Anthropogenic CO₂-mediated freshwater acidification limits survival, calcification, metabolism, and behaviour in stress-tolerant freshwater crustaceans

Dissolution of anthropogenic CO2 is chronically acidifying aquatic ecosystems. Studies indicate that ocean acidification will cause marine life, especially calcifying species, to suffer at the organism and ecosystem levels. In comparison, freshwater acidification has received less attention, rendering its consequences unclear. Here, juvenile Chinese mitten crabs, Eriocheir sinensis, were used as a crustacean model to investigate the impact of CO2-mediated freshwater acidification. Our integrative approach, investigating changes in the animal's acid–base homeostasis, metabolism, calcification, locomotory behaviour, and survival rate, indicates that this economically relevant crustacean will face energetic consequences from future freshwater acidification. These energetic trade-offs allow the animal to maintain its acid–base homeostasis at the cost of reduced metabolic activity, exoskeletal calcification, and locomotion, reducing the animal's overall fitness and increasing its mortality. Results indicate that present-day Chinese mitten crab could be heavily affected by freshwater acidification like their marine counterparts and emphasize the importance of understanding the long-term implications of freshwater acidification on species' fitness.

Rapid recovery of normal gill morphology and blood physiology in brown trout (Salmo trutta) after short-term exposure to toxic concentrations of aqueous aluminium under non-steady state chemical conditions

Freshwater acidification is characterised by elevated concentrations of aqueous aluminium. Global emissions of acidifying agents are reduced due to international agreements, and freshwater acidification has shifted from chronic to a more episodic character. The recovery of fish populations in acidified areas is likely to depend on the individual’s ability to recover from short-time aluminium exposures. We exposed brown trout (Salmo trutta) to an Al-rich medium, nominal concentration 600 µg L–1, for 0.5, 2, 6, 8 and 11 hours, before transfer to circumneutral Al-poor water for recovery. As controls, fish were either exposed for 11 hours to an acidified Al-poor medium or to untreated water. Some mortality during the first 24 hours of the recovery period occurred in fish exposed for 11, 8 and 6 hours to aluminium. No mortality during recovery was observed in the remaining groups. Aluminium exposure led to increased haematocrit and plasma lactate concentration, decreased plasma chloride concentration, deposition of aluminium on gill surfaces, and morphological alteration of the gill structures. The responses depended on exposure time. Aluminium deposited on the gill disappeared and plasma lactate levels were at control levels after 1 day in the recovery water, while haematocrit and plasma chloride levels were at control levels after 14 days of recovery. Gills in fish exposed to aluminium for 11 hours were almost fully recovered after 14 days. We conclude that the toxic response in brown trout exposed to an acutely toxic aluminium challenge is reversible. Moreover, the first 24 hours after aluminium exposures is the most critical period for the fish recovery. Further, it takes no more than 14 days for brown trout to fully recover from an acute toxic aluminium exposure, and only 1 day if the aluminium challenge is moderate.

Anthropogenic CO₂-mediated freshwater acidification limits survival, calcification, metabolism, and behaviour in stress-tolerant freshwater crustaceans

Dissolution of anthropogenic CO2 is chronically acidifying aquatic ecosystems. Studies indicate that ocean acidification will cause marine life, especially calcifying species, to suffer at the organismal and ecosystem levels. In comparison, freshwater acidification has received less attention rendering its consequences unclear. Here, juvenile Chinese mitten crabs, Eriocheir sinensis, were used as a calcifying model to investigate the impacts of CO2-mediated freshwater acidification. Our integrative approach investigating changes in the animal's acid-base homeostasis, metabolism, calcification, locomotory behaviour, and survival rate indicate that the crab will face energetic consequences from future freshwater acidification. These energetic trade-offs allow the animal to maintain its acid-base homeostasis at the cost of reduced metabolic activity, exoskeletal calcification, and locomotion reducing the animal's overall fitness and increasing its mortality. Results suggest that present-day calcifying invertebrates could be heavily affected by freshwater acidification similar to their marine organisms and emphasizes the importance in understanding the long-term implications of freshwater acidification on species fitness.

Comparative Efficacy of Montmorillonite, Calcium Hydroxide, Calcium Carbonate in pH Restoration of Acidified Freshwater Bodies

Freshwater acidification is the result of acid rain precipitating over a freshwater body. There are significant ecological consequences that result from such precipitation, as ecosystems surrounding freshwater bodies are destroyed because many of the organisms in these ecosystems cannot tolerate the pH change caused by acid rain. Current solutions involve a technique known as liming, where powdered calcium carbonate is added to freshwater bodies creating a buffer that helps neutralize the acidity caused by acid rain. However, scientists have been searching for alternative methods to combat the decrease in pH caused by freshwater acidification, by using substitute compounds. In this experiment, we test the efficacy of alternate solutions involving montmorillonite and calcium hydroxide when compared to the currently employed method of using calcium carbonate to combat acidification.

