How will the expected lower wind speed at our region in the world affect lakes? | More lakes will become stratified and stratification will be stronger. |
How would you expect temperature in lake water to change in the future in our region? | Increase in lake water temperature. BUT in spring and fall there is a larger change in temperature compared to winter and summer |
How is precipitation expected to change in the future? | Increase in our region |
How will increased precipitation i DK affect runoff and loading of P en the furute? | Both will increase. Some parts of DK are more sensitive than others. |
What is one important mechanisms why increased runoff leads to increased P loading? | Erosion |
What do you think is the general trend in global distribution of richness of freshwater fish species in the future? | Global warming will likely induce a polewards expansion of the geographical distribution of warm-tolerant species. |
Carps are more warm-tolerant than e.g. trout. What consequences could a larger distribution of carps have on lakes? | More carps have a negative effect on the lakes. The more carps the more resuspension og P from the sediment in the lake because they are benthivores and disturb the sediment. |
What could be the reason for the shift in fish composition observed in this Icelandic lake? | Temperature change! Decrease in Arctic Charr with higher temperatures while Brown trout remain unchanged - they are more heat-tolerant. |
Take a look at these possible implications on fish in temperate regions in the future. Cover the picture and try to remember as many as possible. | h |
When nutrient levels decreases we generally expect fish to become larger. Does that correspond to the pattern seen in this figure? | When nutrients increases fish size generally decreases, but when temperature increases we see an increase in the porportion of small sized fish bream and perch (red line). The pattern is more unclear for the roach. (opposite effects of temp and nutrients on fish size). |
Communities with the same total biomass but dominated by small fish have a higher metabolic rate and excretion rate than communities dominated by larger fish. What consequences for nutrient transport within the lake? | Communities dominated by small, omnivores fish have faster turnover and greater transport of nutrients within the lake -> stronger flux from the littoral and benthic zone to the pelagic |
Explain the figure. | h |
How can temperature affect predation pressure on zooplankton in lakes? | Higher temp = higher predation pressure |
How does the predation pressure differ between temperate and subtropical lakes? | general higher in subtropical lakes |
Explain the differences in community structure and dynamics between temerate (blue) and subtropical (orange) lakes. | h |
What can explain the higher chl-a concentration in dry years? | More P and N are available in dry years. |
The structuring role of submerged plants in warm lakes is not so efficient as in temperate lakes. Do you think that this will benefit the piscivorous or the plankti/benthivores fish most? | In warm lakes the plankti-/benthivores fish are favored by the lacking role of submerged plants. |
How can these three climate related events lead to fish kills?
- Periodic drought
- Anoxic conditions
- Cyanobacteria blooms | - Periodic drought: leads to poor recolonisation - lakes becomes more fragmented and disconnected
- Anoxic conditions: higher temp leads to increased respiration = less oxygen - fish simply die without oxygen ;)
- Cyanobacteria blooms: the toxics created by cyanobacteria can kill fish |
What kind of temperate lake system is most similar to warm systems? | warm systems are very compareable to eutrophic temperate lakes |
Will cold or warm lakes have the highest P release? and will cold og warm lakes have the thickest oxidized sediment-surface layer? | Warm lakes will have higher P release and cold lakes will have thicker oxidized layer. |