River VL 8

Question 1

Why is eutrophication a major problem in many rivers?

Answer 1

Because of the increased potential of HABs due to higher nutrient supply.

Question 2

What were the main causes of low discharge in the Elbe River in 2018 and 2019?

Answer 2

Climate change, particularly long-term trends of heat and drought, caused extreme low discharge in the Elbe River.

Question 3

What is the MOSES project?

Answer 3

The Modular Observation Solutions for Earth Systems (MOSES) is a monitoring initiative that studies hydrological extremes like floods and droughts to analyze their impact on water quality and ecological processes.

Question 4

How does low discharge affect eutrophication in the Elbe River?

Question 5

What e􀆯ects has very high photosynthesis on oxygen saturation and pH-value in a river?

Answer 5

Due to high photosynthesis, the oxygen saturation increases and so does the pH value, meaning that the water gets less acidic (ALKALINE) due to increased respiration

There is a positive relationship between pH-value and oxygen saturation.
- The higher the oxygen saturation (due to higher photosynthesis) the higher the pH-value (less acidic).

Question 6

Why is an unusual intense drought more severe for some fish species than for others (beside the obvious temperature stress)?

Answer 6

Droughts can lead to a connection loss of back waters (Nebengewässer).
* Back waters are spawning areas for some fish species.

Question 7

Name causes for algal sedimentation in rivers:

Answer 7

Causes of Algal Sedimentation in Rivers:
1. Nutrient Overload: Excess nutrients from agricultural runoff and wastewater.
2. Hydrological Changes: Altered water flow from dams and withdrawals.
3. Algal Bloom Die-Off: mostly natural causes.
4. Reduced Water Turbulence: Slow-moving or stagnant water promotes sedimentation.

Question 8

Name effects of algal sedimentation in rivers:

Answer 8

Effects of Algal Sedimentation in Rivers:
1. Oxygen Depletion: Decomposition of algae consumes oxygen, leading to hypoxia or anoxia.
2. Benthic Smothering: Accumulated algae cover and su􀆯ocate bottom-dwelling organisms.
3. Nutrient Release: Decomposing algae release nutrients, potentially causing more blooms.
4. Habitat Alteration: Changes in riverbed habitats, affecting aquatic life.
5. Water Quality Degradation: Increased turbidity and unpleasant odors.