Calcium Decline

Yan, N.D., Mackie, G.L., and Boomer, D. 1989.
Seasonal patterns in metal levels of the net plankton of three Canadian Shield lakes.
The Science of the Total Environment. 87/88: 439-461.

Within a broader analysis of metal levels in crustacean zooplankton, calcium concentrations of daphniids were noted to be significantly higher than other taxonomic groups.

Alstad, N.E.W., Skardal, L., Hessen, D.O. 1999.
The effect of calcium concentration on the calcification of Daphnia magna.
Limnology and Oceanography. 44: 2011-2017.

Experimental studies on the calcification and calcium content of Daphnia magna clearly suggest the potential of calcium limitation.

Hessen, D.O., Alstad, N.E.W., and Skardal, L. 2000.
Calcium limitation in Daphnia magna.
Journal of Plankton Research. 22: 553-568.

Threshold calcium levels required for the survival of the hardwater species Daphnia magna found to be in the 0.1-0.5 mg/L range. Age-specific egg production strongly reduced at Ca concentrations <10 mg/L.

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Keller, W., Dixit, S.S., and Heneberry, J. 2001.
Calcium declines in northeastern Ontario lakes.
Canadian Journal of Fisheries and Aquatic Sciences. 58: 2011-2020.

Inferred historical lakewater calcium concentrations using diatoms as a paleolimnological indicator for six lakes near Sudbury, Ontario showing large declines through much of the 20th century.

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Waervagen, S.B., Rukke, N.A., and Hessen, D.O. 2002.
Calcium content of crustacean zooplankton and its potential role in species distribution.
Freshwater Biology. 47: 1866-1878.

A regional study of Norwegian lakes showing aqueous calcium concentration to influence the distribution of Daphnia species and calcium content to differ among species.
(This study combined with observed declines in aqueous calcium concentrations of the Dorset A-lakes prompted Dr. Norman Yan to have a Masters student examine calcium concentration differences in crustacean zooplankton of Ontario lakes).

Jeziorski, A. and Yan, N.D. 2006.
Species identity and aqueous calcium concentrations as determinants of calcium concentrations of freshwater crustacean zooplankton.
Canadian Journal of Fisheries and Aquatic Sciences. 63: 1007-1013.

A field study examining the calcium concentrations of eight crustacean zooplankton species from nine lakes on the Canadian Shield. Species identity was more important in determining crustacean zooplankton calcium concentration than either lake calcium concentration or seasonality (Daphnia spp. had much greater calcium levels than any of the other species).

Jeziorski, A., Paterson, A.M., Yan, N.D., and Smol, J.P. 2008.
Calcium levels in Daphnia ephippia cannot provide a useful paleolimnological indicator of historical Lakewater Ca concentrations.
Journal of Paleolimnology. 39: 421-425.

An attempt to apply the species-specific Ca concentration of crustacean zooplankton in a paleolimnological approach using their ephippia (resting eggs) that proved to be quite difficult due to the low levels of calcium in the ephippia.

DeSellas, A.M., Paterson, A.M., Sweetman, J.N., and Smol, J.P. 2008
Cladocera assemblages from the surface sediments of south-central Ontario (Canada) lakes and their relationships to measured environmental variables.
Hydrobiologia. 600: 105-119.

A "Top-Bottom" paleolimnological analysis of crustacean zooplankton assemblages from 44 lakes in South-central Ontario found calcium to be one of the five environmental variables significantly influencing assemblage composition (along with SO₄, pH, Z_max and DOC).

Ashforth, D. and Yan, N.D. 2008.
The interactive effects of calcium concentrations and temperature on the survival and reproduction of Daphnia pulex at high and low food concentrations.
Limnology and Oceanography. 53: 420-432.

Examined the calcium needs of Daphnia pulex (the species that had the highest calcium content of the 8 examined in Jeziorski and Yan, 2006) in a laboratory setting and identified a 1.5 mg/L performance threshold.

Jeziorski, A., Yan, N.D., Paterson, A.M., DeSellas, A.M., Turner, M.A., Jeffries, D.S., Keller, B., Weeber, R.C., McNicol, D.K., Palmer, M.E., McIver, K., Arseneau, K., Ginn, B.K., Cumming, B.F., and Smol, J.P. 2008.
The widespread threat of calcium decline in fresh waters.
Science. 322: 1374-1377.

Documented near extirpations of calcium-rich Daphnia spp., in sediment cores from lakes with calcium concentrations that have recently fallen below 1.5mg/L. A large proportion (62 %; 47-81 % by region) of the 770 Canadian Shield lakes examined have calcium concentrations approaching or below this threshold.