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91.
WATER COLUMN PRODUCTIVITY ATTRIBUTABLE TO DISPLACED BENTHIC DIATOMS IN WELL-MIXED SHALLOW ESTUARIES1
We attempted to determine the extent to which benthic diatoms contribute to water column primary productivity in shallow-water estuaries and to elucidate the primary mechanisms responsible for suspending the diatoms. A perliminary study conducted in Mugu Lagoon, California indicated that productivity of ocean water entering the lagoon during flood tides was often several orders of magnitude less than that of the same water mass about 3 h later. Benthic pennate diatoms displaced from the sediments into the water column accounted for the increase. A more detailed study was conducted in Barataria Estuary, Louisiana where, for one month, daily measurements were made of benthic and water column productivity and several other environmental variables. During the month, the relationship between water column and benthic primary productivity varied from strongly negative to weakly negative to positive. K-systems analysis indicated that factors comprised of wave height, meteorological tides, astronomical tides, and benthic productivity and standing crop accounted for the full range of variation in water column productivity. Benthic pennate diatoms, represented an average of 74% of the diatom taxa in water column samples. We conclude that the primary productivity of well-mixed shallow estuarine waters is often greatly aumented by displaced benthic algae. 相似文献
92.
GRAY A. WILLIAMS 《Biological journal of the Linnean Society. Linnean Society of London》1994,51(1-2):189-198
Populations of both species of flat periwinkle were examined at five discrete sites along the Severn Estuary, and at a marine site in Dyfed. The vertical distribution of the two species showed a clear partitioning of the shore – Littorina obtusata occupied the high/mid shore and L. mariae the low shore area. L. obtusata also extended further up the Severn Estuary than L. mariae. Maximum densities of both species were found in Milford Haven. Biometric investigations revealed intra and inter-specific differences in colour morphs, shell damage and size between populations. The possible influence of differential selection pressures at the various sites is discussed. 相似文献
93.
Size and settling velocity distributions of flocs in the Tamar estuary during a tidal cycle 总被引:4,自引:0,他引:4
Data extracted from video recordings of individual estuarine flocs near the estuary bed during the advance and retreat of
the salt intrusion show changes in size and settling velocity distributions. The recordings were taken using INSSEV —IN Situ
SEttling Velocity instrument. Size coupled with effective density variations due to both changes in floc structure and ambient
salinity result in changes in the settling velocity during the tidal cycle. In particular, just after high water slack, the
appearance of high settling velocity medium size flocs and individual particles suggest that the lower density flocs have
been broken up by the intense vertical shear in the currents caused by the salt wedge intrusion. Current shear is shown to
have a significant influence on floc effective density. 相似文献
94.
C C Appleton 《International journal for parasitology》1983,13(3):239-247
The emergence of Austrobilharzia terrigalensis cercariae from the snail Velacumantus australis decreased with decreasing salinity and temperature. This was most marked between 23 and 25 and between 24 and 19°C. Very few cercariae were shed below 23 regardless of temperature. The decrease in cercarial emergence was associated with the decreasing metabolic activity of the intermediate host. The emergence pattern of A. terrigalensis cercariae from V. australis was diurnal. There was a major peak between 08h00 and 10h00 and a minor second one between 16h00 and 18h00. No cercariae were shed between 22h00 and 04h00. Cercariae survived in sea water (35) for up to 48h, with a half-life of 30h. There was evidence that the prevalence of A. terrigalensis infection in the intermediate host population in the Swan estuary was higher during the summer than during the winter. The production of cercariae in the sporocyst also appeared to be a seasonal phenomenon. Mature cercariae were rare in sporocysts examined during the winter months (May–October) and absent altogether from those examined in September. 相似文献
95.
96.
Understanding mechanistic relationships between seagrass and their environmental stressors should be considered for effective management of estuaries and may inform on why change has occurred. We aimed to develop indicators for seagrass health in response to sediment conditions for the Swan-Canning Estuary, south-west Australia. This article describes the development of a new sediment-stress indicator, relating aspects of seagrass productivity with sediment sulfur dynamics. Sulfur stable isotope ratio and total sulfur were measured monthly within the roots, rhizomes and leaves of Halophila ovalis, and significantly varied across sites and months. The growth of seagrass over the summer months appeared restricted by sediment condition, with growth of seagrass lower when sediment derived sulfur and/or total sulfur within rhizome of leaf tissues was higher. H. ovalis appeared quite tolerant of sulfide intrusion within the root compartment, but growth was compromised when sulfide breached the root–rhizome barrier. The tightest correlation between potential sulfur metrics and seagrass growth was observed for the ratio (δ34Sleaf + 30)/(TSleaf), and it is this ratio that we propose may be a useful sediment-stress indicator for seagrass. The study also highlights that sediment condition needs to be considered at the meadow scale. 相似文献
97.
