B e r i c h t e aus dem
I n s t i t u t für Meereskunde an der
Christian-Albrechts-Universiät K i e l Nr. 130
OXYGEN DEPLETION 1980 - 1983 IN COASTAL WATERS OF THE
FEDERAL REPUBLIC OF GERMANY
E d i t e d by S e b a s t i a n A. G e r l a c h w i t h C o n t r i b u t i o n s from
B. Babenerd, J . Backhaus, W. B a l z e r , J . B e r g , M. B o e h l i c h , T. B r e y , U. Brockmann, J.A. F a l k e , S.A. G e r l a c h , H. Graßl, W. H i c k e l ,
U. Horstmann, W. Koeve, E. Rachor, G. Radach, H. Rumohr, M. S t e n g e l , G. Wefer, M. W e i g e l t , B. Z e i t z s c h e l
Kopien d i e s e r A r b e i t können bezogen werden von:
I n s t i t u t für Meereskunde Abt. M e e r e s b o t a n i k
Düsternbrooker Weg 20
2300 K i e l ISSN 0341-8561
Summary
1981 - 1983 o b s e r v a t i o n s on oxygen d e p l e t i o n and f i s h k i l l s i n near-bottom waters o f t h e German B i g h t , o f Danish and Swedish c o a s t s and o f K i e l e r Bucht and Mecklenburger Bucht cause c o n c e r n . A working group was sponsored by t h e M i n i s t e r o f t h e I n t e r i o r o f t h e F e d e r a l R e p u b l i c o f Germany t o a s s e s s , mostly from e x i s t i n g d a t a , whether man made n u t r i e n t i n p u t i n t o c o a s t a l waters may have t r i g g e r e d e x c e p t i o n a l p h y t o p l a n k t o n blooms which, when d e c a y i n g , c o u l d r e s u l t i n oxygen d e p l e t i o n e v e n t s . C a l c u l a t e d f o r t h e r e s p e c t i v e b o d i e s o f water, i n p u t o f phosphorus and n i t r o g e n v i a sewage, r i v e r s , l a n d r u n o f f and atmospheric f a l l o u t , per y e a r , i s o f t h e same o r d e r of magnitude as t h e n u t r i e n t content i n w i n t e r water i n K i e l e r Bucht;
p r o b a b l y i n p u t i s h i g h e r i n t h e German B i g h t . Phosphorus c o n c e n t r a t i o n s i n H e l g o l a n d w i n t e r s u r f a c e water doubled between 1962 and 1982. I n K i e l e r Bucht, however, phosphorus c o n c e n t r a t i o n s were s t a b l e 1957 - 1975. The p e r i o d 1975 - 1983 i s t o o s h o r t f o r a d e f i n i t e statement, t h a t t h e r e i s an i n c r e a s i n g t r e n d f o r phosphate and n i t r a t e , even i f t h e r e i s some e v i d e n c e . Year t o year l o a d s o f n i t r o g e n t r a n s p o r t e d by l a n d r u n o f f and r i v e r s i n t o c o a s t a l waters d i f f e r w i d e l y . F u r t h e r i n v e s t i g a t i o n s w i l l t e l l whether t h e r e a r e c o r r e l a t i o n s w i t h p h y t o p l a n k t o n p r o d u c t i v i t y . Year t o year weather c o n d i t i o n s d i f f e r w i d e l y , t o o , and i t w i l l be worked out whether oxygen d e p l e t i o n can be c o r r e l a t e d t o s p e c i f i c weather c o n d i t i o n s which enhance s t r a t i f i c a t i o n o f t h e water masses. F i n a l l y , more h i s t o r i c a l d a t a w i l l brought forward as evidence f o r e x t r a o r d i n a r y s i t u a t i o n s i n c o a s t a l w a t e r s d u r i n g t h e p a s t decades. Recommendations f o r b i o l o g i c a l m o n i t o r i n g a r e g i v e n .
Zusammenfassung
Beobachtungen 1981 - 1983 über S a u e r s t o f f m a n g e l und F i s c h s t e r b e n i n den bodennahen Wasserschichten d e r Deutschen Bucht, d e r dänischen und schwedischen Küstengewässer und der K i e l e r und Mecklenburger Bucht gaben Anlaß z u r B e s o r g n i s . Der I n n e n m i n i s t e r d e r B u n d e s r e p u b l i k Deutschland b e a u f t r a g t e e i n e A r b e i t s g r u p p e damit, überwiegend durch Bewertung b e r e i t s vorhandener Daten h e r a u s z u f i n d e n , ob d i e vom Menschen z u verantwortenden Einträge an Pflanzennährstoffen i n Küstengewässer außergewöhnliche Planktonblüten ausgelöst haben, welche beim Abbau z u S a u e r s t o f f m a n g e l führen. Auf d i e b e t r e f f e n d e n Wassermengen bezogen i s t d i e Zufuhr von Phosphor und S t i c k s t o f f aus häuslichen Abwässern, m i t Flußwasser und m i t von Ackern und Weiden ablaufendem Wasser und über d i e Atmosphäre, p r o J a h r gerechnet, ebensogroß w i e d i e Gesamtmenge d i e s e r Nährstoffe im Winterwasser der K i e l e r Bucht; der E i n t r a g i s t v e r m u t l i c h sogar größer i n der Deutschen Bucht. D i e P h o s p h o r k o n z e n t r a t i o n e n im oberflächlichen Winterwasser b e i H e l g o l a n d haben s i c h zwischen 1962 und 1982 v e r d o p p e l t . I n der K i e l e r Bucht j e d o c h b l i e b e n d i e P h o s p h o r k o n z e n t r a t i o n e n 1957 b i s 1975 f a s t k o n s t a n t . Der Z e i t r a u m 1975 b i s 1983 i s t zu k u r z , um d e f i n i t i v f e s t z u s t e l l e n , daß es s e i t d e m e i n e n zunehmenden Trend b e i den Phosphat- und N i t r a t k o n z e n t r a t i o n e n g i b t , auch wenn manches dafür s p r i c h t . Von J a h r z u J a h r s i n d d i e F r a c h t e n an S t i c k s t o f f sehr v e r s c h i e d e n , welche m i t dem Abfluß von Land und m i t Flußwasser i n Küstengewässer e i n g e b r a c h t werden. W e i t e r e Untersuchungen müssen z e i g e n , ob es dabei K o r r e l a t i o n e n m i t d e r P h y t o p l a n k t o n - Produktivität g i b t . Von J a h r z u J a h r s i n d auch d i e Wetterbedingungen sehr v e r s c h i e d e n ; es s o l l e r a r b e i t e t werden, i n welchem Umfang S a u e r s t o f f m a n g e l m i t s p e z i f i s c h e n Wetterbedingungen k o r r e l i e r t werden kann, welche d i e S t r a t i f i z i e r u n g der Wassermassen fördern. Schließlich s o l l e n mehr h i s t o r i s c h e Daten aus vergangenen J a h r z e h n t e n e r a r b e i t e t werden, welche Uber außergewöhnliche E r e i g n i s s e i n deutschen Küstengewässern b e r i c h t e n . Es werden Empfehlungen für das b i o l o g i s c h e M o n i t o r i n g gegeben.
1. I n t r o d u c t i o n
1.1. Oxygen d e p l e t i o n events
1.2. Government and r e s e a r c h response 1.3. The o r i g i n o f oxygen d e p l e t i o n
2. Trends i n n u t r i e n t i n p u t i n t o c o a s t a l w a t e r s
2.1. Atmospheric i n p u t
2.2. Input from l a n d i n t o the B e l t Sea 2.3. Input from l a n d i n t o the German B i g h t 2.4. G e n e r a l t r e n d s and t h e r e l a t i o n between
i n p u t and c o n t e n t
3. Trends i n n u t r i e n t c o n c e n t r a t i o n s i n c o a s t a l waters
3.1. A n a l y t i c a l , s t a t i s t i c a l and r e g i o n a l problems
3.2. Trends i n n u t r i e n t c o n c e n t r a t i o n s i n the German B i g h t
3.3. Trends i n n u t r i e n t c o n c e n t r a t i o n s i n K i e l e r Bucht
3.4. P o s s i b l e causes o f i n c r e a s e d n u t r i e n t c o n c e n t r a t i o n s s i n c e 1975
4. Trends i n primary p r o d u c t i o n i n c o a s t a l w a t e r s
4.1. P r i m a r y p r o d u c t i o n i n the German B i g h t 4.2. Comparison w i t h t h e 1976 oxygen d e p l e t i o n
i n New York B i g h t
4.3. P r i m a r y p r o d u c t i o n i n K i e l e r Bucht
1
page
5. The s e d i m e n t a t i o n o f o r g a n i c matter and e f f e c t s from t h e sediment
5.1. The e f f e c t o f g r a z i n g
5.2. The p e r s i s t e n c e o f c o n d i t i o n s i n t h e sediment
6. E u t r o p h i c a t i o n e f f e c t s on h i g h e r l i n k s o f t h e food c h a i n
7. H i s t o r i c evidence o f oxygen d e p l e t i o n
8. Weather e f f e c t s on water s t r a t i f i c a t i o n
and on t h e c u r r e n t p a t t e r n 69
9. C o n c l u s i o n s and recommendations
(which w i l l be f u r t h e r d i s c u s s e d i n t h e
working group) 76
10. Problems o f m o n i t o r i n g
10.1. How oxygen d e p l e t i o n can be d e t e c t e d 77 10.2. How t h e oxygen d e p l e t i o n may be e x p l a i n e d :
the decaying p l a n t approach 78 10.3. What i s t h e o r i g i n o f d e c a y i n g p l a n t m a t e r i a l ? 78
10.4. G r a z i n g may c o n t r o l p h y t o p l a n k t o n p r o d u c t i o n 79 10.5. N u t r i e n t s c o n t r o l primary p r o d u c t i o n i n s p r i n g 79 10.6. C o n d i t i o n s t h a t c o n t r o l primary p r o d u c t i o n
i n summer 80 10.7. How t h e sediment i n f l u e n c e s oxygen and n u t r i e n t s
i n t h e o v e r l y i n g water mass 80 10.8. S t r a t i f i c a t i o n , hydrography and t h e weather 81
10.9. Input o f n u t r i e n t s 82
11. M o n i t o r i n g and marine s c i e n c e 82
12. References 84
1. I n t r o d u c t i o n
1.1 Oxygen d e p l e t i o n e v e n t s
F i r s t i n f o r m a t i o n about reduced oxygen c o n c e n t r a t i o n s i n t h e near-bottom water masses o f o f f s h o r e r e g i o n s o f t h e German B i g h t were gained from b i o l o g i c a l s t u d i e s (Rachor, 1977; R o s e n t h a l e t a l . , 1981). I n summer 1981 i t c o u l d be c o n f i r m e d t h a t a l a r g e a r e a northwest o f H e l g o l a n d , c a l l e d the
"submarine v a l l e y o f the p o s t g l a c i a l E l b e r i v e r " , s u f f e r e d from reduced oxygen c o n c e n t r a t i o n s ( F i g . 1-2); s a t u r a t i o n was o n l y about 40% (Rachor and A l b r e c h t , 1983). Dead f i s h were observed o f f t h e Danish c o a s t (Dyer e t a l . , 1983). I n 1982 an a r e a about 50 n a u t i c a l m i l e s west o f J u t l a n d was h i t by oxygen d e p l e t i o n ; t h e r e s u l t was f i s h k i l l s and dead macrozoobenthos ( D e t h l e f s e n and von Westernhagen, 1983). I n August 1983 Danish a u t h o r i t i e s found low oxygen c o n c e n t r a t i o n s i n t h e same r e g i o n s o f t h e N o r t h Sea which were h i t i n 1981 ( M i l j t f s t y r e l s e n , 1984).
