Water chemistry of the Amazon River
Abstract
On the basis of analytical results of seasonal-cycle sampling, the water chemistry data of the Amazon River are presented. Based on these results, a new calculation of 62 ppm for the mean dissolved salts concentration for South American rivers is 11 per cent lower than previous calculations, and a new calculation of 117 ppm for the mean dissolved salts concentration for the rivers of the world is 2.6 per cent lower than previous calculations.
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Cited by (256)
Predictive models for dissolved oxygen in an urban lake by regression analysis and artificial neural network
2023, Total Environment Research ThemesThis paper portrays predictive models for Dissolved Oxygen (DO) levels in an urban lake using common water quality parameters like Temperature, pH, Conductivity and Oxidation Reduction Potential (ORP). Data were sampled using three real-time industry-standard sensors those are OPTOD, CTZN, and PHEHT, and then interpolated using the ArcGIS interpolation technique. Correlation studies were analyzed through the Machine Learning (ML) algorithm, the correlation study signified a positive linear correlation with DO against pH, temperature, salinity and conductivity and the model was corroborated by R-score which came to 0.687 and RMSE was 0.834. Multiple Linear Regression (MLR) model was developed to predict the DO with the correlated data of water parameters. In addition, an Artificial Neural Network (ANN) method using the Levenberg-Marquardt algorithm was developed to build a model to predict the DO as well. Then, the models’ performance was validated and the R2 accuracies were 0.963 for MLR and 0.93 for ANN and models were checked for the predicted data against the actual data. The appropriateness of the ANN model for forecasting investigated attributes is indicated by the fact that the discrepancy between the forecasted and real ANN model is significantly lesser than that of the regression model. The developed equation in this paper can be used to reveal DO data from unknown urban lake water.
Geochemical characterization, its controlling factors, and comparison between the upstream and downstream segments of the Himalayan Satluj River basin, India
2023, GeochemistrySatluj River Basin (SRB) has special economic significance, representing the country's most incredible hydro-structure with fresh water, a primary source of irrigation and hydroelectric power in Northern India. Therefore, SRB's geochemical characterization is vital for hydropower and agricultural sustainability. This study provides a preliminary characterization of the hydrogeochemical processes controlling the natural water evolution in SRB by observing the spatial variation and qualitative assessment of solute chemistry (major ions and trace/heavy elements) in the Satluj river, associated tributaries, and groundwater. Hydrochemical characteristics displayed the predominance of geogenic weathering processes with carbonates dissolution and silicate weathering as end members that could explain all the geochemical variability within the SRB. The results reveal that the chemical signature of the upstream segment is possibly influenced more by carbonate weathering than silicate weathering, and the trends reverse in the downstream section with the increasing influence of silicate weathering. Dissolved heavy metals (HMs) such as Mn, Cr, Fe, Co, Ni, Cu, Zn, As, Cd, and Pb showed large fluctuations among upstream and downstream sampling sites, indicating diverse environmental conditions. Human health risk assessment (HHRA) studies revealed less or no potential noncarcinogenic via HMs, except for the downstream stretch of tributaries inferring increased non-cancerous risk. Moreover, the HHRA with HMs (Cr, As, Cd, and Pb) manifested high carcinogenic risks for adults and children across the SRB. The finding of this study could be the baseline dataset for assessing the future status, effective management, and better utilization of water resources of the SRB.
Persulfate/Fe2+-based advanced oxidation processes are widely used to treat water contaminated with 2,4-dinitrotoluene (DNT). However, the oxidation of DNT by persulfate/Fe2+ in the presence of the chloride ion (Cl⁻) has not been addressed, and the transformation pathways and toxicities of the intermediate products remain unclear. In this study, the effect of different Cl⁻ concentrations on the oxidation of DNT was investigated by persulfate/Fe2+. After the addition of 1.0 mM Cl⁻ and 6 h of oxidation, the removal efficiency of DNT increased by 68.5%. Scavenging experiments and an electron spin resonance analysis suggested that Cl⁻ caused hydroxyl radicals to increase in content in the persulfate/Fe2+ system, thus promoting the removal of DNT. Eight intermediate products of DNT were accurately detected using high-resolution mass spectrometry, and the transformation pathways of DNT were proposed, including hydroxylation/oxidation, elimination of the nitro group, and chlorination process. The acute and chronic toxicities of the intermediate products decreased during the oxidation process, but chlorinated by-products posed a higher toxicological risk. This result is vital for the practical application and environmental safety evaluation of persulfate/Fe2+-based advanced oxidation.
