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Figure 8
Set-up:
Each bar in this graph represents the annual average for each year during 1996-2004. The years are identified along the bottom of the graph, while phosphorus is scaled on the left side in micrograms per liter (parts per billion). The horizontal line within the graph represents the overall average phosphorus value for this site (an average based on all data). Bars that extend above this line indicate years with higher than average phosphorus values, while bars that extend downward represent years with lower than average phosphorus. |
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Interpretation:
Annual average phosphorus concentrations for 1996-1999 were all above the overall average, ranging from 16 to 21 micrograms per liter. For the period 2002-2004 annual averages have been below the overall average, ranging from 11 to 14 micrograms per liter. While this decrease in phosphorus is relatively small, it is still statistically significant and suggests that there is a long-term trend for less phosphorus in the lower James River Arm of the lake.
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