Fast reaction of macroinvertebrate communities to stagnation and drought in streams with contrasting nutrient availability

Abstract

Small, permanent streams are at risk of becoming stagnant or intermittent because of hydrological changes induced by climate change, which can be further intensified by anthropogenic disruptions, such as water abstraction. Macroinvertebrate communities are vulnerable to such changes because they depend on stream hydromorphological regime. We conducted a fully controlled field experiment in 1 impacted and 1 unimpacted Danish lowland stream with contrasting nutrient availability. We used dams and diversions to create short-term (2-10 wk) stagnant and drought conditions, and we installed pools in the drought area to test their value as refugia for benthic macroinvertebrates. After 2 wk, community composition had changed significantly in all treatments in both streams. The abundance of Chironomidae increased and the abundance of mayflies (Baetis rhodani), stoneflies (Amphinemura standfussi, Leuctra nigra), caddisflies (Silo pallipes, Sericostoma personatum), the amphipod Gammarus pulex, and some Diptera taxa (Simuliidae, Dicranota sp.) decreased relative to the control. Diversity and total abundance did not change in the stagnant or drought treatments, so we do not consider these variables sensitive to effects of short-term flow reductions. Diversity decreased (unimpacted stream) or was not affected (impacted stream) in pools relative to the drought treatment. Thus, pools did not act as a substantial refugium for macroinvertebrates under extreme low-flow conditions. Current velocity and amount of deposited organic material explained most of the change in the macroinvertebrate community. Nutrient availability did not influence the response of the macroinvertebrate community to the treatments, probably because the physicochemical changes were exacerbated in the impacted stream and outweighed the expected higher resilience of this community. Our results clearly demonstrate that short-term stagnation and droughts in lowland streams can cause strong alteration of species composition.

Decreased streamflow impacts fish movement and energetics through reductions to invertebrate drift body size and abundance

“…These results reinforce findings of previous studies where diversity decreased with streamflow (Wooster, Miller, & DeBano, ). The negative correlation between drift diversity and streamflow may be a direct reflection of species presence in the benthic habitat, which is influenced by streamflow (Dewson et al, ; Hille et al, ; Kennedy et al, ; Walters & Post, ). Although numerous other mechanisms are plausible, streamflow is the underlying cause of each of them, suggesting that alterations to streamflow will typically result in changes to community diversity of invertebrate drift in rivers (Wooster et al, ).…”

Responses of benthic algal communities and their traits to experimental changes in fine sediments, nutrients and flow

“…The low-flow phase was started on 28 August 2014 and lasted for 28 days. Here, the flow was reduced to simulate a flow event typical of lowland streams in Central European intensive agricultural landscapes in summer (Graeber, Gelbrecht, Pusch, Anlanger, & von Schiller, 2012;Graeber et al, 2015;Hille et al, 2014). The discharge was lowered from, on average, 5.2 L/s during the normal-flow phase to 1 L/s during the low-flow phase, rendering a current velocity reduction of 83%-93% in the run habitat (further statistics on the hydraulics in the different treatments are available in Appendices S1 and S2).…”

“…In the coastal climates of northern Europe, climate change‐mediated alterations in flow regimes in lowland streams are pronounced and periods with critically low flows are becoming more and more common during summer (Arnell, ). Furthermore, worldwide stream ecosystems are affected by high water abstraction, high loads of fine sediments and elevated nutrient concentrations due to agricultural activities (Graeber, Pusch, Lorenz, & Brauns, ; Hille et al., ; Piggott, Salis, Lear, Townsend, & Matthaei, ; Townsend, Uhlmann, & Matthaei, ; Wagenhoff, Lange, Townsend, & Matthaei, ). Therefore, multiple stress in lowland agricultural streams is a widespread phenomenon that strongly affects biological stream communities, including benthic algae.…”

“…worldwide stream ecosystems are affected by high water abstraction, high loads of fine sediments and elevated nutrient concentrations due to agricultural activities (Graeber, Pusch, Lorenz, & Brauns, 2013;Hille et al, 2014;Piggott, Salis, Lear, Townsend, & Matthaei, 2015;Townsend, Uhlmann, & Matthaei, 2008;Wagenhoff, Lange, Townsend, & Matthaei, 2013). Therefore, multiple stress in lowland agricultural streams is a widespread phenomenon that strongly affects biological stream communities, including benthic algae.…”

Water abstraction in small lowland streams: Unforeseen hypoxia and anoxia effects

“…We manipulated flow reduction in two permanent, lowland forested streams and showed that flow reduction strongly reduced dissolved oxygen, among other environmental changes, to concentrations known to negatively influence the survival of stream biological communities (Connolly et al, 2004). Previous studies on the effects of natural low flows and artificially reduced flows (without complete cessation of flow) on stream invertebrates found no evidence that low or reduced flows affect dissolved O 2 concentrations (see review in Dewson et al, 2007;Hille et al, 2014). This lack of evidence was attributed to the fact that measurements were obtained during day hours; however, low oxygen values have been occasionally recorded (James et al, Verdonschot et al (2015) found anoxia in remnant pools during flow reduction.…”