In K i e l e r Bucht the western p a r t s , i n c l u d i n g E c k e r n f o r d e Bay, F l e n s b u r g F j o r d and K i e l F j o r d a r e w e l l known f o r oxygen d e f i c i e n c y i n t h e n e a r - bottom water d u r i n g summer p e r i o d s . However, i t had never b e f o r e been observed t h a t oxygen d e p l e t i o n a f f e c t e d t h e extended a r e a s i n t h e c e n t r a l and e a s t e r n p a r t o f K i e l e r Bucht, as happened i n September 1981 ( F i g . 3-4).
The s i t u a t i o n was so extreme t h a t f o r a few weeks h i g h c o n c e n t r a t i o n s o f hydrogen s u l f i d e were encountered ( E h r h a r d t and Wenck, 1984) k i l l i n g most of t h e macrozoobenthos s p e c i e s o f t h e r e g i o n ( W e i g e l t , 1983). Danish a u t h o r i t i e s r e p o r t e d 1981 many a r e a s w i t h oxygen d e p l e t i o n as w e l l as f i s h k i l l s i n a d j a c e n t w a t e r s o f the L i t t l e B e l t and Great B e l t and i n the s o u t h e r n K a t t e g a t ( M i l j t f s t y r e l s e n , 1984). Swedish a u t h o r i t i e s have been concerned w i t h oxygen d e p l e t i o n i n Laholm Bay and a d j a c e n t a r e a s o f the S o u t h e a s t e r n K a t t e g a t s i n c e 1980 ( N a t i o n a l Swedish Environment P r o t e c t i o n Board, 1984). I n 1982 Danish a u t h o r i t i e s r e p o r t e d on oxygen d e f i c i e n c y i n K^ge Bay south o f Copenhagen and i n K a l 0 Bay n o r t h o f Aarhus.
In 1983 oxygen d e p l e t i o n was observed i n n e a r l y a l l r e g i o n s o f the Danish B e l t Sea; end o f August 1983 oxygen c o n c e n t r a t i o n s were i n g e n e r a l lower as compared w i t h t h e same season i n 1981. However, i n t h e f i r s t week o f September 1983 s t r o n g winds p r e v a i l e d , so t h a t from 8 t o 12.9.1983 t h e oxygen s i t u a t i o n was normal a g a i n ( M i l j t f s t y r e l s e n , 1984). I n K i e l e r Bucht the s i t u a t i o n was comparable ( s e e Box 2 ) .
3 c o n t i n u e d on p . 12
Box 1
S u b p r o j e c t s of t h e Working Group
E u t r o p h i c a t i o n o f t h e N o r t h Sea and t h e B a l t i c
1. C o o r d i n a t i o n (S.A.Gerlach, Box 3, F i g . 7 I n s t i t u t für Meereskunde K i e l )
2. Documentation o f the oxygen d e p l e t i o n Box 2, Box 11 event 1981 i n K i e l e r Bucht, i t s
e f f e c t s on benthos fauna, and t h e r e g e n e r a t i o n i n subsequent years
(S.A. G e r l a c h , I n s t i t u t für Meereskunde K i e l )
3. Changes i n the macrobenthos o f K i e l e r Box 12, F i g . 29 Bucht 1953 - 1983, and documentation
o f events which p o s s i b l y a r e consequences o f e u t r o p h i c a t i o n s i n c e t h e end o f t h e past century (H.
Rumohr, I n s t i t u t für Meereskunde K i e l )
4. A n a l y s i s o f macrobenthos t r e n d s 1965 Box 10, t o 1983 i n the German B i g h t , and
macrobenthos surveys i n t h e p a r t o f t h e German B i g h t known f o r oxygen d e p l e t i o n (E.Rachor, I n s t i t u t für Meeresforschung Bremerhaven)
5. Weather s i t u a t i o n s which a r e r e l e v a n t Box 15, F i g . 31 f o r c h e m i c a l and b i o l o g i c a l processes
i n c o a s t a l a r e a s o f Germany (H.
Graßl, I n s t i t u t für Meereskunde K i e l )
6. S i m u l a t i o n o f c u r r e n t s i n t h e system Box 14, F i g . 30 North Sea - B a l t i c Sea induced by
wind and t h e i r importance f o r e u t r o p h i c a t i o n e f f e c t s ( J . Backhaus, I n s t i t u t für Meereskunde, Universität Hamburg)
7. Trends i n n u t r i e n t c o n c e n t r a t i o n s a t Box 6, F i g . 11 Helgoland (G. Radach, I n s t i t u t für
Meereskunde Hamburg)
8. Amounts o f n u t r i e n t and p h y t o p l a n k t o n Box 9, F i g . 24 i n the German B i g h t : E v a l u a t i o n o f
p r o d u c t i v i t y data w i t h r e g a r d t o t h e problem o f e u t r o p h i c a t i o n (W. H i c k e l , B i o l o g i s c h e A n s t a l t H e l g o l a n d , L i t o r a l s t a t i o n L i s t / S y l t )
9. E v a l u a t i o n o f n u t r i e n t a n a l y s e s 1979- Box 4, F i g . 8 1983 i n t h e r e g i o n o f t h e German
B i g h t known f o r oxygen d e p l e t i o n ( U . Brockmann, I n s t i t u t für Biochemie und Lebensmittelchemie der Universität Hamburg)
10. Trends i n n u t r i e n t c o n c e n t r a t i o n s i n Box 5
the water o f K i e l e r Bucht (B. Box 7, F i g . 12 Z e i t z s c h e l , I n s t i t u t für Meereskunde
K i e l )
11. The image o f oxygen d e p l e t i o n e v e n t s Box 13 and o f t h e concomitant n u t r i e n t p a t t e r n
i n t h e sediment (G. Wefer, G e o l o g i s c h - P a l a e o n t o l o g i s c h e s I n s t i t u t der Universität K i e l )
12. I n v e s t i g a t i o n s on c h e m i c a l bounds, Box 8 d i a g e n e s i s and a c c u m u l a t i o n r a t e s o f
phosphorus i n sediments o f K i e l e r Bucht. C o n s t r u c t i o n o f a rough budget f o r phosphorus i n p u t and output i n the system K i e l e r Bucht. B i b l i o g r a - p h i c study on t h e importance o f sediment as s i n k , b u f f e r and source i n t h e c y c l i n g o f phosphorus (W. B a l z e r , I n s t i t u t für Meereskunde K i e l )
5
Illlllll 1962 o»yg«n deletion in North Sm ' t 1961 fish mortality
F i £ . 1: L o c a l i t i e s w i t h e v e n t s o f o x y g e n d e p l e - t i o n 1 * 8 1 - 1 9 8 2 .
F r o m M i l j t f s t y r e l s e n , 1 9 8 4 a n d R a c h o r 1 9 8 3 .
F i g . 2i O x y g e n c o n c e n t r a t i o n a n d t e m p e r a t u r e o n a l o o n a u t i c a l m i l e s l o n g p r o f i l e f r o m a s t a t i o n w e s t o f H e l g o l a n d ( H ) i n t o t h e G e r m a n B i g h t , S e p -
t e m b e r 1 9 8 1 .
F r o m R a c h o r a n d A l b r e c h t , 1 9 8 3 .
7 0
10
20 30 40
50 m
10
20 30 40 50
r I
H.
0
0 2 (mg/1)
T I 'C)
m ~---J
Fil. 2: Oxygen concentration and temperature on a
00nautical miles lang profile from a Station west of Helgoland(H) into the German Bight, Sep- tember 1981.
From Rachor and Albrecht, 1983.
7
w n is 20 a s u t.No.
12 3 4 7 I W a « W 20 21 SUt No.
