Physical geography: The carbon and water cycles - Water cycle

River regime

The variability in the rivers discharge throughout the course of a year in reponse to EVT precipitation temperature changes and drainage basin charactistics

Systems in Geography

- A collection of interrelated parts that work together in an environment

- Delimited by boundaries

- Can be defined by a range of spatial scales

- Have inputs, outputs and stores of energy and matter which are transformed or transferred within or out of the system

Open systems

- Transfer both matter and energy into and out of the system

- external factors can influence the system

- eg ecosystems

Closed systems

- Transfer energy into and out of the system, Not matter

- Rare in nature

- eg The water cycle

Isolated systems

- a system that does not transfer energy or matter

- No inputs or outputs

- Rare in nature, only produced in a lab

Equilibrium within a system

- When the output and inputs are equal

- Equilibrium is interrupted when one is larger than the other

Sub-systems

- Smaller systems that operate within the context of a larger system

- Can impact the larger system

Input

Material or energy moving into the system from outside

Output

Material or energy moving from the system to the outside

Energy

Power or driving force

Stores/components

The individual elements or parts of a system

Flows/transfers

The links or relationships between the components

Positive feedback

- Cyclical sequence of events that amplifies or increases change

- Exacerbate the outputs of a system, driving it in one direction and promoting environmental instability

Negative feedback

- a cyclical sequence of events that damps downs or neutralises the change

- Promotes stability and a state of dynamic equilibrium

dynamic equilibrium

State of balance within a constantly changing system

Stores of the water cycle notes

- Most of earths water is stored as saline water (97%) in the oceans

- Of the freshwater stores, ice sheets (68%) and ground water are the majority

- Rivers lakes and ponds account for remarkably small amounts of the water on earth

Transfers of the water cycle notes

- The processes involved in transferring water between stores

- Precipitation transfers water from the atmosphere to the earth surface

- Evaporation moves water from the surface to the atmosphere

- Water may infiltrate the ground or percolate slowly through the rocks as groundwater flow

Aquifers fact

- 30% of all freshwater is stored in aquifers

- water is extracted too fast and exploited

- Aquifers occur in chalk and porous rocks

- If aquifers become over saturated they can cause flooding

Oceanic water

- Contains dissolved salts which allow it to remain liquid after 0 degrees

- pH is changing (decreasing) and links to the increase in atmospheric carbon, which could have a profound impact on marine ecosystems

Sea Ice

- does not raise sea level when it melts as it forms from oceanic water

Ice shelves

- Platforms that form when ice sheets and glaciers move out into the oceans

- raise sea level when they first leave land not when they melt in the water

Ice sheets

- mass of glacial land that extends more than 50,000km sqrd

- Layers of snow pile up and compress over thousands of years

- constantly in motion from its own weight

- Move through ice streams towards the ocean

- Remain stable if the ice lost is equal to the snowfall

Ice caps

- Mass of glacial ice under 50,000 km sqrd

- Major source of ice for glaciers

Alpine Glacier

- Form reservoirs in south east asia

- Found in deep valleys

Permafrost

- Layer of ice on ground, permanently there

Rivers

- Store and transfer of water

- Amazon accounts for 20% of world river flow

Lakes

- generally freshwater

- Greater than 2 hectares

Wetlands

- Areas where water covers the soil

- Support aquatic and terrestrial species

- Main ecosystem of the arctic

Groundwater

- Water that collects underground in the pores and spaces of rock

- Depth that it collects at is known as the water table

Soil water

- Held together with air in unsaturated weathered layers of the earth

Biological water

- All water stored in biomass

- Role of animals as a water source is minimal

Drainage basin

the area of land surrounding a river from which the river receives water and drains this water

Source of a river

Where the river originates, usually from springs or marsh

Confluence

Where tributaries meet the main streams

Tributaries

Extra streams that join the main river.

Mouth of the river

The place where a river drains into the sea

Watershed

The outline of the drainage basin, usually an area of high land.

Floodplain

The area subject to flooding around a river during a given number of years according to historical trends.

