ANALYZING CADMIUM (CD) TRANSPORT DURING AGRICULTURAL BASED MANAGED AQUIFER RECHARGE: LABORATORY SCALE STUDY

Abstract

Unsustainable groundwater extraction provides a living for almost twenty-five per cent of the world's population and contributes to forty per cent of the world's agricultural output. Managed aquifer recharge (MAR) can play an essential role in water resource management by providing water supply resiliency, improving groundwater quality, and providing environmental and agricultural benefits. However, MAR is not reaching its full potential because of increasing population, urban development, and the impacts of climate change. Among various MAR schemes, Agricultural-based managed aquifer recharge (AgMAR) is an emerging nature-based scheme that uses stormwater or floodwater to replenish overexploited aquifers. AgMAR can impact groundwater quality positively or negatively, contingent on the initial quality of the water source. Runoff from intensive agricultural and industrial zones can introduce metals like cadmium to the soil, impacting crop health and potentially endangering groundwater purity. Therefore, this study aims to understand cadmium (Cd) mobility during AgMAR operation through laboratory-scale batch and column experiments. For that, various soil physiochemical properties are measured. Different Cd concentration solutions varying from 10 to 200 ppm were used for the batch experiment to determine the soil Cd adsorption capacity. Two columns of dimensions 20 cm×3 cm are designed, maintaining a 2 cm constant ponding with the peristaltic pump. The Bromide (Br) tracer experiment was first conducted to estimate the soil hydraulic parameters in Hydrus 2-D. After that, the same parameter was used in the Cd column experiment, and solute reaction parameters were calculated. Around 50 ppm of Br and 600 ppm of Cd solution were used in the experiment. Further, Hydrus 2D was used to understand migration patterns of Cd during agriculturally managed aquifer recharge (AgMAR) by integrating various data inputs such as soil properties, initial and boundary conditions, and experimental data. The soil exhibits physiochemical characteristics: bulk density (1.62 g/cm³), texture (61% sand, 24% silt, 15% clay, classified as sandy loam), pH (7.25-7.48), electrical conductivity (125.3-152.9 m℧ cm⁻¹), and soil organic carbon content (1-2%). The adsorption isotherm result showed maximum adsorption of around 439.58 (mg/kg). Furthermore, both scenarios show that the Cd migrates to the root zone depth and reaches the groundwater system when we apply 5 cm constant ponding for 1 year giving valuable insights in ponding duration.