Aquatic ecosystems - Streams and rivers

10 important questions on Aquatic ecosystems - Streams and rivers

What is the River Continuum Concept?

Rivers are open systems interacting with the environment. Due to these interactions and the dynamic hydrology, gradients develop in the longidudinal direction of the river. Gradients = changing physical characteristics. Also the ratio P(photosynthesis)/R(respiration) changes.

What are the characteristics of the upper reach of streams and rivers?

- input (terrestrial) organic matter
- shade by trees
- high flow velocity
- low primary productivity

What are the characteristics of the middle reach of streams and river, compared to the upper reach?

- less input organic matter
- more open: aquatic plants
- lower flow velocity
- high primary productivity
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What are the functional groups of macro-invertebrates?

- shredders: CPROM > 1mm
-collectors: filter/collect FPROM 0,5 mum-1 mm
-predators
-scrapers/grazers: eat periphyton

What is the function of a ditch?

Regulate water flow in time of overflow or drought. Their high biodiversity is valued including their self-purifying capacity. (plants take nutrients and stimulate denitrification.

Where do functional groups of macro-invertebrates live in the RCC?

Predators: spread throughout whole river
shredders: predominantly upper reach and a little in middle reach
grazers: middle reach and a little in upper reach
collectors: predominantly lower reach

How are the conditions in a average ditch?

High nutrient concentration, which results in a thick layer of floating vegetation. Daar onder it is dark and low oxygen. With low nutrient concentration the duckweed is outcompeted by suspended plants.

What are threats to streams and rivers?

-water quality (discharge of waste water)
-regulation of morphology (meanders weghalen etc)
- obstacles (weirs/stuwen)
-dams and reservoirs

Why are oceans more clear than inland waters?

Phytoplankton concentrations and compounds like humic acids are much smaller.

How can streams and rivers be restored?

1. Take away source: water quality (( reduce loading and disccharge of waste water)
2. Water management: reduce peak discharges to prevent weirs
3. Natural morphology
4. Measures
- re-meandering (restore natural profile)
- remove obstacles -> install fish ladders
- retention areas, inundation zones

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