Quantifying and mapping inundation regimes within a large river‐floodplain ecosystem for ecological and management applications

Abstract

Spatial information on the distribution of ecosystem patterns and processes can be a critical component of designing and implementing effective management programs in river‐floodplain ecosystems. For example, translating how flood pulses detected within a stream gauge record are spatially manifested across a river‐valley bottom can be used to evaluate whether the current distribution of physical conditions has the potential to support priority habitats or if intervention is needed to meet desired goals. The size and complexity of large river‐floodplain systems can make mapping inundation dynamics a challenging task. We used a geospatial model to simulate 40 years (1972–2011) of daily surface‐water inundation depths for 11,331 km2 of the Upper Mississippi River System floodplain. We identified discrete inundation events at each 4‐m × 4‐m pixel in the model as sequential days of submergence. We then quantified and mapped four aspects of inundation regime – event frequency, duration, magnitude, and timing – for each pixel. The spatial distribution of inundation regime attributes varied within and among multiple levels of river organization, including navigation pools and geomorphic reaches, but only event timing exhibited a strong down‐river trend. Non‐linear relations among inundation attributes and their geospatial distributions likely reflect complex interactions among topographic, hydrologic, and anthropogenic constraints on flooding dynamics. Together, our results reveal spatial gradients in inundation dynamics not captured by hydrologic data alone. Characterizing such diversity in inundation dynamics is important for testing hypotheses about ecological processes, developing models of ecosystem functions, and informing management actions.

Aquatic vegetation types identified during early and late phases of vegetation recovery in the Upper Mississippi River

“…In the UMR, these ecological processes are likely affecting aquatic vegetation assemblages. As examples, inundation and flooding regimes are complex and spatially variable in this system (VanAppledorn et al, 2021), connectivity between the impounded area and the contiguous backwaters may buffer eutrophication and support diversity (Amoros & Bornette, 2002; Salgado et al, 2019), and biotic facilitation in the late phase of recovery may have buffered the effects of eutrophication on submersed plant diversity (LeBagousse‐Pinguet et al, 2012).…”

“…As an example, reinstating a natural flow regime and lost natural processes like gap formation in dammed rivers may provide heterogeneity needed for the full array of vegetation types (Keddy, 2017). These dynamic processes may be achieved in the UMR with water level management (Heglund et al, 2022) and other inundation regimes (VanAppledorn et al, 2021).…”

Low‐complexity floodplain inundation model performs well for ecological and management applications in a large river ecosystem

“…Our method for quantifying and mapping patterns of surface water inundation is based on the spatial intersection of a slope-detrended digital terrain model (DTM) and water surface elevations. To develop the DTM, we modified the height above nearest drainage (HAND) technique (Nobre et al, 2011(Nobre et al, , 2016Rennó et al, 2008;Rodda, 2005) to address the large, complex mosaic of impounded areas, backwater wetlands, secondary and tertiary channels, and navigation channel found in the UMRS as described in Van Appledorn, De Jager, et al (2021).…”

Drought responses in floodplain forests obtained by remotely sensed and tree‐ring data

“…Climatic and topographic variations within and among floodplains probably lead to varying manifestations of drought within and among floodplain forests. Minor topographic variations within floodplains affect hydrological and therefore ecological processes, including flooding (Van Appledorn et al, 2021) and soil moisture (Lemon, 2020). Heterogeneity in tree water availability might lead to variation in drought responses across floodplains, even for individuals of the same species.…”