Combined Stable Carbon Isotope and C/N Ratios as Indicators of Source and Fate of Organic Matter in the Bangpakong River Estuary, Thailand
Thanomsak Boonphakdeea*, Akihide Kasaib, Tateki Fujiwarab , Pichan Sawangwong a and Voravit Cheevaporna
a Graduate School of Environmental Science, Faculty of Science, Burapha University, Chonburi, 20131, Thailand
b Fisheries and Environmental Oceanography Laboratory, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
Received 15 November 2007; Accepted 12 January 2008
Abstract
Stable carbon isotopes and C/N ratios of particulate organic matter (POM) in suspended solids and surficial sediment were used to define the spatial and temporal variability in an anthropogenic tropical river estuary, the Bangpakong River Estuary. Samples were taken along salinity gradients during the four different river discharges in the beginning, high river discharge and at the end of the wet season, and low river discharge during the dry season. The values of [C/N]a ratio and d13C in the river estuary revealed significant differences from those of the offshore station. Conservative behaviors of [C/N]a and d13C in the estuary during the wet season indicated major contribution of terrigenous C3 plants derived OM. By contrast, during the dry season, marine input mainly dominated OM contribution with an evidence of anthropogenic input to the estuary. These compositions of the bulk sedimentary OM were dominated by paddy rice soils and marine derived OM during the wet and dry seasons, respectively. These results show that the combined stable carbon isotopes and C/N ratios can be used to identify the source and fate of OM even in a river estuary. This tool will be useful to achieve sustainable management in coastal zone.
Keywords: particulate organic matter; stable carbon isotope; the Bangpakong River or Estuary
* corresponding author : nuiosk@yahoo.com