colt 1986 aquacultural-engineering

7/28/2019 Colt 1986 Aquacultural-Engineering

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Aquacultura-', Engine ering 5 1 9 86 - 4 9 - 8 5

G a s S u p e r s a t u r a t i o n - I m p a c t o n t h e D e s i g n a n dO p e r a t i o n o f A q u a t ic S y s t e m sJ o h n C o l t

The Fish Factory , PO Box 5000 . Davis . Cal i fornia 95617 . USA

A B S T R A C TE xp o s u r e t o g a s s u p er s a tu r a t i o n ca n h a ve a s i g n ( f i ca n t imp a c t o na q u a t i c a n im a l s h e ld i n cu l t u r e sy s t ems , r e s tt lt in g in g a s b u b b l e t r a u m a( G B T ) d u e t o t h e f o r n u z t i o n o f g a s b u b b l e s i n t h e ti s su es a n d va s cu la rsvsten-t. Typically. m o st rese arc h on gas s u p er s a tu r a t i o n h a s been co n -d u c t ed o n s a lmo n id s p ec i e s w h i ch w er e exp o s ed t o a cu t e l y l e t h a l l e ve l s .Th e ch r o n i c e ff ec t s o f s u b l e th a l g a s s u p er s a tu r a t i o n l eve ls t h a t ma y b ep r es en t i n ma n y h a t ch er i e s a r e n o t w e l l i d en t i f i ed d u e t o t h e l o w l eve l so f g a s s u p er s a tu r a t i o n i n vo l ved , a d e la y o J ' l - 2 mo . ,t th s b e fo r e t h e st a rto f mo r ta li ty , a l a ck o f t yp ica l c l i n i ca l s i g n s o f g a s b u b b l e t r a u m a a n ds ign i f i can t seaso na l va r ia t ion in the gas leve l s o f ma ny s t tr face watepw.Ga s b u b b l e t r a u m a ca n b e p r o d u ce d b y i t ( fl u en t w a t e r t h a t is s u p er-s a tu r a t ed o r b y p r o d u c t i o n o f g a s s u p er s a tu r a t i o n w i th in t h e h a tch er y.P r even t i o n o f g a s b u b b l e t r a u m a in h a t ch er i e s w i l l r eq u i r e d eg a s s in g o fi n Jh ten t w a t e r a t t d s o m e p r o ce s s w a t e rs , d e s ig n o f u q u a t i c s y s tems t op r e v e n t p r o d u c t i o n o f g a s s u p e r s at u r a ti o n , a n d p r o p e r o p e r a t i on o f th ew a te r s y s t em a n d w a te r q u a l i t y ma in t en a n ce p r o cess e s .

N O M E N C L A T U R EAB PCg) b l ood

&p~p lA quacttltural

C o n s t a n t fo r e a c h g a s ( T a b l e 1 )B a r o m e t ri c p r e s s u re ( r a m H g )M eas ure d con cent ra t ion o f a gas in wat er ( rag l it er -: !A c c e l e r a t i o n o f g r a v it y (m s - : iB l o o d o r ti s su e p r e s s u r e (r am H g )C o m p e n s a t i n g p r e s s u r e d u e t o s u r f a c e t e n s i o n e f f e c t s ( r a mH g)V a p o r p r e s s u r e o f w a t e r (r am H g )P ar t ia l pressure in gas phase ( mm Hg)G a s t e n s i o n i n li q u id p h a s e ( r a m H g )

4,)Engineering 0 1 4 4 - 8 6 0 9 / 8 6 S 0 3 . 5 0 - - E ls ev ie r A p p li ed S ci cn c c


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C h a r a c t e r i s t i c s o f C o m m o n G a s e sG a s M o l e

b a c t i o nA ~ . , m H ~ m g l i t e r -~ ' -~ ~, ~ _ g

i 0 C 2 o ' ( ' 3 0 CN , { } . 7 8 o 8 4O , O . 2 0 9 4 6A r {}.1}(}934C O , ' 0 - 0 0 0 3 4 5H , {)5 x 1{)-"C H ~ i - 7 x 1 0 -~H ,S

0 . 6 0 7 80 - 5 3 i 80 . 4 2 6 00 - 3 8 4 58 . 4 5 ~t'{16{11

0 4 9 5 3

3 2 -3 1 3 S ' 9 7 4 5 - 1 81 3 - 9 4 1 7" 1 3 2 0 ' 2 21 0 " 1 8 1 2 " 4 9 1 4 - 7 3

0"., ~. IS 0. ..! .417 {1 '57 894 3 1 5 0 4 6 9 ' 3 3 4 9 8 0 8

2 . s - 3 7 3 0 . 5 6 3 6 - 5 80 " 1 4 6 6 0 - 1 9 3 1 0 . 2 4 5 6

" P a r ti al p r e s s u r e ( m m F i g = C , 4~ fl , w h e r e C = c o n c e n t r a t i o n in m g l it er < a n d f l =B u n s e n c o e f f i c i e n t i n li t e r ( l it e r a t m < .B a s e d o n C r o z i e r a n d Y a m a m o t o , 1 9 7 4 ) . D o u a b u l a n d R i le y ( 1 9 7 9 ) . Y a m a m o t o e t a l .

( 1 9 7 6 ) a n d W e i s s ( 1 9 7 0 , 1 9 7 4) ." M o l e f r a c tk m o f C O , is i n c re a s in g : a p p r o x i m a t e v a l u e in 1 9 8 5 ( M a c h t a , 1 9 8 3 ) .

T G P

Z/ 3A P

A PuncompAP"

a P o ; , . , , m ea t ' ,0X

T o t a l g a s p r e s s u r e e x p r e s s e d a s a p e r c e n t o f l o c a l b a r o m e t r i cp r e s s u r eD e p t h in w a te r c o l u m n ( m )B u n s e n ' s c o e f f i c i e n t ( li te r ( li te r a r m ) -z )D i f f e r e n c e b e t w e e n t o t a l g a s p r e s s u r e a n d t h e l o c a l b a r o -m e t r ic p r e s su r e m e a s u r e d b v t h e m e m b r a n e d i f f u s io nm e t h o d ( r am H g )D i f f e r e n c e b e t w e e n t o t a l g a s p r e s s u r e a n d t h e l o c a l p r e s s u r e( b a r o m e t r i c + h y d r o s ta t ic p r e s s u r e ) ( m m H g )D i f f e r e n c e b e t w e e n t ot al g as p r e s s u r e i n s i d e a n a n i m a l a n dt h e lo c a l b a r o m e t r i c p r e s su r e ( m m H g )D i f f e r e n c e b e t w e e n t ot a l g a s p r e s s u r e i n s i d e a n a n i m a l a n da ll c o m p e n s a t i n g p r e ss u r e s ( m m H g )D i f f e r e n t i a l p a rt ia l p r e s s u r e o f a g as ( m m H g )D e n s i t y o f w a t e r ( k g m -3 )M o l e f r a c ti o n ( d i m e n s i o n l e s s )

I N T R O D U C T I O NG a s s u p e r s a t u r a ti o n o f w a t e r is a se r i o u s e n v i r o n m e n t a l p r o b l e m a r o u n dt h e w o r l d b o t h in n a tu r a l a n d h a t c h e r y c o n d i t i o n s . M o s t r e s e a r c h o n g a s


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G a s s u p e r s a t u r a t i u n - i m p a c t o n a q u a t i c ~ ys; e;r :s 5 "

supersaturation has been focused on acutely lethal effects on salmon andtrout, especially under conditions typical of the Pacific Northwest ofNorth America. The water quality criterion for gas supersaturation inthe United States was formulated primarily to protect migratingsalmonids where high levels of gas supersaturation are experienced inthe Columbia river, On the other hand. aquatic animals in hatcheriesmay be chronically exposed to gas supersaturation for a significant partof the year. The present water quality criterion for gas supersaturation isinadequate for the protection of animals exposed to chronic gas levels orsensitive non-salmonid fish during their early development.Recent research supports the division of gas bubble trauma (GBT)into two types depending primarily on the level of supersaturation(Fidler, 1984; Alderdice and Jensen, 1985). At high levels of gas super-saturation, acute GBT is associated with formation of bubbles in thevascular systems and tissues and high mortality. The clinical signs ofacute GBT are distinctive and easily recognizable. At lower levels of gassupersaturation, chronic GBT is associated with extravascular formationof bubbles in the gut, buccal cavity, hyperinflation of the swim bladder,and mortality rates of 1-5% over extended time periods. Depending onthe gas levels and variation with time, both types of GBT may beproduced at a given site.Dissolved gas levels in natural waters may have strong seasonalvariations, commonly peaking in the spring or summer, as well ashaving significant year- to-year variat ion.These factors have slowed therecognition that dissolved gas supersaturation can seriously affectmany aquatic animals even if the typical clinical signs of acute gasbubble trauma are not observed.Hatchery animals are at higher risk to gas supersaturation than wildanimals for several reasons, including the reduced depth of mostculture systems, longer exposure, crowding, and differences in nutri-tion and other factors. The source of gas supersaturation in aquaticsystems may be from the influent water or may be produced within thesystem. Heating, aeration, photosynthesis , and air leaks on the suctionside of pumps inside the hatchery have commonly resulted in gasbubble trauma.The purpose of the paper is to review the pathology of gas bubbletrauma especially as it relates to chronic hatchery exposure, outline theprocesses that may produce gas supersaturation in both natural condi-tions and in the hatchery, document problem areas in the design ofaquatic systems and suggest solutions to gas supersaturation problemsin the hatchery. It is hoped that this information will increase the


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5 2 J . C o ba w a r e n e s s o f t h e i m p a c t o f g a s s u p e r s a t u r a t i o n o n a q u a t i c a n i m a l su n d e r h a t c h e r y c o n d i t i o n s a n d h e l p in t h e p r e v e n t i o n o f g a s b u b b l et r a u m a .

W H A T I S G A S S U P E R S A T U R A T I O N ?A i r i s c o m p r i s e d m a i n l y o f f i v e g a s e s : n i t r o g e n , o x y g e n , a r g o n , c a r b o nd i o x i d e a n d w a t e r v a p o r . T h e c o m p o s i t i o n o f d r y a i r is 7 8 " 0 8 4 %n i t r o g e n , 2 0 " 9 4 6 % o x y g e n , 0 - 9 3 4 % a r g o n a n d 0 - 0 3 4 5 % c a r b o nd i o x i d e . T h e p r e s s u r e o f a n i n d i v i d u a l g a s , if it o c c u p i e d t h e e n t i r ev o l u m e b y i ts e lf , is c a l l e d i t s p a r t i a l p r e s s u r e a n d i s e q u a l t o :

p g = X ( B P - Pw ) ( l )T h e p a r ti a l p r e s s u r e o f a g a s d e p e n d s s l ig h t ly o n t e m p e r a t u r e a s P,~ is af u n c t i o n o f t e m p e r a t u r e . T h e p a r t ia l p r e s s u r e i n t h e li q u id isc o m m o n l y c a l l e d g as t e n s i o n a n d is e q u a l t o :

, C ( 2 >T h e p r e s s u r e r e p r e s e n t e d b y a u ni t c o n c e n t r a t i o n o f d i s s o l v e d g a si n c r e a s e s w it h t e m p e r a t u r e a n d v a r ie s w i d e l y a m o n g d i f fe r e n t c as e s(Tab le 1). At eq u i l ib r ium , the pa r t i a l p res su re o f a gas is equ a l to i ts gast e n s i o n :

D ! = DgT h r e e c o n d i t i o n s m a y e x i st f o r a s i n g l e g a s i n s o l u t i o n :

p / = p ~ ( e q u i li b r iu m )p t > p , _ , ( s u p e r sa t u r a te d )p ! < p g ( u n d e r s a t u r a t e d )

( 3 )

