Peter S. K. Knappett

Peter S. K. Knappett
Texas A&M University | TAMU · Department of Geology and Geophysics

PhD, MASc, BSc

About

103
Publications
13,108
Reads
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1,513
Citations
Citations since 2017
57 Research Items
1107 Citations
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Introduction
I study movement of water across interfaces between rivers and aquifers, and aquifers and aquifers. Water is chemically or biologically transformed as it passes from one reservoir to the next. These transformations can become important when they concentrate toxic metals, pathogens or nutrients in drinking water aquifers and rivers. The rate and degree of these transformations can be understood through studying the physical, chemical and biological processes occurring across those interfaces.
Additional affiliations
August 2013 - present
Texas A&M University
Position
  • Professor (Associate)
January 2012 - June 2013
Columbia University
Position
  • Vulnerability of Deep Aquifers to Arsenic Migration
Description
  • arsenic, aquifers, Bangladesh, tubewells
January 2012 - July 2013
Lamont - Doherty Earth Observatory Columbia University
Position
  • Research Associate
Education
January 2006 - April 2010
University of Tennessee
Field of study
  • Geology

Publications

Publications (103)
Article
Full-text available
Shallow, anoxic aquifers within the Ganges–Brahmaputra–Meghna Delta (GBMD) commonly contain elevated concentrations of arsenic (As), iron (Fe) and manganese (Mn). Highly enriched solid-phase concentrations of these elements have been observed within sediments lining the banks of the Meghna River. This zone has been described as a Natural Reactive B...
Article
This study identifies causes of rising arsenic (As) concentrations over 17 years in an inter-montane aquifer system located within the Trans-Mexican-Volcanic-Belt that is extensively developed by long-screened production wells. Arsenic concentrations increased by more than 10 µg/L in 14 % (3/22) of re-sampled wells. Similarly, in a larger scale ana...
Article
Full-text available
In semiarid agricultural regions, aquifers have watered widespread economic development. Falling water tables, however, drive up energy costs and can make the water toxic for human consumption. The study area is located in central Mexico, where arsenic and fluoride are widely present at toxic concentrations in well water. We simulated the holistic...
Article
Full-text available
Semi-arid regions with little surface water commonly experience rapid water table decline rates. To hedge against the falling water table, production wells in central Mexico are commonly installed to depths of several hundred meters below the present water table and constructed as open boreholes or perforated casings across their entire length. Suc...
Article
U/²³⁸U activity ratios and uranium concentrations were measured over a 6-month period in the Brazos River watershed along the Brazos River Alluvial Aquifer to determine the proportion of variable sources supplied to the Brazos River. Results indicate that lithology within the Brazos River watershed substantially impacts uranium isotope systematics...
Article
Full-text available
Nearly half of the world's urban population depends on aquifers for drinking water. These are increasingly vulnerable to pollution and overexploitation. Besides anthropogenic sources, pollutants such as arsenic (As) are also geogenic and their concentrations have, in some cases, been increased by groundwater pumping. Almost 40 % of Mexico's populat...
Article
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 f...
Article
Full-text available
Shallow (<30 m) reducing groundwater commonly contains abundant dissolved arsenic (As) in Bangladesh. We hypothesize that dissolved As in iron (Fe)-rich groundwater discharging to rivers is trapped onto Fe(III)-oxyhydroxides which precipitate in shallow riverbank sediments under the influence of tidal fluctuations. Therefore, the goal of this study...
Cover Page
Full-text available
Behind every human exposure to geogenic contaminants in drinking water or soil are a natural environmental process and a social pathway. Social pathways may include economic constraints, cultural beliefs and practices. These pathways may be forged by enticements of the convenience of cheap, good tasting, shallow groundwater, or affordable land. The...
Article
Hydrochemical and mineralogical analyses were performed to identify the main processes that contribute to the concentration of total inorganic arsenic (iAs) in groundwater within the northern portion of the Laguna Seca aquifer in Guanajuato State, Mexico. The spatial extent of the study area spans across a large graben with pore-waters that contain...
Article
This study simulates the dynamics of exchange fluxes between Brazos River Alluvium Aquifer and the Brazos River, TX, USA. Seven conceptual models for the connection between the river and the aquifer were simulated in HYDRUS 2D using small‐scale, high‐resolution transects across the river. These models assumed varying aquifer lithology and river inc...
Preprint
This study characterizes the dynamics of exchange fluxes between Brazos River Alluvium Aquifer and the Brazos River, TX, USA. Seven alternative conceptual models for the connection between the river and the aquifer were simulated in HYDRUS 2D using small-scale, high-resolution transects across the river. These models assumed varying aquifer litholo...
