The ecological impacts of lakewater calcium decline on softwater boreal ecosystems

Abstract

In recent decades, marked declines in calcium (Ca) concentrations have been noted in many softwater boreal lakes, and are believed to be a long-term consequence of acid deposition as well as other stressors (such as timber harvesting). Reduced Ca availability may act as a potent environmental stressor. Investigations of the direct ecological impacts of lower Ca concentrations in freshwater systems have largely focused on Ca-rich members of the Cladocera; however, a growing body of work, spanning several scientific fields, suggests Ca decline will have profound direct and indirect consequences for aquatic ecosystems. Here, we synthesize recent laboratory analyses and field surveys to provide an overview of these consequences, while highlighting paleolimnological investigations that provide some long-term perspective on the phenomenon. However, considerable questions remain regarding ‘baseline’ or pre-impact conditions, due to the accelerated leaching of Ca from watershed soils during the period of anthropogenic influence. Furthermore, catchment-specific differences in both leaching rates and the initial size of the Ca pool in watershed soils complicate determination of the eventual endpoints of the declines. Despite these uncertainties, persistent low Ca concentrations are anticipated to impede biological recovery from lake acidification, and that ongoing declines will have cascading effects throughout aquatic ecosystems due to the loss of vulnerable taxa. To better understand how reduced Ca availability will continue to change affected surface waters and how these changes will interact with other environmental stressors will require continued investigation of the declines from multiple scientific perspectives.

Reducing repetition of regulatory vertebrate ecotoxicology studies

“…Observations of declining Ca concentrations since the 1970s in eastern North American and Scandinavian lakes have been attributed to decades of accelerated Ca leaching from catchment soils as a result of acidic deposition, and have stimulated research efforts into associated ecological implications using laboratory and field experiments, regional limnological surveys, modeling, and paleolimnology (reviewed in Jeziorski and Smol 2017). 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).…”

“…Calcium decline is a recently identified stressor on aquatic ecosystems, and the cooperation of researchers using complementary approaches resulted in a rapid accumulation of critical knowledge into the issue in a relatively short period of time (Jeziorski and Smol 2017). The example of Ca decline research provides a useful model for how paleolimnological techniques can be seamlessly integrated with other methods of inquiry to generate novel insights, with important advantages from a paleo-ecotoxicological perspective.…”

“…The example of Ca decline research provides a useful model for how paleolimnological techniques can be seamlessly integrated with other methods of inquiry to generate novel insights, with important advantages from a paleo-ecotoxicological perspective. Unlike lake water Ca decline, which often leaves no geochemical signature in the sediments to reconstruct Ca trends over time (Jeziorski and Smol 2017), the deposition histories of many contaminants of interest are routinely reconstructed using lake sediment core archives (Blais et al 2015). Hence, the timing of important ecological shifts in key aquatic biota can be directly linked to historical fluxes of contaminants.…”

Learned Discourse: Timely Scientific Opinions

“…A useful roadmap for what enhanced cooperation could look like can be found by examining recent investigations into the ecological effects of lake water Ca decline, a legacy of acid rain and logging in regions with Ca-poor soils. Observations of declining Ca concentrations since the 1970s in eastern North American and Scandinavian lakes have been attributed to decades of accelerated Ca leaching from catchment soils as a result of acidic deposition, and have stimulated research efforts into associated ecological implications using laboratory and field experiments, regional limnological surveys, modeling, and paleolimnology (reviewed in Jeziorski and Smol 2017). 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).…”

Paleolimnology can provide the missing long‐term perspective in ecotoxicology research

“…A useful roadmap for what enhanced cooperation could look like can be found by examining recent investigations into the ecological effects of lake water Ca decline, a legacy of acid rain and logging in regions with Ca‐poor soils. Observations of declining Ca concentrations since the 1970s in eastern North American and Scandinavian lakes have been attributed to decades of accelerated Ca leaching from catchment soils as a result of acidic deposition, and have stimulated research efforts into associated ecological implications using laboratory and field experiments, regional limnological surveys, modeling, and paleolimnology (reviewed in Jeziorski and Smol ). Early laboratory‐based 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 ).…”