Lake retention time

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Lake retention time (also called the residence time of lake water, or the water age or flushing time) is a calculated quantity expressing the mean time that water (or some dissolved substance) spends in a particular lake. At its simplest this figure is the result of dividing the lake volume by the flow in or out of the lake. It roughly expresses the amount of time taken for a substance introduced into a lake to flow out of it again. The retention time is especially important where pollutants are concerned.

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[edit] Global retention time

The global retention time for a lake (the overall mean time that water spends in the lake) is calculated by dividing the lake volume by either the mean rate of inflow of all tributaries, or by the mean rate of outflow (ideally including evaporation and seepage). This metric assumes that water in the lake is well-mixed (rather than stratified), so that any portion of the lake water is much like any other. In reality, larger and deeper lakes are generally not well-mixed. Many large lakes can be divided into distinct portions with only limited flow between them. Deep lakes are generally stratified, with deeper water mixing infrequently with surface water. These are often better modeled as several distinct sub-volumes of water.[1]

[edit] More specific residence times

It is possible to calculate more specific residence time figures for a particular lake, such as individual residence times for sub-volumes (e.g. particular arms), or a residence time distribution for the various layers of a stratified lake. These figures can often better express the hydrodynamics of the lake. However, any such approach remains a simplification and must be guided by an understanding of the processes operating in the lake.

Two approaches can be used (often in combination) to elucidate how a particular lake works: field measurements and mathematical modeling. One common technique for field measurement is to introduce a tracer into the lake and monitor its movement. This can be a solid tracer, such as a float constructed to be neutrally buoyant within a particular water layer, or sometimes a liquid. This approach is sometimes referred to as using a Lagrangian reference frame. Another field measurement approach, using an Eulerian reference frame, is to capture various properties of the lake water (including mass movement, water temperature, electrical conductivity and levels of dissolved substances, typically oxygen) at various fixed positions in the lake. From these can be constructed an understanding of the dominant processes operating in the various parts of the lake and their range and duration.[1]

Field measurements alone are usually not a reliable basis for generating residence times, mainly because they necessarily represent a small subset of locations and conditions. Therefore the measurements are generally used as the input for numerical models. In theory it would be possible to integrate a system of hydrodynamic equations with variable boundary conditions over a very long period sufficient for inflowing water particles to exit the lake. One could then calculate the traveling times of the particles using a Lagrangian method. However, this approach exceeds the detail available in current hydrodynamic models and the capacity of current computer resources. Instead, residence time models developed for gas and fluid dynamics, chemical engineering, and bio-hydrodynamics can be adapted to generate residence times for sub-volumes of lakes.[1]

[edit] List of residence times of lake water

The residence time listed is taken from the infobox in the associated article.