S u p e r s a t u r a t i o n o f a si n g le g a s m a y n o t p r o d u c e g a s G B T .T h e p o t e n t i a l f o r m a t i o n o f g a s b u b b l e s d e p e n d s o n t h e d i ff e r e n c eb e t w e e n t h e b a r o m e t r i c p r e s s u r e a n d t h e t o ta l g a s p r e s s u r e :t o t a l g a s p r e s s u r e = p ; O , + p ; N 2 + p 1C O 2 + p ; A r + P ,, (4 )

b a r o m e t r i c p r e s s u r e = p ~ O 2 + p ~N 2 + p ~ C O 2 + p~ A r + P~ (5)T h r e e c o n d i t i o n s m a y e x i s t :

t o ta l g a s p r e s s u r e = b a r o m e t r i c p r e s s u r e ( e q u i li b r iu m )


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G a s s ' t p er x a t u r a t io t t - - i m p a c t o n a q u a t i c s y s t e m s 53total gas pressure > barometr ic pressure (supersaturated)total gas pressure < barometr ic pressure (undersaturated)The difference between total gas pressure and barometric pressure

is called the differential pressure and indicated by the symbol AP. Thisparameter can be measured directly with several types of membrane-diffusion instruments (Fickeisen e t a l . , 1975: D'Aoust and Clark, 1980;Bouck, 1982) and is the preferred way of reporting gas supersaturation(Colt, t983). The AP is the best predictor of the danger from gassupersaturation. If the AP< 0, then gas bubbles can not form regard-less of the degree of supersaturation of a single gas.Gas supersaturation may also be reported as a percentage of localbarometric pressure. Since water vapor contributes to the pressurethat inflates bubbles, Colt (1983) r ecommended that total gas pressureas a function of local barometric pressure be computed from:

TGP% = [ -B--P J 100 (6)Some workers subtracted the vapor pressure of water from thenumera tor of eqn (6):

BP+ AP- P,,,TGP% = BP 100 (7)The differences between these two forms of the equation becomeespecially critical at low AP values and in warm water.The actual risk to an individual animal depends on the AP (D'Aouste t a l . , 1980) and the animal's position in the water column (Knittel e tal., 1980). Tile AP value is measured with respect to the water surface.The A P that the animal present exper iences is equal to the differencebetween the total dissolved gas pressure and the local pressurebarometric+hydrostatic pressures). This is the uncompensated APor TGP) and is equal to:

A P u ,l ~o n,~ = A P - , o g Z (8)O P '

TGPu,comp LBP+,%ZJ t00 (9 )The value of ,o~'~ s expressed in mm Hg per meter of water depth, anddepends both on temperature and salinity (Colt, 1984b). At 20C, the


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54 J. Coltvalue of ,o g is equal to 74.3 mm Hg m -~. Therefore. the values ofA P,,,~,,.~r and TGPun~o~p decrease 74.3 mm Hg m -~ and 10.7 percentagepoints'm-~. respectively. Submergence of a few meters can si~nificant']Yreduce the effects of a given AP on aquatic animals.

Equations (8) and (9) assume that both temperature and AP areuniform with depth. In lakes and reservoirs, these assumptions may notbe valid. To compute the AP~,~,,~p and TGPu~o~p under these condi-tions one may use a membrane-diffusion instrument that can belowered to a specific depth, or obtain water samples as a function ofdepth and analyze the dissolved gas concentrations using gaschromatography or Van Slyke apparatus (D'Aoust and Clark, 1980:Mathias and Barica, 1985). Sampling and transport of water samplescan have a critical impact on the accuracy of gas analysis performed inthe laboratory. The AP at the i n s i r e temperature can be computedfrom the equations presented by Colt(1983).While a APuncom p 2> (') is required for the formation of gas bubbles, theactual bubble formation inside an aquatic animal is much more com-plex. It is important to note that bubble formation depends on the localA P , . ~ , , ~ p inside the aquatic animal which may be less than or greaterthan the computed AP,~,~,,mp (eqn (8)) in the water and will va~' withinthe animal. Other compensating pressures (Bouck. 1980) resultingfrom tissue or blood pressure and surface tension effects need to beconsidered. The uncompensated AP inside an animal is thereforeequal to:

A P ',,~ o,, v = A P ' - , o g Z - Pt,,,,,,,~- P,u,,~,~ (10)The actual process of bubble formation may be influenced by thesurface tension of the blood, number and size of nucleation sites forbubble growth, compliance characteristics of the vascular system, gasdiffusion rates through the animals integument, and functionalproperties of the swim bladder, if present (Fidler, 1984).The biological risk of a given AP to aquatic animals depends on theratio of (nitrogen+argon):oxygen. Therefore. information on com-posit ion of the dissolved ~.oases is needed. This information iscommonly repor ted in terms of nitrogen + argon and oxygen satura-tion, differential partial pressures, or as a partial pressure ratio.The reporting of component gases as a per cent of saturation shouldbe discouraged (Coh, 1983). In older works, the per cent saturation ofnitrogen+argon gas may be the only measure of gas supersaturationreported as it was thought initially that only nitrogen+argon wasresponsible for GBT.


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G a s s u p e r s a t u r a t i o n - - i m p a c t o n a q e ta t ic s y s t e m s 5 5T h e p a r t i a l p r e s s u r e r a t i o is e q u a l to :

(N : + Ar):O_. = P _ ' , ' . - A r ~ l )P o :a n d h a s a v a l u e o f 3 .7 7 a t e q u i l i b r iu m . T h e p a r t i a l p r e s s u r e o f o x y g e nc a n b e c o m p u t e d f r o m e q n ( 2 ) , b u t i n t h e m e m b r a n e - d i f f u s i o n m e t h o dt h e g a s te n s i o n o f n i t r o g e n + a r g o n is c o m p u t e d b y d i ff e r e n c e :

p.l = C o . .~., _,,~,*A~ B P + A P - : 0 " . o l S ! - P , , 1 2 )/ ~ ( ) :lT h e v a l u e o f P ~.+A f c o m p u t e d f r o m e q n ( 1 2 ~ i s a c t u a l l y th e g a s t e n s i o n

o f n i t r o g e n + a r g o n + c a r b o n d i o x i d e + a n y o t h e r g a s e s p r e s e n t . U n d e rt y p i c a l c o n d i t i o n s t h e p r e s s u r e c o n t r i b u t i o n f r o m c a r b o n d i o x i d e i s t o os m a l l t o b e m e a s u r e d a c c u r a t e l y a n d i s g r o u p e d w i t h n i tr o g e n + a rg o n .T h e d i f f e r e n t i a l p a r t i a l p r e s s u r e o f a s i n g le g a s is e q u a l t o :AP~ = p : : - p~ 13)

a n d

A d d i t i o n a l i n f o r m a t i o n o np a r a m e t e r s c a n b e f o u n d in C o l t (1 9 8 4 b ) .

r~

a P = = v ag 14)i =1

t h e c o m p u t a t i o n o f g a s s u p e r s a t u r a t i o n

G A S B U B B L E T R A U M AG a s b u b b l e t r a u m a ( G B T ) h a s b e e n r e p o r te d in a w i d e n u m b e r o fo r g a n i s m s , i n c l u d i n g fi s h es ( W e i t k a m p a n d K a t z , 1 9 8 0 ) , s h r i m p( L i g h t n e r e l a l . , 1 9 7 4 ; S u p p l e e a n d L i g h t n e r , 1 9 7 6 ) , o y s t e r s a n d c l a m s( M a l o u f e t a l . , 1 9 7 2 ; G o l d b e r g , 1 9 7 8 ) , a b a l o n e ( E l s t o n , 1 9 8 3 ) a n da m p h i b i a n s ( C o l t e t a l . , 198 4a ,b ) . W he n the APoncomp ins ide an a qua t ica n i m a l i s g r e a t e r t h a n z e r o , b u b b l e s m a y f o rm i n t h e b l o o d a n d t is s ue s .T h e c l i n i c a l s i g n s o f G B T a n d e f f e c t s o n a q u a t i c a n i m a l s d e p e n d o nthe spec ies and l i f e s t age . The b io log ica l e f fec t s o f gas supersa tu ra t iona r e b e s t d o c u m e n t e d i n fi sh a n d e s p e c i a l l y i n t h e s a lm o n i d s . P h y s i c a l a n db io log ica l f ac to rs may modi fy the e f fec t s o f a g iven AP in the ha tcherye n v i r o n m e n t . A d d i t i o n a l i n f o r m a t i o n o n t h e b io l o g ic a l ef fe c ts o f g a ss u p e r s a t u r a t i o n o n f i s h i s p r e s e n t e d b y J e n s e n e t a l . (1985) , Wei tkampa n d K a t z ( 1 9 8 0 ) a n d Wo l k e e t a l . ( 1 9 7 5 ) .


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56 J . C o l tRecent research strongly supports that GBT must be thought of interms of two types: chronic GBT and acute GBT (Fidler, 1984; D. F.Alderdice, pers. comm.). Chronic GBT occurs in salmonids when theAP ranges from 38 to 76 mm Hg, and acute GBT at Ap > 76 mm Hg.

The boundary between the two types of GBT depends on a number ofvariables; the action of some of these is as yet imperfectly understood.They include depth of the animal in the water column, temperature,animal size and ratio of (N z +Ar):O_,. These variables, recognizedearlier by a number of investigators, are now seen as anci lla~~variablesthat modify the AP-ET~0 response.A c u t e G B T

Acute GBT is associated with intravascular symptoms involvingbubble formation in the vascular system and tissues leading to the largearray of clinical signs associated with damage to tissue and vascularocclusions, and resulting in high rates of mortality (up to 100%) inshort exposures (4- 10 days). The specific clinical signs depend on thelife stage and species.E g g sEggs and newly hatched fry appear to be resistant to high AP values. Insteelhead trout ( S a l m o g a i r d n e r i ) , A P values up to 200 mm Hg had noeffect on hatching (Nebeker e t a l . , 1978). In some types of incubationsystems, attachment of bubbles to the e,,,, may float the e ~ out of thesystem and down the drain. The lack of sensitivity of eggs is probablydue to the fact that the pressure within the eggs is higher than 1 atm(Alderdice e t a l . , 1984) and increased solubility of gases in egg yolk(Fidler, 1984). After 1000 h of incubation, the pressure inside the eggsof different salmonids species ranged from 51 to 76 mm Hg abovebarometric pressure (Atderdice e t a l . , 1984).This pressure reduces theAPuncompwithin the egg (eqn (10)).L a r v a e a n d f r yNewly hatched steelhead trout are resistant to AP until about day 16post-hatch (Nebeker e t a l . , 1978). At this point, bubbles formed in themouth, gill cavity and yolk sac. Accumulation of bubbles in the larvaeprevented normal swimming and feeding and eventually trapped thefish at the surface. Over a 90-day exposure starting with fertilization, aAP of approximately 130 mm Hg resulted in 50% mortality.Hyperinflation of the swimbladder has been reported in pinksalmon ( O n c o r h y n c h u s g o r b u s c h a ) subjected to reduced atmospheric


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G a s s , ~ p e ~ a tu r a t io n - - i m p a c t o r a q u a t i c .~):ytetr's 5 7pressure during helicopter transport (Hauck. in press). Hyperinflationof the swimbladder in this case appears to be due to the expansion ofthe gases contained in the swimbladder rather than to transfer of gasesinto the swimbladder. Exophthatmos. cranial swelling, edematous andswollen gill lamallae, hemoperitoneum, gas bubble within the yolk sac,and distention and rupture of the yolk sac membrane were alsoreported.J u v e n i l e s a n d a d u l t sThe 4-day LCs~ value of juvenile and adult fish ranges from 120 to2 2 0 mm Hg (Gray e t a l . , 1982: Weitkamp and Katz, 1980). The 30-dayLC~ of satmonids ranges from 106 to 123 mm Hg (Nebeker and Brett,1976). Acute signs of GBT may develop at AP values as low as60 -87 mm Hg (D. F. Alderdice, pets. comm.).The major clinical signs of acute GBT in juvenile and adult fish areformation of bubbles in the blood (emboli); bubble formation in tissueand organs (emphysema), commonly on the head. in the mouth and inthe fin rays; and protrusion of the eyes (popeye or exophthalmia) Wolkee t a l . , 1975; Weitkamp and Katz, 198()). Formation of bubbles in tissueand organs may result in petechial hemorrhaging, restricted blood flow,necrosis, and increased mortality due to secondary bacterial infectionssuch as A e r o m o n a s h y d r o p h i l i a and V i b r o a ~ i n o l y t i c u s (Colt e t a l . ,t984a,b; Elston, 1983). The formation of c,as bubbles (emboli) and theircirculation in the vascular system may have greater impact on organswith significant mass transfer functions (gills, GI tract and kidneys) dueto smaller capillaries.Gas supersaturation appears to have an "all or nothing" response onthe growth of juvenile fish. Gas levels that result in greater than 50%mortality over 1-3 months had no effect on the growth of surviving fish(Nebeker e t a l . , 1978; Colt e t a l . , in press). The basis of this response isunclear at this time.C h r o n i c G B T

When aquatic animals are exposed to AP values in the range of38-76 mm Hg on a chronic basis, a chronic type of GBT develops andis associated with extravascular symptoms such as bubble formation inthe gut, buccat cavity, hyperinflation or rupture of the swim bladder.and low level mortality over ex tended per iods of time.tn Atlantic salmon S a h n o s a l a r , A P values in the range of 15-40during incubation may result in the formation of a small gas bubble onthe top of the mouth cavity or improper development of the operulum.