02
H,S pmol drrT
15.-179.198l
Fi g > 3; D i s t r i b u t i o n o f t e m p e r a t u r e , s a l i n i t y a n d h y d r o g e n s u l f i d e o n 15-17 S e p t e m b e r 1981 i n K i e l e r B u c h t a n d M e c k l e n b u r g e r B u c h t . T h e p r o f i l e r u n s f r o m Eckernförde B a y ( s t a t i o n 10) , t h e n i n a n e a s t e r l y d i r e c t i o n t h r o u g h V e j s n a e s C h a n n e l ( s t a t i o n s 1 5 - 1 8 ) a n d t h r o u g h F e h m a r n B e l t ( s t a t i o n s 1 9 - 2 1 ) t o a p o s i t i o n i n K a d e t t - C h a n n e l e a s t o f G e d s e r .
F r o m E h r h a r d t a n d W e n c k , 1 9 8 4 .
F i g . 4: D i s t r i b u t i o n o f h y d r o g e n s u l f i d e i n t h e n e a r - b o t t o m w a t e r o r K i e l e r B u c h t a n d M e c k l e n b u r g e r B u c h t 15 - 17 S e p t e m b e r 1 9 8 1 . F r o m E h r h a r d t a n d W e n c k , 1 9 8 4 .
Box 2
Report on S u b p r o j e c t : Macrozoobenthos i n K i e l e r Bucht:
P o p u l a t i o n dynamics i n deep a r e a s 1982 - 1983
M i c h a e l W e i g e l t and S e b a s t i a n A. G e r l a c h Instituí für Meereskunde K i e l
I n l a t e summer 1981 oxygen d e f i c i e n c y k i l l e d most o f macrozoobenthos i n a r e a s o f K i e l e r Bucht w h i c h a r e below
18 - 20 m water depth, w i t h t h e e x c e p t i o n o f t h e clams A r c t i c a islándica, A s t a r t e spp. and t h e p r i a p u l i d worm H a l i c r y p t u s s p i n u l o s u s . Demersal f i s h emigrated t o s h a l l o w e r a r e a s . D u r i n g w i n t e r 1981/82 and summer 1982 r e c o l o n i z a t i o n by o p p o r t u n i s t i c worms P o l y d o r a spp. and C a p i t e l l a c a p i t a t a , subsequently by o t h e r b e n t h i c a n i m a l s o c c u r r e d , so t h a t one y e a r a f t e r t h e oxygen c a t a s t r o p h e b e n t h i c abundance and biomass was r e e s t a b l i s h e d , even i f some s p e c i e s l i k e t h e worm Nephtys spp. d i d n o t appear a g a i n ( W e i g e l t , 1983).
In summer 1982 a g a i n t h e r e was a tendency i n K i e l e r Bucht f o r oxygen d e f i c i e n c y caused by calm weather, but i n August 1982 w e s t e r l y g a l e s (up t o B e a u f o r t 12) p r o v i d e d exchange o f t h e water mass below t h e h a l o c l i n e . The r e c o v e r y o f macrozoobenthos i n t h e deeper p a r t s o f K i e l e r Bucht t h e r e f o r e c o n t i n u e d , and i n summer 1983 s p e c i e s r i c h n e s s , abundance and biomass was g e n e r a l l y h i g h e r compared w i t h summer 1981, i . e . i s b e f o r e t h e oxygen c a t a s t r o p h e o c c u r r e d . I n August 1983 oxygen d e p l e t i o n s t a r t e d a g a i n . C o n c e n t r a t i o n s o f o n l y 1 m l oxygen/1 were found below 20 m water depth. I t cannot be e x c l u d e d t h a t i n some areas oxygen disappeared t o t a l l y , because n e a r l y no f i s h was caught below 20 m water depth, and i n some a r e a s empty s h e l l s o f t h e b i v a l v e Syndosmya a l b a were found, i n o t h e r a r e a s masses o f dead p o l y c h a e t e worms.
S e n s i t i v e zoobenthos s p e c i e s d i e d , r e s i s t a n t ones s u r v i v e d , and o p p o r t u n i s t i c ones invaded t h e a r e a s l a t e r , a f t e r oxygen d e p l e t i o n ceased. However, i n s p r i n g 1984 t h e r e were months w i t h e a s t e r l y winds o r calm weather,
and i n t h e b e g i n n i n g o f June 1984 t h e h a l o c l i n e i n 16 - 18 m water depth was very s t r o n g , and o n l y 3.5 ml oxygen/1 was p r e s e n t i n t h e near-bottom l a y e r . Macrobenthos a t t h i s time was even poorer than i n November 1983. I t c o u l d be a n t i c i p a t e d t h a t another calm summer w i t h oxygen d e p l e t i o n would s e v e r e l y impact even t h e r e s i s t a n t s p e c i e s , because a p p a r e n t l y t h e s h e l l s o f t h e clam A r c t i c a islándica became t h i n n e r and more f r a g i l e between 1981 and 1984 i n d i c a t i n g s t r e s s c o n d i t i o n s even f o r t h i s s p e c i e s . However t h e second h a l f o f June and t h e month o f J u l y 1984 were extremely wet and windy, w i t h f r e q u e n t n o r t h w e s t e r l y g a l e s . T h e r e f o r e oxygen came back t o t h e near-bottom water masses, and one might expect a n o t h e r r e c o v e r y from oxygen d e f i c i e n c y i n 1984.
The above d e s c r i p t i o n i s from j u s t a s u p e r f i c i a l g l a n c e on benthos and f i s h sampled d u r i n g 1982 - 1984. The a c t u a l s o r t i n g and i d e n t i f i c a t i o n work s t a r t e d i n June 1984, and r e a l r e s u l t s w i l l be worked o u t s u b s e q u e n t l y .
R e f e r e n c e :
W e i g e l t , M. ( 1 9 8 3 ) : Untersuchungen z u r S i t u a t i o n des Benthos nach e i n e r ausgedehnten P e r i o d e vollständigen SauerstoffSchwundes im Bodenwasser der K i e l e r Bucht.
D i p l o m a r b e i t , K i e l
11
c o n t i n u e d f r o m p . 3
Even i f t h e r e have been r e p o r t s on f i s h k i l l s i n t h e p a s t from s e v e r a l l o c a l i t i e s , the 1981 oxygen c a t a s t r o p h e seems t o be unique i n d u r a t i o n , e x t e n s i o n and i n t e n s i t y .
Anybody w i t h a b a s i c textbook knowledge o f ecology may come t o t h e c o n c l u s i o n t h a t the oxygen c a t a s t r o p h e of 1981 and subsequent y e a r s i s t h e consequence o f e u t r o p h i c a t i o n : the i n c r e a s i n g or accumulating i n p u t o f p l a n t n u t r i e n t s l i k e n i t r o g e n and phosphorus v i a l a n d r u n o f f , v i a r i v e r s and v i a the atmosphere should r e s u l t i n a f e r t i l i z a t i o n o f the sea water i n c o a s t a l r e g i o n s , and subsequently l e a d t o enhanced phytoplankton and phytobenthos p r o d u c t i o n . When dead, the p l a n t biomass produced s i n k s t o t h e sea bottom, and m i c r o b i a l d e g r a d a t i o n and r e m i n e r a l i z a t i o n of such s u r p l u s dead o r g a n i c substance consumes e x t r a amounts of oxygen. Oxygen d e p l e t i o n then i s the consequence of e u t r o p h i c a t i o n .
1.2 Government and r e s e a r c h response
Governments i n the F e d e r a l R e p u b l i c of Germany, Denmark and Sweden t h e r e f o r e were concerned about the apparent e f f e c t s o f p l a n t n u t r i e n t s i n washing powder, human f e c e s , d a i r y f e c e s , m i n e r a l f e r t i l i z e r and atmospheric f a l l o u t on the e u t r o p h i c a t i o n of c o a s t a l ecosystems. I n a l l t h e s e c o u n t r i e s marine s c i e n t i s t s were asked t o i n v e s t i g a t e t h e s i t u a t i o n and, i f necessary, t o suggest measures t o be t a k e n .
The N a t i o n a l Swedish Environment P r o t e c t i o n Board i n i t i a t e d a study i n 1982 which was completed i n October 1983 ( N a t i o n a l Swedish Environment P r o t e c t i o n Board, 1984). I t l i s t s up numerous gaps i n the s c i e n t i f i c knowledge o f the e u t r o p h i c a t i o n problem and proposes a r e s e a r c h programme
" E u t r o p h i c a t i o n " w i t h p r i o r i t y s t u d i e s i n Laholm-Bay ( K a t t e g a t ) and i n Himmerfjard F j o r d south of Stockholm.
The N a t i o n a l Agency o f Environmental P r o t e c t i o n o f Denmark r e a c t e d upon t h e 1981 oxygen c a t a s t r o p h e by c r e a t i n g a working group o f s c i e n t i s t s who p r o v i d e d a thorough a n a l y s i s of t h e s i t u a t i o n ( M i l j ^ s t y r e l s e n , 1984), w h i c h i s the b a s i s f o r a r e s e a r c h programme underway a t p r e s e n t .
I n t h e F e d e r a l R e p u b l i c of Germany the F e d e r a l M i n i s t e r o f t h e I n t e r i o r t r e a t e d the problem i n d i s c u s s i o n s between e x p e r t s , and i n 1983 a r e s e a r c h p r o j e c t was i n i t i a t e d : E u t r o p h i c a t i o n o f t h e N o r t h Sea and the B a l t i c , which became e f f e c t i v e on 1.4.1984 (see Box 1 ) .
The t a s k o f the working group i s t o e v a l u a t e whether observed cases o f oxygen d e p l e t i o n can be the consequence o f man made n u t r i e n t i n p u t i n t o c o a s t a l waters.
Oxygen d e f i c i e n c y s i m u l t a n e o u s l y o c c u r r e d i n the German B i g h t and i n t h e B e l t Sea; t h e working h y p o t h e s i s had t o be t h a t f a c t o r s are r e s p o n s i b l e t h a t i n f l u e n c e l a r g e sea a r e a s of d i f f e r e n t hydrography. T h e r e f o r e t h e w o r k i n g group d i d not d e a l w i t h the l o c a l or r e g i o n a l i n s h o r e problems i n e s t u a r i n e and f j o r d s i t u a t i o n s .
