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Trophic functioning of macrobenthic fauna in a tropical acidified Bornean estuary(Southeast Asia)

International Journal of Sediment Research 2019年第1期34卷 48-57页

作者： Mohammad Belal Hossain Department of Fisheries and Marine Science Noakhali Science and Technology University

The trophic structure of a community is used to infer ecosystem functioning(e.g. energy transfer and nutrient cycling). Here the trophic structure of the benthic infaunal and epifaunal communities in the Brunei estuary are characterized, and their distribution along an estuarine pH gradient is analyzed using univariate and multivariate techniques. This analysis revealed that surface deposit feeders(e.g., polychaetes) were numerically dominant within the infaunal communities whereas in the epifaunal communities filter feeders(e.g., bivalves) were highly abundant. Species richness for almost all trophic groups increased toward the lower estuary, except for omnivores in the epifaunal communities, which decreased markedly. Both Analysis of Variance(ANOVA) and Analysis of Similarities(ANOSIM) detected significant differences in the density of respective trophic groups among stations. Within infaunal communities, both Biological and Environmental procedure(BIO-ENV) and Canonical Correspondence Analysis(CCA) showed that trophic shifts were associated with environmental gradients. Surface-deposit feeders and omnivores were the most abundant macrobenthos of the upper estuary characterized by low salinity, low pH, and a higher percentage of mud particles. The proportion of filter feeders and carnivores increased with salinity/pH and sand. A more uniform distribution of trophic structure was found in the lower estuary, with high salinity and pH over sandy habitat. In contrast, within epifaunal trophic groups,the percentage of surface deposit feeders and omnivores declined, but filter feeders remarkably increased toward the sea. The proportion of carnivores remained similar at all stations. Non-Metric Multidimensional Scaling(nMDS) ordination for epifaunal trophic groups clearly demarcated higher salinity/pH stations from lower salinity/pH stations, suggesting different trophic compositions along the estuarine pH gradient.

关键词： Macrobenthic communities Trophic structure Environmental factors Acidity tropical estuary

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Finite dispersal of a divergent nepheloid plume by internal hydraulic jump in a tropical mountainous river estuary

Finite dispersal of a divergent nepheloid plume by internal ...

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第九届全国河口海岸学术研讨会

作者： Jiaxue Wu Slate Key Laboratory of Marine Geology,Tongji University, Shanghai 200092, China.

Field investigations were presented into a tropical mountainous river estuary of Herbert, Australia, following a moderate flood event induced by Cyclone Fritz. In-situ mooring and shipboard measurements were conducted using an acoustic Doppler current profiler, a conductivity-temperature-depth unit, and an optical backscatter nephelometer. Owing to the flood discharge onto the shelf, a river plume forms and is deflected under the along-shelf current induced by the trade wind. Intense stratification at the base of plume suppresses vertical mixing, significantly decreases bottom stresses, and separates the water column into two mixed layers. The normal depth of the plume relative to its critical depth is controlled only by the bed slope and the drag coefficient of the interface, independent of river discharge and buoyancy anomaly. A divergent nepheloid dispersal system usually occurs under combined flow segregation and intense stratification. Two nepheloid layers are both confined to the inner shelf under different dispersal mechanisms. The upper nepheloid layer, primarily controlled by advection and settling, is exponentially decayed away from the river mouth. The lower nepheloid layer dominated by settling is detached seaward near the lift-off point. The plume lift-off and subsequent internal jump are crucial processes for the trapping of the plume sediment because a substantial loss of energy occurs, and farther control the pattern of mud deposit on the shelf. Fronts have important influences on the sediment release from the river plume, with different trapping effect in the presence and absence of stratification.

关键词： river plume sediment transport tropical estuary internal hydraulic jump estuarine fronts

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