Dissolved silicon in the Yaquina Estuary, Oregon

Estuarine,

Coastal and Shelf Science (1982) 15, 561-567

Dissolved Silicon in the Yaquina Estuary, Oregon

Richard

J. CaUawaya and David

“Environmental bEnvironmental Oregon 97365,

Protection Protection U.S.A.

Received IO February

1981

T. Specht”

Agency, Corvallis, Oregon 97330, U.S.A. Agency, Marine Science Center, Newport, and in revised form

15

February

and

1982

Keywords: assimilation; diffusion-advection models; residence time; silicon uptake rates; Oregon coast The longitudinal distribution of dissolvedsilicon in the Yaquina Estuary is describedin surface and bottom waters. Non-conservative behaviour is a function of high insolation and low runoff; residencetime is the primary controlling factor.

Introduction The chemistry and distribution of dissolvedreactive silicon (DSi) in estuarieshas recently been summarized by Burton (1976), Liss (1976) and Aston (1979). A seriesof papers by Peterson and his co-workers (1975a, b, 1978)and Conomos(1979) on DSi in San Francisco Bay has contributed greatly to an understanding of the conservative and non-conservative distribution of this important phytoplankton nutrient. Officer & Ryther (1980) argue that silicon is often the controlling nutrient in altering a diatom to a flagellate community. Liss & pointon (1973) stated the controversial nature of DSi observationsup to that time: ‘It is still an unresolved problem as to why removal of dissolved silicate or boron should occur in someestuariesbut not in others.’ Among the factors they suggestedfor further study was estuarine mixing, i.e. transport, dispersion,flushing rates and residencetimes. The problem wassubstantially resolved in a paper by Peterson et al. (1978) in an application of a numerical model to the longitudinal-vertical distribution of DSi in San Francisco Bay: many of the numerical model resultswere essentiallyduplicated by analytical solutions given by Rattray & Officer (1979). They demonstrated that river inflow influenced the estuarine circulation (Festa & Hansen, 1976) and, in turn, the biologically modulated DSi concentration; the interrelationship of flow, mixing and uptake determinesthe nature (conservative/non-conservative) of the distribution. We have examined the distribution of DSi with respect to season,runoff and other parametersin the Yaquina, a small Oregon coastal-plain estuary (Figure I). We adopt an operational definition of ‘dissolved’ fraction asthat passingthrough a pre-rinsed Millipore” type HA membrane filter having a nominal pore diameter of 0.45 pm; the definition is recognized as being somewhatarbitrary. 561 0272-7714/82/1r0561+07

$03.00/o

@ 1982AcademicPressInc. (London)Limited

562

R.J.

Callaway

& D. T. Specht

CHITWOOD GAUGING STATION : 9.1 km

EPA

Figure

I. Location

chart

and station

positions,

Yaquina

Estuary,

GAUGING

Oregon.

Area of study The estuary drainage basin is about 622 kmz; mean tide range at the entrance is 1.80 and 1.92 m at Toledo, 20 km upstream (NOAA, 1980). U.S. Geological Survey stream records at Chitwood were used to gauge the Yaquina River; Elk Creek flow was monitored by us (Callaway et al., 1970). Flows were averagedfor 5 days previous to a samplingtrip (duration 4-6 h) and ranged from 1.3 to 87 m3 s-l. Mean depth to Elk City is about 4 m. Cross-sectionalarea (A) in m2 decreaseswith distance (X) in km upstream of the entrance asA “4.400 exp(-o*rX). Unpublished data (Callaway, Ditsworth & Specht) relate salinity intrusion length in km (&) to river runoff (Q) in ms s-l asL, = 32.2-2-91 log, Q (Y = o-87, n = 9). Salinity difference from top to bottom, 6s, at L,/2 is related to Q by the linear relationship (in this range of observations) 6s = I-I $0.2 Q (Y = 0.99, n = 9). These relations are a function of wind, tidal excursion, fluctuations of river flow, and sampling time and duration; no attempt was made to correct flows for considerationof drainage basin area or bank runoff.

