Response of cyanobacteria and phytoplankton abundance to warming, extreme rainfall events and nutrient enrichment

Abstract

Cyanobacterial blooms are an increasing threat to water quality and global water security caused by the nutrient enrichment of freshwaters. There is also a broad consensus that blooms are increasing with global warming, but the impacts of other concomitant environmental changes, such as an increase in extreme rainfall events, may affect this response. One of the potential effects of high rainfall events on phytoplankton communities is greater loss of biomass through hydraulic flushing. Here we used a shallow lake mesocosm experiment to test the combined effects of: warming (ambient vs. +4°C increase), high rainfall (flushing) events (no events vs. seasonal events) and nutrient loading (eutrophic vs. hypertrophic) on total phytoplankton chlorophyll‐a and cyanobacterial abundance and composition. Our hypotheses were that: (a) total phytoplankton and cyanobacterial abundance would be higher in heated mesocosms; (b) the stimulatory effects of warming on cyanobacterial abundance would be enhanced in higher nutrient mesocosms, resulting in a synergistic interaction; (c) the recovery of biomass from flushing induced losses would be quicker in heated and nutrient‐enriched treatments, and during the growing season. The results supported the first and, in part, the third hypotheses: total phytoplankton and cyanobacterial abundance increased in heated mesocosms with an increase in common bloom‐forming taxa—Microcystis spp. and Dolichospermum spp. Recovery from flushing was slowest in the winter, but unaffected by warming or higher nutrient loading. Contrary to the second hypothesis, an antagonistic interaction between warming and nutrient enrichment was detected for both cyanobacteria and chlorophyll‐a demonstrating that ecological surprises can occur, dependent on the environmental context. While this study highlights the clear need to mitigate against global warming, oversimplification of global change effects on cyanobacteria should be avoided; stressor gradients and seasonal effects should be considered as important factors shaping the response.

The role of changes in environmental quality in multitrait plastic responses to environmental and social change in the model microalgaChlamydomonas reinhardtii

“…Taken together, these data suggest that ameliorated environments (such as CO2 enrichment, temperature increase in some parts of the world, or nutrient enrichment) may at least initially increase variation more than expected based on increases to system carrying capacity (extra energy input) alone (Biswas et al, 2017;Burson et al, 2018;Gudmundsdottir et al, 2011;Richardson et al, 2019;Stevenson et al, 2008).…”

The role of changes in environmental quality in multitrait plastic responses to environmental and social change in the model microalga Chlamydomonas reinhardtii

“…Taken together, these data suggest that ameliorated environments (such as CO 2 enrichment, temperature increase in some parts of the world, or nutrient enrichment) may at least initially increase variation more than expected based on increases to system carrying capacity (extra energy input) alone (Biswas et al., 2017; Burson et al., 2018; Gudmundsdottir et al., 2011; Richardson et al., 2019; Stevenson et al., 2008).…”

Light, but Not Nutrients, Drives Seasonal Congruence of Taxonomic and Functional Diversity of Phytoplankton in a Eutrophic Highland Lake in China

“…Results of previous studies have shown that composition, biomass and diversity of phytoplankton is primarily determined by nutrients (Reynolds and Irish, 1997;Rangel et al, 2012). Results of other studies have shown that succession of phytoplankton communities is controlled by physical conditions such as light (Edwards et al, 2015), water temperature (Rasconi et al, 2017;Neukermans et al, 2018), mean depth (Pinckney et al, 2015), flushing rate (Cañavate et al, 2015) and their interactions (Hart et al, 2015;Edwards et al, 2016;Burson et al, 2018;Richardson et al, 2019). Competition for resources, predation, environmental change and rates of mutation and plasticity will affect succession of taxonomic and functional groupings, but whether there is seasonal congruence between functional and taxonomic groupings or not remains unclear in natural communities.…”