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21.
M.A. Burford D.M. Alongi A.D. McKinnon L.A. Trott 《Estuarine, Coastal and Shelf Science》2008,79(3):440-448
Tropical estuaries are under increasing pressure worldwide from human impacts, but are poorly studied compared with temperate systems. This study examined a tropical macrotidal estuary, Darwin Harbour, in northern Australia, using a combination of direct measurements and literature values to determine the main sources of primary production and the sources of nutrients supporting growth. The main source of primary production was calculated to be the extensive area of fringing mangroves and resulted in a net autotrophic system (PG:R = 2.1). Much of the carbon in the mangrove forests appears to be retained within the forests or respired, as the water column was also net autotrophic despite the carbon inputs. Phytoplankton were the second largest primary producer on a whole-of-harbour basis, with low biomass constrained by light and nutrient availability. The phytoplankton were likely to be nitrogen (N) limited, based on low N:phosphorus (P) ratios, low dissolved bioavailable N concentrations (ammonium (NH4+), nitrate (NO3−), urea), and evidence that phytoplankton growth in bioassays was stimulated by NH4+ addition. The largest new source of N to the system was from the ocean due to higher N concentrations in the incoming tides than the outgoing tides. Atmospheric inputs via N fixation on the intertidal mudflats and subtidal sediments were substantially lower. The rivers feeding into the harbour and sewage were minor N inputs. Nitrogen demand by primary producers was high relative to available N inputs, suggesting that N recycling within the water column and mangrove forests must be important processes. Darwin Harbour is adjacent to the rapidly growing urban area of Darwin city, but overall there is no evidence of anthropogenic nutrient inputs having substantial effects on primary production in Darwin Harbour. 相似文献
22.
M. Furnas D. Alongi D. McKinnon L. Trott M. Skuza 《Continental Shelf Research》2011,31(19-20):1967-1990
Seasonally averaged N and P box model budgets were constructed for two regional-scale sections of the Great Barrier Reef (GBR) shelf, one in the near-pristine far-northern GBR (13.5–14.5°S) and the other in the central GBR (17–18°S) adjacent to more intensively farmed wet tropics watersheds. We were unable to simultaneously balance shelf-scale N and P budgets within seasonal or annual time frames, indicating that magnitudes of a number of key input and, especially, loss processes are still poorly constrained. In most cases, current estimates of system-level N and P sources (rainfall, runoff, upwelling, N-fixation) are less than estimated loss processes (denitrification, cross-shelfbreak mixing and burial). Nutrient dynamics in both shelf sections are dominated by the tightly coupled uptake and mineralization of soluble N and P in the water column and the sedimentation–resuspension of particulate detritus. On an area-averaged basis, internal cycling fluxes are an order of magnitude greater than input–output fluxes. Denitrification in shelf sediments is a significant sink for N while lateral mixing is both a source and sink for P. 相似文献
23.
Benthic food chains of the Amazon (Brazil) and Fly (Papua New Guinea) river deltas and adjacent shelves are compared. Abundance patterns of the major trophic groups (bacteria, meiofauna, and macroinfauna) are similar between regions, with very low densities, or the absence of benthos, within and near the deltas. For muds in the more quiescent areas, benthic abundance and productivity are highest, commonly coinciding with maximum pelagic primary production. Episodes of physical disturbance, erratic food supply, and dilution of river-derived, particulate organic matter foster the development of opportunistic benthic communities of variable diversity and low biomass, dominated by bacteria. These pioneering assemblages are the main food of penaeid shrimp, which dominate the demersal trawl fisheries of both fluvial-dominated regions. 相似文献