Significant influence of urban human activities and marine input on rainwater chemistry in a coastal large city, China

The coastal urban region is generally considered an atmospheric receptor for terrestrial and marine input materials, and rainfall chemistry can trace the wet scavenging process of these materials. Fast urbanization in China's east coastal areas has greatly altered the rainwater chemistry. However, the chemical variations, determinants, and sources of rainfall are unclear. Therefore, the typical coastal city of Fuzhou was selected for 1-year rainwater sampling and inorganic ions were detected to explore above problems. The findings depicted that rainwater ions in Fuzhou were slightly different from those in other coastal cities. Although NO3-, SO42-, Ca2+ and NH4+ dominated the rainwater ions, the marine input Cl- (22 %) and Na+ (11 %) also contributed a considerable percentage to the rainwater ions. Large differences in ion concentrations (2∼28 times) were found in monthly scale due to the rainfall amount. Both natural and anthropogenic determinants influenced the rainwater ions in coastal cities, such as SO2 emission, air SO2 and PM10 content on rainwater SO42-, NO3-, and Ca2+, and soot & dust emission on rainwater SO42-, NO3-, indicating the vital contribution of human activities. Stoichiometry and positive matrix factorization-based sources identification indicated that atmospheric dust/particles were the primary contributor of Ca2+ (83.3 %) and F- (83.7 %), and considerable contributor of SO42- (39.5 %), NO3- (38.3 %) and K+ (41.5 %). Anthropogenic origins, such as urban waste volatilization and fuel combustion emission, contributed 95 % of NH4+, 54.5 % of NO3- and 41.9 % of SO42-, and the traffic sources contribution was relatively higher than fixed emission sources. The marine input represented the vital source of Cl- (77.7 %), Na+ (84.9 %), and Mg2+ (55.3 %). This work highlights the significant influence of urban human activities and marine input on rainwater chemicals and provides new insight into the material cycle between the atmosphere and earth-surface in coastal city.

Characteristics of Ions Composition and Chemical Weathering of Tributary in the Three Gorges Reservoir Region: The Perspective of Stratified Water Sample from Xiaojiang River

River water chemistry offers information on watershed weathering and responds to the global carbon cycle. Watershed weathering processes and water chemistry in stratified water are still unclear in Xiaojiang River, as a major tributary of the Three Gorges Reservoir (TGR) which is the largest reservoir in the world. Major ions of river water at different depths were measured to reveal the ionic composition and chemical weathering properties by principal component analysis and stoichiometry in Xiaojiang River. Ca2+−HCO3− dominated the hydrochemical facies of river. Surface river water had the lowest total dissolved solid (146 mg/L) compared to other layers of water. According to principal component analysis, the major ions were divided into two principal components. PC1 was the weathering end-member of rocks, including the main ions except K+ and NO3–N, and PC2 may be the mixed end-member of atmospheric input and anthropogenic input. From stoichiometry, carbonate weathering dominated the cationic composition, with a contribution ratio of 56.7%, whereas atmospheric input (15.2%) and silicates weathering (13.9%) had similar extent of contribution. Compared with other major tributaries of TGR, Xiaojiang had more intense chemical weathering processes. The weathering rates of carbonates and silicates were 19.33 ± 0.68 ton/km2/year and 3.56 ± 0.58 ton/km2/year, respectively. Sulfuric acid as a proton may have participated less in the weathering processes of Xiaojiang River. The CO2 consumption budgets for silicates and carbonates weathering were 0.8 ± 0.2 × 109 mol/year and 2.8 ± 0.2 × 109 mol/year, respectively. These results enrich the watershed weathering information of TGR tributaries and provide data support for understanding the global carbon cycle.

Physicochemical and metal composition of rainfall in the Johannesburg region, South Africa

The change in the water quality of rainfall impacts water supply through the contamination of surface water and groundwater. The presence of potential sources for metals in the form of aerosol through atmospheric transportation from gold tailings dams, coal mines, and coal-fired power stations increases the risk of water quality deterioration in the Johannesburg region. Rainfall monitoring was conducted for one hydrological year. Rainfall amount was measured, and samples were collected for stable isotope and metal analysis. Some metals show very high concentration in the rainfall with a decreasing order from zinc, cadmium, copper to lead. Their presence in the water is not desirable, as a result of favourable pH and Eh conditions in the rainfall with contaminant inputs from the gold tailing dams, coal mines, and coal-fired power stations. Therefore, the Johannesburg rainfall can be considered as potentially toxic due to the constant input of meals into water supply dams and aquifers recharged by the rainfall.

Migration and Transformation of Heavy Metals in the Soil of the Water-Level Fluctuation Zone in the Three Gorges Reservoir under Simulated Nitrogen Deposition

The accumulation of heavy metals (HMs) in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) area is potentially harmful to the water environment. In order to reveal whether nitrogen (N) deposition is a potential driving factor for the migration and transformation of HMs (Cd, Cr, Cu, Ni, and Pb), a simulated N deposition experiment was performed on the soil in the WFLZ of the TGR. The results showed that the accumulative release amounts of HMs increased with the increase of N deposition. It was found that the Elovich equation, double-constant equation, and parabolic diffusion equation could well describe the release process of Cu, Cd, Cr, and Ni, while the double-constant equation, parabolic diffusion equation, and first-order equation could be applicable for Pb. The exchangeable fractions of HMs increased to varying degrees after the N deposition treatment, wherein Ni was most significant, indicating that N deposition could increase the ecological risk of HM pollution in the TGR area. The results provide insight into the major factors affecting the release of different HMs under N deposition in this vulnerable region ecologically.