1.3. The o r i g i n o f oxygen d e p l e t i o n
Oxygen d e p l e t i o n o c c u r s when oxygen consumption by m i c r o b i a l and o t h e r o x i d a t i o n processes o f carbon, n i t r o g e n and s u l f u r exceeds the sum o f oxygen p r o d u c t i o n by p l a n t p h o t o s y n t h e s i s p l u s a d v e c t i o n of oxygen from a d j a c e n t waters or the atmosphere. The p r o c e s s of oxygen d e p l e t i o n i s time dependent; i t s i n t e n s i t y depends upon t h e a v a i l a b i l i t y o f degradable o r g a n i c substance and on the v i t a l i t y o f degrading microbes and o t h e r a e r o b i c organisms. I f oxygen d e p l e t i o n o c c u r s i n the dark lower compartment o f s t r a t i f i e d w a t e r s , i t proceeds u n t i l e i t h e r the s t r a t i f i c a t i o n i s broken up and m i x i n g w i t h the oxygen r i c h water o c c u r s , or u n t i l the bottom water i s h o r i z o n t a l l y r e p l a c e d by water r i c h i n oxygen. Weather c o n d i t i o n s t h e r e f o r e p l a y a dominant r o l e i n the development of oxygen d e p l e t i o n .
Oxygen d e p l e t i o n i s i n t e n s i f i e d when a d d i t i o n a l degradable o r g a n i c matter becomes a v a i l a b l e i n the deep water o r a t the sediment-water i n t e r f a c e . T h i s may, f o r i n s t a n c e , occur w i t h a sedimenting p l a n k t o n bloom s t i m u l a t e d by the i n p u t of p l a n t n u t r i e n t s . E u t r o p h i c a t i o n t o g e t h e r w i t h weather may t h e r e f o r e p l a y a dominant r o l e i n t h e development o f oxygen d e p l e t i o n .
2. Trends i n n u t r i e n t i n p u t i n t o c o a s t a l waters
2.1 Atmospheric i n p u t
The e v a l u a t i o n o f t r e n d s i n n u t r i e n t i n p u t i n t o c o a s t a l waters was n o t i n the f o c u s o f the working group; data a r e expected t o come from a u t h o r i t i e s concerned w i t h f r e s h w a t e r , waste water and atmospheric p o l l u t i o n . Only a few s c a t t e r e d remarks s h a l l be made. Atmospheric i n p u t o f phosphorus t o the
13
sea i s g e n e r a l l y c o n s i d e r e d t o be o f low i n t e n s i t y . Atmospheric i n p u t o f n i t r o g e n compounds however i s n o t i c e a b l e . I n p u t i n t o t h e German B i g h t 1965 - 1972 was e s t i m a t e d t o be about 1 g N/ma per y e a r , o f about e q u a l amounts o f ammonium and n i t r a t e (Rat der Sachverständigen, 1980, F i g . 4.17).
A c c o r d i n g t o newspaper i n f o r m a t i o n , the e m i s s i o n s o f n i t r o u s o x i d e s i n t o the atmosphere i n c r e a s e d i n the F e d e r a l R e p u b l i c o f Germany from 2 m i l l i o n t i n 1966 t o 3.1 m i l l i o n t i n 1982; 55% o f i t o r i g i n a t e s from t r a f f i c and i s p a r t o f the " a c i d r a i n " which shows i n c r e a s i n g e f f e c t s upon t e r r e s t r i a l v e g e t a t i o n . A c c o r d i n g t o newspaper r e p o r t s , f a r m e r s i n many r e g i o n s o f t h e F e d e r a l R e p u b l i c o f Germany can now r e c k o n w i t h an atmospheric i n p u t of 2 g N/ma per year and may reduce the a p p l i c a t i o n o f m i n e r a l f e r t i l i z e r a c c o r d i n g l y . Danish a u t h o r i t i e s conclude from measurements i n the s o u t h e r n p a r t o f J u t l a n d t h a t the d e p o s i t i o n o f n i t r o g e n from t h e atmosphere i n c r e a s e d from 0.6 g/ma i n 1955 t o 1.5 g/m3 i n 1977 (MiljyÄstyrelsen, 1984).
Atmospheric i n p u t of n i t r o g e n , t h e r e f o r e , i s a s i g n i f i c a n t component o f t o t a l n i t r o g e n i n p u t i n t o c o a s t a l w a t e r s .
For t h e e n t i r e B a l t i c Sea (about 400 000 kma) L a r s s o n e t a l . (1984) e s t i m a t e t h e i n p u t o f n i t r o g e n o x i d e s and ammonium from atmospheric s o u r c e s t o be 322 000 t per y e a r , which i s about h a l f the amount t r a n s p o r t e d by r i v e r s i n t o the B a l t i c Sea (634 900 t ) and much more than c o n t r i b u t i o n s from m u n i c i p i a l s o u r c e s (88 600 t ) and i n d u s t r i a l s o u r c e s (14 200 t ) . The t o t a l amounts t o 1 m i l l i o n t o f n i t r o g e n per y e a r , p l u s about 77 000 t o f phosphorus per year. That i s an annual i n p u t o f 2.5 g n i t r o g e n and 0.2 g phosphorus per m'.
2.2 Input from l a n d i n t o the B e l t Sea
Summarizing data c o l l e c t e d i n the frame of t h e B a l t i c M a r i n e Environment P r o t e c t i o n Commission, L a r s s o n e t a l . (1984) g i v e t h e f o l l o w i n g i n p u t o f n u t r i e n t s from l a n d i n t o B e l t Sea c o a s t a l waters o f t h e F e d e r a l R e p u b l i c o f Germany 1972 - 1974 ( t h a t i s K i e l e r Bucht and Mecklenburger Bucht. For a d e t a i l e d a n a l y s i s see Brandt (1977) who p r e s e n t s s i m i l a r f i g u r e s ) :
t o t a l N t o t a l P
M u n i c i p a l sewage 1 700t/a 400t/a I n d u s t r i a l sewage 1 6 t / a l t / a R i v e r s and d i f f u s e l o a d 20 300t/a 2 600t/a
t o t a l 22 016t/a 3 001t/a
The d r a i n i n g a r e a o f S c h l e s w i g H o l s t e i n t o t h e B e l t Sea i s 5 219 km', w i t h 56.9% farmland , 16.4% g r a s s l a n d w i t h l i v e s t o c k and 4.0% f o r e s t . I t i s i n h a b i t e d by 1 189 000 p e o p l e , o f whom 79% a r e connected t o waste water treatment p l a n t s . The s e a a r e a i n f l u e n c e d i s the f i s h e r i e s zone o f t h e F e d e r a l R e p u b l i c o f Germany o f about 3 400 km*. The annual man made i n p u t i s 1.9 - 6.5 g n i t r o g e n and 0.4 - 0.9 g phosphorus p e r m1.
F o r t h e same a r e a o f S c h l e s w i g - H o l s t e i n , but f o r t h e much d r i e r p e r i o d 1975 - 1976 and a c h i e v e d w i t h d i f f e r e n t methods, Hoffmann (1979) presented t h e f o l l o w i n g d a t a :
M u n i c i p a l sewage d i r e c t l y M u n i c i p a l sewage
v i a r i v e r s Land r u n o f f
t o t a l
t o t a l N 2 731t/a
1 609t/a
2 004t/a
t o t a l P 786t/a
419t/a
6 4 t / a
6 344t/a 1 269t/a
U n f o r t u n a t e l y , they a r e not good f o r any t r e n d a n a l y s i s .
D a n i s h a u t h o r i t i e s t r i e d t o e l a b o r a t e a budget o f n u t r i e n t i n p u t f o r an a r e a which i n c l u d e s t h e K a t t e g a t , t h e Sound, and the B e l t Sea i n c l u d i n g t h e D a n i s h f i s h e r i e s zones o f K i e l e r Bucht, Mecklenburger Bucht and Arkona Sea.
T h i s i s an a r e a o f 38 000 km* ( i n c l u d i n g 21 000 km' o f K a t t e g a t ) , and t h e r e s p e c t i v e d r a i n a g e a r e a i s 57 200 kma p l u s 45 000 km2 which d r a i n i n t o Lake Vanern ( M i l j ^ s t y r e l s e n , 1984). The r e s u l t s a r e p r e s e n t e d i n F i g . 5. and
15 c o n t i n u e d on p . 19
t o t a l n i t r o g e n t / a t o t a l phosphorus t / a
! from from from from from from
Den- Swe- atmos- t o t a l Den- Swe- atmos- t o t a l mark den phere mark den phere
1975 5981o 41868 8467 4444 57o 13481
1976 475o6 3ooo5 8194 4252 57o 13ol6
1977 59622 63959 8462 5ol7 57o 14o49
1978 672o6 5o914 33564 151684 8625 4671 57o 13866 1979 6947o 46913 5o765 167148 8676 4589 57o 13835 19 8o 84654 61o77 35536 181267 9oo9 5co4 57o 14583 1981 9o435 63228 37o4S 19o711 9139 4759 57o 14468
F i g . 5_: T o t a l i n p u t o f n i t r o g e n a n d p h o s p h o r u s i n t o D a n i s h w a t e r s i n c l u d i n g t h e K a t t e g a t a n d t h e S o u n d , 38 o o o k m2.
F r o m M i l j t f s t y r e l s e n , 1 9 8 4 .
l/s per km' 30 -I
25
20
15 -i
10 •
r u
TJ
J
l i
u
U l i
1975 1976 1977 1978 1979 1980 1981
F i g . 6: F r e s h w a t e r r u n o f f f r o m D e n m a r k ( 3 o 4 5 o k m2) T 5 7 5 - 1 9 8 1 .
