Questions about thermocline and/or life zone...

[softwateronly]

 - Deep lakes have a deeper life zone because there's more dissolved oxygen available because of water volume from the 2 turnovers. T/F?

 

 - Can current offer enough energy to keep the water layers mixed with oxygen?  I assume dependent on water volume moved?  Does it also depend on what depth the current and/or the temperature difference is, as it enters the system?  

 

 - In a spring fed lake, would the influx of "new" water offer a deeper life zone?  Would/could that be concentrated near the spring(s)?

 

Thanks,

 

scott

 

 

[Bankc]

Everything can effect it.  For instance, dirty lakes will have a much more shallow thermocline than clear lakes in most circumstances.  My local lake usually has about 1-2 feet of visibility, so it's a fairly dirty lake.  And yet, in the summer, I've seen the thermocline as deep as 40 feet.  The lake itself is about 100 feet deep and there's no natural current (manmade reservoir with water pumped in and out), but plenty of wind.  So the wind chops up the top and helps to mix that water up a good bit, but the water at the bottom just lays motionless.  So the thermocline on this lake doesn't set in as fast as on other, similar lakes, but when it finally does, it tends to go a lot deeper.  And it gets deep fairly quickly.  

 

So I wouldn't worry too much about theory, and pay more attention to what you actually observe.  The theory is better at explaining what has happened than predicting what will happen.   

[WRB]

5 hours ago, softwateronly said:

 - Deep lakes have a deeper life zone because there's more dissolved oxygen available because of water volume from the 2 turnovers. T/F?

 

 - Can current offer enough energy to keep the water layers mixed with oxygen?  I assume dependent on water volume moved?  Does it also depend on what depth the current and/or the temperature difference is, as it enters the system?  

 

 - In a spring fed lake, would the influx of "new" water offer a deeper life zone?  Would/could that be concentrated near the spring(s)?

 

Thanks,

 

scott

 

 

1. Multiple turnovers; winter turnover and fall turnover occurs on some lakes and reservoirs. Depth of water tends to determine thermocline depth.

2. Oxygen for fish must be dissolved DO, current tends to mix the water column evenly in rivers or created multiple thermal layers in reservoirs. Wind driven current mixes DO in the upper water column. Reservoirs pulling water for hydro tend to move water from the bottom of the dam creating multiple layer of DO levels. Water temperature layers are created by lighter weight water on top of heaver weight water, warmer water is lighter, colder water heavier until it reaches 39.4 F then it gets light weight (less density).

Aeration systems pump deep water to the surface using a combination or water air pressure to add DO and mix the water temps.

3. Spring water in devoid of DO. Spring water is between 50-60 F year around providing comfortable water temps.

Thermocline is the first layer of water where the temps drop 3-4 F with a few feet. Life zone is the depth baitfish and bass concentrate. Warm water above 80 F hold less DO the 70 F for example, the fish move down to the higher DO cooler water where a thermocline may have developed. Keep in mind green aquatic plants provide DO during day light and shade attracting baitfish and bass.

Tom 

[Team9nine]

7 hours ago, softwateronly said:

 - Deep lakes have a deeper life zone because there's more dissolved oxygen available because of water volume from the 2 turnovers. T/F?

 

Mostly true, but it depends somewhat on what stage of life they are in (how fertile - oligotrophic, mesotrophic, eutrophic, hypereutrophic, etc.). Generally, the greater the fertility, the more likely to have shallower thermoclines, if any at all depending upon overall depth. 

 

Quote

 - Can current offer enough energy to keep the water layers mixed with oxygen?  I assume dependent on water volume moved?  Does it also depend on what depth the current and/or the temperature difference is, as it enters the system?  

 

Current as in a river system, yes. Current as in wind driven - generally not unless excessive (severe storm related). Again, it partly depends on depth, and @WRB covered some of the less frequent variables you may or may not run into depending on reservoir type, or natural lake. River-run lakes like TVA impoundments that are also used for power generation tend to stay better mixed, and mixed deeper than more stable reservoirs that are typically for flood control purposes.

 

Quote

 - In a spring fed lake, would the influx of "new" water offer a deeper life zone?  Would/could that be concentrated near the spring(s)?

