Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semi-arid region, China

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 Combining double low line 14) and brackish ( n Combining double low line 12) waters were grouped according to electrical conductivity (threshold Combining double low line 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 ( R 2 Combining double low line 0.66), and salinity vs. DIC ( R 2 Combining double low line 0.94). An independent data set collected in May 2012 also confirmed this finding (DOC: R 2 Combining double low line 0.79, DIC: R 2 Combining double low line 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 a 250 : a 365 ( E 250 : E 365) and the spectral slope ratio (Sr, S 275−295/ S 350−400) 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.