F r o m M i l j t f s t y r e l s e n , 1 9 8 4 .
16
J F M A M J J A S O N O
F i g . ]_: L o a d o f t o t a l n i t r o g e n ( N H4 , N 02 + N 03+ o r g a n i c n i t r o g e n ) t r a n s p o r t e d w i t h w a t e r b y t h e r i v e r E l b e i n t h e i n l a n d r e g i o n u p s t r e a m o f G e e s t - h a c h t .
C o m p i l a t e d b y W . K o e v e , I n s t i t u t für M e e r e s k u n d e , K i e l , d a t a p u b l i s h e d b y A r b e i t s g e m e i n s c h a f t für d i e R e i n h a l t u n g d e r E l b e 1 9 7 9 - 1 9 8 3 .
17
Box 3
Report on S u b p r o j e c t : R i v e r f l o w , n i t r o g e n c o n d i t i o n s and n i t r o g e n l o a d s o f the E l b e 1978 - 1982
V. Koeve and S.A. G e r l a c h I n s t i t u t f i i r Meereskunde K i e l
Data p u b l i s h e d 1978 - 1982 by A r b e i t s g e m e i n s c h a f t f i i r d i e R e i n h a l t u n g der E l b e have been a n a l y z e d i n o r d e r t o see whether f o r t h e German B i g h t t h e r e might be a c o r r e l a t i o n between r i v e r f l o w and n i t r o g e n c o n c e n t r a t i o n s i n sea water, s i m i l a r t o t h a t found by Danish a u t h o r i t i e s f o r the Danish B e l t Sea.
Weekly d a t a f o r c o n c e n t r a t i o n s o f n i t r o g e n ( n i t r a t e , n i t r i t e , ammoniak, o r g a n i c n i t r o g e n ) a t s t a t i o n Geesthacht were c a l c u l a t e d w i t h r i v e r f l o w on the same day a t s t a t i o n Neu Darschau. Both s t a t i o n s a r e f a r upstream o f Hamburg and a r e r e p r e s e n t a t i v e f o r t h e r i v e r e n t e r i n g the t e r r i t o r y o f the F e d e r a l R e p u b l i c o f Germany, but not f o r t h e i n p u t of the r i v e r E l b e i n t o the German B i g h t . However data may r e f l e c t g e n e r a l t r e n d s :
r i v e r f l o w (km*/a) n i t r o g e n l o a d (10* t / a )
1978 22.5 160 1979 27.6 175 1980 24.7 170 1981 34.2 265 1982 23.3 180
1981 was an e x t r a o r d i n a r y year w i t h l a r g e r i v e r f l o w and n i t r o g e n l o a d . While i n 1978, 1979 and 1982 n i t r o g e n l o a d s were low between June and September, i n 1980 and 1981 l o a d s were h i g h i n J u l y - August. Every year has i t s c h a r a c t e r i s t i c f l o w p a t t e r n which may w e l l i n f l u e n c e t h e n u t r i e n t s i t u a t i o n i n the German B i g h t .
Reference:
A r b e i t s g e m e i n s c h a f t f i i r d i e R e i n h a l t u n g der E l b e (1977 - 1983): Wassergutedaten der E l b e von Schnackenburg b i s z u r See
c o n t i n u e d f r o m p . 15
amount t o a t o t a l i n p u t o f about 150 OOOt/a o f t o t a l n i t r o g e n (4 g N/m1, i n c r e a s i n g tendency, 20% from t h e atmosphere) and o f about 14 OOOt/a o f t o t a l phosphorus (0.36 g P/mJ, no t r e n d , 5% from t h e atmosphere). The i n c r e a s i n g tendency o f n i t r o g e n i n p u t i s e x p l a i n e d by an i n c r e a s e o f r a i n w a t e r r u n o f f d u r i n g 1976 t o 1981, demonstrated f o r t h e Danish drainage a r e a o f 30 450 km' ( F i g . 6 ) .
Danish ( M i l j ^ s t y r e l s e n , 1984) and Swedish a u t h o r i t i e s ( N a t i o n a l Swedish E n v i r o n m e n t a l P r o t e c t i o n Board, 1984) can d e t e c t h i g h c o n c e n t r a t i o n s o f n i t r o g e n i n l a n d r u n o f f a f t e r heavy r a i n f a l l . There seems t o be a c o r r e l a t i o n between l a n d r u n o f f and w i n t e r c o n c e n t r a t i o n s o f n i t r o g e n i n c o a s t a l w a t e r s . The amounts o f n i t r o g e n t r a n s p o r t e d by l a n d r u n o f f have i n c r e a s e d i n past decades, as the use o f m i n e r a l f e r t i l i z e r has i n c r e a s e d , and i n c r e a s i n g q u a n t i t i e s o f l i q u i d manure from c a t t l e , p i g and c h i c k e n f a r m i n g a r e spread on a g r i c u l t u r e l a n d .
2.3 Input from l a n d i n t o t h e German B i g h t
We a r e n o t i n a p o s i t i o n t o e s t a b l i s h budgets f o r t h e German B i g h t which i s i n f l u e n c e d , i n a d d i t i o n , by water from t h e R i v e r Rhine. Postma (1978) c a l c u l a t e s w i t h a phosphorus l o a d o f t h e Rhine o f 3 OOOt/a i n 1932,
7 OOOt/a i n 1955, 30 OOOt/a i n 1970, t o demonstrate t h e i n c r e a s i n g tendency i n t h e past decades. I t seems probable t h a t n u t r i e n t i n p u t s i n t o t h e German B i g h t , when c a l c u l a t e d p e r s e a s u r f a c e u n i t , a r e even g r e a t e r than f i g u r e s f o r t h e B a l t i c and t h e B e l t Sea.
I n order t o t e s t t h e h y p o t h e s i s brought forward by Danish and Swedish s c i e n t i s t s t h a t i n c r e a s e d n i t r o g e n r u n o f f a f t e r heavy r a i n f a l l c o u l d be a i m p o r t a n t e u t r o p h i c a t i o n f a c t o r , we a n a l y z e d the p a t t e r n o f n i t r o g e n l o a d s which a r e c a r r i e d by t h e r i v e r E l b e b e f o r e i t e n t e r s t h e Hamburg a r e a ( s e e Box 3 ) . The c o n c e n t r a t i o n s o f t o t a l n i t r o g e n do n o t vary very much, except immediately a f t e r t h e onset o f heavy r a i n f a l l . Probably t h e e f f e c t o f r u n n i n g water i n e r o d i n g n i t r o g e n compounds from s o i l i s c o u n t e r a c t e d by the d i l u t i o n e f f e c t which r a i n w a t e r has on t h e c o n c e n t r a t i o n o f n i t r o g e n i n sewage. So t h e n i t r o g e n l o a d s a r e r a t h e r w e l l c o r r e l a t e d w i t h the f r e s h w a t e r f l o w . T h e i r e f f e c t s upon t h e c o a s t a l ecosystem o f t h e German B i g h t should be d i f f e r e n t i n w i n t e r when t h e water i s v e r t i c a l l y mixed and i n summer when r i v e r i n e water w i t h i t s n u t r i e n t l o a d spreads d u r i n g p e r i o d s o f calm weather on the s u r f a c e o f t h e German B i g h t ( F i g . 8 ) .
19
2.4 G e n e r a l t r e n d s and t h e r e l a t i o n between i n p u t and c o n t e n t
Phosphate i n p u t i n c r e a s e d most d r a s t i c a l l y i n t h e 1950s and 1960s w i t h t h e i n t r o d u c t i o n o f washing powder and w i t h t h e tendency t o a b o l i s h s e p t i c t a n k s and o t h e r l o c a l means o f waste water treatment and t o connect i n c r e a s i n g percentages o f our p o p u l a t i o n d i r e c t l y v i a sewage p i p e s and r i v e r s t o t h e sea. I n the 1970s w i t h i n c r e a s i n g numbers o f waste water treatment p l a n t s o p e r a t i n g one c o u l d expect d e c r e a s i n g i n p u t o f phosphorus t o t h e s e a . N i t r o g e n compounds from waste water s h o u l d f o l l o w t h e same p a t t e r n as phosphorus i n p u t . However, atmospheric p o l l u t i o n w i t h n i t r o g e n i n c r e a s e d i n the 1970s, as d i d the use o f m i n e r a l f e r t i l i z e r and l i q u i d manure on a g r i c u l t u r e l a n d ; i t seems probable t h a t t h e i n p u t o f n i t r o g e n t o t h e s e a i s i n c r e a s i n g even now. B e t t e r data s h o u l d be worked out and p u b l i s h e d .
For a g r o s s c a l c u l a t i o n o f the s i t u a t i o n i n c o a s t a l w a t e r s o f t h e F e d e r a l R e p u b l i c of Germany we may a t l e a s t r e c k o n w i t h an a n n u a l i n p u t o f 5 g n i t r o g e n ( n i t r a t e and ammonium) and 0.5 g phosphorus per ms. N u t r i e n t c o n c e n t r a t i o n s o f sea water i n w i n t e r a r e i n t h e o r d e r o f 0.3 g n i t r o g e n and 0.03 g phosphorus per m', or 6 g and 0.6 g per m' i n a water column o f 20 m. The annual i n p u t corresponds w i t h t h e t o t a l n u t r i e n t c o n t e n t i n t h e l a r g e bodies o f water r e p r e s e n t e d by German B i g h t and K i e l e r B u c h t .
