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7/23/2019 Fluxes and Mass Balances.1997 http://slidepdf.com/reader/full/fluxes-and-mass-balances1997 1/8 ~ ) Pergamon PII: S0025-326X(96)00133--6 Marine Pollution Bulletin, Vol. 34, No. 5, pp. 290-297, 1997 ((3 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0025-326X /97 $17.00 + 0.00 Fluxes and Mass Balances of Nutrients in a Semi-Intensive Shrimp Farm in North-Western Mexico F. PAEZ-OSUNA*, S. R. GUERRERO-GALV/~N*, A. C. RUIZ-FERNANDEZ* and R. ESPINOZA-ANGULOt * Laboratorio de Quimica Marina, Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Aut6norna de Mdxico, Apdo. Postal 811, Mazatldn 82000, Sinaloa, Mdxico tSociedad Cooperativa de Producci6n Pesquera Clementina S.C.L., Pto. Salina Cruz No. 13, Parque Ind. Bonfil, Mazatldn, Sinaloa, MOxico Fluxes of suspended solids, chlorophyll a and nutrients (phosphorus, nitrate, nitrite and ammonia) were estimated in a semi-intensive shrimp farm in north-west Mexico for two consecutive cycles of production encompassing both the dry and wet seasons. A mass balance model was developed for nitrogen and phosphorus and fluxes estimated included shrimp feed, fertilization, shrimp stocked, harvest, macrofauna associated, water exchange, filling and drainage. O f the total nitrogen and phosphorus input to the ponds, 35.5 and 6.1 were recovered in 1822 kg ha -1 of shrimp harvested. Volatilization of ammonia and adsorption by sediments of phosphorus constituted 27.4 and 63.5 , respectively; the estimated environmental losses of nitrogen and phosphorus per t of shrimp produced were 28.6 kg and 4.6 kg, respectively. Assuming that all the shrimp farms in Sinaloa (Mexico), operate according to the model, the farms could represent a load corresponding to the untreated sewage generated by 56 200-192 750 and 43 500-149 170 people in terms of nitrogen and phosphorus discharged annually. © 1997 Elsevier Science Ltd Keywords: nutrient; fluxes; mass balance; shrimp farms. The development of large-scale shrimp farming is relatively recent and has been largely stimulated by the substantial and increasing demand from Japanese, European and North American markets (Chua, 1992). Over one million hectares of coastal lowlands have been converted into shrimp farms worldwide, mainly in China, Indonesia, Thailand, Ecuador, India, Vietnam, Bangladesh, Philippines, Honduras, Colombia and Mexico (Rosenberry, 1992). In Mexico, the state of Sinaloa produced 8610 t of shrimp in 1994 in 149 shrimp farms (SEMARNP, 1995), of which approxi- mately 70% (5670 ha pond area) were operated with semi-intensive management. The increase and development of shrimp farming has generated considerable concern about the effects of aquaculture pond effluents on the nearby aquatic ecosystems and some studies addressing the problem of aquaculture pond effluents have been carried out (Ziemann et al., 1992; Hopkins et al., 1993; Briggs and Funge-Smith, 1994). However, there are few specific studies on the chemical fluxes and characteristics of effluents in terms of mass balances for semi-intensive shrimp farm facilities. Knowledge of these values is essential for making planning decisions related to the potential impacts that may result from shrimp farm operations. This information also has biogeochemical importance for the understanding of coastal environ- ment processes influenced by organic and nutrient inputs (Hall et al., 1990). In a previous work (Guerrero-Galvfin, 1993), seasonal and diurnal changes in water quality parameters measured at one semi-intensive shrimp farm in the north-west coast of Mexico, during twq consecutive production cycles were reported. This paper presents the estimated fluxes of suspended solids, organic matter, chlorophyll a and nutrients lost to the adjacent coastal ecosystem. Additionally, a mass balance model for phosphorus and nitrogen was developed for the dry season on a per-hectare basis (1822kg shrimp harvested) for one semi-intensive shrimp farm. Materials and Methods Study site The shrimp farm is located on the Pacific coast of Mexico (Southern Gulf of California) adjacent to the Estero de Urias lagoon system, which empties into Mazatlan Harbor. The Estero de Urias lagoon is a saline vertically mixed water body (salinity range 25.8- 38.4) with an average mixed tidal amplitude of 1.5 m 290
Transcript
Page 1: Fluxes and Mass Balances.1997

