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Chemical processes in benthic flux chambers and anoxic basin waters
225
Netherlands Journal of Sea Research 20 (2/3): 225-228 (1986)
CHEMICAL PROCESSES IN BENTHIC FLUX CHAMBERS AND ANOXIC BASIN WATERS DAVID DYRSSEN Department of Analytical and Marine Chemistry, Chalmers University of Technology and University of G6teborg, S-412 96 GSteborg, Sweden
ABSTRACT Many chemical constituents are measured in investigations of chemical reactions in marine systems, In this paper the fluxes of sulphide and carbonate are considered in anoxic sea water. The deviation from simple stoichiometric relations is shown and explanations are suggested. Two unusual compounds were measured. 1. INTRODUCTION An important process in the sea is the transfer of particulate matter from the surface to the bottom. The particles are commonly of biogenic origin consisting of soft organic matter and hard parts, which to a large extent are biogenic opal and calcium carbonate. This biogenic material is mixed with particulate inorganic matter, usually riverborne. The fresh organic matter decays to a large degree within two weeks, and it is this early decay that returns important nutrients to the bottom water. In areas with effective mixing the effect on the concentrations of the constituents in the bottom water will be small. In a benthic flux chamber, however, where the bottom water is enclosed in a plastic chamber, the shifts of many constituents can be measured together with their release rates, in moles per day and surface area. The use of a benthic flux chamber (Fig. 1) furthermore permits the measurement of release rates under both oxic and anoxic conditions. Also in basins with stagnant water the concentration shifts may be quite large. Two wellstudied anoxic basins with permanent steady-state conditions are the Norwegian fjord Framvaren and the Black Sea (DYRSSEN, 1985). The renewal of the basin water is so slow that the decay rate of organic matter produces more hydrogen sulphide than is consumed by the oxygen in the fresh sea water flowing into the basin over the sill. The main chemical reactions are reduction of sulphate by carbohydrates ac-
cording to SO42- + 2 CH20 ~ HS
+ HCO3 - + 002 + H20
and oxygen consumption ½ 02 + H2S ~ S + H20 The sulphur formed by this reaction may react with HS to polysulphides HSx , with Fe 2+, HS- and HS~ to FeS and FeS2 or with sulphate to other sulphoxides (e.g. thiosulphate, S2032-). In a previous investigation the vertical dispersion of constituents in a fjord basin was measured with rhodamine (SVENSSON,1980). In this way it was possible to calculate the flux of some constituents
02
!/
J !
/ / /
I
Fig. 1. The benthic flux chamber with stirrer, oxygen supply, sample withdrawal syringe and sample volume compensator (plastic bag).
226
D. DYRSSEN
130 m
from the depth profiles and their concentrations. The flux of sulphide was found to be in the same order as the flux determined in benthic chambers (DYRSSEN & SVENSSON,
1982).
In this article we shall use recent data to make such comparisons between benthic chambers and stagnant basins and show how some processes are more pronounced in benthic chamber experiments, while other processes are easier to detect in anoxic basins. We also wish to thank Henk Postma for his participation as a lecturer in our international course on "Sediment-seawater interactions". The benthic chamber experiments were furthermore stimulated by the cooperation with his graduate student Dr. Michiel Rutgers van der Loeff. 2. A FLUX CALCULATION Framvaren is a Norwegian fjord with permanent anoxic (sulphidic) bottom water (SKEI, 1983). Most constituents have a constant concentration from 150 m down to the bottom at 183 m. Fig. 2, which is based on Fig. 2 in the article of SKEI (1983), shows the cross-section of the bottom of the fjord below 150 m. The length of this section is about 2380 m. The bottom surface is about 3.7 x 105 m 2. The water surface at 150 m (A15o) is about 3.1 x 105 m 2. The volume of the basin water below 150 m is about 7 . 4 x 106 m 3. From the experiments with benthic flux chambers (HALL, 1984) the rate of sulphide production was estimated at 4.7 m m o l . m 2.d 1 (Part III, Table 1), which is close to the value of 4.9 to 5.8 mmol. m 2. d- 1 calculated by DYRSSEN & SVENSSON (1982) for Byfjorden. From these data is it possible to calculate the time (t) it would take to form the present day concentration of sulphide (6.25 mM)
