Koontz, J., D.G. Huggins, C.C. Freeman, D.S. Baker - Central Plains ...

CDF
100
90
80
70
60
50
40
30
20
10
0
0 1 2 3 4 5 6 7
atrazine µg/L
Figure 37. Cumulative distribution frequency (CDF) of atrazine of in reference (Phase I) and
random (Phase II) populations.
Resampled sites
Four sites were resampled from Phase I (2005) and Phase II (2008); only three have all tiers of
assessment data. Forney Lake, which lies in the Western Corn Belt Plains, was completely
drained during summer 2005 when this area experienced drought conditions. Only disturbance
assessments and FQA data were obtained there. The disturbance assessment score for 2005 and
2008 were very similar, 12 and 13 respectively. FQI was 12.02 in 2005 and 16.26 in 2008.
Richness values in 2005 (40 all plants, 32 native plants) were considerably higher than in 2008
(18 for both). The dramatic difference in the scores is undoubtedly a consequence of the
hydrological disturbance of drought and deluge, which promotes changes in plant community
diversity. In 2005 there was only one hydrophyte species reported; there were six in 2008. The
most dramatic shift in plant community structure was seen in the number of therophytes
(annuals) present, which dropped from 20 in 2005 to one in 2008. Manipulation of wetland
water level has been one of the most endearing best management practices for maintaining
wetland floristic quality (Mitsch and Gooselink 2008).
The other three sites are located in the Central Irregular Plains ecoregion and all three assessment
tiers were accomplished during both survey phases. Swan Lake is a lacustrine, unconsolidated
bed wetland type. There were noticeable differences in floristic and water quality as well as
macroinvertebrate MMI scores. Though there are differences in the disturbance assessment
scores, the difference is limited considering that scoring was reported by a different evaluator
each year. In 2005 the disturbance assessment score was 12; in 2008 it was 14, with the most
changes occurring in the hydrological attributes section – a section that be expected to change
somewhat due to differing climatic conditions. Floristic quality assessments and
macroinvertebrate metric indices indicated that this site had become more degraded in overall
quality over the three-year period. Water chemistry measures show a trend in higher
concentrations of nutrients and lower pesticide concentrations in the 2005 sampling season. It is
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Phase One
Phase Two