Responses of Freshwater Calcifiers to Carbon-Dioxide-Induced Acidification

Abstract

Increased anthropogenic carbon dioxide (CO2) in the atmosphere can enter surface waters and depress pH. In marine systems, this phenomenon, termed ocean acidification (OA), can modify a variety of physiological, ecological, and chemical processes. Shell-forming organisms are particularly sensitive to this chemical shift, though responses vary amongst taxa. Although analogous chemical changes occur in freshwater systems via absorption of CO2 into lakes, rivers, and streams, effects on freshwater calcifiers have received far less attention, despite the ecological importance of these organisms to freshwater systems. We exposed four common and widespread species of freshwater calcifiers to a range of pCO2 conditions to determine how CO2-induced reductions in freshwater pH impact calcium carbonate shell formation. We incubated the signal crayfish, Pacifastacus leniusculus, the Asian clam, Corbicula fluminea, the montane pea clam, Pisidium sp., and the eastern pearlshell mussel, Margaritifera margaritifera, under low pCO2 conditions (pCO2 = 616 ± 151 µatm; pH = 7.91 ± 0.11), under moderately elevated pCO2 conditions (pCO2 = 1026 ± 239 uatm; pH = 7.67 ± 0.10), and under extremely elevated pCO2 conditions (pCO2 = 2380 ± 693 uatm; pH = 7.32 ± 0.12). Three of these species exhibited a negative linear response to increasing pCO2 (decreasing pH), while the fourth, the pea clam, exhibited a parabolic response. Additional experiments revealed that feeding rates of the crayfish decreased under the highest pCO2 treatment, potentially contributing to or driving the negative calcification response of the crayfish to elevated pCO2 by depriving them of energy needed for biocalcification. These results highlight the potential for freshwater taxa to be deleteriously impacted by increased atmospheric pCO2, the variable nature of these responses, and the need for further study of this process in freshwater systems.

Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities

“…A recent synthesis of 22 predominantly laboratory‐based CO 2 ‐enrichment studies on freshwater microalgae found that elevated CO 2 generally lowers pH and increases DIC, algal productivity and nutrient uptake, but growth responses vary by algal type and sometimes between species of the same type (Brown et al., 2020; Hu & Gao, 2008). CO 2 ‐enrichment studies on freshwater invertebrates have primarily focused on direct effects (e.g., behavior, acidification effects on calcification), mostly via single‐species laboratory experiments (e.g., Hasler et al., 2017; Ninokawa & Ries, 2022; Ramaekers et al., 2022). In some cases, invertebrates have been studied in laboratory microcosms containing algae (or leaf litter; see Alto et al., 2005), allowing assessment of indirect invertebrate responses.…”

Acidification Of Northeastern USA Lakes From Rising Anthropogenic‐Sourced Atmospheric Carbon Dioxide and Its Effects on Aluminum Speciation

“…Although the effect of rising atmospheric CO 2 on ocean acidification and hence marine calcifying organisms has elicited substantial concern (Andersson et al., 2008; Kawahata et al., 2019; Kleypas et al., 1999), the potential impact to freshwater calcifiers from increasing pCO 2 atm has only recently been addressed (Ninokawa & Ries, 2022). Rising atmospheric CO 2 increases the carbonic acid concentrations (H 2 CO 3 *) of surface waters according to Henry's Law (i.e., $${a}_{{\mathrm{H}}_{2}\mathrm{C}{\mathrm{O}}_{3}^{\ast }}={K}_{\mathrm{C}{\mathrm{O}}_{2}}\text{pC}{\mathrm{O}}_{2}^{\text{atm}}$$), which subsequently dissociates to HCO 3 − and H + , shifting the carbonate buffer system toward HCO 3 − as CO 3 2− reacts with H + (Orr, 2011; Orr et al., 2005).…”

“…Unlike the ocean, freshwater systems are commonly undersaturated with respect to aragonite and calcite. Hence, freshwater calcifying organisms can tolerate substantially lower carbonate mineral saturation states than marine calcifiers (Ninokawa & Ries, 2022). Nevertheless, the much lower alkalinity and pH buffering capacity of freshwater systems compared to the ocean can still negatively impact freshwater calcifiers (Ninokawa & Ries, 2022), especially as rising atmospheric CO 2 drives these systems to progressively lower saturation states with respect to carbonate minerals (Beaune et al., 2018).…”

“…Hence, freshwater calcifying organisms can tolerate substantially lower carbonate mineral saturation states than marine calcifiers (Ninokawa & Ries, 2022). Nevertheless, the much lower alkalinity and pH buffering capacity of freshwater systems compared to the ocean can still negatively impact freshwater calcifiers (Ninokawa & Ries, 2022), especially as rising atmospheric CO 2 drives these systems to progressively lower saturation states with respect to carbonate minerals (Beaune et al., 2018). Our modeling demonstrates that $${a}_{\mathrm{C}{\mathrm{O}}_{3}^{2-}}$$ will decrease in the studied lakes as pCO 2 atm increases during the 21st century, pushing carbonate mineral saturation states to even more undersaturated conditions (Figure 2).…”

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Acidification of the ocean from rising atmospheric CO 2 concentrations (pCO 2 atm ) derived from anthropogenic activities, chief among which is the combustion of fossil fuels, is of concern for several reasons including ensuring the sustainability of important shellfish fisheries and marine ecosystems (Doney et al, 2009;Orr et al, 2005;Waldbusser et al, 2015). Despite efforts to understand and predict the impacts of human-driven rises in pCO 2 atm on ocean acidification (Balch et al, 2022;Millero et al, 2009), less effort has focused on the likelihood these processes will also lead to acidification of terrestrial, freshwater systems (e.g., Ninokawa & Ries, 2022;Phillips et al, 2015). Acidification of lakes and streams by increasing atmospheric CO 2 could be more marked and occur more rapidly than in marine systems as most terrestrial freshwaters exhibit lower alkalinities than the ocean and hence possess lower buffering capacities.A complicating factor in the study of lake acidification by rising pCO 2 atm is that most lakes appear to be supersaturated with respect to CO 2 (e.g., Cole et al, 1994;Lazzarino et al, 2009;Raymond et al, 2013).

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