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Widespread diminishing anthropogenic effects on calcium in freshwaters

TitleWidespread diminishing anthropogenic effects on calcium in freshwaters
Publication TypeJournal Article
Year of Publication2019
AuthorsWeyhenmeyer GA, Hartman J, Hessen DO, Kopacek J, Hejzlar J, Jacquet S, Hamilton SK, Verburg P, Leach TH, Schmid M, Flaim G, Noges T, Noges P, Wentzky VC, Rogora M, Rusak JA, Kosten S, Paterson AM, Teubner K, Higgins SN, Lawrence G, Kangur K, Kokorite I, Cerasino L, Funk C, Harvey R, Moatar F, deWit HA, Zechmeister T
JournalScientific Reports
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 with 20.7% of
the water samples showing Ca concentrations ≤ 1.5 mg L , 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

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