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

Abstract

Summary Lowland stream ecosystems are subjected to multiple anthropogenic stressors, usually nutrient enrichment in combination with sedimentation of fine particles and low flow periods in summer. Here, we investigated the temporal development of the benthic algae community in response to these three stressors and linkages to the trait characteristics of the community to explore the mechanisms responsible for stress‐induced community changes. We investigated the response of benthic algae species composition, traits (life forms, cell size categories), biovolume and chlorophyll a (Chl‐a) concentration to low flow in combination with nutrient enrichment and fine sedimentation in twelve large outdoor stream flumes (12 m long) resembling small streams in size and habitat characteristics. The experiment consisted of two phases: a normal‐flow phase followed by a low‐flow phase (90% current velocity reduction), each spanning 4 weeks. We applied a eutrophication scenario (mean increases of 1.14–5.48 mg N/L and 0.01–0.06 mg P/L in the flumes for dissolved inorganic nitrogen and phosphate respectively) throughout the experiment. Under low flow, we supplemented this with a fine sedimentation scenario (>90% stream bed cover). We took samples once in the normal‐flow phase and every week during the low‐flow phase. We observed strong responses in the benthic algae community to sudden changes in low flow and fine sedimentation, mediating rapid species turnover with a decreased algal biovolume and increased abundance of large, motile species. However, we did not observe any pronounced responses to nutrient enrichment. In contrast to the observations for other variables, we found a continuous increase in Chl‐a concentration during low flow. This was likely due to continuous fine sedimentation during this phase, reducing light availability which probably resulted in an increase of cell‐level Chl‐a concentration in response to light limitation and lower rates of light‐induced Chl‐a degradation. The rapid response of the benthic algal community to the applied stressors suggests that even short periods of major stressor exposure may significantly affect benthic algae in lowland systems. We suggest that short‐term stress events may have cascading effects on several important ecosystem processes given the importance of benthic algae for the productivity of these systems.

Diatoms as indicators of the effects of river impoundment at multiple spatial scales

“…A number of studies involving benthic diatom assemblages or algal communities have related community changes to abiotic factors other than water quality. The relationship between diatoms and river discharge has been demonstrated (Molloy, 1992;Passy, 2001;Neif et al, 2017) and a number of studies on river regulation have related diatom assemblage changes to flow alteration (Peterson, 1986;Growns, 1999;Cibils Martina, Principe & Gari, 2013). Taxa within the low-profile guild are likely to thrive in frequently disturbed habitats, whereas high-profile taxa are typically prevalent in conditions with little physical disturbance (Passy, 2007;Stenger-Kovács et al, 2013).…”

“…The influence of temperature on diatom assemblages has also been reported (Bergey, Desianti & Cooper, 2017), and thermal alteration by impoundment has been shown to induce changes to assemblage composition within a short time-period (Blinn, Truitt & Pickart, 1989). In addition, the relationship between diatom motility and fine sediment has been demonstrated, although some studies indicated that there may be confounding effects of other environmental pressures (Jones et al, 2014;Neif et al, 2017;Jones et al, 2017).…”

Sediment inputs from retrogressive thaw slumps drive algal biomass accumulation but not decomposition in Arctic streams, NWT

“…This suggests that algal biomass accumulation was extremely limited once TSS levels exceeded the threshold. Algae growing in systems that are beyond the TSS threshold are likely highly tolerant to sedimentation and may be more resistant to sediment scour (Francoeur & Biggs, 2006;Neif et al, 2017) or have the ability to photo-acclimate to low-light conditions (Hill, Ryon, & Schilling, 1995;Rhee & Gotham, 1981). Van Nieuwenhuyse and LaPerriere (1986) saw a 50% decrease in primary production in streams in the interior highlands of Alaska at levels of 200 mg/L TSS.…”

Peer Review #1 of "Diatoms as indicators of the effects of river impoundment at multiple spatial scales (v0.1)"

“…A number of studies involving benthic diatom assemblages or algal communities have related community changes to abiotic factors other than water quality. The relationship between diatoms and river discharge has been demonstrated (Molloy, 1992;Passy, 2001;Neif et al, 2017) and a number of studies on river regulation have related diatom assemblage changes to flow alteration (Peterson, 1986;Growns, 1999;Cibils Martina et al, 2013). Taxa within the low-profile guild are likely to thrive in frequently disturbed habitats, whereas high-profile taxa are typically prevalent in conditions with little physical disturbance (Passy, 2007;Stenger-Kovács et al, 2013).…”

“…The influence of temperature on diatom assemblages has also been reported (Bergey et al, 2017), and thermal alteration by impoundment has been shown to induce changes to assemblage composition within a short time-period (Blinn et al, 1989). In addition, the relationship between diatom motility and fine sediment has been demonstrated, although some studies indicated that there may be confounding effects of other environmental pressures (Jones et al, 2014;Neif et al, 2017;Jones et al, 2017).…”