Class notes

Class notes SUST1000 (SUST1400) - week 11 (Element cluster - water)

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Course
SUST1000 (SUST1400)

Institution
Dalhousie University (Dal )

Will Langford, Our Blue Planet Steve Mannell, The Quest for Pure Water Steve Mannell, Water, Disease, and Public Health Will Langford, Chlorine, Chemistry, and the Ambivalence of Scientific Improvement Steve Mannell, The Sanitary City: Toronto,

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Uploaded on March 28, 2023
Number of pages 15
Written in 2022/2023
Type Class notes
Professor(s) Steve mannell, will langford
Contains All classes in week 11 (element cluster - water)

sustainability
dalhousie sustainability
sustainability issues with water

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Will Langford, Our Blue Planet

All right. We begin this cluster with a water facts lecture.And here, the image that you've
seen before, Apollo 17,taking an image of the earth from space and the dominant color
is blue and that blue comes from water. So it's an image that has led the Earth to be
described as a blue planet. And it just shows the importance of water, the kind of
dominant feature of water, and suggests at least that the kind of uniqueness that the
earth offers in sustaining life through that important element of water. So we only have
one earth. There's a finite amount of water on the planet. And the total volume of water
on Earth is one point four billion cubic kilometers. But a lot of that is salinated. A lot of
it's in the ocean and freshwater only makes up thirty five million cubic kilometers or 2.5
percent of the total. About 70 percent of that is in ice and snow. 30 percent is
underground aquifers and a small fraction is in the atmosphere. Which all means that
the actual usable freshwater, the freshwater that's in aquifers or at the surface in lakes
and rivers is very small. It's well, well under one percent of the total water on Earth. So
about two hundred thousand cubic kilometers.

So it's an actually quite a precious and limited resource. And at least in terms of what
humans can actually use. That water is generally accessible through watersheds, so
watershed is a drainage basin, an area where off land, where water converges into a
single common outlet. So that might be a river or a lake or a bay. So all the rainfall and
the snowmelt converge. And as you can see in this diagram, a surface water and
groundwater move together. So whether it's the water seat underground or is remaining
at the surface, all moving in the same direction. And hydrologists talk about hierarchical
patterns of watersheds. So those at higher elevations contribute to even bigger
watersheds, lower down. So this is a movement by way of gravity. Hence you can map
the world's large scale drainage patterns like this, where water is all leading towards an
ocean one way or the other. The exception on this map is in grey. So endorheic basins
are those The exception on this map is in grey. So endorheic basins are those they're
landlocked and the areas in grey also indicate deserts. So deserts and landlocked

, watersheds overlap. But all the other fresh water is headed for the ocean. So the main
source of freshwater resources that humans can access are in aquifers and aquifers are
an underground layer of water that is held in place by rock or other loose material like
gravel, sand, silt and clay. So groundwater and geology are really closely linked. And
how waters able to move, how it's able to collect is shaped by the geological features.
So here you get a kind of cross section of aquifers. The water table is along the top
there. It's the surface edge level saturation of water as water is able to go in the ground
through various pores and fractures in the ground. You also see different aquifers.
They're shallow ones and deeper ones. Each aquifer is confined by a bed of rock. And
these kind of confining beds are not very permeable. So for water to get from one
aquifer to the next, it takes quite a bit of time. And humans extract water. And one of the
key ways to do that is to dig a well. So by digging a well, by digging a hole in the
ground, water is able to collect in the well and then humans are able to bring it up to the
surface, to pump it to the surface and extract water from these aquifers. Very deep at
the bottom here, the deepest aquifers are have been referred to as fossil water. They're
deep in the ground and they have contained water that has been there for millennia,
been left undisturbed. So each level of aquifer, the shallow ones, the deep ones can
recharge over time. They can refill with water. As the water permeates the ground. But
that kind of recharging happens on variable timescales. So, you know, it might take a
few days, a few good days of rain near the surface. But deep down, that water has been
there for a very, very long time. So recently, human beings have addressed the issue of
water scarcity by by doing just that, digging down and accessing wells and pumping into
the surface with diesel powered pumps, which are, you know, cheap. So it's cheap and
easy to get water to the surface. So various NGOs think water. This is one of the things
they're doing. They're helping with, well, construction. They're making sure that diesel
pumps get to people to access water. And, you know, in development economics and
development thinking, you know, not only do humans need water, but development
economists have observed that for people who don't have ready access to water, it's
really time consuming. It takes a lot of labor for people to access water. And that kind of
domestic chore of getting water often fell to girls and young women. you know, cut the
amount of time that it takes to extract water. You know, it may help improve the
economy and allow girls and young women to attend school instead of, you know,
getting that essential water that the family needed. The issue with these pumping
systems, of course, is the aforementioned one of timescales that only the shallowest
aquifers replenish quickly. The deep ones take a really long time and the deep ones are
replenishing at a rate that has nothing to do with the human lifespan. The human
lifespan is short compared to how long it takes those aquifers to recharge. So in this
sense, groundwater isn't a renewable source. So if humans are digging down, extracting
this freshwater from aquifers, they're often doing it at a quicker rate than it can be
replenished. And this presents a sustainability problem. Well, water access really
matters. And one of the reasons for this is the importance of water in the body. Water

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