Geomorphic Controls on Floodplain Connectivity, Ecosystem Services, and Sensitivity to Climate Change: An Example From the Lower Missouri River

• Published in: Water resources research Vol. 58; no. 6
• Main Authors: Jacobson, Robert B., Bouska, Kristen L., Bulliner, Edward A., Lindner, Garth A., Paukert, Craig P.
• Format: Journal Article
• Language: English
• Published: 01.06.2022
• Subjects: climate impacts; floodplain dynamics; geomorphology: fluvial; regional planning
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2021WR031204

Floodplains of large rivers are exploited for agricultural production, industrial and municipal development, and transportation infrastructure. Recently, increased frequency of costly floods has prompted consideration of whether offsetting benefits might accrue from management of floodplains for ecosystem services. We employed a simple inundation model for 800 km of the Lower Missouri River, USA, to evaluate spatial and temporal distributions of ecological floodplain inundation metrics and how those distributions might vary with levee removal and climatic change. The model evaluates inundation at 30 × 30 m resolution on a daily basis over 82 years of record. We quantified provisioning of waterfowl habitat and potential denitrification. Spatial variability is affected by ongoing geomorphic adjustments that affect floodplain connectivity. Statistical models indicate that available floodplain area and recent aggradation are predictive of most inundation metrics. Connectivity is sensitive to climate‐change scenarios that predict increased floodplain inundation during spring waterfowl migrations; the greatest sensitivity to future climate exists where channel‐floodplain geomorphology presently enhances floodplain connectivity. Evaluation of floodplain denitrification indicates that on average, the nonleveed part of the floodplain could denitrify 0.05%–1.7% of the mean annual nitrogen load of the river. Levee removal could increase this rate to only 3.6% of the nitrogen load. The capacity of floodplain connectivity to influence certain ecosystem services is highly variable in space along the Lower Missouri River and may be appreciably influenced by climate change. Hence, decisions to optimize management of large‐river floodplains are likely to be highly location dependent. Plain Language Summary Increased flooding on large, highly engineered rivers has prompted reconsideration of how to increase resiliency to flooding while also increasing net socioeconomic benefits. These concerns have prompted managers to consider how ecosystem services—such as provision of wildlife habitat or nutrient processing—may contribute to bottom‐line decisions about levee system designs. On the Lower Missouri River, USA, ongoing erosion and deposition along the channel exert a strong control on flooding patterns. Recognition of where and when floodplain areas flood, and a full accounting of costs and benefits of flooding, can be a useful component of floodplain management, especially when flooding potential varies substantially along the river. Key Points Resiliency of large‐river floodplains to floods can be highly spatially variable, dependent on geomorphic channel adjustments Floodplain habitat for waterfowl increases significantly in areas of decreased channel conveyance and increased floodplain area Denitrification potential, on average, is only 3.6% of N flux, showing that nutrient mitigation strategies in the floodplain are limited