MULTIVARIATE TREND TESTING OF LAKE WATER QUALITY<sup>1</sup>

Loftis, Jim C.; Taylor, Charles H.; Newell, Avis D.; Chapman, Phillip L.

doi:10.1111/j.1752-1688.1991.tb01446.x

Cited by 34 publications

(17 citation statements)

References 9 publications

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“…For trend analyses, Seasonal Kendall with Covariance Inversion for correction of serial correlation, described by Loftis et al (1991) was used to test the significance of trends. This non-parametric method was used since the data were autocorrelated in time with a strong seasonal variation.…”

Section: Methodsmentioning

confidence: 99%

Increasing concentrations of arsenic and vanadium in (southern) Swedish streams

Wällstedt

Björkvald

Gustafsson

2010

Applied Geochemistry

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The aim of this study was to investigate temporal trends and controlling factors of As and V in running waters throughout Sweden. For this purpose, data on stream water chemistry from 62 streams of varying catchment size and characteristics, included in the Swedish environmental monitoring programmes were evaluated. The geochemical software Visual MINTEQ was used to model the speciation and trend analyses were performed on total concentrations of As and V as well as modelled fractions (dissolved species as well as arsenate and vanadate adsorbed to ferrihydrite). The trend analyses showed increasing total concentrations of As and V in southern Sweden. Concentrations of As and V correlated significantly to Fe concentrations in 59 and 60 of the 62 streams respectively, indicating that Fe is an important determining factor for As and V concentrations in Swedish streams. This was confirmed by the geochemical modelling that indicated that the adsorbed fraction is the dominant form of As and V and that the concentrations of As and V in Swedish streams are thus highly determined by concentrations of colloidal or particulate Fe. It is therefore suggested that the increasing trends of As and V are to a large extent due to increasing concentrations of colloidal Fe, which is stabilised by increasing concentrations of DOC. Further the geochemical modelling indicates that the dissolved fraction of As and V generally is small, with the exception of a few streams with high pH and/or phosphate concentrations.

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Section: Methodsmentioning

confidence: 99%

Increasing concentrations of arsenic and vanadium in (southern) Swedish streams

Wällstedt

Björkvald

Gustafsson

2010

Applied Geochemistry

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“…An advantage of the Dietz-Killeen method is that it is unaffected by the directions of the individual univariate trends, up or down. Use of multivariate methods "controls the overall significance level" and there were very few cases in a study of lake water quality "where the univariate methods perform better" (Loftis et al 1991b). Dietz and Killeen (1981) also note that their multivariate test was able to reject H when separate univariate …”

Section: Commentsmentioning

confidence: 99%

“…(after Loftis et al 1991b) Table 10 shows selected output from a computer program (in R) applied to the cod indices, ages 1 to 6, for 1983 to 2004: the Mann-Kendall statistics (K); their covariances (V), and the Spearman rank correlations of the observed values. The highest correlations occur among the older age groups.…”

Section: Dietz and Killeen Test For Multivariate Monotone Trendmentioning

confidence: 99%

A selection of nonparametric statistical methods for assessing trends in trawl survey indicators as part of an ecosystem approach to fisheries management (EAFM)

Cotter

2009

Aquat. Living Resour.

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-A selection of ten uni-and multivariate, nonparametric statistical methods thought to be useful for assessing trends in indicators estimated from trawl surveys is described. Nonparametric methods make minimal assumptions about the data and can therefore be suitable when parametric modelling methods, as typically preferred by fisheries scientists, are not suitable. The various methods described are sensitive to a variety of specific features of a trend thereby allowing many different forms of variation over time to be identified, e.g. changes in level, sloping straight or curved lines, and differing cyclicities. In contrast, model-based investigations can be constrained in this regard if the single model which is adopted and fitted to the trend is a simplification of its form.

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“…Multivariate tests also control the overall Type I error rate. Descriptions and comparisons of multivariate hypothesis tests can be found in Loftis et al 55 …”

Section: % Significant Detectionsmentioning

confidence: 99%