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58 J , ( k ) l tThe gas bubble may disappear, but heavy mortality may occur 6-8weeks later when the fish start to feed (Peterson, 1971 ).

In striped bass larvae (M o r o n e s a x a l i t i s gas supersaturation resultedin over-inflation of the swim bladder and formation of gas in the gut(Cornacchia and Colt, 1984). Clinical signs of GBT were observed atAP values as low as 2 2 mm Hg and mortality' was increased at42 mm Hg. Mortality may have been due to the rupture of the swimbladder as none of the typical clinical signs of acute GBT wereobserved. The period of maximum sensitivity appeared to occur nearthe first filling of the swim bladder and the beginning of feeding. Theaccumulation of gas in these small larvae commonly floated them tothe surface. Flotat ion problems, over-inf lation of the swim bladder andthe accumulation of gas in the gut are the most common clinical signsof GBT observed in small marine fish larvae (Dannevig and Dannevig,1950; Henley, 1952; Kraul, 1983).Chronic GBT appears to have no effect on growth of fish (Wrightand McLean, 1984; Colt et al . , in press). Exposure of juvenile chinooksalmon to AP values in the range of 30-46 mm Hg for 122 daysresulted in a mortality of 4-1% compared to 1-6% in controls (Wrightand McLean. 1984).An cillary or M odifying FactorsPhysical and biological factors can significantly modify the effects of agiven AP. Some of the most important factors in aquatic systems arediscussed below.D e p t hThe APLl,~,,mr decreases by approximately 74"3 mm Hg m -I (Colt,1984b) if the A P and t emperature are uniform with depth. The abilityto detect lethal gas levels and avoid acute GBT by sounding does notappear to be well -developed in fish (Weitkamp and Katz, 1980).Recent work with coho salmon ( O n c o r h y n c h u s k i s u t c h ) shows that fishincreased their mean depth to alleviate the symptoms of GBT up to aA P o f 84 mm I--Ig(Shrimpton, 1985). Above this AP, the fish no longerremained below a depth that compensated for the AP and increasedsigns of stress were evident. Increasing the depth of the culture systemscan offer passive depth compensation by allowing the fish access togreater depths (Ebel, 1969; Lund and Heggberget. 1985).( N i t r ogen + ar gon): oxyg enIncreasing the partial pressure ratio of (nitrogen+argon):oxygenincreases the lethal effects of a given AP (Nebeker er al., 1976, 1979;


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Gas supersaturation -- impact on aquatic systems 59R u c k e r , 1 9 7 6 ). R e g a r d l e s s o f th e v a l u e o f t hi s ra t io , t h e A P 'i n s i d e th e a n i m a l m u s t b e g r e a t e r t h a n 0 f o r th e i n f l at i o n o f g a sb u b b l e s .Feeding and dietF a s ti n g a p p e a r s t o i n c r ea s e t h e im p a c t o f a g i ve n A P ( C o r n a c c h i a a n dC o l t , 1 9 8 4 ; B o u c k a n d K i n g , in p r e s s) . F i s h r e c e i v i n g 3 0 0 n ag a s c o r b i ca c id k g -t o f f o o d w e r e m o r e t o l e r a n t o f g as s u p e r s a t u r a t io n ( B o u c k a n dK i ng , in p r e s s ) t ha n f i s h r e c e i v i ng no v i t a m i n C . F i s h r e c e i v i ng 10 00 nagk g -L v i t a m i n C w e r e i n t e r m e d i a t e i n r e s p o n s e .Intermittent exposureJ u v e n i le s a l m o n a n d t r o u t c a n t o le r a t e an a c u te l y l et ha l A P 1 70 m m H g )f o r 16 h da y -~ if t he y a r e r e t u r ne d t o s a t u r a t e d w a t e r f l-)r t he o t h e r 8 h( M e e k i n a n d T u r n e r , 1 9 74 ).P r o d u c t i o n o f g a s b u b b l e d i s e a s e in sa t u r a te d w a t e rI t i s c o m m o n l y a s s u m e d t h a t t h e A P i n s i d e a n a q u a t i c a n i m a l i s l e s st h a n o r e q u a l t o t h e , 5 P o f t h e w a t e r . T h i s a s s u m p t i o n Is d e f i n i t e lyi n c o r r e c t f o r o x y g e n in tw o i m p o r t a n t o r g a n s o f fi sh e s: r e te m i r a b i le o ft h e s w i m b l a d d e r a n d c h o r o i d a l r e t e m i r a b i l e o f t h e e y e {F bin ge, 1 9 8 3 ).T h e s e o r g a n s u s e a c o u n t e r c u r r e n t - c o n c e n t r a t i n g m e c h a n i s m t os e c r e t e o x y g e n i n t o t h e s w i m b l a d d e r o r p r o d u c e h i g h o x y g e n p a r t i a lp r e s s u r e s in t h e r e ti n a . It is p r o b a b l y n o t a c o i n c i d e n c e th a t t h e s e t w oo r g a n s c o m m o n l y s h o w c l i n ic a l s ig n s o f G B T .

E x o p h t h a l m i a h a s b e e n o b s e r v e d in A t l a n t i c c o d {Gadus m o r h u a )a n d r o c k f i s h (Sebastes s p p .) h e l d i n s a t u r a t e d w a t e r s ( D e h a d r a i , 1 9 6 6:E n g e l m a n et al., 1 9 8 4 ) . G a s b u b b l e s w e r e o b s e r v e d i n t h e e v e s o f t h ec o d . F i s h t h a t a r e v i s u a l f e e d e r s t y p i c a l l y h a v e h i g h o x y g e n p a r t i a lp r e s s u r e s in th e r e t i n a (W i t te n b e r g a n d W i t te n b e r g , 1 9 74 ) a n d m a y b ea t a g r e a t e r r i sk , e s p e c i a l ly s p e c i e s t h a t i n h a b i t t h e m i d w a t e r o r b o t t o mz o n e s . I n a d e q u a t e h y d r o s t a t i c c o m p e n s a t i o n m a y r e s u l t i n t h e f o r m a -t io n o f g as b u b b l e s if s u c h s p e c i e s a r e h e l d in s h a l lo w r e a r i n g s y s t e m se v e n w h e n t h e A P ~< 0 .W a t e r q t , a l i t y c r i t e r i a a n d ' s a f e ' A PT h e w a t e r c r i te r i o n f o r g a s s u p e r s a t u r a t i o n e s t a b l is h e d b v t h e U SE n v i r o n m e n t a l P r o t e c t io n A g e n c y is 1 10 % o f b a r o m e t r i c p r e s s u r e o r7 6 m m H g . T h i s c r i te r i o n i s i n a d e q u a t e t o p r o t e c t t h e m o r e s e n s i t iv es p e c ie s o f n o n - s a l m o n i d f is h o r s a l m o n i d s e x p o s e d t o c h r o n i c g ass u p e r s a t u r a t i o n .


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6 0 ./ . C o / t

D e t a i l e d i n f o r m a t i o n o n t h e c h r o n i c e f fe c ts o f g as s u p e r s a t u r a t i o no n a q u a t i c a n i m a l s i s l a c k i n g . S m a l l m a r i n e f i s h l a r v a e s u c h a s s t r i p e dba s s . he r r i ng i iClupea harengus) a n d m u l l e t (M ugiI cephalus) a p p e a r t ob e v e r y s e n s it iv e to G B T . B a s e d o n p r o d u c t i o n p r o b l e m s , t h e A t l a n t ics a l m o n a n d L a k e t r o u t (Salvelinus namaycush) a r e m o r e s e n s i t i v e t og a s s u p e r s a t u r a t i o n t h a n r a i n b o w t r o u t (Sahn o gairdneri) o r s t e e l h e a dt ro u t . A P v a l u e s in th e r a n g e o f 2 0 - 4 0 m m H g m a y p r o v e l e th a l t os o m e o f t h e m o r e s e n s it iv e s p e c ie s . F o r s o m e f is h, G B T m a y b ep r o d u c e d b y A P v a l u e s l es s t h a n o r e q u a l t o z e ro w h e n h e l d i n s h a l lo wr e a r i n g s y s t e m s .

M E C H A N I S M S F O R T H E P R O D U C T I O N O F G A SS U P E R S A T U R A T I O N

G a s s u p e r s a t u r a t i o n c a n b e p r o d u c e d b y a v a r i e ty o f p h y s i c al an d b io -l og ic a l p r o c e s s e s . S e v e n m e c h a n i s m s c a n p r o d u c e g a s s u p e r s a t u r a t i o na n d in a s p e c i f ic s it u a t i o n s e v e r a l m e c h a n i s m s m a y b e in v o l v e d .P r e v e n t i o n o f g a s b u b b l e d i s e a s e i n h a t c h e r i e s w i l l r e q u i r e a n u n d e r -s t a n d i n g o f t h e b as ic m e c h a n i s m s th a t p r o d u c e g as s u p e r s a t u r a t i o n .D i s c u s s i o n o f ga s s u p e r s a t u r a t i o n w ill b e b a s e d o n A P v a lu e s , o r APo, inc a se s w h e r e o n l y o x y g e n w a s d e t e r m i n e d .H e a t i n g o f w a t e r sT h e s o l u b il i t y o f g a se s d e c r e a s e s w i th i n c r e a s i n g t e m p e r a t u r e . F o re x a m p l e , t h e s o l u b i l i t y o f n i t r o g e n a t 1 0 C is 1 8 " 1 4 m g l i te r - t, b u t iso n l y 1 6 .3 6 m g l i t e r - t a t 1_ C . T h e r e f o r e , if s a t u r a t e d w a t e r a t 1 0C ish e a t e d w i t h o u t a l lo w i n g t h is e x c e ss t o e s c a p e , t h e n i t r o g e n c o n c e n t r a -t i o n w o u l d b e 1 1 0 ' 9 % o f s a t u r a t i o n o r e q u a l t o a A P N,_.~ ,~ v a l u e o f+ 6 4 -5 m m H g . T h e A P r e s u lt in g f r o m h e a t in g s a t u r a t e d w a t e r i ni ti al lya t 0 , 15, 30 C is s h ow n i n F i g . 1 . F o r a g i ve n i nc r e a s e i n t e m pe r a t u r e , t her e s u l t in g A P is g r e a t e r a t a l o w e r i ni ti al t e m p e r a t u r e .I c e f o r m a t i o nT h e s o l u b i li ty o f g a s e s i s i n c r e a s e d a s w a t e r is c o o l e d a n d , u n l e s s g a s ist r a n s f e r r e d i n to t h e w a t e r , n e g a ti v e A P v a lu e s w il l b e p r o d u c e d . A s i cef o r m s , d i s s o l v e d g a s e s a r e q u a n t i t a t i v e l y e x p e l l e d a n d c o n c e n t r a t e d i nt h e r e m a i n i n g w a t e r . In s h a l lo w l a ke s w i th a p p r e c i a b l e i ce f o r m a t i o n( i . e . p o t h o l e l a k e s i n C a n a d a ) , l e t h a l d i s s o l v e d g a s l e v e l s m a y b ef o r m e d u n d e r t h e i ce i n t h e s p r i n g ( M a t h i a s a n d B a r i c a , 1 9 8 5) . A s i ce


