Resistance, resilience and recovery: aquatic bacterial dynamics after water column disturbance

Abstract

For lake microbes, water column mixing acts as a disturbance because it homogenizes thermal and chemical gradients known to define the distributions of microbial taxa. Our first objective was to isolate hypothesized drivers of lake bacterial response to water column mixing. To accomplish this, we designed an enclosure experiment with three treatments to independently test key biogeochemical changes induced by mixing: oxygen addition to the hypolimnion, nutrient addition to the epilimnion, and full water column mixing. We used molecular fingerprinting to observe bacterial community dynamics in the treatment and control enclosures, and in ambient lake water. We found that oxygen and nutrient amendments simulated the physical-chemical water column environment following mixing and resulted in similar bacterial communities to the mixing treatment, affirming that these were important drivers of community change. These results demonstrate that specific environmental changes can replicate broad disturbance effects on microbial communities. Our second objective was to characterize bacterial community stability by quantifying community resistance, recovery and resilience to an episodic disturbance. The communities in the nutrient and oxygen amendments changed quickly (had low resistance), but generally matched the control composition by the 10th day after treatment, exhibiting resilience. These results imply that aquatic bacterial assemblages are generally stable in the face of disturbance.

Stochasticity, succession, and environmental perturbations in a fluidic ecosystem

“…The epilimnion microbial community diversity consistently increased after a whole-ecosystem perturbation (26). All of the epilimnion microbial communities recovered after perturbations by typhoons (49), nutrient addition or mixing (50), and whole-ecosystem mixing (26), which is consistent with the scenario A prediction. However, due to the lack of sufficient replicate data for null model analysis, it is not clear how compositional stochasticity changed with time in response to disturbances.…”

“…Lake mixing increases the oxygen concentration in the anoxic hypolimnion, which likely stresses the anaerobic hypolimnion communities, explaining the measured decrease in microbial diversity (26). Similarly, all of the hypolimnion microbial communities recovered following perturbation by typhoons (49), oxygen addition or mixing (50), and whole-ecosystem mixing (26). The high degree of resilience of the hypolimnion microbial communities is consistent with the prediction of scenario B.…”

“…The experimental results with lake epilimnion microbial communities (26,(48)(49)(50)(51) also support scenario A. Generally, lake mixing increases nutrient input to the nutrient limited epilimnion (50), which should stimulate microbial diversity. The epilimnion microbial community diversity consistently increased after a whole-ecosystem perturbation (26).…”

“…Several studies have also examined the resilience of lake microbial communities after disturbances (26,(48)(49)(50)(51). The experimental results with lake epilimnion microbial communities (26,(48)(49)(50)(51) also support scenario A.…”

“…The results showed that the β-diversity of the communities (animals and plants) in the drought ponds were significantly less than that in the permanent ponds, indicating that drought decreased the stochasticity in the dry ponds. For another example, the experimental results on the lake hypolimnion microbial communities from the lake mixing studies also appear to support scenario B (26,49,50). Lake mixing increases the oxygen concentration in the anoxic hypolimnion, which likely stresses the anaerobic hypolimnion communities, explaining the measured decrease in microbial diversity (26).…”