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In situ determination of suspended particulate matter and dissolved organic matter concentrations in an estuarine environment by means of an optical beam attenuance meter
Estuarine and Coastal Marine Science (z98o) xo, 455-466
In situ Determination of Suspended Particulate Matter and Dissolved Organic Matter Concentrations in an Estuarine Environment by Means of an Optical Beam Attenuance Meter
G. V. Winters and D. E. Buckley Environmental Marine Geology, Atlantic Geoscience Centre, Geological Survey of Canada, Bedford hzstitute of Oceanography, Dartmouth, Nova Scotia, Canada B2 Y 4A2 Received 27 August x979
Keywords: in situ spectroscopy; suspended matter; organic matter An optical technique was developed for the in sltu estimation of estuarine suspended particulate matter (SPM) and dissolved organic matter (DOM) concentrations in water. Measurements were made in the laboratory and the field, and attenuance coefficients were determined at wavelength bands centered at 475 nm and at 680 nm. Laboratory measurement of attenuance caused by Kaolinite suspensions and hurnie acid solutions were used to determine the wavelength selectivity or the 475 nm/68o nm band ratio for SPM and DOM. T h e light attenuated by kaolinite suspensions and SPM is attributed to both absorbance and scattering (A~+Bs) , but for dissolved humic acid, it is attributed only to absorbance, (A~). The optical band attenuance ratio (K) is constant for each type of substance, i.e. K s = (A4~5+Bp)/(A6~°+B,) and K~ = A 475 s ]tl 680 , . The factor K s is dependent on the average particle characteristics and is constant for a given water mass. In this study Ks for the kaolinite and SPM was x'z, and K~ was found to be 7"2 for dissolved humie acid. Mathematical expressions, applicable to complex aqueous mixtures were formulated to differentiate bet~veen changes in attenuance coefficients resulting from (x) concentration variations of kaolinite suspensions or SPM and (2) dissolved humic acid or D O M [(A6S°+Bp) and A 47s, respectively]. (A6SvO+Bs) = ( K , C - o - - C , n ) [ ( K , - - K , ) A 475 = ( C ' " - - K , C " * ) / ( x - - K , / K , )
Introduction T h e loss of radiant flux from a beam of light, passing through a column of water, due to the processes of absorption and scattering is measured as attenuance. This process provides a sensitive means of measuring the quality of water. T h e relative influences of natural constituents in marine waters, with regard to the attenuance of light were reviewed by Ivanoff et al. (x96I) and were summarized by Jerlov (I968 , x976 ) in which the standard equation used to describe light attenuation is: 455 o3oz-3524/8oto4o455+*z $o2.oo/o
~ *980 Academic Press Inc. (London) Ltd.
456
G. V . Winters & D . E . B u c k l e y
In ( I d l o ) = - - o 2 .
(x)
in which I0 and Is are the incident and resultant light intensities respectively. The value a represents the total attenuance coefficient and Z is the cell path length. The total attenuance, a. absorbance by which varies with wavelength, X, is attributed to attenuance by water, a~,, particles, A~; scatterance by particles, B v; and absorbance by 'yellow substance' or dissolved humic-like organic matter, A~. a x = a ,A+ A p +AB p + A y
A
(2)
The wavelength dependence of scattering by particles and attenuance by dissolved sea salts is considered to be negligible in the visible region. Because the attenuance coefficient for water is constant at a specific wavelength, the corrected attenuance coefficient, C ~, can be determined as follows: C ~,
A = a £- - a w ~- A pA+ B v + A y A
(3)
An optical beam attenuance meter, equipped with interference light filters and a 2o cm cell path length, was used to measure attenuance coefficients at selected wavelength bands of 45o-5oo nm (reported as 475 nm) and 66o-7o0 nm (reported as 680 nm). The value for aw was experimentally determined from a sample of deionized and micro-filtered water. This meter, designed by Larsen (I973) was intended for use in water depths less than IOOOm. In this report, procedures for obtaining continuous data using this in situ instrument, representative of the concentration of suspended particulate matter (SPM) and dissolved (filter passing, 0"4 lam) organic matter (DOM) are outlined. The validity of the in situ • determinations can be verified using samples collected and analysed in the laboratory. Theory Corrected attenuance coefficients are determined at two wavelength bands. C475 = A 475 p +Bv+A
475 y
(3a)
C68O = A 680 p +Bp+A
680 y
(3b)
The attenuance wavelength selectivity or the 475]68o band ratio is constant for each substance. The 475]68o band ratio for SPM, Kr, is equal to the ratio of particle absorbance plus scatterance at wavelength bands 475 vs 68o nm. Kp = (AgS+B
)/CA
°+Bp)
(4)
The 475]680 band ratio for DOM, Ky, is equal to the ratio of absorbance by the DOM at wavelength bands 475 vs 680 nm. K , = A475/A680 ._ y , . _ ,
(S)
Equations (6) and (7), below, were derived from these latter equations. C '~* = A 4 ~ 5 ( x - - K r I K , ) + K , C
6s°
(6)
The 475]680 band ratio for SPM, K v, can be determined experimentally using a linear least squares regression analyses of C a75 vs C ~° data, provided that either (I) the DOM concentrations are negligible; or (2) the DOM concentration is constant. Under these conditions, any changes in the attenuance coefficients are due to changes in the concentration of SPM.
Optical beam attenuance meter
457
The 475[68o band ratio, Kr, for DOM also can be determined in a similar manner, from the following equation:
C'75 = --(A~° q-Bv)(K,--Kv)A-K, C"s°
(7)
Conditions must prevail such that either (,) the SPM concentrations are negligible; or (z) the SPM concentration is constant. From equation (7), the SPM selective attenuanee can be described as follows:
K;C~so--C475 ( A ~ ° + B ' ) --
K,--K,
(S)
Absorbance and scatterance by particles at ). = 680 nm can be described as a function of the corrected attenuance coefficients at both wavelengths and the 475/68o band ratios for both substances. In a similar manner, the DOM selective attenuance can be described as a function of the corrected attenuanee coefficients at both wavelengths and the 475[68o band ratios for both substances.
A~s
C475--K, C6s° =
x-K,/-r,:,
(9)
The selective attenuance coefficients (A~°nt-Bv) and A ~ 5 are equated with SPM and DOM, respectively. Experlment
Experimental samples To test the above equations, four types of experimental samples were prepared (Table x): (x) kaolinite suspensions of varying concentrations (particle size < 5 gm); (2) kaolinite suspensions of varying concentrations in the presence of a constant amount of dissolved humie acid (filtered through a 0.4 Inn membrane filter); (3) dissolved humie acid solutions of varying concentrations; and (4) mixtures containing varying concentrations of both substances. The kaolinite (No. 5, Lamar Pit, S. Carolina) was prepared by grinding with a mortar and pestol and size fractionated using a process of sedimentation devised and outlined by Buckley (x972). The humie acid consisted of natural material recovered from the LaHave River (Nova Scotia, Canada) above the tidal zone, and x km above Bridgewater and, thus any town sewage outflows. The humie material was concentrated by low temperature evaporation and the humie acid then was separated by precipitation at pH 3 (King, x967; Rashid & King, x969).