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G a s s t ~ p e r s a ' u r a t i o n - - i m p a c t o n a q t~ a gic s vs re ~n .f 6 1180 /160 /14o lnitialTemperature'C~ / /

,:o j / / /I ~ )

E~ 8 o

3o

2O

AT,CF i g . 1 . E f f c c t s o f h c a t i n g o n A l ' a s ~ u m i n g n o g a s t r a n s f e r C o l t , 1 9 8 4 b ).

f o r m s o n t h e su r f a c e o f t h e l a k e , t r a n s f e r o f g a s to t h e a t m o s p h e r e isp r e v e n t e d .T h e m a g n i t u d e o f t h e r e s u lt in g A P w ill d e p e n d o n t h e ra ti o o fi c e : to t a l l a k e v o l u m e ( ic e + w a t e r) , t e m p e r a t u r e a t f r e e z e - u p , f in a l t e m -p e r a t u r e a n d d i s s o l v e d o x y g e n ( F i g . 2 ) . I n l a k e s , t h e r e s u l t i n g A P i sh i g h l y n o n - u n i f o r m i n t h e v e rt i c a l d i r e c t i o n ( M a t h i a s a n d B a r ic a ,1 98 5 ) a n d A P v a lu e s b o t h a b o v e a n d b e l o w t ho s e c o m p u t e d f ro ms o l u t e f r e e z e - o u t c o n s i d e r a t i o n s (F ig . 2) m a y b e p r e s e n t .M ixing of waters o f different temperatureT h e v a r i a t i o n o f g a s so l u b i l i ty w i t h t e m p e r a t u r e is n o t l i n e ar . T h e m i x -i ng o f w a t e rs o f d i f f e r e n t t e m p e r a t u r e s c a n r e su l t in s u p e r s a t u r a t e d g asl ev e ls , e v e n if b o t h w a t e r s a r e i n it ia l ly at e q u i l i b r i u m . T h e z 3P p r o -d u c e d b y m i x i n g e q u a l f l o w s o f w a t e r a t 7~, a n d To + A T is p r e s e n t e d i nF i g . 3 . R e l a t i v e l y h i g h d i f f e r e n c e s i n w a t e r t e m p e r a t u r e s a r e r e q u i r e dt o p r o d u c e s ig n i fi c a nt A P v a lu e s .


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6 2 J . Colt8O4)

7OO

I " / 'D i s so lv e d O x y g e n , m g 1 - - 7

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- I 0 0o.o o.t 0.2 0.3 0.4 0,sV o lu m e o f I c e / V o l u m e o f I c e . W a t e r

F i g . 2 . M a x i n m m A P r e s u l t i n g f r o m s o l u t e f r e e z e - o u t ( b a r o m e t r i c p r e s s u r e = 7 6 0 m mHg. water assumed to be at equilibrium at a freeze-up temperature = I-0C. and finaltem pera ture = 5-0C).

A i r e n t r a i n m e n t

A n y t i m e t h a t a i r a n d w a t e r a r e i n c o n t a c t a t p r e s s u r e s h i g h e r t h a na t m o s p h e r i c , ga s s u p e r s a t u r a t i o n m a y b e p r o d u c e d . F o r e x a m p l e , th isc a n o c c u r i f b u b b l e s a r e c a r r i e d d o w n in th e w a t e r c o l u m n b e l o w as p il lw a y . T h e h y d r o s t a t i c p r e s s u r e o f w a t e r is e q u a l t o7 3 -4 m m H g m -~ a t 2 0 C ( C o l t , 1 9 8 4 b ) . T h e s o l u b i l i t y o f g a s e s i s p r o -p o r t i o n a l t o t h e to ta l p r e s s u r e . T h e r e f o r e , t h e to t al ga s s o l u b i li t y a t1 0 . 4 m i s a b o u t d o u b l e t h e v a l u e a t t h e s u r f a c e a n d r e p r e s e n t s a A P o f7 6 0 m m H g . T h e A P r e su l ti n g f r o m b u b b l e e n t r a i n m e n t d e p e n d sp r i m a r i l y o n t h e d e p t h o f b u b b l e s u b m e r g e n c e , t h e a m o u n t o f a ire n t r a i n e d , a n d t h e d e g r e e o f m i x i n g a n d t u r b u l e n c e . N o g e n e r a l p r o c e -d u r e is a v a i l a b le f or t h e c o m p u t a t i o n o f A P v a l u e s r e s u l ti n g fr o m a i re n t r a i n m e n t , b u t t y p ic a l ly v a l u e s r a n g e f r o m 18 to 4 4 m m H g m -~ o f


15/37

O a s s u p e r s a t u r a ti o r , - - i m p a c t o n a q u a t i c s y s t e m s 6 ":45

35

--c~ ~ nitial C /(To)s Temperature ,Ezo I15,o + '] 0

4 8 12 Ib 20

T o - A T , CF i g . 3 . E f f e c t s o f m i x i n g e q u a l f lo w s o f s a t u r a t e d w a t e r a t l ~ a n d + / ~ , - A T ( C o l t .

1 9 8 4 b ) .

b u b b l e s u b m e r g e n c e (C o l t a n d W e s t e rs , 1 98 2: C o r n a c c h i a a n d C o l t,1 9 8 4 ) .T h e s a m e m e c h a n i s m w il l p r o d u c e g as s u p e r s a t u r a t i o n w h e n e v e rw a t e r a n d a ir a r e i n c o n t a c t a t e l e v a t e d p r e s s u r e s . T h i s m a y o c c u r i f a ir

i s s u c k e d i n t o a p r e s s u r i z e d w a t e r s y s t e m d u e t o l e a k s o n t h e s u c t i o ns id e o f t h e p u m p , i n t a k e s t r u c tu r e s t h a t a re n o t a d e q u a t e l y s u b m e r g e d ,o r t h e u se o f s u b m e r g e d a e r a t io n d e v ic e s .

T h e r a te o f d i s s o l u t i o n o f a ir a n d o x y g e n a p p e a r s t o be a p p r o x i -m a t e l y i 0 t i m e s h i g h e r in s e a w a t e r t h a n in f r e s h w a t e r (K i ls , 1 9 7 6 /1 9 77 ; B o u c k a n d K i n g , 1 9 8 3 ). T h i s i n c r e a s e d t r a n s f e r a p p e a r s d u e t or e d u c e d b u b b l e s iz e r e s u lt in g f r o m i n c r e a s e d s u r fa c e t e n s i o n . T h u s ,s m a l l a i r l e a k s i n a m a r i n e s y s t e m m a y r e s u l t i n h i g h e r A P v a t u e s t h a nin a f r e s h w a t e r s y s t e m a n d b e m o r e d i ff i cu l t t o d e t e c t a s n o b u b b l e sm a y b e p r e s e n t in t h e d i s c h a r g e d w a t e r.


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6 4 J . Col t

Photosynthes i s:A l ga e a n d v a s c u l a r a q u a t i c p l a n t s p r o d u c e o x T g e n d u r i n g t h e d ay :

L i g h t e n e r g yC O ~ + H , O ~ C H , O + O , (1 4)

D u r i n g t h e n i g h t , t h e r e a c t i o n i s r e v e r s e d a n d o x y g e n is c o n s u m e d . T h en e t p r o d u c t i o n d e p e n d s p r i m a r i l y o n a l g ae d e n s i ty , so l a r r a d ia t i o n a n dt u r b i d i t y ( R o m a i r e a n d B o y d , 1 9 7 9 ) . I n s t r e a m s , r o o t e d a q u a t i c p l a n t so r a t ta c h e d a lg a e m a y b e m o r e i m p o r t a n t s o u r c e s o f d i s s o lv e d o x yg e n

~ D e b a n d B o w e r s , 1 9b .~ i. D u r i n g t h e d a y , o x y g e nh a n s u s p e n d e d a lg a e ; " "w i ll b e t r a n s f e r r e d t o t h e a t m o s p h e r e , b u t h i g h le v e l s o f d i s s o l v e do x y g e n m a y a c c u m u l a t e d u r i n g p e r i o d s o f i n t e n s e so l a r r a d i a ti o n a n dl ow w i n d v e l o c it ie s . In t h e f o r w a r d d i r e c t i o n , p h o t o s y n t h e s i s p r o d u c e sa n e t i n c r e a s e i n t h e A P a s th e p a r t ia l p r e s s u r e o f t h e c a r b o n d i o x i d ec o n s u m e d is s m a l l ( T a b l e 1).Pressure changesT h e A P i s e q u a l t o t h e d i f f e r e n c e b e t w e e n t h e t o t a l g a s p r e s s u r e a n dt h e l o c a l b a r o m e t r i c p r e s s u r e . A t a g i v e n t o t a l g a s p r e s s u r e , d e c r e a s e db a r o m e t r i c p r e s s u r e w ill i n c r e a s e t h e A t : T y p i c al c h a n g e s d u e t o s t o r ma c ti vi ty ' a r e i n t h e r a n g e o f + 5 t o - 1 7 m m H g ( C r a ig a n d W e is s,1 9 7 1 ) . A m o r e s i g n i f i c a n t p r e s s u r e d e c r e a s e o c c u r s i n t h e a i r p l a n e o rh e l i c o p t e r t r a n s p o r t o f a q u a t i c a n i m a l s . T h e v a r ia t io n o f a t m o s p h e r i cp r e s s u r e w i th e l e v a t i o n a n d t h e r e s u lt in g A P a r e p r e s e n t e d in T a b l e 2 ,C o m m e r c i a l j e t a i r cr a ft f ly at a p p r o x i m a t e l y 10 0 0 0 m ( b a r o m e t r i cp r e s s u r e = 1 99 m m H g ) b u t p r e s s u r i z e t h e a ir p l a n e a n d c a r g o a r e a t o3 0 0 0 m i b a r o m e t r ic p r e ss u r e = 5 2 6 m m H g).Phys io logica l processD e t a i l e d d o c u m e n t a t i o n o n t he p r o d u c t i o n o f g as b u b b l e s i n t h e s w imb l a d d e r o r e y e o f f is h h e l d in s h a l l o w r e a r i n g s y s t e m s i s l a c k i n g a t t hi st im e . M a x i m u m o x y g e n p a r t ia l p r e s s u r e in t h e r e t i n a o f f is h r a n g e sf r o m 4 0 0 t o 1 3 0 0 m m H g ( W i t t e n b e r g a n d W i t t e n b e r g , 1 9 7 4) .T o c o m -p l e t e ly c o m p e n s a t e f o r t h e s e p a r t ia l p r e s s u re s . 3 - 1 0 m o f w a t e r d e p t hw i l l b e r e q u i r e d . I n f o r m a t i o n i s n o t a v a i l a b l e o n A P o r A P x , + , , , r i n t h ee y e . T h e r e l a t i v e s e n s it i v it y o f v a r i o u s f is h s p e c i e s t o g a s s u p e r s a t u r a -t io n c o r r e l a t e s r o u g h l y w i t h t h e i r o x y g e n p a r t ia l p r e s s u r e i n t h e e y e .


