Application of natural and artificial fallout radionuclides to determining sedimentation rates in New Zealand lakes
Whitehead, N.E.; Ditchburn, R.G.; McCabe, W.J.; Mason, W.J.; Irwin, J.; Pickrill, R.A.; Fish, G.R.
New Zealand Journal of Marine and Freshwater Research 32(3): 489-503
ISSN/ISBN: 0028-8330 DOI: 10.1080/00288330.1998.9516838
Sedimentation rates have been estimated for New Zealand lakes Rotoiti, Taupo, Ngahewa, Tikitapu, Okareka, Pukaki, Rotorua, Waikaremoana, Wakatipu, Tekapo, and Ohau, and also the Falls Dam, Central Otago, the Pauatahanui Inlet (Wellington), and Lake Vanda (Antarctica). Sedimentation rates were able to be calculated using the (super 210) Pb and (super 210) Po methods in 26 out of 28 cores. For the (super 137) Cs method (shown equivalent to the previous methods) calculable rates were obtained in 13 out of 19 cores. An age estimation was always possible by one of the methods. Values of (super 147) Pm and (super 144) Ce showed that most surface layers were undisturbed, hence the hypothetical mixing often invoked to explain (super 137) Cs profiles lacking the expected 1965 peak is incorrect for most of these cores. Deficits in surface layer (super 210) Pb caused by (super 222) Rn loss did not affect the estimates of sedimentation rate. One core contained a record dated back to 1800 A.D. Deposition rates of (super 210) Pb depended on rainfall, not river input. Some local geothermal activity emits (super 222) Rn and deposits more (super 210) Pb than usual for New Zealand lakes, but otherwise absolute (super 210) Pb levels are generally very low compared to other studies. Depostion rates varied from a low of 0.11 kg m (super -2) yr (super -1) (Lake Tikitapu) to a high of 28 kg m (super -2) yr (super -1) (one Lake Pukaki core).