BIOGEOCHEMISTRY OF NUTRIENTS, TRACE METALS AND ORGANIC MICROPOLLUTANTS IN THE NORTH SEA.

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1 BIOGEOCHEMISTRY OF NUTRIENTS, TRACE METALS AND ORGANIC MICROPOLLUTANTS IN THE NORTH SEA. SUBPROJECT:BIOGEOCHEMISTRY OF NUTRIENTS AND TRACE METALS IN THE NORTH SEA. Vrije Universiteit Brussel Dienst analytische en milieuchemie Prof. Dr. W. Baeyens, S. De Galan, M. De Gieter, Dr. M. Leermakers, Dr. N. Brion

2 Objectives: our research : biogeochemical cycling in aquatic systems T North Sea T Scheldt estuary T Scheldt and tributaries T marine biota in the North Sea quantification and qualification of the nitrogen cycle study of dissolved trace metals in the water column special attention for biogeochemical cycling of Hg and As

3 North Sea: spatio-temporal trends in nutrient concentrations Variation in Nutrient concentrations in the Southern Bight of the North Sea Min-Max 25%-75% Median value nitrate concentration: shows high variation - average : 18.3 µm - range: DL µm phosphate concentration : - rather low throughout the year - average:.8 µm Silicate concentration: - average: 8 µm - range: DL -32 µm -2 nitrate phosphate silicate Seasonal variation of nitrate in the Southern Bight of the North Sea Min-Max 25%-75% Median value temporal behavior: -example: nitrate - clear seasonal trend : highest [nitrate] in winter, lowest in spring and summer reconstitution of winter stock biological activity -2 spring summer autumn winter

4 North Sea: spatio-temporal trends in nutrient concentrations Example : dissolved silicate concentration (µm Silicate concentrations in the North Sea spring autumn Low salinity zone is strongly influenced by the Scheldt outflow and coastal inputs significantly higher nutrient pools compared to the high salinity zone 2.. CH1 B H7 NS2 NS4 Channel Belgian Coastal Zone Central North Sea Channel and central North Sea: low nutrient pools clear seasonal and spatial variation in nutrient concentrations in the North Sea

5 Nitrogen pools in the North Sea spring 1% 8% 6% 4% 2% DON NO3tot NH4 The ammonium pool is almost negligible % CH1 CH2 NS1 NS2 NS3 NS4 33 summer Most of the time: the dissolved organic nitrogen pool (DON) is dominant 1% 8% 6% 4% 2% % CH1 CH2 NS1 NS2 NS3 NS4 33 DON NO3tot NH4 The DON pool can account for up to 95% of the N pool autumn 1% 8% 6% 4% 2% DON NO3tot NH4 The DON pool in the North Sea plays an important role in the nitrogen cycle % S NS 1 NS 2 NS 3 NS 4

6 Absolute uptake rates absolute uptake (µm/h) absolute uptake (µm/h) B989 B9821 B991 B9916 B9922 B9 B nitrate absolute uptake (µm/h) campaign B989 B9821 B991 B9916 B9922 B9 B ammonium urea.121 campaign B989 B9821 B991 B9916 B9922 B9 B24 campaign selected station: 33 Nitrate uptake rates are higher than those for ammonium and urea - highest nitrate uptake in spring - highest ammonium uptake at the end of summer low ammonium uptake rates lowest urea uptake rates

7 The Scheldt estuary: The Scheldt receives high amounts of waste (mostly untreated) causes high microbial activity and anoxic conditions upstream Dissolved O 2 (mg.l -1 ) u oxygen depletion Chl-a (µg.l-1) Salinity 1 (psu) ph 8.4 Salinity 8.2 (psu) u high chlorophyll-a levels u shift to lower ph Salinity (psu) gradients of O 2, ph and ionic strength influence mass transport to the sea

8 Nutrient distribution in the Scheldt estuary ammonium in the Scheldt estuary concentration (µm) spring summer autumn winter salinity (psu) nitrate in the Scheldt estuary concentration (µm) 5 spring 4 summer 3 autumn 2 winter salinity (psu) TDN in the Scheldt estuary Trend in NH 4 significantly related with oxygen depletion nutrient concentrations are very high decreasing concentrations with increasing salinity concentration (µm) salinity (psu) spring summer autumn winter longitudinal profile has a linear shape

