The Widespread Threat of Calcium Decline in Fresh Waters

Abstract

Calcium concentrations are now commonly declining in softwater boreal lakes. Although the mechanisms leading to these declines are generally well known, the consequences for the aquatic biota have not yet been reported. By examining crustacean zooplankton remains preserved in lake sediment cores, we document near extirpations of calcium-rich Daphnia species, which are keystone herbivores in pelagic food webs, concurrent with declining lake-water calcium. A large proportion (62%, 47 to 81% by region) of the Canadian Shield lakes we examined has a calcium concentration approaching or below the threshold at which laboratory Daphnia populations suffer reduced survival and fecundity. The ecological impacts of environmental calcium loss are likely to be both widespread and pronounced.

Reducing repetition of regulatory vertebrate ecotoxicology studies

“…A Cladocera-based paleolimnological investigation in Plastic Lake, Ontario, Canada, revealed a decline in Daphnia fossil remains consistent with declines in lake water Ca (below critical thresholds identified in laboratory studies) recorded over the monitoring record (Jeziorski et al 2008). A regional snapshot of cladoceran assemblage changes between present-day and preindustrial times revealed that Daphnia have decreased in all lakes examined in south-central Ontario with current Ca concentrations below 2.5 mg/L, but in contrast, Daphnia have increased since preindustrial times in lakes with >2.5 mg Ca per liter (Jeziorski et al 2008). Collectively, these independent datasets provided strong evidence that lake water Ca decline is a dominant driver of zooplankton community dynamics in soft-water lakes with a legacy of acidic deposition.…”

“…Early laboratorybased studies identified several large Cladocera (crustacean zooplankton) species as vulnerable to Ca decline, and a threshold response for Daphnia pulex was determined when Ca concentrations fell below 1.5 to 2.0 mg/L (Ashforth and Yan 2008). A Cladocera-based paleolimnological investigation in Plastic Lake, Ontario, Canada, revealed a decline in Daphnia fossil remains consistent with declines in lake water Ca (below critical thresholds identified in laboratory studies) recorded over the monitoring record (Jeziorski et al 2008). A regional snapshot of cladoceran assemblage changes between present-day and preindustrial times revealed that Daphnia have decreased in all lakes examined in south-central Ontario with current Ca concentrations below 2.5 mg/L, but in contrast, Daphnia have increased since preindustrial times in lakes with >2.5 mg Ca per liter (Jeziorski et al 2008).…”

Physiological and molecular responses to calcium supplementation inMicrocystis aeruginosa(Cyanobacteria)

“…Nevertheless, there is little direct evidence of the physiological and molecular mechanisms by which Ca 2 ' exerts its effects. Lake-water calcium concentrations are currently declining in many softwater lakes worldwide, which have been considered a novel and a widespread threat to aquatic biota in freshwater ecosystems (Clair et al 2007;Jeziorski et al 2008). Recently, an interesting result was elucidated by Korosi et al (2012), who found that an anomalous algal bloom was linked to lake-water calcium decline through the effect of calcium reductions on Daphnia.…”

“…Recently, an interesting result was elucidated by Korosi et al (2012), who found that an anomalous algal bloom was linked to lake-water calcium decline through the effect of calcium reductions on Daphnia. Previous studies have shown that low ambient calcium concentrations significantly affected freshwater daphniids, gammarids and crayfish (Jeziorski et al 2008;Cairns & Yan 2009). However, to date, no detailed study has examined the relationship between calcium concentration and Microcystis, especially in relation to physiological and molecular effects.…”

Implications for the use of sedimentary invertebrate communities to infer past presence of fish

“…Many of the study lakes are very acidic and have an acidification history that may have affected the infrequency of Daphnia in the dataset. Recently, Jeziorski et al (2008) showed that acidic deposition and lack of calcium in Canadian boreal shield lakes, comparable to boreal lakes in Finland, nearly extirpated some Daphnia species. Therefore, the cause behind scarcity of Daphnia may be the chemical composition of the water.…”