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Course: AP®︎/College Environmental science > Unit 4
Lesson 4: Intro to sustainable practicesIntroduction to sustainability
Sustainability refers to humans living on Earth and their use of resources without depletion of the resources for future generations. Environmental indicators that can guide humans to sustainability include biological diversity, food production, average global surface temperatures and CO2 concentrations, human population, and resource depletion. Sustainable yield is the amount of a renewable resource that can be taken without reducing the available supply. Created by Khan Academy.
Want to join the conversation?
- How does one calculate the maximum sustainable yield?(2 votes)
- Is sustainability play a huge part with humans?(1 vote)
- Of course! It's important to the survival of living things. To understand this, let's say a person likes to hunt animals. He only hunts in the forest next to his house. One day, a scientist told him to stop hunting. If he continues hunting, the forest will no longer have any animals. Then the food chain will get unstable, and when species get accidentally introduced, they can be dangerous (as seen in "Introduced species and biodiversity" in the Populations unit. There is another, more severe, consequence: the ecosystem collapsing. On the other hand, if the person stops hunting, then none of those things will happen. Similarly, if a city disturbed the environment a lot and continued to do so, the natural factors in the city would be disturbed, and the human factors would also be affected. The natural and human factors of other cities could possibly be affected too. But if the city's laws changed to protect the environment, none of that would happen. There are a lot of other things that make sustainability matter. One example is that climate change can directly affect us, and taking action can help.(2 votes)
- What are some ways that humans can live more sustainably and reduce their impact on the enviroment.(1 vote)
Video transcript
- [Instructor] Let's talk
about sustainability. You've probably come across
the word "sustainable" at some point in your life. If I decided to continue to
talk for the rest of this video without taking a breath,
you might tell me, "Mia, that's just not sustainable." In this scenario, which I obviously would never
even dream of attempting, I'd be depleting the oxygen in my lungs without replacing it. Using resources faster than
they can be replenished is not sustainable. But what does
"sustainability" really mean? Well, the word "sustain" means
"to maintain" or "to hold," so sustainability is
the ability of something to be maintained over a period of time. In environmental science, when
we talk about sustainability, we're talking about the
ability of the Earth's systems to survive and adapt to changing
environmental conditions and maintain the health of ecosystems. It's like a delicate balance where each process doesn't take
too much or produce too much so that all the other
processes can keep on going. And theoretically, when
all these processes are doing their jobs, this
balance could last forever. But some things that humans
do can disrupt this balance. Let's take a look at an example. In the early years of the United States, enslaved and free farm
workers in the American South planted or were forced to plant cotton, a plant that needs to use the nitrogen in the soil to survive. But when they planted cotton in the same fields year after year, the cotton plants would
deplete the nitrogen levels in the soil. This constant depletion of
nitrogen was not sustainable and the cotton crops suffered. In the early 20th century, agricultural scientist and
inventor George Washington Carver suggested that farmers could alternate between growing cotton and
growing nitrogen-fixing plants like peanuts or sweet potatoes. This is a more sustainable way of farming, as the nitrogen-fixing plants
would replace the nitrogen that the cotton plants
took out of the soil. Since then, we've discovered a way of putting nitrogen back into the soil using chemically-synthesized fertilizers. But sustainability is more complicated than just replacing depleted resources. When farmers use too much fertilizer or use poor methods of
fertilizer application, all that fertilizer can run
off into neighboring waterways. This excess nitrogen in the water could cause a lot of algae to grow. The thing about algae is that
when it grows too rapidly, it also dies rapidly, and the microbes that decompose the algae hog the available oxygen in the water, which makes it difficult
for other organisms living in the water to breathe. So, when the fertilizer runoff causes too much algae to grow, it creates an imbalance in the ecosystem and harms the other organisms that rely on the dissolved
oxygen in the water, so the addition of too much fertilizer is also unsustainable. But how could a farmer know whether they're using
fertilizer sustainably? Well, they could look out
for environmental indicators. Environmental indicators are basically when the Earth tells us, "Hey, there's something
unsustainable in this ecosystem." But instead of just telling
us that straight out, it tells us in a variety of clues. For our farmer, environmental
indicators can be things like the amount of dissolved
oxygen in the water, the biological diversity in the area, or even how much algae goes
in nearby water sources. The series of events triggered
by fertilizer pollution could deplete the amount
of oxygen in the water, so species that live in the water that require a lot of oxygen to survive could begin to die off. These species are called
indicator species. Because they're known to survive in very specific circumstances, spotting these species is an indication that there is a lot of
oxygen in the water. If these species are absent,
then that will be an indication that the pollution has reduced the amount of dissolved
oxygen in the pond. The farmer could then
change their behavior. In this way, environmental
indicators can guide humans to make sustainable choices. Another way humans can use
environmental indicators to make decisions about natural resources is by monitoring populations
and estimating their growth. Imagine that you have a
pond in your backyard. And let's imagine that you have searched for all of the correct
environmental indicators so you know that the fish in your pond are not suffering from pollution. One day, you decide to go fishing. It might be tempting to
fish as much as you can so that you can invite all of your friends and have a big happy fish feast. But if you decided to take all
of the fish out of the pond, then there wouldn't be
any left to reproduce, so your feast next year
would be pretty sad. Even if you just left a
couple of fish in the pool, they might not be able to reproduce enough to replenish the population. Other environmental factors might cause the small fish population to go down even further. The fish might catch
diseases, run out of food, or end up being some
other creature's feast. There's some maximum number
of fish that you could take so that there's enough
fish left in the pond to reproduce and replenish the population. This number is called the
maximum sustainable yield. Basically, you want to catch the most fish to have the maximum yield
while still being sustainable. If you fish more than the
maximum sustainable yield, then the fish will be captured more quickly than they can reproduce and the population will slowly decline. If you fish less than the
maximum sustainable yield, then the fish population
will grow exponentially until they reach the maximum capacity that the ecosystem can support. Some of the fish will eventually die from density-dependent factors like lack of food and disease. On a bigger scale than
your imaginary pond, natural resource managers try to estimate what the maximum sustainable yield will be each fishing season. This is why fishery managers regulate the amount of
certain types of fish each fisher is allowed to catch per year. This is to make sure that next
year we will still have fish. So, if we study the Earth's ecosystems and understand how we
impact the environment, then we can find ways to
interact with ecosystems more sustainably. And, really, that's what
environmental science is all about.