ESS 328 Limnology

Fall 2020

Chapter 7 Lakes and Reservoirs

Stratification / Turnover / Mixing

Heat, light, density difference with depth

Annual cycle for a temperate lake

Thermal (Summer) Stratification

Epilimnion

Metalimnion (Thermocline)

Hypolimnion --- COLD Handout

©2010 Elsevier, Inc.

FIGURE 7.11

Temperature as a function of depth for Triangle Lake, Oregon, on October 1, 1983, and positions of epilimnion,

metalimnion, and hypolimnion. (Data from R. W. Castenholz).

Thermal resistance to mixing

©2010 Elsevier, Inc.

FIGURE 7.12

Stability of the thermocline in Linsley Pond, Connecticut, before and after a hurricane on September 21, 1938, with

wind speeds up to 100 km h21. (From G. E. Hutchinson, A Treatise on Limnology, Vol. 1, Geography, Physics and

Chemistry. John Wiley & Sons, Inc., 1957. Reprinted by permission of John Wiley & Sons, Inc.).

FIGURE 7.10

Holomixis

Lake mixing

– Amictic

– Monomictic

Warm

Cold

– Dimictic

– Meromictic

– Polymictic

Depth-Time Isopleths

Implications

Stratification

Turnover (mixing)