adams 1985 aquacultural-engineering

7/28/2019 Adams 1985 Aquacultural-Engineering

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Aqua cu l t u ra l Eng i neer ing 4 (1985) 305-311

S h o r t C o m m u n i c a ti o nC a r b o n a t e M i n e r a l F il tr a n ts w i th N e w S u r f a c e s R e d u c eA l k a l i n i ty i n S e a w a t e r a n d A r t if ic ia l S e a w a t e r :P r e l im i n a r y F i n d in g s

A B S T R A C TSi l ica sand ( si li ca), coral (aragoni te ) , and oys ter she l l (ca lc i t e ) were gr oun dto s imi lar par t i c le s i zes a nd p lace d in seawater and ar t i fi c ia l seawater (GP 2M e d i um ) . A l ka l i n i t y a nd pH values o f t he a r t i fi c ia l s eawa t e r dec reased sub -s t an t ia l ly ove r 24 h wh en i n con t a c t w i t h cora l and oys t e r she l l; t he e f f e c t si n seawa t e r were m i nor . O nce a l ka l i n i ty has been r educed , t he m a i n t enanceo f s tab l e p H a t va lues t yp i ca l o f s eawa t er is m a de m ore d i f fi cu l t . The da t a,wh ich are pre l iminary , have prac t ica l appl ica t ion .

I N T R O D U C T I O NT h e c a r b o n a t e m i n e r a l s a r a g o n i t e , c a l c i te , m a g n e s i a n c a l c i te a n d d o l o -m i t e a r e c o m m o n l y u s e d fi lt ra n ts i n t h e c u l t u r e a nd m a i n t e n a n c e o fm a r i n e o r g a n is m s . T h e s e m a t e r ia l s r e p o r t e d l y p r e v e n t t h e p H f r o md e c l i n i n g t o d a n g e r o u s l y l o w l e v e ls . T o s e r v e a s b u f f e r s i n e n v i r o n -m e n t s o f " - p H 8 t h a t b e c o m e i n c re a s i n gl y a c i d ic , c a r b o n a t e m i n e r a l sw o u l d h a v e t o d i s s o lv e a n d c o n t r i b u t e a n i o n s t o t h e s o l u t io n . A n yb u f f e r i n g a c t i v i t y w o u l d b e e x h i b i t e d b y a c h a n g e in a l k a li n i ty , d e f i n e da s t h e n e t n e g a t i v e c h a r g e o f a l l i o n s t h a t i n t e r a c t w i t h H . O n n o n -g e o l o g i c t i m e s c al es t h e o n l y s p e c i e s i n s e a w a t e r th a t m a k e i m p o r t a n tc o n t r i b u t i o n s t o t h e a l k a l in i t y a re b i c a r b o n a t e , c a r b o n a t e , a n d b o r a t e .Contr ibut ion No. 42 , Sea Research Foundation Inc.305Aquacu l t u ra l Eng i neer i ng 01 44-8 609 /85/ $03 .30 - Elsevier AppliedPublishers Ltd, England, 1985. Printed in Great Britain Science


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306 G . A d a m s , S . S p o t t eMATERIALS AND METHODS

Seawater was collected in Long Island Sound off the southwestern tipof Fishers Island on an incoming tide. The water was vacuum-filteredaboard ship through 0.3 t~m sintered glass filters (Gelman, type AE,No. 61631, 47 mm). While at sea, the filtrate (~3 liters) was stored ina glass bottle kept on ice. Fresh seawater was collected and filteredbefore each trial. Salinity values were 32.0 to 33.0~oo both before andafter the experiments, respectively. Artificial seawater was a singlebatch of GP2 Medium (Spotte e t a l . , 1984) with trace ions (solutionsC and D) excluded. This solution contains major ion concentrationstypical of offshore seawater as reported by Brewer (1975). Salinity ofthe artificial seawater before the experiment was 36-0 to 37.5%o andmeasured 36.5 to 38.0%0 at the end. All solutions were refrigerateduntil immediately before use.