Field observations The attenuance meter recorded 739 in situ measurements in the Miramichi estuary in February i977. l~,~easurements were made under the winter ice. Total salinity, current speed and direction, and tidal heights also were monitored. These results are reported by Winters & Buckley (I978). The Miramichi estuary is situated in a mlcrotidal zone (tidal range < 2 m) on the eastern New Brunswick shore of the southern Gulf of St. Lawrence. It is a shallow funnel shaped
458
G. V. Winters & D. E. Buckley
T~zaz z. Experimental results Kaolinite Humic acid (mg 1-x) (mg 1-x)
C 4v5 (m -x)
C's° (m -z)
0"00
0"0
0"0
0"0
3"75
o.o o.o
0.6
o"5
z~
z'2
o-o o-o
2"7
2"2 4"4
0"0
0'0
0"0
0"0
o'o
0"6 X'2 2~
0"2
o'o
0"7
o'I
Z'2
o'z
o'o o'o
4"8 9"6 29"2
2'3 4"6 8.8
0"3 o'6 z'2
o'o 5"3 z z-o z5"S 2z'o 25"7
z3"z x3"z z3.z z3"z x3"z z3"z
5"2 6.2 7"2 8.z 9"0 9"5
3z'o 36"8
z3"z z3"z z3"z
to.6 zz'8
o'7 x.6 2"5 3"3 4"1 4"7 5"6
z2.8
7"z
0"0
0"0
0"0
0"0
o.o
o'o
z9"2 z9"2
8.8 8.8
z'2
3"75
z'2
I'4
0"7
3"75 7"5 7'5
I'2 2"4 2"4
z'4 z'8 3"0
0"8 z"S z'8
z5"o
4"8
5"5
3"0
z5"o 3o'0 3o'o
4"8 9"6 9"6
5"5 zo'z zo'3
3"2 6"o 6.2
7"5o z5"o 30"0
o'o o'o
o'o
42"8
5"2
6"4
x'o
Suspensions of kaolinite and solutions of humic acid were prepared in deionized water filtered through a o'22 tm~ filter. Corrected attenuance measurements were made in the laboratory using the 2o cm cell on the in situ attenuance meter fitted with a calibration tank.
estuary, consisting of an inner drowned river channel and an outer shallow basinal area which is partially enclosed b y a Holocene barrier-island system (Rashid & Reinson, i979). D u r i n g winter when the estuary is covered with ice, the vertical estuarine circulation in the drowned river channel approaches that of a highly stratified estuary. Observations considered in this report are restricted to the central (station z) and the lower (station 4) drowned river channel portion of this estuary. I n order to determine the total S P M concentrations water samples were collected and filtered through o. 4 p m membrane filters (Table 2). No samples were analysed for D O M . In gtu attenuance observations were made two to five minutes prior to the collection of water samples.
Optical beam attenuance meter
459
TABL~ 2. Field samples Sample station
Depth (m)
z 2 z 2 2
x 8 8 2 8
Julian day fraction
Total salinity (~oo)
2
2
z
8
47"5000 47"5000 47"6458 47"78x3 47"78z3 47"9375 47"9375
4 4 4 4 4 4 4
x 7 7 2 7 z 7
42"5625 42"5625 42"7083 47"4792 47"4792 47"6389 47"6458
SPM (rag 1 -t)
C~ (m -x)
C eS° (m -1)
5"57 8"42 x2"o7 9"56 x3"84 7"27 Io-76
4"4x 7"22 64"75 4"33 8"99
5"4 6.6 z9"4 5"2 6"9
1"6 2"7 2x'4 x'9 4"z
7"29
4"3
x'7
x3"73
5"5
3"6
x2"o8 zS'XZ 20'99 I2-89 x9"x8 x4"88 23"23
z.ox o'56 2"63 2"23 4"5t 2"03 xo'43
2"9 /'7 3"0 3"8 3"8 3"7 6.0
0-6 0"4 z'5 x-o x"5 0"9 4"3
Water samples collected from the Miramichi Estuary were analysed for total salinity and SPM concer~tration. T h e corrected light attenuance values for C ~u and C es° were measured in situ.
Results
Experimental samples In Figures x, z and 3 the corrected attenuance coefficients for the experimental samples are plotted for wavelength band 475 vs 680 nm. The 475/68o band ratio for the kaolinite suspensions, K p, is i.z9+o.o 5 in Figure I and x.x64-o.o8 in Figure 2. For later computations, K.p, is reduced to z significant figures (i.e. agp = x.z). In the case of kaolinite alone, Figure z, the linear least squares regression line passes through the origin, but in Figure z the Y-axis intercept is at 4"3 m-1 because of the presence of a constant humie acid concentration. In Figure 3 the 475•680 band ratio for the dissolved humie acid, K r, is 7.24-0. 5. The regression line passes through the origin. !
3
L
z
1
s
y
~
J
/
N=5 • =0.9997 Significance level for r
5
~
~
= 1.19+- 0"05 (99% confidence interval)
I /
/ O
f
t
*
t
=
i
!
