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The Importance of Water
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About the lecture
In this module, we think about the importance of water in both social and physical processes, focusing on three key features of water and their impacts: (i) its thermal properties – water is densest when it is a liquid and requires a large amount of energy to change temperature, which is very significant for rock weathering and the climate system; (ii) its property of surface tension, which enables the important process of capillary action; (iii) its chemical properties – water is a highly effective solvent, meaning that it carries substances vital for life and drives oceanic carbon storage.
About the lecturer
Professor Joseph Holden is Chair of Physical Geography at the University of Leeds, where he also directs the research centre water@leeds. He researches a range of areas within physical geography, such as the carbon dynamics of peatlands and the impacts of land use on hydrological processes. His publications include Water Resources: An Integrated Approach (editor, 2013), Physical Geography: The Basics (2011), and An Introduction to Physical Geography and the Environment (editor, 2004).
Hello. My name is Joseph Holden.
00:00:05I am professor of physical Geography at the University of Leeds,
00:00:07where I'm based in the School of Geography.
00:00:10I'm also director of Water at Leeds, which is a large,
00:00:12interdisciplinary water research centre.
00:00:15In this first module, we're gonna be talking about the basics of water.
00:00:19Now water is essential for life.
00:00:23Control of water was critical for
00:00:25the development of civilisation throughout history.
00:00:28And, of course, it's formed a really important part of human culture.
00:00:30Water covers 73% of the Earth's surface in oceans,
00:00:33lakes and rivers.
00:00:38It's one of the few substances in the
00:00:41natural environment that's found in solid form,
00:00:43liquid form and gas form
00:00:46and all these forms.
00:00:48It helps shape the environment on Earth
00:00:49through weathering erosion and transport of energy.
00:00:52Uh, and material.
00:00:56So think, for example, of glaciers, which are scouring the landscape.
00:00:58Think of water which might be eroding soil from a field or moving pebbles and rivers,
00:01:02but also think about how ocean currents might
00:01:07be transferring warm water from the tropics,
00:01:10northwards or southwards towards the poles.
00:01:12Now, in other units.
00:01:16On this course, we'll talk a bit more about the stores and flows of water
00:01:17and how humans have modified these.
00:01:22But for now, I'd like us to think about three key features of water
00:01:24and why these are important for understanding Earth's physical environment.
00:01:28These are the thermal properties,
00:01:33surface tension
00:01:35and the chemical properties.
00:01:37first of all thermal properties now fresh water is really
00:01:39unusual because it's most dense when it's a liquid.
00:01:42It's actually densest when it's at four degrees C for most
00:01:46substances, their most dense when there are solid
00:01:50but not in the case of water.
00:01:53So when ice forms,
00:01:54it expands by about 9% and this means it floats on the surface of the liquid water.
00:01:55Now that's pretty lucky,
00:02:01because if it was more dense when it formed on the surface of seas or lakes,
00:02:03it would then sink into that lake, crushing all of the living creatures within it.
00:02:07And, of course, when you get ice formation on the lake or a sea,
00:02:12it actually protect that underlying water from fully freezing as quickly.
00:02:15So that's why major lakes don't necessarily freeze entirely during winter.
00:02:19Now, uh, the expansion process of ice moving from water to ice,
00:02:25actually important for things like weathering of rock so you
00:02:31might get water going to small crack in a rock.
00:02:35And then over time it might expand and then contract again,
00:02:37expand and contract again every time it freezes and melts.
00:02:40And this then weakens the rock and can eventually,
00:02:44large cracks will shatter the rock completely.
00:02:46That's a form of rock weathering.
00:02:48One.
00:02:51The critical things about the thermal properties of water is that it
00:02:52takes a lot of energy to change the temperature of water.
00:02:54In fact, it's probably more energy than any other liquid except ammonia.
00:02:59But when you cool that water down, that energy is also released now.
00:03:04This is really important in the natural environment, because
00:03:07if you're living in a coastal location, for example,
00:03:10in the winter you're likely to be a lot have a
00:03:13warmer environment than if you're in the middle of a continent.
00:03:16Because the sea around your coastal landscape still has
00:03:18some of that warmth from the previous summer,
00:03:23it takes months for that water to cool down.
