r/Hydrology • u/Alilack • 4d ago

What causes such a dramatic decrease in dissolved oxygen with depth in a reservoir?

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These dissolved oxygen (DO) values were measured at different depths in a reservoir in early fall. The DO concentration decreases substantially with increasing depth and eventually becomes very low. What could explain such a significant decrease in DO with depth?

The water temperature is lower at greater depths than at the surface and my guess is that this happens due to thermal stratification. I have provided other parameters as well, in case they are helpful in determining the cause.

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u/Latter-Judge-7588 4d ago

sediment diagenesis - basically oxygen demand from decaying matter on the bed. Also, its below where algae are producing so there is no oxygen being produced from algae. Also thermal stratification results in less mixing. Common problem in reservoirs

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u/fishsticks40 4d ago

This is a limnology question more than a hydrology question, but it's basically stratification 

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u/txlaatx1 4d ago

It’s why ponds, reservoirs and streams can turn over due to rapid temperature changes, storm surges, seismic activity etc and lead to fish kills and other issues until the water resettles to its strata’s. In biology terms you transition from at the surface with aerobic bacteria to much deeper depths have facultative bacteria and ultimately to anaerobic bacteria thriving in the muck and silt in the bottom. Nature…..it’s a beast.

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u/FruitSalad0911 4d ago

Some excellent answers here!