Showing papers by "Kazi Matin Ahmed published in 2020"

Arsenic contamination of Bangladesh aquifers exacerbated by clay layers.

Abstract: Confining clay layers typically protect groundwater aquifers against downward intrusion of contaminants. In the context of groundwater arsenic in Bangladesh, we challenge this notion here by showing that organic carbon drawn from a clay layer into a low-arsenic pre-Holocene (>12 kyr-old) aquifer promotes the reductive dissolution of iron oxides and the release of arsenic. The finding explains a steady rise in arsenic concentrations in a pre-Holocene aquifer below such a clay layer and the repeated failure of a structurally sound community well. Tritium measurements indicate that groundwater from the affected depth interval (40–50 m) was recharged >60 years ago. Deeper (55–65 m) groundwater in the same pre-Holocene aquifer was recharged only 10–50 years ago but is still low in arsenic. Proximity to a confining clay layer that expels organic carbon as an indirect response to groundwater pumping, rather than directly accelerated recharge, caused arsenic contamination of this pre-Holocene aquifer. Generally it is thought that confining clay layers provide protection to low-arsenic groundwaters against intrusion of shallower, high-arsenic groundwater bodies. Here, the authors show that impermeable clay layers can increase arsenic input to underlying groundwater systems due to reduction of iron oxides coupled to carbon oxidation.

Origin of Groundwater Arsenic in a Rural Pleistocene Aquifer in Bangladesh Depressurized by Distal Municipal Pumping

Abstract: Across South Asia, millions of villagers have reduced their exposure to high-arsenic (As) groundwater by switching to low-As wells. Isotopic tracers and flow modeling are used in this study to understand the groundwater flow system of a semi-confined aquifer of Pleistocene (>10 kyr) age in Bangladesh that is generally low in As but has been perturbed by massive pumping at a distance of about 25 km for the municipal water supply of Dhaka. A 10- to 15-m-thick clay aquitard caps much of the intermediate aquifer (>40- to 90-m depth) in the 3-km2 study area, with some interruptions by younger channel sand deposits indicative of river scouring. Hydraulic heads in the intermediate aquifer below the clay-capped areas are 1-2 m lower than in the high-As shallow aquifer above the clay layer. In contrast, similar heads in the shallow and intermediate aquifer are observed where the clay layer is missing. The head distribution suggests a pattern of downward flow through interruptions in the aquitard and lateral advection from the sandy areas to the confined portion of the aquifer. The interpreted flow system is consistent with 3H-3He ages, stable isotope data, and groundwater flow modeling. Lateral flow could explain an association of elevated As with high methane concentrations within layers of gray sand below certain clay-capped portions of the Pleistocene aquifer. An influx of dissolved organic carbon from the clay layer itself leading to a reduction of initially orange sands has also likely contributed to the rise of As.

Multi-hazard Groundwater Risks to Water Supply from Shallow Depths: Challenges to Achieving the Sustainable Development Goals in Bangladesh

Abstract: Groundwater currently provides 98% of all drinking-water supply in Bangladesh. Groundwater is found throughout Bangladesh but its quality (i.e., arsenic and salinity contamination) and quantity (i.e., water-storage depletion) vary across hydrological environments, posing unique challenges to certain geographical areas and population groups. Yet, no national-scale, multi-parameter groundwater hazard maps currently exist enabling water resources managers and policy makers to identify vulnerable areas to public health. We develop, for the first time, groundwater multi-hazard maps at the national scale of Bangladesh combining information on arsenic, salinity, and water storage. We apply geospatial techniques in ‘R’ programming language and ArcGIS environment, linking hydrological indicators for water quality and quantity to construct risk maps. A range of socioeconomic variables including access to drinking and irrigation water supplies and social vulnerability (i.e., poverty) are overlaid on these risk maps to estimate exposures. Our multi-parameter groundwater hazard maps show that a considerable proportion of land area (5–24% under extremely high to high risks) in Bangladesh is currently under combined risk of arsenic and salinity contamination, and groundwater-storage depletion. As small as 6.5 million (2.2 million poor) to 24.4 million (8.6 million poor) people are exposed to a combined risk of high arsenic, salinity, and groundwater-storage depletion. Our groundwater hazard maps reveal areas and exposure of population groups to water risks posed by arsenic and salinity contamination and depletion of water storage. These geospatial hazard maps can potentially guide policy makers in prioritizing mitigation and adaptation measures in order to achieve the United Nation’s Sustainable Development Goals across the water, agriculture, and public health sectors in Bangladesh.

