Similar zooplankton responses to low pH and calcium may impair long‐term recovery from acidification

Abstract

Throughout much of the 20th century, unprecedented industrial emissions have led to widespread acidification of regions in North America and Europe and, as lake water pH dropped, aquatic ecosystems have experienced dramatic declines in biodiversity. International emission‐control agreements have led to sweeping increases in lake pH, however acid‐structured zooplankton communities still persist in many lakes. Concomitantly, calcium concentrations have been declining as a legacy of acidification and are approaching or have reached concentrations that could represent a barrier to the re‐establishment of zooplankton communities similar to those in non‐acidified or circumneutral reference lakes. To understand how declining calcium may influence the re‐establishment of zooplankton in acid‐damaged lakes we manipulated calcium and pH using a factorial in‐lake mesocosm experiment and assessed their individual and combined effects on a regionally diverse zooplankton assemblage. We found that the impacts of low calcium on zooplankton species were similar to those of acidification and, consequently, may prevent the recovery of acid‐structured communities. Abundance of the larger bodied and acid‐sensitive Daphnia pulex/pulicaria increased in high pH treatments, albeit nonsignificantly yet, by the end of our experiment, only two individuals were sampled among our 10 low calcium enclosures. In contrast, small acid‐tolerant cladocerans, such as Daphnia catawba, Daphnia ambigua, and eubosminids maintained significantly higher abundances in low calcium treatments relative to all other treatment combinations. Although we did not detect an effect of calcium on mean body size, the disproportionately high abundance of small cladocerans in low calcium treatments resulted in low calcium communities with higher overall abundance and lower cladoceran evenness. Our results, along with a landscape comparison demonstrating parallel changes in zooplankton relative abundance from 34 historically acidified lakes, suggests that declining calcium will be an important, on‐going factor that may limit the recovery of zooplankton, despite regional improvements in lake pH.

The recovery of crustacean zooplankton from acidification depends on lake type

“…However, the lack of biotic responses in those lakes may also be caused by the persistent low pH (average values during the last 5 years of sampling: 5.3 ± 0.2, no significant increases during the study period) and the combination of low calcium and high humic content. Low calcium concentration has been shown to limit the recovery of zooplankton after acidification independently of improvement in pH (Ross & Arnott, 2022) and, when associated with high content of humic matter, it even causes declines in zooplankton biomass (Leach et al, 2019). On the other hand, humic substances can buffer against detrimental effects of aluminum (Besser et al, 2019;Herrmann, 2001;Locke, 1991).…”

“…Gray and Arnott (2009) showed that zooplankton response to the recovery of surface‐water chemistry could vary from limited recovery of species richness in heavily acidified lakes to full recovery in moderately acidified lakes. The recovery of zooplankton from acidification seems to be more strongly affected by physico‐chemical variables, such as persisting low pH, calcium concentration (Ross & Arnott, 2022), and content of organic matter (Leach et al, 2019), than by recolonization from external sources (Keller et al, 2002). Climate change has also been shown to affect several facets of zooplankton communities, such as species distribution, body size, abundances, diversity, food web interactions, and phenology (Carter & Schindler, 2012; Vadadi‐Fülöp et al, 2012).…”

“…In line with previous assessments, we expected that physico‐chemical recovery would lead to changes in zooplankton communities, namely, increases in number of species, number of acid‐sensitive species and functional diversity. As calcium and organic matter concentration strongly influence zooplankton communities (Leach et al, 2019; Ross & Arnott, 2022), we also expected the changes in zooplankton communities to vary across the different lake types, with stronger recovery at lakes with higher concentrations of calcium and mixed responses at lakes with higher concentrations of humic substances.…”

Current Status of Ponds in India: A Framework for Restoration, Policies and Circular Economy

“…Freshwater acidification is harmful to various aquatic organisms. Climate warming and changes in water chemistry profoundly affect the pond’s pH (Ross and Arnott 2022 ). The rise in atmospheric carbon dioxide lowers the pH in ponds.…”

Novel Near-Infrared-II In Vivo Visualization Revealed Rapid Calcium Intestine Turnover in Daphnia magna with Delayed Impact by Cadmium and Acidification

“…6,7 D. magna required high levels of Ca from the surrounding medium to support regular molting, development, reproduction, and other physiological functions. 8 Within D. magna, Ca was primarily distributed in the exoskeleton in the form of carbonates and phosphates. 9 It was reported that Ca concentration of D. magna increased with the Ca contents in the aqueous environment.…”