I
2
3
4
5
6
7
8
C6eO(m-=) Figure x. Comparison of light attenuance coemcJents (corrected for the attenuance by" water) at wavelength 475 vs 68o n m for samples containing varying concentrations of suspended kaolinite,
460
G. IT. IVinters £~ D . E. Buckley
|4
i
13
i
,
~
i
'
•
N-9 • =0"998
41 0
t I
, 2
/
= 5
I 4
I 5
, 6
; 7
,I 8
c~8O(m-I)
Figure 2. Comparison of light attenuance coefficients (corrected for the attenuance by water) at wavelength 475 vr 680 nm for samples containing varying concentrations of suspended kaolinite in the presence of z3"z mg l-a dissolved humie acid. ,~
8
i
,
/ i
7I 6 'E
N=7 • =0.999 nifieonee level for • <0.001
i
5 4
Slope =K~. = 7-2 +-0.5 (99% confidence interval)
i
i
i
c68Olm-I )
Figure 3. Comparison of light attenuance coefficients (corrected for the attenuance by water) at wavelength 475 vs 680 nm for samples containing varying concentrations of dissolved humic acid. Equation 8 and 9, which were derived to determine the selective attenuanee by particles and dissolved organic matter, respectively, can now be further simplified by substituting the expe=imental values for Kp and Ky. Corrected attcnuance coefficients for all experimental samples (Table x) were converted to the selective attenuance coefficients (//~°+Bp) and ~/475 y ° The results are depicted in Figures 4 and 5 for the estimations of kaolinite particle concentrations and dissolved humic acid concentrations respectively. The significance level
Optical beam attenuance meter
$
J
N=32 • =0-991 SiQnificancelevel far • <0"001 ~
46x
' 1
i
i
./ /~o
/,
"
e
-~" 5 'E
~4
/_
+
@
_ J~ ~v/
•
SIope=(ApCm°+Bp)/Kaolinlte - o l 6 _ + o OI
l
1
I0
0
-
(99% confidenceinterval) l
I
20 30 Kaolinite(mg L")
40
50
Figure 4- Calibration of selective attenuance coefficients for kaolinite particles. Kaolinite ~ 6"24-o'4 (A e*0 p + B ~ ) . T h e selective attenuance coefficients for kaolinite were determined from C 47. and C 68° measurements by employing equation (8) and the values for Kp and K, determined for kaolinite particles and humic acid solutions respectively. 8
i
i
i
/
t
N=32
7
r =0.981 Significance level for t < 0 . 0 0 1
6
,E5 3
2 A
Slope=A47S/lHumicacid)
I
(99% confidenceinterval)
o
/
=0.41+0.03
2'o
25
Dissolvedhumic acid (rag l "t) Figure 5. Calibration of selective attenuance coefficients for dissolved humic acid. H u m i c acid = 2"44-o'2 A ' ~ 5. T h e selective attenuance coefficients for dissolved humlc acid were determined from C 4~5 and C 68° measurements by employing equation (9) and the values for Kp and K , determined for kaolinite particles and humic acid solutions respectively.
of the correlation coefficient, r, is .(o.ooi in both figures, and the linear least squares regression line, in each case, passes through the origin. In Figure 4, the slope of the regression line is o.i64-o.oi and the kaolinite estimation equation is as follows: Kaolinite (ragt-*) = 6"z+°'4(A~°+Bv) Similarly, in Figures 5, the slope of the regression line is o'414-o'o 3 and the humic acid estimation equation is: Humie acid (ragt-l) -----2"44-o'2A4~s
462
G. V. Winters &, D. E. Buckley
FieM observations The bulk of the field data are reported elsewhere (Winters et al., 1978; Winters & Buekley, x978). The total in situ monitoring data set contained 739 observation points. The attenuance coefficients increased most noticeably in the bottom waters during peak tidal current speeds. This fact was attributed to the resuspension of bottom sediments (Figure 6). To determine the 475/68o band ratio of the SPM (Figure 7), only observations within 2. 5 m of the bottom and where the total salinity was >22~oo were used. This selection was Z ~
9.8 9'9 o
2
16.5
22.2 ~ 4
"6 23.3
a 6
23.6
23"6
8
23-6 0
4.0 C (m-I}
8"0
Figure 6. Depth vs corrected attenuance profiles at wavelengths 68o and 475 nm. Observations were made during maximum tidal current speed, on a rising tide. The water column was sharply stratified due to the migration of the salt wedge up the estuary.
• =0"979 8
/
Significance level
for •<0.001
e
•
~/,
/
/.
7 6 I
E
5
L4 3
/
e
-
Slope =Kp=HS_+0.07 (99% confidence Inferval)
o
)
!
,
4
i
;
7
8
cemOCm-,I Figure 7. Comparison of in sltu light attenuance (corrected for the attenuanee of water) at wavelength 475 vr 68o rim, to determine the 475/68o band ratio of the SPM. Observations considered were restricted to those within 2"5 m of the bottom with a total salinity > 2 2 ~ .
Optical beam attenuance meter
463
made on the basis of data (Winters et al., z978) which indicated that the estuarine water layers could be characterized by two end members, (z) a bottom layer with salinity >2z~oo containing relatively high concentrations of resuspended sediments and (2) a surface fresh water layer having relatively low concentrations of suspended sediments, but having a brown coloration typical of river water containing high concentration of dissolved organic matter (humie materials). The 475/68o band ratio, K v, determined from the bottom water layers w a s I'18-4-o'o 7. This value of Kv, for the average SPI~ (resulting from bottom sediment resuspension), is similar to that observed for the 475/68o band ratio for the experimental suspensions of kaolinite, (z.2).
5
4
•
i
*
f
,
I
M:36 • =0.921 Significonce level for • < 0.001
, 3
2
Slope =K~ =6.8 _+0.8 (99% confidence Inlervol) I
0
r
!
!
!
!
I
I
2
3
4
5
6
7
8
csSO(rn-l) Figure 8. Comparison of in s~tu light attenuance (corrected for the attenuance by water) at wavelength 475 vs 680 n m to determine the 475[68o band ratio for the D O M . T h e observations considered were restricted to the surface freshwater layer which appeared to be rich i n dissolved organic matter and contained negligible concentrations of SPM.
To determine the 475[68o band ratio for the DOM (Figure 8), the observations were restricted to the surface fresh water layer which appeared to be rich in dissolved organ!c matter. This was done to obtain the upper limiting value for the ratio of corrected attenuance coefficient at wavelength bands 475 vs 68o nm (i.e. negligible SPM concentration). The 475/68o band ratio, Ky, was equal to 6"8~o.8. This value of Ky for DOM is similar to that observed for the experimental solution of humic acid (7.z+o.5). Now, having determined the 475[68o band ratios, K v and Ky, both in the laboratory and from field observations, the selective attenuance coefficients for the field observations can be determined in a similar manner as that described for the experimental samples (SPM concentrations and corrected attenuance coefficients are listed in Table z). The criteria for the estuarine sample collection was based on tidal phase; and the statistics requirement for the normal distribution of data for both dependent and independent parameters was not acI~ieved. However, the data populations for the SPM concentrations and the selective attenuanee coefficients, A~°-t-Bv, were log normal distributions. Log transforms for both parameters are plotted in Figure 9. The correlhtion equation is as follows: SPM = y6(A~°-t-Br) °'9'
464
G. IF. Winters & D. E. Buckley
i i L L , m ~ | 2-30 /,4 :)20 N=I4 15 • = 0.972 / I0 Significance level for • < 0 . 0 0 1 ~
5 • °
•
nE t~ +
° °
~
•
o
~'X Oq
0.1
o o:s
i
25 SPM (rag t -I}
F i g u r e 9. C o m p a r i s o n o f t h e selective a t t e n u a n c e coefficients attributed to S P M w i t h m e a s u r e d concentrations o f S P M .
