Swedish experiences on the importance of N and P

Transcription

1 Danish Coastal Eutrophication Conference Copenhagen Swedish experiences on the importance of N and P Ragnar Elmgren & Ulf Larsson Dept. Ecology, Environment & Plant Sciences Stockholm University

2 Danish Coastal Eutrophication Conference Copenhagen Swedish experiences on the importance of N and P: Are they relevant for Denmark? Ragnar Elmgren & Ulf Larsson Dept. Ecology, Environment & Plant Sciences Stockholm University

3 Talk outline Focus on the Baltic Sea proper Baltic Sea background Himmerfjärden, a Baltic coastal area where both N & P are important - Does N removal improve status? - What is the importance of P? - Are other factors important? - Is nutrient removal the only option? 3

4 Why only the Baltic? This is where the controversy is - N removal, it is argued, will be canceled by N 2 -fixation by toxic blooms of cyanobacteria - Baltic proper is nitrogen-limited, with huge blooms of nitrogen-fixing cyanobacteria - If nitrogen-fixers can eliminate marine nitrogen limitation, we should see it here! Main Swedish problem area - Baltic influences Swedish west coast 4

5 The Baltic Sea: Enclosed Large catchment Shallow Brackish Stratified hence naturally sensitive 5

6 Baltic oxygen deficiency worse than ever Deficiency in 2% of volume, half of that totally anoxic Source SMHI

7 Baltic Environmental management: Helsinki convention, signed 1974, in force 198 Several EU directives Baltic Sea Action Plan 27 Is it working? 7

8 Nutrient load on the Baltic Sea Bo Gustafsson, Baltic Nest Institute, Stockholm University 62 ton/yr? N P 21 ton/yr 8

9 DIN µm DIP µm Landsort Deep, winter Inorganic Nitrogen and Phosphorus, -1m DIN DIP 1,9,8,7, ,5,4,3,2,

10 The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 TN Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP H B

11 The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 Experiment with lowered N/P ratio TN Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP H B

12 The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since % nitrogen removal TN Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP H B

13 The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since % nitrogen removal TN Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP H B

14 The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 No nitrogen removal in spring TN Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP H B

15 The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 Nitrogen removal turned off for 2 yrs TN Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP H B

16 DIP µg/l Himmerfjärden , phosphate Dissolved inorganic phosphorus -1 m B1 H4 H4 B1 16

17 DIP µg/l Himmerfjärden , phosphate Dissolved inorganic phosphorus -1 m B1 H4 H4 B1 17

18 Chlorophyll a µg/l DIP µg/l DIN µg/l Himmerfjärden , nutrients and phytoplankton Dissolved inorganic phosphorus -1 m B1 H Dissolved inorganic nitrogen -1 m Chlorophyll a, upper mixed layer, Mar-Oct B1-2 m H4-14 m P limitation in spring 18

19 Chloropyll a -14m µg/l Himmerfjärden March-October Chlorophyll a vs sewage N y =.68x r 2 = TN emission, tonnes/yr 19

20 WFD status classification, phytoplankton biovolume Station H4 Phytoplankton biovolume June- August 2, 1,5 mm 3 L -1 1, Poor,5, Moderate Good 2

21 More N 2 -fixing cyanobacteria when removing N meter L Aphanizomenon abundance vs sewage N, June-September Sewage N, tonnes/year 21

22 Nitrogen removal can reduce coastal eutrophication! - N 2 -fixation compensates only partly (Annually <1%, summer <5%) - No toxic blooms Response is quick, within the year! P removal is also beneficial, but whole Baltic needed! 22

23 Is nutrient removal the only option? P precipitation and oxygenation are being tried, may be useful complements Mussel culture was tried, but failed Trophic cascades from fish may help, both in plankton and bottom vegetation An offshore discharge may be the only option for meeting the WFD requirements Nutrient removal still the main option!

24 Relevance for Denmark? Similar nutrient concentrations Filtering animals can be more effective in shallow Danish waters of higher salinity But principles apply: Benefit of nitrogen removal should be similar, or even greater where higher salinity reduces N 2 -fixation 24

25 Thank you for listening! To a contribution from BEAM, Baltic Ecosystem Adaptive Management, Stockholm University s Strategic Marine Environmental Research Program 25