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| Titel |
Dating of streamwater using tritium in a post nuclear bomb pulse world: continuous variation of mean transit time with streamflow |
| VerfasserIn |
U. Morgenstern, M. K. Stewart, R. Stenger |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 14, no. 11 ; Nr. 14, no. 11 (2010-11-18), S.2289-2301 |
| Datensatznummer |
250012484
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| Publikation (Nr.) |
 copernicus.org/hess-14-2289-2010.pdf |
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| Zusammenfassung |
| Tritium measurements of streamwater draining the Toenepi catchment, a small
dairy farming area in Waikato, New Zealand, have shown that the mean transit
time of the water varies with the flow rate of the stream. Mean transit
times through the catchment are 2–5 years during high baseflow conditions
in winter, increasing to 30–40 years as baseflow decreases in summer, and
then dramatically older water during drought conditions with mean transit
time of more than 100 years. Older water is gained in the lower reaches of
the stream, compared to younger water in the headwater catchment. The
groundwater store supplying baseflow was estimated from the mean transit
time and average baseflow to be 15.4 × 106 m3 of water, about 1 m
water equivalent over the catchment and 2.3 times total annual streamflow.
Nitrate is relatively high at higher flow rates in winter, but is low at
times of low flow with old water. This reflects both lower nitrate loading
in the catchment several decades ago as compared to current intensive dairy
farming, and denitrification processes occurring in the older groundwater.
Silica, leached from the aquifer material and accumulating in the water in
proportion to contact time, is high at times of low streamflow with old
water. There was a good correlation between silica concentration and
streamwater age, which potentially allows silica concentrations to be used
as a proxy for age when calibrated by tritium measurements. This study shows
that tritium dating of stream water is possible with single tritium
measurements now that bomb-test tritium has effectively disappeared from
hydrological systems in New Zealand, without the need for time-series data. |
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