Topic 4 Water and aquatic food production systems and societies

4.1 Introduction to water systems

Summary of topic 4.1

Ecosystems

• There are 3 main types of ecosystem:1. Marine (sea, estuary, salt marsh, mangrove)2. Freshwater (river, lake, wetland)3. Terrestrial

• Most global ecosystems are therefore water-based

Aquatic ecosystems

1. Marine Ecosystems

2. Freshwater Ecosystems

Distribution of Earth’s Water

Compared to all of the water on Earth, there is very little freshwater. Of this freshwater, very little is easily available to humans.

Water systems• Water exists within a system• All systems include inputs and outputs (flows), processes

and storages, and feedbacks

storage

Energy or matter in(INPUT)

Energy or matter out(OUTPUT)

TRANSFORMATION

(Feedback mechanism to control input – and maintain EQUILIBRIUM)

process

In this system flows consist of matter rather than energy and processes are physical rather than chemical

Water systems

• Storages include:– Organisms– Soil– The atmosphere (as water vapour)– Water bodies

• Oceans• Groundwater (aquifers)• Lakes• Rivers• Glaciers• Ice caps

Water systems• Flows include

– Evapotranspiration (evaporation coupled with transpiration)– Sublimation (solid directly to gas at high pressures)– Evaporation– Condensation– Advection (movement by winds)– Precipitation– Melting– Freezing– Flooding– Surface runoff– Infiltration (movement of surface water into soil)– Percolation (movement of water through soil and rock pores)– Streamflow– Currents

The Water Cycle(The Hydrological Cycle)The

This shows the connections between flows and storages. It occurs between the atmosphere, lithosphere and biosphere

Note: All flows in the water cycle are ultimately driven by solar radiation

How does the water cycle affect global climate?• There are differences in temperature and salinity throughout the

world’s oceans• This results in differences in water density (which leads to

movements of huge masses of water)• The greatest of these is the Ocean Conveyor Belt• The northern part of the Conveyor is the Gulf Stream • Warmer water rises to the surface and is advected by winds• Colder water sinks and is moved by deep-water currents• The Ocean Conveyor Belt therefore distributes heat around the

world and helps to control climate • There are worries that continued anthropomorphic climate

change will lead to disruption of the Ocean Conveyor Belt (and therefore result in a positive feedback effect)

The Ocean Conveyor Belt

The Ocean Conveyor BeltThe Day After Tomorrow – Gulf Stream stops

Human impacts on the water cycle • Unsustainable water use

– There are over a billion people without access to clean drinking water and more than 2.6 billion without proper sanitation (water is a replenishable but finite resource). Water demand is increasing in both MEDCs and LEDCs

• Changes to flows and storages– Humans affect this on the small and large scales e.g. large-scale

agricultural irrigation, abstraction of groundwater and surface water and desalination of seawater

• Water pollution– Rivers and lakes become polluted when they are used for the

disposal of domestic and industrial wastes

Questions

1. List possible storages of global water2. List possible flows of global water3. List and evaluate human impacts on the

water cycle