Lake Location Basin countries Residence time
Klingnauer Stausee Aargau Switzerland 0000000.000 0.13 days
Lake Hévíz Hévíz Hungary 0000000.003 1 day (?)
Lake Wohlen Canton of Berne Switzerland 0000000.006 2.1 days
Lake St. Clair Canada, United States 0000000.019 7 days (2-30 days)
Lake Arapuni North Island New Zealand 0000000.019 1 week
Råcksta Träsk Sweden 0000000.048 2-3 weeks
Lake Cristallina Ticino Switzerland 0000000.058 2-4 weeks
Prospect reservoir Prospect, New South Wales Australia 0000000.096 30-40 days
Sicklasjön Sweden 0000000.100 0.1 year
Devils Lake Lincoln County, Oregon United States 0000000.150 .15 years
Lough Derg Ireland 0000000.150 0.15 years
Lake Biel Switzerland 0000000.159 58 days
Hacksjön Sweden 0000000.200 0.2 years
Kamloops Lake British Columbia Canada 0000000.200 ca. 0.2 years (20-340 days)
Laduviken Sweden 0000000.250 3 months
Trehörningen Sweden 0000000.270 0.27 years
Lake Lesina Province of Foggia, Puglia Italy 0000000.274 100 days (summer 306 days, winter 31 days)
Hüttnersee Hütten, Canton of Zurich Switzerland 0000000.329 120 days
Lake Lauerz Canton of Schwyz Switzerland 0000000.338 0.3378 years
Sobradinho Brazil 0000000.350 0.35 years
Magelungen Sweden 0000000.375 4-5 months
Lappkärret Sweden 0000000.417 5 months
Mettmenhaslisee Canton of Zurich Switzerland 0000000.493 180 days
Egelsee Bubikon, Canton of Zurich Switzerland 0000000.493 180 days
Lac de Vouglans France 0000000.493 180 days
Clinton Lake DeWitt County, Illinois United States 0000000.500 6 months
Lake Coeur d'Alene Northern Idaho United States 0000000.500 0.5 years
Kyrksjön Sweden 0000000.583 7 months
Faaker See Carinthia Austria 0000000.650 7.8 months
Lake Silvaplana Switzerland 0000000.685 c. 250 days
Långsjön Sweden 0000000.792 9-10 months
Lake Sarnen Switzerland 0000000.800 0.8 years
Lake Lovozero Kola Peninsula, Murmansk Oblast Russia 0000000.833 10 months
Drevviken Sweden 0000000.875 10-11 months
Judarn Sweden 0000000.917 11 months
Khanka Lake Heilongjiang Province,China and Primorsky Krai, Russia China, Russia 0000001.000 1 year
Greifensee Switzerland 0000001.118 408 days
Lake Zurich Switzerland 0000001.205 440 days
Tegernsee Bavaria, Germany Germany 0000001.280 1.28 years
Deer Creek Reservoir Utah United States 0000001.300 1.3 year
Lake Walen Switzerland 0000001.426 1.4258 years
Lake Murten Switzerland 0000001.600 1.6 years
Oeschinen Lake Bernese Oberland Switzerland 0000001.610 1.61 years
Ältasjön Sweden 0000001.800 1.8 years
Long Lost Lake Clearwater County, Minnesota United States 0000001.800 1.8 years
Lake Thun Canton of Berne Switzerland 0000001.874 684 days
Gömmaren Sweden 0000001.900 1.9 years
Loch Lomond Scotland 0000001.900 1.9 years
Türlersee Switzerland 0000002.000 730 days
Lake Tutira Hawke's Bay New Zealand 0000002.000 2 years
Pfäffikersee Switzerland 0000002.085 2.085 years
Wilersee Canton of Zug Switzerland 0000002.200 2.2 years
Lake Sils Switzerland 0000002.200 2.2 years
Päijänne Finland 0000002.500 2.5 years
Lake Erie Canada, United States 0000002.600 2.6 years
Lake Brienz Canton of Berne Switzerland 0000002.690 2.69 years
Ammersee Upper Bavaria Germany 0000002.700 2.7 years
Trekanten Sweden 0000003.100 3.1 years
Lake Champlain Canada, United States 0000003.300 3.3 years
Lake Lucerne Switzerland 0000003.400 3.4 years
Flathead Lake Montana United States 0000003.400 3.4 years
Lake Hallwil Aargau Switzerland 0000003.900 3.9 years
Flaten Sweden 0000004.000 4 years
Lake Annecy France 0000004.000 4 years
Lake Maggiore Italy, Switzerland Italy, Switzerland 0000004.000 4 years
Lake Baldegg Switzerland 0000004.200 4.2 years
Lake Constance Germany, Switzerland, Austria Germany, Switzerland, Austria, Liechtenstein 0000004.300 4.3 years
Corey Lake Michigan United States 0000004.400 4.4 years
Lake Como Northern Italy Italy, Switzerland 0000004.500 4.5 years
Sea of Galilee Israel 0000005.000 5 years
Sebago Lake Cumberland County, Maine United States 0000005.250 5.1 to 5.4 years
Bay Lake Crow Wing County, Minnesota United States 0000005.500 4-7 years
Lago di Mergozzo Piedmont Italy 0000006.000 6 years
Lake Ontario Canada, United States 0000006.000 6 years
Lago di Candia Province of Turin Italy 0000006.500 6 or 7 years
Lac La Nonne Alberta Canada 0000006.500 6.5 years
Ägerisee Canton of Zug Switzerland 0000006.800 6.8 years
Moose Lake Alberta Canada 0000007.500 7.5 years
Millstätter See Carinthia Austria 0000007.500 7.5 years
Lake Lugano Ticino, Lombardy Switzerland, Italy 0000008.200 8.2 years
Lake Neuchâtel Switzerland 0000008.200 8.2 years
Lake Orta Piedmont Italy 0000008.900 8.9 years
Quesnel Lake British Columbia Canada 0000010.100 10.1 years
Lake Taupo North Island, New Zealand New Zealand 0000010.500 10.5 years
Wörthersee west of Klagenfurt Austria 0000010.500 10.5 years
Lake Chelan Washington, USA United States 0000010.600 10.6 years
Lake Geneva Switzerland, France 0000011.400 11.4 years
Lake Wakatipu South Island New Zealand 0000012.000 c. 12 years
Higgins Lake Michigan United States 0000012.500 12.5 years
Lake Zug Switzerland 0000014.700 14.7 years
Lake Sempach Switzerland 0000016.900 16.9 years
Skaneateles Lake United States 0000018.000 18 years
Cayuga Lake United States 0000018.200 18.2 years
Bear Lake Idaho/Utah United States 0000019.600 19.6 years
Lake Huron Canada, United States 0000022.000 22 years
Lake Garda Northern Italy Italy 0000026.800 26.8 years
Crystal Lake Benzie County, Michigan United States 0000045.000 30 to 60 years
Okanagan Lake British Columbia Canada 0000052.800 52.8 years
Lake Ohrid the Republic of Macedonia,
Albania		 0000070.000 70 years
Lake Michigan United States 0000099.000 99 years
Clinton Lake Douglas County, Kansas United States 0000100.000 100 years
Arendsee Saxony-Anhalt Germany 0000100.000 100 years
Gull Lake Alberta Canada 0000101.000 >100 years
Crater Lake Oregon United States 0000157.000 157 years
Lake Superior Canada, United States 0000191.000 191 years
Caspian Sea Azerbaijan, Iran, Kazakhstan, Russia, Turkmenistan 0000250.000 250 years
Lake Baikal Russia 0000350.000 350 years
Lake Tahoe California, Nevada United States 0000650.000 650 years
Lakes Qaban Russia 0002000.000 several thousand years
Lake Poyang People's Republic of China 0005000.000 5,000 years
Lake Vostok (Antarctica) 1000000.000 1,000,000 years

[edit] References

  1. ^ a b c Duwe, Kurt (2003-01-03), D24: Realistic Residence Times Studies, Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas, EUROLAKES, <http://www.hydromod.de/Eurolakes/results/D24.pdf>. Retrieved on 11 December 2007 

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