By the annual a d d i t i o n o f t h e same amount o f n u t r i e n t s as the a c t u a l content o f the water, one should expect a d o u b l i n g o f the c o n c e n t r a t i o n s . Otherwise the s u r p l u s must be exported i n t o o t h e r a r e a s by f l u s h i n g o f t h e water, o r has t o be d e p o s i t e d i n the sediment, o r i t must go t o t h e atmosphere. Apparently the e l i m i n a t i o n p r o c e s s e s a r e w o r k i n g q u i t e e f f e c t i v e l y . C o n s i d e r a b l e amounts o f anthropogenic n i t r o g e n and phosphorus have been imported i n t o c o a s t a l a r e a s f o r s e v e r a l decades. However, t h e i n c r e a s e of n u t r i e n t c o n c e n t r a t i o n s i n c o a s t a l w a t e r s ( o u t s i d e e s t u a r i e s and f j o r d s ) d u r i n g the p a s t 25 years seems t o be r a t h e r s m a l l , l e s s t h a n a mere d o u b l i n g over the e n t i r e p e r i o d .
3. Trends i n n u t r i e n t c o n c e n t r a t i o n s i n c o a s t a l waters
3.1 A n a l y t i c a l , s t a t i s t i c a l and r e g i o n a l problems
Even though no m o n i t o r i n g programme was o f f i c i a l l y e f f e c t i v e , t h e r e a r e two l o n g term s e r i e s of n u t r i e n t a n a l y s e s a v a i l a b l e f o r the German B i g h t ( H e l g o l a n d ) and f o r the K i e l e r Bucht ( B o k n i s E c k ) . Before r e f e r r i n g t o r e s u l t s and consequences we must, however, p o i n t t o some problems.
One problem a r e a n a l y t i c a l t e c h n i q u e s which f o r n i t r o g e n compounds have been a v a i l a b l e o n l y f o r a few decades so t h a t pre-1970 d a t a a r e r a r e . Another d i f f i c u l t y i s t h a t s e a s o n a l v a r i a t i o n s a r e g r e a t e r t h a n v a r i a t i o n on a l o n g e r t i m e s c a l e . D u r i n g w i n t e r , when the c o a s t a l waters may be w e l l mixed and when p l a n t p o p u l a t i o n s a r e a t a minimum, n u t r i e n t c o n c e n t r a t i o n s i n the water are a t a maximum, p o s s i b l y i n steady s t a t e w i t h the much h i g h e r pore water c o n c e n t r a t i o n s and o t h e r compounds i n the sediment. I n summer a l a r g e percentage of the n u t r i e n t content i n the water i s e n c l o s e d i n t h e c e l l s o f p h y t o p l a n k t o n , macroalgae and e e l g r a s s , so t h a t c o n c e n t r a t i o n s i n the water o f t e n a r e below the l e v e l of d e t e c t i o n , and data a r e sometimes dubious.
Another problem i s the inhomogeneous d i s t r i b u t i o n o f n u t r i e n t s c l o s e t o sewage o u t f a l l s and r i v e r mouths. I n the German B i g h t t h e tongue o f r i v e r i n e water coming from the r i v e r s Weser and E l b e depends on the i n t e n s i t y of f r e s h w a t e r r u n o f f and on the wind and c u r r e n t regime. With s o u t h w e s t e r l y winds t h i s tongue may be pressed t o the e a s t , so t h a t i t r u n s northward very c l o s e t o the coast o f S c h l e s w i g - H o l s t e i n (see Box 4 and F i g . 8 ) . Helgoland as a f i x e d s t a t i o n i s sometimes s i t u a t e d w i t h i n t h i s tongue, sometimes o u t s i d e . N u t r i e n t c o n c e n t r a t i o n s t h e r e f o r e d i f f e r very much from p e r i o d t o p e r i o d . High c o n c e n t r a t i o n s o f n i t r a t e were found i n June 1981 when t h e Ceratium phytoplankton bloom o c c u r r e d (see Box 9 and F i g . 2 4 ) . One should c o r r e l a t e the n u t r i e n t p a t t e r n w i t h weather data (see Box 15 and
Note: Q u a n t i t i e s o f p l a n t n u t r i e n t s a r e r e f e r r e d t o e i t h e r i n mass u n i t s or i n molar e q u i v a l e n t s .
F i g . 3 2 ) ,
1 u mol (= 1 ug - a t ) n i t r o g e n 1 u mol (= 1 ug - a t ) phosphorus
14 ug N 31 ug P
21 c o n t i n u e d on p . 30
Box 4
Report on S u b p r o j e c t : Summer c o n c e n t r a t i o n s o f n u t r i e n t s i n the German B i g h t 1979 - 1982
U. Brockmann
I n s t i t u t für Biochemie und Lebensmittelchemie der Universität Hamburg
Hydrographie and n u t r i e n t c o n d i t i o n s were a n a l y z e d on s i x c r u i s e s which cover the a r e a from 6° 24' t o 8° 1 0fE and from 5 3c5 0 ' t o 55°10'N. They were done i n June 1979, June 1980, June 1981, and i n August-September 1981, 1982 and 1983.
The n u t r i e n t s i t u a t i o n o f s u r f a c e waters d i f f e r s v e r y much from year t o y e a r . I n June 1979, two days w i t h e a s t e r l y winds of 13 m/s t r a n s p o r t e d water r i c h i n n u t r i e n t s towards the west, and subsequent days w i t h s o u t h w e s t e r l y winds brought t h e water back i n t o t h e i n v e s t i g a t e d a r e a , w h i c h then was mostly covered w i t h s u r f a c e water o f above 1 ug-at n i t r a t e / 1 , l a r g e p a r t s above 10 p g - a t / 1 . By c o n t r a s t , i n June 1980 and June 1981, w i t h w e s t e r l y winds o f about 9 m/s, t h e r i v e r i n e water was prevented from s p r e a d i n g over t h e e n t i r e German B i g h t . The tongue o f water w i t h more t h a n 5 ug-at n i t r a t e / 1 was r e s t r i c t e d t o the s o u t h e a s t e r n p a r t i n 1980, t o the western p a r t o f the German B i g h t i n 1981. At t h e end o f August 1982 and i n the f i r s t week o f September 1983 s o u t h w e s t e r l y winds of 15 m/s, l a t e r 9 m/s p r e v a i l e d . T h e y pressed the tongue of r i v e r i n e water c l o s e t o t h e Waddensea o f S c h l e s w i g - H o l s t e i n , t h a t i s e a s t o f the a r e a i n v e s t i g a t e d , so t h a t c o n c e n t r a t i o n s of above 1 ug-at n i t r a t e / 1 were o n l y measured i n the e s t u a r i n e r e g i o n o f the E l b e r i v e r .
I n v e r t i c a l p r o f i l e s , a l r e a d y i n June a t h e r m o c l i n e i s developed. Compared w i t h w i n t e r c o n d i t i o n s , t h e r e i s a decrease o f n u t r i e n t s not o n l y i n t h e upper w a t e r masses, but a l s o below the t h e r m o c l i n e . I n August and September n u t r i e n t l e v e l s i n the lower compartment i n c r e a s e , but i t i s d i f f i c u l t t o e v a l u a t e t h e r e s p e c t i v e c o n t r i b u t i o n s o f b e n t h i c r e m i n e r a l i z a t i o n , o f import v i a N o r t h Sea deep water or import from the Waddensea. C o n c e n t r a t i o n s o f d i s s o l v e d
o r g a n i c n i t r o g e n a r e s e v e r a l t i m e s h i g h e r than c o n c e n t r a t i o n s o f n i t r a t e . Phosphate c o n c e n t r a t i o n s i n c r e a s e i n water masses where oxygen d e f i c i e n c y i s observed. W i t h wind from e a s t o r n o r t h w e s t , s u r f a c e l a y e r s o f r i v e r i n e water r i c h i n n u t r i e n t s can be s i t u a t e d i n top o f t h o s e a r e a s where oxygen d e f i c i e n c y was observed i n t h e deep w a t e r .
23
Box 5
Report on S u b p r o j e c t : The use o f s a t e l l i t e d a t a f o r the e v a l u a t i o n o f e u t r o p h i c a t i o n p r o c e s s e s i n German B i g h t
and B a l t i c Sea.
U l r i c h Horstmann and B e r n t Z e i t z s c h e l I n s t i t u t f u r Meereskunde, K i e l
Data from t h e C o a s t a l Zone C o l o r Scanner o f the s a t e l l i t e Nimbus - G were used. 168 p i c t u r e s from 1979 t o 1984 a r e a v a i l a b l e i n channel 3 (550 nm). 8 p i c t u r e s have been processed. However, t h e r e a r e d i f f i c u l t i e s i n i d e n t i f y i n g c h l o r o p h y l l , probably due t o h i g h G e l b s t o f f c o n c e n t r a t i o n s and due t o i n t e r a c t i o n s o f a e r o s o l s i g n a l s w i t h suspended matter s i g n a l s . Ground t r u t h data would be necessary t o c o n t r o l the r e s u l t s o b t a i n e d from p r o c e s s i n g t h e p i c t u r e s , b e f o r e p i c t u r e s from space c o u l d be c o n s i d e r e d as u s e f u l i n s t r u m e n t s t o m o n i t o r r e g i o n a l e f f e c t s o f e u t r o p h i c a t i o n i n c o a s t a l waters o f t h e F e d e r a l R e p u b l i c o f Germany.
I n f u t u r e , when r e s e a r c h v e s s e l c r u i s e s a r e made f o r h y d r o g r a p h i c and phytoplankton r e s e a r c h i n t h e German B i g h t and i n the B e l t Sea, one s h o u l d a p p l y f o r synchronous s a t e l l i t e i n f o r m a t i o n , i f p o s s i b l e r e c e i v e d on l i n e on the r e s e a r c h v e s s e l , but i n a d d i t i o n i n a form o f documentation which can be processed l a t e r .
F i g . 8_: Q u a s i s y n o p t i c d i s t r i b u t i o n o f n i t r a t e i n s u r f a c e w a t e r s ô ï t h e G e r m a n B i g h t d u r i n g s i x c r u i s e s . F i g u r e s r e f e r t o / u g - a t / 1 .
