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Eutrophication and dead zones

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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 you referring to well and then trophic or trophy ax 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 phosphorus being a rate limiting factor for how fast plants can grow we talked about that in the nitrogen and the phosphorus 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 in the land where we're growing our crops so these are all the crops that we're growing and in order to ensure that the crops grow as much as they can we add fertilizer to it and a lot of that fertilizer it might be nitrogen it might be phosphorus in the form of phosphates so we add fertilizer fertile I fertilizers and the biggest culprit here that we it tends to be phosphates the phosphorus in them and that helps the plants grow more that helps the plants grow more and what seems like a good thing but there's another side effect that happens because of this as the water as the water either due to rain or irrigation for the crops as the water flows from those crops into local streams and rivers and it'll eventually find its way into local streams and rivers those streams and rivers are going 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 they 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 that it 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 you to 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 what a there's living things here well the issue is what happens once this algae dies because once this algae dies and it starts to and it's 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 a respiration there 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 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 peat 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 going to 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 this is potential eutrophication right in this picture let me draw let me show you some more this is another one and you've probably seen this especially places that might have sewage runoff it's it's really happening because there's extra nutrients that are allowing this out these algal blooms or al-jalal algal I don't know to to go out of control and when they 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 and as you can think 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 these algal 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 nitrogen seems like a good thing it's helping us grow more crops but we have to be very careful with where it actually ends up
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