Ecological assessment methods for lakes, Norway Odd Terje Sandlund Input from M. Mjelde (NIVA) and colleagues at NINA

Agenda  Background  The face of HyMo in Norwegian lakes  Quality elements in relation to HyMo  Macrophytes  Zoobenthos  Fish  Present and future research directions © OT Sandlund

Background  # lakes >0.04 km 2 :  # HP-regulated lakes/reservoirs: 905  0-10 Mm 3 : ~375  Mm 3 : ~388  Mm 3 : ~133  >1000 Mm 3 : ~9  Most regulated lakes are alpine/subalpine  Nearly all contain brown trout

Water level fluctuations Natural lake Urban water supply reservoir Regulated lake (traditional operation)

Macrophyte index, Hellsten et al  WIc – developed in collaboration between Fi, Se, No  Based on the ratio between sensitive and tolerant species  Provides one value (between +100 and -100) for each water body N S - # sensitive spp. present N T - # tolerant spp. present N - total # spp.

10, 25, 50, 75, 90 percentiles indicated. Sorted by the 75 percentile WISER: Hellsten et al. 2011

Species sensitive to water drawdown Species tolerant to water drawdown Hellsten & Mjelde (2009)

WIc for large oligotrophic, low-calcium and periodically ice covered lakes WISER: Hellsten et al. 2011

Reference value: WIc(i) = 29 (75th percentile of the index values for natural and semi-natural Finnish and Norwegian lakes) High/good boundary: WIc(i) = 10 (25th percentile of the index values for natural and semi-natural lakes) Good/moderate boundary: WIc(i) = -20 (corresponds to a winter drawdown of m, when Isoetes lacustris disappears) WISER: Hellsten et al. 2011

Macroinvertebrates in regulated lakes Lotic Lentic Ephemeroptera Plecoptera Petrin et al. in revision ß-diversity

Tolerance limits for important fish prey in HP mountain reservoirs (Rognerud & Brabrand 2010) Organism Tolerance limit, regulation amplitude Gammarus lacustris6 m Gastropods8 m Trichoptera larvae10-12 m Chironomid larvaeNo tolerance limit detected Lepidurus arcticus No tolerance limit detected, but timing of reservoir filling in spring essential EurycercusNo tolerance limit detected BytrotrephesNo tolerance limit detected Daphnia sp.No tolerance limit detected

 CPUE trout in unregulated vs. regulated lakes:  F 1,363 =10,54, t=-3,24, p=0,001  But with inclusion of other factors:  Allo-/sympatry + lake area + air temp in July + # days with snow  Regulation excluded from the model –  allo-/sympatry dominant factor Brown trout in lakes: Initial analysis (CPUE as biomass) (Helland et al. 2010) Population abundance (measured as gill net CPUE, kg)

Brown trout in lakes  Population abundance (measured as gill net CPUE, kg) (Helland et al. 2010)

Remote sensing of lake productivity? >70% of TOC explained by catchment NDVI, based on modelled values for > lakes Red points: TOC in ~70 lowland lakes Larsen et al Ulvan et al A.G. Finstad, unpubl.

Ongoing work: Lake characters vs. regulation Full model:  Trout biomass ~ regulation + NDVI + ice cover + NDVI/ice cover + regulation/ice cover + regulation/NDVI (Finstad, Helland et al., in prep) Google maps

Trout CPUE (biomass) in allopatry  Strong negative effect of regulation (p<0.001)  Strong positive effect of NDVI (p<0.001)  Non-significant positive effect of ice cover (p=0.057) © OT Sandlund

Trout CPUE (biomass) in sympatry  Negative effect of regulation (p=0.016)  Negative effect of ice cover (p=0.009)  Positive effect of interaction term regulation:ice cover (p=0.022)  Non-significant positive effect of NDVI (p=0.060) © OT Sandlund

The impact of sympatry, an example ● b.t. in allopatry ● b.t. in sympatry with Arctic charr

Summary  Macrophytes: «Proper» index developed for HyMo in lakes (WIc, Hellsten et al. 2011)  Invertebrates: some indications on regulation response: ß-diversity higher in natural lakes  Fish: clear response in brown trout biomass after correction for lake productivity, climate and productivity  Indications are that macrophyte G/M boundaries are stricter than invertebrate and fish G/M boundaries

Where are we going?  Climate change research on lakes and fish ecology have provided promising results of relevance for HyMo in WFD  We need to work with low-diversity systems (because that’s what we have!)  Which QEs are relevant in HyMo lakes?  How do we define Good/Moderate vs. HWMB boundaries?  Should we struggle to avoid HMWB-status for lakes / reservoirs?

Cooperation and expertise for a sustainable future  Photo: P. Jordhøy, J. Thomassen, E. B. Thorstad, A. Staverløkk, T. Aarvak, B. Løken/Samfoto © OT Sandlund