Three filtrants were tested: silica sand, oyster shell, and coral. Oystershell and coral were chosen because they represent different poly-morphs of CaCO3 (calcite and aragonite, respectively). Silica sandcontains no carbonates except as soluble surface precipitates. Sourceswere: silica sand (Ottawa Silica Co., Ledyard, Connecticut), crushedcoral (Instant Ocean Hatcheries, Dade City, Florida), and crushedoyst er shell (Agway, Westerly, Rhode Island). The mineral compositionof each material was confirmed by X-ray power diffraction analysis.The silica sand was rinsed sequentially with 3 N HC1 and deionizedwater to remove surface carbonates. All materials were pulverized,ground in a stainless steel commercial blender, and sieved. Particlesranging from 212 to 500/.tm were collected, and lots of 1"0, 10-0and 50-0 ml were weighed and stored in covered glass containers. Volumemeasure was used in an att empt to equalize the mineral surface areas.Temperature was measured with mercury thermometers to +0"5C.Salinity was measured with a hand-held, temperature-compensatingrefractometer (Aquafauna Bio-Marine, Hawthorne, California). Separ-ate pH meters (Orion Model 701A, Orion Research Incorporated, Cam-bridge, Massachusetts) and electrode pairs (Orion 900200 double-junction reference electrode coupled with an Orion 910100 glass pHelectrode) were used to determine pH and alkalinity. The alkalinityprocedure of Almgren and Fonselius (1976) was used. It requiresplotting a calibration curve for a specific electrode pair; afterwards, no


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Carbona te mineral f i l t rant s and b uf fer ing 307o t h e r e l e c t r o d e p a i r c a n b e s u b s t i t u t e d . B o t h s e ts o f m e t e r s an d e le c -t r o d e p a i rs w e r e c a l i b r a te d w i t h N B S b u f f e r s ta n d a r d s o f p H 7 a n d 1 0 .

A l l t ri al s w e r e c o n d u c t e d a t r o o m t e m p e r a t u r e . I n e a c h tr ia l 8 0 0 m lo f s e a w a t e r o r G P 2 M e d i u m w e r e p o u r e d i n to e a c h o f f o u r l - l i te rb o i l i n g fl a sk s . T h e s o l u t i o n s w e r e a e r a t e d t h r o u g h g la s s t u b i n g a t9 4 0 m l r a in -x f o r a m i n i m u m o f 1 2 h , w h i c h a l l o w e d t h e p a r ti a l p r e s s u r eo f C O 2 in t h e s o l u t i o n s t o a p p r o a c h s t e a d y s ta t e a n d t e m p e r a t u r e t oe q u i l i b r a t e a t 2 1 C +- 1 C. V o l u m e f l o w o f a ir w a s r e g u l a t e d b y i nd iv i-d u a l m e t e r s . A t r ia l b e g a n w h e n t h e t e s t f i l tr a n t v o l u m e s o f 1 .0 , 1 0 . 0a n d 5 0 - 0 m l w e r e t r a n s f e r r e d t o t h e fl a sk s c o n t a i n i n g t h e t e s t s o l u t i o n s .B e f o r e s t a r t i n g a t ri al , t h e a e r a t i o n t u b i n g w a s r e m o v e d a n d t h e f l a sk sw e r e s w i r l e d to d i s s o l v e s a lt s f r o m t h e s i de s . V o l u m e s o f 5 0 0 m l f r o me a c h f l a sk w e r e t r a n s f e r r e d t o s e p a r a t e l - li t e r, t h r e e - n e c k , r o u n d -b o t t o m e d f la s ks . T h e g la ss e l e c t r o d e w a s p l a c e d in t h e l e ft n e c k o ft h e f l a s k , t h e r e f e r e n c e e l e c t r o d e i n t h e c e n t e r , a n d t h e a e r a t i o n t u b i n gi n t h e r ig h t n e c k , a n d t h e i ni ti al p H v a l u e w a s m e a s u r e d . A e r a t i o n c o n -t i n u e d f o r 2 4 h t o s t ir t h e s o l u t i o n s a n d a l l o w C O 2 i n t h e s o l u t i o n a n da ir to a p p r o a c h e q u i l i b r i u m w i t h a t m o s p h e r i c C O 2. S u b s e q u e n t l yt h e p H w a s m e a s u r e d i n th e f la s k s a t 1, 2 , 4 , 8 , a n d 2 4 h. T h e re m a i n -in g 3 0 0 m l w e r e u s e d t o d e t e r m i n e t i m e 0 v a l u e s o f a l k a l i n i t y a n ds a l in i t y . A l k a l i n i t y w a s a l w a y s m e a s u r e d i n t r ip l i c a te . A t 2 4 h s o m eo f t h e w a t e r w a s f i l te r e d t h r o u g h a 0 . 3 / a m s i n t e r e d g la s s f il te r , a n dt h e f i n a l a l k a l i n i t y a n d s a l i n i t y w e r e m e a s u r e d .

P r e l im i n a r y e x p e r i m e n t s u s in g s e a w a t e r a n d a r t if ic i al s e a w a t e rw e r e c o n d u c t e d w i t h o u t f il tr a nt s t o d e t e r m i n e n o r m a l p H f l u c tu a t io n si n t h e c o n t r o l s o l u t i o n s .