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Ga s supersatur at ion ~ i m p a c t o n a q u a t i c s y s t e m s 6 5TABLE 2

Variation of Barometric Prcssure with Elevationand Resu lt ing A P (U S Standard A tmosphere . 1976)E l e v a t i o n B a r o m e t r i c p r e s s u r e A P

i m ~ ~m m f i g ~m m t ~ )- 500 8O6 - 46

0 760 0500 716 44

1 000 674 861 501) 63 4 1262 000 593 1672 500 560 2003 000 526 2343 500 493 2674 000 462 2985 O00 405 3556 000 354 4067 000 3o8 4528 000 267 4939 00() 231 529

10 000 199 561

B a c t e r i a l a c t i o nB a c t e ri a l a c t io n m a y i n c r e a s e o r d e c r e a s e t h e A P d e p e n d i n g o n t h e r e a c-t i o n a n d t h e s o l u b i l i t i e s o f t h e g a s e s c o n s u m e d a n d p r o d u c e d . T h e p r o -d u c t i o n o f H , S a n d C O 2 w i ll h a v e l it t le e f f e c t o n A P ( T a b l e 1 ). T h ep r o d u c t i o n o f H , w i l l h a v e a t r e m e n d o u s i m p a c t o n A P , w h i le 0 2 , C H ~ ,O , a n d H 2 h a v e i n t e r m e d i a t e e f f e c t s . B a c t e r i a l a c t i o n m a y h a v e a s i g n if i-c a n t e f f e c t o n g a s l e v e l s a s w a t e r p a s s e s t h r o u g h t h e s o i l l a y e r a n d i n t h eb o t t o m w a t e r s o f l a k e a n d r e s e r v o ir s .

G A S S U P E R S A T U R A T I O N I N S U R F A C E A N DG R O U N D W A T E R S

G a s s u p e r s a t u r a t i o n i n n a t u r a l w a t e r s d e p e n d s o n b o t h t h e t y p e o fw a t e r b o d y a n d l o c a l i n f l u e n c e s s u c h a s d a m s a n d e le c t r ic a l g e n e r a t in gp l a n t s . S o m e w a t e r s o u r c e s h a v e b o t h a d a i ly a n d s e a s o n a l v a r i a ti o n i ng a s s u p e r s a t u r a t i o n . A s i n g l e g a s d e t e r m i n a t i o n m a y r e s u lt in a n i n -c o r r e c t a s s u m p t i o n a b o u t t h e r is k f r o m g a s s u p e r s a t u r a t i o n a t a g i v e ns i t e .


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66 Z Co#

G r o u n d w a t e r s a n d s p r i n g w a t e r sT h e A P v a l u e s o f g r o u n d w a t e r s a n d s p r i n g s a re h i g h l y v a r ia b l e ,d e p e n d i n g o n t h e c o n d i t i o n s a t t h e r e c h a r g e a r e a a n d s u b s e q u e n t t e m -p e r a t u r e c h a n g e s o f th e w a t e r. A s t h e w a t e r p a s s e s t h r o u g h t h e so il a n du n s a t u r a t e d z o n e , b a c t e r i a m a y r e m o v e a s i g n if i c an t a m o u n t o f o x y g e na n d a d d c a r b o n d i o x i d e t o th e w a t e r.

G a s s u p e r s a t u r a ti o n m a y b e p r o d u c e d b y t he e n t r a p m e n t o f b u b b l esi n t h e c a p i l l a r y f r i n g e o f t h e b o u n d a r y b e t w e e n t h e u n s a t u r a t e d a n ds a t u r a t e d z o n e s a n d t h e i r t r a n s p o r t b e l o w t h e w a t e r t a b l e ( H e r z b e r ga n d M a z o r , 1 9 7 9 ; H e a t o n a n d V o g e l, 19 81 ). T h e i m p o r t a n c e o f t h i sm e c h a n i s m w i l l d e p e n d o n t h e s p e c i f i c s u b s u r f a c e c o n d i t i o n s i n t h er e c h a r g e a r e a a n d t h e r a t e o f r e c h a r g e .

T h e c h a n g e in t e m p e r a t u r e b e t w e e n t h e b o t t o m o f t h e u n s a t u r a te dz o n e a n d f i n a l d i s c h a r g e a r e a w i l l d e t e r m i n e t h e i n c r e a s e i n A P d u e t ohea t ing . In I s rae l and Sou th Afr ica , the t empera tu re o f the wa te r a t theb o t t o m o f t h e u n s a t u r a t e d z o n e i s a p p r o x i m a t e l y e q u a l t o t h e m e a na n n u a l t e m p e r a t u r e o f t h e r e c h a r g e a r e a ( H e r z b e r g a n d M a z o r , 1 9 7 9;H e a t o n a n d V o g e l , 1 9 8 1 ) . T h e t e m p e r a t u r e a t t h e b o t t o m o f t h e u n -s a t u r a t e d z o n e in a re a s o f m o r e n o r m a l r a in f a ll ( o r r e c h a r g e d u e t o s n o wm e l t ) i s n o t d o c u m e n t e d , b u t m a y b e n e a r e r t o t h e a v e r a g e a i r t e m p e r a -t u r e d u r i n g t h e r e c h a r g e p e r i o d . D e e p c i r c u l a t i o n o f t h e w a t e r o r g e o -the rmal hea t ing may resu l t in s ign i f i can t hea t ing o f the wa te r andincreases in the AP.D e p e n d i n g o n t h e h y d r o l o g i c c o n d i t i o n s , th e A P o f g r o u n d w a t e r s a n ds p r i n g s m a y r a n g e f r o m n e g a t i v e v a l u e s t o a p p r o x i m a t e l y3 0 0 - 5 0 0 m m H g (M a r s h, 1 91 0 ; M a t s u e e t a l . , 1953; Col t e t a l . , 1984a) .S o m e s p r i n g s s h o w r e la t iv e l y c o n s t a n t A P v a l u es o v e r t h e y e a r (M a t s u ee t a l . , 1 9 5 3 ) , b u t o t h e r s s h o w a s e a s o n a l m a x i m u m d u r i n g t h e w i n t e r( H e r z b e r g a n d M a z o r , 1 97 9). S i n c e t h e A P d e p e n d s o n s o m a n y lo c a lf a c to r s , h ig h sp a t ia l v a r i a b i li t y o f A P is c o m m o n i n g r o u n d w a t e r a n ds p r i n g w a t e r s . H i g h A P v a l u e s c o u p l e d w i t h l o w d i s s o l v e d o x y g e n c o n -c e n t r a t i o n s h a v e c o m m o n l y r e s u l te d i n m o r t a l i ty o f f is h w h e n u n t r e a t e dw e ll o r s p r i n g w a t e r h a s b e e n u s ed .S t r e a m sIn sp r ing- fed s t reams , the AP va lues c lose to the sp r ing wi l l r e f l ec t theA P o f th e s p r i n g w a t e r . N a t u r a l a i r e n t r a i n m e n t i n f a st fl o w i n g s t re a m s ,r a p i d s o r w a t e r fa l ls a n d n a t u r a l h e a t i n g m a y b e t h e p r i m a r y m e c h a n i s m sf o r t h e p r o d u c t i o n o f g a s s u p e r a t u r a t i o n i n s tr e a m s . M a x i m u m l ev e lsm a y r a n g e f r o m 4 0 t o 1 50 m m H g ( L i n d r o t h , 1 9 5 7 ; H a r v e y a n d C o o p e r ,1962; Bo uck, 1976, 1984; Col t , 1984a) and oc cur in the spr in g or ear ly


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Gas s,~per.saturation -- imp act on aquat ic systems 6 7

summer. The AP resulting from air entrainment appears to be a directfunction of stream flow and therefore may va~ on a daily basis (Harveyand Cooper, 1962). The diel variation of temperature may be larger inslow flowing streams and channels, especially if riparian trees and vege-tation have been removed (Baltz and Movie. 1984). The resulting APvalues in streams do not appear to produce gas bubble disease in wildfish (Ha~'ey and Copper, 1962: Bouck, 1976), but may result in signifi-cant mortality if the water is used in hatcheries without treatment.The production of gas supersaturation by solute freeze-out (Mathiasand Barica, 1985) in small ice-covered streams is unknown at this time. Ithas generally been assumed that gas supersaturation is not a problem instreams until the spring-time increase in flow and temperature.R i v e r s

The gas levels in rivers will be highly influenced by upstream condi-tions. As the hydraulic gradient decreases, natural air entrainmentbecomes less important, and the AP may decrease due to gas transferto the atmosphere. This effect may be offset by increased heating andphotosynthesis (Colt, 1984a). In slow-moving rivers dominated bythese last two mechanisms, there may be a significant diel fluctuationin AP, the maximum occurring during the late afternoon.The operation of dams and hydroelectric facilities can have a majoreffect on dissolved gas supersaturation. Air entrainment at spillways canproduce AP values in the range of 200-350 mm Hg (Beiningen andEbet, 1970; Heggberget, 1984). Maximum levels occur in the springduring maximum runoff (Legg, 1978) and AP values at a given dam areproportional to the flow passing over the spillway (D'Aoust and Clark,1980), although the individual characteristics of each dam will influencethe AP produced. The partial pressure ratio of (nitrogen +argon):oxygen ,,,,'ill be close to equilibrium below the dam, but biological con-sumption of oxygen or photosynthesis may increase or decrease thisratio in the downstream direction. The transfer of gas to the atmosphereis ve~" slow, especially in conditions as in the Snake and ColumbiaRivers, where the rivers are a series of reservoirs, without any free-flow-ing section between the dams. Spillway entrainment can result in majormortality of adult and juvenile fish (Beiningen and Ebel, 1970) undernatural conditions.Even in cases when no spilling of water occurs, dams may have a signi-ficant impact on the duration and level of gas supersaturation below thedam. Dams capture the highly supersaturated water during the springrunoff and release it over the next 6 months (Colt, 1984a). This is


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68 ~ Co#e s p e c i a ll y i m p o r t a n t a s m a n y l a r g e s a l m o n a n d t r o u t h a t c h e r i e s a r e s i te db e lo w l a rg e da m s . T h e s e f is h a r e e x p o s e d t o h ig h e r u n c o m p e n s a t e d A Pv a l u e s d u e t o t h e s h a l l o w d e p t h o f t y p i c a l c u l t u r e s y s t e m s a n d a r ee x p o s e d f o r l o n g e r p e r i o d s o f t i m e t h a n o c c u r r e d i n t h e r i v e r p r i o r t oc o m p l e t i o n o f t h e d a m . Wh i l e b i o l o g i c a l o x y g e n c o n s u m p t i o n m a y t e n dt o r e d u c e t h e A P w i t h i n t h e r e s e r v o i r , s o l a r h e a t i n g a n d p h o t o s y n t h e s i sc a n i n c r e a se i t ( H a r v e y , 1 9 67 ; G e e n , 1 9 7 5) . C h r o n i c g a s s u p e r s a t u r a t i o ne x p o s u r e r e s u l ti n g f r o m d a m s m a y in c r e a s e d i s e a s e p r o b l e m s i n h a t c h e r yf is h ( C o l t, 1 9 8 4 a) . D u r i n g l o w f lo w c o n d i t i o n s , v a c u u m b r e a k e r s m a y b eu s e d t o p r e v e n t n e g a t i v e t u r b i n e p r e s s u r e s . T h i s p r o c e d u r e c a n r e s u l t i nh i g h l e v e l s o f g a s s u p e r s a t u r a t i o n a n d f i s h m o r t a l i t y ( M a c D o n a l d a n dHyat t , 1973) .

