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Six oceanographic moorings were maintained for 8 weeks across the mouth of the mangrove-fringed Fly River estuary from April to June 1995 in the southeast trade wind season. A further 4 moorings were deployed for 8 weeks along the estuary channel in 1992, also in the southeast trade wind season. These data were used to estimate net exchange of suspended sediment between the estuary and the Gulf of Papua. A net inflow of fine sediment into the estuary from the coastal ocean was found to be considerable, about 40 tonnes s-1 or about 10 times the riverine inflow rate, resulting in a calculated, spatially averaged vertical accretion rate of 2 mm year-1. Mangroves may account for trapping 6% of the riverine sediment inflow or about 1/4 of the riverine clay inflow. If this sediment was distributed only over the observed accumulation zones near islands the local accumulation rates in these zones would reach 4 cm year-1. Estimates of soft sediment mass accumulation rates (1–10 kg m-2 year-1) in the channel from Pb-210 and C-14 measurements from cores of deltaic mangrove mud cannot account for this accumulation rate on a 100–1000 year time scale. The fate of the remaining sediment is unknown, it may be exported from the estuary in the monsoon season. 相似文献
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Ayukai Tenshi Miller Diane Wolanski Eric Spagnol Simon 《Mangroves and Salt Marshes》1998,2(4):223-230
In Coral and Conn Creek, northeastern Australia, the variations in concentrations of nitrate, phosphate, silicate, dissolved organic carbon (DOC) and particulate organic carbon (POC) were measured over tidal cycles on five occasions and along each creek on four occasions. The fluxes of these five properties were then estimated using two methods. The first method is the socalled Eulerian method, whereby water flow and material concentration are measured at a fixed station near the creek mouth and the net flux is calculated by adding up flux increments over a tidal cycle. The second method first derives the longitudinal eddy diffusion coefficient from the salt mass balance equation and then calculates material fluxes from their observed gradients along the creek. The use of the latter method is permitted only in the absence of freshwater inputs.The Eulerian method was not sensitive enough to examine whether there was any statistically significant difference in fluxes of nutrients, DOC and POC between ebb and flood periods. This casts some doubt over the meaning of individual flux estimates. It is, however, worth mentioning that 17 out of 25 flux estimates were positive (= import) in Coral Creek, whereas only eight positive flux estimates occurred in Conn Creek. In Coral Creek, the average flux values for nitrate, phosphate and DOC were positive, but negative for silicate and POC. In contrast, the average flux values for all properties were negative in Conn Creek. This may be due to the difference in amount of freshwater input between Coral and Conn Creek.The presence of freshwater inputs from upstream sources restricted the use of the salt mass balance equation to the Coral Creek data collected in September, 1996. However, the study of the variability of nutrient, DOC and POC concentrations along the creek could provide valuable insight into their behavior in Coral and Conn Creek. For example, the concentrations of silicate and DOC were consistently higher upstream than downstream and the distance–concentration relationship was statistically significant in seven out of eight measurements. The concentrations of nitrate and POC also decreased from upstream to downstream, but the trend was statistically significant in only 2–3 measurements. The concentration of phosphate was higher downstream than upstream in four measurements and in two of these four measurements, the trend was statistically significant. These results suggest that in Coral and Conn Creek, silicate and DOC are usually exported to adjacent coastal waters, whereas the import and export of nitrate, phosphate and POC are often finely balanced. 相似文献
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The seagrass beds in the mangrove-fringed shallow coastal waters ofHinchinbrook Channel, Australia, survive in shallow coastal waters. They aresheltered from excessive sedimentation and turbidity by the plankton andvegetative detritus generating a marine snow that accelerates the settlingof fine mud out of suspension. 相似文献
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A field and model study was undertaken in 1996/1997 of the dynamics of water, fine sediment and particulate carbon in the northern region of the mangrovefringed Hinchinbrook Channel, Australia. The currents were primarily tidal and modulated by the wind. Biological detritus acted as a coagulant for the fine cohesive sediment in suspension in the mangrovefringed, muddy coastal waters. Plankton and bacteria were the major aggregating agents at neap tides, and mangrove detritus at spring tides. The microaggregates were typically several hundreds of micrometer in diameter and enhanced the settling rate. The fate of fine sediment and particulate carbon was controlled by the dynamics of the coastal boundary layer, a turbid shallow coastal water zone along the mangrovefringed coast. A tidallymodulated, turbidity maximum zone was found in this layer. Wind stirring increased the turbidity by a factor of five.The channel behaves as a sink trapping fine sediment and particulate carbon. However, the sink was leaky because the dynamics of the coastal boundary layer generated a net outflow of fine sediment out of the channel along the western coast. The biologically enhanced settling of cohesive sediment limited the offshore extent of the muddy suspension to within a few hundreds of meters from the coast.At spring flood tides, some of this particulate carbon was advected into the mangrove forest where it would remain trapped. On a yearly basis about six times as much particulate carbon was exported out of Hinchinbrook Channel through the coastal boundary layer than was trapped in the fringing mangroves. 相似文献
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