R E S U L T SA l k a l i n i ty a n d p H m e a s u r e m e n t s a r e s h o w n in T a b l e 1 a n d F i g. 1.

S i l i c a s a n d . T h e p H v a l u e c h a n g e d b y < 0 . 0 3 p H u n i t a n d t h e a l ka -l i n it y b y < 0 . 0 7 m e q l i te r -x ( 2 - 4 % ) i n a ll tr ia l s w i t h s il ic a s a n d i n b o t hs e a w a t e r a n d a r t i f i c i a l s e a w a t e r .

C o r a l . T h e g r e a t e st p H c h a n g e i n s e a w a t e r w a s a d e c r e a s e o f 0- 0 5u n i t t h a t o c c u r r e d i n t h e 5 0 m l s a m p l e . T h e g r e a t e s t c h a n g e i n a lk a -l in i ty , a l s o o b s e r v e d i n t h e 5 0 m l s a m p l e , w a s - - 0 . 1 9 m e q l i t e r -x o r- - 1 1% . I n a r t i fi c ia l s e a w a t e r t h e p H o f t h e 5 0 m l s a m p l e d r o p p e d b y


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3 0 8 G. Adams, S . Spot teT A B L E 1

A l k a l i n i t y a n d p H D a t a o v e r 2 4 h f o r T h r e e V o l u m e s o f F i l t r a n t s A d d e d t o 5 0 0 m lo f S e a w a t e r o r A r t i f ic i a l S e a w a t e r . A l k a l i n i t y D a t a a r e G i v e n a s M e a n s -+ S t a n d a r d

D e v i a t io n s o f T r i p l ic a t e M e a s u r e m e n t sFilrrant Vol . Ini t ial (0 h) p H Final (24 h)(mO pH Alk . l h 2 h 4 h 8 h pH Alk .(m eq liter -1) [m eq liter -1)

SeawaterS i l i c a 0 - 0 0 8 . 0 4 1 . 8 6 -+ 0 . 0 1 8 . 0 6 8 . 0 4 8 - 0 2 7 . 9 2 8 . 0 6 1 . 9 0 -+ 0 - 0 1

1 - 0 0 8 . 0 2 1 - 9 2 - + 0 - 0 2 8 . 0 6 8 . 0 7 8 - 0 7 8 . 0 2 8 . 0 6 1 . 9 2 + - 0 . 0 21 0 - 0 0 8 . 0 3 1 - 8 9 -+ 0 . 0 1 8 . 0 5 8 . 0 4 8 - 0 2 7 . 9 8 8 - 0 6 1 . 9 1 -+ 0 - 0 25 0 . 0 8 . 0 4 1 . 9 1 -+ 0 . 0 1 8 . 0 1 8 . 0 1 7 . 9 9 7 - 9 0 8 . 0 4 1 - 8 7 -+ 0 . 0 1

O y s t e r 0 - 0 0 8 . 0 4 1 . 9 5 - + 0 . 0 4 8 - 0 7 8 . 0 2 8 . 0 0 7 . 9 3 8 . 1 0 1 . 9 7 - + 0 - 0 1s h e l l 1 - 0 0 8 . 0 6 1. 9 2- + 0 . 0 0 8 . 0 7 8 . 0 1 7 - 9 7 7 - 8 8 8 . 0 9 1 . 9 4 -+ 0 - 0 1

1 0 - 0 0 8 . 0 6 1 . 9 3 +- 0 . 0 1 8 - 0 6 7 . 9 7 7 . 9 3 7 . 8 2 8 - 0 8 1 - 9 0 -+ 0 . 0 15 0 . 0 0 8 . 0 6 1 - 8 9 + 0 . 0 0 8 . 0 4 7 . 9 6 7 . 9 3 7 -8 1 8 . 0 5 1 - 7 5 -+ 0 . 0 1

C o r a l 0 - 0 0 8 - 0 8 1 . 7 8 -+ 0 . 0 2 8 - 0 9 8 . 1 0 8 . 0 9 8 - 0 9 8 . 0 9 1 - 8 5 +- 0 - 0 01 - 0 0 8 . 0 9 1 . 7 4 -+ 0 . 0 3 8 . 0 8 8 - 0 5 8 - 0 1 8 - 0 2 8 . 0 9 1 . 7 8 --- 0 . 0 0