E lec t r i ca l genera to r fac i l i t i e s requ i re coo l ing f low in the range o f0 . l - 4 .0 m 3 s -L a n d r a is e t h e w a t e r t e m p e r a t u r e b y 5 - 2 0 C . D e p e n d i n go n t h e i n it ia l t e m p e r a t u r e a n d A T, t h e r e s u l t in g A P m a y r a n g e f r o m 2 0 0t o 3 0 0 m g H g ( C o l t, 1 9 8 4 b) . T h e d i s c h a r g e f r o m p o w e r p l a n t s m a y b ed e s i g n e d s o t h e h e a t e d p l u m e d o e s n o t r is e to t h e w a t e r s u rf a c e. I f t h ep lume r i ses to the su r face , l a rva l f i sh in th i s zone may be se r ious lyaffec ted.L a k e s a n d r e se r v o ir s

W a r m i n g o f l a k e s d u r i n g t h e s p r i n g a n d s u m m e r c a n p r o d u c e g a ss u p e r s a t u r a t i o n n e a r th e t h e r m o c l i n e ( H a r v e y , 1 96 7). P h o t o s y n t h e s i sa l s o i n c r e a s e s t h e o x y g e n c o n c e n t r a t i o n a b o v e t h e t h e r m o c l i n e . T h em a x i m u m A P w a s in t h e ra n g e o f 1 0 0 - 1 5 0 m m H g ( H a r v e y , 1 96 7) .I n t a k e s t r u c t u r e s f o r h a t c h e r i e s s h o u l d b e d e s i g n e d t o w i t h d r a w w a t e re i t h e r a b o v e o r b e l o w t h e t h e r m o c l i n e i f u s e d d u r i n g t h e s u m m e r .I n s h a l l o w l a k e s , h i g h l i g h t l e v e l s a n d l o w w i n d l e v e l s m a y r e s u l t i n~ P o : v a l u e s fr o m p h o t o s y n t h e s i s i n ex c e s s o f 3 0 0 m m H g , r e s u l ti n g inm a j o r f i s h m o r t a l i t y ( W o o d b u r y , 1 9 4 1 ) . S o l a r h e a t i n g m a y a l s o c o n -t r ib u t e t o th e s u p e r s a t u r a t i o n o f b o t h n i t r o g e n + a r g o n a n d o x y g e n b u tt h e s p e c i fi c i m p a c t o f t h is p r o c e s s is n o t w e l l d o c u m e n t e d .I n s h a l l o w l a k e s w i t h a p p r e c i a b l e i c e f o r m a t i o n , s o l u t e f r e e z e - o u tc a n p r o d u c e l e t h a l g a s s u p e r s a t u r a t i o n . D u r i n g t h e w i n t e r , b i o l o g i c a lc o n s u m p t i o n o f o x y g e n m a y r e d u c e t h e d i s s o l v e d o x y g e n c o n c e n t r a -t i o n t o n e a r z e r o . D u r i n g t h e s p r i n g , p h o t o s y n t h e s i s w i l l i n c r e a s e t h ed i s s o l v e d o x y g e n t o s a t u r a t i o n o r a b o v e b e f o r e t h e ic e is t o t a l l y m e l t e d .T h e i n c r e a s e i n o x y g e n t e n s i o n d u e t o p h o t o s y n t h e s i s p l u s t h en i t r o g e n + a r g o n t e n s i o n r e s u l t in g f r o m i ce f o r m a t i o n m a y p r o d u c e A Pv a lu e s a s h i g h a s 5 6 0 m m H g ( M a t h i a s a n d B a r i c a , 1 9 8 5 ) . T h e m a x i -m u m A P o c c u r r e d i n t h e m i d - w a t e r z o n e . D i l u t i o n w i t h m e l t in g i ce a n d


21/37

G a s s u p e r s a t u r a t i o n - i m p a c t o n a q u a t i c s y s t e m s 6 9

b e n t h ic o r s e d i m e n t o x y g e n d e m a n d r e d u c e d t h e A P in th e s u rf a ce a n db o t t o m z o n e s , r e s p e c t iv e l y . G a s s u p e r s a t u r a t i o n w i ll p r o b a b l y l im i t t h es t o c k i n g o f t h e s e t y p e s o f la k e s u n t i l a l l t h e i c e h a s m e l t e d a n d t h e l a k eh a s r e - e q u i l i b r a t e d w i t h t h e a t m o s p h e r e . A n y w a t e r o b t a i n e d f r o mt h e s e t y p e s o f l a k e s s h o u l d b e d e g a s s e d b e f o r e u s e .A e r a t i o n o f r e s e r v o i r s t o p r e v e n t t h e r m a l s t r a t i f i c a t i o n o r o x y g e nd e p l e t io n c a n a ls o p r o d u c e A P v a l ue s in t h e ra n g e o f 3 0 - 8 0 m m H g( F as t, 1 9 7 9) . T h e m a x i m u m v a l u es o c c u r r e d b e l o w 3 0 m . T h e i m p a c to f t h i s m e c h a n i s m w i l l d e p e n d o n t h e p l a c e m e n t o f w a t e r w i t h d r a w a ls t ruc tu re s a s the z3P in the u pp er l aye rs i s r e la t ive ly low.T h e r m a l d i s c h a r g e s f r o m p o w e r p l a n t s c a n p r o d u c e h i g h l o ca l A Pv a l u e s a n d r e s u l t i n g a s b u b b l e d i s e a s e ( D e m o n t a n d M i l le r , 1 9 7 1 ). T h ei n c i d e n c e o f g as b u b b l e d i s e a s e is h i g h e s t i n th e w i n t e r m o n t h s .M unicipal w ater suppliesT h e A P i n m u n i c i p a l w a t e r s u p p l i e s w i l l r e f l e c t t h e A P o f t h e w a t e rs o u r ce . S i g n if ic a n t a m o u n t s o f a ir m a y b e e n t r a i n e d d u r i n g t r e a t m e n t .H e a t i n g o f w a t e r i n t h e w a t e r d i s t r i b u t io n s y s t e m c a n i n c r e a s e t h e A P,w h i l e b i o l o g i c a l o x y g e n c o n s u m p t i o n c a n r e d u c e i t . M u n i c i p a l w a t e r sf rom deep we l l s m ay con ta in z~P va lues h igh eno ugh to be l e tha l (Col t e ta l . , 1984a) .Aquaculture pondsP h o t o s y n t h e s i s a n d s o l a r h e a t in g c a n p r o d u c e A P o : v a l u es i n t h e r a n g e o f2 0 0 - 4 5 0 m m H g ( T a k a s h i a n d Y o s h i h i r o , 1 97 5; R o m a i r e a n d B o y d ,1979). A t the h igh er A P va lues , a lmo s t com ple te m or ta l i ty o f go ld f i sh( C a r a s s i u s a u r a t u s ) resu l ted . Disso lved oxygen concen t ra t ions wi l l typ i -ca l ly show a d ie l f luc tua t ion , the m axim um APo: va lues occ ur r ing in thela te a f t e rnoon . L i t t l e in fo rmat ion i s ava i l ab le on AP va lues o f APN:+Arv a l u e s i n p o n d s . I n s t r i p e d b a s s p o n d s i n A l a b a m a , m a x i m u m s e a s o n a lA P va lues ranged f rom 300 to 400 m m Hg (Parker e t a l. , 1984) . APX:+Avalues we re con s i s ten t ly pos i t ive , ind ica t ing tha t so la r hea t ing is a s ign if i-c a n t s o u r c e o f s u p e r s a t u r a t i o n .B a y sP h o t o s y n t h e s i s a n d s o l a r h e a t i n g i n b a y s w i t h r e s t r i c t e d c i r c u l a t i o n c a np r o d u c e A P o : v a lu e s i n t h e ra n g e o f 2 0 0 - 2 5 0 m m H g (R e n f r o , 1 9 6 3 )a n d r e s u lt i n m a j o r m o r t a l i ty o f f is h . T h e h i g h e s t A P o , v a l ue s o c c u r r e daf te r severa l c lays o f in tense so la r rad ia t ion and low wind leve l s . L i t t l e


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7 0 J . Co!t

information on Ap values or AP,~..A~ is available. In large bays, bubblesmay penetrate the water column to a depth of 2-3 times the wave height(Kanwisher, 1963) and tend to enhance gas transfer into the water(Atkinson, 1973). This mechanism would produce both nitrogen + argonand oxygen supersaturation.The use of thermal discharges from power plants may cause gasbubble disease if such waters are used in fish culture without degassing(Marcello and Strawn. 1972). The incidence of gas bubble diseaseappears to be more serious in the late fall and winter. For a given A T.higher AP values are produced at lower temperatures (Colt. 1984b).OceansInjection of air by breaking waves can introduce a significant amountof gas in the ocean (Craig and Weiss, 1971; Bieri, 1974). Photo-synthesis can produce APo: values in the range of 50-11() mm Hg(Ramsey, 1962a,b). Maximum Af~: values from photosynthesis occurduring the summer. The direct use of coastal waters for aquatic culturesystems can result in lethal gas bubble disease (Stickney, 1968).

During periods of strong solar radiation and low wind levels, solarheating may increase the surface layer by 2-3C (Bruce and Beatty,1982). This temperature increase coupled with increased salinity due toevaporation may result in gas supersaturation in the surface layer of theocean. This gas supersaturation may have a significant effect on posi-tively phototactic fish larvae.Attraction of fish into heated effluent and production of gas bubbledisease is well documented for power plants on the east coast of theUnited States (McLeod, 1978). Juvenile and adult menhaden(Bevoortia 0,rannus) appear to be the species most commonly attractedinto the heated discharge.

Nitrogen concentrations in the Eastern Atlantic were always super-saturated (Oudot, 1982). The maximum value occurred at the top ofthe thermocline.

PRODUCTION OF GAS SUPERSATURATION WITHIN THEHATCHERYGas bubble disease in hatcheries may be caused by use of surface orgroundwaters that are supersaturated or by production within thehatchery. Degassing of influent water therefore will not prevent all gasbubble disease. Prevention of gas bubble disease in the hatchery" willrequire careful consideration in the physical design and operation of


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Gas supersan~ration - - im pa c t on aqua t ic s)~ terns 71a q u a t ic s y s te m s . T h e u s e o f c o n v e n t i o n a l e n g i n e e r i n g d e s ig n c r i t e ri aa re i n a d e q u a t e f o r t h e d e s i ~ o f s o m e c o m p o n e n t s o f a q u a ti c s ys te m s .C o n d i t i o n s t h a t m a y p r o d u c e l e th a l l e v el s o f g as s u p e r s a t u r a t i o nc o m m o n l y h a v e n o e f f e c t o n t h e e f f i c i e n c y o f w a t e r s y s t e m s , t h e i ro p e r a t i o n , o r p u b l i c h e a l t h , a n d t h e r e f o r e a r e n o t c o n s i d e r e d i n c o n -v e n t i o n a l d e s i g n .H e a t i n g o f w a t er sW h e n w a t e r is h e a t e d m o r e t h a n a fe w d e g r e e s C e ls iu s , th e w a t e r m u s tb e d e g a s s e d p r i o r t o u s e . I t d o e s n o t m a t t e r i f t h e w a t e r i s d i r e c t l yh e a t e d in a b o i l e r o r w a t e r h e a t e r t o t h e fin a l t e m p e r a t u r e o r p r o d u c e db y m i x i n g h e a t e d w a t e r a n d c o l d w a t e r. E l e v a t e d h y d r o s t a t i c p r e s su r ein h e a t e d w a t e r p i p i n g p r e v e n t s d e g a s s i n g u n t i l t h e w a t e r is d i s c h a r g e d .t n s ta t ic o r r e c y c l e s y s t e m s w i t h l o w w a t e r e x c h a n g e r a te s , n a t u r a l g a st r a n sf e r o r d i f fu s e d a e r a t i o n m a y b e a d e q u a t e t o r e m o v e g as s u p e r -s a t u r a t io n . I n t h e s e t y p e s o f s y s t e m s , t h e A P v a l u e s s h o u l d b e m o n i -t o r e d t o v e r if y a c c e p t a b l e g a s le v e ls . W h e n t h e s e t y p e s o f s y s t e m s a r ei n it ia l ly f il le d w i th w a t e r , a n i m a l s s h o u l d n o t b e a d d e d f o r s e v e r a l d a y st o a l lo w t i m e f o r t h e g a s l e v e l s t o e q u i l i b r a t e .M i x i n g o f w a t e r s o f d i f fe r e n t t e m p e r a t u r e sW h e n t w o w a t e r s o f d i f f e r e n t t e m p e r a t u r e s a r e m i x e d , t h e r e s u l t i n gf lo w m a y n e e d t o b e d e g a s s e d p r i o r t o u s e. T h e r e s u lt in g A P f r o mm i x i n g s a t u r a t e d w a t e r s o f d i f f e r e n t t e m p e r a t u r e s is l a r g e r a t l o w i ni ti alt e m p e r a t u r e s ( C o l t , 1 9 8 4 b . T h e n e e d f o r d e g a s s i n g w ill d e p e n d o n t h eA P p r o d u c e d , t h e d e p t h o f c u l t u re s y s t e m u s e d , a n d t h e se n s it iv i ty o fs p e c i e s a n d l if e s t a g e u s e d i n t h e s p e c i f i c s y s t e m .A i r e n t r a i n m e n tE n t r a i n m e n t o f a ir i n to p r e s s u r i z e d w a t e r s y s t e m s is p r o b a b l y t h e m o s tc o m m o n m e c h a n i s m f o r t h e p r o d u c t i o n o f g as su p e r s a tu r a t io n w i th int h e h a t c h e r y . T h i s m a y o c c u r a t th e i n t a k e , a t w a t e r c o n t r o l s t r u c t u r e s ,l o c a t i o n s w i t h i n t h e w a t e r s y s t e m s w i t h s u b a t m o s p h e r i c p r e s s u r e s o rb e d u e t o i m p r o p e r o p e r a t i o n o f w a t e r q u a li ty u n i t p r o c e ss e s . S p ec if ice x a m p l e s o f a ir e n t r a i n m e n t in t h e h a t c h e r y a r e l is te d in T a b l e 3 . T h i sli st m a y n o t i n c l u d e a ll c o n d i t i o n s t h a t r e s u lt i n a i r b e i n g e n t r a i n e d i na q u a c u l t u r e s y s te m s .