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~ ) Pergam on

PII: S0025-326X(96)00133--6

Marine Pol lu t ion Bul let in , Vol . 34 , No. 5, pp . 290-297 , 1997

((3 1997 Elsev ie r Science L td

Al l r i gh t s re se rv ed . P r i n t ed i n Grea t Br i t a i n

0025-326X / 97 $ 17 . 00 + 0 . 00

F l u x e s an d M a s s B a l a n c e s o f N u t r ie n t s

i n a S e m i - I n t e n s i v e S h r i m p F a r m i n

N o r t h - W e s t e r n M e x i c o

F . P A E Z - O S U N A * , S. R . G U E R R E R O - G A L V / ~ N * , A . C . R U I Z - F E R N A N D E Z * a n d R . E S P I N O Z A - A N G U L O t

*L a b o r a t o r i o d e Q u i m i c a M a r i n a , I n s t i t u t o d e C i e n ci as d e l M a r y L i m n o l o g i a , U n i v e r si d a d N a c i o n a l A u t 6 n o r n a d e

M d x i c o , A p d o . P o s t a l 8 1 1 , M a z a t l d n 8 2 0 0 0 , S i n a lo a , M d x i c o

t S o c i e d a d C o o p e r a t i v a d e P r o d u c c i 6 n P e s q u e r a C l e m e n t i n a S . C . L . , P t o . S a l i n a C r u z N o . 1 3 , P a r q u e I n d . B o n f i l ,

M a z a t l d n , S i n a l o a , M O x i c o

Fluxes of suspended sol ids, chlorophyl l a and nutr ients

(phosphoru s, nitrate , ni tri te and amm onia) were est imated

in a semi- intensive shrimp farm in north-west Mexico for

two c onse c ut ive c yc l e s o f pr oduc t ion e nc ompass ing both

the dr y and we t se asons . A mass ba lanc e mode l was

developed for ni trogen and phosphorus and f luxes

estimated included shrimp feed, ferti l ization, shrimp

stocked, harvest , macrofauna associated, water exchange ,

f il ling an d drainage . O f the total ni trogen and phosphorus

input to the ponds, 35 .5 and 6.1 were recovered in

1822 kg ha -1 o f shr imp har vested . Vo la t i li za t ion o f

ammonia and adsor pt ion by se dime nts o f phosphor us

const i tuted 27 .4 and 63 .5 , respect ive ly; the est imated

environmental losses of ni trogen and phosphorus per t of

shrimp produced were 28 .6 kg and 4.6 kg, respect ively.

Assum ing that a l l the shr imp farms in S ina loa (M e xic o ) ,

operate according to the model , the farms could represent

a load correspon ding to the untreated sewag e generated

b y 5 6 2 0 0 - 1 9 2 7 5 0 a n d 4 3 5 0 0 - 1 4 9 1 7 0 p e op l e i n t e rm s o f

ni trogen and phospho rus discharged annual ly. © 199 7

Elsevier Science Ltd

Keywords: nutrient; fluxes; mass balance; shrimp farms.

T h e d ev e l o p men t o f l a rg e - s ca l e s h r i mp f a rmi n g i s

r e l a t i v e l y r e cen t an d h a s b een l a rg e l y s t i mu l a t ed b y

t h e s u b s t an t i a l an d i n c r ea s i n g d eman d f ro m J ap an es e ,

E u r o p e a n a n d N o r t h A m e r i c a n m a r k e t s ( C h u a , 1 99 2) .

O v e r o n e m i l l io n h ec t a r e s o f co a s t a l l o w l an d s h av e b een

co n v e r t ed i n t o s h r i mp f a rms w o r l d w i d e , ma i n l y i n

Ch i n a , I n d o n es i a , T h a i l an d , Ecu ad o r , I n d i a , V i e t n am,

B an g l ad e s h , Ph i l i p p i n e s , H o n d u ra s , Co l o mb i a an d

Mex i co (R o s en b e r ry , 1 9 9 2 ) . I n M ex i co , t h e s t at e o f

S i n a l o a p ro d u ced 8 61 0 t o f s h r i mp i n 1 9 9 4 i n 1 49

s h r im p f a r m s ( S E M A R N P , 1 9 9 5) , o f w h i c h ap p r o x i-

ma t e l y 7 0 % (56 7 0 h a p o n d a r ea ) w e re o p e ra t ed w i t h

s emi - i n t en s i v e man ag emen t .

