Would you expect the DO (dissolved oxygen) of water taken from a lake at 7am to be higher or lower than 5pm?

Question

i know the lake will be colder in the morning and colder water holds more DO but wouldn't the full day of autotophic production raise the levels?

Answer 1

Lower

Why?

The plants, algae, and phytoplankton have had all day to carry on photosynthesis and put oxygen into the water by 5 pm. Conversely, at 7 am, it's been dark all night and all the producers and consumers in the water have been using up oxygen as they carry on cellular respiration.

As far as the temperature goes, the photosynthesis factor should outweigh the temperature factor. One characteristic of water is that it resists temperature change, and there shouldn't be a large change in the temperature during the day. Especially not in a lake with any kind of depth at all.

Answer 2

Here's my opinion on the answers provided by Jay and ecolink. Jay does not know. Ecolink has it.

It's not just temperature that's important, bio-activity is the major factor. Also remember, there is a lot of variability. In winter you will not see much if any change in DO levels.

Answer 3

If more oxygen can disolve in a cold liquid, what would you expect? Would the lake be cooler after being in the dark all night or after it has been in the sun all day?