Article
Full-text available
This note introduces the estimation of aquifer diffusivity (D) through simultaneous inversion of the attenuation and lag of multiple head fluctuation frequencies due to a dynamic source or boundary, that is, a river. Spectral analysis, with optimized moving time window length and step size, was used to extract the dominant constituents and their at...
Article
The impacts of long-term pumping on groundwater flow patterns and groundwater chemistry are unclear in the Manas River Basin, an arid inland basin in Northwest China. In this study, hydraulic heads, hydrochemistry and environmental isotopic tracers were analyzed to reveal groundwater flow patterns, recharge sources and deduce hydrogeochemical proce...
Article
High fluoride (F− ) concentrations in groundwater are a recognized environmental health concern, and over 200 million people around the world routinely drink well water with F− concentrations that exceed safety guidelines. Groundwater in the Independence Basin of Central Mexico reaches F− concentrations of 15.5 mg L− 1, which are over an order of m...
Article
This paper underscores the importance of spatially dense geophysical data sets for making informed decisions in water management strategies. Such decisions may require understanding how site‐specific subsurface architecture – especially hydraulic connectivity – impacts the response of a shallow aquifer to anthropogenic hydrologic disturbances (e.g....
Presentation
Geologically sourced arsenic (As) commonly contaminates pore-waters of shallow (<50 m) alluvial aquifers across deltas in south Asia. Consumption of As from drinking water causes chronic health problems, learning disabilities, and early mortality through a host of diseases. This shallow groundwater flows towards low-lying rivers. Within riverbanks,...
Conference Paper
Elevated concentrations of arsenic (As) in groundwater pose serious health concerns, affecting millions of people globally. Shallow aquifer sediments enriched with Fe-oxy(hydroxides) have been shown to release adsorbed As under reducing conditions. Recent studies have suggested that the mixing of oxic river water and reduced groundwater with ambien...
Article
Full-text available
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 perturb...
Article
Full-text available
Over the past decades, groundwater quality has deteriorated worldwide by nitrate pollution due to the intensive use of fertilizers in agriculture, release of untreated urban sewage and industrial wastewater, and atmospheric deposition. Likewise, groundwater is increasingly polluted by sulfate due to the release of domestic, municipal and industrial...
Article
Full-text available
Confining clay layers typically protect groundwater aquifers against downward intrusion of contaminants. In the context of groundwater arsenic in Bangladesh, we challenge this notion here by showing that organic carbon drawn from a clay layer into a low-arsenic pre-Holocene (>12 kyr-old) aquifer promotes the reductive dissolution of iron oxides and...
Article
Full-text available
The Allende–Piedras Negras (APN) aquifer is located between the states of Texas (United States [U.S.]) and Coahuila (Mexico). The Rio Grande crosses the aquifer, acting as a natural and political divide between the countries. However, it remains unclear whether the APN aquifer can be considered a truly transboundary aquifer flow system, which would...
Article
Full-text available
Highlights: Areas with accelerating drawdown can be utilized to identify unregistered wells. Forecasting future water-table change is possible with annual measurements. Groundwater availability is indirectly influenced by La Niña and El Niño phenomena. Water-table velocity and acceleration maps are useful for water resource management. ABSTRACT...
Conference Paper
Full-text available
Groundwater is the main source of drinking water in Bangladesh where the shallow alluvial aquifers (<50 m) typically have toxic concentrations of geogenic arsenic (As). The Meghna River, one of the main rivers in the country, gains water from these aquifers for most of the year, but As concentrations in the river are near detection limit. In additi...
Conference Paper
Full-text available
The distribution of arsenic (As) and its release mechanisms in sedimentary aquifers have been studied for several decades. Complex hydrogeology, redox biogeochemistry and presence of dissolved organic matter (DOM) in the aquifers appear to control As oxyanion release. Currently, reductive dissolution of As-bearing iron minerals by the bacteria fuel...
Article
The impacts of long‐term pumping on groundwater chemistry remain unclear in the Manas River Basin, Northwest China. In this study, major ions within five surface water and 105 groundwater samples were analyzed to identify hydrogeochemical processes affecting groundwater composition and evolution along the regional‐scale groundwater flow paths using...
Article
Full-text available
Fluoride (F), naturally found in aquifers around the world at toxic concentrations, causes disease in millions of people. The long-term stability, however, of those concentrations within intensively pumped aquifers is poorly characterized. We assessed long-term stability in the spatial distribution of F concentrations in an intensively pumped aquif...
Article