1 0 - 0 0 8 . 0 8 1 - 7 8 - + 0 - 0 1 8 . 0 5 8 . 0 2 7 . 9 6 7 - 9 6 8 . 0 6 1 - 6 9 - + 0 . 0 15 0 - 0 0 8 - 0 9 1 . 7 1 -+ 0 . 0 2 8 . 0 3 8 . 0 0 7 . 9 8 7 . 9 6 8 . 0 3 1 . 5 2 - + 0 . 0 1

Arti f icial seawaterS i li c a 0 - 0 0 8 . 1 3 2 . 5 9 + - 0 . 0 2 8 . 1 5 8 - 1 7 8 . 1 6 8 . 1 2 8 -1 5 2 . 6 4 + - 0 . 0 1

1 - 0 0 8 . 1 2 2 .5 1 - + 0 . 0 3 8 . 1 4 8 - 1 5 8 . 1 5 8 - 0 6 8 - 1 5 2 . 5 8 - + 0 . 0 21 0 . 0 0 8 . 1 3 2 - 5 5 + - 0 . 0 2 8 - 1 3 8 . 1 4 8 . 1 0 8 . 0 4 8 . 1 4 2 . 5 9 + 0 . 0 25 0 . 0 0 8 . 1 3 2 . 5 0 + - 0 . 0 2 8 - 1 0 8 . 1 2 8 . 1 2 8 . 0 6 8 . 1 4 2 . 4 8 + - 0 -0 1

O y s t e r 0 . 0 0 8 . 1 4 2 . 3 8 -+ 0 . 0 5 8 . 1 4 8 - 1 4 8 . 1 4 8 -1 0 8 . 1 0 2 . 4 6 +- 0 . 0 2s h e l l 1 - 0 0 8 - 1 4 2 . 3 5 + 0 - 0 1 8 - 1 4 8 . 1 4 8 - 1 5 8 . 0 9 8 - 0 9 2 . 3 3 -+ 0 . 0 2

1 0 . 0 0 8 - 1 4 2 . 3 7 +- 0 - 0 1 8 - 1 2 8 . 1 0 8 - 0 7 8 - 0 3 8 . 0 5 2 . 0 1 +- 0 - 0 25 0 - 0 0 8 - 1 4 2 . 4 7 +- 0 - 0 1 8 . 1 0 8 - 0 9 8 - 1 0 8 - 0 4 8 - 0 2 1 - 7 6 - + 0 . 0 1

C o r a l 0 - 0 0 8 . 1 2 2 . 5 5 +- 0 - 0 1 8 . 1 4 8 - 1 5 8 . 1 2 8 - 1 6 8 . 1 6 2 . 5 4 +- 0 . 0 01 . 0 0 8 . 1 4 2 . 5 2 + 0 - 0 1 8 . 1 3 8 - 1 3 8 - 1 0 8 . 1 4 8 . 1 3 2 . 2 9 - + 0 - 0 1

1 0 . 0 0 8 . 1 4 2 . 5 3 + - 0 - 0 0 8 . 0 8 8 . 0 7 8 - 03 8 .0 1 8 . 0 0 1 4 . 9 - + 0 . 0 25 0 - 0 0 8 . 1 4 2 - 4 6 - + 0 . 0 1 8 . 0 0 7 . 9 9 7 . 9 5 7 . 9 5 7 - 9 3 1 . 3 3 +- 0 . 0 250 -00 2 -32 -+ 0 .0 3 a 1 .21 +- 0 .0 2 a

a D a t a f o r a r e p e a t e d t r i a l ( s e e t e x t ) .


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Carbonate mineral filtrants and buffering

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Fig. 1. Plot o f alkalinity and pH o f seawater and artificial seawater (GP2 M edium)2 4 h a f t e r a d d i t i o n o f f i l tr a n t s . C l o s e d ci rc l es r e p re s e n t c o n d i t i o n s a t t h e s t a rt .A r r o w h e a d s i n d i c a te c o n d i t i o n s a f t e r 2 4 h . N u m b e r s represent the v o l um e o f a

f i l t r a n t ( i n m l ) added. D ashed l ine i s a repea ted t r ia l .

0 - 2 1 u n i t , a n d a lk a l in i ty d r o p p e d b y 1 - 13 m e q l it er -1 o r - - 4 6 % . T h ec h a n g e in t h e 5 0 m l s a m p l e s e e m e d i n o r d i n a t e l y g r ea t , a n d t h is p ar to f t h e e x p e r i m e n t w a s r e p e a t e d 2 w e e k s l a te r u s i n g a d i f f e r e n t b a t c ho f a r t if ic i a l s e a w a t e r . R e s u l t s w e r e s i m i la r . T h e p H a g a i n d e c r e a s e d b y0 " 21 u n i t . A l k a l i n i t y d e c r e a s e d 1 "1 1 m e q l it e r - 1 ( - - 4 8 % ) , c o m p a r e dw i t h t h e i n it i al v a l u e o f a d e c r e a s e o f 1" 1 3 m e q l it e r - x.


