4.3 Inundation Patterns and Diverse Habitat Structures as
a Driver of Complexity
Our use of ponded, overflow and free-flowing as the delineated
inundation types is based on known physical changes occurring as a
result of structural forcing through changes in channel morphology, the
presence of large wood, and increased beaver activity (Naiman, Johnston,
& Kelley, 1988; Johnson, Renik, Windels, & Hafs., 2018; Bartelt,
2021). Variable inundation types can be considered a direct metric of
habitat complexity, due to the habitat forming processes that accompany
changes in flow. Our conclusions are supported by the flood pulse
concept proposed by Junk, Bayley and Sparks (1989), wherein floodplains
are characterized as being periodically flooded by lateral overflow of
the main course of a river, forming a mosaic of lotic habitats that
consist of channels and lentic features, along with the seasonally
inundated floodplain (Girard, Fantin-Cruz, Loverde de Oliveira, &
Hamilton, 2010). Combined seasonal flood pulses and the spatially
variable physical structures they produce result in a spatiotemporally
variable mosaic of habitat-forming structures, flow paths and inundation
hydroperiods (Junk et al., 1989; Mertes, 1997; Poff et al. 1997). This
variability inherent to the flood pulse concept is a key driver of
ecological complexity that is often most apparent in the biotic and
abiotic responses of the surrounding ecosystem. We found this to be
especially prevalent in our riverscape, where a diverse distribution of
inundation types and complex geomorphic units throughout our target
reach of river support research that highlights the relationship between
inundation patterns, channel mobility and habitat diversity (e.g.,
Tiegs, O’Leary, Pohl, & Munill, 2005; Hohensinner Jungwirth, Muhar, &
Schmutz, 2014; Chone & Biron, 2016).
We considered substrate type as one potential metric of habitat
diversity in our analyses of wash, reference and boundary habitat based
on limited pebble count surveys. We observed that reference reaches
contained more diverse substrate types than boundary habitat; however,
we want to emphasize that our reach selection was limited by access in
an incredibly remote region of south-central Utah. As a result, we were
limited to reference reaches where access was often correlated with
factors in the surrounding landscape that often affect substrate in
these desert rivers (e.g., tributary junctions, anthropogenic structures
and proximity to the confluence with the Green River; Walsworth et al.,
2013), and these impacts likely had significant effects on channel
morphology, habitat condition and geomorphic complexity. We suggest that
the remainder of degraded habitat along the lower SRR, where these
factors are not as prevalent, would experience less diversity in
substrate type.