TY - JOUR
T1 - Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater
AU - Mailloux, Brian J.
AU - Trembath-Reichert, Elizabeth
AU - Cheung, Jennifer
AU - Watson, Marlena
AU - Stute, Martin
AU - Freyer, Greg A.
AU - Ferguson, Andrew S.
AU - Ahmed, Kazi Matin
AU - Alam, Md Jahangir
AU - Buchholz, Bruce A.
AU - Thomas, James
AU - Layton, Alice C.
AU - Zheng, Yan
AU - Bostick, Benjamin C.
AU - Van Geen, Alexander
PY - 2013/4/2
Y1 - 2013/4/2
N2 - Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC driving this microbial reduction-carbon deposited with the sediments or exogenous carbon transported by groundwater- is still debated despite its importance in regulating aquifer redox status and groundwater As levels. Here, we used the radiocarbon (14C) signature of microbial DNA isolated from groundwater samples to determine the relative importance of surface and sediment- derived OC. Three DNA samples collected from the shallow, high-As aquifer and one sample fromthe underlying, low-As aquifer were consistently younger than the total sediment carbon, by as much as several thousand years. This difference and the dominance of heterotrophic microorganisms implies that younger, surface-derived OC is advected within the aquifer, albeit more slowly than groundwater, and represents a critical pool of OC for aquifer microbial communities. The vertical profile shows that downward transport of dissolved OC is occurring on anthropogenic timescales, but bomb 14C-labeled dissolved OC has not yet accumulated in DNA and is not fueling reduction. These results indicate that advected OC controls aquifer redox status and confirm that As release is a natural process that predates human perturbations to groundwater flow. Anthropogenic perturbations, however, could affect groundwater redox conditions and As levels in the future.
AB - Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC driving this microbial reduction-carbon deposited with the sediments or exogenous carbon transported by groundwater- is still debated despite its importance in regulating aquifer redox status and groundwater As levels. Here, we used the radiocarbon (14C) signature of microbial DNA isolated from groundwater samples to determine the relative importance of surface and sediment- derived OC. Three DNA samples collected from the shallow, high-As aquifer and one sample fromthe underlying, low-As aquifer were consistently younger than the total sediment carbon, by as much as several thousand years. This difference and the dominance of heterotrophic microorganisms implies that younger, surface-derived OC is advected within the aquifer, albeit more slowly than groundwater, and represents a critical pool of OC for aquifer microbial communities. The vertical profile shows that downward transport of dissolved OC is occurring on anthropogenic timescales, but bomb 14C-labeled dissolved OC has not yet accumulated in DNA and is not fueling reduction. These results indicate that advected OC controls aquifer redox status and confirm that As release is a natural process that predates human perturbations to groundwater flow. Anthropogenic perturbations, however, could affect groundwater redox conditions and As levels in the future.
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U2 - 10.1073/pnas.1213141110
DO - 10.1073/pnas.1213141110
M3 - Article
C2 - 23487743
AN - SCOPUS:84875833264
SN - 0027-8424
VL - 110
SP - 5331
EP - 5335
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 14
ER -