Discussion Laboratory measurements and field observations indicate that a significant amount of light is attenuated by SPM and DOM, at both wavelength bands 475 and 68o nm. It was found that the 475]68o band ratio of attenuated light, at selected wavelengths, was significantly different for SPM when compared with DOM. Thus, if the observations of in sltu attenuance coefficients are to be calibrated with the quantitative determination of either component, it is necessary to simultaneously consider the presences of both components. Although field samples were not analysed for DO~,I, the 475[68o band ratios (Ky and K~,) determined by analyses of the in situ monitoring data, provided a means for determining the presence of the DOBI. The 475•68o band ratio of the Bliramichi DOM was similar to that observed for the dissolved humie acid recovered from the LaHave River. The former value for the 475/68o band ratio was compared with those calculated for'humic acids with varying degrees of chemical maturity (computed from optical density data presented by Kononova et al., x966). The observed value of K~ for the Miramichi estuary is large and is similar to that computed for a young or chemically immature humic acid with a relatively low condensation of aromatic compounds and with predominant branched-chain compounds. This is thetype of riverine DOM which is expected to be prevalent in the surface layers of an estuary (Rashid, x978). Also, the major fraction of dissolved organic matter in coastal sea water, which is maeromolecu]ar in nature, has been referred to as humic substance. These substances comlarise as much as 9o% of the dissolved organic matter in sea water (Williams, z97z ; Duursma, x965 ; Degens, z97o ). In future it may be possible to determine a general 475/68o band ratio, K~ for this general classification of organic matter often found in estuarine and coastal marine environments. The reported precision for this attenuanee meter is 5% (Larsen, x973). The laboratory experi~nental results reported in this paper indicate a relative error of 6% (99% confidence interval) for the kaolinite suspensions and humic acid solutions. Detection limit for SPM was 2 mg 1-1 as determined from the computation of the standard error for the estimation of ' Y' given 'X' for the least squares linear regression for a 2o cm optical path length.
Optical beam attenuance meter
465
The relative error for the estimation of SPM was xo% (99% confidence interval). The DOM detection limit was I m g 1-1 (determined from the humic acid experimental results) for a 2o em optical path length. These detection limits would be proportionately lowered to about o.4 mg I -x for SPM and o'z mg 1-1 for DOM, when the attenuance optical path length is increased to xoo era. The ultimately attainable relative error for the SPM and DOM concentration is 6%. This in situ light attenuanee method for estimating estuarine SPM and DOM concentrations has inherent shortcomings. Average light attenuating properties (i.e. 475[68o band ratios K v and Ky) must be assumed for each of the attenuating species, for a given water mass. In a dynamic estuarine environment the specific attenuating properties of each species may be subject to frequent changes (thus requiring frequent sample collection for calibrations). Also, the components concentrations may change rapidly. Thus, sequential in situ attenuance measurement and sample collection can cause additional error in the concentrations estimations. Calibration sampling criteria rc/ust be based on the least squares regression analyses statistical requirement that data populations be normally distributed. Then it will not be necessary to subject SPM and DOM concentration data and their respective selective attenuance coefficients ( A ~ ° + B p and A~) to needless arbitrary transformation to force the data to fit normal distribution curves. Two suggested procedures for minimizing of calibration error are; (x) simultaneous in situ monitoring and sample collection using a pump to sample immediately adjacent to the attenuance meter optical cell, or (2) sample collecting and immediate field laboratory attenuance measurement. Then, following either of these options, the SPM can be filtered from the sample (for quantitative determination). Attenuance coefficients for the remaining filtrate are recorded. Then the 475]68o band ratio K~ (for DOM) is equal to the slope of the linear least squares regression line for C 475 vs C as°, and the intercept should equal o. The results for the DOM concentration determination can then be used to select samples of negligible or nearly constant DOM concentrations, and linear least squares regression analyses for C 475 vs C es° (for corresponding in situ or field laboratory neat samples) can be used to determine the 475]68o band ratio Kp (for SPM). The selective attenuanee coefficients A 6so p + B j, and A~S are then determined and calibrated for SPM and DOM concentration estimations, respectively. In any field application of this instrumental technique there is a great advantage in being able to obtain direct and continuous observations of the concentration and type of light attenuating substances in the water column.
References ]]uckley, D. E. z972 Geochemical interactions of suspended siIicate with river and marine estuarine water, z4th International Geological Congress, section xo, pp. 282-290. Degens, E. T. x97o Molecular nature of nitrogenous compounds in sea water and recent marine sediments. In Organic Matter in Natural waters. (Hood, D. W., ed.), Institute of Marine Science, University of Alaska, pp. 77-xo6. Duursma, E. D. x965 The dissolved organic constituents of sea water. In Chemical Oceanography. (Riley, J. P. 8: Skirrow, G., eds). vol. x, Academic Press, pp. 433-475. Ivanoff, A., Jerlov, N. & Waterrnna, T. H. x96x Limnology and Oceanography 6, xz9-x48. Jerlov, N. G. x968 Optical Oceanography. Elsevier Publishing Company, New York, pp. 47-62. Jerlov, N. G. x976 2~farine optics. Elsevier Oceanography Series, No. x4, Elsevier Scientific Publishing Company, New York, pp. 23x. King, L. H. x967 Isolation and characterization of'organic matter from glacial marine sediments on the Scotian Shelf. Bedford Institute of Oceanography, Report x967-4, Dartmouth, Nova Scotia, Canada, pp. x8.
