Many marine phanerogam species are highly sensitive to changes in environmental conditions...

Many marine phanerogam species are highly sensitive to changes in environmental conditions. In the article “Posidonia oceanica: A biological indicator of past and present mercury contamination in the Mediterranean Sea” [Marine Environmental Research, 45 : 101 – 111], the researchers report the mercury concentrations over a period of about 20 years at several locations in the Mediterranean Sea. Samples of Posidonia oceanica were collected by scuba diving at a depth of 10m. For each site, 45 orthotropic shoots were sampled and the mercury concentration was determined. The average mercury concentration is recorded in the following table for each of the sampled years.

a. Generate a time series plot of the mercury concentrations and place lines for both sites on the same graph. Comment on any trends in the lines across the years of data. Are the trends similar for both sites?

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b. Select the most appropriate measure of center for the mercury concentrations. Compare the center for the two sites.

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c. When comparing the center and variability of the two sites, should the years 1969- 1972 be used for site 2?

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b. Which measure appears to best represent the center of the data?

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c. Calculate the range and standard deviation, s.

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d. Use the range approximation to estimates. How close is the approximation to the true Value?

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e. Construct the intervals

Count the number of demands between failures falling in each of the three intervals. Convert these numbers to percentages and compare your results to the Empirical Rule.

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f. Why do you think the Empirical Rule and your percentages do not match well?