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Eutrophication and dead zones
Video transcript
- We're now going to talk about something called eutrophication. Eutrophication. And it comes from, or it's derived from, the Greek for well nourished. Eu referring to well and
then trophic or trophia, referring to nourished, or nourishment. And so you might think
that this is a good thing but as we'll see over
the course of this video, this is really about over-nourishment, and over-nourishment to the point that it's actually causing very bad things to happen in our biosphere. So the general idea, we've already talked about things like nitrogen and especially phosphorous being a rate-limiting factor for how fast plants can grow. We talked about that in the nitrogen and the phosphorous cycle videos. And because of that, we humans have added a lot of nitrogen and
especially phosphates to plants in order to grow them better, because we need the plants to live, to have more food. So what has happened is, so let's say that this right
over here is some land. And this is, let's say that's a farm, right over there on the land
where we're growing our crops. So these are all the
crops that we're growing. In order to ensure that the crops grow as much as they can, we add fertilizer to it, and a lot of
that fertilizer might be nitrogen, it might be
phosphorous in the form of phosphates, so we add fertilizer. And the biggest culprit
here tends to be phosphates, the phosphorous in them,
and that helps the plants grow more. That helps the plants grow more, which seems like a good thing, but there's another side effect that happens because of this. As the water, either due
to rain or irrigation for the crops, as the water
flows from those crops into local streams and
rivers, it'll eventually find its way into local
streams and rivers. those streams and rivers
and lakes are going to have an excess of those
fertilizers, in particular maybe those phosphates. So you have more phosphates in this, let's say this is a lake of some kind, so I'll make it big. Let's say this is a lake
of it and we already know that things like phosphates
are the rate-limiting factors for plants. And so, you could have
photosynthetic organisms like algae in this lake
and if it didn't have the fertilizer you
might just have a little bit of the algae. But now since they're getting
all of these phosphates, the algae can go crazy. The algae can go crazy and grow all over the surface of the lake. And so this is where that algae is getting over-nourished. It's getting way more
phosphates than would have typically happened just if
there wasn't fertilizer, if there wasn't this runoff happening. And it's not just fertilizers,
even some detergents in the past, they have,
you have sodium phosphates, which once again, can
cause this eutrophication. And you might say okay,
well why is this bad? It could just make the
surface of the water a little bit less clear,
a little bit green, but hey, there's living things here. Well the issue is what
happens once this algae dies. Once this algae dies, and it starts to float down, that can
be food for bacteria. That could be food for bacteria, and as the bacteria consume it, they also use oxygen. We've already talked
about the role of oxygen in respiration. The bacteria will
consume all of the oxygen in the water. Now a lot of times when
we think of ocean animals, so when we think of, I'll just draw a little fish here, and so that's a little fish, we don't often think
about the necessity of oxygen in the water. But ocean animals need
oxygen just like we do, and they get that oxygen, waves can crash and as the
waves crash it brings in oxygen from the surface that ocean animals can
use in order to live, in order to do their respiration. But now all of a sudden,
if this bacteria, because they're able to decompose all this algae that is dying, if they're
consuming all of the oxygen, well it depletes
the oxygen from the water so that the ocean animals
can't live there anymore. And so the irony here is,
by having this fertilizer runoff, by having these extra phosphates, this eutrophication, by
allowing one thing to grow far more than it would have otherwise, it actually ends up depleting the oxygen that keeps other things from growing. And it actually creates
what we call dead zones. So this fish is going
to die and other animals like it aren't going to
live because there's not gonna be enough oxygen in that water. And then we have a Dead Zone. And this is a serious problem. We have some pictures here. This is potential
eutrophication in this picture. Let me show you some more. This is another one, and
you've probably seen this, especially in places that
might have sewage runoff. It's really happening because
there's extra nutrients that are allowing these
algal blooms or aldral algo, I don't know, to go out
of control and when they decompose the bacteria is
sopping up all the oxygen, nothing else can live. And this is happening on a macro scale. So right over here is
kind of a global picture of dead zones that we
have and you see them all through the world. And you see they are
typically concentrated where we have more industrialized nations, where we have either more
agriculture happening, more industrial agriculture, where they might be using more
fertilizer and also where you might have more runoff
from cities that will have nutrients like the
phosphates, that will cause this eutrophication to happen. And if you were to zoom
in, let's say on the Caspian Sea, you can
see this in more detail, you can visually see this. So, right over here is a satellite image of the Caspian Sea and you
can see the eutrophication. You can see the algeal, algal
blooms throughout this area. It's making the water less clear. So this is a serious
ecological thing that we have to think about. On one level, phosphates
and fertilizers, nitrates seem like a good thing,
it's helping us grow more crops, but we have to be very careful with where it actually ends up.