Human impact on aquatic environments| AP Environmental science| Khan Academy

When you go to the beach and you look at the ocean, it oftentimes might look fine. But as we'll see in this video, we human beings have been stressing aquatic environments, and if we're not careful, we might completely ruin them.

For example, this is what a healthy coral reef looks like. Coral are fascinating organisms; you can view them as little animals that are fixed in place because they're releasing this calcium carbonate, the same things that eggshells are made of, that they’re fixed to. Then that builds the coral reef. But they can exist; they have their homeostasis in a particular temperature range and a given amount of various chemicals that are in the water.

Now we know that human beings are causing the climate to warm, and that's also causing ocean temperatures to warm. As ocean temperatures warm, many of our coral reefs are not able to be as sustainable. For example, this is a less healthy coral reef. Some of the coral is still alive and seemingly doing okay, but in other places, you see what is known as bleaching, where the reef is now white, and that's because in those situations, the coral is essentially dying off.

Now you might say, "Well, this is unfortunate because coral reefs are very beautiful," and now it is less beautiful. But what are the other impacts? Well, all sorts of organisms and animals live in coral reefs, get their food from it, and get their shelter from it. If the coral reefs start to die off, then the animals are going to die off. On top of that, these coral reefs, that the coral are essentially building as they live, they prevent erosion on the coastlines.

So one change that affects one organism or one part of an ecosystem can have a lot of follow-on effects on other parts of the ecosystem. Another perhaps more obvious way that we've been not being nice to aquatic environments is things like oil spills. You've probably seen this on the news; when you have major oil spills, they tend to be pretty disturbing images.

But this right here is a bird that is covered in oil, and you can imagine when a bird is covered in oil, it's not going to be able to fly, it's not going to be able to swim, it's not going to be able to have food, and in a lot of cases, it is likely to die. Just as we described with the coral reef, this doesn't just affect the bird; it affects the entire ecosystem, including human beings.

This is just the effect on a bird. It has effects on fish; it has effects on the just natural balance that occurs in that aquatic environment. Now another idea that is less talked about is this notion of oceanic dead zones. This right over here is a picture of the Gulf Coast, right off the coast of Louisiana. I was actually born right around there.

What it shows is every year this hypoxic zone, which is a zone of low oxygen levels in the water, forms off the coast. This shows how bad it is. The red areas are the really bad, very low oxygen. Sometimes you might forget; you might say, "Okay, for all of us who live on the land or in the air, we breathe oxygen," but organisms in the water need oxygen as well—oxygen that has been dissolved in the water.

What's interesting is why this forms; it's actually a little bit counterintuitive. It turns out that chemicals from human runoff, especially fertilizer, might not realize it, but this is the delta of the Mississippi River, and that has runoff from as far north as Minnesota and Chicago, as well as sewage. That farm runoff, and that fertilizer, and that sewage, as it comes into the Gulf, actually promotes algae formation.

You might say, "Oh, that's good, some more life is growing." But so much algae gets formed, and when that algae finally dies and decomposes, the decomposers actually use the oxygen. Remember, when you are actually trying to metabolize things, you're using oxygen in order to extract that energy. So the oxygen in the ocean in that area gets depleted, and then you have a situation where almost nothing can live in these zones right over here.

This is just a sample of the things that we are doing to our aquatic environment. There are other things; there are elemental sources of mercury that we throw into aquatic environments, and it makes the water highly toxic. There's obviously other forms of trash pollution that we put into the water, but this is just to give you a sense and to start giving an appreciation about how imbalanced everything is, and how in one part of the country, say in Chicago, waste that's going into the Mississippi River can affect aquatic environments thousands of miles away.