Effects of Flow Dynamics on the Aquatic‐terrestrial Transition Zone (Attz) of Lower Missouri River Sandbars With Implications for Selected Biota

Abstract

Sandbars are an important aquatic terrestrial transition zone (ATTZ) in the active channel of rivers that provide a variety of habitat conditions for riverine biota. Channelization and flow regulation in many large rivers have diminished sandbar habitats and their rehabilitation is a priority. We developed sandbar-specific models of discharge-area relationships to determine how changes in flow regime affect the area of different habitat types within the submerged sandbar ATTZ (depth) and exposed sandbar ATTZ (elevation) for a representative sample of Lower Missouri River sandbars. We defined six different structural habitat types within the sandbar ATTZ based on depth or exposed elevation ranges that are important to different biota during at least part of their annual cycle for either survival or reproduction. Scenarios included the modelled natural flow regime, current managed flow regime and two environmental flow options, all modelled within the contemporary river active channel. Thirteen point and wing-dike sandbars were evaluated under four different flow scenarios to explore the effects of flow regime on seasonal habitat availability for foraging of migratory shorebirds and wading birds, nesting of softshell turtles and nursery of riverine fishes. Managed flows provided more foraging habitat for shorebirds and wading birds and more nursery habitat for riverine fishes within the channelized reach sandbar ATTZ than the natural flow regime or modelled environmental flows. Reduced summer flows occurring under natural and environmental flow alternatives increased exposed sandbar nesting habitat for softshell turtle hatchling emergence. Results reveal how management of channelized and flow regulated large rivers could benefit from a modelling framework that couples hydrologic and geomorphic characteristics to predict habitat conditions for a variety of biota. Published in 2011 by John Wiley & Sons, Ltd.

Influence of Riparian and Watershed Alterations on Sandbars in a Great Plains River

“…Channelization structures also are intermittently present throughout the Kansas River, which constrict flow to a narrowed main channel (Pinter et al, 2010) and may reduce sediment availability and deposition through reducing lateral channel migration and artificially increasing bankfull stream power. Channelization structures may also create favourable hydraulic situations for the persistence of some sandbars (Tracy-Smith et al, 2012). Furthermore, the bend series with the greatest proportion of urban riparian cover were in the downstream-most sections of the river, which are also subject to dredging, channelization, and backwater from the Missouri River, which together may have confounded the influence of riparian urban cover.…”

“…Reduction of sandbar habitat in the Missouri River drainage has reduced nesting success of the federally threatened piping plover (Charadrius melodus) and the federally endangered least tern (Sterna albifons) (Kirsch, 1996;Stucker et al, 2012;Buenau et al, 2013). Sandbars are associated with increased heterogeneity in depths and water velocities, which may provide a nursery habitat for young fishes and increase biodiversity (Jacobson and Galat, 2006;Wyzga et al, 2009;Tracy-Smith et al, 2012). The federally endangered pallid sturgeon (Scaphirhynchus albus) and other native riverine fishes may select for river reaches with more sandbars, potentially because of enhanced feeding opportunities in complex channels (Bramblett and White, 2001;Eitzmann and Paukert, 2010a).…”

Flood Effects Provide Evidence of an Alternate Stable State from Dam Management on the Upper Missouri River

“…Flood pulses create a dynamic edge as the 'moving littoral', or shoreline, traverses the ATTZ with changing river stage. Tracy-Smith et al (2012) suggest that the ATTZ also includes the margins of islands and sandbars whose locations, areas and morphologies are constantly changing with the river's stage and sediment dynamics. These landforms are important for many species of turtles, fish and birds including Tern and Plover, which use the shoreline and delta deposits for habitat (Catlin et al, 2011).…”

“…In this study, we define shoals as locations where the elevation is between bankfull water level and minimum water level minus 0.9 m (3 ft; Figure 3). This elevation range was selected as it represents areas, which may experience different flow characteristics and ecologic function (Tracy-Smith et al, 2012). The shoal metric is calculated as the ratio of shoal width to the total width of the channel, representing the percentage of the river channel, which experiences shoal conditions.…”

“…In addition, the reduction in shoaling areas has implications for the in-channel ATTZ, which has ecological significance for riverine fauna. The 'moving littoral' along the channel margins, islands and sandbars, created by changing water levels, determines the disturbance regime of many riverine species including soft-shelled turtles, shorebirds, riverine fishes and fish-eating birds (Tracy-Smith et al, 2012).…”