L. Hellings K. Van den Driessche W. Baeyens E. Keppens F. Dehairs 《Biogeochemistry》2000,51(2):141-160
Processes affecting the concentration and isotopiccomposition of dissolved inorganic carbon (DIC) wereinvestigated in pore waters of two freshwaterintertidal areas of the Scheldt Estuary, Belgium. Porewater 13CDIC values from marshes andmudflats varied from –27 to +13.4, these very largevariations reflect the contribution of differentcarbon sources to the DIC pool.In pore waters of the upper mudflat, river water DICand dissolution of calcite contribute to a lesserextent (10% and 16% respectively) to the total DICpool. Results indicate that inorganic carbon added tothe pore water of the mudflats has a 13Cvalue of +20.3 in May 1998. These strongly enriched13CDIC values suggest that the majorcontribution (up to three-quarters) to total DIC isCO2 derived from methanogenesis.In pore waters of the marshes, CO2 derived fromorganic matter degradation (–27.5) and river DIC(–11.5 to –16.1) are the major sources of inorganiccarbon contribution to the total DIC pool. In porewaters from a marsh site colonised by willow trees,the contribution from CO2 derived from organicmatter degradation is larger than in pore waters froman area with only reed vegetation. In the latter caseriver water DIC is the major source of pore waterDIC. 相似文献
98.
Archaeaplankton in the Columbia River, its estuary and the adjacent coastal ocean, USA 总被引:4,自引:0,他引:4
PCR-amplified 16S rRNA genes from particle-attached and free-living Archaea in the Columbia River estuary, particle-attached Archaea in the river, and Archaea in the adjacent coastal ocean were cloned, and 43 partial sequences were determined. There was a high diversity of Archaea in the estuary, especially among the particle-attached Archaea, with representatives from four major phylogenetic clusters. Eighteen of 21 estuarine clones were closely related to clones from the river and the coastal ocean or to clusters of marine and soil clones identified in other studies. This contrasts with a similar study of the estuarine bacterial community that found 62% of bacterial 16S rRNA clones to be unique to the estuary. Archaea in the estuary were primarily allochthonous, and therefore, unlike the bacteria, probably do not form a native estuarine community. 相似文献
99.
Modification of saltmarsh for mosquito control in Australia alters habitat use by nekton 总被引:2,自引:2,他引:0
The most common modification of saltmarsh habitat for mosquito control in Australia is runnelling, a system of shallow channels increasing seawater exchange in pools high on the marsh. Local effects within the immediate vicinity of runnels were examined by testing the hypothesis that fish assemblages immediately alongside runnels differ from those further away. Nekton assemblages were sampled using pop nets in winter (May) and summer (December) on a saltmarsh in southeast Queensland, alongside runnels and further (30 m) away, at two distances from a mangrove-lined intertidal creek. Nekton assemblages were dominated numerically (50–80%) by one or two species of small fish (Ambassis marianus, Mugilogobius stigmaticus), and a commercially important prawn, Fenneropenaeus merguiensis. In winter, nekton assemblages alongside runnels were significantly different from those further away. Species richness, total nekton densities and densities of several individual species were higher away from runnels, but only at sites far from the creek. No differences in species richness or densities were found in summer. During both periods, nekton assemblages differed strongly with distance from the creek, with more species and higher densities of most species near the creek. For most species, the overall effect of runnelling appears to be a reduction in abundances in the immediate vicinity of runnels, at some times of year. This is probably related to lower prey availability near runnels. Given the extent of runnelling in some parts of Australia, even this local reduction in densities extending no more than 30 m from runnels means that nekton may be adversely affected over a large total area. The apparent influence of runnels on nekton densities highlights the potential effects of saltmarsh modification on non-target animals that should be considered as this management technique becomes more prevalent. 相似文献
100.
We measured the extent of movement of carbon and its assimilation by invertebrates among estuarine habitats by analysing carbon
stable isotopes of invertebrates collected along transects crossing the boundary of two habitats. The habitats were dominated
by autotrophs with distinct isotope values: (1) mudflats containing benthic microalgae (mean −22.6, SE 0.6‰) and (2) seagrass
and its associated epiphytic algae (similar values, pooled mean −9.8, 0.5‰). Three species of invertebrates were analysed:
a palaemonid shrimp, Macrobrachium intermedium, and two polychaete worms, Nephtys australiensis and Australonereis ehlersi. All species had a similar narrow range of isotope values (−9 to −14‰), and showed no statistically significant relationship
between position along transect and isotope values. Animals were relying on carbon from seagrass meadows whether they were
in seagrass or on mudflats hundreds of metres away. Particulate organic matter collected from superficial sediments along
the transects had similar values to animals (mean −11.1, SE 1.3‰) and also showed no significant relationship with position.
The isotope values of these relatively immobile invertebrates and the particulate detritus suggest that carbon moves from
subtidal seagrass meadows to mudflats as particulate matter and is assimilated by invertebrates. This assimilation might be
direct in the case of the detritivorous worm, A. ehlersi, but must be via invertebrate prey in the case of the carnivorous worm, N. australiensis and the scavenging shrimp, M. intermedium. The extent of movement of carbon among habitats, especially towards shallower habitats, is surprising since in theory, carbon
is more likely to move offshore in situations such as the current study where habitats are in relatively open, unprotected
waters. 相似文献