Crater Lake, Oregon -589 m deep and possibly the clearest lake in the world, Transparency up to 90 m. Thermocline very deep for its size No rooted plants. Mud doesn’t accumulate on the bottom till > 90 m depth Some of the most spectacular tectonic lakes are formed in volcanic craters. Why is this lake so different from most lakes?

Physical features of lakes that determine habitat characteristics inflow from the watershed/Catchment Water residence time Morphometry, Mean depth and volume Thermal stratification and physical mixing wind./currents/wave action Sediment deposition Light extinction

Assume runoff coefficient of 0.15 m Drainage area =7.9 km 2 Lake area =0.9 km 2 How much water would you expect flows into this lake /yr? How much water flows into lake Beauvais lake in a year from its watershed? Evaporation from lake surface exceeds precipitation by mm/yr How much water flows out of the lake?

Assume runoff coefficient of 0.15 m Drainage area =7.9 km 2 Lakearea =0.9 km 2 How much water would you expect flows into this lake /yr? P ─ E on lake surface = ─ m/yr Q i = r * DA = 0.15 m/yr * 7 x 10 6 m 2 = 1.05 x 10 6 m 3 /yr What is the net evaporation in a year? (P-E)*A = ─ m * lake area = ─ 0.085m/yr * 9 x 10 5 m 2 = x 10 4 m 3 /yr How much water flows out of the lake in a year? Q o = Q i + (P-E)*A = 1.05 x 10 6 m 3 /yr + (─ 7.65 x 10 4 m 3 /yr) = 9.75 x 10 5 m 3 /yr

Definition of water residence time and flushing rate Chapter 4

Lake Area = 0.9 km 2 Mean depth= 4.3 m Lake Volume = 3.8 x 10 6 m 3 Water residence time= Mean renewal rate=

Water residence time Mean flushing rate Lake Area = 0.9 km 2 Mean depth= 4.3 m Lake Volume = 3.8 x 10 6 m 3 Water residence time= Mean renewal rate=

How much of the water flowing into this lake from its watershed could you allocate for irrigation before the lake would gradually begin to disappear? Answer Over 92%

Lake management—the water inflow budget or what happens when you over allocate? The Aral Sea in the former Soviet Union—mismanaging the river water inflow Allocation to desert irrigation > inflow minus evaporation Fig. 5.19

. Effects Ecosystem collapse, loss of biodiversity, worsening of water-salt balance in the agricultural areas, pollution of rivers and drinking water, changing of the regional climate – all these are new environmental developments in Central Asia.

Calculating volume and mean depth Mean depth = Volume/surface area The hypsographic curve Area under the curve = volume Fig. 7.1 in text

The thermocline occurs deeper in large lakes because wind energy is transmitted to greater depths Wind energy increases with fetch In small lakes convection also plays a role in determining thermocline depth In deep lakes only the surface layers are well mixed and quite warm, whereas the deeper parts remain cold. Lakes partition themselves into temperature zones Thermal stratification in lakes Fig in text