H = H e l g o l a n d .
u n p u b l i s h e d r e s u l t s k i n d l y p r o v i d e d b y D r . U . B r o c k m a n n , I n s t i t u t für B i o c h e m i e u n d L e b e n s m i t t e l c h e m i e d e r U n i v e r s i t ä t H a m b u r g .
s* 5- *• 3- 7 r o* r r r e s- 6- 7- r F i g . 9_z G e n e r a l i z e d d i s t r i b u t i o n o f p h o s p h a t e c o n c e n t r a t i o n s i n t h e N o r t h S e a d u r i n g w i n t e r . F i g u r e s r e f e r t o 10~7/iig-at/l a n d s h o u l d b e m u l t i - p l i e d b y 3.1 t o g e t c o n c e n t r a t i o n s i n / u g / 1 .
F i g u r e o f Mc I n t y r e a n d J o h n s o n 1 9 7 5 r e p r o d u c e d f r o m G e r l a c h , 1 9 8 1 .
80-r -
60- 40-
20-
<H .
1950 1971 £ 55 F i g , l o ; T r e n d s o f y e a r l y m e a n p h o s p h a t e - p h o s - p h o r u s c o n c e n t r a t i o n s a t s t a t i o n M a r s d i e p ( b e t - w e e n t h e i s l a n d o f T e x e l a n d t h e D u t c h m a i n l a n d )
1 9 5 o - 1 9 8 3 .
F r o m d e W i t e t a l . , 1 9 8 2 .
26
F i g . 1 1 : C o n c e n t r a t i o n s o f p h o s p h a t e i n s u r f a c e w a t e r s a t H e l g o l a n d 1 9 6 2 - 1 9 8 1 , a n d l i n e a r r e g r e s s i o n o v e r t h e e n t i r e p e r i o d .
U n p u b l i s h e d r e s u l t k i n d l y p r o v i d e d b y D r . R a d a c h , I n s t i t u t für M e e r e s k u n d e , U n i v e r s i t ä t H a m b u r g .
Box 6
Report on S u b p r o j e c t : Trends i n c o n c e n t r a t i o n s o f p l a n t n u t r i e n t s a t H e l g o l a n d Reede 1962 -1981
G. Radach und J . Berg
I n s t i t u t für Meereskunde, Universität Hamburg
The b e s t data s e t a v a i l a b l e on v a r i a t i o n o f parameters i n the German B i g h t i s from s u r f a c e w a t e r s a t a s t a t i o n between t h e i s l a n d of H e l g o l a n d and Düne, sampled s i n c e 1962 5 times per week by s c i e n t i s t s and t e c h n i c i a n s o f B i o l o g i s c h e A n s t a l t H e l g o l a n d . R e s u l t s r e g a r d i n g phosphate, n i t r o g e n compounds, s i l i c a t e , s a l i n i t y and temperature have been p u b l i s h e d ( J a h r e s b e r i c h t e B i o l o g i s c h e A n s t a l t H e l g o l a n d ) from 1978 onward o r have been presented as monthly means (Hagmeier, 1978), c o r r e c t e d f o r s a l i n i t y i n order t o e l i m i n a t e the i n f l u e n c e o f the changing p o s i t i o n of t h e tongue o f E l b e r i v e r water ( L u c h t and G i l l b r i c h t , 1978), o r u s i n g d a t a from s p e c i f i c months o f t h e year ( G i l l b r i c h t , 1983). I n g e n e r a l , an i n c r e a s i n g t r e n d o f phosphate c o n c e n t r a t i o n s c o u l d be demonstrated; however, the s i t u a t i o n i s r a t h e r c o m p l i c a t e d , w i t h l a r g e f l u c t u a t i o n s from year t o y e a r .
A new approach was s t a r t e d t o p r o c e s s a l l a v a i l a b l e data w i t h a p p r o p r i a t e computer programmes. The problem i s t h a t s e a s o n a l v a r i a t i o n s o f most parameters are l a r g e r than v a r i a t i o n s on l a r g e r time s c a l e s . Another problem i s t h a t data depend on f r e s h w a t e r and n u t r i e n t i n p u t v i a the r i v e r s E l b e and V e s e r ; H e l g o l a n d i s sometimes i n t h e c e n t e r o f the tongue o f r i v e r water, sometimes t h e i s l a n d i s e a s t , sometimes west o f t h i s tongue, depending on wind and c u r r e n t s . Data depend f u r t h e r on the t o t a l amount o f f r e s h w a t e r r u n o f f and on the i n t e n s i t y w i t h which t h e f r e s h w a t e r i s mixed w i t h t h e sea water o f deeper l a y e r s i n t h e German B i g h t .
The aim o f t h i s p r o j e c t i s t o c o r r e l a t e d a t a measured a t Helgoland w i t h E l b e r i v e r r u n o f f and w i t h m e t e o r o l o g i c a l o b s e r v a t i o n s a t E l b e 1 l i g h t v e s s e l .
I n a f i r s t approach i t was t e s t e d whether t h e s i t u a t i o n
can be d e s c r i b e d by l i n e a r r e g r e s s i o n s c o v e r i n g t h e e n t i r e p e r i o d 1962 - 1981 (20 y e a r s ) .
S u r f a c e water temperatures i n c r e a s e d from 1962 t o 1981 by 1.1 ° C, which c o n f i r m s r e s u l t s found f o r t h e p e r i o d 1960 - 1973 by Becker und Kohnke (1978).
S a l i n i t y has no s i g n i f i c a n t t r e n d . S i l i c a t e decreased from 1966 t o 1981.
Phosphate c o n c e n t r a t i o n s i n c r e a s e d from about 0.5 ug - a t / 1 i n 1962 t o about 1.0 ug - a t / 1 i n 1981 ( s i g n i f i c a n t a t t h e 99% l e v e l ) . T h i s t r e n d i s a l s o obvious when o n l y w i n t e r c o n c e n t r a t i o n s a r e c o n s i d e r e d .
As t h e r e i s no t r e n d i n s a l i n i t y , t h e c o n c l u s i o n should be t h a t t h e i n c r e a s e o f phosphate i n s e a water a t s t a t i o n Helgoland was n o t caused by a g e n e r a l change o f water masses i n t h i s r e g i o n . T h e r e f o r e t h e phosphate t r e n d may be due t o i n c r e a s e d man made n u t r i e n t i n p u t v i a t h e r i v e r s .
S t a t i s t i c a l a n a l y s i s o f time i n t e r v a l s s h o r t e r than 20 y e a r s , and o t h e r s t a t i s t i c a l procedures ( f i l t e r i n g o u t o f h i g h frequency components) have t o be a p p l i e d , b e f o r e a meaningful c o r r e l a t i o n w i t h r i v e r data and m e t e o r o l o g i c a l d a t a can be undertaken.
R e f e r e n c e s :
Hagmeier, E. (1978): V a r i a t i o n s i n phytoplankton near H e l g o l a n d . Rapp. P.-v. Reun. Cons. i n t . E x p l o r . Mer 172: 361 - 363
L u c h t , H. and M. G i l l b r i c h t (1978): Long-term o b s e r v a t i o n s o f n u t r i e n t c o n t e n t s near Helgoland i n r e l a t i o n t o n u t r i e n t i n p u t o f the R i v e r E l b e . Rapp. P.-v.
Reun. Cons. i n t . E x p l o r . Mer 172: 358 - 360
G i l l b r i c h t , M. (1963): E i n e "red t i d e " i n der südlichen Nordsee und i h r e Beziehungen z u r Umwelt. Helgoländer Meeresuntersuchungen 36: 393 - 426
B e c k e r , G. and D. Kohnke (1978): Long-term v a r i a t i o n s o f temperature and s a l i n i t y i n t h e i n n e r German B i g h t . Rapp.
P.-v. Reun. Cons. i n t . E x p l o r . Mer 172: 335 - 344
29
c o n t i n u e d f r o m p . 21
w i t h the s i m u l a t e d c u r r e n t s i t u a t i o n (see Box 14) and w i t h n i t r o g e n l o a d s o f t h e r i v e r s (see Box 3 and F i g . 7 ) . For t h e f u t u r e t h e r e i s some hope t h a t o b s e r v a t i o n from space may b e t t e r a l l o w t o d e t e c t the p o s i t i o n o f r i v e r i n e water masses (see Box 5 ) .
I f we l o o k a t the d i s t r i b u t i o n of n u t r i e n t s i n s u r f a c e w i n t e r water o f the e n t i r e North Sea ( F i g . 9) i t becomes c l e a r t h a t Helgoland i s s i t u a t e d i n a r e g i o n c h a r a c t e r i z e d by a g r a d i e n t o f n u t r i e n t c o n c e n t r a t i o n s . A c c o r d i n g t o t h e dominant wind regime, e s t u a r i n e water from the r i v e r Rhine i s t r a n s p o r t e d v e r y c l o s e t o the Dutch and N i e d e r s a c h s e n Waddensea i n eastward d i r e c t i o n . T h i s stream r e c e i v e s n u t r i e n t i n p u t s from t h e m i n e r a l i z a t i o n o f o r g a n i c matter i n t h e Waddensea, g e t s the n u t r i e n t i n p u t from the r i v e r s Ems, Weser, E l b e and E i d e r and from t h e S c h l e s w i g - H o l s t e i n Waddensea, and runs northward c l o s e t o the J u t l a n d c o a s t o f Denmark. What answer c o u l d we expect from l o n g term measurements a t s t a t i o n H e l g o l a n d r e g a r d i n g e u t r o p h i c a t i o n ? Whether the g r a d i e n t from h i g h i n s h o r e n u t r i e n t c o n c e n t r a t i o n s t o low open North Sea c o n c e n t r a t i o n s has changed i n the past decades, whether i t s i s o l i n e s f o r average n u t r i e n t c o n c e n t r a t i o n s i n w i n t e r have moved from southeast t o northwest.