60m
Fig. 2. The cross-section of the Framvaren basin below 150 m. The width of the narrow fjord basin (cf. SKEI, 1983) is 130 m at a depth of 150 m and 60 m at the bottom. Thus, Ft5o = 3720 Kz mol. d 1 This flux can be compared with the release rate from the bottom Fb = 3.7 x 105 x 0.0047 = 1739 mol- d- 1. If F15o=Fb then Kz=0.47 m2.d -t or 0.054 cm2.s -t. This value of the vertical diffusion coefficient corresponds to the values found experimentally for bottom water of Byfjorden by SVENSSON (1980). GADE & EDWARDS (1980) have found values in the order of 0.01 cm 2-s 1 for the vertical diffusivity in Framvaren. Thus, it is not unlikely that we have now reached a steady state. 3. COMPARISON OF THE RELEASE OF SULPHIDE AND CARBONATE The oxidation of carbohydrate and the reduction of sulphate should be related by the simple stoichiometric relation 2 CH20 + S O 4 2 H20
~
HS
+ HCO:~ + 0 0 2 4-
Thus ACt/&S(-II)t = 2. O-
\
t x 3.7 x 105 x 0.0047 = 6.25; t = 73 years 7.4 x 106 The time history of Framvaren since the deglaciation is, however, much longer (SKEI, 1983) and there should be a certain upward flux of sulphide since the concentrations are lower above 150 m. The flux at 150 m is then
"~
50-
100-
F15o = A15oKz x dc/dz 150-
where Atso= 3.1 x 105 m 2 For the depth range 130 m to 150 m (see Fig. 3) the concentration gradient is approximately dc/dz = 0.24 mM/20 m = 0.012 tool. m 4
,5 - - ,
1
1to
l
i
i
2
3
4
i
5
6
i 7
1,5
i 8
2o o,
rnMw
S (-II) t
Fig. 3. Depth profiles of total sulphide and total carbonate in mmoles per kg sea water.
BENTHIC CHAMBERS AND ANOXIC BASINS
The data from our latest measurements are given in Table 1. The values of total carbonate should be corrected for the initial carbonate. When the value is used at 20 m, the correction is 1.91S/20.99. The depth profiles of total sulphide and total carbonate are plotted in Fig. 3 and the total sulphide is plotted against the corrected value of total carbonate in Fig. 4, in the depth range 22 to 170 m. From this figure the value of ACt/AS(-II)t=16/6=2.67. From the experiments with the benthic flux c h a m b e r (HALL, 1984) the ratio of the net fluxes were 1 0 . 4 + 0 . 2 / 4 . 7 + 0 . 1 =2.21 +0.09. The difference could be explained if the processes that remove sulphide in the basin water were h a m p e r e d in the benthic c h a m b e r experiments. Such removal processes are the removal of sulphur, produced from oxygen in the fresh inflow, by the formation of pyrite. The existence of framboids in Framvaren has been demonstrated by SKEI (1983). In the experiments with the benthic chamber (HALL, 1984) the total carbonate was corrected for the dissolution of calcium carbonate. Leif Anderson (personal communication) has shown that there is a slight increase of calcium in Framvaren, but the increase is only about 0.62 mMw. This would cause a minor correction in the ratio of total carbonate to total sulphide. TABLE 1 Salinities and concentrations of sulphide and total carbonate in mmoles per kg sea water at different depths in Framvaren, South Norway. The sampling was carried out on February 19 and 20, 1985 Dep~
S
S(-I 0 .
Ct
C~corr)
0 2 4 8 12 14 16 18 20 22 24 26 30 40 50 70 80 90 100 110 130 150 160 170
5.588 11.035 11.390 14.741 15.650 18.803 18.902 20.038 20.990 21.344 21.210 21217 21.699 21.458 21.678 21.749 22.15 22.558 22.73 22.892 32.21 23.52 23.67 23.807
0 0 0 0 0 0 0 0 0 0.072 0.103 0.173 0.319 0.495 0.670 1.435 1.934 3.304 4.581 4.888 5.897 6.045 6.421 5.961
0.447 0.831 0.772 1.013 1.162 1.420 1.382 1.716 1.910 2.246 2.286 2.496 2.942 3.467 4.177 5.428 7.127 11.284 14.468 15.726 17.680 18.167 18.528 18.211
- 0.061 - 0.173 - 0.264 -0.328 - 0.262 -0.291 -0.338 - 0.107 0 0.304 0.356 0.565 1.011 1.514 2.204 3.449 5.111 9.236 12.400 13.643 15.568 16.027 16.374 16.045
227
S (-II) t mMw 65432-
lope -6/16
1-
i
ct
!
