Hydrogeochemical evolution of shallow and deeper aquifers in central Bangladesh: arsenic mobilization process and health risk implications from the potable use of groundwater

Protection of groundwater quality from various natural and anthropogenic forces is a prime concern in Bangladesh. In this study, we utilized groundwater geochemistry of shallow and deeper aquifers to investigate the hydrogeochemical processes controlling water quality, and the sources and mechanism of Arsenic (As) release to water and associated human health risks in the Faridpur district, Bangladesh. Analysis of hydrochemical facies indicated that groundwaters were Ca–Mg–HCO3\ua0type and that water–rock interactions were the dominant factors controlling their major-ion chemical composition. The dissolution of calcite, dolomite, and silicates, as well as cation exchange processes regulated the major ions chemistry in the groundwater. Dissolved fluoride (F−) concentrations (0.02–0.4\ua0mg/L) were lower than the drinking water standard of 1.5\ua0mg/L set by the World Health Organization (WHO). Arsenic contamination of groundwater is among the biggest health threats in Bangladesh. The measured As concentration (0.01–1.46\ua0mg/L with a mean of 0.12\ua0mg/L) exceeded the maximum permissible limit of Bangladesh and WHO for drinking water. The estimated carcinogenic risk of As exceeded the upper benchmark of 1 × 10–4\ua0for both adult and children, and health threats from shallow groundwater were more severe than the deeper water. The vertical distribution of As resembled Fe and Mn with their higher concentrations in shallow Holocene aquifers and lower in deeper Pleistocene aquifers. Speciation calculation indicated the majority of groundwater samples were oversaturated with respect to siderite, calcite, and dolomite, while undersaturated with respect to rhodochrosite. The saturation state of the minerals along with other processes may exert kinetic control on As, Fe, and Mn distribution in groundwater and lead to their lack of statistically significant correlations. Microbially mediated reductive dissolution of Fe and Mn oxyhydroxides is envisaged as the primary controlling mechanism of As mobilization in Faridpur groundwater. Pyrite oxidation was not postulated as a plausible explanation of As pollution

Evaluation of Water Quality for Sustainable Agriculture in Bangladesh

Sustainable groundwater quality has become a major concern for the agro-based country like Bangladesh. Integrated approaches of various irrigation water quality indices and geostatistical modeling were applied to evaluate the suitability and for spatial mapping of groundwater quality of Faridpur District in central Bangladesh. The irrigation water quality index (IWQI) revealed that majority of the samples were suitable for irrigation. Similar outcomes were recorded from other indices including Na%, sodium adsorption ratio (SAR), residual sodium bicarbonate (RSBC), total hardness (TH), Kelley's ratio (KR), and magnesium adsorption ratio (MAR). Classifications based on Wilcox diagram and permeability index (PI) plot indicated a similar conclusion wherein almost all the samples were safe for agricultural uses without posing considerable effect on the soil fertility and overall crop yield. Principal component analysis (PCA) grouped the major cations and anions into three principal components including dissolution of calcite minerals, leaching of silicate sediments, and ion exchange process. Spatial mapping of IWQI identified that groundwater in the northern side of Faridpur region were more suitable for irrigational uses relative to central and southern side, possibly due to gradients of domestic discharges and agricultural activates from north to south side. These findings would provide useful information to water distributors, managers, and decision makers for taking adaptive measures in irrigation water quality management systems

Hyperspectral characteristics and inversion model estimation of winter wheat under different elevated CO2 concentrations

