Report on Stream X, Pre- and Post- Valley Fill. Date: Nov 2010

In June 2010, valley fill operations were undertaken just above stream X. We compared macroinvert samples from November 2009 ('pristine') and Nov 2010 ('valley fill') to determine the effect of valley fill on stream habitat.

Richness decreased from 18 to 9, showing that there is much less range of habitat in the valley fill site.

Percent dominance increased slightly, from 38 to 43%. Likewise, Simpson's Dominance Index rose from 0.18 to 0.26. Most importantly, the dominant species shifted from the intolerant baetid mayfly to the super-tolerant blackfly, indicating a decline in habitat quality.

Percent %EPT fell from 61 to 33%, confirming a decline in habitat quality and suggesting poor habitat for fish. Eight of the 11 EPT taxa at the pristine site were lost after valley fill, and no new EPT taxa were gained. Meanwhile, aquatic worms, which are very pollution tolerant, were found only after valley fill. Finally, while we found only 25 blackfly, chironomid, and mosquito larvae at the pristine site, we found 154 after valley fill.

To conclude, valley fill appears to have reduced the range of habitat available, and species found after valley are consistent with de-oxygenated, muddy, and polluted water.