Abstract
Transport fluxes and properties of riverine organic carbon in the tropical monsoon region were the vital parameters in the global riverine organic carbon fluxes budget. The study focused on the riverine organic carbon in the Changhuajiang River (CHJR), locating at the mid-west of the Hainan Island, China. Dissolved organic carbon (DOC) concentrations in the CHJR ranged from 0.22 mg/L to 11.75 mg/L with an average of 1.75 mg/L, which was lower than the average of global rivers and had a significantly temporal and spatial variation. Output flux of riverine DOC was calculated as 0.55 t/km2/y, which could be revised up to 1.03 t/km2/y, considering that the riverine discharge before dam construction. A linear model of riverine DOC flux suitable in CHJR basin was established, which involved the factors, such as soil organic carbon, runoff depth and slope, etc. There was a large variation of POC concentrations in the CHJR where the average POC concentration in the dry season was 2.41 times of the wet season. Riverine POC flux in CHJR basin was calculated as 1.78 t/km2/y, higher than the average of global rivers and far lower than those in other domestic larger rivers. About 8.28 × 103 t POC were exported yearly in CHJR, of which, 7.15 × 103 t originated from terrestrial ecosystem and 1.13 × 103 t stemmed from aquatic ecosystem. Meanwhile, about 87.74% of terrestrial source happened in the wet season and 12.26% in the dry season. This research revealed that the riverine organic carbon mainly stemmed from the surface erosion processes in the drainage basin during the wet season.
Highlights
As the key channel linking marine and terrestrial ecosystem, global rivers played an important role on the global carbon cycle[1,2]
Transport fluxes and properties of riverine organic carbon in Changhuajiang River (CHJR) located at tropical monsoon region were discussed
From the perspective of spatial variation, particulate organic carbon (POC) contents of total suspended solid (TSS) in the upper reach were higher than those in the lower reach in the wet season, and this spatial distribution pattern was the opposite in the dry season, due to the impact of seasonal water storage in the DGB Reservoir
Summary
As the key channel linking marine and terrestrial ecosystem, global rivers played an important role on the global carbon cycle[1,2]. It was possible that particulate organic carbon (POC), which was carried by particulate suspension, occupied a large proportion, but enough supporting materials should be provided In the latter, the parameters applied for establishing fluvial fluxes models were sometimes regional, which hardly represented the overall situation of global rivers. The CHJR discharges 22.3 × 108 m3 water (at the Baoqiao hydrologic station, representing 90% of the total basin area), accounting for 53.48% of the average runoff (41.7 × 108 m3) over years[18]. Their 18.7 × 108 m3 was exported in wet season and 3.6 × 108 m3 in dry season. Temperature, pH, conductivity (Cond) and total dissolved solid (TDS) were monitored by TM Ultrameter Model 9 P with the accuracy of ±0.10 °C, ±0.20, ±1 μS/cm, and ±0.2 mg/L in situ
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