00:03:26Crucially, there's a huge amount of energy, which is used when water changes state.
00:03:30So perhaps when it goes from a liquid to a gas so water vapour.
00:03:35So that energy might mean that you get evaporation of water from, say,
00:03:39the oceans in the tropics,
00:03:45and that then goes into the atmosphere in
00:03:47an invisible water vapour so the gas is invisible
00:03:49and then elsewhere, perhaps moving towards the poles.
00:03:52The water vapour might condense back to a liquid, and when it does,
00:03:55it releases that huge amount of energy it took to
00:03:59convert it originally from the liquid to the gas.
00:04:02So that means you're getting energy transfer in
00:04:05the atmosphere through the movement of water vapour.
00:04:08That's really important.
00:04:11And it's also a really important greenhouse gas, a natural greenhouse gas.
00:04:12In fact, you might be surprised to know
00:04:16that water vapour is responsible for 60%
00:04:18of the natural greenhouse gas greenhouse effect.
00:04:22So, of course, this is this is actually fundamental to how we got life on Earth.
00:04:25The global climate is temperate enough for us
00:04:29to tolerate because of that natural greenhouse effect.
00:04:32A second feature of water is about surface tension,
00:04:39so it's common to all liquids this so liquid
00:04:43its molecules are moving around in that liquid
00:04:46that kind of attract each other together.
00:04:48But when you're at the surface of the liquid.
00:04:50There's nothing outside the liquid wanting to attract the liquid.
00:04:52So naturally a liquid wants to form a sphere,
00:04:54pulling itself in towards itself so that
00:04:57the liquid public schools attract each other
00:04:59so that that creates this tension on the surface of
00:05:02the liquid cause everything is pulling towards the centre.
00:05:06But when a liquid then comes into contact with a solid matter, say,
00:05:08a plant root or something like that,
00:05:12it is also attracted to that solid matter.
00:05:15So what can happen is water can be drawn up into the plant because
00:05:17there's an attraction from the thin outside layer of the liquid,
00:05:21but also the liquid that then moves there, pulls the rest of the liquid with it,
00:05:25and that sort of sucks it upwards.
00:05:29And this is capillary action
00:05:30that's really important in soils and means.
00:05:32Actually, you get upward movement of water on a hill slope,
00:05:35so not all water moves downhill.
00:05:39Just imagine a tissue that you place above a cup of water.
00:05:41The water is drawn up into that tissue by capillary action,
00:05:44and then a third important feature of water is its chemical properties.
00:05:47It's a really fantastic solvent.
00:05:52In fact, of any substance,
00:05:54water dissolves and carries with it more than anything else.
00:05:56So one benefit of this it means it carries important nutrients to plants.
00:06:00But also it means that pollution might be easily transported
00:06:05through the landscape and into rivers into the sea.
00:06:09At the fact that it's a good solution.
00:06:13Allege it means that water also plays a critical
00:06:15role in all forms of weathering of rock.
00:06:17It might simply every time it rains,
00:06:20dissolves some of that rock away and then wash it away into rivers and lakes.
00:06:22But also rainwater contains within it some carbon dioxide from the atmosphere,
00:06:26so it's actually a bit acidic.
00:06:31It's carbonic acid,
00:06:32and that acid can react with materials and minerals on rock,
00:06:34which in turn means that the carbon locks into those
00:06:38minerals and then it gets washed away into the oceans.
00:06:42And this is actually taking carbon out of
00:06:45the atmosphere and putting it into the oceans
00:06:47and shows us how a crucial part of the global carbon cycle
00:06:50is driven by the water cycle because our world is so interconnected
00:06:54
Cite this Lecture
APA style
Holden, J. (2023, March 06). 5 The Water Cycle and Insecurity - The Importance of Water [Video]. MASSOLIT. https://massolit.io/options/5-the-water-cycle-and-insecurity?auth=0&lesson=12894&option=9542&type=lesson
MLA style
Holden, J. "5 The Water Cycle and Insecurity – The Importance of Water." MASSOLIT, uploaded by MASSOLIT, 06 Mar 2023, https://massolit.io/options/5-the-water-cycle-and-insecurity?auth=0&lesson=12894&option=9542&type=lesson