Water and carbon cycles - A level Geography

What is negative feedback?

Effects of an action are nullified by changes to the inputs /outputs/processes

Define a store/component

Part of a system where energy/mass is stored or transformed

Define system

A set of interrelated events or components working together

What are the five main earth sub-systems?

- Hydrosphere
- Lithosphere
- Atmosphere
- Cryosphere
- Biosphere

What is an isolated system?

No interactions with anything outside the system boundary (the univerese)

What is a closed system?

Energy is transferred into and out of system. All matter is enclosed and is not transferred beyond the system. (e.g. global water + carbon cycle)

What is an open system?

Matter and energy can be transferred from system into the surrounding environment (e.g. the drainage basin)

What is a dynamic equilibrium?

When a system has inputs and outputs but they are balanced, so the size of the system remains the same

Define positive feedback

Effects of an action are amplified by changes to inputs/outputs/processes

Give an example of positive feedback

More CO2 means global temperatures rise, which increases ocean temperatures, which causes dissolved CO2 stored in the ocean to be released

Give an example of negative feedback

Increase in CO2, causes temperature to rise, which means more plant growth, which means more CO2 is absorbed

Define system boundary

Outer edge of system ; Interface between one system and another

Define system element

Kinds of things or substances composing the system. They may be atoms or molecules, or larger bodies of matter

Define a cascading system

A chain of open systems where the output from one open system forms the input in another (e.g. rivers)

Define flow/transfer

A form of linkage between one store/component that involves movement of energy or mass

Define input

The addition of matter and/or energy into a system

Define output

Movement of matter and/or energy out of a system

What are the five subsystems on Earth?

Atmosphere, Lithosphere, Hydrosphere, Biosphere and Cryosphere

What are 4 examples of water stores?

Ocean, groundwater, rivers, trees/vegetation, animals

What percentage of water is fresh water?

2.5% (98.8% of which is locked up as ice)

How much water is there estimated to be in total in the hydrosphere?

1.388 billion km3

What are aquifers?

Large reservoirs of freshwater deep below the rock. Commonly found in porous (contain air pockets) and permeable (allow water through) rocks e.g. chalk and sandstone

What is the risk when aquifers found in Africa, Middle East and Australia are exploited for irrigation?

- Aquifers containing freshwater formed 1000's of years ago
- Water used to water crops and drinking water
- Increased risk of seawater infiltrating rocks creating a saline aquifer

What is a water budget?

The ability for soil to store and transfer water

What is a water table?

The upper limit of the zone of saturation

What is the water table affected by?

- Groundwater flow
- Water abstraction by humans
- Recharge (how quickly water enters ground)

How does water vapor act as a greenhouse gas?

Absorbs, reflects and scatters incoming solar radiation, keeping the atmosphere at a temp to sustain life

Why does water vapor become a positive feedback system?

Warm air is able to hold more water vapor, which further warms up the air as it's a greenhouse gas

How many oceans are there?

5 Oceans: Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and the Arctic Ocean.

How much of Earth's surface do oceans cover?

72%

Why do oceans remain liquid at 0 degrees?

As they are saline

What are oceans pH?

- Oceans are alkaline (pH=8.4)
- Becoming more acidic as more carbon is absorbed which forms carbonic acid

What are the five different examples of Cryospheric water stores?

- Sea ice
- Ice sheets
- Ice caps
- Alpine glaciers
- Permafrost

What four categories does terrestrial water fall into?

- Surface water e.g. lakes and rivers
- Ground water e.g. Aquifers
- Soil water e.g. soil budget
- Biological water

Where do rivers transfer water from?

Rivers transfer water from the ground, soils and the atmosphere to a store (wetlands, lakes or oceans)

What percentage of water in the hydrosphere do rivers make up?

0.0002%

What is the worlds largest river?

The Amazon, accounting for 1/5th of the world's total river flow

What are lakes?

Lakes are stores of freshwater found in hollows on the land surface and must be larger than two hectares

Where are majority of lakes found?

- Norther Hemisphere, at high latitudes
- Canada has at least 2 million lakes

What are wetlands?

- Areas of marsh, fen, peatland or water, which can be natural or artificial, permanent or temporary and static or flowing
- There is a dominance of vegetation

Why might wetlands form?

- Soil type
- Topography
- Climate
- Hydrology
- Water chemistry
- Vegetation
- Human disturbance

Why is the amount of groundwater reducing rapidly?

Due to extensive extraction for use in irrigating agricultural land in dry areas

What is soil moisture important in controlling?