5
10
15
mMw
Fig. 4. Sulphide concentrations vs. total carbonate concentration corrected for the initial (preformed) carbonate.
4. THE C:N:P RATIO In Fig. 5 the concentrations of a m m o n i u m and phosphate in Framvaren are plotted against the corrected concentration of total carbonate from Table 1. The N/P ratio is close to 15, but in spite of the lack of data at some depths the C/N and C/P ratios are higher than the normal C/NIP ratios of 105/15/1 in plankton. The simplest way to explain this is to take into account that tree-leaves constitute an additional source of degradable organic matter. Since leaves can be regarded as a carbohydrate with very small amounts of nitrogen and phosphorous it is possible to use the following model substance (CH20)L(C H20)105(N H3)15(H3PO4). NH~
PO~
1.5-
0.1
0.5
0.05
10
115
Ct
Fig. 5. Ammonium (solid circles) and phosphate (open circles) concentrations vs. the corrected concentrations of total carbonate in Framvaren.
228
D. DYRSSEN
~NJ
- - S CH2 CH2OH
I
R Fig. 6, Reaction product of o-phthaldialdehydecontaining a thiol and an amino group. Using the C/N and C/P ratios from Fig. 5, we can calculate the coefficient L L + 1 0 5 = 1 0 .3 ; L=50 15 L + 105 -151; L=46 1 The mean value of L is 48 + 2. This means that about 1/3 of the degradable organic matter is terrestrial (leaves) and 2/3 marine. The release of ammonium in the benthic flux-chamber experiments (HALL, 1984) was very low, indicating a slow breakdown of proteins or a bacterial consumption of nitrogen. 5. HUMIC SUBSTANCES AND TWO UNUSUAL COMPOUNDS It has been shown in benthic flux-chamber experiments (HALL, 1984) that humic substances are released from sediments under anoxic conditions. Also in Framvaren one finds a straight-line relationship between the concentrations of humic substances and sulphide. In the potentiometric titration of sulphide in Framvaren with mercury(ll) chloride one finds a second equivalence point that corresponds to thiols (DYRSSEN & WEDBORG, 1986). These were also found in the Black sea (DYRSSEN et al., 1985), and should be investigated by the flux-chamber technique.
Methyl amine is released from anoxic marine sediments. This result was obtained in a benthic fluxchamber experiment (HALL, 1984) by use of the liquid chromatographic method of LINDROTH & MOPPER (1979) for the determination of amino acids. The reagent forms the product shown in Fig. 6 with a thiol and an amino group. The reaction can thus be used to determine thiols as well as compounds with amino groups (MOPPER & DELMAS, 1984). 6. REFERENCES
DYRSSEN,D., 1985, Stagnant sulphidic basin waters.--Sci. Total Environment, in press. DYRSSEN, D. & T. SVENSSON, 1982. On the calculation of release rates from stagnant basin sediments.--Chem. Geol, 36: 349-351. OYRSSEN, D. & M. WEDBORG, 1986. Titration of sulphide and thiols in natural waters,--Anal. Chim. Acta 180: 473-479. DYRSSEN, D., C. HARALDSSON, S. WESTERLUND& K. AREN, 1985. Indication of thiols in the Black Sea deep water.--Mar. Chem. 17: 323-327, GAOL, H.G. & A. EOWARDS, 1980. Deep water renewal in fjords. In: H.J. FREELAND,D.M. FARMER& C.D. LEVINGS. "Fjord Oceanography". Plenum Press, New York: 453-489. HALL, P., 1984. Chemical fluxes at the sediment - seawater interface; in-situ investigations with benthic chambers. Thesis, University of G6teborg. LINDROTH, P. & K. MOPPER, 1979. HPLC determination of submicromole amounts of amino acids by precolumn derivatization with o-phthalaldehyde.--Anal Chem. 51: 1667-1674. MOPPER, K. & D. DELMAS, 1984. Trace determination of biological thiols by liquid chromatography and precolumn fluorometric labeling with o-phthalaldehyde.--Anal. Chem. 56: 2557-2560. SKEW, J., 1983. Geochemical and sedimentological considerations of a permanently anoxic fjord - Framvaren, South Norway.--Sediment. Geol. 36: 131-145. SVENSSON, T., 1980. Tracer measurement of mixing in the deep water of a small, stratified sill fjord. In: H.J. FREELAND, D.M. FARMER & C.D. LEVINGS. "Fjord oceanography". Plenum Press, New York: 233-240.