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310 G. Adams, S. SpotteO y s t e r s h e l l . The greatest change in pH in seawater samples was

+0.05 unit, whereas the pH of the 50 ml sample in artificial seawaterchanged by --0.21 unit. The alkalinity changes in the seawater sampleswere small except in the 50 ml sample which decreased by 0.14 meqliter -~ or 7%. The alkalinity of the artificial seawater decreased by0.71 meq liter -1 or 29% in the 50 ml sample.

DISCUSSIONSeawaters in the mixed layer of temperate and tropical oceans aretypically supersaturated with calcite and aragonite (Berner, 1974),and a high degree of supersaturation is required before a perceptiblerate of calcite precipitation can be established on carbonate mineralsurfaces (Berner, 1975). The seawater and artificial seawater used inour experiments were supersaturated with respect to both aragonateand calcite. The ion products in each case, as compared with solubilitymeasurements in Table 3 of Mucci (1983), were: aragonite 150%,calcite 260% (seawater), and aragonite 270%, calcite 275% (artificialseawater). All trials seemed poised to lose CaCO3 by precipitationupon introduction of suitable surfaces. In an experiment similar toours Wollast et a l . (1980) added reagent grade calcite to a systemclosed to the atmosphere. When the system was opened the followingreaction occurred:

Ca 2+ + 2HCO3- = CaCOa(s) + CO2 + H20as CO2 was swept out, the concentration of CO~- increased, and addi-tional CaCO3 precipitated. Moles of CO2 driven into the atmospherewere equal to moles of CO32- precipitated. The loss of alkalinity weobserved is consistent with this reaction because CO~- was lost.In qualitative terms our preliminary findings can be summarized thisway. Silica had no discernible affect on alkalinity and pH in either sea-water or artificial seawater. In the case of alkalinity the magnitude ofthe changes were similar to the standard deviations of the measure-ments. Addition of a carbonate mineral in all situations reduced thealkalinity and pH of seawater and artificial seawater, but the reductionsin artificial seawater were consistently greater. In both solutions largeradditions of filtrant (i.e. larger solid-to-solution ratios) resulted ingreater reductions in alkalinity and pH. Decreases in both factors werealways greater with coral than oyste r shell.


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Carbonate m ineral f i l trants and buffering 311When new carbonate filtrants are placed in contact with seawater and

artificial seawater alka linity is lost rapidly, pH declines, and t he concen-trations of calcium and magnesium are altered. To help minimize thesechanges we r eco mmen d that new filtrants be soaked in seawater orartificial seawater for at least 24 h prior to use. Afterward, the solutionshould be discarded. The alternative of adding sufficient sodium bicar-bonate to counteract the reduction in alkalinity will not prevent theinitial loss of cations.

ACKNOWLEDGEMENTSThe manuscript was reviewed by James W. Atz, Joseph P. Bidwell,John D. Buck, Robert L. Jenkins, and Richard M. Segedi. Patricia M.Bubucis provided technical assistance.

REFERENCES

Almgren, T. & Fonselius, S. H. (1976). Determination of alkalinity and totalcarbonate. In: Methods o f Seawater Ana lys is , ed. K. Grasshoff, Verlag Chemic,Weinheim, pp. 97-115.Berner, R. A. (1974). Physical chemistry of carbonates in the oceans. In: Studies inPaleo-Oceanography, ed. W. H. Hay, SEPM, Tulsa, pp. 37-43.

Berner, R. A. (1975). The role of magnesium in the crystal growth of calcite andaragonite from sea water. Geochim. Cosmochim. Acta, 39,489-504.Mucci, A. (1983). The solubility of calcite and aragonite in seawater at varioussalinities, temperatures, and one atmosphere total pressure. Am. J . Sci . , 283,780-99.Spotte, S., Adams, G. & Bubucis, P. M. (1984). GP2 Medium is an artificial sea-water for culture or maintenance of marine organisms. Zo o Biol. , 3,229-40.Wollast, R., Garrels, R. M. & Mackenzie, F. T. (1980). Calcite-seawater reactions in

ocean surface waters. Am . J . Sc i. , 280, 831-48.Gary Adams and Stephen Spo tteM y s t ic M a r in e l i fe A q u a r i u m ,S e a R e s e a r c h F o u n d a t i o n I nc . ,M y s t i c C T 0 6 3 5 5 , U S A

adams 1985 aquacultural-engineering

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