Effects of river ice break‐up on organic‐matter dynamics and feeding ecology of aquatic insects

Abstract

Disturbance shapes the structure and function of aquatic communities and ecosystems, but the dynamics of ice are a less studied dimension of the disturbance‐regime of rivers. We investigated effects of a river‐ice regime on organic‐matter dynamics and feeding ecology of aquatic insects. Samples of biofilm and aquatic insects for gut content analysis were collected monthly from Big Creek, a sixth ‐ order tributary of the Middle Fork Salmon River in central Idaho, USA, during winter 2010–2011. Our results indicate that river ice affects both quantity and quality of organic matter available to, and used by, consumers. Specifically, scour from December and February ice break‐up events reduced biofilm biomass by one‐half and one‐third, respectively, whereas quality (chlorophyll‐a: ash‐free dry mass) increased. Diets of scrapers, Rhithrogena (Heptageniidae) and Bibiocephala (Blephariceridae), collector‐gatherers, Baetis (Baetidae), and collector‐filterers, Simulium (Simulidae) appeared to follow patterns of organic matter. Following ice break‐up events, diets of these taxa had increased proportions of diatom frustules, which are high‐quality food resources due to their relatively high nutrient content. Other taxa, such as collector‐gatherers, non‐Tanypodinae (Chironomidae), and the collector‐filterer, Arctopsyche grandis (Hydropsychidae), consistently consumed high proportions of diatom frustules and insect material, respectively, suggesting they were able to feed more selectively throughout winter. Our study indicates that ice regimes in temperate rivers can affect organic‐matter dynamics and feeding ecology of aquatic insects, a possibility that deserves additional investigation, particularly in light of potential changes to the ice regimes of rivers with changing climate.

Dietary composition and fatty acid content of giant salmonflies (Pteronarcys californica) in two Rocky Mountain rivers

“…Filamentous green algae are likely the source of ALA, diatoms are likely the source of EPA, and terrestrial detritus is likely the source of LIN, the precursor to ARA of shredding invertebrates (Cummins et al, 1989). However, our findings contrast with previous studies of salmonfly diets which found a much greater dependence on autochthonous material, including diatoms and animal parts (Blackadar et al, 2020;Freilich, 1991;. Both seasonal and site-specific factors may contribute to the differences between our findings and previous studies.…”

“…Salmonflies are often classified as shredders and presumed to consume allochthonous detritus. However, the few studies that have quantified salmonfly diets by gut content analysis indicate substantial variation in allochthony by location and season, with sometimes heavy reliance on autochthonous production (Blackadar et al, 2020;. In addition to traditional methods of gut content analysis, fatty acid (polyunsaturated fatty acid [PUFA]) composition of macroinvertebrate tissues can provide information on origins and quality of macroinvertebrate diets (Lau et al, 2009;Torres-Ruiz et al, 2007).…”

The Ecology of River Ice

“…Thus, it is important to consider how the hydrogeomorphic setting of river channels influences how ice develops on that template and influences underlying productivity patterns (e.g., relative balance of benthic vs. pelagic productivity). For instance, ice tends to form and break up later in larger, deeper channels as a result of their thermal inertia (Buffin-Bélanger et al, 2013;Turcotte et al, 2012) and lateral variation of ice duration across the channel is common, as ice tends to form earlier and break up later in shallow, higher residence time locations like off-channel areas, backwaters, or channel margins (Blackadar et al, 2020;Brown et al, 2011;Danks, 2007). Therefore, typically productive channel margins and backwaters will have limited light for longer periods during the winter, while along the thalweg or the main channel, the flow may be too turbulent for primary producer communities to establish (Uehlinger, 2006;Uehlinger & Naegeli, 1998; Figure 2).…”

“…Though metabolism may be low during the winter months, either due to low temperature or light impediment from ice, annual productivity and metabolism often depend on the timing and length of the snow-covered season (Casson et al, 2012;Mulholland et al, 2009). In addition, winter ice breakup and freeze-up were shown to be a driving force in maintaining "good quality" algal biomass and subsequent insect diversity throughout the year (Blackadar et al, 2020). In contrast to the milder winters of deciduous headwater catchments, Arctic streams (above the Arctic Circle) experience long winters and are likely to completely freeze due to low sustained winter temperatures and reduced flow (Huryn et al, 2014;Shogren et al, 2020).…”

Effects of River-Ice Breakup on Sediment Transport and Implications to Stream Environments: A Review

“…Excess deposition of sediment in coarse substrates will cover and inundate the gravels, thereby eliminating the habitat where many invertebrates live [91][92][93][94]. Ice regimes in temperate rivers can also affect organic-matter dynamics and feeding ecology of aquatic insects [95].…”