Groundwater recharge processes in an Asian mega-delta: hydrometric evidence from Bangladesh

Abstract: Groundwater is used intensively in Asian mega-deltas yet the processes by which groundwater is replenished in these deltaic systems remain inadequately understood. Drawing insight from hourly monitoring of groundwater levels and rainfall in two contrasting settings, comprising permeable surficial deposits of Holocene age and Plio-Pleistocene terrace deposits, together with longer-term, lower-frequency records of groundwater levels, river stage, and rainfall from the Bengal Basin, conceptual models of recharge processes in these two depositional environments are developed. The representivity of these conceptual models across the Bengal Basin in Bangladesh is explored by way of statistical cluster analysis of groundwater-level time series data. Observational records reveal that both diffuse and focused recharge processes occur in Holocene deposits, whereas recharge in Plio-Pleistocene deposits is dominated by indirect leakage from river channels where incision has enabled a direct hydraulic connection between river channels and the Plio-Pleistocene aquifer underlying surficial clays. Seasonal cycles of recharge and discharge including the onset of dry-season groundwater-fed irrigation are well characterised by compiled observational records. Groundwater depletion, evident from declining groundwater levels with a diminished seasonality, is pronounced in Plio-Pleistocene environments where direct recharge is inhibited by the surficial clays. In contrast, intensive shallow groundwater abstraction in Holocene environments can enhance direct and indirect recharge via a more permeable surface geology. The vital contributions of indirect recharge of shallow groundwater identified in both depositional settings in the Bengal Basin highlight the critical limitation of using models that exclude this process in the estimation of groundwater recharge in Asian mega-deltas.

Why Do People Remain Attached to Unsafe Drinking Water Options? Quantitative Evidence from Southwestern Bangladesh

Abstract: The acceptance of newly implemented, safe drinking water options is not guaranteed. In the Khulna and Satkhira districts, Bangladesh, pond water is pathogen-contaminated, while groundwater from shallow tubewells may be arsenic- or saline-contaminated. This study aims to determine why, as well as the extent to which, people are expected to remain attached to using these unsafe water options, compared to the following four safer drinking water options: deep tubewells, pond sand filters, vendor water, and rainwater harvesting. Through 262 surveys, this study explores whether five explanatory factors (risk, attitude, norms, reliability, and habit) pose barriers to switching from unsafe to safe drinking water options or whether they could act as facilitators of such a switch. Users’ attachment to using pond water is generally low (facilitators: risk and attitude. Barrier: norms). Users are more attached to shallow tubewells (no facilitators. Barriers: reliability and habit). The safe alternatives (deep tubewell, rain water harvesting, pond sand filter, and vendor water) score significantly better than pond water and are estimated to have the potential to be adopted by pond water users. Deep tubewell, rain water harvesting, and pond sand filter also score better than shallow tubewells and could also have the potential to replace them. These findings may be used to optimise implementation strategies for safer drinking water alternatives.

Associations of drinking rainwater with macro-mineral intake and cardiometabolic health: a pooled cohort analysis in Bangladesh, 2016-2019.

Abstract: This study explores the associations of drinking rainwater with mineral intake and cardiometabolic health in the Bangladeshi population. We pooled 10030 person-visit data on drinking water sources, blood pressure (BP) and 24-h urine minerals. Fasting blood glucose (FBG) was measured in 3724 person-visits, and lipids in 1118 person-visits. We measured concentrations of sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) in 253 rainwater, 935 groundwater and 130 pond water samples. We used multilevel linear or gamma regression models with participant-, household- and community-level random intercepts to estimate the associations of rainwater consumption with urine minerals and cardiometabolic biomarkers. Rainwater samples had the lowest concentrations of Na, K, Ca and Mg. Rainwater drinkers had lower urine minerals than coastal groundwater drinkers: -13.42 (95% CI: -18.27, -8.57) mmol Na/24 h, -2.00 (95% CI: -3.16, -0.85) mmol K/24 h and -0.57 (95% CI: -1.02, -0.16) mmol Mg/24 h. The ratio of median 24-hour urinary Ca for rainwater versus coastal groundwater drinkers was 0.72 (95% CI: 0.64, 0.80). Rainwater drinkers had 2.15 (95% CI: 1.02, 3.27) mm Hg higher systolic BP, 1.82 (95% CI: 1.19, 2.54) mm Hg higher diastolic BP, 0.59 (95% CI: 0.17, 1.01) mmol/L higher FBG and -2.02 (95% CI: -5.85, 0.81) mg/dl change in high-density lipoprotein cholesterol compared with the coastal groundwater drinkers. Drinking rainwater was associated with worse cardiometabolic health measures, which may be due to the lower intake of salubrious Ca, Mg and K.

