The River Ecosystem

Ecosystem: a system of interactions between living things and their environment

A river ecosystem consists of inter-related living & non-living parts. The river ecosystem provides us with free ecosystem services.

Flow (or hydrology) is the central driving force of a river’s ecology.

The living (biological) parts of an ecosystem create stability & resiliency by moderating environmental change.


Geomorphology is the general configuration of the earth’s surface, the distribution of the land, water, etc.

Geomorphology is largely determined by topography and geology. These in turn dictate how water flows across the landscape, i.e. the ecosystem’s hydrology

However hydrology in turn affects geomorphology. Floods and high flows carve and shape river channels and valleys, and deposit sediments to create wide, flat floodplains, thereby changing the geomorphology

For example, the Battle River valley was largely shaped by large post-glacial rivers, which is why such a small river sits in such a large valley.

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River Pathways


Water flow is the central, driving part of a river ecosystem. It serves as a river’s own unique signature, and determines a river’s ‘horsepower’.

Flow consists of five components:

  • Magnitude
  • Frequency
  • Duration
  • Timing
  • Rate of Change

These components can be depicted in a hydrograph, like the following.

See hydrographs for the Battle River.

Different Flows for Different Roles

The flow or hydrology of a river changes with the season and year to year. Different types of flows play different roles in the river ecosystem:

  • Large, infrequent floods (a) shape the river valley and its floodplains. They also flush-out large blockages and boulders, and deposit fertile sediments on floodplains.
  • Seasonal Floods & Flushing Flows (b-e): Periodic or seasonal flooding is needed to stimulate germination of riparian plants. Flushing flows also clean-out sediments & pollutants, maintain deep narrow channels, and create fish habitat such as pools and riffles.
  • Low flows (f) provide the minimum survival conditions for aquatic life & riparian plants. They also trigger some plants, fish and insects to enter senescence (hibernation), and help purge some weed species from riparian areas.


There are four types of connectivity in a river ecosystem:

  • Lateral
  • Longitudinal
  • Vertical
  • Temporal

Lateral connectivity: Is the river able to connect with its floodplain (during floods etc.)? Is there a connection between the aquatic and terrestrial (upland) environments? Is there a healthy riparian area?

Vertical Connectivity: is the river connected to underlying groundwater/aquifers?

Longitudinal connectivity: how connected is the river along its length? Is it broken up by dams, weirs or natural obstacles?

Temporal connectivity: how is the river connected over time – does it dry up into disconnected pools during the dry season?


Connectivity is important because it ensures natural river processes continue to occur (channel maintenance, floodplain evolution).

It is also important because isolated (fragmented) habitats, whether aquatic or terrestrial, have fewer species (biodiversity), and it is difficult for species to re-colonize isolated habitats.

Connectivity also ensures there is a flow of energy and nutrients between and within aquatic and terrestrial (land) environments. For example, in the fall, leaves are washed into the river and provide important food for aquatic insects.

Water Quality

Water quality has physical, biological and chemical characteristics.

Physical characteristics include:

  • Temperature
  • Taste
  • Colour
  • Odour
  • Turbidity (clarity)

Chemical characteristics include everything that dissolves in water:

  • Dissolved oxygen and carbon dioxide
  • Nutrients: nitrates and phosphorous (natural & fertilizer run-off)
  • Iron, manganese (naturally occurring)
  • Heavy metals: mercury, lead, arsenic, cadmium (industrial waste, natural)
  • Dioxins, Furans, pesticides, hydrocarbons
  • Hundreds of other chemicals

Biological characteristics include living things found in water, such as:

  • Viruses, bacteria, protozoans, microscopic algae, zooplankton (tiny animals), etc.
  • Most are harmless to humans
  • Some of these organisms are pathogenic (make people sick): eg. fecal colliform (bacteria), giardia & cryptosporidium (protozoans)
  • Pathogenic organism often enter the water through human & animal waste


Living systems in a river are comprised of individual organisms (living things) such as: bacteria, fungi, plants, insects, animals

These organisms work together and interact with non-living systems to form larger ecosystems: e.g. floodplains, riparian areas, wetlands, and the river itself.

Living systems use complex feedback loops to:

  • moderate the flow of the Battle River
  • provide stability during environmental change (such as drought or flood)


For example, riparian vegetation reduces flood impacts by stabilizing riverbanks and absorbing and storing water. Riparian vegetation and wetlands also resist drought by storing water and creating a cool micro-climate that minimizes evaporation. During drier months, wetlands and riparian areas slowly release water back to the river.

Rolling Down the River EventWolf Creek WMP Meeting