Midlertidig ændring af vandstand som redskab til vedligeholdelse af lobeliesøer

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1 Lake Skærsø, Denmark Midlertidig ændring af vandstand som redskab til vedligeholdelse af lobeliesøer Anna-Marie Klamt, Kasper Reitzel, Frede Ø. Andersen, Henning S. Jensen CLEAR temadag 24 May 2016 Syddansk Universitet, Odense

2 Lake Skærsø - location Århus Lake Skærsø Odense Copenhagen

3 Possible effects of a drawdown - on phosphorus binding capacity Død og nedbrydning Frigivelse af organisk stof og næringssalte På littoral vegetation Overlevelse Vækst og spredning Kompakte mineralske sedimenter Effekt af vandstandssænkning Organisk stof Iltnedtrængning Organisk stofomsætning Frigivelse af næringssalte På sedimenter Increase in formation of oxidized Fe forms Increase in P binding capacity Phosphorus Increase in crystallization of metal oxyhydroxides Decrease in P binding capacity

4 Experimental set-up - drying and rewetting of intact littoral sediment cores A) with plants B) without plants

5 Results - effect of drying on sediment properties 120 A) with plants initial 80 dried molar ratio 40 * * 0 various Fe:P ratios decrease in Fe:P ratios

6 Results - effect of drying on sediment properties 120 A) with plants B) without plants initial initial 80 dried dried molar ratio 40 * * 0 0 * various Fe:P ratios various Fe:P ratios decrease in Fe:P ratios

7 Results - effect of rewetting on water quality (flux experiments) 500 A) with plants B) without plants cumulative TDP-flux [µmol m -2 ] for different times control dried and control rewetted rewetted 7 d 14 d 21 d 27 d 34 d release of phosphorus

8 Results - effect of rewetting on water quality (flux experiments) 500 A) with plants B) without plants cumulative TDP-flux [µmol m -2 ] for different times control dried and rewetted control dried and rewetted 7 d 14 d 21 d 27 d 34 d release of phosphorus

9 Results - effect of rewetting on water quality (flux experiments) A) with plants

10 Results - effect of rewetting on water quality (flux experiments) 500 A) with plants B) without plants cumulative TDP-flux [µmol m -2 ] for different times control dried and rewetted control dried and rewetted 7 d 14 d 21 d 27 d 34 d release of phosphorus effect on the lake: assumption: 0.65 m drawdown and exposure of 20 % of the lake bottom (with plants) increase in TP concentration by approximately 2.4 %

11 Results - effect of drying and rewetting on P binding capacity (P uptake experiment) B) without plants (only) 0 cumulative DIP flux [µmol m d -1 ] no significant difference control dried and rewetted P binding capacity was retained during drying and rewetting confirmed by a long-term small-scale experiment

12 Possible effects of a drawdown - on phosphorus binding capacity Død og nedbrydning Frigivelse af organisk stof og næringssalte På littoral vegetation Overlevelse Vækst og spredning Kompakte mineralske sedimenter Effekt af vandstandssænkning Organisk stof Iltnedtrængning Organisk stofomsætning Frigivelse af næringssalte På sedimenter Increase in formation of oxidized Fe forms Increase in P binding capacity Phosphorus variable or no change in P binding capacity Increase in crystallization of metal oxyhydroxides Decrease in P binding capacity

13 Summary 1. Decrease in Fe:P ratios/increase in saturation of P sorption sites during drying 2. release of P upon rewetting, BUT: mainly organic P forms low amounts with little effect on TP in the lake 3. continuously high P binding capacity after drying and rewetting (only tested for cores without plants)

14 Summary 1. Decrease in Fe:P ratios/increase in saturation of P sorption sites during drying 2. release of P upon rewetting, BUT: mainly organic P forms low amounts with little effect on TP in the lake 3. continuously high P binding capacity after drying and rewetting (only tested for cores without plants) water level drawdowns can be an appropriate restoration measure for endangered Lobelia lakes, given that isoetid plants spread during desiccation period LITERATURE: Klamt, A.-M., K. Reitzel, F. Andersen, and H. Jensen Simulated drawdown and rewetting of littoral sediments: implications for Lobelia lake management. Hydrobiologia: Nygaard, R., A.-M. Klamt, S. M. Døssing, H. S. Jensen, K. Reitzel, and F. Ø. Andersen Midlertidig vandstandssænkning i Skærsø? Vand & Jord:

15 Tak for opmærksomheden!

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17 Effekt af vandstandssænkning - på planter og organisk stof Død og nedbrydning Frigivelse af organisk stof og næringssalte På littoral vegetation Overlevelse Vækst og spredning Effekt af vandstandssænkning Kompakte mineralske sedimenter Organisk stof Ilt nedtrækning Organisk stofomsætning Frigivelse af næringssalte På sedimenter Increase in formation of oxidized Fe forms Increase in P binding capacity Phosphorus Increase in crystallization of metal oxyhydroxides Decrease in P binding capacity