Tracking Dissolved Trace and Heavy Metals in the Ganga River From Source to Sink: A Baseline to Judge Future Changes

Abstract

Understanding how dissolved trace elements chemically evolve in the Ganga River from source to sink is important to understand subcatchment contributions and chemical variability across space and time but remains poorly constrained. What exists is site-specific data sets that are focused on capturing contamination "hotspots." Here, we present riverine trace element concentrations of 38 targeted locations in the Ganga Basin. Samples in the headwater and the upstream segments of the river were collected during the premonsoon, monsoon, and postmonsoon seasons of 2014, 2015, and 2016, and the downstream samples were collected in 2016. In addition, monthly time-series samples were collected at a downstream site to capture the geochemical variability at a higher temporal-resolution. To evaluate the geogenic contributions, groundwater, rainwater, snow, glacier-ice, and sediment samples were also analyzed. We find that the river chemistry displays a wide spatio-temporal variability. Headwater samples are characterized by high concentrations of trace elements that are primarily controlled by ice meltwater, intense weathering, and interactions with glacial flour and are therefore geogenic in nature. Moreover, high concentrations of trace metals were also observed in a few localized downstream sites. However, such enriched signals are not persistent further downstream as they get diluted by the joining of large tributaries. We show that the dissolved trace element concentrations in the Ganga River are low compared to existing datasets and are comparable to the global average river water composition. We additionally quantified the present-day "baseline" concentration ranges to facilitate future water quality assessment in the Ganga Basin. 1. Introduction Global freshwater availability and quality are constantly changing. A simple explanation for such behavior is climate change and pollution associated with population increase (

A Time-Series Record during COVID-19 Lockdown Shows the High Resilience of Dissolved Heavy Metals in the Ganga River

“…The major ions (except NO 3 – and PO 4 2– ) and trace elements (e.g., Rb, Sr, Li, and As) exhibit temporal variability, and their concentrations are quite similar to premonsoon (March to May) pre-COVID-19 concentrations . In general, Rb, Sr, Li, and As concentrations increased with time, that of Ca 2+ did not, and concentrations of V, Cr, Co, Ni, and Cu do not show any systematic temporal trends (Table S1, S2 and Figure S2).…”

“…The tributary catchment polygons were defined topographically using the “Watershed” cloud-based geoprocessing tool in ArcGIS (Esri Corp.). Rainfall data at each tributary catchment were summed to obtain the catchment daily precipitation upstream of our sampling site . The discharge and amount of daily precipitation in the catchment are listed in Table S1.…”

“…Even in terms of industrial wastewater generation, Uttar Pradesh also leads all other states in the Ganga Basin, generating 269 million liters per day (MLD), which is 54% of the total wastewater generated in the entire basin. As a result, the stretch of the Ganga river upstream of Prayagraj always reports the highest concentrations of trace metals, which become diluted downstream by joining of large tributaries, namely, the Ghaghara, Son, Gandak, and Kosi rivers …”

Influences on tidal channel and aquaculture shrimp pond water chemical composition in Southwest Bangladesh

“…While these models do not identify the mechanisms that control As and Se concentrations in shrimp ponds and tidal channel waters, they are very useful in gauging what elements/geochemical parameters are most important in influencing As and Se concentrations in surface waters. This extends to upstream (non-headwaters) Ganges River samples [ 15 ], their Table S4), where Cu, Vi, and Ni result in a great multiple linear predictive model fit for As (adjusted R 2 = 0.64, p = 7.2e-15) (Additional file 1 : Table A8). Additionally, when examining tidal channel samples from Ayers et al [ 8 ], predicting As with Cu, V, Ni, and P results in a great overall fit as well (adjusted R 2 = 0 0.74, p = 0.024) (Additional file 1 : Table A9).…”

“…Recently, in the Ganges River system, “hot spots” of elevated trace element concentrations (relative to “background” in the study) were observed near large urban and industrial areas, but these concentrations became diluted by other river tributaries downstream [ 15 ]. Thus, a city like Khulna could be a source of Se or other trace elements, and dilution is limited until either the tidal channels empty into the Bay of Bengal or it becomes peak monsoon season.…”