@article {2705,
	title = {Origin of Groundwater Arsenic in a Rural Pleistocene Aquifer in Bangladesh Depressurized by Distal Municipal Pumping},
	journal = {Water Resources Research},
	volume = {56},
	year = {2020},
	month = {Jan-07-2020},
	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{\textendash}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.},
	keywords = {Arsenic, Dhaka Bangladesh, groundwater pumping, modeling},
	issn = {0043-1397},
	doi = {10.1029/2020WR027178},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020WR027178},
	author = {Mozumder, M. R. H. and Michael, H. A. and Mihajlov, I. and Khan, M. R. and Knappett, P. S. K. and Bostick, B. C. and Mailloux, B. J. and Ahmed, K. M. and Choudhury, I. and Koffman, T. and Ellis, T. and Whaley-Martin, K. and San Pedro, R. and Slater, G. and Stute, M. and Schlosser, P. and Geen, A.}
}
@article {346,
	title = {Constraining carbon sources and growth rates of freshwater microbialites in Pavilion Lake using 14C analysis},
	journal = {Geobiology},
	volume = {7},
	year = {2009},
	note = {id: 2055; PT: J; UT: WOS:000271633500006},
	pages = {544-555},
	abstract = {This study determined the natural abundance isotopic compositions (13C, 14C) of the primary carbon pools and microbial communities associated with modern freshwater microbialites located in Pavilion Lake, British Columbia, Canada. The Delta 14C of dissolved inorganic carbon (DIC) was constant throughout the water column and consistent with a primarily atmospheric source. Observed depletions in DIC 14C values compared with atmospheric CO(2) indicated effects due either to DIC residence time and/or inputs of 14C-depleted groundwater. Mass balance comparisons of local and regional groundwater indicate that groundwater DIC could contribute a maximum of 9-13\% of the DIC. 14C analysis of microbial phospholipid fatty acids from microbialite communities had Delta 14C values comparable with lake water DIC, demonstrating that lake water DIC was their primary carbon source. Microbialite carbonate was also primarily derived from DIC. However, some depletion in microbialite carbonate 14C relative to lake water DIC occurred, due either to residence time or mixing with a 14C-depleted carbon source. A detrital branch covered with microbialite growth was used to estimate a microbialite growth rate of 0.05 mm year-1 for the past 1000 years, faster than previous estimates for this system. These results demonstrate that the microbialites are actively growing and that the primary carbon source for both microbial communities and recent carbonate is DIC originating from the atmosphere. While these data cannot conclusively differentiate between abiotic and biotic formation mechanisms, the evidence for minor inputs of groundwater-derived DIC is consistent with the previously hypothesized biological origin of the Pavilion Lake microbialites.},
	issn = {1472-4677},
	doi = {10.1111/j.1472-4669.2009.00215.x},
	author = {Brady, A. L. and Slater, G. and Laval, B. and Lim, D. S.}
}
