Treatment of nondetects in multivariate analysis of groundwater geochemistry data

Farnham, Irene; Singh, Ashok K.; Stetzenbach, Klaus J.; Johannesson, Karen H.

doi:10.1016/s0169-7439(01)00201-5

Cited by 204 publications

(95 citation statements)

References 17 publications

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“…Then, each concentration was normalized with the corresponding mean and standard deviation values to obtain equal weights in the analysis and to avoid bias by parameters showing highest concentrations (Davis, 1986). For speciation and PCA, concentrations below (77) c (31) r (28) i (58) 12.2 (6.9-25.9) 0 (0-1.5) s (7) c (5) r (5) i (4) (2) c (2) r (1) i (2) d (1) the DL were set to half of the DL (Farnham et al, 2002 , were estimated from the regional distribution observed in the present study, or from previous studies. Table 2 summarizes the descriptive statistics of analytical results for the 144 groundwater samples.…”

Section: Methodsmentioning

confidence: 99%

Groundwater Quality, Geochemical Processes and Groundwater Evolution in the Chateauguay River Watershed, Quebec, Canada

Blanchette¹,

Lefebvre²,

Nastev³

et al. 2010

Canadian Water Resources Journal

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A hydrogeochemical study was carried out in the Quebec portion of the Chateauguay River watershed. The objective was to characterize the chemical composition of groundwater in order to evaluate its quality and assess geochemical variations related to the geological and hydrogeological settings. Bulk groundwater samples were collected from 144 wells distributed evenly over the study area. Nine of the wells were sampled with a multi-level packer system, for a total of 22 multi-level samples. Groundwater shows a wide range of compositions as indicated by 12 water types defined on the basis of major ions with a weak variation of chemical composition with depth. The predominant water type, Ca-HCO 3 , occurs in most geological and hydrogeological settings. Principal Component Analysis (PCA) and geochemical graphs were used to identify the major processes that exert a control over the chemical composition of the groundwater. Approximately 80% of the geochemical variation can be explained by mixing between fresh recharge water with more saline water associated with the former Champlain Sea, which invaded the aquifer. Secondary processes are related to ion exchange and the potential dissolution of minerals. A cross-section along a major flow path shows that the geochemical evolution of groundwater leads to relations between water type groups, geochemical processes, and groundwater flow conditions. The hydrogeochemical conceptual model infers that carbonate dissolution during recharge leads to one end-member, a Ca-HCO 3 type water, which further evolves along its flow path due through ion exchange and mixing with remnant Champlain Sea water (Na-Cl), the other endmember. 504Canadian Water Resources Journal/Revue canadienne des ressources hydriques

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Section: Methodsmentioning

confidence: 99%

Groundwater Quality, Geochemical Processes and Groundwater Evolution in the Chateauguay River Watershed, Quebec, Canada

Blanchette¹,

Lefebvre²,

Nastev³

et al. 2010

Canadian Water Resources Journal

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“…All other statistical analyses of inorganic elements in environmental media were conducted on untransformed data. For correlation and regression analyses, the marker gene concentrations were assumed to be one-half the analytical detection limit when they were not detected (13,40). All box plots include (i) the 25th and 75th percentiles, represented by the ends of the boxes, (ii) the median, indicated by a horizontal line within the boxes, (iii) error bars defining the 10th and 90th percentiles, and (iv) outliers indicated by circles (if applicable).…”

Section: P(h\t) ϭ P(t\h)p(h) P(t\h)p(h) ϩ P(t\hј)p(hј)mentioning

confidence: 99%

Correlation of Quantitative PCR for a Poultry-Specific Brevibacterium Marker Gene with Bacterial and Chemical Indicators of Water Pollution in a Watershed Impacted by Land Application of Poultry Litter

