Sources of Spatial‐temporal Variability in Groundwater Quality Data and Methods of Control

Keith, Susan J.; Wilson, L. G.; Fitch, H.R.; Esposito, David M.

doi:10.1111/j.1745-6592.1983.tb01196.x

Cited by 22 publications

(5 citation statements)

References 9 publications

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“…The limit of detection for flow cytometry has been reported at 100 to 1000 cells/mL (Vives‐Rego et al ) and this is more than an order of magnitude smaller than the bacterial and VLP abundances measured in this study indicating that the variability observed in microbial abundances is not likely to be due to the flow cytometry enumeration method. It is possible that the high levels of microbial heterogeneity could instead be an artifact of bore purging (for a fuller discussion see Keith et al ). For example, over pumping can cause excessive silt or clay fines to be drawn into the immediate vicinity of the well leading to colmation of sediment interstices, potentially altering the hydraulic conductivity and transportation of microbes through the aquifer.…”

Section: Discussionmentioning

confidence: 99%

Variability in Bacteria and Virus‐Like Particle Abundances During Purging of Unconfined Aquifers

et al. 2013

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Standard methodologies for sampling the physicochemical conditions of groundwater recommend purging a bore for three bore volumes to avoid sampling the stagnant water within a bore and instead gain samples representative of the aquifer. However, there are currently no methodological standards addressing the amount of purging required to gain representative biological samples to assess groundwater bacterial and viral abundances. The objective of this study was to examine how bacterial and viral abundances change during the purging of bore volumes. Six bores infiltrating into unconfined aquifers were pumped for five or six bore volumes each and bacteria and virus-like particles (VLPs) were enumerated from each bore volume using flow cytometry. In examination of the individual bores trends in bacterial abundances were observed to increase, decrease, or remain constant with each purged bore volume. Furthermore, triplicates taken at each bore volume indicated substantial variations in VLP and bacterial abundances that are often larger than the differences between bore volumes. This indicates a high level of small scale heterogeneity in microbial community abundance in groundwater samples, and we suggest that this may be an intrinsic feature of bore biology. The heterogeneity observed may be driven by bottom up processes (variability in the distribution of organic and inorganic nutrients), top-down processes (grazing and viral lysis), physical heterogeneities in the bore, or technical artifacts associated with the purging process. We suggest that a more detailed understanding of the ecology underpinning this variability is required to adequately describe the microbiological characteristics of groundwater ecosystems.

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Section: Discussionmentioning

confidence: 99%

Variability in Bacteria and Virus‐Like Particle Abundances During Purging of Unconfined Aquifers

et al. 2013

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“…While temporal variability was more limited than spatial variability in this study, temporal variability can still be inherent in high‐capacity wells. Past work has pointed to greater variability in the concentration of contaminants sampled from high‐capacity wells due to pumping rates (Gosselin et al., 1994; Keith et al., 1983; Nightingale & Bianchi, 1980).…”

Section: Discussionmentioning

confidence: 99%

“…While temporal variability was more limited than spatial variability in this study, temporal variability can still be inherent in high-capacity wells. Past work has pointed to greater variability in the concentration of contaminants sampled from high-capacity wells due to pumping rates (Gosselin et al, 1994;Keith et al, 1983;Nightingale & Bianchi, 1980). Spatial variability in N concentration may be explained by a range of factors not included in our study, such as direction of groundwater flow, depth to water table, variation in soil texture, age of well, localized weather, management strategies, and historical land use.…”

Section: Greater Variability In Nitrate Concentration Across Space Th...mentioning

confidence: 90%

Quantifying the spatiotemporal variability of nitrate in irrigation water across the Wisconsin Central Sands

