Geochemistry of the dissolved loads during high-flow season of rivers in the southeastern coastal region of China: anthropogenic impact on chemical weathering and carbon sequestration

Abstract

Abstract. The southeastern coastal region is one of the most developed and populated areas in China. Meanwhile, it has been severely impacted by acid rain over many years. The chemical compositions and carbon isotope compositions of dissolved inorganic carbon (δ 13 C DIC ) in river water in the high-flow season were investigated to estimate the chemical weathering and associated atmospheric CO 2 consumption rates as well as the acid-deposition disturbance. Mass balance calculations indicated that the dissolved loads of major rivers in the Southeast Coastal River Basin (SECRB) were contributed to by atmospheric (14.3 %, 6.6 %-23.4 %), anthropogenic (15.7 %, 0 %-41.1 %), silicate weathering (39.5 %, 17.8 %-74.0 %) and carbonate weathering inputs (30.6 %, 3.9 %-62.0 %). The silicate and carbonate chemical weathering rates for these river watersheds were 14.2-35.8 and 1.8-52.1 t km −2 a −1 , respectively. The associated mean CO 2 consumption rate by silicate weathering for the whole SECRB was 191 × 10 3 mol km −2 a −1 . The chemical and δ 13 C DIC evidence indicated that sulfuric and nitric acid (mainly from acid deposition) were significantly involved in the chemical weathering of rocks. There was an overestimation of CO 2 consumption at 0.19 × 10 12 g C a −1 if sulfuric and nitric acid were ignored, which accounted for about 33.6 % of the total CO 2 consumption by silicate weathering in the SECRB. This study quantitatively highlights the role of acid deposition in chemical weathering, suggesting that the anthropogenic impact should be seriously considered in estimations of chemical weathering and associated CO 2 consumption.

Hydro-Geochemistry of the River Water in the Jiulongjiang River Basin, Southeast China: Implications of Anthropogenic Inputs and Chemical Weathering

“…The JR consists of mainstream (North River) and major tributaries (West, South, Yanshi, Xinqiao, Shuangyang, Xinan, Longjing, Chuanchang, Huashan and Longshan River) with an area over 500 km 2 . Average annual temperature in the JRB varies from 19.9 °C to 21.1 °C [27]. Because of the influence of a seasonal monsoonal climate, approximately 75% of the total water discharge occurs during summer from April to September [29].…”

“…The JRB consists of silicate and carbonate rocks, no obvious evaporite distribution in the study area. A large number of magmatic activities took place in the Mesozoic, and the proportions of magmatic rocks is over 60% [27]. The outcrop intrusive rocks are mainly biotite granite and granodiorite.…”

“…The nonnegligible role of acid deposition during the weathering process has been reported in some river basins [14,23,24,25]. Compared to carbonate weathering, the silicate weathering reaction is more easily accelerated by strong acids from rainfall owing to their relatively weak buffeting capability [26,27].…”

“…Therefore, this is a suitable area in which the influence of acid rain can be studied. Although previous research had assessed the chemical composition of river water in the JRB [27], all river water samples were only collected and analyzed in the summer of 2010. In this paper, systematic analysis of the Jiulongjiang River (JR) have been implemented to show the spatiotemporal variation characteristics of major ions and material flux in 2017–2018.…”

Fe, Rather Than Soil Organic Matter, as a Controlling Factor of Hg Distribution in Subsurface Forest Soil in an Iron Mining Area

“…The total discharge water is approximately 75% in the catchment with the impact of a seasonal monsoonal climate from April to September [18]. The study area with the subtropical oceanic monsoon climate has an annual temperature from 19.9 • C to 21.1 • C [19]. The terrain in the upper reaches of the river is mountainous, and there is extensive cover of the forest and a few anthropogenic activities in the upper reaches, where the mean annual mean precipitation is about 2000 mm.…”