Weidhaas¹,

Macbeth²,

Olsen³

et al. 2011

Appl Environ Microbiol

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The impact of fecal contamination from human and agricultural animal waste on water quality is a major public health concern. Identification of the dominant source(s) of fecal pollution in a watershed is necessary for assessing the safety of recreational water and protecting water resources. A field study was conducted using quantitative PCR (qPCR) for the 16S rRNA gene of Brevibacterium sp. LA35 to track feces-contaminated poultry litter in environmental samples. Based on sensitivity and specificity characteristics of the qPCR method, the Bayesian conditional probability that detection of the LA35 marker gene in a water sample represented a true-positive result was 93%. The marker's covariance with fecal indicator bacteria (FIB) and metals associated with poultry litter was also assessed in litter, runoff, surface water, and groundwater samples. LA35 was detected in water and soil samples collected throughout the watershed, and its concentration covaried with concentrations of Escherichia coli, enterococci, As, Cu, P, and Zn. Significantly greater concentrations of FIB, As, Cu, P, and Zn were observed in edge-of-field runoff samples in which LA35 was detected, compared to samples in which it was not detected. Furthermore, As, Cu, P, and Zn concentrations covaried in environmental samples in which LA35 was detected and typically did not in samples in which the marker gene was not detected. The covariance of the poultry-specific LA35 marker gene with these known contaminants from poultry feces provides further evidence that it is a useful tool for assessing the impact of poultry-derived fecal pollution in environmental waters.

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“…Co, Ni, As and Pb were below DLs in a small number of adult samples. One method of treating values generated by an element falling below DLs is to substitute them with a constant, such as 0.5 times the DL (Farnham et al 2002). Statistical analyses on the adult stylets were performed using both the original values and substituted values based on 0.5 times the DL (Pb = 0.008, Co = 0.006, Ni = 0.032, and As = 0.081); however, the results were the same (the latter are presented).…”

Section: Methodsmentioning

confidence: 99%

Stylet elemental signatures indicate population structure in a holobenthic octopus species, Octopus pallidus

Doubleday¹,

Pecl²,

Semmens³

et al. 2008

Mar. Ecol. Prog. Ser.

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Targeted trace elemental analysis was used to investigate the population structure and dispersal patterns of the holobenthic octopus species Octopus pallidus (Hoyle, 1885). Multi-elemental signatures within the pre-hatch region of the stylet (an internal 'shell') were used to determine the common origins and levels of connectivity of individuals collected from 5 locations in Tasmania. To determine whether hatchling elemental signatures could be used as tags for natal origin, hatchling stylets from 3 of the 5 locations were also analysed. We analyzed 12 elements using laser ablation inductively-coupled plasma-mass spectrometry (LA-ICPMS). Of the 12 elements, 7 were excellent spatial discriminators. There was evidence of high-level structuring with distinct groupings between all sites (the 2 closest being 85 km apart) within the adult O. pallidus population, suggesting that all adults had hatched in or near their respective collection sites. The hatchling signatures showed significant spatial variation, and a high percentage of individuals could successfully be traced back to their collection locations. However, they could not be used to trace adults back to their natal site, due to significant differences in element concentrations in hatchling and adult stylets, which was likely the result of differences in Ca concentration. This study presents the first insights into the population structure of a holobenthic octopus species using stylet elemental signatures, which will have important implications for the sustainable management of O. pallidus.

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Treatment of nondetects in multivariate analysis of groundwater geochemistry data

Cited by 204 publications

References 17 publications

Groundwater Quality, Geochemical Processes and Groundwater Evolution in the Chateauguay River Watershed, Quebec, Canada

Groundwater Quality, Geochemical Processes and Groundwater Evolution in the Chateauguay River Watershed, Quebec, Canada

Correlation of Quantitative PCR for a Poultry-Specific Brevibacterium Marker Gene with Bacterial and Chemical Indicators of Water Pollution in a Watershed Impacted by Land Application of Poultry Litter

Stylet elemental signatures indicate population structure in a holobenthic octopus species, Octopus pallidus

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