T h e i n c re a s e a n d d e v e l o p m e n t o f s h r i m p f a r m i n g h a s

g en e ra t ed co n s i d e r ab l e co n ce rn ab o u t t h e e f f e c t s o f

aq u acu l t u r e p o n d e f f l u en t s o n t h e n ea rb y aq u a t i c

eco s y s t ems an d s o me s t u d i e s ad d re s s i n g t h e p ro b l em

o f aq u acu l t u r e p o n d e f f l u en t s h av e b een ca r r i ed o u t

( Z i e m a n n et al., 1 9 9 2 ; H o p k i n s et al., 1993; Briggs and

Fu n g e -Sm i t h , 1 9 9 4 ) . H o w ev e r , t h e r e a r e f ew s p ec if ic

s t u d i e s o n t h e ch emi ca l f l u x e s an d ch a r ac t e r i s t i c s o f

ef f luen ts in te rms o f mass ba lances fo r semi- in tens ive

shr imp farm fac i l i t i es . Knowledge o f these va lues i s

e s s en t i a l f o r mak i n g p l an n i n g d ec i s i o n s r e l a t ed t o t h e

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

o p e ra t i o n s . T h i s i n fo rma t i o n a l s o h a s b i o g eo ch emi ca l

i mp o r t an ce fo r t h e u n d e r s t an d i n g o f co a s t a l en v i ro n -

men t p ro ce s s e s i n f l u en ced b y o rg an i c an d n u t r i en t

inpu ts (Hal l et al., 1990).

I n a p r ev i o u s w o rk (Gu e r r e ro -Ga l v f i n , 1 9 9 3 ) ,

s ea s o n a l an d d i u rn a l ch an g es i n w a t e r q u a l i t y

p a r ame t e r s meas u red a t o n e s emi - i n t en s i v e s h r i mp

fa rm i n t h e n o r t h -w es t co a s t o f Mex i co , d u r i n g t w q

co n s ecu t i v e p ro d u c t i o n cy c l e s w e re r ep o r t ed . T h i s

p ap e r p r e s en t s t h e e s t i ma t ed f l u x e s o f s u s p en d ed

s o l i d s , o rg an i c ma t t e r , ch l o ro p h y l l a an d n u t r i en t s

l o s t t o t h e ad j acen t co a s t a l e co s y s t em. Ad d i t i o n a l l y , a

m a s s b a l a nc e m o d e l f o r p h o s p h o r u s a n d n i t ro g e n w a s

d ev e l o p ed fo r t h e d ry s ea s o n o n a p e r -h ec t a r e b a s i s

(1 8 2 2 k g s h r i mp h a rv e s t ed ) f o r o n e s emi - i n t en s i v e

s h r i mp f a rm.

M a t e r i a l s a n d M e t h o d s

S t u d y s i t e

T h e s h r i mp f a rm i s l o ca t ed o n t h e Pac i f i c co a s t o f

Mex i co (So u t h e rn Gu l f o f Ca l i f o rn i a ) ad j a cen t t o t h e

Es t e ro d e U r i a s l ag o o n s y s t em, w h i ch emp t i e s i n t o

Maza t l an H a rb o r . T h e Es t e ro d e U r i a s l ag o o n i s a

s a li n e v e r t ic a l l y mi x ed w a t e r b o d y ( s a li n i ty r an g e 2 5 .8 -

3 8.4) w i t h an av e r ag e mi x ed t i d a l am p l i t u d e o f 1 .5 m

290

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Volume 34/Number 5/May 1997

and water velocities of 0-0.50 cm s - l (P~ez-Osuna e t

al ., 1990).

P o n d s y s t e m

In 1990-1991 the farm had seven earthen ponds with

a total pond area of 45 ha. The farm has one intake

structure and a reservoir channel supplying the ponds

with water by gravity flow. Filling and exchange water

are pumped from the Estero Confites, which is a small

channel that communicates with the main lagoon

system (Fig. 1). Ponds drain through an effluent ditch

which carries water back to the adjacent lagoon body,

some distance from the intake pumps. Minimal short-

circuiting of discharge and pumped intake water is

thought to occur. During the present work water in

ponds was exchanged continuously at rates of 3-

5 da y- l; however, during rainy seasons, the ex-

changes were higher (6-20 ) depending on the

amount of precipitation.