Netherlands Journal of Sea Research 20 (2/3): 225-228 (1986)
CHEMICAL PROCESSES IN BENTHIC FLUX CHAMBERS AND ANOXIC BASIN WATERS DAVID DYRSSEN Department of Analytical and Marine Chemistry, Chalmers University of Technology and University of G6teborg, S-412 96 GSteborg, Sweden
ABSTRACT Many chemical constituents are measured in investigations of chemical reactions in marine systems, In this paper the fluxes of sulphide and carbonate are considered in anoxic sea water. The deviation from simple stoichiometric relations is shown and explanations are suggested. Two unusual compounds were measured. 1. INTRODUCTION An important process in the sea is the transfer of particulate matter from the surface to the bottom. The particles are commonly of biogenic origin consisting of soft organic matter and hard parts, which to a large extent are biogenic opal and calcium carbonate. This biogenic material is mixed with particulate inorganic matter, usually riverborne. The fresh organic matter decays to a large degree within two weeks, and it is this early decay that returns important nutrients to the bottom water. In areas with effective mixing the effect on the concentrations of the constituents in the bottom water will be small. In a benthic flux chamber, however, where the bottom water is enclosed in a plastic chamber, the shifts of many constituents can be measured together with their release rates, in moles per day and surface area. The use of a benthic flux chamber (Fig. 1) furthermore permits the measurement of release rates under both oxic and anoxic conditions. Also in basins with stagnant water the concentration shifts may be quite large. Two wellstudied anoxic basins with permanent steady-state conditions are the Norwegian fjord Framvaren and the Black Sea (DYRSSEN, 1985). The renewal of the basin water is so slow that the decay rate of organic matter produces more hydrogen sulphide than is consumed by the oxygen in the fresh sea water flowing into the basin over the sill. The main chemical reactions are reduction of sulphate by carbohydrates ac-
cording to SO42- + 2 CH20 ~ HS
+ HCO3 - + 002 + H20
and oxygen consumption ½ 02 + H2S ~ S + H20 The sulphur formed by this reaction may react with HS to polysulphides HSx , with Fe 2+, HS- and HS~ to FeS and FeS2 or with sulphate to other sulphoxides (e.g. thiosulphate, S2032-). In a previous investigation the vertical dispersion of constituents in a fjord basin was measured with rhodamine (SVENSSON,1980). In this way it was possible to calculate the flux of some constituents
02
!/
J !
/ / /
I
Fig. 1. The benthic flux chamber with stirrer, oxygen supply, sample withdrawal syringe and sample volume compensator (plastic bag).
226
D. DYRSSEN
130 m
from the depth profiles and their concentrations. The flux of sulphide was found to be in the same order as the flux determined in benthic chambers (DYRSSEN & SVENSSON,
1982).
In this article we shall use recent data to make such comparisons between benthic chambers and stagnant basins and show how some processes are more pronounced in benthic chamber experiments, while other processes are easier to detect in anoxic basins. We also wish to thank Henk Postma for his participation as a lecturer in our international course on "Sediment-seawater interactions". The benthic chamber experiments were furthermore stimulated by the cooperation with his graduate student Dr. Michiel Rutgers van der Loeff. 2. A FLUX CALCULATION Framvaren is a Norwegian fjord with permanent anoxic (sulphidic) bottom water (SKEI, 1983). Most constituents have a constant concentration from 150 m down to the bottom at 183 m. Fig. 2, which is based on Fig. 2 in the article of SKEI (1983), shows the cross-section of the bottom of the fjord below 150 m. The length of this section is about 2380 m. The bottom surface is about 3.7 x 105 m 2. The water surface at 150 m (A15o) is about 3.1 x 105 m 2. The volume of the basin water below 150 m is about 7 . 4 x 106 m 3. From the experiments with benthic flux chambers (HALL, 1984) the rate of sulphide production was estimated at 4.7 m m o l . m 2.d 1 (Part III, Table 1), which is close to the value of 4.9 to 5.8 mmol. m 2. d- 1 calculated by DYRSSEN & SVENSSON (1982) for Byfjorden. From these data is it possible to calculate the time (t) it would take to form the present day concentration of sulphide (6.25 mM)
