude. It is quite likely that these changes negatively modified marsh distribution, increased regressive succession and, thus, lowered the quality of tidal freshwater marshes. 相似文献
7.
Adult Cancer magister make forays into hyposaline estuarine habitats during times of high food abundance. However, as weak osmoregulators, they
are poorly equipped to deal with the concurrent demands of osmoregulation and digestion. Therefore, the potential interaction
between nutritional status and feeding in a physiologically challenging environment was investigated. Changes in the proportion
of crabs feeding, the amount of food consumed, the time spent feeding, and the efficiency with which a meal was consumed were
examined in response to the length and severity of hyposaline exposure, and the duration of starvation. Reductions in the
(a) number of animals feeding, (b) the amount of food consumed, and (c) the time spent feeding were observed in salinities
where C. magister actively osmoregulates the concentration of its internal fluids. Although this reduction in feeding was likely a stress response,
the crabs were able evaluate the level of salinity stress: there was a dose-dependent reduction in feeding, and they were
able to discriminate between salinities separated by as little as 3.5‰. The likelihood that animals would feed in low salinity
increased with starvation. Thus, the aversion to food uptake in physiologically stressful conditions may be overridden by
the need to procure nutrients. In the natural environment, we suggest that C. magister are employing an ‘eat and run’ strategy, moving into the estuary, consuming a meal, and retreating to higher salinities to
digest. 相似文献
8.
Empirical data quantifying the long-term movement patterns of coral reef top predators are needed in order to design marine
protected areas (MPAs) that will provide these fishes with effective, long-term protection. Acoustic telemetry was used to
quantify the movements of a large coral reef top predator (Aprion virescens, Lutjanidae; Hawaiian name ‘uku’) at five atolls in the Northwestern Hawaiian Islands Marine National Monument (NWHIMNM)
from May 2005 to September 2006. The study atolls were located between 23.8°N, 166.2°W and 28.5°N, 178.3°W, and were separated
from their nearest receiver-equipped neighbor by distances ranging from 100 to 478 km. No inter-atoll movements by uku were
detected but individuals were seasonally site-attached to core activity areas of up to 12 km in length, and ranged up to 19 km
across atolls. Within their core areas, tagged uku exhibited diel and tidal habitat shifts, with the latter resulting in round
trips of up to 24 km in 24 h. Seasonal uku migrations resulted in extended winter (October–April) absences from summer (May–September)
core activity areas and may be linked to summer spawning. Large MPAs (i.e., entire islands, atolls or banks) would probably
be required for full protection of resident populations of adult uku, but such ‘island-scale’ MPAs will not benefit fisheries
unless there is significant larval supply from MPAs to neighboring fished areas, or adult emigration over time scales exceeding
the 16-month monitoring period of this study. A mixed management strategy of combining smaller MPAs with conventional measures
(e.g., minimum size limits, catch, and effort restrictions) may be the best approach for sustaining uku fisheries. However,
this would still require relatively large MPAs (12 km in length) to contain uku short-term (diel and tidal) movements, and
seasonal migrations would still take uku beyond the boundaries of MPAs of this size. These fluxes across MPA boundaries could
supply fish to fisheries but, if high exploitation rates exist, fishing could eliminate key MPA benefits such as increased
numbers of large, highly fecund individuals.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
9.
In natural systems, mixing is driven by turbulence, but current knowledge is limited in estuarine zones where predictions
of contaminant dispersion are often inaccurate. A series of detailed field studies was conducted in a small sub-tropical creek
in eastern Australia. Hydrodynamic, physio-chemical and ecological measurements were conducted simultaneously to assess the
complexity of the estuarine zone, notably the interactions between turbulence and environment. The measurements were typically
performed at high frequency over a tidal cycle. The results provide an original data set to complement long-term monitoring
and a basis for a more detailed study of mixing in sub-tropical systems. Unlike many long-term observations, velocity and
water quality scalars were measured herein with sufficient spatial and temporal resolutions to determine quantities of interest
in the study of turbulence, while ecological indicators were sampled systematically and simultaneously. In particular the
results yielded contrasted outcomes, and the finding impacts on the selection process for key water quality indicators. 相似文献
10.
Eelgrass (Zostera marina L.) in the Dutch Wadden Sea historically covered an area varying from 65–150 km2 in the eulittoral as well as the sublittoral zones. At present, this area comprises less than 1 km2 eulittoral eelgrass stands, with an associated decrease in habitat diversity. The causes for this decline are presumably
connected with the ‘wasting disease’ and the closure of the former Zuiderzee in the early 1930s resulting in increased tidal
range and increased currents. After a slight recovery of the eelgrass populations on the intertidal flats a definite decline
started in the early 1970s, possibly connected to increased turbidity. The present water quality and turbidity do not negatively
influence eelgrass growth up to a depth of at least 0.6m below Mean Sea Level. Based on mesocosm experiments and field experiments
it is concluded that re-establishment of eelgrass should be possible in sheltered bays and on unexposed tidal flats. The most
suitable depths for a reintroduction are those between 0 and 20–40 cm below mean sea level. 相似文献