Two ponds (1 and 5 in Fig. 1) were chosen for the

present study. Pond 1 has a mean depth o f 0.8 m and an

area of 7.3 ha (58 400 m 3 in volume); pond 5, is 0.8 m

deep and 8.4 ha (67 200 m3). The pond management

team reported (pers. comm.) tha t the historic yields of

the ponds were different, with one pond producing

about 20 greater production than the other. Before

stocking, each pond was fertilized with 4.5 kg ha-1 of

triple superphosphate (46 P205) and 19.5 kg ha-1 of

urea (45 N) during the dry season, and 9 kg ha-1 of

triple superphosphate and 39.5 kg ha-~ of urea during

the rainy season. Postlarval (PL) P e n a e u s v a n n a m e i of

approximately 8 -1 0mm in length (0.8-1.1 mg in

weight) were stocked into production ponds at a density

of 14 m -2 and 20 m -2 for the dry and rainy season,

respectively. Feed was supplied daily to the ponds from

a small boat. A total o f 2.2 and 3.8 t h a- ~ of feed were

provided during the dry and rainy seasons, respectively.

The composition of feed was: dry matter 88.0 ; lipids

8.0 ; crude protein 35.0 . Production for ponds 1 and

5 during the dry season was 1856 and 1788 kg ha -1

crop - l , respectively; while during the rainy season it

was 2160 and 2089 kg ha -I crop - l, respectively. Feed

conversion ratios (dry wt feed added/wet wt of shrimp

produced) were 1.18-1.23 and 1.76-1.82 for the dry and

rainy seasons for ponds 1 and 5, respectively. The ponds

were filled and the grow-out cycle for the dry and rainy

season began on March 22 and August 18 (1991), and

the culture cycles lasted 95 and 165 days, respectively.

At harvest, ponds were drained and shrimps were

captured in a net bag placed over the outlet in the sluice-

j /

0

< ~ P a c i f i c O c e a n

• r m ' ~

1

2 3 krn

Fig. 1 Map of Estero de Urias lagoon system (Mazatlan Harbor,

Sinaloa, Mexico) showing location of study s ite. Numbers

indicate the shrimp ponds sampled.

291

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g a t e. T h e en t i r e c r o p a n d s u b s am p l e s o f in d i v i d u a l

s h r i m p s w e r e w e i g h ed t o d e t e r m i n e h a r v e s t s i z e , m ean

w e i g h t s an d s u r v i v a l r a t e s . F u r t h e r d e t a i l s ab o u t t h e

s u r v iv a l , g r o w t h r a t e , an d h a r v e s t w e i g h t s a r e p r e s en t ed

in Guer rero -Galv~n (1993) .

S a m p l i n g a n d a n a l y t i c a l m e t h o d s

A w a t e r s am p l i n g r eg i m e w as d ev e l o p ed t o e s t i m a t e

the i n f luence o f f a rmin g a c t i v i t i es (i .e . f eed ing r a t es , t ime

o f cu lt u r e ), s e a s o n a l f l u c t u a t i o n s , an d t o ev a l u a t e

d i u r n a l f l u c t u a t i o n s o n t h e w a t e r q u a l i t y . A N i s k i n

h o r i zo n t a l s am p l e r w as u s ed t o co l l e c t w a t e r s am p l e s i n

t h e t w o p o n d s an d t h e i n le t w a t e r a t i n t e r v a ls o f 2 w eek s

( s am p l i n g t i m e w as b e t w een t h e 0 3 0 0 an d 0 5 0 0 h ) an d

t w i ce w eek l y ( b e t w een t h e 1 50 0 an d 1 60 0 h ) d u r i n g t h e

d r y an d r a i n y s ea s o n s , r e s p ec t i v e l y . D i u r n a l w a t e r

s am p l e s ( 2 4 h s a m p l i n g p e r i o d s ) w e r e co ll e c t ed ev e r y

2 h o n s p ec i f ic d ay s o n l y d u r i n g t h e d r y s ea s o n . O n

cu l t u r e d ay 3 6 / 3 7 an d 7 8 / 7 9 f r o m p o n d 1 , an d o n

cu l t u r e d ay 6 4 / 6 5 an d 9 2 / 9 3 , f r o m p o n d 5 an d t h e

Es t e r o C o n f i t e s a t t h e p u m p i n g s t a t i o n .