466
G. IT. Winters ~ D. E. Buckley
Kononovoa, M. M., Nowakowshi, T. Z. & Newman, A. C. P. I966 Soil Organic 3Carter. 2nd English ed., Pergamon Press Ltd., London W.I, pp. 544. Larsen, E. x973 An bz situ optical beam attenuance meter. Bedford Institute of Oceanography, Report series BI-R-73-3, Dartmouth, Nova Scotia, Canada, pp. 74. Rashid, M. A. & King, L. H. x969 Molecular weight distribution measurements on humie and fulvie acid fractions from marine clays on the Seotian Shelf. Geochimica et Cosmochimica Acta, 33~ x47-xSX. Rashid, M. A. x978 Personal communication. Atlantic Geoscience Centre, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada. Rashid, M. A. & Reinson, G. E. x979 Organic matter in surfieial sediments of the Miramiehi estuary, New Brunswick, Canada. Estuarine and Coastal Marine Science 8~ 23-36. Williams, P. M. I97 r The distribution and cycling of organic matter in the ocean. In Organic Compounds in Aquatic Environments. (Faust, S. J. & Hunter, J. V., eds), Marcel Dekker, pp. x45-x63. Winters, G. V., Fitzgerald, R. A. & Buckley, D. E. x978 Analyses of water column and bottom sediment samples from the Miramiehi estuary, New Brunswick. Bedford Institute of Oceanography, Data Series, BI-D-78-8, Dartmouth, Nova Scotia, Canada, pp. 8x. Winters, G. V. & Buckley, D. E. z978 bz situ monitoring data on the water column in the Miramlchi estuary, New Brunswick. Bedford Institute of Oceanography, Data Series, ]3I-D-78-9, Dartmouth, Nova Scotia, Canada, pp. z3L
In situ Determination of Suspended Particulate Matter and Dissolved Organic Matter Concentrations in an Estuarine Environment by Means of an Optical Beam Attenuance Meter
G. V. Winters and D. E. Buckley Environmental Marine Geology, Atlantic Geoscience Centre, Geological Survey of Canada, Bedford hzstitute of Oceanography, Dartmouth, Nova Scotia, Canada B2 Y 4A2 Received 27 August x979
Keywords: in situ spectroscopy; suspended matter; organic matter An optical technique was developed for the in sltu estimation of estuarine suspended particulate matter (SPM) and dissolved organic matter (DOM) concentrations in water. Measurements were made in the laboratory and the field, and attenuance coefficients were determined at wavelength bands centered at 475 nm and at 680 nm. Laboratory measurement of attenuance caused by Kaolinite suspensions and hurnie acid solutions were used to determine the wavelength selectivity or the 475 nm/68o nm band ratio for SPM and DOM. T h e light attenuated by kaolinite suspensions and SPM is attributed to both absorbance and scattering (A~+Bs) , but for dissolved humic acid, it is attributed only to absorbance, (A~). The optical band attenuance ratio (K) is constant for each type of substance, i.e. K s = (A4~5+Bp)/(A6~°+B,) and K~ = A 475 s ]tl 680 , . The factor K s is dependent on the average particle characteristics and is constant for a given water mass. In this study Ks for the kaolinite and SPM was x'z, and K~ was found to be 7"2 for dissolved humie acid. Mathematical expressions, applicable to complex aqueous mixtures were formulated to differentiate bet~veen changes in attenuance coefficients resulting from (x) concentration variations of kaolinite suspensions or SPM and (2) dissolved humic acid or D O M [(A6S°+Bp) and A 47s, respectively]. (A6SvO+Bs) = ( K , C - o - - C , n ) [ ( K , - - K , ) A 475 = ( C ' " - - K , C " * ) / ( x - - K , / K , )
Introduction T h e loss of radiant flux from a beam of light, passing through a column of water, due to the processes of absorption and scattering is measured as attenuance. This process provides a sensitive means of measuring the quality of water. T h e relative influences of natural constituents in marine waters, with regard to the attenuance of light were reviewed by Ivanoff et al. (x96I) and were summarized by Jerlov (I968 , x976 ) in which the standard equation used to describe light attenuation is: 455 o3oz-3524/8oto4o455+*z $o2.oo/o
~ *980 Academic Press Inc. (London) Ltd.
456
G. V . Winters & D . E . B u c k l e y
In ( I d l o ) = - - o 2 .
(x)
in which I0 and Is are the incident and resultant light intensities respectively. The value a represents the total attenuance coefficient and Z is the cell path length. The total attenuance, a. absorbance by which varies with wavelength, X, is attributed to attenuance by water, a~,, particles, A~; scatterance by particles, B v; and absorbance by 'yellow substance' or dissolved humic-like organic matter, A~. a x = a ,A+ A p +AB p + A y
A
(2)
The wavelength dependence of scattering by particles and attenuance by dissolved sea salts is considered to be negligible in the visible region. Because the attenuance coefficient for water is constant at a specific wavelength, the corrected attenuance coefficient, C ~, can be determined as follows: C ~,
A = a £- - a w ~- A pA+ B v + A y A
(3)
An optical beam attenuance meter, equipped with interference light filters and a 2o cm cell path length, was used to measure attenuance coefficients at selected wavelength bands of 45o-5oo nm (reported as 475 nm) and 66o-7o0 nm (reported as 680 nm). The value for aw was experimentally determined from a sample of deionized and micro-filtered water. This meter, designed by Larsen (I973) was intended for use in water depths less than IOOOm. In this report, procedures for obtaining continuous data using this in situ instrument, representative of the concentration of suspended particulate matter (SPM) and dissolved (filter passing, 0"4 lam) organic matter (DOM) are outlined. The validity of the in situ • determinations can be verified using samples collected and analysed in the laboratory. Theory Corrected attenuance coefficients are determined at two wavelength bands. C475 = A 475 p +Bv+A
475 y
(3a)
C68O = A 680 p +Bp+A
680 y
(3b)
The attenuance wavelength selectivity or the 475]68o band ratio is constant for each substance. The 475]68o band ratio for SPM, Kr, is equal to the ratio of particle absorbance plus scatterance at wavelength bands 475 vs 68o nm. Kp = (AgS+B
)/CA
°+Bp)
(4)
The 475]680 band ratio for DOM, Ky, is equal to the ratio of absorbance by the DOM at wavelength bands 475 vs 680 nm. K , = A475/A680 ._ y , . _ ,
(S)
Equations (6) and (7), below, were derived from these latter equations. C '~* = A 4 ~ 5 ( x - - K r I K , ) + K , C
6s°
(6)
The 475]680 band ratio for SPM, K v, can be determined experimentally using a linear least squares regression analyses of C a75 vs C ~° data, provided that either (I) the DOM concentrations are negligible; or (2) the DOM concentration is constant. Under these conditions, any changes in the attenuance coefficients are due to changes in the concentration of SPM.
Optical beam attenuance meter
457
The 475[68o band ratio, Kr, for DOM also can be determined in a similar manner, from the following equation:
C'75 = --(A~° q-Bv)(K,--Kv)A-K, C"s°
(7)
Conditions must prevail such that either (,) the SPM concentrations are negligible; or (z) the SPM concentration is constant. From equation (7), the SPM selective attenuanee can be described as follows:
K;C~so--C475 ( A ~ ° + B ' ) --
K,--K,
(S)
Absorbance and scatterance by particles at ). = 680 nm can be described as a function of the corrected attenuance coefficients at both wavelengths and the 475/68o band ratios for both substances. In a similar manner, the DOM selective attenuance can be described as a function of the corrected attenuanee coefficients at both wavelengths and the 475[68o band ratios for both substances.
A~s
C475--K, C6s° =
x-K,/-r,:,
(9)
The selective attenuance coefficients (A~°nt-Bv) and A ~ 5 are equated with SPM and DOM, respectively. Experlment
Experimental samples To test the above equations, four types of experimental samples were prepared (Table x): (x) kaolinite suspensions of varying concentrations (particle size < 5 gm); (2) kaolinite suspensions of varying concentrations in the presence of a constant amount of dissolved humie acid (filtered through a 0.4 Inn membrane filter); (3) dissolved humie acid solutions of varying concentrations; and (4) mixtures containing varying concentrations of both substances. The kaolinite (No. 5, Lamar Pit, S. Carolina) was prepared by grinding with a mortar and pestol and size fractionated using a process of sedimentation devised and outlined by Buckley (x972). The humie acid consisted of natural material recovered from the LaHave River (Nova Scotia, Canada) above the tidal zone, and x km above Bridgewater and, thus any town sewage outflows. The humie material was concentrated by low temperature evaporation and the humie acid then was separated by precipitation at pH 3 (King, x967; Rashid & King, x969).
