ESS UNIT 4: Water and Aquatic Food Production Systems and Societies

Hydrological Cycle

Hydrological Cycle

system of water flows and storages that may be disputed by human activity

Impact of Human Activity on the Hydrological Cycle

• Humans extract water from various points of the hydrological cycle, thereby altering the natural flow of water.

• Deforestation (Loss of the forest removes trees as water stores, which means run-off is likely to flow through more quickly, reducing the opportunity of infiltration and percolation. Soil erosion increases.

• Urbanisation (prevents water from soaking into the ground and percolating into aquifers, degradation of aquatic habitats, surface run-off).

• Agriculture (water pollution by animal waste, pesticide, and fertilizer run off, salinisation, reduction of water supply)

Access to water issues

• Lack of knowledge and skills

• Lack of finances between urban and rural areas, rich and poor, and social groups

• Lack of political will to make water a priority

• Climate change (changes in precipitation patterns, and rise on sea level contaminating waters)

Increase demand for water

• Growth in population

• Increase in affluence and standard of living

• Change to a more meat-based diet

• Growth of industry

• Increase in urbanisation

Water stress

when demand exceeds the available supply over a certain time period or when the quality of water restricts its use.

Water scarcity

Physical water scarcity occurs when there is not enough water to meet demand. Economic water scarcity occurs due to the lack of finances, for instance the cost of treating water to make it safe to drink

Issues contributing to water stress include

• Excessive abstraction of surface waters and groundwater

• Pollution of surface and groundwater resources

• Inefficient use of water

• Climate change

Managing water resources

Reservoirs, Artificial recharge, Rainfall harvesting schemes, Desalination, Water transfer, Use of greywater, and reducing demand.

Marine trophic levels

1. Primary Producers: The base of the food web, include phytoplankton and seaweeds.

2. Primary consumers include the zooplankton, small floating animals in the sea that graze on the phytoplankton.

3. Secondary consumers are small predators such as some fish

4. Tertiary consumers include top predators such as large fish, marine mammals and birds.

Marine Productivity Levels

Primary producers support a diverse range of food webs including many fisheries which humans are dependent on. Primary production is dependent on the amount of sunlight, suitable temperature and available nutrient levels.

Food products from aquatic ecosystems

• Algae used for human consumption and used as a thickening agent

• Fish used for human consumption and used for pet food, beauty, fertilizers.

• Shellfish, Molluscs, Crustaceans, Echinoderms

• Hunting of seals

Freshwater Productivity Levels

1. Primary producers: phytoplankton and macrophytes. Phytoplankton includes freshwater varieties of diatoms, dinoflagellates, and cyanobacteria.

2. Primary consumers:  zooplankton (e.g. waterfleas, copepods) and water snails.

3. Secondary consumers: fish (e.g. perch, smelt, minnows), birds (e.g. ducks) and frogs.

4. Tertiary consumers: large fish (e.g. trout, charr and piranhas), large birds (e.g. kingfisher) and mammals (e.g. otters and humans).

Fisheries

• Use of nets (damages the seabed and can kill organisms that live there such as corals, and bycatch)

• Fish yield and maximum sustainable yield: With a very high fishing effort, species are harvested at a greater rate than they can reproduce and grow, hence exceed sustainable levels.

Managing fish stocks

• Use of quotas: Reduction in fishing effort, Reducing the number of boats fishing, boat size, type of fishing gear used, and limits on size of nets and mesh size. Setting limits on the minimum size of fish that are allowed to be caught. Restricting fishing times, such as having a closed season when fishing is not allowed.

• Use of exclusion zones including Marine Protected Areas (MPAs): Fishing is banned in exclusion zones and in MPAs. Conservation areas which may represent areas of high biodiversity or provide habitats to threatened species.

Aquaculture

the farming of aquatic organisms: fish, molluscs, crustaceans, aquatic plants, crocodiles, alligators, turtles, and amphibians.

Environmental impacts of aquaculture

• Loss of habitat

• Spread of diseases

• Escaped species may autocomplete native species

• Use of hormones

• Increase in organic sediments (the waste precipitates to below the fish cages where it accumulates. This sediment can smother organisms)

• Increase in nutrients (Soluble nutrients released from the uneaten fish food and fish faeces increase the overall dissolved levels of nutrients in the water)

Managing impacts of aquaculture

• Effective application of any medicines

• Reducing the waste from uneaten feed

• Aerate the water to prevent anoxic conditions.

• Sufficient movement and exchange of water to:

  • Reduce nutrient levels in the water.

  • Reduce phytoplankton levels in the water and disperse any blooms.

  • Reduce build-up of waste by dispersing it.

Sources of Water Pollution - Inland and coastal pollution

• Domestic Sewage: most universal pollutant, mainly organic, consisting of carbohydrates, proteins, fats, ammonium compounds...

• Industrial discharge: include organic matter, toxic metals or synthetic non-biodegradable compounds

• Agricultural run-off: Fertilizers are washed into nearby streams or rivers, this can result in an increase in organic material and suspended solids to the water.

• Urban run-off: As rainwater flows through an urban area, it picks up pollutants from the catchment

• Land development: Land clearance for building may involve forest clearance which can increase soil erosion.

• Landfill sites: Disposal of waste on land can lead to leachates entering groundwater or surface waters.

• Others: Acid mine drainage, atmospheric input

Sources of Water Pollution - Marine based sources

• Outfall pipes: can be used to discharge material directly from the land to the sea

• Exploitation of resources: Extraction of materials such as oil or gravel beneath the sea bed may cause marine pollution.

• Shipping activities: can contribute to marine pollution via Disposal of litter and other waste at sea.

Effects of Water Pollution

Organic pollution: sewage effluent, farm runoff and waste from the food and drink industry (e.g. diaries, food processing, brewing and distilleries).

Synthetic non-biodegradable compounds: Invasive species, hot water, oil, noise pollution, light pollution, plastic debris, and pathogens.

Assessing Water Quality

Physical and chemical parameters:

• pH often reflects the local geology and soil.

• Temperature normally reflects changes in ambient temperature

• Suspended solids are small particles that can block sunlight penetrating through the water reducing photosynthesis

• Total dissolved solids and conductivity

• Dissolved oxygen used as indication of the quality of the water.

• Nutrients and Metals

Biological Monitoring:

• Using biological species as an indicator

• Biotic indices are used to determine water quality using aquatic organism.

• Microbial test

Water Pollution Management

• Domestic sewage effluent: Collection and treatment of sewage effluent can be used to reduce its impact on the environment.

• Industrial discharge: Pollution from industrial discharge can involve replacing the chemical causing pollution with an alternative.

• Stopping human activities that lead to pollution e.g. through education, legislation and economic measures

• The amount of pollutant used and released into the environment can be controlled