Abstract
Abstract. Spatiotemporal variations of dissolved organic carbon (DOC) and inorganic carbon (DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China, were examined with data collected during 2008–2011. Fresh (n = 14) and brackish (n = 12) waters were grouped according to electrical conductivity (threshold = 1000 μS cm−1) Significant differences in the average DOC and DIC concentrations were observed between the fresh (5.63 mg L−1, 37.39 mg L−1) and the brackish waters (15.33 mg L−1, 142.93 mg L−1). Colored dissolved organic matter (CDOM) and DOC concentrations were mainly controlled by climatic–hydrologic conditions. The investigation indicated that the outflow conditions in the semi-arid region had condensed effects on the dissolved carbon, resulting in close relationships between salinity vs. DOC (R2 = 0.66), and salinity vs. DIC (R2 = 0.94). An independent data set collected in May 2012 also confirmed this finding (DOC: R2 = 0.79, DIC: R2 = 0.91), highlighting the potential of quantifying DOC and DIC via salinity measurements for waters dispersed in the plain. Indices based on the CDOM absorption spectra (e.g., the DOC-specific CDOM absorption (SUVA254), absorption ratio a250 : a365 (E250 : E365) and the spectral slope ratio (Sr, S275−295/S350−400) were applied to characterize CDOM composition and quality. Our results indicate that high molecular weight CDOM fractions are more abundant in the fresh waters than the brackish waters.
Highlights
Dissolved organic matter (DOM) is one of the largest bioactive reservoirs on the earth’s surface (Cole et al, 2007; Para et al, 2010)
The dissolved organic carbon (DOC) concentrations in fresh waters ranged from 1.01 mg L−1 in Longhupao Lake (LHP) to 14.23 mg L−1 in Boluo Lake (BLL)
A large variation of DOC concentration was revealed in the brackish waters, ranging from 3.6 mg L−1 in Nanyin Reservoir (NYR) to 32.6 mg L−1 in Zhongneipao (ZNP)
Summary
Dissolved organic matter (DOM) is one of the largest bioactive reservoirs on the earth’s surface (Cole et al, 2007; Para et al, 2010). DOM of inland waters, its colored fraction (CDOM), influences light attenuation in waters (Vodacek et al, 1997; Zhang et al, 2007; Williamson and Rose, 2010; Stedmon et al, 2011), which in turn affects the transport and bio-availability of materials such as trace metals and organic pollutants (Cory et al, 2006; Schlesinger et al, 2011; Ledesma et al, 2012). Studies have indicated that concentrations of DOC in inland waters tend to decrease with increasing water residence times due to increased photobleaching and microbial activities
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