Post by olhillbilly on Jul 9, 2009 18:10:42 GMT -6
The loss of dissolved oxygen in lake water during the summer months is generally associated with a process that is called thermal stratification. This phenomenon involves the development of temperature “layers”, in which the water near the surface is uniformly warm to a depth that varies throughout the summer. Under the surface layer (referred to as the epilimnion) there is a zone of transition (thermocline) in which the water temperature drops rapidly. From the transition zone to the bottom of the lake is the layer of water that is the coldest (hypolimnion), and the most dense (heavy). During the summer months the coldest layer near the bottom is physically and chemically separated from the surface.
The bottom sediments in biologically productive lakes are rich in organic matter that has accumulated over time (algae and other plankton, and organic soil material). As this matter is degraded by microbes, oxygen is consumed from the overlying water. During the stratification period there may be no opportunity for oxygen to be replenished. Depending on the extent of the oxygen loss, coldwater fishery habitat may be reduced. Another possible result of oxygen depression or depletion is the potential release of biologically-available phosphorus from the bottom sediments.
Dissolved oxygen is replenished during the fall, when short days and cool air temperatures cause the lake to de-stratify or “mix”. This process is also referred to as “turning over”. Most lakes turn over twice each year - once in the fall and again in the spring. The degree to which individual lakes experience thermal stratification depends on the depth and volume of the lake and the orientation of the lake basin to prevailing winds. Annual weather patterns and individual weather events strongly influence the degree and duration of thermal stratification.
One more thing to add to this is how Dissolved Oxygen (DO) content relates to the angler and to the fish since both are connected. DO content is at it's lowest during hot summer days. The fish will position themselves during daylight hours in the highest DO they can find. Since there is more DO in colder water...this means they will be deeper. But keep in mind that there is not enough DO underneath the thermocline to support any life. Therefore one should limit their summertime fishing to areas at and above the thermocline. The thermocline is nonexistent during the cooler months. Keep in mind that this only applies to lakes, ponds, strip pits, and the likes. There is no thermocline in a river since the moving water constantly replenishes the DO content. The thermocline can be found by turning your sensitivity level to high on your fishfinder and adjusting down until you pick up the TC on your screen. It will appear as a horizontal line located between the surface and the bottom. During the evening hours the water will begin to cool down, and as that happens the DO content of the water will be more widespread...prompting the fish to move around and feed instead of staying put. This is not to assume fish cant be caught during the day. You'll just need to locate where the fish are loafing near an adequate supply of DO and take the fight to them. Mobility is the key during daylight hours to consistently find where the fish are. They typically will school near favorable conditions....such as not only the DO factor...but also some type of cover/shade to shield their eyes since they have no eyelids, and also some form of available forage to eat.
==============================================
A more extensive article may be found here. >>
www.islandnet.com/~see/weather/elements/turnlakes.htm
A very good read.
The bottom sediments in biologically productive lakes are rich in organic matter that has accumulated over time (algae and other plankton, and organic soil material). As this matter is degraded by microbes, oxygen is consumed from the overlying water. During the stratification period there may be no opportunity for oxygen to be replenished. Depending on the extent of the oxygen loss, coldwater fishery habitat may be reduced. Another possible result of oxygen depression or depletion is the potential release of biologically-available phosphorus from the bottom sediments.
Dissolved oxygen is replenished during the fall, when short days and cool air temperatures cause the lake to de-stratify or “mix”. This process is also referred to as “turning over”. Most lakes turn over twice each year - once in the fall and again in the spring. The degree to which individual lakes experience thermal stratification depends on the depth and volume of the lake and the orientation of the lake basin to prevailing winds. Annual weather patterns and individual weather events strongly influence the degree and duration of thermal stratification.
One more thing to add to this is how Dissolved Oxygen (DO) content relates to the angler and to the fish since both are connected. DO content is at it's lowest during hot summer days. The fish will position themselves during daylight hours in the highest DO they can find. Since there is more DO in colder water...this means they will be deeper. But keep in mind that there is not enough DO underneath the thermocline to support any life. Therefore one should limit their summertime fishing to areas at and above the thermocline. The thermocline is nonexistent during the cooler months. Keep in mind that this only applies to lakes, ponds, strip pits, and the likes. There is no thermocline in a river since the moving water constantly replenishes the DO content. The thermocline can be found by turning your sensitivity level to high on your fishfinder and adjusting down until you pick up the TC on your screen. It will appear as a horizontal line located between the surface and the bottom. During the evening hours the water will begin to cool down, and as that happens the DO content of the water will be more widespread...prompting the fish to move around and feed instead of staying put. This is not to assume fish cant be caught during the day. You'll just need to locate where the fish are loafing near an adequate supply of DO and take the fight to them. Mobility is the key during daylight hours to consistently find where the fish are. They typically will school near favorable conditions....such as not only the DO factor...but also some type of cover/shade to shield their eyes since they have no eyelids, and also some form of available forage to eat.
==============================================
A more extensive article may be found here. >>
www.islandnet.com/~see/weather/elements/turnlakes.htm
A very good read.
