||Global warming due to enhanced greenhouse effect that makes the global carbon cycle became a hot issue in the past few decades. River export of carbon is an important part of global carbon cycle, but most current studies presumed that the carbon export by rivers remains unchanged despite all the other changes. The organic carbon exported by river can be distinguished into two types: particular organic carbon (POC) and dissolved organic carbon (DOC). Past data showed that the major form of the river exported organic carbon was in dissolved form with DOC accounting for 60% of total organic carbon (TOC). In Taiwan the river export of carbon is dominated by the particular form, but most of it is fossil carbon. TO the biogenic organic carbon in river loads, both the POC and DOC are equally important. For this study, we used DOC data obtained from 2002-2005, and the discharge data of Danshuei River Basin from the Water Resource Agency to investigate the export of dissolved organic carbon. Since several parts of the discharge data were missing, we used the TOPMODEL simulate the discharge in order to make up for the missing data. To avoid the reservoir effect, we choose the middle-upper sections of the main channel and, the tributaries that were not affected by the reservoir. The Danshuei River System comprises three major tributaries, namely, the Da-Han Creek, the Shin-Dien Creek and the Keelung River. There are two reservoirs in the Danshuei River System: the Shimen Reservoir on the Da-Han Creek and the Fei-tsui reservoir on the Shin-Dien Creek.|
The yields of DOC in different watersheds of the middle-upper section of the Danshuei River System was 12-45kg-C/km2/yr, which were averaged from results calculated by four different methods, which resulted in variations of 10-30% between methods. By contrast, watersheds in the downstream area gave yields of 50-115kg-C/km2/yr with a similar between methods variation of 5-25%. The seasonal variation of DOC export showed a range of about three folds, with nearly 75% exported in the wet season. The DOC yields in the Danshuei River Basin were positively correlated with temperature and population density and also correlated with some types of landuse/cover. They exhibited positive correlations with percentages of paddy, building and bamboo, and negative correlation with the percentage of natural forest, whereas they showed no significant correlation with that of artificial forest. The lack of correlation with the artificial forest might cause by weeding, which may bare some area and cause accumulation of litter on the ground. Such conditions may result in leakage of DOC out of the system and diminish the carbon retaining effects of the forest. It is noted that the apparent positive correlation with the percentage of bamboo in the watershed rested upon only one high point. More data are needed to confirm such a trend.
Arnold, J.G., P.M. Allen, R. Muttiah, and G. Bernhardt. 1995. Automated base flow separation and recession analysis techniques. Ground Water 33(6): 1010-1018.
Arnold, J.G and P.M. Allen. 1999. Automated methods for estimating baseflow and ground water recharge from streamflow records. Journal of the American Water Resources Association 35(2): 411-424.
A. Foulquier, F. Malard, F. Mermillod-Blondin, T. Datry, L. Simon, B. Montuelle and J. Gibert. 2010.
Vertical change in dissolved organic carbon and oxygen at the water table region of an aquifer recharged with stormwater: biological uptake or mixing? Biogeochemistry 99: 31-47.
Billett, M. F., Parker-Jervis, F., FitzPatrick, E. A. and Cresser, M. S. 1990. Forest soil chemical changes between 1949/50 and 1987. Journal of Soil Science. 41: 45-133.
David B. Baker, R. Peter Richards, Timothy T. Loftus, and Jack W. Kramer. 2004. A new flashiness index: characteristics and applications to Midwestern rivers and streams. Journal of the American Water Resources Association 503-522.
Hope D, Billett MF, Ronnie M, Brown TAW 1997. Export of Organic carbon in British Rivers. Hydrological Processes 11, 325-344.
Huang J.-C., Lee T.-Y., Kao S.-J. 2009. Simulating typhoon-induced storm hydrographs in subtropical mountainous watershed: an integrated 3-layer TOPMODEL. Hydrology and Earth System Sciences 13: 27-40.
Kao S.-J. ,and K.K. Liu. 1996. Particulate organic carbon export from a subtropical mountainous river (Lanyang Hsi) in Taiwan. Limnology and Oceanography 41(8): 1749-1757.
Kao S.-J. ,and K.K. Liu. 1997. Fluxes of dissolved and nonfossil particulate organic carbon from an Oceania small river (Lanyang Hsi) in Taiwan. Biogeochemistry 39: 255-269.
Kao S.-J., Lee T.-Y., J.D. Milliman. 2005. Calculating Highly Fluctuated Suspended Sediment Fluxes from Mountainous Rivers in Taiwan. TAO 16(3): 653-675.
Michel Meybeck. 1982. CARBON, NITROGEN, AND PHOSPHORUS TRANSPORT BY WORLD RIVER. AMERICAN JOURNAL OF SCIENCE 282: 401-450.
P. Porcal., J.-F. Koprivnjak., L.A. Molot., and P.J. Dillon. 2009. Humic substances-Part 7: the biogeochemistry of dissolved organic carbon and its interactions with climate change. Environ Science Pollut Research 16:714-726.
Smith SV, Hollibaugh JT. 1993 Coastal metabolism and the oceanic organic carbon balance. Rev Geophys 31:75–89
Siegenthaler U.,& J. L. Sarmiento. 1993. Atmospheric carbon dioxide and the ocean. Nature 365:119-125.
Williams H. McDowell and Clyde E. Asbury. 1994. Export of carbon, nitrogen, and major ions from three tropical montane watersheds. Limnology and Oceanography 39(1): 111-125.
Williams H. McDowell and Gene E. Likens. 1988. Origin, Composition, And Flux of dissolved organic carbon in the Hubbard Brook valley. Ecological Monographs. 58(3): 177-195.
Willams Michael., Charles Hopkinson., Edward Rastetter., Joseph Vallino and Luc Claessens. 2004. Relationships of land use and stream solute concentrations in the Ipswich river basin, Northeastern Massachusetts. Water, Air, and Soil Pollution 161:55-74.
Yapo, P.O., Gupta, H.V., Sorooshian, S. (1998) Multi-objective global optimization for hydrologic models, Journal of Hydrology 204, 83-97.