60m
Fig. 2. The cross-section of the Framvaren basin below 150 m. The width of the narrow fjord basin (cf. SKEI, 1983) is 130 m at a depth of 150 m and 60 m at the bottom. Thus, Ft5o = 3720 Kz mol. d 1 This flux can be compared with the release rate from the bottom Fb = 3.7 x 105 x 0.0047 = 1739 mol- d- 1. If F15o=Fb then Kz=0.47 m2.d -t or 0.054 cm2.s -t. This value of the vertical diffusion coefficient corresponds to the values found experimentally for bottom water of Byfjorden by SVENSSON (1980). GADE & EDWARDS (1980) have found values in the order of 0.01 cm 2-s 1 for the vertical diffusivity in Framvaren. Thus, it is not unlikely that we have now reached a steady state. 3. COMPARISON OF THE RELEASE OF SULPHIDE AND CARBONATE The oxidation of carbohydrate and the reduction of sulphate should be related by the simple stoichiometric relation 2 CH20 + S O 4 2 H20
~
HS
+ HCO:~ + 0 0 2 4-
Thus ACt/&S(-II)t = 2. O-
\
t x 3.7 x 105 x 0.0047 = 6.25; t = 73 years 7.4 x 106 The time history of Framvaren since the deglaciation is, however, much longer (SKEI, 1983) and there should be a certain upward flux of sulphide since the concentrations are lower above 150 m. The flux at 150 m is then
"~
50-
100-
F15o = A15oKz x dc/dz 150-
where Atso= 3.1 x 105 m 2 For the depth range 130 m to 150 m (see Fig. 3) the concentration gradient is approximately dc/dz = 0.24 mM/20 m = 0.012 tool. m 4
,5 - - ,
1
1to
l
i
i
2
3
4
i
5
6
i 7
1,5
i 8
2o o,
rnMw
S (-II) t
Fig. 3. Depth profiles of total sulphide and total carbonate in mmoles per kg sea water.
BENTHIC CHAMBERS AND ANOXIC BASINS
The data from our latest measurements are given in Table 1. The values of total carbonate should be corrected for the initial carbonate. When the value is used at 20 m, the correction is 1.91S/20.99. The depth profiles of total sulphide and total carbonate are plotted in Fig. 3 and the total sulphide is plotted against the corrected value of total carbonate in Fig. 4, in the depth range 22 to 170 m. From this figure the value of ACt/AS(-II)t=16/6=2.67. From the experiments with the benthic flux c h a m b e r (HALL, 1984) the ratio of the net fluxes were 1 0 . 4 + 0 . 2 / 4 . 7 + 0 . 1 =2.21 +0.09. The difference could be explained if the processes that remove sulphide in the basin water were h a m p e r e d in the benthic c h a m b e r experiments. Such removal processes are the removal of sulphur, produced from oxygen in the fresh inflow, by the formation of pyrite. The existence of framboids in Framvaren has been demonstrated by SKEI (1983). In the experiments with the benthic chamber (HALL, 1984) the total carbonate was corrected for the dissolution of calcium carbonate. Leif Anderson (personal communication) has shown that there is a slight increase of calcium in Framvaren, but the increase is only about 0.62 mMw. This would cause a minor correction in the ratio of total carbonate to total sulphide. TABLE 1 Salinities and concentrations of sulphide and total carbonate in mmoles per kg sea water at different depths in Framvaren, South Norway. The sampling was carried out on February 19 and 20, 1985 Dep~
S
S(-I 0 .
Ct
C~corr)
0 2 4 8 12 14 16 18 20 22 24 26 30 40 50 70 80 90 100 110 130 150 160 170
5.588 11.035 11.390 14.741 15.650 18.803 18.902 20.038 20.990 21.344 21.210 21217 21.699 21.458 21.678 21.749 22.15 22.558 22.73 22.892 32.21 23.52 23.67 23.807
0 0 0 0 0 0 0 0 0 0.072 0.103 0.173 0.319 0.495 0.670 1.435 1.934 3.304 4.581 4.888 5.897 6.045 6.421 5.961
0.447 0.831 0.772 1.013 1.162 1.420 1.382 1.716 1.910 2.246 2.286 2.496 2.942 3.467 4.177 5.428 7.127 11.284 14.468 15.726 17.680 18.167 18.528 18.211
- 0.061 - 0.173 - 0.264 -0.328 - 0.262 -0.291 -0.338 - 0.107 0 0.304 0.356 0.565 1.011 1.514 2.204 3.449 5.111 9.236 12.400 13.643 15.568 16.027 16.374 16.045
227
S (-II) t mMw 65432-
lope -6/16
1-
i
ct
!