M a n y o f t i l e e x a m p l e s i n T a b l e 3 o c c u r s e a s o n a l l y , d u r i n g s p e c i f i ct i mes o r i n s pec i f i c pa r t s o f t he f ac i l i t y . T h i s , coup l ed w i t h t he f ac t t ha t


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72 J . C o l tT A B L E 3

E x a m p l e s a n d C h a r a c t e r is t ic s o f A i r E n t r a i n m e n t in H a t c h e r ie sE xa m ple Character is tics Reference

I n a d e q u a t e s u b m e r g e n c e M a y o c c u r d u r i n g e x t r e m e S e r fl in g et al. (1974 )of i n t ake s t ruc t u re l ow t i de i n m a r i nere su l t i ng in a i r be i ng sy s t em s o r du r i ng l owd r a w n i n to p i p e f lo w c o n d i t i o n s in

C o n t r o l s tr u c t u r e f o ro p e n c h a n n e l f lo w

C l o g g i n g o f i n t a k es t r u c t u r e s o t h a t p i p ei s no t f l ow i ngc o m p l e t e l y f ull

L e a k s o n t h e s u c t i o n s i d eo f th e p u m p

L e a k s i n a r e a s o f s u b -a t m o s p h e r i c p r e s s u r ein w a t e r s y s t e m s

s t r e a m s a n d r i v e r sO v e r - p u m p i n g o f w e lls.

M a y o c c u r d u r in gd r ? ' s e a s o n o r p e r i o d so f l o w r e c h a r g e

\ b r t e x i n g d u e t o in a d e -q u a t e s u b m e r g e n c e ,p o o r d e s i g n o f in t a k es t r u c t u r e o r h ig h w a t e ru s a g e . C a n a l s o o c c u r i nc o n s t a n t h e a d t a n k s a n dh y d r o e l e c t r i c r e s e r v o i r ,r equ i r i ng i n s t a l l a t i on o fba f f l e s o r an t i -vo r t exp l a t e

D r o p s t r u c t u r e s o r w e i r sm a y e n t r a in a ir . M a y b cm o r e i m p o r t a n t it w a t e rand a i r en t e r s a p re s -s u r e w a t e r s y s t e m

M a y b e m o r e s e r io u s i ns y s t e m s t h a t h a v e al a r g e d r o p in e l e v a ti o nb e t w e e n i n t a k e a n d t h eaquacu l t u re f ac i l i t y

L eaks i n suc t i on p i p i ng .M o r c s c r i o u s i n m a r i n cs y s t e m s d u e t o g r e a t e rd i s so l u t i on r a t e o f a ir

A i r l e a k t h r o u g h t h e s h a ftsea l s

N e a r l y c l o s e d v a l v e c a ns u c k a i r i n to s y s t e m . M a yb e m o r e i m p o r t a n t inm a r i n e s y s t e m u s in gvalves wi th fu l l un ions

C o n t r a c t i o n o f f le x ib l eh o s e a n d t u b i n g m a y a ls os u c k a ir a r o u n d t h e h o s ec o n n e c t i o n . M a y a l soo c c u r a t m e d i c a t i o nin jec t ion s i t e i n tub ing

W e s t g a r d ( 1 9 6 4 )

W e s t g a r d ( 1 9 6 4 )

H a r v e y a n d S m i t h ( 1 9 6 1 ),W y a t t a n d B e i n i n g e n( 1 9 7 1 )

M a r s h ( 1 9 1 0 ) , M a r s h a n dG o r h a m ( 19 0 5)

D a n n e v i g an d D a n n e v i g( 1 9 5 0 )


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Gas supersa tura t ion - - impa c t on aquat i c sys temsT A B L E 3 - - cotrtit , ue d

E xa m pl e Characteristics ReferenceOperation of dual watersystems

Operation of sand filter

Aeration

Air-lift pumps

Draining of unused linesmay introduce air. Whenthese lines are pressur-ized. the remaining airmay dissolveExcessive water demandmay suck air into watersystem. May occur whentanks are being filled orin periods of excessivewater usageThe use of submergedaeration devices canproduce high AP values.May be more serious inseries re-use systemsusing highly efficientsubmerged aeratorsThe resuhing AI' dependson submergcnce. Maybe important in thedesign of larval rcarin,,systems

Johnson 1976

Colt and ' -~"'vesters ~19a=)

Cornacchia and Colt/1984i

exposure to moderate gas levels may require several months ofexposu re before mortal i ty is observed , may mak e i t diff icult to deter-mine that gas super satu rat i on is the cause of the mortal i ty and toidentify the source of the gas supersatur at ion.

P h o t o s y n t h e s i s

Marine fish and crustacean larvae may be raised with phytoplankton inwhat is called "green water cul ture '. High light inten sities ( > 3-0 x 10 ~qu an ta s -1 cm -2) an d high algal de nsiti es (Secchi disc


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~ ',- , J . C o l t

A i r tr a n s p o r t o f a n i m a l sTransport of animals by helicopter or ai rplane can result in gas bubbledisease due to reduced barometric pressure. The maximum AP thataquatic animals will be exposed to will depend on the barometric pres-sure at the hatchery and the pressure in the cargo area. For animalsinitiallv at equi librium at sea level, pressurization of the cargo area to3000 m will result in a .AP of 234 mm Hg (Table 2). Animals packedin plastic bags and cardboard boxes may be exposed to pressuressomewhat less than the pressure in the caroo area as box restricts theexpansion of the bag and the reduction of pressure. Animals trans-ported in helicopters may be at greater risk due to the lack of pres-surization and a larger rate of vertical climb and resulting pressurereduction. Prevention of gas bubble disease fore this mechanism mayrequire a pressurized transport container and release of animals belowthe water surface to reduce the AP.~,,~,,mp. Stripping of nitrogen + argongas from the transport water by pure oxygen or reduction of watertemperature will reduce the risk due to gas bubble disease, but willhave no effect on hyperinflation of the swim bladder.P h y s i o l o g i c a l p r o c e s s e sThe natural or physiological production of high AP values within theanimal appears to occur in Atlantic cod and rockfish (Dehadrai, 1966;Engelman et al . . 1984) and may help to explain the basis for swimbladder stress syndrome of sea bass ( D i c e n t r a r c h u s h l b r a x ) (Johnsonand Katavic, 1984) and other small marine fish larvae. The preventionof gas bubble disease in sensitive species may require the use of adeeper culture system to reduce the AP~,,~.mp.

PREVENTION OF GAS BUBBLE TRAUMAThe prevention of gas bubble trauma (GBT) within the hatchery, willdepend on degassing of influent water and some process waters, thedesign and operat ion of aquatic systems to prevent production of gassupersaturation within the hatchery, and possibly design changes andmanagement practices for sensitive animals. The monitoring of APvalues of the influent waters and at key points in the hatchery may helpto identify problems and allow correction before major mortalityOCCURS.


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G a s s ; ~ p e r s a m r a t i o n - - i m p a c t o n a q u a t i c s .y s te r .s 7 5

Des ign changes in the ha t ch e~The prevention of the production of gas supersaturation within thehatcher3" will require careful design and proper operation and main-tenance, Aquatic systems should be designed to minimize the amountof maintenance and monitoring required. Hatcheu staff generally arequite busy with the usual operational duties and may find it impossibleto monitor for air leaks and other problems that can cause gas super-saturation.D e g a s s i n gDegassing will be required when the influent water is supersaturated,after heating of water, and after mixing of waters of different tempera-tures. The design of degassing systems for water sources with a signifi-cant seasonal variation may require a deta iled monitor ing programover at least 1 year or more. Information on AP, dissolved oxygenand temperature should be collected on a weekly basis. Continuousmonitoring of AP (D'Aoust and Clark, 1980; Bouck, 1982) and dis-solved oxygen may allow automatic control of the degassing systemand reduce power costs. A variety of devices have been used fordegassing.

P a c k e d c o l u m n . One of the most widely used devices is the packedcolumn. This consists of a column filled with high surface area plasticmedia. The water runs down through the media in a thin film. Thepacked column can reliably produce AP values in the range of 15-20mm Hg (Bouck e t a l . , 1984). Detailed design procedures for this pro-cess have been presented by Colt and Bouck (1984) and McLean andBoreham (1980). The maximum hydraulic capacity of a columndepends on the size of the media used. For given media, the removalefficiency of the column is independent of flowrate up to a maximumflowrate and then decreases rapidly (Bouck e t a l . , 1984).The height of the column required to produce a given AP dependsstrongly on the influent AP. As the water criterion for gas supersatura-tion is increased !i.e. absolute value decreased), the height of therequired packed column increases significantly (Colt and Bouck,1984). Theoretically, a column of infinite height is required to producea APequat to zero.f 2 t c u u m d e g a s s i n g . For some sensitive species, it may be necessaryto produce AP values equal to or less than zero. In such circumstancesvacuum packed columns can be used (Fuss, 1983), and can be used to


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76 Z Co~

r e d u c e t h e c o l u m n h e i g h t a n d p u m p i n g c o s ts . If v a c u u m d e g a s s in g isu s e d f o r l o w d i s s o l v e d o x y g e n w a t e r , t h e d i s s o l v e d o . ~ ' g e n i n t h ee f fl u e n t m a y b e t o o l o w to b e u s e d in a n a q u a t i c s y s t e m ( M a r k i n g e t a l . ,1 9 8 3 : C o l t a n d B o u c k , 1 98 4).. P r i o r t o u s e o f v a c u u m d e g a s s i n g , it m a yb e n e c e s sa r y to p a ss t h e w a t e r t h r o u g h a n a t m o s p h e r i c p r e s s u rep a c k e d c o l u m n t o i n c r e a s e t h e d i s s o l v e d o x y g e n c o n c e n t r a t i o n( M a r k i n g e t a l . , 1 9 8 3 i .

