Rivers as Ecosystems

Environment – all the abiotic conditions that surround the living organisms in the river e.g. current speed, water temperature, pH, amount of silt.

Habitat – the place where an organism lives  e.g. under the rocks, in the reeds, in the river bank, in a river bank tree.

Population – all the members of a single species that live in a habitat e.g. populations of salmon, a population of crayfish

Community – all the populations of different organisms that live together in a habitat

Ecosystem – a community and the habitat in which it lives

Biodiversity – the variety of different species living in a habitat. The greater the number of different species in a habitat, the greater its biodiversity.

Should we care about Biodiversity?

Human activities are causing a rapid decline in biodiversity worldwide.

Why is it important that we try to conserve biodiversity?
Do you think we are morally obliged to conserve biodiversity?

— The Convention about Life on Earth, Convention on Biodiversity web site.

Try and list all the benefits we get from biodiversity.

Biodiversity boosts ecosystem productivity, a productive ecosystem provides a number of natural services for everyone:

  • Ecosystem services, such as
    • Protection of water resources
    • Soils formation and protection
    • Nutrient storage and recycling
    • Pollution breakdown and absorption
    • Contribution to climate stability
    • Maintenance of ecosystems
    • Recovery from unpredictable events
  • Biological resources, such as
    • Food
    • Medicinal resources and pharmaceutical drugs
    • Wood products
    • Ornamental plants
    • Breeding stocks, population reservoirs
    • Future resources
    • Diversity in genes, species and ecosystems
  • Social benefits, such as
    • Research, education and monitoring
    • Recreation and tourism
    • Cultural values

Which of these services do we get from river systems?

Humans and Rivers

Water pollution is caused by the discharge of harmful substances into rivers, lakes and seas.

Some common pollutants of rivers are:

  • Sewage
  • Fertilisers washed off agricultural land
  • Pesticides washed off agricultural land
  • Sediment
  • Detergents from urban areas which have high levels of phosphate

Pollutants with high nutrient levels can cause eutrophication. The extra nutrients cause algae and other plants to grow faster. During the night the plants respire and when the plants die they are decomposed by microorganisms. Both these processes use up oxygen and reduce the amount of oxygen available for fish and insects which may then die.

Lots of fish died in the River Ure a few years ago. Try and explain why this might have happened using the pictures below:

Indicator species

Testing water chemistry can show whether a river is polluted but it only gives a snapshot. The animals in the river are responding to water quality throughout their whole life span.

Many aquatic invertebrate animals cannot survive in polluted water, so their presence or absence indicates the extent to which a body of water is polluted. They are good indicator species.

We can classify the invertebrates on how sensitive they are to pollution from 1 (very tolerant to pollution) to 10 (very sensitive to pollution). If we get lots of species with high scores then the water must be clean. Species with high scores include mayfly nymphs, stonefly nymphs caddisfly larvae and dragonfly larvae. Species with low scores include freshwater worms, leeches, freshwater louse and blood worms. What score do you think each of the animals shown below gets?