Ch 4 : Water, Food Production Systems and Society

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)

 \n 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