Methods From July 1976 to December 1977 sampleswere obtained every 6-8 weeksat the stations shown in Figure I. Vertical profiles of temperature and salinity were madewith a Beckman RSg-3 meter or an InterOceans Model 513D continuously recording conductivity-temperature-turbidity-depth meter. Water sampleswere collected by hand pump 0.5 m below the surface and 0.5 m above the bottom and stored in 10-l acid-washedand rinsed Cubitainers@. They were immediately placed in ice chestsfor transport to the laboratory in Corvallis and maintained at 4 “C in the dark until further subsamplingand preservation (usually within 36 h) for subsequentanalysis.

Dissolved silicon in the Yaquina Estuary

I4

(a)

October

1976

563

( e)

Q-1.3 m3s-’ L,=35km,aS=2%

12 Moy

Q: IO.4 L,=2Skm,

1977

m3 s-l as=4x

600 4-

OW@ 0

0

0 29

“.

0 da I

0

I

Q

I

(b)

20

O=3.5m3

Jonuory

1977

8,’

,

I

( f )

5-l

22

August

1977

0=l.9m3s-’ 8S=4°/oo

6-

L,=3lkm,

as=Ovoo

4-

T

o”

4

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I

3 March

1977

eQ* L

t

0

I

( e) 20 December 0=87m3 5-l L, =20km, 8S=20°&

s-1 as=IoxO @ O~Oooaa

0

00 O0

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km,

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l

0

o 02,

I

I

(d)

2 I April

l

I

1977

I

I

20

30

40

Distance

upstream

(km)

upstream,

Yaquina

IO

Q= 73m3 s-’ L,=26km,8S=4%o 6

l ’

8

50

@@aoD@0 0

2

a

4 I-..--Oo

$ IO

20

Distance

30 upstream

40

50 J

(km)

Figure z. Reactive silica as Si WS. distance samples (0), bottom samples (0).

Estuary.

Surface

Relative chlorophyll a in oivo fluorescencewas measuredin the laboratory within 12 h with a G. K. Turner Model III fluorometer (Lorenzen, 1966). The fluorometer wasmodified for chlorophyll according to Lorenzen, except that ro-ml matched cuvettes were used, and calibration was with coproporphyrin-I. Reactive silicate reported asSi was analysedby the heteropoly blue method (Technicon, 1973).

Results and discussion DSi and river fIoev

DSi vs. distance upstreamis shown in Figure 2; Q, L, and 6s are given for each survey. DSi at the oceanend ranged from about 0.2 to 2.6 mg 1-r and at the river end from 3.4 to 6.5 mg 1-i. The higher ocean-endvalue occurred during a high freshwater runoff period. This compareswith world averagesof
564

R. J. Callaway &3 D. T. Specht

(a)

14 October s-l

0=l,3m3

1976

( e)

;;$i.~

foe

4

I

0

I

(bl

I

I 1977

(f )

{z;h;g77

0 r =-0.996,

2-

00

%a

I

a

(

22 August O= I.9 m3 5’:

m

n = 26

1977

o/=-0.999.n=23 0 l

%

(d)

