Characteristics of Carbon and Nitrogen in the Downstream Columnar Sediment of Maozhou River, Shenzhen

Abstract

Based on the determinations of total nitrogen (TN), organic matter (OM), carbon-nitrogen ratio (C/N), δ15 N, and δ13 C on 12 sediment cores, the distribution characteristics and the sources of nitrogen and organic matter were analyzed in sediments from the lower reaches and main tributaries of the Maozhou River. The results showed that the average concentrations of total nitrogen (TN) and organic matter (OM) were 1815.37 mg·kg-1 and 22 401.68 mg·kg-1, respectively, in the Maozhou River sediments, which were higher than in TaihuLake and ChaohuLake. The levels of TN and OM in the study area were high and varied greatly with the increase of depth. The δ15 N content in the sediments of the MaozhouRiver downstream ranged from 2.20 ‰ to 32.78 ‰, while the δ13 C content ranged from -27.53 ‰ to -21.95 ‰. The average concentrations of δ15 N and δ13 C were 6.78 ‰ and -25.41 ‰. Moreover, the C/N ratio ranged from 0.49 to -18.23. The δ13 C varied slightly with the increase of depth, while δ15 N and C/N varied greatly. A source analysis in the study area indicated that C3 plants and chemical fertilizer were the main sources in the surface sediments (0-40 cm) downstream of the Maozhou River. Furthermore, algae were the main sources of organic matter in the deep sediments downstream of the Maozhou River and in tributary sediments of the Shajing River. Nitrogen in the surface sediments (0-40 cm) downstream of the Maozhou River mainly comes from inorganic fertilizer and soil organic nitrogen, while nitrogen in the Maozhou River deep sediments and Shajing River sediments mainly come from soil erosion and soil organic nitrogen.