Comparative Efficacy of Montmorillonite, Calcium Hydroxide, Calcium Carbonate in pH Restoration of Acidified Freshwater Bodies

Freshwater acidification is the result of acid rain precipitating over a freshwater body. There are significant ecological consequences that result from such precipitation, as ecosystems surrounding freshwater bodies are destroyed because many of the organisms in these ecosystems cannot tolerate the pH change caused by acid rain. Current solutions involve a technique known as liming, where powdered calcium carbonate is added to freshwater bodies creating a buffer that helps neutralize the acidity caused by acid rain. However, scientists have been searching for alternative methods to combat the decrease in pH caused by freshwater acidification, by using substitute compounds. In this experiment, we test the efficacy of alternate solutions involving montmorillonite and calcium hydroxide when compared to the currently employed method of using calcium carbonate to combat acidification.

Outlook: Crustaceans in the Anthropocene

Since the mid-20th century we have been living in a new geological epoch, Anthropocene, characterized by an overwhelming impact of human activity on the Earth’s ecosystems, leading to mass species extinction by habitat destruction, pollution, global climate warming, and homogenization of biota by intra- and intercontinental transfer of species. Crustaceans are among the most diverse and species-rich animal groups inhabiting predominantly aquatic ecosystems, listed as among the most threatened ecosystems. Global threats include ocean and freshwater acidification, eutrophication, pesticide, hormone and antibiotic load, coastline modification, habitat destruction, overharvesting, and the introduction of invasive species. Many crustaceans are threatened by human-induced modifications of habitats, while others are themselves threats—crustaceans are among the most common invasive species. Those non-indigenous species, when established and integrated, become important components of existing communities, strongly influencing other components directly and indirectly, including by species replacement. They are a threat mostly to species with similar ecological niches, most often to other crustaceans. It is hard to be optimistic about the future of crustacean biodiversity. We may rather expect that growing human pressure will variously further accelerate the non-natural dispersal and extinction rate.

Identifying global trends and drivers of freshwater aluminium concentrations using GloFAD (Global Freshwater Acidification Database)

<p>Aluminum is toxic to most aquatic and terrestrial organisms. Increased Al concentrations in soils and freshwaters are a direct result of human activity, via increases in acid deposition. Elevated Al concentrations pose a wide variety of threats to ecosystems and society, from causing human neurotoxicity, reducing carbon sequestration in forests, threatening biodiversity, and increasing the cost of water treatment. Freshwater aluminium concentrations increased across Europe and North America between the 1960s and 1990s, predominantly due to ecosystem acidification. Following acidic deposition reduction legislation enacted in the 1990s, the problems of acidification and increased freshwater aluminium concentrations were considered solved. However, recently and unexpectedly, Sterling et al. identified aluminum concentrations to be increasing across North America and Scandinavia. Sterling et al. proposed a conceptual model suggesting these widespread increases in freshwater aluminium concentrations resulted from a hysteresis of base cation and dissolved organic carbon (DOC) response to decreasing acidic deposition, where base cation increase is slow compared to that of DOC, resulting in elevated freshwater aluminium concentrations. This process can be exacerbated by further increases in DOC due to increasing global surface temperatures. The Sterling et al. conceptual model is supported by prior work by Weyhenmeyer et al. (2019, Scientific Reports) and Monteith et al., 2007, Nature) who identified widespread decreasing calcium and increasing DOC concentrations. In this study, we aim to validate the Sterling et al. model and identify if it is generalizable to other regions with decreasing calcium and increasing DOC trends, irrespective acidification status. Additionally, we aim to characterize other regions across the globe which are at risk of elevated aluminium concentrations. To fulfill these research goals, we compiled a large-sample water chemistry database from existing national and global datasets – GloFAD (Global Freshwater Acidification Database). The database is comprised of over 11 million unique samples spanning nearly 286,000 sites located between Antarctica and Russia, 18 years (2000 to 2019), and 40 water chemistry parameters. Preliminary analysis shows that aluminium is increasing in 27% to 71% of sites, dependent on the species, base cations are decreasing for 62% to 70% of sites, freshwater organic carbon is increasing for 58% to 64% of sites, and water temperature is increasing in 61% of sites. Increasing dissolved aluminium trends are strongly significantly correlated with decreasing base cation trends (calcium τ = -0.71 and magnesium τ = -0.59, α < 0.05) but not with DOC concentrations (τ = -0.08). The lack of correlation with DOC indicates that drivers of increasing aluminium trends may differ based on the acidification status of the watershed and that regional models of freshwater aluminium chemistry may not be globally applicable. The widespread decreasing base cation trends and strong correlation between decreasing base cation and increasing aluminium trends indicates that increasing aluminium concentrations may become more widespread, posing a threat to aquatic and terrestrial organisms, potentially including humans, reducing carbon sequestration in forests, threatening biodiversity, and increasing water treatment costs.</p>