Loss of Potential Aquatic-Terrestrial Subsidies Along the Missouri River Floodplain

Abstract

The floodplains of large rivers have been heavily modified due to riparian development and channel modifications, both of which can eliminate shallow off-channel habitats. The importance of these habitats for aquatic organisms like fishes is well studied. However, loss of off-channel habitat also eliminates habitats for the production of emerging aquatic insects, which subsidize riparian consumers in terrestrial food webs. We used field collections of insect emergence, historical mapping, and statistical modeling to estimate the loss of insect emergence due to channel modifications along eight segments of the Missouri River (USA), encompassing 1566 river km, between 1890 and 2012. We estimate annual production of emerging aquatic insects declined by a median of 36,000 kgC (95% CrI: 3000 to 450,000) between 1890 and 2012 (a 34% loss), due to the loss of surface area in backwaters and related off-channel habitats. Under a conservative assumption that riparian birds obtain 24% of their annual energy budget from adult aquatic insects, this amount of insect loss would be enough to subsidize approximately 790,000 riparian woodland birds during the breeding and nesting period (May to August; 95% CrI: 57,000 to 10,000,000). Most of the loss is concentrated in the lower reaches of the Missouri River, which historically had a wide floodplain, a meandering channel, and a high density of off-channel habitats, but which were substantially reduced due to channelization and bank stabilization. Our results indicate that the loss of off-channel habitats in large river floodplains has the potential to substantially affect energy availability for riparian insectivores, further demonstrating the importance of maintaining and restoring these habitats for linked aquatic-terrestrial ecosystems.

Metabolic Profiling and Integration of Metabolomic and Transcriptomic Data From Pectoralis Muscle Reveal Winter-Adaptive Metabolic Responses of Black-Capped Chickadee and American Goldfinch

“…The low dietary intake of arthropods, especially aquatic insects, in winter by both species could potentially help explain reduced levels of dietary PUFAs and this could potentially impact metabolic performance. However, woodland birds like chickadees and goldfinches, consumed few aquatic arthropods, even in spring, late summer, and autumn in riparian areas in our study area (Liu, 2015;Wesner et al, 2020). Also, because goldfinches eat mostly seeds all year, aquatic resources probably aren't very important dietary items.…”

Conservation Across Aquatic-Terrestrial Boundaries: Linking Continental-Scale Water Quality to Emergent Aquatic Insects and Declining Aerial Insectivorous Birds

“…We show at the scale of the contiguous US, the impacts of land use and water quality were related to reduced relative abundances of emergent insects. In particular, we illustrate that insects with adult stages that disperse in flight from water to land are positively related to the relative abundance of pollution sensitive insect orders (EPT), and negatively correlated with pollution tolerance, suggesting a potential large-scale loss of this nutritional subsidy to terrestrial environments from impaired aquatic ecosystems (Wesner et al, 2020). For context, Bartrons et al (2013) estimated that total insect emergence from lakes and streams in Wisconsin alone was ∼6,800 metric tons of carbon year −1 , with 79% of the total from lentic systems.…”

Past and recent farming degrades aquatic insect genetic diversity

“…Conversion of perennial grasslands to annual crops in the 1900s contributed to substantial soil erosion and sedimentation of streams in the US Great Plains (Cook et al, 2009; Hurt, 2002). Thus, the pre‐1950 extensification of agriculture would have impacted populations of aquatic insects both by degrading riparian habitat, as well as by altering the water quality of streams and rivers, which would in turn disrupt nutrient cycling between aquatic and terrestrial habitats (Wesner et al, 2019).…”

“…Here, we consider whether patterns of genetic variation among aquatic insects can be linked to historical and contemporary patterns of agricultural land use, while accounting for other potentially influential factors such as climate and sampling effects. Aquatic insects are known to be responsive to environmental degradation and climate change, and their populations are threatened from numerous anthropogenic pressures, including: habitat removal, such as when rivers are dammed for power generation or deepened for navigation (e.g., Wesner et al, 2019); point source or runoff pollution, such as when waterbodies become polluted with toxic agricultural and industrial chemicals (Henrik Barmentlo et al, 2021); and sedimentation, such as when extractive activities lead to higher sediment loads that promote eutrophication and subsequent oxygen depletion (Carpenter et al, 1998). Moreover, aquatic insects are important sources of food for animals and other invertebrates, as well as a conduit for cycling of nutrients within and between aquatic and terrestrial habitats (Baxter et al, 2005; Muehlbauer et al, 2014; Nakano & Murakami, 2001).…”