The transition area between rivers and their adjacent riparian aquifers, which partly comprise the hyporheic zone, hosts important biochemical reactions which control water quality in these areas. The rates of these reactions and metabolic processes are temperature‐dependent. Yet, the thermal dynamics of riparian aquifers, especially during floodin...
Article
Past studies modeling stream-aquifer interaction commonly account for vertical anisotropy in hydraulic conductivity, but rarely address horizontal anisotropy, which may exist in certain sedimentary environments. If present, horizontal anisotropy will greatly impact stream depletion and the amount of recharge a pumped aquifer captures from the river...
Article
Full-text available
As water grows scarcer in semi-arid and arid regions around the world, new tools are needed to quantify fluxes of water and chemicals between aquifers and rivers. In this study we quantify the volumetric flux of subsurface water to a 24 km reach of the Brazos River, a lowland river that meanders through the Brazos River Alluvium Aquifer (BRAA), wit...
Conference Paper
Elevated levels of dissolved arsenic (As), iron (Fe) and manganese (Mn) are seen in the shallow groundwaters of southeast Bangladesh on the Ganges Brahmaputra Meghna River delta. This study takes a multi disciplinary approach to understand the extent of the natural reactive barrier (NRB) along the Meghna River and evaluate the role of the NRB in As...
Article
Microbial communities are the driving force behind the degradation of contaminants like aromatic hydrocarbons in groundwater ecosystems. However, little is known about the response of native microbial communities to contamination in pristine environments as well as their potential to recover from a contamination event. Here, we used an indoor aquif...
Article
Hyporheic exchange induced by periodic river fluctuations leads to important biogeochemical processes, particularly nitrogen cycling, in riparian zones (RZs) where chemically distinct surface water and groundwater mix. We developed a two-dimensional coupled flow, reactive transport model to study the role of bank storage induced by river fluctuatio...
Article
Oceanic tidal fluctuations which propagate long distances up coastal rivers can be exploited to constrain hydraulic properties of riverbank aquifers. These estimates, however, may be sensitive to degree of aquifer confinement and aquifer anisotropy. We analyzed the hydraulic properties of a tidally influenced aquifer along the Meghna River in Bangl...
Article
Full-text available
Many of the world's megacities depend on groundwater from geologically complex aquifers that are over-exploited and threatened by contamination. Here, using the example of Dhaka, Bangladesh, we illustrate how interactions between aquifer heterogeneity and groundwater exploitation jeopardize groundwater resources regionally. Groundwater pumping in D...
Data
Supplementary Figures 1-17, Supplementary Tables 1-2
Article
Full-text available
One of the mainstays of mitigation to reduce the exposure of the rural population of Bangladesh to arsenic (As) from private, mostly <90-m deep wells over the past 15 years has been the installation of over 300,000 deeper community wells. A comprehensive testing campaign previously conducted across a 180 km(2) of area of Bangladesh identified 9 out...
Article
Periodic releases from an upstream dam cause rapid stage fluctuations in the Lower Colorado River near Austin, Texas, USA. These daily pulses modulate fluid exchange and residence times in the hyporheic zone where biogeochemical reactions are typically pronounced. The effects of a small flood pulse under low-flow conditions on surface-water/groundw...
Conference Paper
The elevated dissolved fluoride and arsenic concentrations in the Independence Aquifer located in the central plains of Mexico in the state of Guanajuato, bounded by the three Sierras acting as a natural boundary to the recharge zones to the aquifer, is a point of concern for its inhabitants. The high relief of the Sierra Santa Barbara, El Cubo and...
Article
Full-text available
The contamination of drinking water from both arsenic and microbial pathogens occurs in Bangladesh. A general metagenomic survey of well water and surface water provided information on the types of pathogens present and may help elucidate arsenic metabolic pathways and potential assay targets for monitoring surface-to-ground water pathogen transpor...
Conference Paper
Groundwater pumping beneath Dhaka, a mega-city in Bangladesh, has created an extensive drawdown cone. Outside the city, shallow groundwater is often contaminated with dangerous concentrations of arsenic (As) and deep groundwater is considered a reliable source of As-safe drinking water. Unfortunately, vertical head gradients induced by Dhaka pumpin...
Conference Paper
Full-text available
Deep aquifers (>100m) are increasingly relied upon for arsenic free drinking water in rural Bangladesh. The long term sustainability of this drinking water source is in question due to the massive depressurization by urban pumping. In places where confining clay layers are absent deep aquifer depressurization will draw young water into the deep aqu...
Article
The injection of a mixed toluene and D2O (conservative tracer) pulse into a pristine mesoscale aquifer enabled a first direct experimental comparison of contaminant-specific isotopic fractionation from sorption versus biodegradation and transverse dispersion on a relevant scale. Water samples were taken from two vertically resolved sampling ports a...