- The exchange of water and heat between the land surface and atmosphere through evapotranspiration
- Plays an important role in development of weather patterns and production of precipitation

What water store has the longest residency time?

Deep groundwater = 10,000 years

Soil moisture has the lowest residency time (1-2 months) why is this?

- Water percolates into the bedrock
- Water is taken up by plants and transpired to the atmosphere
- Transferred into rivers via throughflow
- Evaporated into the atmosphere

When does evaporation occur?

When heat energy from solar radiation is transferred to surface water, causing change in state (liquid to solid)

What is evaporation affected by?

- Amount of solar energy available
- Availability of water
- Humidity of air (higher humidity = less evaporation)
- Air temperature (warmer air holds more vapor = more evaporation)

What is transpiration?

- The loss of water vapor through the stomata of leaves
- As water evaporates it uses energy (latent heat) which cools surroundings

What is dew point?

- As air cools it is able to hold less vapor
- If cooled sufficiently, air will reach saturation (dew point)
- Excess vapor in the air is then condensed back into a liquid

What are two things required for vapor molecules to condense?

- Small particles to condense on (e.g. smoke, salt, dust)
- Surfaces that are cooler than the dew point temperature (e.g. leaves, grass, windows)

If both Antarctica and Greenland were to fully melt how many meters would sea levels rise by?

66m

At the peak of the last age (18,000 years ago) how much of the Earth's surface was covered by glaciers and ice sheets?

1/3 (Sea levels where 100m lower)

During warmer periods in the past, 3 million years ago, how much higher were ocean levels than today?

50m

How do rising sea levels cause a positive feedback system?

Destabilise ice shelves, triggering calving (chunks of ice breaking away) and further melting

What are stores in a hillslope water cycle?

- Interception
- Surface storage
- Soil water
- River channel
- Groundwater

What are transfers in a hillslope water cycle?

- Evapotranspiration
- Precipitation
- Overland flow
- Streamflow
- Throughflow
- Groundwater flow
- Infiltration
- Percolation

What impact does deforestation have on local water stores?

- Removal of trees reduces interception and infiltration
- Increased surface runoff and overland flow reduces water in the area causing drier climate

What impact do farming methods have on local water stores?

- Ditches drain land and encourage water to flow quickly into rivers. Irrigation increases the amount of water on the ground and agricultural machinery compresses soil
- Local stores will deplete as water is less able to infiltrate soils

What are two other things that increase surface run off and therefore result in the depletion of local water stores?

- Impermeable urban ground
- Frozen ground

What happens to water that is trapped on the ground surface?

- Stored as surface storage
- Evaporate
- Flow downslope as overland flow - often leads to flooding

What is a drainage basin?

- The area of land drained by a river and it's tributaries
- Edge of a drainage basin is marked by a boundary of high land, called a watershed

What kind of system is a drainage basin?

An open system (inputs, stores and transfers)

What is a river confluence?

The point where two river channels join to become a bigger river channel

Describe 'throughflow'

- Water flows laterally through the soil channel
- Mainly along 'pipes' caused by animal activity or growth of plant roots

What is the water balance equation used for?

- In order to get a better understanding of the drainage basin system
- Helps hydrologists plan for future water supply and flood control within an individual basin

What is the water balance equation?

Precipitation = Total Runoff + Evapotranspiration +/- Changes in water storage

How does time of year influence differences in runoff percentages?

Growth of vegetation leads to increased rates of interception and evapotranspiration

How long is the River Wye in Wales?

215 Km (5th longest river in Wales)

How is the upper part of the River Wye basin characterised?

- Steep slopes, acidic soils and grassland
- Much of the area was originally forested but cleared for sheep grazing (more overland flow)

What did the ditches that were dug in around the River Why to make draining more effective cause?

Increased speed of water transfer, making river more prone to flooding

Are the rocks in the upper basin of the River Wye permable or not?

- Impermeable underlying rock which means overland flow is encouraged
- Increases risk of flooding downstream, particularly in Hereford

What does a storm hydrograph show?

The variations in a river's discharge over a short period of time, usually during/after a rainstorm

What is river discharge?

The amount of water in the river passing a given point at a given time

What is the rising limb on a storm hydrograph?

The period of rising river discharge following a period of rainfall

What is the falling limb on a storm hydrograph?

The period of time when the river's discharge is falling after it has reached peak discharge

What is the lag time on a storm hydrograoh?

The time between peak rainfall and peak discharge

What is the base flow on a storm hydrograph?

Average level of discharge of the river caused by water flowing into the river from tributaries and groundwater

What is evapotranspiration?

The process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.