Water Stratification In Lakes

Oxygen and nutrients get distributed throughout the water column as the water mixes.

Water stratification in lakes. In sufficiently deep lakes thermal stratification holds until cooler autumn and winter temperatures force a circu lation into deep waters. Once the ice melts the water column can be mixed by the wind. Most lakes in minnesota are considered dimictic meaning they mix twice a year spring and fall. Then as the weather becomes warmer the surface water warms again and sets up summer stratification.

Many shallow lakes however do not stratify in the summer or stratify for short periods only throughout the summer. Lakes with this pattern of two mixing periods are referred to as dimictic. Covered in ice all year. During winter any additional cooling below 4 c results in stratification of water column so dimictic lakes usually have an inverse thermal stratification with water at 0 c below ice and then with temperatures increasing to near 4 c at the lake s base.

Some small shallow lakes may not experience seasonal thermal stratification because the wind mixes the entire lake. Stratification in estuaries is in some respects similar to stratification in lakes although in estuaries the density difference is primarily due to the difference in salinity between freshwater and ocean water instead of being primarily due to temperature differences. Typically stratified lakes show three distinct layers the epilimnion comprising the top warm layer the thermocline. The middle layer which may change depth throughout the day and the colder hypolimnion extending to the floor of the lake.

Lake stratification is the tendency of lakes to form separate and distinct thermal layers during warm weather. Thermal stratification which contributes much to lake structure is a direct result of heating by the sun. Shallow lakes behave differently and can mix more often. Water never gets warmer than 4 c and turnover occurs once in summer.

To assess if environmental differences other than water quality may affect the outcome of the benthic quality index a comparison of the application of four different methods benthic quality index mdash bqies lake habitat modification score mdash lhms lake habitat quality assessment mdash lhqa and organisation for economic co operation and development mdash oecd used to classify the lake. This pattern spring turnover summer stratification fall turnover winter stratification is typical for temperate lakes. Thermal stratification is the phenomenon in which lakes develop two discrete layers of water of different temperatures. Thermal stratification of a lake depends on the lake s depth shape and size.

This mixing pattern is typical of lakes in the antarctic. Other lakes such as lake erie have a combination of geographic location and water depth that regularly produces thermal stratification. The warm surface water layer is called epilimn ion while the colder wate r layer beneath which has not been mixed into the epilimn ion over the stratification period is called hypolimnion. Lakes in the arctic are often cold.