Eutrophication Status of the Wadden Sea

Justus van BeusekomWadden Sea Station Sylt

Alfred-Wegener-Institute for Polar and Marine ResearchList/Sylt

Overview

•Recent Trends (QSR 2004)– Trends in River Input

– Trends in Eutrophication Proxies• Seasonal Cycle of NH4 + NO2

• Summer Phytoplankton Biomass

•Historic levels

Trends in River input:Discharge

1975 1980 1985 1990 1995 2000 2005Year

0

10

20

30

40

50

60

70

80

90

100

110

120

130

Dis

char

ge (

km³/

year

)

Elbe, W eser

R hine, M aas, N oordzeekanaal, IJsselm eer, Em s

Annua l D ischarge Sou thern and Cen tra l R ive rs

Trends in River InputTotal Nitrogen - Input

1975 1980 1985 1990 1995 2000 2005Year

0

200000

400000

600000

800000

Tot

al N

itrog

en L

oad

(Ton

nes/

year

)

Elbe, W eser

R hine, M aas, N oordzeekanaal, IJsselm eer, Em s

Annua l T N Load Southern and Cen tra l R ivers

Trends in River InputTotal Phosphorus - Input

1975 1980 1985 1990 1995 2000 2005Year

0

20000

40000

60000

Tot

al P

hosp

horu

s Lo

ad (

Ton

nes/

year

)

Elbe, W eser

R hine, M aas, N oordzeekanaal, IJsselm eer, Em s

Annua l T P Load Sou thern and Centra l R ive rs

Trends in River InputSpecific TN Input

1975 1980 1985 1990 1995 2000 2005Year

0

2000

4000

6000

8000

Spe

cific

TN

Loa

d (m

g/m

³)

R hine, M aas, N oordzeekanaal, IJsselm eer, Em s

E lbe, W eser

Specific T N Load

Trends in River InputSpecific Phosphorus Input

1975 1980 1985 1990 1995 2000 2005Year

0

200

400

600

Spe

cific

TP

Loa

d (m

g/m

³)

Elbe, W eser

R hine, M aas, N oordzeekanaal, IJsselm eer, Em s

Specific T P Load

Trends in River input:Conclusions

•Interannual Difference related to Variation in Riverine Freshwater Discharge

•Decreasing trend in the specific nutrient loads– All areas show similar Trends

– TP decrease faster than TN decrease• TN decrease: 2.1 - 2.2% year-1 • TP decrease: 3.3 - 2.5 % year-1

Indicators of Eutrophication

Eutrophication Criteria:

•Changes in the seasonal cycle of nitrogen(NH4 + NO2 levels in autumn)

QSR 2004

•Summer Chlorophyll

Changes in the seasonal cycle of nitrogen(NH4 + NO2 levels in autumn)

2 4 6 8 10 12M onth

0

2

4

6

8N

H4

(µ

M)Sylt Rømø Bight

Mean Annual Cycle

Changes in the seasonal cycle of nitrogen(NH4 + NO2 levels in autumn)

Multiple regression analysis

•dependent:– Autumn NH4 + NO2

•independent:– Riverine input (Rhine Meuse; Dec-Aug)

– Chlorophyll (autumn)

– Temperature (autumn)

Changes in the seasonal cycle of nitrogen(NH4 + NO2 levels in autumn)

•Significant effect of Rhine/Meuse in the Southern Wadden Sea

• Western Dutch Wadden Sea• Eastern Dutch Wadden Sea• Norderney

•No significant relations in the Northern Wadden Sea

Changes in the seasonal cycle of nitrogen(NH4 + NO2 levels in autumn)

Western Dutch Wadden Sea

150 200 250 300 350 400TN load R hine/M euse (1000 Tonnes)

D ecem ber -August

0

10

20

30

mea

n [N

H4

+ N

O2

] (µ

M)

Se

ptem

ber

-Nov

embe

r

1983

Changes in the seasonal cycle of nitrogen(NH4 + NO2 levels in autumn)

Western Dutch Wadden Sea

Pre-industria l 1960-1962 1978-2002 1978-2002

0

4

8

12

16

20

Aut

umn

NH

4 +

NO

2 (

µM

)(S

ept.

- N

ov.)

Low TN load High TN load

Trends in Summer Chlorophyll(Common Driver: Rhine/Meuse)

Area Period Mean

Trend/Factor

Correlation

Western Dutch Wadden Sea 1976-2002

18.0 Yes/2.7 r²=0.43; n=27; p=0.0002

Eastern Dutch Wadden Sea 1976-2002

19.9 No Trend

Lower Saxon Wadden Sea (Norderney)

1988-2002

16.6 Yes/2.1 r²=0.308; n=18; p=0.008

Southern Schleswig-Holstein

1990-2002

14.2 No Trend* r²=0.002; n=13; p=0.868

Northern Schleswig-Holstein

1990-2002

7.4 No Trend* r²=0.12; n=13; p=0.245

Sylt-Rømø-Bight 1984-2002

6.3 Yes/2.7 r²=0.345; n=19; p=0.008

Danish Wadden Sea 1990-2002

8.6 No Trend* r²=0.18; n=12; p=0.15

Spatial Trends in Summer Chlorophyll

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0

Longitude (°E )

51.5

52.0

52.5

53.0

53.5

54.0

54.5

55.0

55.5

Lat

itude

(°N

)

Elbe

M arsdieparea

Western Dutch Wadden Sea

Weser

Eastern Dutch Wadden Sea

Ems

Maasslu is

Rhine

Lobith

Meuse

Haringvlie t

IJssel

IJsselmeer

Sylt-Romo-Bight

18.019.9

16.614.2

7.4

6.3

8.6

Contrasting Eutrophication Status of the Northern and Southern Wadden Sea?

0 4 8 12 16 20A utum n N H 4 + N O 2 (µM )

0

5

10

15

20

25S

umm

er C

hlor

ophy

ll (µ

g/g)

W D W S

ED W S

N ney

SR B

D W S

Y = 0.84 * X + 1 .4N = 5R ² = 0.87

Conclusions

• Large Interannual Differences in Nutrient Discharge

• Decreasing Trend in Nutrient Loads

• Decreasing Trends in Eutrophication Status

• No Universal Indicator (yet)– Southern Wadden Sea: NH4 + NO2

– Entire Wadden Sea: Summer Chlorophyll(some areas)

• Presently: about 5 Times above Pre- Industrial Levels

• Southern Wadden Sea more Eutrophic the Northern Wadden Sea

Relative Importance of Rivers Influencing the Wadden Sea

Mean relative contribution of major fresh water sources to nutrient input into the southern (1977-2002) and central Wadden Sea (1980 to 2002). For the Eider and Danish rivers, data since 1990, resp. 1995 were used as reported to OSPAR (Hereira, pers. comm.).

Southern Wadden Sea

Source Discharge Total Nitrogen Total Phosphorus

Haringvliet 27.5% 27.2% 22.1%

Maassluis 47.4% 47.2% 57.2%

Noordzeekanaal 3.0% 2.9% 4.6%

IJsselmeer 19.3% 17.6% 13.8%

Ems 2.8% 4.6% 2.3%

Central and Northern Wadden Sea

Source Discharge Total Nitrogen Total Phosphorus

Weser 31.1% 31.7% 30.1%

Elbe 62.0% 61.9% 64.3%

Eider 2.5% 2.2% 2.5%

County Ribe 3.4% 3.2% 2.1%

Jylland 0.9% 1.0% 0.9%