Field observations The attenuance meter recorded 739 in situ measurements in the Miramichi estuary in February i977. l~,~easurements were made under the winter ice. Total salinity, current speed and direction, and tidal heights also were monitored. These results are reported by Winters & Buckley (I978). The Miramichi estuary is situated in a mlcrotidal zone (tidal range < 2 m) on the eastern New Brunswick shore of the southern Gulf of St. Lawrence. It is a shallow funnel shaped
458
G. V. Winters & D. E. Buckley
T~zaz z. Experimental results Kaolinite Humic acid (mg 1-x) (mg 1-x)
C 4v5 (m -x)
C's° (m -z)
0"00
0"0
0"0
0"0
3"75
o.o o.o
0.6
o"5
z~
z'2
o-o o-o
2"7
2"2 4"4
0"0
0'0
0"0
0"0
o'o
0"6 X'2 2~
0"2
o'o
0"7
o'I
Z'2
o'z
o'o o'o
4"8 9"6 29"2
2'3 4"6 8.8
0"3 o'6 z'2
o'o 5"3 z z-o z5"S 2z'o 25"7
z3"z x3"z z3.z z3"z x3"z z3"z
5"2 6.2 7"2 8.z 9"0 9"5
3z'o 36"8
z3"z z3"z z3"z
to.6 zz'8
o'7 x.6 2"5 3"3 4"1 4"7 5"6
z2.8
7"z
0"0
0"0
0"0
0"0
o.o
o'o
z9"2 z9"2
8.8 8.8
z'2
3"75
z'2
I'4
0"7
3"75 7"5 7'5
I'2 2"4 2"4
z'4 z'8 3"0
0"8 z"S z'8
z5"o
4"8
5"5
3"0
z5"o 3o'0 3o'o
4"8 9"6 9"6
5"5 zo'z zo'3
3"2 6"o 6.2
7"5o z5"o 30"0
o'o o'o
o'o
42"8
5"2
6"4
x'o
Suspensions of kaolinite and solutions of humic acid were prepared in deionized water filtered through a o'22 tm~ filter. Corrected attenuance measurements were made in the laboratory using the 2o cm cell on the in situ attenuance meter fitted with a calibration tank.
estuary, consisting of an inner drowned river channel and an outer shallow basinal area which is partially enclosed b y a Holocene barrier-island system (Rashid & Reinson, i979). D u r i n g winter when the estuary is covered with ice, the vertical estuarine circulation in the drowned river channel approaches that of a highly stratified estuary. Observations considered in this report are restricted to the central (station z) and the lower (station 4) drowned river channel portion of this estuary. I n order to determine the total S P M concentrations water samples were collected and filtered through o. 4 p m membrane filters (Table 2). No samples were analysed for D O M . In gtu attenuance observations were made two to five minutes prior to the collection of water samples.
Optical beam attenuance meter
459
TABL~ 2. Field samples Sample station
Depth (m)
z 2 z 2 2
x 8 8 2 8
Julian day fraction
Total salinity (~oo)
2
2
z
8
47"5000 47"5000 47"6458 47"78x3 47"78z3 47"9375 47"9375
4 4 4 4 4 4 4
x 7 7 2 7 z 7
42"5625 42"5625 42"7083 47"4792 47"4792 47"6389 47"6458
SPM (rag 1 -t)
C~ (m -x)
C eS° (m -1)
5"57 8"42 x2"o7 9"56 x3"84 7"27 Io-76
4"4x 7"22 64"75 4"33 8"99
5"4 6.6 z9"4 5"2 6"9
1"6 2"7 2x'4 x'9 4"z
7"29
4"3
x'7
x3"73
5"5
3"6
x2"o8 zS'XZ 20'99 I2-89 x9"x8 x4"88 23"23
z.ox o'56 2"63 2"23 4"5t 2"03 xo'43
2"9 /'7 3"0 3"8 3"8 3"7 6.0
0-6 0"4 z'5 x-o x"5 0"9 4"3
Water samples collected from the Miramichi Estuary were analysed for total salinity and SPM concer~tration. T h e corrected light attenuance values for C ~u and C es° were measured in situ.
Results
Experimental samples In Figures x, z and 3 the corrected attenuance coefficients for the experimental samples are plotted for wavelength band 475 vs 680 nm. The 475/68o band ratio for the kaolinite suspensions, K p, is i.z9+o.o 5 in Figure I and x.x64-o.o8 in Figure 2. For later computations, K.p, is reduced to z significant figures (i.e. agp = x.z). In the case of kaolinite alone, Figure z, the linear least squares regression line passes through the origin, but in Figure z the Y-axis intercept is at 4"3 m-1 because of the presence of a constant humie acid concentration. In Figure 3 the 475•680 band ratio for the dissolved humie acid, K r, is 7.24-0. 5. The regression line passes through the origin. !
3
L
z
1
s
y
~
J
/
N=5 • =0.9997 Significance level for r
5
~
~
= 1.19+- 0"05 (99% confidence interval)
I /
/ O
f
t
*
t
=
i
!