,*

1

~~~~~

4-

0,

1977

yf::;y?

I

20 Jonuory s-l

0=35m3

12 May m3 s-I

0=10,4

I

21 April Or7.8 m3s-I DSi =5.65-0.145 r=-0.998, n=2l

1

I

1977

IO

I

l

20 Salinity

I

30

40

50

(%d

4Oe

0

2-

ee I

Oo

IO

I

20 Solinity

Figure bottom

3. Reactive silica samples (e).

I 30

I 40

50

(%o) as Si VS. salinity,

Yaquina

Estuary.

Surface

samples

(0),

The vertical DSi difference is similar to the vertical salinity (S) structure. In the freshwater portion (X>L,), there is no vertical DSi difference (complete mixing). In the saline portion (X-4,), the magnitude of the difference is primarily a function of Q. For Qz%,) at flows of Q>s ma s-l. Conservative and non-conservative distributions of DSi Plots of chemical constituents vs. salinity have been used to demonstrate uptake, addition or conservation of a given constituent within an estuary. Liss (1976) has discussedthe usefulnessof the concept and its pitfalls. If a straight-line relationship exists(theoretical dilution line), changeswith salinity are due to simple mixing and dilution. If the data points lie above or below the theoretical dilution line, the non-conservative relations are attributable to addition to, or removal from, the estuarine water, respectively. These concepts were extended by Petersonet al. (19756, 1978). Figure 3 showsDSi vs. S for all surveys. Figures 3(a) and (f )suggest(non-1inear)removal; the remainder are linear (conservative). The linear and exponential (natural log transform-

Dissolved silicon in the Yaquina Estuary

565

ation) correlation coefficients are all <-0.94. In Figure 3(f), r = 0.99 if the two ocean endpoints are dropped. The non-linear distributions occur at Q valuesof 1.3 and 1.9 m3 s-l. Linear relations are present for Q as low as3.5 m s-l [Figure g(b)]. Although the exponential correlation coefficient for Figure 3(a) is Y = -0.95, the relationship can be representedby two straight lines asindicated; losscan then be approximated by the method of Hydes & Liss (1977) as extended by Officer (1979). Denoting C,*as the S = ogOextrapolation of the linear lower estuary salinity distribution and C, as the freshwater endpoint DSi concentration, then the fractional losswithin the estuary (G) is given as G = (C,-C,*)/Cp42%. Th’IS compareswith world values reported by Liss (1976) as ranging up to 30%. Part of the difference betweenour finding and Liss’ssummary is due to the method of evaluating loss,and the lack of endpoint samplesused by others. As further shown by Officer, the zone of non-linear uptake [B in Figure 3(a)] may be relatively restricted and lie between two non-uptake (linear decrease)regions. For this date the B zone is in a region of high phytoplankton population as inferred from the relative fluorescence (RF) values shown in Figure 4(u). The uptake rate coefficients (2) can be Q G--co* where c = 3 mg 1-l isthe averageconcentrationin region B expressedasA= - v ( c 1 of volume V. For VW 2 x 10~m3, a = 0.039 day-l. RF values on this date were the greatest of any survey. In general, values were high during high insolation, low runoff periods. The linear, low insolation, high runoff RF values were all z$&,. Uptake computed asabove resultedin G = 46% C=3mgl-l, V=3x10Em3 and 1=o.o42day- l. While maximum RF values were about eight times greater for Figure 3(a) than 3(n, fl ow wasabout 0.7 times asgreat while G and il values were about equal. Since we did not identify the plankton population associated with RF, we cannot speculateasto 1; G, in addition, would require more information than 1500 (0) 1250

-

3 E

750

-o

.-9 z‘0

500-

(b) 0

0

cc

0 250

00

8 6 OO

I IO

O* I 20

0

d

poo L 0

3Q Solinity

Figure 4. Relative and (b) zz August

0.0 IO

.o”‘~ 20

30

Wk.J

fluorescence OS. salinity, Yaquina Estuary, (a) 14 October 1977. Surface samples (O), bottom samples (0).

1976

566

R.J.

Callaway

6

D.

T. Specht

