Figure 4.3: Summary data for dissolved oxygen and visual clarity from the NRWQN over a 17-year period (1989-2005)
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Note: Lines, from bottom to top, correspond to values of the 5th, 20th, 50th, 80th and 95th percentiles for each year (n of sites = 77).
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This figure shows dissolved oxygen and visual clarity trends. Median dissolved oxygen figures are stable over the 1989-2005 time period. Most fluctuation is observed in the poorly oxygenated rivers. Clarity values tended to show weak positive correlations with time with a significant improving trend for the 20th percentile.
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