 

 

Very possible because springs offer a stable input of cooler water, and cooler water holds more oxygen. That inflow would also be from the bottom, and cooler water is more dense than warmer water, so it would tend to stay in the lower levels of the water column, and subsequently aid in mixing. Again though, overall nutrient levels in the lake will play a role, as will current/mixing sources.

[WRB]

What fresh water bass anglers over look is thermal breaks.

Thermocline is Horizontal, thermal break is vertical, often coupled with water color changes. It’s easy to forget we live in a 3D world looking 2D sonar screens.

Tom

[softwateronly]

I appreciate all the knowledge being shared.  Been getting through the demystifying structure threads trying to determine if I can eliminate any deep water this year on my lake.  It's an odd lake in that it's very similar to a low flow, damned reservoir, but instead a natural lake that drains a watershed through marsh land to a controlled river, the St Joe.  There is a consistent movement of water from North to South, numerous springs, and over 85% of the lake is 20' or deeper.  There is large fish biodiversity and a healthy population of 5+lb bass and 35" pike for a small lake, but they almost exclusively live deep.

 

Without electronics and dropping live bait to depth, I'm unsure if I can safely eliminate water.  It's only 250 acres but time will be limited more this year than expected because of work.  Your responses will help me be a lot more efficient.

 

4 hours ago, WRB said:

What fresh water bass anglers over look is thermal breaks.

Thermocline is Horizontal, thermal break is vertical, often coupled with water color changes. It’s easy to forget we live in a 3D world looking a sonar screens.

Tom

If you're up for it, would love to learn more.  Vertical thermal break in relation to finding the depth that bass live most comfortably because of DO in relation to temp, water color changes in reference to lack of phytoplankton below light penetration levels?

 

 

scott  

[MGF]

The comments about springs got me thinking. I was a long time cave diver but I never became much of a hydrologist like others I knew but some observations regarding springs. The underground aquafer will remain close to the average temp for the area. Florida caves are seventy something deg F while Missouri (along rt 44) are mid 50's. I saw the Missouri springs vary by a few degrees from winter to summer. I never noticed that in Florida...at least not to the same degree.

 

I never had any way to measure dissolved O2 but I used to dive a spring (and associated cave) in Missouri where the lighted cavern zone (where light from the entrance can be seen) was often loaded with fish...pan fish, trout and small mouth bass.

 

On occasion some of those trout and bass would follow us 900 feet back into the cave to depths greater than 160 feet. There must have been a fair amount of dissolved O2. this was a "spring" which means that all the flow was out. The water comes from far away and deep in the earth. LOL so I don't know where the O2 is coming from. This spring formed a run which fed a small river.

 

Another Missouri spring I used to dive emerged into a reservoir in the Mark Twain National forest. The entrance was at about 30 ft but was a spring run feeding the river before the reservoir was formed. The interesting thing here was that the lake vis was usually near zero...I mean can't see your hand in front of your face "zero"...winter was a little better. The spring water was very clear...colder than the lake in summer but warmer than the lake in winter. There was a sheer drop at 20 ft just above the spring entrance and this was about where you could see and feel the line between the clear spring water and the lake water.

 

I know I saw fish there but I wasn't doing much fishing during those years and do to the nature of those particular dives had things other than fish watching on my mind. That cave was a very deep dive and that ledge at 20 ft was last in a long line of decompression stops.

 

In the shallow parts of that cave 30 ft to 70 ft I saw piles of dead fish...looked like carp. It's a spring so the flow is out...they had to intentionally swim in against the flow. there was also decomposition. I'm not really sure what that tells us about dissolved O2.

 

Looking back I wish I had paid more attention to the fish or even combined the diving and fishing more. I saw so many fish, so close and so easy that I lost interest in catching them for a time.

 

Sorry of this wandered too far off topic but I'll bet at least some of you would get a kick out of having the bass follow you for a change. LOL

 

 

 

[scaleface]

@MGF  very interesting .

[Dens228]

21 hours ago, Bankc said:

Everything can effect it.  For instance, dirty lakes will have a much more shallow thermocline than clear lakes in most circumstances.  My local lake usually has about 1-2 feet of visibility, so it's a fairly dirty lake.  And yet, in the summer, I've seen the thermocline as deep as 40 feet.  The lake itself is about 100 feet deep and there's no natural current (manmade reservoir with water pumped in and out), but plenty of wind.  So the wind chops up the top and helps to mix that water up a good bit, but the water at the bottom just lays motionless.  So the thermocline on this lake doesn't set in as fast as on other, similar lakes, but when it finally does, it tends to go a lot deeper.  And it gets deep fairly quickly.  