W a t e r s a m p l e s w e r e t a k e n 2 0 c m b e l o w t h e w a t e r

s u r f ace c l o s e t o t h e s l u ice g a t e o f p o n d s 1 an d 5 (s t a t i o n s

l a an d 5 a ) an d a t t h e p u m p i n g s t a t i o n a t E s t e r o

C o n f i t e s ( s t a t i o n b ) . Each s am p l e w as d i v i d ed i n to c l e an

co n t a i n e r s a s f o l l o w s :

1. w a t e r f i lt e red t h r o u g h W h a t m an n G F / C f il te r s t o

d e t e r m i n e d i s s o l v ed n u t r i en ts ( p h o s p h a t e , P O 4 3 , ni -

t r a te , N O 3 an d n i tr i te , N O { ) an d s a l in i ty ;

2 . four a l i q uo t s o f 10 ml unf i l t e r ed wa ter t o ana lyse

am m o n i a w e r e p l a ced i n g l a s s -v i a ls w i t h 5 m l o f p h en o l -

e t h an o l ( 0 . 8 %) ;

3 . a 3 0 0 - m l B O D g l a s s b o t t l e f o r d i s s o l v ed o x y g en

m eas u r em en t s ;

4 . t w o p r e - a s h ed ( 5 0 0 °C ) an d w e i g h ed G F / C g l a s s f ib r e

f i l t e r s i n g l ass d i shes t o measure suspended so l i d s and

s u s p en d ed o r g an i c m a t t e r ; an d

5 . o n e f i l t e r G F / C i n a b l a ck v i a l w i t h m e t h an o l f o r

ch lo rophy l l a ana lys i s .

T h e eq u a t i o n u s ed t o d e t e r m i n e t h e ch l o r o p h y l l

p i g m e n t w a s th a t o f S C O R / U N E S C O a s q u o t e d in

S t r i ck l an d an d P a r s o n s ( 1 9 7 2 ) . Ex cep t i n g d i s s o l v ed

o x y g en w h i ch w as m eas u r ed i n t h e f i e l d , a l l s am p l e s

w er e ca r r i ed i m m ed i a t e l y i n co o l e r s t o t h e l ab o r a t o r y

f o r an a ly s i s. I n t h e 2 4 h s am p l i n g p e r i o d s , t h e s am p l e s

w er e m a i n t a i n ed o n i ce , an d t r an s p o r t ed t o t h e

l ab o r a t o r y , w h e r e t h ey w e r e s t o r ed r e f r i g e r a t ed ( 4 ° C )

u n t il an a l y s i s co n d u c t ed w i t h i n 3 d ay s o f col l e c ti o n .

T h e f o l l o w i n g an a l y s e s w e r e co n d u c t ed u s i n g p r o ce -

dures ou t l i ned in S t r i ck l and and Par sons (1972) :

d i s s o l v ed o x y g en ( W i n k l e r m e t h o d ) , n i t r i t e ( d i azo t i z a -

t i o n m e t h o d ) , n i t r a t e ( cad m i u m r ed u c t i o n f o l lo w ed b y

d i a z o t i z a t i o n ) , p h o s p h a t e ( p h o s p h o m o l y b d e n u m p r o c e -

d u r e ) , p H ( p o t en t i o m e t e r ) , an d s a l i n i t y ( co n d u c t i v i t y /

s a l i n o m e t e r) . T o t a l am m o n i a w as d e t e r m i n ed b y t h e

p h en a t e t e ch n i q u e ( S o l o r zan o , 1 9 6 9 ) an d ch l o r o p h y l l a

w as ex t r a c t ed i n m e t h an o l an d d e t e r m i n ed s p ec t r o -

p h o t o m e t r i ca l l y ( H o l m - H an s en an d R i em an n , 1 9 7 8 ) .

292

Marine P ollution Bulletin

T o t a l s u s p en d ed s o l i d s an d o r g an i c s o l i d s w e r e

e s t i m a t ed g r av i m e t r i c a l l y ( A P H A , 1 9 8 9 ) . T h e p r ec i s i o n

of the d i f f er en t de t erm inat ions , expresse d as coef f ic i en t

o f v a r ia t i o n , w as e s t i m a t ed t o b e : d i s s o l v ed o x y g en

2 .3% , n i t r i t e 3% a t 1 .2 gM , n i t r a t e +n i t r i t e 9°/'0 a t

6 . 0 g M , p h o s p h a t e 3 % a t 5 .5 g M , s a l i n it y 0 .5 %, an d

t o t a l a m m o n i a 9 % a t 2 0 g M .