O t h e r d e v i c e s . W h i l e t h e p a c k e d c o l u m n d e g a s s e r i s p r o b a b l y t h em o s t e f f i c i e n t ( B o u c k e t a l . , 1 9 8 4 ) , t h e r e m a y b e c a s e s w h e r e t h e i r u s ei s n o t c o n v e n i e n t a s t h i s m e t h o d r e q u i r e s a p i p e d w a t e r s u p p l y . U n d e rc o n d i t i o n s w h e r e a d e q u a t e h e a d i s a v a i l a b l e , c a s c a d e s , s i m p l e w e i r s ,s p l as h b o a r d s , l a t ti c e a e r a t o r s o r c o r r u g a t e d i n c l in e d p l a n e s m a y b eu s e d ( R u c k e r a n d H o d g e b o o m , 1 95 3; H a s k e l t e t a l . , 1 9 6 0 ; C h e s n e s sa n d S t e p h e n s , 1 9 7 I : T e b b u t t , 1 9 7 2 ).

D i f f u s e d a e r a t i o n s y s t e m s h a v e a l s o b e e n u s e d t o d e g a s w a t e r s( D e n n i s o n a n d M a r c h y s h y n , 1 9 7 3 ; P e n r o s e a n d S q u i re s , 1 9 76 ). It isi m p o r t a n t t o r e a l i z e t h a t d i f f u s e d a e r a t i o n s y s t e m s o r o t h e r t y p e s o fs u b m e r g e d a e r a t o r s c a n n o t r e d u c e t h e A P to z e r o . F o r d i f fu s e r d e p t h so f I - 2 m , th e m i n i m u m A P p r o d u c e d b y th e s e t y p e s o f a e r a t o r s is int h e ra n g e o f 2 0 - 4 0 m m H g ( C o l t a n d W e s te r s. 1 98 2) .

k i n d e r c o n d i t i o n s o f h i g h s o l id s l o a d i n g a n d l e af f all, c l o g g i n g m a yb e a s e r i o u s p r o b l e m i n a p a c k e d c o l u m n . H o r i z o n t a l s c r e e n s c a n b eu s e d u n d e r t h e s e c o n d i t i o n s ( H a r t m a n , 1983~. T h e i n d i v id u a l s c r e e n sc a n b e r e m o v e d a n d c l e a n e d w h i l e t h e u n it is o p e r a t in g .

U n d e r l a b o r a t o r y c o n d i t i o n s , p la s t ic s p r a y n o z z l e s u s e d in d r i p i r ri -g a t io n s y s t e m s c a n p r o d u c e A P v a lu e s n e a r z e r o f o r f lo w s in th e r a n g eo f 10 - 20 l i te r -t h -~. T h e no z z l e c a n be p l a c e d i n s i de 5(1 m m d i a m e t e rP V C p i p e, a p p r o x i m a t e l y 1 m l o n g . T h e s e s y s te m s a r e i n e x p e n s i v e a n de f f e c t i ve f o r s m a l l f l ow s .W a t e r s u p p l yT h e w a t e r s u p p l y m u s t b e d e s i g n e d t o p r e v e n t e n t r a i n m e n t o f a ir i n tot h e s y st em . T h i s m a y i n c l u d e s p e ci al d e s ig n o f t h e i n ta k e a n d w a t e r c o n -t ro l s t r u c t u r e t o e n s u r e a d e q u a t e s u b m e r g e n c e o f t h e i n t a k e p i p e,i n s t a l l a t i o n o f a u t o m a t i c s c r e e n c l e a n i n g d e v i c e s , i n s t a l l a t i o n o f l o ww a t e r a l a r m s f o r b o t h s u r f a c e w a t e r s a n d w e l l w a t e r s , a n d t h e u s e o fm e c h a n i c a l p u m p s e al s r a th e r t h a n p a c k i n g s e als .

F o l lo w i n g c o n s t r u c t i o n , t h e c o m p l e t e w a t e r s y s te m s h o u l d b e p r es -s u r e t e s t e d t o e n s u r e t h e l a c k o f a n y l e a k s th a t c o u l d a d m i t a ir . W h e na i r i s e n t r a i n e d , i t m a y b e p o s s i b l e t o h e a r t h e a i r a s i t m o v e s t h r o u g ht h e s y s te m . T h i s m a y b e e s p e c i a l l y e v i d e n t a t e l b o w s a n d v a lv e s . T o


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G a s s u p e r s a t u r a t i o n - - i m p a c t o n a q,. ,~ ad c s ~ t e r n s 7 7

h e a r t h e a i r , i t i s n e c e s s a u t o p l a c e o n e ' s e a r o n t h e p i p e . A f t e r t h es y s t e m is o p e r a t i n g , t h e A P o f t h e p r o c e s s w a t e r s h o u l d b e t e s te du n d e r t h e f u ll r a n g e o f p o s s ib l e o p e r a t i o n a l c o n d i t i o n s . I t s h o u l d b en o t e d t ha t a ir e n t r a i n m e n t a r o u n d v a lv e s c an o n l y o c c u r i f t h e v a lu e isp a r t ia l ly c l o s e d . A n y w a t e r l e a k s f r o m v a lv e s w h e n f u ll y o p e n s h o u l db e c o r r e c t e d a s t h is s a m e l e a k w i ll e n t r a i n a i r if t h e v a l v e is p a r t i a l lyc l o s e d .Water quali O, ma intenan ce processes

T h e u s e o f s u b m e r g e d a e r a t o r s c a n p r o d u c e l e th a l g as s u p e r s a t u r a t i o n( C o l t a n d W e s t e r s, 1 9 8 2) . T h i s i n c l u d e s d i f fu s e d a e r a t o r s , j e t o r v e n t u r ia e r a t o r s , u - t u b e a e r a t o r s a n d a ir -l if t p u m p s . T h e a m o u n t o f g as s u p e r -s a t u ra t io n p r o d u c e d d e p e n d s p r i m a r i l y o n b u b b l e s u b m e r g e n c e a n dt h e s p e c if i c t y p e o f u n it . T h e r e d u c t i o n o f a e r a t o r b a s i n d e p t h w i llr e d u c e t h e A P , b u t w i ll a l so r e d u c e t h e t r a n s f e r e f f i c i e n c y o f t h ea e r a t o r . I f p u r e o x y g e n is u s e d r a t h e r t h a n a i r, G B T is n o t a s s e r i o u s ap r o b l e m w i th t h e u s e o f s u b m e r g e d a e r at io n . T h e u se o f s u b m e r g e da e r a t o r s w i th p u r e o x y g e n m a y b e e c o n o m i c if t h e o x y g e n i n t h e of f- g asis r e c y c l e d ( S p e e c e , 1 98 1 ).

T h e a ir -l if t p u m p m a y b e u s e d b o th f o r p u m p i n g a n d a e r a t io n .W h i l e t h i s d e v i c e i s u s e d e x t e n s i v e l y i n a q u a r i u m s o r l a r v a l s y s t e m s( S p o t t e , 1 9 7 9 ), c li n i c al s ig n s o f g a s b u b b l e c a n b e p r o d u c e d in s o m es e n s i t i v e s p e c i e s w i t h a s l i tt le as l m o f d i f f u s e r s u b m e r g e n c e( C o r n a c c h i a a n d C o l t, 1 9 84 ).Dep th of cul ture sys temF o r s p e c i es o r d e v e l o p m e n t a l s t ag e s m o r e s e n s it iv e t o g a s s u p e r s a t u r a -t i o n , i n c r e a s e d w a t e r d e p t h m a y b e d e s i r a b l e . S i l o s o r v e r t i c a l t a n k sm a y b e u s e fu l i n s o m e a p p l i c a t i o n s .Positive pressure h atchery buildingsF o r t h e c u l t u r e o f s e n s i t i v e l a r v a l f o r m s , m a i n t a i n i n g t h e p r e s s u r ei n s id e t h e f a ci li ty at + 5 0 m m H g h i g h e r t h a n t h e lo c a l b a r o m e t r i cp r e s s u r e c o u l d d e c r e a s e t h e n e e d t o i n c r e a s e t h e w a t e r d e p t h o r i n s t a l lv a c u u m d e g a s s in g . S o m e t y p e o f d o u b l e d o o r o r " ai rl oc k ' w o u l d b en e e d e d to p r e v e n t lo ss o f p r e s s u r e w h e n p e r s o n n e l o r e q u i p m e n t w e r em o v e d i n t o t h e p o s i t i v e p r e s s u r e a r e a . T h e e c o n o m i c s a n d f e a s i b i l i t yo f t h is p r o c e s s a r e n o t w e l l d e f i n e d a t t h is t im e .OperationsT h e o p e r a t i o n a l p e r s o n n e l m u s t e n s u r e t h at ex c e s s iv e w a t e r f lo w s a r en o t u s e d d u r i n g f i ll in g o f ta n k s o r c u l t u r e s y s t e m s , th a t a ll a i r is


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78 J . (22d~"removed from dual water systems prior to use, and that screens areroutinely checked and cleaned. During tow water condit ions in streamsor marine systems, the intake structure should be checked for vortex-ing. Installation of temporary baffles may be needed.M o n i t o r i n gRoutine monitoring of the AP. dissolved oxygen and temperatureshould be performed on a weekly basis in production and researchfacilities. After the water system is completed and operational, thepresence of small leaks in the suction piping or shaft seals may be diffi-cult to detect except by monitoring the AP. The development ofmembrane-diffusion instruments capable of continuous operation andinexpensive digital computers will allow collection of high quality gassupersaturation data without the need for excessive opera tor time.Continuous monitor ing may be neede d if the AP varies widely on adaily basis. This information may allow operation of degassing systemsonly when needed.G e t t in g b y in a n e m e r g e n c yWhen high AP values are detected in a culture system, the probablesource of the gas supersaturation should be determined and corrected.In operat ing systems, it may be impossible to quickly correct the prob-lem as the source may be external to the facility or the malfunctioningcomponent may not be able to be shut down and repaired. If a secon-dary source of non-supersaturated water is available, the most sensi-tive species or life stages should be protected. Switching between thetwo water supplies to achieve intermittent exposure can reduce theeffect of high AP values (Meekin and Turner, 1974).Emergency degassing can significantly reduce the AP, especially ifthe AP is in the acutely lethal range. A simple discharge into a bucketcan remove roughly 5t)% of the AP(Bou ck e t a l . , 1984). Water can besprayed into the system, allowed to run down an inclined plane, or adiffused air system placed in the culture system. Since many facilitieshave supersaturated water for part of the year, the construction of apermanent degassing unit for all facilities is recommended .R e s e a r c h a n d e d u c a t i o n a l n e e d sThe mechanisms that produce gas supersaturation and common pro-cesses that may produce gas supersaturation in both natural conditionsand hatchery conditions are not often understood or appreciated bythose who design or operate aquaculture facilities. Both groups must


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G a.5- s u p e r s a t u r a t i o e , - - i m p a c t o n ~ q u ., at ic 5 ~ s g e m s 7 ~)

b e b e t t e r e d u c a t e d t o id e nt if y ' t h e c a u s e s a n d s o l u t i o n s t o ga s s u p e r -s a t u r a t io n p r o b l e m s . A d d i t i o n a l d o c u m e n t a t i o n o f t h e s e a s o n a l v a r i a-t i o n i n s t r e a m s , r i v e r s a n d l a k e s i s n e e d e d , e s p e c i a l l y in c o l d c l i m a t e sw h e r e t h e s o l u te f r e e z e - o u t m e c h a n i s m M a t h i a s a n d B a ri c a . 1 9 85 )m a y b e i m p o r t a n t .R e c e n t w o r k o n d e g a s s i n g h a s d e v e l o p e d r e a s o n a b le d e s ig n p r o c e -d u r e s f o r t h e p a c k e d c o l u m n d e g a s se r M c L e a n a n d B o r e h a m , 1 98 0;C o l t a n d B o u c k , 1 98 4', a n d its v a c u u m m o d i f i c a t i o n ( F us s , 1 9 8 3; C o l ta n d B o u c k , t 9 8 4 ) . A n u m b e r o f f u ll -s c a le s y s t e m s h a v e b e e n b u i l t a n dt he o p e r a t i o n a l c h a r a c te r i s ti c s o f t h e s e u n it s u n d e r p r o d u c t i o n c o n d i -t io n s s h o u l d b e a v a i l a b le i n t h e n e a r f u t

colt 1986 aquacultural-engineering

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