9 Biogeochemical behavior of redox sensitive trace elements Example : dissolved As-transport - longitudinal profile has a convex shape suggests strong mobilization at freshwater/ salt water interface indicates influence of biological activity evidence was also found for influence of Fe and Mn redox chemistry Dissolved As (µg spring summer autumn winter Salinity (psu)

10 Marine Biota : - 25 species of seafish and shellfish were investigated for total Hg and As BUT : Hg and As occur in a wide range of species, several of them more toxic than others THUS : speciation needed! speciation techniques were developed to be able to distinguish between : - total Hg and monomethyl Hg - total As and arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid and arsenobetaine

11 8 7 6 AsT (mg/kg ww Total As mg/kg ww Dogfish (23) Zware metalen Ray (2) Conger (1) Cod (5) Pollack (1) Pouting (5) Saithe (5) Whiting (5) Ling (5) Hake (1) Angler (2) Pomfret (2) Seabass (1) Mullet (1) Dab (27) Plaice (33) Lemon Sole (25) Witch (5) Sole (45) Sandsole (14) Brill (6) Megrim (11) Turbot (1) Gurnard (1) John Dory (1) Toxic As.3-.6 mg/kg ww AsTox (mg/kg ww Dogfish (23) Ray (2) Conger (1) Cod (5) Pollack (1) Pouting (5) Saithe (5) Whiting (5) Ling (5) Hake (1) Angler (2) Pomfret (2) Seabass (1) Mullet (1) Dab (27) Plaice (33) Lemon Sole (25) Witch (5) Sole (45) Sandsole (14) Brill (6) Megrim (11) Turbot (1) Gurnard (1) John Dory (1)

12 Arsenic in seafish : - Total concentrations are much higher than the legal limits (varying from.1 mg.kg -1 in Venezuela to 1 mg.kg -1 in Hong Kong) BUT toxic fractions constitutes only 1-2 % of the total concentrations THUS speciation information is needed to investigate possible harm of seafood ingestion to human health - Normalization was applied to divide species in classes of harmless to harmful benthic fish (flatfish) generally contain more As than pelagic fish - Differences in As-concentrations according to sampling area could be found for some species - Unlike for Hg, no evidence of biomagnification could be found for As

13 BIOGEOCHEMISTRY OF NUTRIENTS, TRACE METALS AND ORGANIC MICROPOLLUTANTS IN THE NORTH SEA. SUBPROJECT: BIOGEOCHEMICAL BEHAVIOUR OF PARTICULATE TRACE ELEMENTS IN THE NORTH SEA Université Libre de Bruxelles Laboratoire d Océanographie Chimique et Géochimie des Eaux R. Wollast, N. Roevros, V. Herzl, M. Loijens, B. Bastin, L. Chou

14 Area of Investigation

15 Distribution of particulate elements Spatial and temporal variations of the composition of the suspended matter in terms of major (Na, K, Ca, Mg, Fe, Si, Al, Corg, Cinorg) and minor elements (Mn, Cr, Ni, Co, Cu, Zn, Cd, Pb) in the Southern North Sea.

16 Major elements in relation with aluminium 25 Organic carbon 15 Calcium 5 Iron 2 4 Corg (%) 15 1 Ca (%) 1 5 Fe (%) Al (%) Al (%) Al (%) 3 Silicium 2 Magnesium 2 Potassium Si (%) 1 Mg (%) 1.5 K (%) Al (%) Al (%) Al (%) April 1998 Sept-Oct 1998

17 Trace metals in relation with aluminium Ni (µg/g) R² =.68 Nickel Al (%) Co (µg/g) R² =.88 Cobalt Al (%) Cd (µg/g) R² =.35 Cadmium Al (%) Cr (µg/g) R² =.7 Chromium Mn (µg/g) R² =.36 Manganese Pb (µg/g) R² =.45 Lead Al (%) Al (%) Al (%) April 1998 Sept-Oct 1998

18 Distribution of the log K D 6 log Kd Pb Zn Ni Cu Cd 4 Channel III II I IV North Affinity for the particulate phase: Pb > Zn > Ni > Cu > Cd

19 Acidimetric titration Investigation of the mobility and thus the potential bio-availability of the particulate trace metals by performing batch titration experiments of suspended matter by a strong acid (1N HCl). 8 6 Measured ph Theorical ph ph Volume HCl 1N (ml)

