Freshwater biota and rising pCO₂?

Abstract

Rising atmospheric carbon dioxide (CO 2 ) has caused a suite of environmental issues, however, little is known about how the partial pressure of CO 2 (pCO 2 ) in freshwater will be affected by climate change. Freshwater pCO 2 varies across systems and is controlled by a diverse array of factors, making it difficult to make predictions about future levels of pCO 2 . Recent evidence suggests that increasing levels of atmospheric CO 2 may directly increase freshwater pCO 2 levels in lakes, but rising atmospheric CO 2 may also indirectly impact freshwater pCO 2 levels in a variety of systems by affecting other contributing factors such as soil respiration, terrestrial productivity and climate regimes. Although future freshwater pCO 2 levels remain uncertain, studies have considered the potential impacts of changes to pCO 2 levels on freshwater biota. Studies to date have focused on impacts of elevated pCO 2 on plankton and macrophytes, and have shown that phytoplankton nutritional quality is reduced, plankton community structure is altered, photosynthesis rates increase and macrophyte distribution shifts with increasing pCO 2 . However, a number of key knowledge gaps remain and gaining a better understanding of how freshwater pCO 2 levels are regulated and how these levels may impact biota, will be important for predicting future responses to climate change.

Zebrafish (Danio rerio) behaviour is largely unaffected by elevated pCO2

“…Other behavioural tests could be performed on zebrafish in elevated pCO 2 to verify the results of the detour test. In addition, a better understanding is needed of the mechanisms regulating freshwater pCO 2 and how freshwater pCO 2 responds to climate change (Hasler et al ., 2016). …”

“…Thus, elevated pCO 2 may potentially impair GABA functioning through the same mechanism as in marine fish. Ultimately, rising freshwater pCO 2 could potentially threaten freshwater fish populations in the same way as in marine ecosystems (Munday et al ., 2010); however, much less is known about future changes in freshwater pCO 2 compared with predictions for ocean pCO 2 (Hasler et al ., 2016). …”

CO2-driven experimental acidification effects on aquatic macroinvertebrates in a tropical stream

“…Decreased pH has been shown by this study to be linked to increased concentrations of gaseous CO 2 dissolving into the stream. There is also now empirical data associated with the tolerance of macroinvertebrate taxa, particularly insects, to deviations from environmental CO 2 levels, an area Hasler et al (2016) identify as a knowledge gap. According to Small et al (2012), seasonal pH patterns are amplified by drought years, with lower pH drops experienced during the ensuing wet season.…”

“…In order to model stream conditions resulting from increased dissolved CO 2 , gaseous CO 2 was added directly to the stream to cause an experimental decline in pH. It is well known that a major stream buffering system is the carbonate-bicarbonate system, in which gaseous CO 2 exchange at the water surface reacts with water molecules to form H 2 CO 3 , a weak acid which protonates easily to produce H C and HCO 3 -ions (Small et al 2012;Ard on et al 2013;Hasler et al 2016). With the addition of injected gaseous CO 2 , the equilibrium of this reaction may be driven to produce more H 2 CO 3 and cause the stream to become acidified.…”

Physiological responses of three species of unionid mussels to intermittent exposure to elevated carbon dioxide

“…Over the past several decades, levels of CO 2 in the atmosphere have been increasing as a result of the anthropogenic burning of fossil fuels, which has led to a concomitant increase in the partial pressure of CO 2 gas ( p CO 2 ) in marine ecosystems (Shirayama and Thornton, 2005). Unlike marine systems, there is no consensus regarding how p CO 2 will change in freshwater as a result of climate change (Hasler et al ., 2016). In freshwater, p CO 2 can vary across and within watersheds (Butman and Raymond, 2011), as well as episodically and on seasonal and diel cycles within water bodies (Maberly, 1996).…”