What s up the dam? Ecological impacts of water level fluctuations in reservoirs

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1 What s up the dam? Ecological impacts of water level fluctuations in reservoirs Antti Eloranta Post-doctoral researcher NINA Trondheim

2 HydroBalance Why focus on reservoirs? >900 reservoirs in Norway reservoir "Green batteries" for Europe? Provide important ecological services Most studies done in rivers

3 HydroBalance WP4: Environmental impacts of new operational regimes Task 4.1: Modelling present ecological variation along environmental gradients Main idea: Disentagle present effects of natural variation and hydropower on fish and food webs Combine ecological models (Task 4.1) and hydro-dynamic models (Task 4.2) to predict future ecological effects (Task 4.3)

4 Potential impacts of rapid water level fluctuations Physical and chemical changes Lake shoreline, water quality, temperature, ice-cover period Unregulated Heavily regulated Source:

5 Potential impacts of rapid water level fluctuations Physical and chemical changes Lake shoreline, water quality, temperature, ice-cover period Biological changes Lake productivity Species composition Fish diet, growth and production Heavily regulated Unregulated

6 How to study ecological impacts? Modelling environmental gradients Frequency (km2) Area 2 ) Altitude (m a.s.l.) Altitude (m a.s.l.)

7 How to study ecological impacts? Detailed food-web studies Habitat use Food webs Growth Modelling = large-scale environmental gradients Food webs = information about individual fish and ecosystem Drawings from Eloranta s PhD thesis (2013)

8 Initial results yield along environmental gradients Modelling catches from standardized test fishings in 335 lakes yield decreases with increasing fish diversity Fish diversity shapes the response of trout yield to environmental variation Brown Brown trout trout yield yield (ln (ln CPUE) CPUE) (a) (a) (b) Fish species richness NDVI Submitted to Journal of Animal Ecology Fish ln community Area (km 2 )

9 Initial results Impacts on lake food webs Lake size and fish diversity shape food webs in natural lakes Does water level fluctuations influence energy flow & food chain length in reservoirs? Yes, but only slightly Lake characteristics and fish species, habitat, size etc. needs to be included in full modelling Trophic position Littoral reliance Trophic position Littoral reliance a ab b P = a a b P < Govdajavri Cazajavri Unregulated Heavily 0 mregulated 5-17 m m Regulation amplitude

10 Future plans & studies More lakes and reservoirs Both for modelling & foodweb studies Fish yield against actual regulation patterns Impacts on fish growth and parasites Water level (m a.s.l.) Fundin Savalen Tyin Time

11 Tusen takk!

12 Studying food webs Stable isotope analysis Trophic fractionation: δ 13 C: 0-1 δ 15 N: Pelagic Littoral Trophic δ 15 N ( ) level Energy δ 13 C ( ) source 15

13 1) Unregulated lakes Initial results: 100 % 80 % Fish diets in reservoirs 60 % 40 % 20 % Benthic (and terrestrial) invertebrates more important food than pelagic zooplankton 0 % 100 % 80 % 60 % 40 % Fjerdev. Storv. Fjellfrøsv. Fjellfrøsv. Charr 2) Slightly regulated lakes Cazaj. Charr and charr have often different diets when living in the same lake 20 % 0 % 100 % Forsanv. Slunkaj. Rekv. Rekv. Charr 3) Heavily regulated lakes Sirkelv. Sirkelv. Charr No clear pattern from littoral to pelagic diet with increasing regulation level 80 % 60 % 40 % 20 % 0 % Jernv. Jernv. Charr Govdaj. Charr Rihpoj. Charr Zooplankton Benthic crustaceans Molluscs Benthic insects Surface insects Fish