I
2
3
4
5
6
7
8
C6eO(m-=) Figure x. Comparison of light attenuance coemcJents (corrected for the attenuance by" water) at wavelength 475 vs 68o n m for samples containing varying concentrations of suspended kaolinite,
460
G. IT. IVinters £~ D . E. Buckley
|4
i
13
i
,
~
i
'
•
N-9 • =0"998
41 0
t I
, 2
/
= 5
I 4
I 5
, 6
; 7
,I 8
c~8O(m-I)
Figure 2. Comparison of light attenuance coefficients (corrected for the attenuance by water) at wavelength 475 vr 680 nm for samples containing varying concentrations of suspended kaolinite in the presence of z3"z mg l-a dissolved humie acid. ,~
8
i
,
/ i
7I 6 'E
N=7 • =0.999 nifieonee level for • <0.001
i
5 4
Slope =K~. = 7-2 +-0.5 (99% confidence interval)
i
i
i
c68Olm-I )
Figure 3. Comparison of light attenuance coefficients (corrected for the attenuance by water) at wavelength 475 vs 680 nm for samples containing varying concentrations of dissolved humic acid. Equation 8 and 9, which were derived to determine the selective attenuanee by particles and dissolved organic matter, respectively, can now be further simplified by substituting the expe=imental values for Kp and Ky. Corrected attcnuance coefficients for all experimental samples (Table x) were converted to the selective attenuance coefficients (//~°+Bp) and ~/475 y ° The results are depicted in Figures 4 and 5 for the estimations of kaolinite particle concentrations and dissolved humic acid concentrations respectively. The significance level
Optical beam attenuance meter
$
J
N=32 • =0-991 SiQnificancelevel far • <0"001 ~
46x
' 1
i
i
./ /~o
/,
"
e
-~" 5 'E
~4
/_
+
@
_ J~ ~v/
•
SIope=(ApCm°+Bp)/Kaolinlte - o l 6 _ + o OI
l
1
I0
0
-
(99% confidenceinterval) l
I
20 30 Kaolinite(mg L")
40
50
Figure 4- Calibration of selective attenuance coefficients for kaolinite particles. Kaolinite ~ 6"24-o'4 (A e*0 p + B ~ ) . T h e selective attenuance coefficients for kaolinite were determined from C 47. and C 68° measurements by employing equation (8) and the values for Kp and K, determined for kaolinite particles and humic acid solutions respectively. 8
i
i
i
/
t
N=32
7
r =0.981 Significance level for t < 0 . 0 0 1
6
,E5 3
2 A
Slope=A47S/lHumicacid)
I
(99% confidenceinterval)
o
/
=0.41+0.03
2'o
25
Dissolvedhumic acid (rag l "t) Figure 5. Calibration of selective attenuance coefficients for dissolved humic acid. H u m i c acid = 2"44-o'2 A ' ~ 5. T h e selective attenuance coefficients for dissolved humlc acid were determined from C 4~5 and C 68° measurements by employing equation (9) and the values for Kp and K , determined for kaolinite particles and humic acid solutions respectively.
of the correlation coefficient, r, is .(o.ooi in both figures, and the linear least squares regression line, in each case, passes through the origin. In Figure 4, the slope of the regression line is o.i64-o.oi and the kaolinite estimation equation is as follows: Kaolinite (ragt-*) = 6"z+°'4(A~°+Bv) Similarly, in Figures 5, the slope of the regression line is o'414-o'o 3 and the humic acid estimation equation is: Humie acid (ragt-l) -----2"44-o'2A4~s
462
G. V. Winters &, D. E. Buckley
FieM observations The bulk of the field data are reported elsewhere (Winters et al., 1978; Winters & Buekley, x978). The total in situ monitoring data set contained 739 observation points. The attenuance coefficients increased most noticeably in the bottom waters during peak tidal current speeds. This fact was attributed to the resuspension of bottom sediments (Figure 6). To determine the 475/68o band ratio of the SPM (Figure 7), only observations within 2. 5 m of the bottom and where the total salinity was >22~oo were used. This selection was Z ~
9.8 9'9 o
2
16.5
22.2 ~ 4
"6 23.3
a 6
23.6
23"6
8
23-6 0
4.0 C (m-I}
8"0
Figure 6. Depth vs corrected attenuance profiles at wavelengths 68o and 475 nm. Observations were made during maximum tidal current speed, on a rising tide. The water column was sharply stratified due to the migration of the salt wedge up the estuary.
• =0"979 8
/
Significance level
for •<0.001
e
•
~/,
/
/.
7 6 I
E
5
L4 3
/
e
-
Slope =Kp=HS_+0.07 (99% confidence Inferval)
o
)
!
,
4
i
;
7
8
cemOCm-,I Figure 7. Comparison of in sltu light attenuance (corrected for the attenuanee of water) at wavelength 475 vr 68o rim, to determine the 475/68o band ratio of the SPM. Observations considered were restricted to those within 2"5 m of the bottom with a total salinity > 2 2 ~ .
Optical beam attenuance meter
463
made on the basis of data (Winters et al., z978) which indicated that the estuarine water layers could be characterized by two end members, (z) a bottom layer with salinity >2z~oo containing relatively high concentrations of resuspended sediments and (2) a surface fresh water layer having relatively low concentrations of suspended sediments, but having a brown coloration typical of river water containing high concentration of dissolved organic matter (humie materials). The 475/68o band ratio, K v, determined from the bottom water layers w a s I'18-4-o'o 7. This value of Kv, for the average SPI~ (resulting from bottom sediment resuspension), is similar to that observed for the 475/68o band ratio for the experimental suspensions of kaolinite, (z.2).
5
4
•
i
*
f
,
I
M:36 • =0.921 Significonce level for • < 0.001
, 3
2
Slope =K~ =6.8 _+0.8 (99% confidence Inlervol) I
0
r
!
!
!
!
I
I
2
3
4
5
6
7
8
csSO(rn-l) Figure 8. Comparison of in s~tu light attenuance (corrected for the attenuance by water) at wavelength 475 vs 680 n m to determine the 475[68o band ratio for the D O M . T h e observations considered were restricted to the surface freshwater layer which appeared to be rich i n dissolved organic matter and contained negligible concentrations of SPM.
To determine the 475[68o band ratio for the DOM (Figure 8), the observations were restricted to the surface fresh water layer which appeared to be rich in dissolved organ!c matter. This was done to obtain the upper limiting value for the ratio of corrected attenuance coefficient at wavelength bands 475 vs 68o nm (i.e. negligible SPM concentration). The 475/68o band ratio, Ky, was equal to 6"8~o.8. This value of Ky for DOM is similar to that observed for the experimental solution of humic acid (7.z+o.5). Now, having determined the 475[68o band ratios, K v and Ky, both in the laboratory and from field observations, the selective attenuance coefficients for the field observations can be determined in a similar manner as that described for the experimental samples (SPM concentrations and corrected attenuance coefficients are listed in Table z). The criteria for the estuarine sample collection was based on tidal phase; and the statistics requirement for the normal distribution of data for both dependent and independent parameters was not acI~ieved. However, the data populations for the SPM concentrations and the selective attenuanee coefficients, A~°-t-Bv, were log normal distributions. Log transforms for both parameters are plotted in Figure 9. The correlhtion equation is as follows: SPM = y6(A~°-t-Br) °'9'
464
G. IF. Winters & D. E. Buckley
i i L L , m ~ | 2-30 /,4 :)20 N=I4 15 • = 0.972 / I0 Significance level for • < 0 . 0 0 1 ~
5 • °
•
nE t~ +
° °
~
•
o
~'X Oq
0.1
o o:s
i
25 SPM (rag t -I}
F i g u r e 9. C o m p a r i s o n o f t h e selective a t t e n u a n c e coefficients attributed to S P M w i t h m e a s u r e d concentrations o f S P M .
