4. Water, aquatic food production systems and societies
4.1 Introduction to water systems
The hydrological cycle:
World’s water cycle is driven by then sun
Allows constant recycling of water between the oceans, the atmosphere
and the land
o Movement between these storages is known as hydrological cycle
Fresh water and Earth’s water:
Oceans play vital role in hydrological cycle: 74% of total precipitation
falls over oceans and 84% of all evaporation comes from oceans
Only 2.5% is freshwater
o 87% in ice caps and glaciers
o 12% is groundwater
o Rest in lakes, rivers, soil, atmospheric water vapor
Cycle has two main inputs: solar energy and precipitation
Two major outputs: evapotranspiration and runoff
, Flows:
o Evotranspiration (combined loss of water though transpiration and
evaporation
o Sublimation (ice changing to water vapor)
o Condensation (water vapor changing to liquid)
o Evaporation (liquid to gas)
o Precipitation
o Freezing
4.2 Access to fresh water
Effect of climate change:
Likely that over next few decades some areas will become drier as result of
global warming, so water resources will be reduced
Increasing demand for water:
Concept of water scarcity: water availability to the demands of water
Demand for water increases with population growth, the need for more
food, industrialization and urbanization
70% water use for farming
20% water use for industry
As societies become richer, demand for water increases
4.3 Aquatic food production systems
Demand for aquatic food resources: continues to increase as human population
grows, standards of living rise and diets change
Photosynthesis and aquatic food webs:
Highest rates of productivity found in shallow seas and near coastal areas
In aquatic systems, most food is harvested from higher trophic levels
where total storages are much smaller
4.1 Introduction to water systems
The hydrological cycle:
World’s water cycle is driven by then sun
Allows constant recycling of water between the oceans, the atmosphere
and the land
o Movement between these storages is known as hydrological cycle
Fresh water and Earth’s water:
Oceans play vital role in hydrological cycle: 74% of total precipitation
falls over oceans and 84% of all evaporation comes from oceans
Only 2.5% is freshwater
o 87% in ice caps and glaciers
o 12% is groundwater
o Rest in lakes, rivers, soil, atmospheric water vapor
Cycle has two main inputs: solar energy and precipitation
Two major outputs: evapotranspiration and runoff
, Flows:
o Evotranspiration (combined loss of water though transpiration and
evaporation
o Sublimation (ice changing to water vapor)
o Condensation (water vapor changing to liquid)
o Evaporation (liquid to gas)
o Precipitation
o Freezing
4.2 Access to fresh water
Effect of climate change:
Likely that over next few decades some areas will become drier as result of
global warming, so water resources will be reduced
Increasing demand for water:
Concept of water scarcity: water availability to the demands of water
Demand for water increases with population growth, the need for more
food, industrialization and urbanization
70% water use for farming
20% water use for industry
As societies become richer, demand for water increases
4.3 Aquatic food production systems
Demand for aquatic food resources: continues to increase as human population
grows, standards of living rise and diets change
Photosynthesis and aquatic food webs:
Highest rates of productivity found in shallow seas and near coastal areas
In aquatic systems, most food is harvested from higher trophic levels
where total storages are much smaller