5
10
15
mMw
Fig. 4. Sulphide concentrations vs. total carbonate concentration corrected for the initial (preformed) carbonate.
4. THE C:N:P RATIO In Fig. 5 the concentrations of a m m o n i u m and phosphate in Framvaren are plotted against the corrected concentration of total carbonate from Table 1. The N/P ratio is close to 15, but in spite of the lack of data at some depths the C/N and C/P ratios are higher than the normal C/NIP ratios of 105/15/1 in plankton. The simplest way to explain this is to take into account that tree-leaves constitute an additional source of degradable organic matter. Since leaves can be regarded as a carbohydrate with very small amounts of nitrogen and phosphorous it is possible to use the following model substance (CH20)L(C H20)105(N H3)15(H3PO4). NH~
PO~
1.5-
0.1
0.5
0.05
10
115
Ct
Fig. 5. Ammonium (solid circles) and phosphate (open circles) concentrations vs. the corrected concentrations of total carbonate in Framvaren.
228
D. DYRSSEN
~NJ
- - S CH2 CH2OH
I
R Fig. 6, Reaction product of o-phthaldialdehydecontaining a thiol and an amino group. Using the C/N and C/P ratios from Fig. 5, we can calculate the coefficient L L + 1 0 5 = 1 0 .3 ; L=50 15 L + 105 -151; L=46 1 The mean value of L is 48 + 2. This means that about 1/3 of the degradable organic matter is terrestrial (leaves) and 2/3 marine. The release of ammonium in the benthic flux-chamber experiments (HALL, 1984) was very low, indicating a slow breakdown of proteins or a bacterial consumption of nitrogen. 5. HUMIC SUBSTANCES AND TWO UNUSUAL COMPOUNDS It has been shown in benthic flux-chamber experiments (HALL, 1984) that humic substances are released from sediments under anoxic conditions. Also in Framvaren one finds a straight-line relationship between the concentrations of humic substances and sulphide. In the potentiometric titration of sulphide in Framvaren with mercury(ll) chloride one finds a second equivalence point that corresponds to thiols (DYRSSEN & WEDBORG, 1986). These were also found in the Black sea (DYRSSEN et al., 1985), and should be investigated by the flux-chamber technique.
Methyl amine is released from anoxic marine sediments. This result was obtained in a benthic fluxchamber experiment (HALL, 1984) by use of the liquid chromatographic method of LINDROTH & MOPPER (1979) for the determination of amino acids. The reagent forms the product shown in Fig. 6 with a thiol and an amino group. The reaction can thus be used to determine thiols as well as compounds with amino groups (MOPPER & DELMAS, 1984). 6. REFERENCES
DYRSSEN,D., 1985, Stagnant sulphidic basin waters.--Sci. Total Environment, in press. DYRSSEN, D. & T. SVENSSON, 1982. On the calculation of release rates from stagnant basin sediments.--Chem. Geol, 36: 349-351. OYRSSEN, D. & M. WEDBORG, 1986. Titration of sulphide and thiols in natural waters,--Anal. Chim. Acta 180: 473-479. DYRSSEN, D., C. HARALDSSON, S. WESTERLUND& K. AREN, 1985. Indication of thiols in the Black Sea deep water.--Mar. Chem. 17: 323-327, GAOL, H.G. & A. EOWARDS, 1980. Deep water renewal in fjords. In: H.J. FREELAND,D.M. FARMER& C.D. LEVINGS. "Fjord Oceanography". Plenum Press, New York: 453-489. HALL, P., 1984. Chemical fluxes at the sediment - seawater interface; in-situ investigations with benthic chambers. Thesis, University of G6teborg. LINDROTH, P. & K. MOPPER, 1979. HPLC determination of submicromole amounts of amino acids by precolumn derivatization with o-phthalaldehyde.--Anal Chem. 51: 1667-1674. MOPPER, K. & D. DELMAS, 1984. Trace determination of biological thiols by liquid chromatography and precolumn fluorometric labeling with o-phthalaldehyde.--Anal. Chem. 56: 2557-2560. SKEW, J., 1983. Geochemical and sedimentological considerations of a permanently anoxic fjord - Framvaren, South Norway.--Sediment. Geol. 36: 131-145. SVENSSON, T., 1980. Tracer measurement of mixing in the deep water of a small, stratified sill fjord. In: H.J. FREELAND, D.M. FARMER & C.D. LEVINGS. "Fjord oceanography". Plenum Press, New York: 233-240.