Viewing a single comment thread. View all comments

Kingreaper t1_jadjc2x wrote

Reply to comment by GeorgeCauldron7 in ELI5: Why is it that when fertilizers make their way into waterways, all the oxygen disappears, killing the fish? by Psychological-Dog994

> So does the algae itself consume oxygen (aerobic respiration?), or produce oxygen (photosynthesis?) in order to survive? Sorry, I study inorganic geochemistry but don't know much of anything about biology or botany. > >

The Algae both consumes and produces oxygen - at first it's necessarily producing more than it consumes, in order to get the carbon it needs to grow in size, but when it's as big as it's going to get those numbers start balancing out.

Add in the fact that dead algae decaying take oxygen solely from the water, while living algae photosynthesising put their oxygen both into the water below and the air above, and you get a net decrease in oxygen over time (barring gas transfer, which as mentioned is blocked by the matting effect)

Another part of the problem is that the algae only produces oxygen in the daytime, and consumes it constantly, so at night the oxygen level in the water drops - and if something can't survive at night-time oxygen levels then it dies, and starts decaying, further lowering the oxygen levels.

2

glampringthefoehamme t1_jadkekh wrote

Can we use the algae as fertilizer? As in, direct ask runoff to large ponds with non-harmful algae, allow it to absorb the leftover nutrients, harvest abs dry the algae, and then use it as fertilizer later?

1

GeorgeCauldron7 t1_jadww4u wrote

So is it safe to say that if algae is present in a body of water, then you can expect the overall effect to be a net decrease in oxygen?

1