Lake management, restoration and the impact of global climate change

Erik Jeppesen, Martin Søndergaard, Lone

Liboriussen & Torben L. Lauridsen

Department of Bioscience, Aarhus University, Vejlsøvej 25, PO Box 314, DK-8600 Silkeborg, Denmark

Eutrophication

Reduce the external loading –it works!!

Diffuse pollution a hot topic in DK !

5 mill. people (great sewage treatment) and 20 mill. pigs and cattle, walking around even without any underpants!!!!!

Consumption of fertilisers in Denmark 1935 - 2001

Wrong N:P ratio

P will accumulatein the soil as in DK

China

Lake Taihu

Climate change challenge -

Reduce the external loading much more!!!

Eutrophication

Reduce the external loading –it works!!

Lake Constance 530 km2, mean depth 100 m

NEW special issues!!

Loch Levenalso evaluatingrole of climate

1-200 m in mean depth 0.05-12 years hydraulic retention time

Plake= Pin/(1+√tw), tw = y-1

after 5 years

after 10 years

after 15 years

P response time to loading reductionis typically 10-15 years

WISER compilation 2011–similar results

-not very sensitive to depth and retention time

- however in my lake.....

Surveys of Danish lakesbad guys good guys

within 5 years!

Shallow

Daphnia Small cladocerans

Shallow

Daphnia Small cladocerans

Cladoceransbecome larger

Bring the zoopies back to the lakes!!!

I am simply the

best!!!

Take home message!

Bottom-up and top-down forces goes hand in hand when lakes recover from eutrophication!!!

and rememberme!!

Why slow recovery of lakes• Chemical based delay

– Internal loading, accumulated phosphorus in the sediment

• Biological based delay– fish stock dominated by zooplanktivorous species

leading to low grazing control on phytoplankton and higher resuspension

– submerged macrophytes delayed in recovery due to lack of seed bank, waterfowl grazing, etc.

Lake restoration methods (to combat eutrophication)

Bold: methods used in Denmark*) Methods investigated in CLEAR

Commonly used methods:

Lake Brabrand: dredging of 500.000 m³ sediment

Principle: phosphorus rich sediment removed to reduce the internal loading of phosphorus.

NPAC

2/3 sep

Phoslock

ALU-treatment

Lake Hald – hypolimnetic oxygenation,

(210 tons O2 per year 1985-)

Lake restoration by removing fish

Planting of macrophytes as lake restoration in Lake Taihu, (disappeared soon again)

Fish removalNo fish removal

Fish removal in Huizhou West Lake.

Lake Engelsholm, Denmark

Before: 1989-93After: 1994-1999

jubiiiiiii

Presentation of data 90 %

75 %

Median

25 %

10 %

•Relative units (relative to before restoration)

•Significant difference marked with blue color

•log scale

Søndergaard et al, 2008

Biovolume of main phytoplankton classes

Søndergaard et a, 2008

• Repeated measures needed – not so big effort 2nd time

• Combining methods perhaps more cost-effective

Climate change challenge -

Reduce the external loading much more!!!

Loading depending on runoff

33-42% increase in the last 80 years due to increase in discharge – present days fertilisation

Diffuse N Diffuse diss. P

Runoff (mm y-1)

fish removal

Multiple regression 250 lakes – 800 lake yearslog(algae biomass) = a*log(TP)+ b*log(TN) + c*log (mean

depth)+d*log(water temp) + e – data from August only (late summer)

Slope bluegreen algae

Jeppesen et al ,2009

a b c d

Model: log(cyanobacteria biomass) = log(TP), log (mean depth), log(water temp.)

Jeppesen et al, in press

TP=0.1 mg l-1 , mean depth =3 m

TP=0.1 mg l-1 , mean depth =3 m

Jeppesen et al, 2011

Seasonal phosphorus retention in 16 Danish lakes with different P levels. Based on mass balance measurements (19-26 annual samplings during 8 years).

When it gets warmer…..

Søndergaard et al, 2003

Cats know it!!

Good guys Bad guys

Roach

Bream

Pike

Perch (when big)

Fish species in Denmark

Review- submitted to Hydrobiologia a few days ago

Impacts of climate warming on lake fish assemblages: evidence from 24 European long-term data series

Erik Jeppesen , Thomas Mehner, Ian J. Winfield, Külli Kangur, Jouko Sarvala, Daniel Gerdeaux, Martti Rask, Hilmar J. Malmquist, Kerstin Holmgren, Pietro Volta, Susana Romo, Reiner Eckmann, Alfred Sandström, Saúl Blanco, Andu Kangur, Henrik Ragnarsson Stabo, Mariana Meerhoff, Anne-Mari Ventelä, Martin Søndergaard, Torben L. Lauridsen

Gylleström et al 2003 L&O

Biomass ratios

Planktivorous fish:zooplankton

Zooplankton:Chlorophyll a

Carp are the worst!!!!!

reallybad guy!!

good guy

Azores – Mid AtlanticFishless lake stocked with carp in 1895

good guyvery good guy

very bad guy

Catfish not too good either

Masser af småfisk……Mesh size : 5-90 mm

Swedish lakes

Jeppesen et al, 2010

as piscivorouswhen large

August samples – Danish lakes

Slope

Jeppesen et al., 2010

log(algae biomass) = a*log(TP)+ b*log(TN) + c*log (mean depth)+d*log(water temp) + e – data from August only (late summer)

Jeppesen et al, in press

More bad guys and smaller size leads to (more) turbid conditions

Climate change challenge -

Reduce the external loading much more!!!

Artificial wetlands

Carlos C. Hoffman

Bring the river valleys back to the rivers!!