Major Elements in the Upstream of Three Gorges Reservoir: An Investigation of Chemical Weathering and Water Quality during Flood Events

Rivers transport terrestrial matter into the ocean, constituting a fundamental channel between inland and oceanic ecosystem and affect global climate change. To reveal chemical weathering processes and environmental health risks during flood periods, water samples were collected in the upper reaches of Three Gorges Reservoir (TGR) in 2020. HCO3− and Ca2+ were the most abundant anions and cations of the river water, respectively. The range of HCO3− concentration was between 1.81 and 3.02 mmol/L, while the mean content of Ca2+ was 1.03 mmol/L. The results of the Piper diagram and element ratios revealed that the river solutes were mainly contributed by carbonate weathering and gypsum-rich evaporite dissolution. A mass balance model indicated that the contribution order of sources to cations in the main channel (Yibin-Luzhou) was evaporites > carbonates > atmospheric input > silicates. The order in the Chongqing—Three Gorges Dam was carbonates > atmospheric input > evaporites > silicates. These results showed a lithologic control on hydrochemical characteristics. Most sampling sites were suitable for agricultural irrigation according to the water quality assessment. However, indexes sodium adsorption ratio (SAR) and soluble sodium percentage (Na%) were higher than 1.0 in Yibin-Luzhou and 30% in Yibin–Chongqing, respectively, suggesting a potential sodium hazard. In addition, except Tuojiang River and Shennong River, the risk of sodium hazard in tributaries was relatively low. High Na+ concentration in irrigation water can damage soil structure and function and ultimately affect agricultural production. Water quality in the upstream of a Piper diagram should attract enough attention.

Nature and sources of ionic species in rainwater during monsoon periods in and around sixteenth-seventeenth century CE monuments in Yamuna River basin, India

The nature and sources of ionic species were studied in the monsoon rainwater collected from two monuments of the sixteenth-seventeenth century CE in the Yamuna River basin from 2016 to 2018. The results showed the acidic pH of the rainwater with high dissolved SO₄^-2 and NO₃^-, and soil-derived components (Ca⁺², Mg⁺², and K⁺). The anionic (SO₄^-2, NO₃^-, Cl^-, F^-, and HCO₃^-) and cationic (Ca⁺², Mg⁺², K⁺, NH₄⁺, and Na⁺) concentrations showed regional differences in yearly contribution mainly from the fossil fuel combustion, soil dust, and farm residue burning. The rainwater analysis showed low dissolved ions at SCTK (Sheikh Chilli's Tomb, Kurukshetra) compared to KBMP (Kabuli Bagh Mosque, Panipat). The mean concentration of SO₄^-2 was 1.5 times higher than the NO₃^- apportioning the sulfate as a dominant acidifying constituent in rainwater. Pearson's correlation and principal component analysis (PCA) showed terrestrial and marine origins of dissolved ions in the rainwater. The Na-normalized molar ratios and the analysis of sea salt and non-sea salt fractions indicate the dominance of non-marine contributions in the precipitation. Based on neutralization factors, cations showed neutralization of rainwater acidity as follows: NF_Ca⁺² > NF_Mg⁺² > NF_NH4⁺ > NF_K⁺. The potential index showed the dominance of the neutralization potential (NP) on acidic potential (AP) at both locations.

Nitrogen wet deposition in the Three Gorges Reservoir area: Characteristics, fluxes, and contributions to the aquatic environment

Measurements of nitrate nitrogen (NO₃^--N), ammonia nitrogen (NH₄⁺-N), and dissolved organic nitrogen (DON) in precipitation were conducted at six different sites in the hinterland of the Three Gorges Reservoir (TGR) area from January 2016 to December 2017. The characteristics and the sources of nitrogen (N) species were identified. N flux of wet deposition in the hinterland of the TGR area were 13.56 ± 2.95 kg N ha^-1 yr^-1, of which the proportions of NO₃^--N, NH₄⁺-N and DON were 60.9%, 25.1% and 14.0%, respectively. N flux in urban area was significantly higher than those in suburban, agricultural, and wetland areas. Industrial activities, biomass burning, and secondary transformation were the main contributors of N in urban area. In agricultural area, biomass burning, crustal, and manure were main sources of N. In suburban area, mixed emissions from industry, agriculture, and crustal sources were primary contributors of N. For wetlands, the major contributions were from industrial sector and biomass burning. Additional, analysis of regional distribution of dissolved N deposition in the TGR area was conducted by combining current study data and previously published data between 2000 and 2017. N flux of wet deposition in the entire TGR area ranged from 12.17 to 51.93 kg N ha^-1 yr^-1, with an average of 26.81 kg N ha^-1 yr^-1. Regional N distribution was greatest in the tail region, followed by the head region, and then the hinterland in the TGR area. The amount of N entering the TGR directly through atmospheric wet deposition was 2906 t yr^-1, accounting for 2.1% of the total N inputs. N load from wet deposition had exceeded the critical loads from that of the water, forest, and even some farmland ecosystems in the TGR area. Decreasing NH₃ emissions from agricultural activities is the key to alleviate the regional N deposition.