N i t r o g e n a n d p h o sp h o r u s c o n t e n t i n s h r im p a n d s h r i m p

f e e d

W h o l e s h r i m p n i t r o g e n a n d p h o s p h o r u s c o n t e n t s

w e r e d e t e r m i n ed f o l l o w i n g t h e m e t h o d s d e s c r i b ed b y

Pf i ez-Osuna et a l . (1993) and Pf i ez-Osuna et a l . (1991),

r e s p ec t i v e l y . T h e n i t r o g en co n cen t r a t i o n i n s h r i m p f eed

w as a s s u m ed t o b e 5 . 6 % ( 3 5 % p r o t e i n ) a cco r d i n g t o t h e

m an u f ac t u r e r s p ec i f i c a ti o n s an d p h o s p h o r u s co n cen t r a -

t i o n w as d e t e r m i n ed b y t h e p r o ced u r e d e s c r i b ed b y

Pf i ez-Osuna et a l . ( 1 9 9 1 ) . F o r p h o s p h o r u s an a l y s i s , a

f i s h h o m o g en a t e M A - B - 3 / T M r e f e r en ce m a t e r i a l

( I A EA , 1 98 8) w as u s ed t o ch eck t h e a cc u r acy o f t h e

m e t h o d o l o g y .

R e s u l t s

D a t a a n a l y s i s

I n o r d e r t o av o i d ex t r em e l y a t y p i ca l v a l u e s t h a t

co u l d a f f ec t te s t r e s u lt s , w a t e r q u a l i t y d a t a w e r e

screened fo r ou t l i e r s befo re t he s t a t i s t i ca l ana lys i s ,

u s i n g B o x an d W h i s k e r p l o t , an a l g o r i t h m i c p r o ced u r e

descr ibed by Tukey (1977) and O t t (1988) . Ex t r eme

values were def ined as t he da t a po in t s t ha t l i e 1 .5 t imes

ou t s i d e the i n t erquar t i l e r ange o f t he i r neares t quar t i l e

( I g n a t i ad e s

et al.,

1992). Tab le 1 p rese n t s t h e s t a t i s t i cs

s u m m a r y o f d a t a a f t e r t h e ex c l u s i o n o f o u t l ie r s ( l es s

t h an 5 % o f t h e t o t a l d a t a ) . I n t h e ca s e o f a ty p i ca l

v a l u e s , th e s e w e r e s u b s t i t u t ed b y t h e v a l u e o f t h e n ea r e s t

q u a r ti l e . S i n ce t h e m eas u r em en t s o f d i s s o l v ed o x y g en

w er e o f p o o r r ep r o d u c i b i l it y d u r i n g t h e r a i n y s ea s o n ,

d a t a f o r t h i s p e r i o d w e r e o m i t t ed . S ea s o n a l an d d i u r n a l

v a r i a t i o n s , an d t h e d i f f e r en ce s am o n g v a l u e s w e r e

d i s cu s s ed an d r ep o r t ed i n a p r ev i o u s w o r k ( G u e r r e r o -

Galvf in , 1993) .

E s t i m a t i o n o f t h e c h e m i c a l f l u x e s

Ei g h t w a t e r q u a l i t y p a r am e t e r s w e r e s t u d i ed b y

d e t e r m i n i n g t h e ch em i ca l fl u x o f e ach d i s ch a r g e o v e r

t h e p r o d u c t i o n d u r i n g t h e d r y an d r a i n y s ea s o n s . T h e

f o l l o w i n g co n s i d e r a t i o n s an d a s s u m p t i o n s w e r e u s ed t o

ca l cu l a t e t he chemica l f l uxes :

• M e t h o d ( a ) i n v o l v ed li n ea rl y i n t e r p o l a ti n g b i w eek l y

o r s em i w eek l y w a t e r q u a l i t y d a t a t o c r ea t e an e s t i m a t e

o f d a il y v a l u e s. D a i l y co n ce n t r a t i o n s w e r e m u l t i p li ed b y

d a i l y f l ow s t o d e t e r m i n a t e t h e t o t a l m as s o f e ach

p a r am e t e r i n d i s ch a r g e w a t e r . T h e m as s o f e ach

p a r a m e t e r w h i c h e n t e r e d p o n d s f r o m t h e a d j a c e n t

l ag o o n ( Es t e r o d e U r i a s ) t h r o u g h w a t e r ex ch an g e

( e s t i m a t ed f r o m i n l e t w a t e r s am p l i n g d a t a ) w as

s u b t r a c t ed f r o m t h e d a i l y d i s ch a r g e . F i n a l l y , d a i l y