Discussion Laboratory measurements and field observations indicate that a significant amount of light is attenuated by SPM and DOM, at both wavelength bands 475 and 68o nm. It was found that the 475]68o band ratio of attenuated light, at selected wavelengths, was significantly different for SPM when compared with DOM. Thus, if the observations of in sltu attenuance coefficients are to be calibrated with the quantitative determination of either component, it is necessary to simultaneously consider the presences of both components. Although field samples were not analysed for DO~,I, the 475[68o band ratios (Ky and K~,) determined by analyses of the in situ monitoring data, provided a means for determining the presence of the DOBI. The 475•68o band ratio of the Bliramichi DOM was similar to that observed for the dissolved humie acid recovered from the LaHave River. The former value for the 475/68o band ratio was compared with those calculated for'humic acids with varying degrees of chemical maturity (computed from optical density data presented by Kononova et al., x966). The observed value of K~ for the Miramichi estuary is large and is similar to that computed for a young or chemically immature humic acid with a relatively low condensation of aromatic compounds and with predominant branched-chain compounds. This is thetype of riverine DOM which is expected to be prevalent in the surface layers of an estuary (Rashid, x978). Also, the major fraction of dissolved organic matter in coastal sea water, which is maeromolecu]ar in nature, has been referred to as humic substance. These substances comlarise as much as 9o% of the dissolved organic matter in sea water (Williams, z97z ; Duursma, x965 ; Degens, z97o ). In future it may be possible to determine a general 475/68o band ratio, K~ for this general classification of organic matter often found in estuarine and coastal marine environments. The reported precision for this attenuanee meter is 5% (Larsen, x973). The laboratory experi~nental results reported in this paper indicate a relative error of 6% (99% confidence interval) for the kaolinite suspensions and humic acid solutions. Detection limit for SPM was 2 mg 1-1 as determined from the computation of the standard error for the estimation of ' Y' given 'X' for the least squares linear regression for a 2o cm optical path length.
Optical beam attenuance meter
465
The relative error for the estimation of SPM was xo% (99% confidence interval). The DOM detection limit was I m g 1-1 (determined from the humic acid experimental results) for a 2o em optical path length. These detection limits would be proportionately lowered to about o.4 mg I -x for SPM and o'z mg 1-1 for DOM, when the attenuance optical path length is increased to xoo era. The ultimately attainable relative error for the SPM and DOM concentration is 6%. This in situ light attenuanee method for estimating estuarine SPM and DOM concentrations has inherent shortcomings. Average light attenuating properties (i.e. 475[68o band ratios K v and Ky) must be assumed for each of the attenuating species, for a given water mass. In a dynamic estuarine environment the specific attenuating properties of each species may be subject to frequent changes (thus requiring frequent sample collection for calibrations). Also, the components concentrations may change rapidly. Thus, sequential in situ attenuance measurement and sample collection can cause additional error in the concentrations estimations. Calibration sampling criteria rc/ust be based on the least squares regression analyses statistical requirement that data populations be normally distributed. Then it will not be necessary to subject SPM and DOM concentration data and their respective selective attenuance coefficients ( A ~ ° + B p and A~) to needless arbitrary transformation to force the data to fit normal distribution curves. Two suggested procedures for minimizing of calibration error are; (x) simultaneous in situ monitoring and sample collection using a pump to sample immediately adjacent to the attenuance meter optical cell, or (2) sample collecting and immediate field laboratory attenuance measurement. Then, following either of these options, the SPM can be filtered from the sample (for quantitative determination). Attenuance coefficients for the remaining filtrate are recorded. Then the 475]68o band ratio K~ (for DOM) is equal to the slope of the linear least squares regression line for C 475 vs C as°, and the intercept should equal o. The results for the DOM concentration determination can then be used to select samples of negligible or nearly constant DOM concentrations, and linear least squares regression analyses for C 475 vs C es° (for corresponding in situ or field laboratory neat samples) can be used to determine the 475]68o band ratio Kp (for SPM). The selective attenuanee coefficients A 6so p + B j, and A~S are then determined and calibrated for SPM and DOM concentration estimations, respectively. In any field application of this instrumental technique there is a great advantage in being able to obtain direct and continuous observations of the concentration and type of light attenuating substances in the water column.
References ]]uckley, D. E. z972 Geochemical interactions of suspended siIicate with river and marine estuarine water, z4th International Geological Congress, section xo, pp. 282-290. Degens, E. T. x97o Molecular nature of nitrogenous compounds in sea water and recent marine sediments. In Organic Matter in Natural waters. (Hood, D. W., ed.), Institute of Marine Science, University of Alaska, pp. 77-xo6. Duursma, E. D. x965 The dissolved organic constituents of sea water. In Chemical Oceanography. (Riley, J. P. 8: Skirrow, G., eds). vol. x, Academic Press, pp. 433-475. Ivanoff, A., Jerlov, N. & Waterrnna, T. H. x96x Limnology and Oceanography 6, xz9-x48. Jerlov, N. G. x968 Optical Oceanography. Elsevier Publishing Company, New York, pp. 47-62. Jerlov, N. G. x976 2~farine optics. Elsevier Oceanography Series, No. x4, Elsevier Scientific Publishing Company, New York, pp. 23x. King, L. H. x967 Isolation and characterization of'organic matter from glacial marine sediments on the Scotian Shelf. Bedford Institute of Oceanography, Report x967-4, Dartmouth, Nova Scotia, Canada, pp. x8.
466
G. IT. Winters ~ D. E. Buckley
Kononovoa, M. M., Nowakowshi, T. Z. & Newman, A. C. P. I966 Soil Organic 3Carter. 2nd English ed., Pergamon Press Ltd., London W.I, pp. 544. Larsen, E. x973 An bz situ optical beam attenuance meter. Bedford Institute of Oceanography, Report series BI-R-73-3, Dartmouth, Nova Scotia, Canada, pp. 74. Rashid, M. A. & King, L. H. x969 Molecular weight distribution measurements on humie and fulvie acid fractions from marine clays on the Seotian Shelf. Geochimica et Cosmochimica Acta, 33~ x47-xSX. Rashid, M. A. x978 Personal communication. Atlantic Geoscience Centre, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada. Rashid, M. A. & Reinson, G. E. x979 Organic matter in surfieial sediments of the Miramiehi estuary, New Brunswick, Canada. Estuarine and Coastal Marine Science 8~ 23-36. Williams, P. M. I97 r The distribution and cycling of organic matter in the ocean. In Organic Compounds in Aquatic Environments. (Faust, S. J. & Hunter, J. V., eds), Marcel Dekker, pp. x45-x63. Winters, G. V., Fitzgerald, R. A. & Buckley, D. E. x978 Analyses of water column and bottom sediment samples from the Miramiehi estuary, New Brunswick. Bedford Institute of Oceanography, Data Series, BI-D-78-8, Dartmouth, Nova Scotia, Canada, pp. 8x. Winters, G. V. & Buckley, D. E. z978 bz situ monitoring data on the water column in the Miramlchi estuary, New Brunswick. Bedford Institute of Oceanography, Data Series, ]3I-D-78-9, Dartmouth, Nova Scotia, Canada, pp. z3L