New Zealand Journal of Marine and Freshwater Research abstracts
Application of natural and artificial fallout radionuclides to determining
sedimentation rates in New Zealand lakes
N. E. WHITEHEAD
R. G. DITCHBURN
W. J. MCCABE
W. J. MASON+
Nuclear Sciences Group
Institute of Geological and Nuclear Sciences
P. O. Box 31 312
Lower Hutt, New Zealand
J. IRWIN
R. A. PICKRILL
New Zealand Oceanographic Institute
Department of Scientific and Industrial Research
Greta Point, Wellington
New Zealand
G. R. FISH
Ministry of Agriculture and Fisheries
Private Bag
Rotorua, New Zealand
Abstract 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 210Pb and
210Po methods in 26 out of 28 cores. For the 137Cs 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 147Pm and 144Ce showed that most surface layers
were undisturbed, hence the hypothetical mixing often invoked to explain
137Cs profiles lacking the expected 1965 peak is incorrect for most
of these cores. Deficits in surface layer 210Pb caused by
222Rn loss did not affect the estimates of sedimentation rate. One
core contained a record dated back to 1800 A.D. Deposition rates of
210Pb depended on rainfall, not river input. Some local geothermal
activity emits 222Rn and deposits more 210Pb than usual
for New Zealand lakes, but otherwise absolute 210Pb levels are
generally very low compared to other studies. Deposition rates varied from a
low of 0.11 kg m-2 yr-1 (Lake Tikitapu) to a high of
28 kg m-2 yr-1 (one Lake Pukaki core).
Keywords sedimentation; Pb-210; Cs-137; Ce-144; Pm-147;
Rn-222; Lake Rotoiti (North Island); Lake Rotorua; Lake Taupo; Lake Ngahewa;
Lake Tikitapu; Lake Okareka; Lake Pukaki; Lake Waikaremoana; Lake Wakatipu;
Lake Tekapo; Lake Ohau; Falls Dam; Lake Vanda; Pauatahanui
+ Deceased.
M97029
Received 4 July 1997; accepted 11
February 1998
PDF file of entire paper: medium quality (1057K); (scanned from paper original: notes about this process)
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