Campbell,

Masarik,

Heineman

et al. 2023

J of Env Quality

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The Wisconsin Central Sands (WCS) is home to large scale vegetable production on sandy soils and managed with frequent irrigation, fertigation, and widespread nitrogen fertilizer application, all of which make the region highly susceptible to nitrate loss to groundwater. While the groundwater is used as the primary source of drinking water for many communities and rural residences across the region, it is also used for irrigation. Considering high levels of nitrate found in the groundwater, it has been proposed that growers more accurately account for the nitrate in their irrigation water as part of nitrogen management plans. Our objectives were to 1) determine the magnitude of nitrate in irrigation water, 2) quantify the spatiotemporal variability of nitrate, and 3) determine key predictors of nitrate concentration in the region. We sampled irrigation water from 38 fields across six farms from 2018–2020. Across the three years of our study, nitrate concentration varied more across space than time. On average, our samples tested at 19.0 mg L−1 nitrate‐nitrogen, or nearly two times the EPA threshold for safe drinking water, equivalent to 48.1 kg ha−1 of applied nitrate‐nitrogen with 25.4 cm (or 10 inches) of irrigation. To better understand the spatiotemporal variability in nitrate levels, week of sampling, year, well depth, well casing, and nitrogen application rate were analyzed for their role as predictor variables. Based on our linear mixed effects model, nitrogen application rate was the greatest predictor of the nitrate concentration of irrigation water (p < .05).This article is protected by copyright. All rights reserved

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“…Well construction practices, sampling techniques, and laboratory analyses are also documented sources of variability in ground water quality data (Barcelona et al 1989;Keith et al 1983;Wilson and Rouse 1983;Nightingale and Bianchi 1979), while other possible sources have been identified (Pettyjohn 1976). To overcome the artifact causes of spatial and temporal variability of data in ground water studies, investigators constructed pumps of inert material and inflatable packers, studied the sorptive characteristics of a variety of sampling materials, and developed low-flow sampling techniques (Puls and Barcelona 1996).…”

Section: Introductionmentioning

confidence: 99%

Design of an MTBE Remediation Technology Evaluation

Azadpour-Keeley¹,

Barcelona²

2006

Groundwater Monitoring Rem

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This study examines the intrinsic variability of dissolved methyl tert‐butyl ether (MTBE) concentrations in ground water during the course of a pilot‐scale bioremedial technology trial in Port Hueneme, California. A pretrial natural gradient tracer experiment using bromide was conducted in an anaerobic test section of the aquifer to characterize hydrogeology. The results showed the presence of a complex velocity field in terms of vertical stratification and preferential flowpaths. The hydraulic conductivity at the test area varied by >2 orders of magnitude, and the effects of vertical stratification were made apparent by the tracers’ detection pattern, which was predominately higher in the lower part of the aquifer. Since historically the lower portion of the aquifer significantly influenced MTBE transport, it was emphasized by increasing the sampling frequency for MTBE and tracers during the pilot test that involved the intermittent addition of oxygen and propane into the aquifer. A second tracer experiment using bromide and deuterated MTBE (2H12‐MTBE) was conducted at the onset of the technology trial and after the aquifer was made aerobic. The continuous metering of the tracer solutions into the test area was maintained for 300 d. The results showed that 2H12‐MTBE behaved as a conservative tracer since (1) its concentrations increased throughout the study approaching its designed injected level and (2) the pattern of its detection resembled that of bromide. On the other hand, 2H12‐MTBE, which was purposefully introduced into the aquifer, behaved differently from that of the existing dissolved MTBE plume that emanated from a non–aqueous phase liquid (NAPL) source over a decade ago, thereby undergoing years of diffusion. The data imply that a detailed understanding of the complexity of the flow field was not possible by observing the intrinsic MTBE data alone.

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Sources of Spatial‐temporal Variability in Groundwater Quality Data and Methods of Control

Cited by 22 publications

References 9 publications

Variability in Bacteria and Virus‐Like Particle Abundances During Purging of Unconfined Aquifers

Variability in Bacteria and Virus‐Like Particle Abundances During Purging of Unconfined Aquifers

Quantifying the spatiotemporal variability of nitrate in irrigation water across the Wisconsin Central Sands

Design of an MTBE Remediation Technology Evaluation

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