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

major wetland classes when ANOVA and Tukey-Kramer tests were performed using wetland
surface area as a factor. However, size significantly differed between lacustrine and both
palustrine and riverine sites as indicated by Kruskal-Wallace non-parametric analysis and Z tests
(p = 0.006). When area (acres) was placed in a Pearson correlation matrix, it was found to
correlate positively with orthophosphate (PO4), total phosphorus, and atrazine concentrations
with all relationships being significant (p = 0.05). When robust linear regression analysis was
performed, the relationships between area and both PO4 and total phosphorus concentrations
were not significant and adjusted R 2 values were essentially zero. The relationship between area
and atrazine concentrations remained significant, but the amount of variance explained was small
(p = 0.013, R 2 = 0.10). Further analysis and discussion of the atrazine concentrations of the
wetland population will consider the significance of this relationship.
Depth to Flood
Depth to flood (DTF) was used as a surrogate for flood return period. The value of DTF was
calculated using the KARS floodplain model and defined as the river height above river channel
height needed to create a surface connection to the wetland either by backfill or sidespilling at
the topographically lowest wetland boundary (Kastens 2008). Kruskal-Wallace non-parametric
medians analysis revealed that the riverine class (n = 6) was significantly lower in depth to flood
than lacustrine (n = 21) or palustrine (n = 32) classes (p = 0.043, regular Z variables significant).
This should be expected given that riverine sites are either backwater channels or sloughs that
become connected with the Missouri River channel at much more frequent intervals than sites
more set back from the channel. ANOVA and Kruskal-Wallace tests revealed significant
differences in DTF between the sample populations within the Western Corn Belt Plains and the
Central Irregular Plains. The mean DTF value for the CIP wetlands was 7.81 while the WCB
wetland population had a mean value of 3.71. The Interior River Valleys and Hills sample
population (n = 5) had a mean DTF value of 4.72, which was not significantly different from
either the WCB or CIP wetland population values. The fact that DTF values positively
correlated with the linear distance from the Missouri River channel (R 2 = 0.91, p < 0.001)
reflects the fact that floodplain valley widens and contracts along its lower portion and that sites
within the CIP have greater distances of overland flow and significantly less connectivity with
the floodplain (Figure 22).
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