Possible Amazonian contribution to Sargassum enhancement on the Amazon Continental Shelf
2022, Science of the Total EnvironmentThe Amazon Continental Shelf (ACS) has a coastline of ∼1000 km and is situated in a humid equatorial region with two distinct seasons, wet and dry, and two transitional climatic periods. A total of eight oceanographic cruises were conducted to investigate the dynamics of the inorganic nutrients dissolved in the surface layer of the water column of the ACS and their associations with Sargassum blooms. An excess of nitrogen-N* (NH4+ = 0.01–9.30 μmol l−1) was verified through the salinity gradient from the continent to the ACS, mainly during the period of maximum discharge of the Amazon and Tocantins-Pará rivers. The highest NH4+ concentrations coincided with the occurrence of macrophyte (Sargassum sp.) blooms in the mesohaline and oceanic regions. During this period the high values of NH4+ accompany the low values of Sea Surface Salinity (SSS), indicating the advection of the Amazonian plume towards the Caribbean Sea. In the Sargassum belts we observed a N:P ratio = 60:1 during wet period, while outside this region, the N:P ratio was 34:1. According to DIN vs. AOU ratio, we observed that heterotrophic processes prevail over productive processes, mainly in the mesohaline and low salinity regions.
Nitrogen concentrations from runoff, mainly from hydrographic basins, showed significant increases in the last decade, mainly due to anthropogenic factors such as agriculture, deforestation, livestock, urban sewage (domestic and industrial), and demographic growth of the population in the Tocantins-Pará Basin. Additionally, associations of diatoms and cyanobacteria provide more nitrogen in the mesohaline and oceanic regions that nourishes Sargassum blooms. Seasonal comparisons (October and April) of Sargassum belts with other studies, indicated that currents play a fundamental role in the transport of these macrophytes from the east edge (Africa) to the west edge (Brazil and French Guiana) towards the Caribbean Sea in the tropical Atlantic.
Major ion chemistry and silicate weathering rate of a small Western Ghats river, Sharavati, southwestern India
2022, Applied GeochemistryTropical, small mountainous rivers draining granite/granitic gneiss exhibit intense weathering rates and associated carbon dioxide sequestration, which has implications on the global CO2 budget. However, there is paucity of data from these catchments. This study aimed to understand silicate weathering rates (SWR) and CO2 sequestration rates (CCR) in a small tropical mountainous river, Sharavati in the southwestern India. Bicarbonates, Cl−, Na+, Ca2+ and silica, are predominant in the river, indicating their source from catchment rocks and atmosphere. Groundwater shows a similar abundance of major ions, indicating identical sources. Intense chemical weathering due to hot and humid climate, heavy monsoonal rains and associated river discharge are the main controlling factors of major ion chemistry in the Sharavati river. The presence of clay mineral kaolinite in the catchment corroborates with the above controlling factors. The calculated silicate weathering rate (SWR) is 27 t km−2. y−1 and associated carbon dioxide consumption rate (CCR) is 3.9 × 105 mol km−2. y−1. When compared to other small tropical river basins having similar climate and lithology, CCR of Sharavati is comparable to Jiuhua Mountain rivers, (South China) and twice that of Sorocaba River (Brazil). CCR is 3.9 times higher than the global average on account of the peculiarity of the terrain. It can be concluded from a comparative study of small tropical rivers, that rainfall and runoff are the main parameters controlling the weathering rates irrespective of catchment lithology.
Chemical weathering and CO<inf>2</inf> consumption in a multi-lithological karstic critical zone: Long term hydrochemical trends and isotopic survey
2021, Chemical GeologyThe chemical weathering (CW) of rocks at the Earth's surface plays a key role in the global carbon cycle along multiple pathways. Although karst systems are hotspot carbonated areas, they are not always monolithological. It is therefore challenging to estimate the CW of these complex areas. The interannual, seasonal, and spatial variations of CW rates and CO2 consumption were investigated using a long-term hydrogeochemical database (1994–2019) from a mountainous karstic catchment in southwestern France (Baget Catchment). A geochemical and isotopic spatial sampling allowed the identification of the main mineral or lithological sources in the catchment, which controlled the water chemistry. The CW budget showed that the (Ca2+ + Mg2+) fluxes originated from carbonate dissolution (1.14 mol·m−2·yr−1 equivalent to 74%) and silicate weathering (18%) by carbonic acid solutions. Gypsum dissolution and carbonate weathering by sulphuric acid from pyrite oxidation contribute equally to 4%, although the former accounts for 66% of the dissolved sulphate fluxes. During a summer sampling survey, an innovative sulphur isotopic approach based on δ34SSO4, allowed us to demonstrate that the ore-nature sulphuric acid drove 9.0% of total carbonate dissolution and represented only 16.8% of the dissolved sulphate stream fluxes. Hydrological conditions, temperature, vegetation, the epikarst (quasi-permanent shallow and discontinuous saturated layer under the soil), and the water dynamics were the key factors influencing the inter-annual and inter-seasonal variations of the CW rates and CO2 consumption. In addition, the carbon isotopic signature evidenced geochemical processes such as CO2 outgassing and calcite precipitation processes. The latter could remove up to 74% of HCO3− from streamwaters, depending on the hydrological conditions at the outlet between 2016 and 2019. Finally, this study highlights that CW rates and CO2 consumption may vary over inter-annual and inter-seasonal scales, and spatially even for a small catchment. Furthermore, the global CO2 consumption appears to be mainly driven by the runoff intensity in karst hydrosystems, where carbonate dissolution was found to consume 71% of the total weathering CO2 uptake.