Trends observed a t Helgoland cannot be e x t r a p o l a t e d f o r the N o r t h Sea f u r t h e r o f f s h o r e . There e u t r o p h i c a t i o n e f f e c t s w i l l be l e s s d i s t i n c t . A t the o t h e r s i d e , t r e n d s observed a t Helgoland cannot be e x t r a p o l a t e d f o r t h e more i n s h o r e s i t u a t i o n s between Helgoland and t h e e s t u a r i e s of Weser and E l b e . E u t r o p h i c a t i o n e f f e c t s t h e r e should be much more n o t i c e a b l e due t o t h e s t e e p e r g r a d i e n t of n u t r i e n t c o n c e n t r a t i o n s , i n d i c a t e d by the i s o l i n e s of F i g . 9. Data from Helgoland stand o n l y f o r waters which have a s i m i l a r p o s i t i o n between the open North Sea and i n s h o r e c o n d i t i o n s .
3.2 Trends i n n u t r i e n t c o n c e n t r a t i o n s i n the German B i g h t
The o n l y l o n g term s e t o f data a v a i l a b l e from the German B i g h t a r e the samples c o l l e c t e d f i v e times per week a t Helgoland 1962 - 1984. The new a n a l y s i s o f d a t a (see Box 6 and F i g . 11) c o n f i r m s e a r l i e r statements ( F i g . 20) t h a t t h e r e i s an i n c r e a s e i n mean phosphate c o n c e n t r a t i o n s from about 0.5 pg - a t F / l i n 1962 t o about 1.0 /ug - a t P / l i n 1981. Subsequent s t a t i s t i c a l treatment w i l l d e f i n e p o s s i b l e t r e n d s d u r i n g s h o r t e r i n t e r v a l s o f time and d u r i n g s p e c i f i c seasons o f the y e a r . They w i l l be c o r r e l a t e d
w i t h meteorology, hydrography and f r e s h w a t e r r u n o f f . N i t r o g e n d a t a and s i l i c a t e d a t a w i l l be i n c l u d e d i n the study.
The e v i d e n c e f o r i n c r e a s i n g n u t r i e n t c o n c e n t r a t i o n s a t Helgoland i s s u s t a i n e d from the N e t h e r l a n d s . I n c r e a s i n g phosphate c o n c e n t r a t i o n s have been observed i n the Marsdiep s i n c e 1950, and c o n c e n t r a t i o n s 1979 - 1981 are about f i v e times h i g h e r than i n 1950 ( F i g . 10). The s t a t i o n , however,is more i n s h o r e than H e l g o l a n d . The i n c r e a s e of n i t r o g e n compounds i s l e s s s p e c t a c u l a r , but a d o u b l i n g between 1961/62 and 1971 has been documented (De Wit e t a l . , 1982).
I n c o n c l u s i o n , a t r e n d o f i n c r e a s i n g n u t r i e n t c o n c e n t r a t i o n s over the past 20 - 25 y e a r s has been documented. I t seems probable t h a t man i s r e s p o n s i b l e f o r t h i s i n c r e a s e , and t h a t the e u t r o p h i c a t i o n e f f e c t s observed i n the German B i g h t a r e , a t l e a s t p a r t l y , man made.
3.3 Trends i n n u t r i e n t c o n c e n t r a t i o n i n K i e l e r Bucht
There i s a good time s e r i e s a v a i l a b l e f o r t o t a l phosphorus c o n c e n t r a t i o n s a t s t a t i o n Boknis Eck i n the western p a r t of K i e l e r Bucht, s t a r t i n g i n 1958 (see Box 7 ) . The s e r i e s was i n t e r r u p t e d 1976 - 1979, but t h e r e i s some hope t h a t i t w i l l be supplemented by o t h e r i n f o r m a t i o n from t h i s p e r i o d .
D u r i n g the o b s e r v a t i o n p e r i o d 1958 - 1975 t h e r e was no s i g n i f i c a n t t r e n d i n t o t a l phosphorus c o n c e n t r a t i o n s . However, d a t a from w i n t e r 1980, 1981 and 1984 a r e h i g h e r , so t h a t r e c e n t years w i n t e r c o n c e n t r a t i o n s e x h i b i t an i n c r e a s i n g t r e n d ( F i g . 12). T h i s i s i n accordance w i t h d a t a from s t a t i o n s south o f Langeland and Fehmarnbelt achieved out i n the framework o f the Danish B e l t P r o j e c t ( A e r t e b j e r g e t a l . , 1981) and summarized by Danish a u t h o r i t i e s ( M i l j f l l s t y r e l s e n , 1984). There was a decrease 1975 t o 1978 and an i n c r e a s e 1980 t o 1983 i n phosphate, and an i n c r e a s e 1975 t o 1983 i n t o t a l i n o r g a n i c n i t r o g e n c o n c e n t r a t i o n s ( F i g . 13 - 14). S i m i l a r o b s e r v a t i o n s were made i n t h e K a t t e g a t and i n the Great B e l t , where phosphate w i n t e r c o n c e n t r a t i o n s i n 1981 - 1983 were about as h i g h as i n 1975.
C e r t a i n l y , the p e r i o d 1975 t o 1983 i s too s h o r t f o r a d e f i n i t e statement t h a t t h e r e i s an i n c r e a s i n g t r e n d i n n u t r i e n t c o n c e n t r a t i o n s . I t might w e l l be t h a t h i g h c o n c e n t r a t i o n s a r e the r e s u l t of s p e c i a l m e t e o r o l o g i c a l and h y d r o g r a p h i c a l c o n d i t i o n s , and t h a t the y e a r s 1980 - 1983 a r e compensated by o t h e r years w i t h low c o n d i t i o n s , both r e f l e c t i n g extremes of t h e normal v a r i a b i l i t y . However, the e v a l u a t i o n of t h e s i t u a t i o n cannot w a i t f o r some
31 c o n t i n u e d on p. 35
Box 7
Report on S u b p r o j e c t : Trends i n n u t r i e n t c o n c e n t r a t i o n s i n K i e l e r Bucht.
B r i g i t t a Babenerd and B e r n t Z e i t z s c h e l I n s t i t u t f u r Meereskunde K i e l
N u t r i e n t a n a l y s e s from waters o f K i e l e r Bucht date back t o 1903; however, t h e o n l y l o n g term s e r i e s which can be used i s t o t a l phosphorus from s t a t i o n B o k n i s Eck 1958 - 1975 (Krey e t a l . 1978). B o k n i s Eck i s s i t u a t e d i n t h e western p a r t o f K i e l e r Bucht where oxygen d e p l e t i o n i s a r e g u l a r f e a t u r e n e a r l y every year and, i n consequence, phosphorus c o n c e n t r a t i o n s i n t h e water below t h e h a l o c l i n e i n c r e a s e very much i n l a t e summer, which can be demonstrated by average v a l u e s f o r 1958 - 1975 (Babenerd, 1980).
I f one a n a l y z e s a l l t o t a l phosphate d a t a from 1958 t o 1975, t h e r e i s no t r e n d , n o t i n d i f f e r e n t water depths, not i n s p e c i a l seasons o f t h e y e a r . However, i n 1958 - 1966 t h e v a r i a b i l i t y o f d a t a i s l a r g e r t h a n 1967 - 1975.
There i s a d d i t i o n a l i n f o r m a t i o n from 1980-81 and from 1984 on t o t a l phosphorus a t B o k n i s Eck s t a t i o n i n w i n t e r (January - F e b r u a r y ) . I n t h e s e y e a r s c o n c e n t r a t i o n s were h i g h e r than i n t h e p e r i o d 1958 - 1975.
There a r e many a d d i t i o n a l p u b l i s h e d and u n p u b l i s h e d d a t a on n u t r i e n t s i n K i e l e r Bucht, which a t p r e s e n t a r e i n t h e p r o c e s s o f c r i t i c a l e v a l u a t i o n . I t seems t h a t w i n t e r phosphate - phosphorus c o n c e n t r a t i o n s a t B o k n i s Eck were below 1.0 ug-at/1 1958 - 1961, were about 1.0 jug-at/1 i n 1972 - 1978 and above 1.0 ug-at/1 i n 1980, 1981 and 1984, but f u r t h e r c o n f i r m a t i o n i s n e c e s s a r y . There i s no c l e a r t r e n d f o r t o t a l i n o r g a n i c n i t r o g e n ; i t seems t h a t s i l i c a t e decreased from 1973 t o 1982. F o r near-shore a r e a s l i k e S t r a n d e r Bucht ( s i t u a t e d s o u t h o f t h e B u l k sewage o u t f a l l ) i t seems t h a t phosphate c o n c e n t r a t i o n s i n 1935/36 (Wattenberg and Meyer, 1936) were much lower compared w i t h 1983/84 ( d a t a o f C . S t i e n e n , I f M K i e l ) .
R e f e r e n c e s :
K r e y , J . , B. Babenerd, J . Lenz (1978): Beobachtungen z u r P r o d u k t i o n s b i o l o g i e des P l a n k t o n s i n der K i e l e r Bucht:
1957 - 1975. 1. Datenband. Ber. I n s t . Meereskunde K i e l 54, 1-113
Babenerd, B. (1980): Untersuchungen z u r P r o d u k t i o n s - b i o l o g i e des P l a n k t o n s i n der K i e l e r Bucht - m i t e i n e r Auswertung d e r m o n a t l i c h e n T e r m i n f a h r t e n aus den J a h r e n 1957 - 1975. D i s s e r t a t i o n U n i v . K i e l , S. 1 - 2 2 6
Wattenberg, H. and H. Meyer (1937): Der j a h r e s z e i t l i c h e Gang des G e h a l t e s des Meerwassers an Planktonnährstoffen i n d e r K i e l e r Bucht im J a h r e 1935. K i e l e r Meeresforschungen 1, 264 - 278
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