TY - JOUR
T1 - Contribution of sedimentary organic matter to arsenic mobilization along a potential natural reactive barrier (NRB) near a river
T2 - The Meghna river, Bangladesh
AU - Varner, Thomas S.
AU - Kulkarni, Harshad V.
AU - Nguyen, William
AU - Kwak, Kyungwon
AU - Cardenas, M. Bayani
AU - Knappett, Peter S.K.
AU - Ojeda, Ann S.
AU - Malina, Natalia
AU - Bhuiyan, Mesbah Uddin
AU - Ahmed, Kazi M.
AU - Datta, Saugata
N1 - Funding Information:
We acknowledge the field assistance received from the residents of Nayapara and colleagues from the University of Dhaka. A special thank you to Ashely Aguilar and Protik Banerjee for laboratory assistance, and Reid Buskirk from Texas A&M University for method validation for the Principal Components Analysis. We would like to thank Dr. Alexis Godet for X-Ray Fluorescence Analysis at the University of Texas at San Antonio, and Dr. Humayun Akhter from the Department of Geology at the University of Dhaka for assistance with field logistics. Funding was provided to Peter S. Knappett, M. Bayani Cardenas, and Saugata Datta by the National Science Foundation Hydrologic Sciences grant numbers EAR- 1852652 , EAR- 1852653 , and EAR- 1940772 , respectively.
Funding Information:
We acknowledge the field assistance received from the residents of Nayapara and colleagues from the University of Dhaka. A special thank you to Ashely Aguilar and Protik Banerjee for laboratory assistance, and Reid Buskirk from Texas A&M University for method validation for the Principal Components Analysis. We would like to thank Dr. Alexis Godet for X-Ray Fluorescence Analysis at the University of Texas at San Antonio, and Dr. Humayun Akhter from the Department of Geology at the University of Dhaka for assistance with field logistics. Funding was provided to Peter S. Knappett, M. Bayani Cardenas, and Saugata Datta by the National Science Foundation Hydrologic Sciences grant numbers EAR- 1852652, EAR- 1852653, and EAR- 1940772, respectively.
Publisher Copyright:
© 2022
PY - 2022/12
Y1 - 2022/12
N2 - Elevated dissolved arsenic (As) concentrations in the shallow aquifers of Bangladesh are primarily caused by microbially-mediated reduction of As-bearing iron (Fe) (oxy)hydroxides in organic matter (OM) rich, reducing environments. Along the Meghna River in Bangladesh, interactions between the river and groundwater within the hyporheic zone cause fluctuating redox conditions responsible for the formation of a Fe-rich natural reactive barrier (NRB) capable of sequestering As. To understand the NRB's impact on As mobility, the geochemistry of riverbank sediment (<3 m depth) and the underlying aquifer sediment (up to 37 m depth) was analyzed. A 24-hr sediment-water extraction experiment was performed to simulate interactions of these sediments with oxic river water. The sediment and the sediment-water extracts were analyzed for inorganic and organic chemical parameters. Results revealed no differences between the elemental composition of riverbank and aquifer sediments, which contained 40 ± 12 g/kg of Fe and 7 ± 2 mg/kg of As, respectively. Yet the amounts of inorganic and organic constituents extracted were substantially different between riverbank and aquifer sediments. The water extracted 6.4 ± 16.1 mg/kg of Fe and 0.03 ± 0.02 mg/kg of As from riverbank sediments, compared to 154.0 ± 98.1 mg/kg of Fe and 0.55 ± 0.40 mg/kg of As from aquifer sediments. The riverbank and aquifer sands contained similar amounts of sedimentary organic matter (SOM) (17,705.2 ± 5157.6 mg/kg). However, the water-extractable fraction of SOM varied substantially, i.e., 67.4 ± 72.3 mg/kg in riverbank sands, and 1330.3 ± 226.6 mg/kg in aquifer sands. Detailed characterization showed that the riverbank SOM was protein-like, fresh, low molecular weight, and labile, whereas SOM in aquifer sands was humic-like, older, high molecular weight, and recalcitrant. During the dry season, oxic conditions in the riverbank may promote aerobic metabolisms, limiting As mobility within the NRB.
AB - Elevated dissolved arsenic (As) concentrations in the shallow aquifers of Bangladesh are primarily caused by microbially-mediated reduction of As-bearing iron (Fe) (oxy)hydroxides in organic matter (OM) rich, reducing environments. Along the Meghna River in Bangladesh, interactions between the river and groundwater within the hyporheic zone cause fluctuating redox conditions responsible for the formation of a Fe-rich natural reactive barrier (NRB) capable of sequestering As. To understand the NRB's impact on As mobility, the geochemistry of riverbank sediment (<3 m depth) and the underlying aquifer sediment (up to 37 m depth) was analyzed. A 24-hr sediment-water extraction experiment was performed to simulate interactions of these sediments with oxic river water. The sediment and the sediment-water extracts were analyzed for inorganic and organic chemical parameters. Results revealed no differences between the elemental composition of riverbank and aquifer sediments, which contained 40 ± 12 g/kg of Fe and 7 ± 2 mg/kg of As, respectively. Yet the amounts of inorganic and organic constituents extracted were substantially different between riverbank and aquifer sediments. The water extracted 6.4 ± 16.1 mg/kg of Fe and 0.03 ± 0.02 mg/kg of As from riverbank sediments, compared to 154.0 ± 98.1 mg/kg of Fe and 0.55 ± 0.40 mg/kg of As from aquifer sediments. The riverbank and aquifer sands contained similar amounts of sedimentary organic matter (SOM) (17,705.2 ± 5157.6 mg/kg). However, the water-extractable fraction of SOM varied substantially, i.e., 67.4 ± 72.3 mg/kg in riverbank sands, and 1330.3 ± 226.6 mg/kg in aquifer sands. Detailed characterization showed that the riverbank SOM was protein-like, fresh, low molecular weight, and labile, whereas SOM in aquifer sands was humic-like, older, high molecular weight, and recalcitrant. During the dry season, oxic conditions in the riverbank may promote aerobic metabolisms, limiting As mobility within the NRB.
KW - Arsenic
KW - Hyporheic zone
KW - Meghna river
KW - Organic matter
KW - Redox transition
UR - http://www.scopus.com/inward/record.url?scp=85138164805&partnerID=8YFLogxK
U2 - 10.1016/j.chemosphere.2022.136289
DO - 10.1016/j.chemosphere.2022.136289
M3 - Article
C2 - 36058378
AN - SCOPUS:85138164805
VL - 308
JO - Chemosphere
JF - Chemosphere
SN - 0045-6535
M1 - 136289
ER -