As carbon dioxide (CO2) is required for plants photosynthesis, elevated CO2 (eCO(2)) concentrations have potential impacts on plant growth and development. The leaf area index (LAI) and soil and plant analysis development (SPAD), which are often used for characterize the chlorophyll content of plants, are important parameters for characterizing plant growth. The purpose of this study was to investigate the effects of different eCO(2) concentrations on winter wheat growth and select sensitive spectral parameters to establish LAI and SPAD estimation models. A field experiment in which winter wheat was exposed to different eCO(2) concentrations was performed using open-top chambers (OTCs) during the winter wheat growing season from 2017 to 2018. The experimental treatments consisted of exposure to the ambient CO2 concentration (CK), 80 mu mol mol(-1) CO2 above CK (T (1)), and 200 mu mol mol(-1) CO2 above CK (T (2)). The canopy spectral reflectance, LAI, and SPAD were measured during the main growth stages of the winter wheat. The results showed that no significant differences in LAI and SPAD were found under different treatments. Different eCO(2) concentrations did not change the reflectance curves, solely affecting the reflectance. Elevated CO2 conditions induced the red edge parameters red shift first and then blue shift. The first derivative reflectance at 755 nm (R' (755)), red edge position (lambda (Red)), ratio of the red edge area to the blue edge area (SDRed/SDBlue), and normalized value of the red edge area and blue edge area ((SDRed - SDBlue)/(SDRed + SDBlue)) were highly correlated with the LAI. The first derivative reflectance at 764 nm (R' (764)), SDRed/SDBlue, ratio of the red edge area to the yellow edge area (SDRed/SDYellow), (SDRed - SDBlue)/(SDRed + SDBlue), and normalized value of the red edge area and yellow edge area ((SDRed - SDYellow)/(SDRed + SDYellow)) were significantly correlated with the SPAD. The optimal regression model for the LAI was y = 0.49x (0.74), simulated by SDRed/SDBlue; that for the SPAD was y = - 0.035x (2)-1.96x + 25.83, simulated by SDRed/SDYellow. The coefficient of determination (R (2)) values were 0.49 and 0.61, respectively, and the root mean square error (RMSE) values were 0.38 and 1.51, respectively. Overall, our results indicate that inversion models based on SDRed/SDBlue and SDRed/SDYellow can be used to estimate the LAI and SPAD values under eCO(2) concentration conditions during the winter wheat growth period

Effect of Warming and Elevated O₃ Concentration on CO₂ Emissions in a Wheat-Soybean Rotation Cropland

A deeper understanding of the effects of experimental warming and elevated ozone (O3) concentration on carbon dioxide (CO2) fluxes is imperative for reducing potential CO2 emissions in agroecosystems, but are less understood particularly in rotational wheat (Triticum aestivum)—soybean (Glycine max) croplands. In order to understand such effects on CO2 fluxes from winter wheat-soybean rotation, a field experiment was conducted by using the open-top chamber (OTCs) during the growing seasons of 2012 and 2013 at an agro-ecological station in southeast China. The experimental treatments included the control (CK), experimental warming (T, crop canopy temperature increased by ~2 °C), elevated O3 concentration (O, O3 concentration about 100 ppb) along with temperature enhancement (OT, elevated ~2 °C temperature plus 100 ppb O3). The results showed that warming significantly increased the mean CO2 fluxes (MCF) and the cumulative amount of CO2 (CAC) from soil and soil-crop systems, while elevated O3 and warming enhancement (OT) significantly reduced MCF and CAC. Besides, warming significantly reduced the biomass of winter-wheat, but it insignificantly decreased the biomass of soybean in the harvest period. The O and OT treatments significantly reduced the biomass of winter-wheat and soybean cropping systems in the harvest time. Both warming and elevated O3 concentration decreased the temperature sensitivity coefficients (Q10) in soil respiration during the experimental period. Overall, our results indicate that elevated O3 concentration compensates the effect of warming on CO2 emission to some extents, which has a positive feedback impact on the climate system

Spatiotemporal nexus between vegetation change and extreme climatic indices and their possible causes of change

Climate extremes have a significant impact on vegetation. However, little is known about vegetation response to climatic extremes in Bangladesh. The association of Normalized Difference Vegetation Index (NDVI) with nine extreme precipitation and temperature indices was evaluated to identify the nexus between vegetation and climatic extremes and their associations in Bangladesh for the period 1986–2017. Moreover, detrended fluctuation analysis (DFA) and Morlet wavelet analysis (MWA) were employed to evaluate the possible future trends and decipher the existing periodic cycles, respectively in the time series of NDVI and climate extremes. Besides, atmospheric variables of ECMWF ERA5 were used to examine the casual circulation mechanism responsible for climatic extremes of Bangladesh. The results revealed that the monthly NDVI is positively associated with extreme rainfall with spatiotemporal heterogeneity. Warm temperature indices showed a significant negative association with NDVI on the seasonal scale, while precipitation and cold temperature extremes showed a positive association with yearly NDVI. The DEA revealed a continuous increase in temperature extreme in the future, while no change in precipitation extremes. NDVI also revealed a significant association with extreme temperature indices with a time lag of one month and with precipitation extreme without time lag. Spatial analysis indicated insensitivity of marshy vegetation type to climate extremes in winter. The study revealed that elevated summer geopotential height, no visible anticyclonic center, reduced high cloud cover, and low solar radiation with higher humidity contributed to climatic extremes in Bangladesh. The nexus between NDVI and climatic extremes established in this study indicated that increasing warm temperature extremes due to global warming might have severe implications on Bangladesh's ecology and the environment in the future