Several publications say that water age is "the time elapsed for dissolved substances to be transported from one point to another", which could be easily understood when there is only one single inflow or tributary of a lake. Because the "one point" in the concepet mentioned above is actually the inflow/tributary and the "another point" could be any location in the lake. The water age maybe reflects the time spent of water particles moving from the inflow to the specific position. However, what is the meaning of water age of a lake if there are multiple inflows? What does the "one point" mean?
Keep in mind also that water enters lakes through the subsurface as well, and this can vary widely among lakes. So, the water age will also reflect this contribution from groundwater as well
I am more familiar with water age concepts in stream/river environments than in lakes. But I have to disagree that water age applies to dissolved substances. Terms such as "water age", "water residence time", or "water transit time" apply exclusively to the water itself and not necessarily to the dissolved substances. One reason is that the solutes are subject to biogeochemical processes along the flow pathway, and may not reflect the age of the water itself. Finally, when hydrologists refer to water age or transit time, they are generally referring to the elapsed time from when the water enters the catchment (as rain or snow) to the point where the water sample is collected---perhaps in a stream or lake. If you would like to read more on the perspective of catchment hydrologists on application of water age, residence time, transit time, etc., I would suggest that you read two papers:
Kevin J. McGuire, Jeffrey J. McDonnell, A review and evaluation of catchment
transit time modeling, Journal of Hydrology (2006) 330, 543– 563.
J.J. McDonnell et al., How old is streamwater? Open questions in catchment transit time conceptualization, modelling and analysis, Hydrol. Process. 24, 1745–1754 (2010).
Geochemists measure the age of water by comparing Oxygen 18 vs. Oxygen 16. Oxygen 16 or O16 is the weight of the bulk of oxygen on earth, while O18 is an isotope or variant of oxygen. The ratio is calibrated and provides historical information about the water.
Therefore, you might want to look into the geochemical or geological literature. Geochemica et Cosmochemica is one of the leading journals in the field.
Age of water or residence time is measured from tritium analysis of water sample. You need to know the base line tritium value of incoming water in the lake. In case of multiple inflows , May be snowmelt / Rain water, You need to know the Tritium contents of all sources then you are taking one composite sample from the lake and will get average tritium value for the lake. The half life for Tritium is 12.3 years using simple radioactive decay formula. It can be calculated. The main issue is about baseline value in case of multiple flows i.e i you have to focus on nature of incoming flows if they are from the same origin or not i.e from rain or snowmelt or under ground recharge. Then tritium analysis of source water will give you baseline. Suppose your lake is being recharges from rain water either it is coming in the form of multiple flows then rain water tritium analysis will give you baseline.
Dear Hengda Qi,
I agree with Saira Butt . You can take a look to our paper about Lake Ladoga age of water .
RADIOACTIVE NUCLIDES AS INDICATORS OF THE TIME OF WATER EXCHANGE IN LAKE LADOGA
BLINOV A.V. , LAZAREV V.E., KARETNIKOV S.G., NAUMENKO M.A., NOLTE E.
DOKLADY EARTH SCIENCES, vol.392,№7,1008-1010.
http://elibrary.ru/item.asp?id=13437350
Best Regards
The elapsed transport time for a parcel of water on surface or underground, leave the interface of any inland drain/river or tidal inlets of the sea to a specific point within the lagoon.
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