Carbon dioxide and methane emissions from Tanswei River in Northern Taiwan

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To investigate the Green House Gas (GHG) emissions from rivers in Taiwan, environmental conditions, water qualities, and emissions of CO2 and CH4 were determined in the Tanswei River of Northern Taiwan, and the correlations between GHG emissions and water quality were also studied. Atmospheric CO2 concentrations were 347.4-409.7, 342.8-417.3 and 348.5-417.0 ppm in the up–, mid– and down–stream areas, respectively; while atmospheric CH4 concentrations were 1.59-1.98, 1.74-2.20 and 1.60-2.43 ppm, respectively. Using the headspace method with brown color bottle, CO2 concentrations were 665–6 917, 1 485–9 369 and 1 443–9 637 ppm, respectively; while CH4 concentrations fell into the range of 11.8-309.0, 66.0-6 288.2 and 24.1-4 627.5 ppm, respectively. Using the static–chamber method, CO2 emission rates were -22.3-140.5, -31.7-194.7 and -27.5-226.6mg m-2 h-1, respectively; and CH4 emission rates were 0.02-5.52, 1.55-144.54 and 0.11-14.10mg m-2 h-1, respectively. CO2 and CH4 emission rates had higher values in the mid– and down–stream areas than those in the up–stream area because of the input of industrial, livestock and domestic wastewaters in mid– and down–stream areas. CO2 emission rates were negative might be because of the measurement times were at noon and some photosynthetic microbes and microalgae in the water were undergoing active photosynthesis. There is a good correlation between the results of headspace and static–chamber methods. CO2 emissions had very significant positive correlations with Biochemical Oxygen Demand (BOD) and Suspended Organic Matter (SOM); and significant negative correlation with Dissolved Oxygen (DO). CH4 emission had very significant positive correlations with BOD, SOM and ammonium nitrogen (NH4-N); significant positive correlation with Suspended Inorganic Matter (SIM); very significant negative correlation with DO; and significant negative correlation with redox potential (Eh). DO, Eh, SOM, SIM and NH4-N were the major factors that affected CO2 and CH4 emissions from water. In the assessment of carbon deposited amount from river to ocean, the annual carbon flows of Tanswei River were estimated with the annual flow amounts and COD, it were 8.9×103, 1.8×104, 3.9×104, 2.7×104 and 1.2×104 tons in 2003, 2004, 2005, 2006 and 2007, respectively.