 

So I wouldn't worry too much about theory, and pay more attention to what you actually observe.  The theory is better at explaining what has happened than predicting what will happen.   

So very true.........my main fishing water is a large quarry.  For the last several years by June the visibility is about 10 feet or so in most spots.  The thermocline has been around 16-feet give or take a foot over those years.   Last year for the first time I can remember they decided to do a weed kill. The water was murky all summer and was still murky when it iced over.   All summer the shallowest thermocline was about 20 feet.   Go figure. 

[WRB]

23 hours ago, softwateronly said:

I appreciate all the knowledge being shared.  Been getting through the demystifying structure threads trying to determine if I can eliminate any deep water this year on my lake.  It's an odd lake in that it's very similar to a low flow, damned reservoir, but instead a natural lake that drains a watershed through marsh land to a controlled river, the St Joe.  There is a consistent movement of water from North to South, numerous springs, and over 85% of the lake is 20' or deeper.  There is large fish biodiversity and a healthy population of 5+lb bass and 35" pike for a small lake, but they almost exclusively live deep.

 

Without electronics and dropping live bait to depth, I'm unsure if I can safely eliminate water.  It's only 250 acres but time will be limited more this year than expected because of work.  Your responses will help me be a lot more efficient.

 

If you're up for it, would love to learn more.  Vertical thermal break in relation to finding the depth that bass live most comfortably because of DO in relation to temp, water color changes in reference to lack of phytoplankton below light penetration levels?

 

 

scott  

Dissolved oxygen in water is measured in milligrams per liter mg/L. LMB can service in water with 3 mg/L to 13 mg/L severe stress outside this DO range.

Water temps affect DO range in regards to min and max, over 90F and warmer 3mg/L is difficult unless green vegetation or aeration supplements the DO. 

38F and colder 13 mg/L is difficult to reduce unless the bass find warmer water or warmer spring water the lower mix with supper saturated DO levels.

The earth warms the ground so bass go deeper nearer the bottom to find water 40F or warmer.

Thermoclines are not like a sheet it’s a Horizontal temperature break zone the can very in thickness and depth. Wind for example bends a thermal layer, current can mix it up.

Very gin clear water has lower particulate content for the sun light to warm and cools faster then colored water with higher particulate content. Phytoplankton appear green in the water.

Phytoplankton is vegetable drawn toward the surface by sunlight. Threadfin Shad feed on Phytoplankton.

Zooplankton is brownish in the water, animal drawn to aquatic plants to feed on micro organisms. Gizzard Shad and small fish feed on Zooplankton. 

Thermal breaks is a transition zone where different temperature water come together vertically, usually visual being different colors. Very clear changing greenish usually indicates a temperature break, not always.

Tom

[softwateronly]

On 3/16/2021 at 6:32 PM, WRB said:

Dissolved oxygen in water is measured in milligrams per liter mg/L. LMB can service in water with 3 mg/L to 13 mg/L severe stress outside this DO range.

Water temps affect DO range in regards to min and max, over 90F and warmer 3mg/L is difficult unless green vegetation or aeration supplements the DO. 

38F and colder 13 mg/L is difficult to reduce unless the bass find warmer water or warmer spring water the lower mix with supper saturated DO levels.

The earth warms the ground so bass go deeper nearer the bottom to find water 40F or warmer.

Thermoclines are not like a sheet it’s a Horizontal temperature break zone the can very in thickness and depth. Wind for example bends a thermal layer, current can mix it up.

Very gin clear water has lower particulate content for the sun light to warm and cools faster then colored water with higher particulate content. Phytoplankton appear green in the water.

Phytoplankton is vegetable drawn toward the surface by sunlight. Threadfin Shad feed on Phytoplankton.

Zooplankton is brownish in the water, animal drawn to aquatic plants to feed on micro organisms. Gizzard Shad and small fish feed on Zooplankton. 

Thermal breaks is a transition zone where different temperature water come together vertically, usually visual being different colors. Very clear changing greenish usually indicates a temperature break, not always.

Tom

Beautiful.

 

Much appreciated

 

scott