Deltin 7

S Debnath, MM Ahmed, SB Belhaouari, T Amagasa, M Rahman. . Applied Intelligence 53 (11), 14448-14469.

JCR Impact Factor (2022): 8.5, Q1 Journal in Computer Science Area

Managed  (MAR) has been applied as Aquifer Storage, Transfer, and Recovery (ASTR) to provide fresh  for local communities at 99 locations in southwest Bangladesh since 2009. Aerobic freshwater from ponds is filtered and subsequently infiltrated into anaerobic shallow brackish aquifers. At approximately 45% of these sites, relatively higher levels of Fe and As were observed in recovered water, which requires a better understanding of the hydrogeochemical processes that govern the Fe, Mn, and As levels in these MAR systems. Therefore, two representative sites with As above (74 ± 11 μg/L at site GMF11) and below (19 ± 6 μg/L at site JJS91), the Bangladesh drinking water standard of 50 μg/L were weekly monitored on hydrochemical changes from Dec 2017 to Dec 2018. Hydrogeochemical processes occurring during storage were quantified with inverse and forward geochemical mass balance models developed with PHREEQC. The following processes explained the changes in water quality: 1) mixing of infiltration water with native groundwater (∼90%:∼10%); 2) consumption of O2 by a) dissolved Fe2+ that subsequently precipitated as Fe(OH)3 at GMF11 and by b) dissolved and sedimentary organic matter (OM) at site JJS91; 3) reduction of SO4 coupled to the oxidation of OM at both sites; and 4) mixing corrosion and freshening induced cation-exchange (Ca ; Na desorption) triggering  and  dissolution at GMF11. Dissolution of these occurred to a lesser extent at JJS91, while cation exchange (Na sorption; Ca desorption) suggested that the freshwater was displaced by brackish groundwater because of inadequate infiltration at JJS91. Distinct pH values in recovered water reflected the dominance of Fe2+ versus OM oxidation. Siderite dissolution led to 4.3 ± 3.1 and 1.0 ± 0.5 mg/L Fe in recovered water at GMF11 and JJS91, respectively. Elevated As and Mn levels in recovered water were caused for max. 20% by mixing with native groundwater and for min. 80% by mobilization processes, mainly by desorption of As from Fe-oxides and by the dissolution of Mn-bearing siderite. Recommendations are provided to improve recovered water quality.

Riverbank migration is a common phenomenon in the floodplains of Bangladesh. The continuous changes in river morphology affect its surrounding land-use patterns which pose threats to the life and property of people living near the rivers. The present study utilized thirty-one (1989-2020) years of satellite data to track the erosion-accretion and its influence on land-use and land-cover (LULC) change of Hizla Upazila using GIS-based Modified Normalized Difference Water Index (MNDWI) and Google Earth Engine (GEE) respectively. Statistical analysis revealed the average erosion rate (5.03 km2) is lower than accretion (5.72 km2), resulting in a net land gain of 24.93 Km2. The spatial distribution of erosional activity suggests that the central and western parts of Hizla Upazila are mostly affected, compared to the eastern part, where new deltas are forming. This phenomenon is attributed to the westward movement of the Lower Meghna River (LMR), making the central and western parts of Hizla more vulnerable. The pattern of land-use change manifests that nearby settlements and vegetation are primarily at risk due to channel migration. A significant decrease in total water area (2.1%) and an increase in bare land area (5.1%) between 1997-2010 indicates substantial deposition. Concurrently, there was a decrease in the total settlement (1.53 km2) and vegetation area (9.8 Km2), indicating natural hazards like floods and high-intensity rainfall. The overall kappa accuracy for LULC is over 85% demonstrating its suitability for forecasting. The outcomes of this study will aid the local community, policymakers, and researchers in mitigating risk and ensuring sustainability.