Danish Coastal Eutrophication Conference Copenhagen 213-6-19 Swedish experiences on the importance of N and P Ragnar Elmgren & Ulf Larsson Dept. Ecology, Environment & Plant Sciences Stockholm University
Danish Coastal Eutrophication Conference Copenhagen 213-6-19 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
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
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
The Baltic Sea: Enclosed Large catchment Shallow Brackish Stratified hence naturally sensitive 5
Baltic oxygen deficiency worse than ever Deficiency in 2% of volume, half of that totally anoxic Source SMHI
Baltic Environmental management: Helsinki convention, signed 1974, in force 198 Several EU directives Baltic Sea Action Plan 27 Is it working? 7
Nutrient load on the Baltic Sea 185-26 Bo Gustafsson, Baltic Nest Institute, Stockholm University 62 ton/yr? N P 21 ton/yr 8
DIN µm DIP µm Landsort Deep, winter Inorganic Nitrogen and Phosphorus, -1m 16 14 12 1 DIN DIP 1,9,8,7,6 8 6 4 2,5,4,3,2,1 1955 1975 1995 215 9
The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 TN 91 78 65 52 39 Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP 12 1 8 6 H4 26 13 4 2 B1 197 198 199 2 21 1
The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 Experiment with lowered N/P ratio TN 91 78 65 52 39 Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP 12 1 8 6 H4 26 13 4 2 B1 197 198 199 2 21 11
The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 5% nitrogen removal TN 91 78 65 52 39 Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP 12 1 8 6 H4 26 13 4 2 B1 197 198 199 2 21 12
The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 85% nitrogen removal TN 91 78 65 52 39 Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP 12 1 8 6 H4 26 13 4 2 B1 197 198 199 2 21 13
The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 No nitrogen removal in spring TN 91 78 65 52 39 Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP 12 1 8 6 H4 26 13 4 2 B1 197 198 199 2 21 14
The Himmerfjärden case: Coastal area with large sewage treatment plant, studied since 1976 Nitrogen removal turned off for 2 yrs TN 91 78 65 52 39 Plant loads, tonnes/year Plant loads, tonnes/ year TN TP TP 12 1 8 6 H4 26 13 4 2 B1 197 198 199 2 21 15
DIP µg/l Himmerfjärden 1977-211, phosphate Dissolved inorganic phosphorus -1 m 18 16 14 12 1 8 6 4 2 1975 198 1985 199 1995 2 25 21 B1 H4 H4 B1 16
DIP µg/l Himmerfjärden 1977-211, phosphate Dissolved inorganic phosphorus -1 m 18 16 14 12 1 8 6 4 2 1975 198 1985 199 1995 2 25 21 B1 H4 H4 B1 17
Chlorophyll a µg/l DIP µg/l DIN µg/l Himmerfjärden 1977-211, nutrients and phytoplankton Dissolved inorganic phosphorus -1 m 18 16 14 12 1 8 6 4 2 1975 198 1985 199 1995 2 25 21 B1 H4 18 16 14 12 1 9 8 7 6 5 4 3 2 1 1975 198 1985 199 1995 2 25 21 8 6 4 2 Dissolved inorganic nitrogen -1 m 1975 198 1985 199 1995 2 25 21 Chlorophyll a, upper mixed layer, Mar-Oct B1-2 m H4-14 m P limitation in spring 18
Chloropyll a -14m µg/l 9 8 7 6 5 4 3 2 1 Himmerfjärden March-October Chlorophyll a vs sewage N y =.68x + 2.44 r 2 =.71 2 4 6 8 1 TN emission, tonnes/yr 19
WFD status classification, phytoplankton biovolume Station H4 Phytoplankton biovolume June- August 2, 1,5 mm 3 L -1 1, Poor,5, Moderate Good 2
More N 2 -fixing cyanobacteria when removing N meter L -1 16 14 12 1 8 6 4 2 Aphanizomenon abundance vs sewage N, June-September 1977-1996 1997-211 1997 28 27 1 2 3 4 5 6 7 8 9 1 Sewage N, tonnes/year 21
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
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!
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
Thank you for listening! To a contribution from BEAM, Baltic Ecosystem Adaptive Management, Stockholm University s Strategic Marine Environmental Research Program 25