provided by a single set of observations as to its applicability in a steady-state analysis. In general, however, it has been found (Karentz & McIntire, 1977) that the distribution of diatom species in the Yaquina is strongly influenced by runoff and that plankton assemblages in spring, summer and fall had fewer diatom species and exhibited a more rapid rate of change of species composition than in winter. In this small coastal-plain estuary it is clear that residence time is the dominant factor determining whether the longitudinal distribution of silicon is described as either ‘conservative’ or ‘non-conservative’, conditions for removal being present. This result was derived from our quasisynoptic, essentially one-dimensional, sampling scheme. Preliminary examination of our data for dissolved manganese (Callaway, Specht & Ditsworth, in preparation) show apparent addition of manganese modulated in such a way as to approach linearity with an increase in flow. Residence time must be fully considered in any discussion of chemical processes in estuaries. This has not been the general practice in the estuarine chemical oceanographic literature; the reasons have been those of simple omission or the difficulty in determining residence time in most cases.

Acknowledgements We wish to thank George Ditsworth and Allen Teeter for assistance in the field and Daniel Krawczyk for supervising the chemical analyses. In addition, we thank Drs J. D. Burton, R. Ozretich and C. B. Officer for critical review of the manuscript and valuable suggestions for its improvement.

References Aston,

S. R. 1979 Estuarine chemistry. In Chemical Oceanography Volume VII, 2nd ed. (Riley, J. P. & Chester, R., eds). Academic Press, New York. pp. 362-440. Burton, J. D. 1976 Basic properties and processes in estuarine chemistry. In Estuarine Chemistry. (Burton, J. D. & Liss, P. S., eds). Academic Press, London. pp. 1-36. Callaway, R. J., Ditsworth, G. R. & Cutchin, D. L. 1970 Salinity, runoff and wind measurements, Yaquina Estuary, Oregon. Working Paper 70. U.S. FWPCA, Corvallis, Oregon 42 pp. NTIS #PB210112. Conomos, T. J. 1979 Properties and circulation of San Francisco Bay waters. In San Francisco Buy: The U&arrized Estuary (T. J. Conomos, ed.). AAAS, Washington, D.C. 493 pp. Festa, J. F. & Hansen, D. V. 1976 A two dimensional numerical model of estuarine circulation: The effects of altering depth and river discharge. Estuarine and Coastal Marine Science 4, 309-323. Hydes, D. J. & Liss, P. S. 1977 The behaviour of dissolved aluminium in estuarine and coastal waters. Estuarine and Coastal Marine Science 5, 755-769. Karentz, D. & McIntire, C. D. 1977 Distribution of diatoms in the plankton of Yaquina Estuary, Oregon. Journal of Phycology 13,379-388. Liss, P. S. 1976 Conservative and nonconservative behavior of dissolved constituents during estuarine mixing. In Estuarine Chemistry (Burton, J. D.,& Liss, P. S., eds). Academic Press, London. 93-130 PP. Liss, P. S. & Pointon, M. J. 1973 Removal of dissolved boron and silicon during estuarine mixing of sea and river waters. Geochimica et Cosmochimica Acta 37, 1493-1498. Livingstone, D. A. 1963 Chemical composition of rivers and lakes. Professional Papers, U.S. Geological Survey 440-G. 64 pp. Lorenzen, C. J. 1966 A method for the continuous measurement of in vivo chlorophyll concentration Deep-Sea Research 13, 223-227. U.S. Department of Commerce 1980 National Oceanographic and Atmospheric Administration, Tide Tables, West Coast of North and South America. 234 pp. Officer. C. B. 1979 Discussion of the behaviour of nonconservative dissolved constituents in estuaries. E&a&e d;B Coastal Marine Science 9, 91-94. Officer, C. B. & Ryther, J. N. 1980 The possible importance of silicon in marine eutrophication. Marine Ecology-Progress Series 3, 83-9 I.

Dissolved silicon in the Yaquina Estuary

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Peterson, D. H., Conomos, T. J., Broenkow, W. W. & Doherty, P. C. 1975~2 Location of the non-tidal current null zone in northern San Francisco Bay. Estuarine and Coastal Marine Science 3, I-I I. Peterson, D. H., Conomos, T. J., Broenkow, W. W. & Scrivani, E. P. 1975b Processes controlling the dissolved silica distribution in San Francisco Bay. In Estuarine Research Volume I (Cronin, L. E., ed.). Academic Press, New York. pp. 153-187. Peterson, D. H., Festa, J. F. & Conomos, T. J. 1978 Numerical simulation of dissolved silica in the San Francisco Bay. Estuarine and Coastal Marine Science 7,99-116. Rattray, Jr., M. & Officer, C. B. 1979 Distribution of a non-conservative constituent in an estuary with application to the numerical simulation of dissolved silica in the San Francisco Bay. Estuarine

and Coastal Marine Science 8,489-494. Technicon Instruments rag-71W. Technicon

Corporation Industrial

1973 Silicates in water and wastewater. Systems, Tarrytown, N.Y. 10591. 2 pp.

Industrial Method No.