School of Geography and Planning, Sun Yat-Sen University, Guangzhou, China.
School of Environmental Science and Engineering, Sun Yat-Sen University, No. 132, Wai Huan Dong road, University Town, Guangzhou, 510006, People's Republic of China.
Environ Sci Pollut Res Int. 2020 Jul;27(19):24542-24557. doi: 10.1007/s11356-020-08454-4. Epub 2020 Apr 19.
Under natural conditions, the dissolved inorganic carbon (DIC) in river water is dominantly derived from carbonate or silicate dissolution by carbonic acid. However, sulfuric and nitric acids produced by human activities provide additional acidity for chemical weathering, which would affect the DIC flux and change its isotopic composition. To identify the natural and anthropogenic impacts on DIC, the major ion concentrations and stable carbon isotopes of the DIC (δC-DIC) of river waters were measured in the Pearl River Delta (PRD) region, which is one of the most developed and populated areas in China. The mass balance calculations for DIC-apportionment showed that carbonate dissolution by carbonic acid was the dominant origin of DIC in the Beijiang (BJ) River (67%) and Xijiang (XJ) River (78%) and silicate dissolution by carbonic acid was the dominant origin of DIC in the Guangzhou (GZ) Channel (37%) and Dongjiang (DJ) River (50%), which was related to the lithology of the catchment. The contribution of carbonate dissolution by sulfuric and nitric acids, which represented the contribution of human activities to the total DIC concentrations in river water, showed high proportions in the GZ Channel and DJ River, with averages of 42% and 34%, respectively, which were associated with a high degree of urbanization. Evidence of hydrochemical parameters and δC-DIC signatures indicated that human activities had impacts on the DIC pool. Carbonate dissolution by sulfuric and nitric acids caused by human activities changed DIC apportionments rather than the DIC flux, and this part of DIC would ultimately become a source of CO to the atmosphere on the geological timescale and affects the CO budget. An increase in nutrient concentration due to increased sewage discharge in the urbanized area could promote phytoplankton photosynthesis, which could change the DIC pool and increase the δC-DIC value. This study quantitatively highlights the influence of human activities on DIC apportionment in river water, suggesting that anthropogenic impacts should be seriously considered when evaluating the evolution of DIC.
在自然条件下，河水的溶解无机碳（DIC）主要来源于碳酸溶解碳酸盐或硅酸盐产生的碳酸。然而，人类活动产生的硫酸和硝酸为化学风化提供了额外的酸度，这将影响 DIC 的通量并改变其同位素组成。为了确定 DIC 受到的自然和人为影响，对中国最发达和人口最稠密的地区之一珠江三角洲（PRD）的河水主要离子浓度和 DIC 的稳定碳同位素（δC-DIC）进行了测量。DIC 分配的质量平衡计算表明，在北江（BJ）河（67%）和西江（XJ）河（78%）中，碳酸溶解碳酸盐是 DIC 的主要来源，在广州水道（GZ）和东江（DJ）河（37%）和（50%）中，碳酸溶解硅酸盐是 DIC 的主要来源，这与流域的岩性有关。硫酸和硝酸溶解碳酸盐代表人类活动对河水总 DIC 浓度的贡献，在 GZ 水道和 DJ 河中的比例较高，平均值分别为 42%和 34%，这与高度城市化有关。水化学参数和 δC-DIC 特征的证据表明，人类活动对 DIC 库有影响。人类活动造成的硫酸和硝酸溶解碳酸盐改变了 DIC 的分配，而不是 DIC 的通量，这部分 DIC 最终将成为地质时间尺度上大气 CO 的来源，并影响 CO 预算。由于城市化地区污水排放量增加导致营养物浓度增加，可能会促进浮游植物光合作用，从而改变 DIC 库并增加 δC-DIC 值。本研究定量强调了人类活动对河水 DIC 分配的影响，表明在评估 DIC 的演变时，应认真考虑人为影响。
