INTERPRETATION OF SITE SUMMARIES

The intention of the site summary section is to give a quick overview of the state of any particular site. The reader can refer to the text of the report for more complete details.

Each Site Summary page summarizes information on a specific site - either a near shore, off shore, or watershed site. Three kinds of information are presented: Information about actual values, information about the relative rank of that actual value in relation to all other measurements taken at same type of site (near shore, off shore, or watershed), and information about how that actual value compares to critical values for that substance.

Actual Values
Measurements of several dozen different substances and characteristics of water and sediment are presented. These measurements are grouped together in charts (i.e., all sediment chemistry measurements are charted together). Some sites have more charts than other sites, because not all tests were conducted at all sites. All charts are bar charts, and the actual numerical value of each substance or characteristic measured appears above its bar. See the "key" page following this page for information about the abbreviations used and units for the numerical values.

Z Scores
Measurements are given both as actual measured values and as "z scores". Z scores demonstrate the relation of any particular measurement to all others of the same type or class, telling us whether a particular measurement is close to the average for such measurements or far away from the average. An average measurement would always have a z score of 0 (zero). A measurement that was above the average would always have a positive z score (i.e., its bar will extend above the line), while a measurement that was below the average would always have a negative z-score (i.e., its bar will extend below the line). A measurement with a z score of +1 or -1 is greater than or less than two-thirds of all other measurements of that type. A measurement with a z score of +2 or -2 is greater than or less than 95% of all other measurements of that type. And a measurement with a z score of +3 or -3 is greater than or less than 99% of all other measurements in its class.

Colors
There are published standards that we are calling "critical values" for some kinds of measures, but not all. Actual values for measurements taken in water and sediment should not exceed the critical values where these exist. When a bar is colored red, that measurement exceeds the critical value. When a bar is colored green, that measurement does not exceed the critical value. When a bar is colored gray, there is no published critical value for that sort of measurement.

Example
In the 2003 site summary, for the Milk River (near shore site n1), the E. coli actual concentration value is displayed above the bar as 80.6 CFU/100 mL. The bar extends above the line, and the z score of that actual value is more than +3, indicating that site n1 has an E. coli concentration higher than 99% of the near shore sample sites. However, the color of the bar is green, indicating that the critical value for E. coli (130 CFU/100 mL) has not been exceeded at site n1.

Site Summaries

Back To Top