Precipitation

Rain, snow, sleet and hail

Infiltration

When water enters into the soil

Interception

When water is caught by trees and plants

Stem flow

water lands on plants and travels down their stems

overland flow

anywhere water flows over the lands surface

through flow

the movement of water down through the soil

Transpiration

where water vapour comes out of leaves

Evapotranspiration

water rises as vapour from the ground and is released from the leaves

ground water

water stored deep in the ground

soil water

water held between soil particles

ground water flow

when water flows through the groundwater

percolation

when water enters permeable rock

surface storage

lakes, ponds and puddles

ground water storage

water stored underground in bedrock

Drainage basin

The area of land surrounding a river from which the river receives water and subsequently drains this water.

Source

Where the river originates from usually from springs or marsh

Floodplain

Area of flat land around the river

Watershed

The outline of the drainage basin, generally an area of high land

Mouth

Where the river drains into the sea

Tribituary

Extra streams that join the main river

Confluence

Where tributaries meet the main streams

The soil water budget

the amount of water stored in the soil over the course of a year

Seasonal changes in precipitation

- Summer - Less rainfall, more frequent storms

- Winter - Large amounts of rainfall and some snowfall

Vegetation and interception seasonal changes

- Summer - More vegetation and leaves (increased transpiration and interception)

- Winter - Less vegetation and leaves

Seasonal changes in evaporation

- Summer - Hotter temperatures lead to more evaporation

- Winter - Cooler temperatures lead to less evaporation

Seasonal changes in soil water

- Summer - dry soils encourage infiltration. However hard baked soils encourage overland flow.

- Winter - Soils may become saturated, leading to overland flow.

Seasonal changes in river channel flow

- Summer - low flow conditions more likely

- Winter - High flow conditions more likely

Urbanisation affecting change in the water cycle

- Replacement of vegetated ground with impermeable concrete and tarmac

- Water cannot infiltrate the soil, which increases overland flow and makes flooding more likely

- Soil water and ground water stores are reduced

Farming practices - irrigation changes in water cycle over time

- Application of water for crops

- Used to enable crop growth in unable to grow elements

- Removes water from rivers, leading to downstream flooding or a lack of water for domestic and industrial use

- Inefficient (sprinklers) causing increased evaporation and a water loss of 30%+

- Soil salinity can also be increased due to evaporation which has a long term negative effect on soil quality

Farming practices - land drainage changes in water over time

- Carried out to stop overwatering of crops

- removes excess water from the soil

- Network of 60-110 cm below surface plastic tubing known as tile drainage

- When water table is higher than the tile, water flows into the tubing and through the holes

- This lowers the water table to the depth of the tubing

Land use changes - deforestation

- Reduced evapotranspiration which increases surface runoff

- Leads to reduced precipitation as the water may have left the area, reducing water in the river channel

- Increased soil erosion, which reduces the soil water stores available

Land use changes - Urbanisation

- Increased impermeable surfaces lead to increased surface runoff and reduced soil moisture (increased flood risk)

- Urban areas are designed to transport water out of an area quickly, leading to the drainage basin being fast paced, potentially flashy hydrograph.

- Reduced interception through the removal of vegetation

Water abstractions impact on the water cycle

- Water is moved from one area with a low demand to an area with high demand.

- reduces the water levels in groundwater, lakes or reservoirs

- Over exploitation of river Po in Milan has led to 25-40 m decrease in groundwater levels over 80 years

Eutrophication

1. Nutrient load up - excessive nutrients from fertilisers are flushed from the land into lakes and rivers by rainfall

2. Plants flourish - Pollutants cause aquatic plant growth of algae, duckweed and other plants

3. Algae blooms, oxygen is depleted - Algae blooms prevent sunlight from reaching other plants. The plants die, and oxygen in the water is depleted

4. Decomposition - dead plants are broken down by bacteria decomposers, using up even more oxygen in the water

5. Death of the ecosystem - Oxygen levels reach a point where no life is possible. Fish and other organisms die