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.