Fluxes of nutrients and dissolved and particulate organic carbon in two mangrove creeks in northeastern Australia
Tóm tắt
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 so‐called 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.
Tài liệu tham khảo
Alongi, D.M. 1990. Abundances of benthic microfauna in relation to outwelling of mangrove detritus in a tropical coastal lagoon. Marine Ecology Progress Series 63: 53–63.
Alongi, D.M. 1996. The dynamics of benthic nutrient pools and fluxes in tropical mangrove forests. Journal of Marine Research 54: 123–148.
Alongi, D.M. 1998. Coastal Ecosystem Processes. CRC Press, Boca Raton, Florida.
Boto, K.G. and Wellington, J. 1983. Phosphorus and nitrogen nutritional status of a northern Australian mangrove forest. Marine Ecology Progress Series 11: 63–69.
Boto, K.G. and Wellington, J. 1988. Seasonal variations in concentrations and fluxes of dissolved organic and inorganic materials in a tropical, tidally-dominated, mangrove waterways. Marine Ecology Progress Series 50: 151–160.
Clough, B.F. 1992. Primary productivity and growth of mangrove forests. pp. 225–249. In: Robertson, A.I. and Alongi, D.M. (eds), Tropical Mangrove Ecosystems – Coastal and Estuarine Series 41. American Geophysical Union, Washington.
Clough, B.F., Ong, J.E. and Gong, G.W. 1997. Estimating leaf area index and photosynthetic production in canopies of the mangrove Rhizophora apiculata. Marine Ecology Progress Series 159: 285–292.
Daniel, P.A. and Robertson, A.I. 1990. Epibenthos of mangrove waterways and open embayments: community structure and the relationship between exported mangrove detritus and epifaunal standing stocks. Estuarine, Coastal and Shelf Sciences 31: 599–619.
Imberger, J., Berman, T., Christian, R.R., Sherr, E.B., Whitney, D.E., Pomeroy, L.R., Wiegert, R.G. and Wiebe, W.J. 1983. The influence of water motion on the distribution and transport of materials in a salt marsh estuary. Limnology and Oceanography 28: 201–214.
Kjerfve, B., Stevenson, L.H. and Proehl, J.A. 1981. Estimation of material fluxes in an estuarine cross section: a critical analysis of spatial measurement density and errors. Limnology and Oceanography 26: 325–335.
Moran, M.A., Wicks, R.J. and Hodson, R.E. 1990. Export of dissolved organic matter from a mangrove swamp ecosystem: evidence from natural fluorescence, dissolved lignin phenols, and bacterial secondary production. Marine Ecology Progress Series 76: 175–184.
Odum, W.E. and Heald, E.J. 1975. The detritus-based food web of an estuarine mangrove community. pp. 265–286. In: Cronin, L.E. (ed.), Estuarine Research, Volume 1. Academic Press, New York.
Robertson, A.I. and Blaber, S.J.M. 1992. Plankton, epibenthos and fish communities. pp. 173–224. In: Robertson, A.I. and Alongi, D.M. (eds), Tropical Mangrove Ecosystems – Coastal and Estuarine Series 41. American Geophysical Union, Washington.
Robertson, A.I., Alongi, D.M. and Boto, K.G. 1992. Food chains and carbon fluxes. pp. 293–326. In: Robertson, A.I. and Alongi, D.M. (eds), Tropical Mangrove Ecosystems – Coastal and Estuarine Series 41. American Geophysical Union, Washington.
Ryle, V.D., Mueller, H.R. and Gentian, P. 1981. Automated analysis of nutrients in tropical seawater. Australian Institute of Marine Science Oceanography Series OS-81-2.
Simpson, J.H., Gong, W.K. and Ong, J.E. 1997. The determination of the net fluxes from a mangrove estuary system. Estuaries 20: 103–109.
Sugimura, Y. and Suzuki, Y. 1988. A high temperature catalytic oxidation method for non-volatile dissolved organic carbon in seawater by direct injection of a liquid sample. Marine Chemistry 24: 105–131.
Twilley, R.R. 1985. The exchange of organic carbon in basin mangrove forests in a southwest Florida estuary. Estuarine, Coastal and Shelf Science 20: 543–557.
Wattayakorn, G., Wolanski, E. and Kjerfve, B. 1990. Mixing, trapping and outwelling in the Klong Ngao mangrove swamp, Thailand. Estuarine, Coastal and Shelf Sciences 31: 667–688.
Wolanski, E., Jones, M. and Bunt, J.S. 1980. Hydrodynamics of a tidal creek-mangrove swamp system. Australian Journal of Marine and Freshwater Research 31: 431–450.
Wolanski, E. 1985. Numerical modeling of flows in a tidal creekmangrove swamp system. Proceedings of the 21st Congress for the International Association for Hydraulic Research 3: 80–85.
Wolanski, E., Spagnol, S. and Ayukai, T. 1998. Field and model studies of the fate of particulate carbon in mangrovefringed Hinchinbrook Channel, Australia. Mangroves and Salt Marshes 2: 205–221.