Demand for Information on Environmental Health Risk, Mode of Delivery, and Behavioral Change: Evidence from Sonargaon, Bangladesh.

Abstract: Millions of villagers in Bangladesh are exposed to arsenic by drinking contaminated water from private wells. Testing for arsenic can encourage switching from unsafe wells to safer sources. This study describes results from a cluster randomized controlled trial conducted in 112 villages in Bangladesh to evaluate the effectiveness of different test selling schemes at inducing switching from unsafe wells. At a price of about USD0.60, only one in four households purchased a test. Sales were not increased by informal inter-household agreements to share water from wells found to be safe, or by visual reminders of well status in the form of metal placards mounted on the well pump. However, switching away from unsafe wells almost doubled in response to agreements or placards relative to the one in three proportion of households who switched away from an unsafe well with simple individual sales.

Microbiological water quality of Managed Aquifer Recharge systems in the salinity-prone southwest coastal Bangladesh

Abstract: Managed aquifer recharge (MAR), a hydro-geological intervention designed to dilute groundwater salinity, pumps pond water treated through a slow sand filter into the underground aquifers. We evaluated the microbiological safety of the resulting MAR water at sites from three districts in southwest coastal Bangladesh. We collected monthly paired pond-MAR water samples from July 2016-June 2017 and enumerated fecal coliforms and E. coli using the IDEXX quanti-tray technique, by the most probable number (MPN) method. We used WHO risk categories for microbiological quality; no risk ( 10 MPN per 100 mL water). We estimated the difference in mean log10 MPN in pond and MAR water using linear mixed effect models with random intercepts and cluster adjusted robust standard error. Almost all pond water samples (292/299, 98%) had moderate- to high-risk level (>10 MPN) fecal coliforms and E. coli (283/299, 95%). In contrast, 81% (242/300) of MAR water samples had no or low risk level fecal coliforms (0-10 MPN), of which 60% (179/300) had no fecal coliforms. We detected no or low risk level E. coli in 94% (283/300) of MAR water samples of these 80% (240/300) had no E. coli. MAR samples had lower mean log10 MPN fecal coliforms (-2.37; 95% CI: -2.56, -2.19) and E. coli (-2.26; 95% CI: - 2.43, -2.09) than pond water; microbial reductions remained consistent during the wet (May-October) and dry seasons. MAR-systems provided water with reduced fecal indicator bacteria compared to infiltered pond water.

Effectiveness of insect growth regulators for management of legume pod borer, Maruca vitrata F. in yard long bean

Abstract: The legume pod borer, Maruca vitrata (Lepidoptera: Crambidae) is considered the most serious pest of yard long bean. An experiment was conducted in the field laboratory of the Department of Entomology, Bangladesh Agricultural University, Mymensingh during kharif season 2016 to evaluate the effectiveness of two commonly used insect growth regulators (IGR), burofezin and lufenuron with different doses and a widely used chemical insecticide nitro 505 EC as recommended dose for the management of legume pod borer. The treatments were arranged in Randomized Complete Block Design along with an untreated control with three replications of each treatment. The efficacy of the treatments was evaluated based on the percentage flower and pod infestation, percentage larval survivability and marketable pod yield. It was found that all the treatments were significantly effective against pod borer than the untreated control. The highest efficacy was found from the buprofezin among the treatments. Buprofezin @ 0.75 mL L−1 exhibited the best performance resulting 64.16 and 70.60% reduction of flower and pod infestation, respectively consequently providing 43.95% surviving larvae and 40.35% increase of pod yield with the benefit cost ratio1.47. This result was followed by buprofezin @ 0.5 mL L−1 and provided the results as 61.96%, 67.46%, 44.06%, 40.11%, and 1.48 flower infestation, pod infestation, surviving larvae, yield increase and benefit cost ration, respectively. Therefore, buprofezin @ 0.5mL L−1 might be recommended for the effective and economic management of legume pod borer in the yard long bean field.