Widespread diminishing anthropogenic effects on calcium in freshwaters

Abstract

Calcium (Ca) is an essential element for almost all living organisms. Here, we examined global variation and controls of freshwater Ca concentrations, using 440 599 water samples from 43 184 inland water sites in 57 countries. We found that the global median Ca concentration was 4.0 mg L −1 with 20.7% of the water samples showing Ca concentrations ≤ 1.5 mg L −1 , a threshold considered critical for the survival of many Ca-demanding organisms. Spatially, freshwater Ca concentrations were strongly and proportionally linked to carbonate alkalinity, with the highest Ca and carbonate alkalinity in waters with a pH around 8.0 and decreasing in concentrations towards lower pH. However, on a temporal scale, by analyzing decadal trends in >200 water bodies since the 1980s, we observed a frequent decoupling between carbonate alkalinity and Ca concentrations, which we attributed mainly to the influence of anthropogenic acid deposition. As acid deposition has been ameliorated, in many freshwaters carbonate alkalinity concentrations have increased or remained constant, while Ca concentrations have rapidly declined towards or even below pre-industrial conditions as a consequence of recovery from anthropogenic acidification. Thus, a paradoxical outcome of the successful remediation of acid deposition is a globally widespread freshwater Ca concentration decline towards critically low levels for many aquatic organisms.

Ionic aluminium concentrations exceed thresholds for aquatic health in Nova Scotian rivers, even during conditions of high dissolved organic carbon and low flow

“…The catchments with the highest Al i levels had particularly low Ca levels; this is cause for concern, as Ca protects against Al i toxicity, and highlights the coincident threats of Ca depletion and elevated Al. Recent work has identified globally widespread low levels and S. M. Sterling et al: Ionic aluminium concentrations exceed thresholds declines in Ca (Weyhenmeyer et al, 2019), raising the question of what other regions may also have Al i levels exceeding toxic thresholds. The serious potential consequences of high Al i highlight the importance of actions to further reduce acid emissions and deposition, as critical loads are still exceeded across the province (Keys, 2015), and to adapt forest management practices to avoid base cation removal and depletion.…”

“…Acid-sensitive areas of Nova Scotia, Canada, here abbreviated as NS A (see Clair et al, 2007), with once-famous wild Atlantic salmon populations, were heavily impacted by sulfur deposition at the end of the last century, which originated from coal burning in Central Canada and the Northeastern USA (Hindar, 2001;Summers and Whelpdale, 1976). NS A catchments are particularly sensitive to acid deposition due to base-cation-poor and slowly weathering bedrock that generates thin soils with a low acid neutralizing capacity (ANC), extensive wetlands, and episodic sea salt inputs (Clair et al, 2011;Freedman and Clair, 1987;Watt et al, 2000;Whitfield et al, 2006). Al was not considered to be a threat to Atlantic salmon in Nova Scotia because of the high natural levels of DOC in NS A rivers following preliminary research by Lacroix and Townsend (1987) and Lacroix (1989).…”

Short‐term homeostatic regulation of blood/interstitial fluid Ca2+ concentration by the scales of anadromous sea trout Salmo trutta L. during smoltification and migration

“…As a result, fish scales, especially those abundantly available from farmed salmon, might transpire to be a low‐cost, complementary model for investigating the development, disease, injury, repair and regeneration of mammalian bone (Laizé et al ., 2014; Mariotti et al ., 2015; Metz et al ., 2012; Pasqualetti et al ., 2012b; Suzuki et al ., 2016; Yoshikubo et al ., 2005), as well as a source of hydroxyapatite for use as a substitute bone scaffold or regenerative material (Pon‐On et al ., 2016), and/or collagen for other biomedical applications such as enhanced wound‐healing (Shalaby et al ., 2020). Finally, a recent worrying report, concerning data collected from 57 countries, suggests a global fall in FW [Ca 2+ ] (Weyhenmeyer et al ., 2019). If this trend continues, then it might pose a considerable threat to both potamodromous and diadromous fish species with respect to stressing their physiological ability to cope with calciotropic challenges, as well as that of their key prey species.…”

Divalent heavy metals and uranyl cations incorporated in calcite change its dissolution process

“…Due to ocean acidification 20 , the dissolution of marine CaCO 3 (including sediments and coral reef) has been reported worldwide 21 – 24 . On the continent, the concentrations of Ca in freshwater increased due to terrestrial rock dissolution as a result of climate change and anthropogenic acid deposition 25 , 26 . Meanwhile, the carbonate bonded metal will release into the environment, which could make calcite a potential source of heavy metals 27 , 28 .…”