20 Major elements 12 Calcium 8 Magnesium.8 Silicium % dissolved % dissolved % dissolved ph ph ph 1 Manganese 3.5 Aluminium 2 Iron % dissolved % dissolved % dissolved ph ph ph April 1998 Sept-Oct 1998

21 Trace metals 125 Cadmium 12 Cobalt 25 Nickel % dissolved 75 5 % dissolved % dissolved ph ph ph 8 Zinc 7 Lead 12 Chromium % dissolved % dissolved % dissolved ph ph ph April 1998 Sept-Oct 1998

22 Associated elements Fe dissolved (%) Co dissolved (%) Cr dissolved (%) Al dissolved (%) Mn dissolved (%) Fe dissolved (%) Mn dissolved (%) Ca dissolved (%) Ni dissolved (%) Co dissolved (%) Cd dissolved (%) Zn dissolved (%) April 1998 Sept-Oct 1998

23 Transfer of trace elements between the dissolved and particulate phases Study of the mechanism and rate of uptake of trace metals by suspended matter using radionuclides ( 54 Mn, 63 Ni, 65 Zn, 19 Cd) during incubation experiments of natural samples.

24 14 C incorporation experiments (July 1999) Station 33 Influence of light intensity Photosynthetic parameters µgc/l Time (hours) 2 Rate: 1. µg C l -1 h -1 Station 7 µg C/l µe/m2.sec 8 : max = 3.33 :g C l -1 h -1 " =.23 :g C l -1 h -1 (:E m -2 s -1 ) µg C/l 1 µg C/l 4 : max = 267 :g C l -1 h Time (hours) µe/m2.sec " =.226 :g C l -1 h -1 (:E m -2 s -1 ) -1 Rate: 22 µg C l -1 h -1

25 Use of specific conditions CONDITIONS PROCESSES Light Photosynthesis Photoreaction Dark Abiotic Bacterial short term incub. Isotopic exchange Use of specific inhibitors INHIBITOR DCMU Antibiotics Sodium Azide INHIBITION Photosynthesis Bacterial activity Biotic process

26 Radionuclides incorporation experiments - Trace Metals Influence of light intensity Station 33 Station % Uptake Ni Mn Zn Cd % Uptake Ni Mn Zn Cd Light (µe/m2.sec) Light (µe/m2.sec) - No influence of light intensity except a slight photoinhibition of Mn transfer Influence of biological activity - Inhibition by sodium azide 5 Station 7 - Manganese 1 Station 7 - Zinc 4 8 % Uptake 3 2 % Uptake 6 4 abiotique 1 abiotique Light (µe/m2.sec) Light (µe/m2.sec) - Strong influence of biological activity on Mn uptake - Strong abiotic uptake of Zn

27 SPECIFIC INCORPORATION Cd Zn Mn Ni Station 33 % % % % photo bact inorg exch photo bact inorg exch photo bact inorg exch photo bact inorg exch K = h -1 K = h -1 K = h -1 K= h Station 7 % % % % photo bact inorg exch photo bact inorg exch photo bact inorg exch photo bact inorg exch K = h -1 K = h -1 K = h -1 K = h -1

28 CONCLUSIONS! In the coastal area under the influence of the Scheldt plume, the concentrations of particulate trace metals may be higher than that of the dissolved species, partly due to high values of the partition coefficient Kd. Most of the trace metals are associated with detrital alumino-silicates and Fe/Mn oxy-hydroxides of continental origin.! Titration experiments with HCl developed during our study allowed a better evaluation of the mobility of the various particulate elements. In particular, it has been shown that the dissolution of most trace elements begins as soon as the ph drops below 7. However, in the case of Pb and Cr, the dissolution starts only at ph below 5.! The use of radioactive trace elements allowed the assessment of biotic and abiotic fast reactions transferring the metals between the dissolved and particulate phases. As a consequence, the residence times of dissolved trace elements in surface waters are short (of the order of a few days). The particulate phase may act as a buffer to maintain the stock of dissolved elements constant.

29 ACKNOWLEDGEMENTS The present research was supported by the Belgian Federal Office for Scientific, Technical and Cultural Affairs (Contract N MN/DD/11 to Prof. W. Baeyens and Contract N MN/DD/13 to Prof. R. Wollast). The two subprojects presented are part of a network research co-ordinated by Prof. R. Van Grieken of the Universitaire Instelling Antwerpen. We would like to thank the captain and the crew members of the RV Belgica for their logistic and technical assistance during the various cruises in the North Sea.