Ch 4 - Water, Food Production Systems and Society

4.1 - Introduction to Water systems

• Hydrological cycle: system of water flows and storages that may be disputed by human activity

  • energy from solar radiation driven this cycle

• Water budget: quantitative estimate of the amount of water in storages and flows of the water cycle

  • Renewable resources: atmosphere, rivers

  • Non-renewable resources: oceans, icecaps

  • Middle group: groundwater aquifers

Human impact on the water cycle:

1. Withdrawals: domestic use, irrigation in agriculture and industry

2. Discharges: by adding pollutants to water

3. Changing speed at which water can flow and where it flows

4. Diverting rivers or sections of rivers

• Transfers: occur when it stays in the same state:

  • Flooding

  • Surface runoff

  • Stream flows and current

• Transformations: when it changes state to and from water:

  • Evaporation: liquid to water

  • Condensation: water vapour to liquid

  • Freezing: solid snow to ice

• Ocean currents: are movements of water both horizontally and vertically

  • have an important role in energy discharges that influence changes

• Surface currents: moved by the wind

  • earth’s rotation deflects them and increases their circular movement

• Deep water currents (thermohaline currents): influenced by the oceanic conveyor belt

  • difference in water density (salt and temperature)

  • warm water vs. cold water

  • movement of water (warm and cold)

• Cold ocean currents run from poles to the equator, warm water currents flow from the equator to the poles

• Water has higher specific heat capacity (amount of heat needed to raise the temperature of the unit of matter by 1 degree celsius)

Ocean currents and climate:

1. Affects location in terms of climate

2. Difference temperature and whether

3. Land close to seas and oceans has mild climate with moderate winters and cool summers

4.2 - Access to Freshwater

• Access to an adequate supply of freshwater varies widely

  • Climate change may disrupt rainfall patterns and further affect thus access

• Demand for freshwater increases as population, irrigation and industrialization increases

• Freshwater supply may become limited

• Scarcity of water resources can lead to conflict between human populations especially when resources are shared

Humans use freshwater for:

1. Domestic purposes used at home

2. Agriculture, irrigation for animals

3. Hydroelectric power generation

4. Transportation

5. Making boundaries between nation rivers

Sources of freshwater:

1. Surface freshwater

2. Underground aquifers (water can be extracted from surface or wells)

   • Freshwater conflict:

     • climate change distributing rainfall patterns (causing inequalities)

     • irrigation which leads to soil degradation

   • Solutions:

     • increase freshwater supplies by reservoirs, desalination plants rainwater and harvesting

     • irrigation: select drought resistant crops

• Irrigation: results in soil degradation especially in dry areas

  • Our water supply is sufficient, however, like food, distribution is uneven

• Salinization: process of naturally dissolving minerals in the top layer  of the soil which makes it too salty (saline) for further agriculture

4.3 - Aquatic Food production systems

• Continental shelf: extension of continents under the seas and oceans (creates shallow water)

  • has 50% of oceanic productivity but 15% of its area

  • light reaches shallow seas so producers can be photosynthesize

  • countries can claim, exploit, and harvest it

• Zooplankton: single-celled animals that eat phytoplankton and their waste

• Fishery: when fish are harvested in a certain way

  • 90% oceans and 10% freshwater

  • 70% of the world’s fisheries are exploited

• Aquaculture: farming aquatic organisms (coastal and inland) involving interventions in the rearing process to enhance production

  • Impacts of fish harms: loss of habitat, pollution, spread of diseases, escaped species may survive to interbreed with wild fish, escaped species may autocomplete native species

• Maximum Sustainable yield (MSY):

  • SY: increase in natural capital (natural income that can be exploited each year without depleting original stock)

  • MSY: highest amount that can be taken without permanently deleting the stock

4.4 - Soil degradation and conservation

• Pollutants can be: anthropogenic or natural, point or nonpoint source, organic or inorganic, direct or indirect

  1. Organic

     • pollutant: sewage, animal waste, pesticide

     • example: human waste, insecurities

     • effects: eutrophication, loss of biodiversity

  2. Inorganic:

     • pollutant: nitrates and phosphates radioactive material, heavy toxic material

     • example: industry, nuclear power stations, fertilisers

     • effects: eutrophication, bioaccumulation, biomagnification

  3. Both:

     • pollutant: solid domestic waste, debris, suspended solids

     • example: silt form construction, household garage

     • effects: damage controls, plastics

• Freshwater pollution: agricultural runoff, sewage, solid domestic waste

• Marine pollution: rivers, human pollution, pipelines

Measuring water pollution:

1. BOD: amount of dissolved oxygen required to breakdown organic material in a given volume of water

2. Indicator species: plants and animals that show something about the environment by their presence, absence, abundance

3. Biotic index: indirectly measures pollution by assessing the impact on species within the community according the their tolerance, diversity, and relative abundance

4. Eutrophication: when lakes and coastal waters receive inputs of nutrients (nitrates and phosphates) that result in an excess growth of plants and phytoplankton

• The eutrophication process:

  • Fertiliser enters rivers/lakes

  • High level of phosphates, algae grows faster

  • More algae, more food for zooplankton or small animals that feed on them. A lack of zooplankton animals means that these are less to eat algae

  • Algae die and are decomposed by aerobic bacteria

  • Not enough oxygen is present therefore everything dies and the food chain collapses

  • oxygen levels fall lower, dead organic material sediments on the lake or the river bed and turbidity increases

  • All life is gone and sediment settles to leave a clear blue lake. This process in which bodies of water become enriched with nutrients and minerals

• Biochemical oxygen demand: amount of DO required to break down organic material in a given volume of water

  • biological monitoring and indicator species can be used to determine levels of pollution

  • strengths: stationally, sensitive and representative

  • weaknesses: identification