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

摘要

Spatiotemporal variations of dissolved organic carbon (DOC) and inorganic carbon(DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China, wereexamined 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 theaverage 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–hydrologicconditions. The investigation indicated that the outflow conditions in thesemi-arid region had condensed effects on the dissolved carbon, resulting inclose relationships between salinity vs. DOC (R2 = 0.66), and salinity vs. DIC(R2 = 0.94). An independent data set collected in May 2012 alsoconfirmed this finding (DOC: R2 = 0.79, DIC: R2 = 0.91),highlighting the potential of quantifying DOC and DIC via salinitymeasurements for waters dispersed in the plain. Indices based on the CDOMabsorption spectra (e.g., the DOC-specific CDOM absorption (SUVA₂₅₄),absorption ratio a₂₅₀ : a₃₆₅ (E₂₅₀ : E₃₆₅) and the spectralslope ratio (Sr, S_275−295/S_350−400) were applied to characterizeCDOM composition and quality. Our results indicate that high molecular weightCDOM fractions are more abundant in the fresh waters than the brackishwaters.