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V o l u m e 3 4 / N u m b e r 5 / M a y 1 9 9 7

T A B L E 1

W a t e r q u a l i t y o f i n l e t a n d o u t l e t w a t e r f o r t w o p o n d s i n a s e m i - in t e n s iv e s h r i m p f a r m i n n o r t h - w e s t c o a s t o f M e x i c o , 1 9 9 1 -1 9 9 2. O u t l e t w a t e r d a t a

f o r d r y s e a s o n a r e f ro m p o n d s a n d 5 ; f o r r a i n y s e a s o n o u t l e t w a t e r d a t a a r e o n l y f r o m p o n d 1 . M e a n v a l u e 4 - s t a n d a r d d e v i a t i o n ; s a m p l e s iz e a re i n

p a r e n t h e s e s .

D r y s e a s o n R a i n y s e a s o n

P a r a m e t e r I n l e t O u t l e t I n l e t O u t l e t

Sal init y 41.74-0.9 (26) 48.34-0.6 (26) 27.74-12.0 (38) 29.44-7.5 (33)

N itr ite (IxM) 0.44-0.1 (14) 0.74-0.3 (44) 1.24-2.2 (40) 0.34-0.3 (46)

N itr at e (~tM) 0.44-0.2 (14) 0.54-1.1 (44) 13.24-4.8 (40) 0.54-0.8 (46)

A m m on iu m (I~M) 17.54-7.0 (14) 11.54-7.0 (44) 12.44-9.9 (40) 16.74-15.1 (46)

Ph osp ha te (~tM) 1.44-0.3 (14) 1.7+ i.1 (44) 2.54-2.4 (40) 0.84-0.6 (46)

Tot al sus pen ded solids (mg I - l) i 74.04-22.0 (14) 94.04-27.0 (44) 48.04-18.0 (40) 67.04-23.0 (46)

Org anic susp end ed solid s (mg 1- ) 8 .74-3.9 (14) 17.84-7.2 (44) 4.14-1.6 (40) 13.84-6.8 (46)

Diss olved oxyg en ( t tM) 98.04-160.0 (14) 104.04-83.0 (44) - - - -

Ch loro ph yll a (mg 1-1) 1.65:1.0 (14) 10.04-8.0 (44) 3.64-4.1 (40) 27 .6+ i7 .4 (46)

T A B L E 2

S t a g e s o f t h e g r o w - o u t c y c le d u r i n g t h e d r y s e a s o n i n a s e m i - i n t e n si v e

s h r i m p f a r m i n n o r t h - w e s t M e x i c o .

S t a g e D u r a t i o n ( d a y s) R e m a r k s

I n i t i a l 0 - 36

I n t e r m e d i a t e 3 7 - 7 0

F i n a l 7 1 - 9 5 ( o r m o r e )

Pon d f i l led , f e r t i l i zed and

s t o c k e d . F e e d 0 - 2 0 k g h a - 1

d a y - 1 W a t e r e x c h a n g e r eg i m e , 4 %

F e e d 2 0 -3 0 k g h a - i d a y - i . W a t e r

e x c h a n g e r e g im e , 4 %

H a r v e s t . F e e d 2 5 - 3 5 k g h a - 1

d a y - i . W a t e r e x c h a n g e r e g im e , 6 %

d i s ch a r g e v a l u e s f o r e ach p a r am e t e r w e r e ad d ed f o r

e a c h s e a s o n a n d c o n v e r t e d t o k g h a - ~ c r o p - i .

s M e t h o d ( b ) i n v o l v ed u s e o f d i u r n a l w a t e r q u a l i ty d a t a

d u r i n g t h r ee s t ag e s o f t h e cu l t u r e p e r i o d ( T ab l e 2 ): i )

t he i n i t i a l s t age , was charac t er i zed by r e l a t i ve ly l ow

c o n c e n t r a t io n s f o r m o s t o f t h e m e a s u r e d w a t e r q u a l i ty

p a r am e t e r s . T h es e co n d i t i o n s w e r e a s s u m ed t o p r ev a i l

f r o m t h e f i r st t o t h e f i f th w e ek o f t h e g r o w - o u t cy c le ;

t h e r e f o re , t h e d i u r n a l d a t a o f d ay 3 6 w e r e u s ed t o

ca l cu l a t e t hese f l uxes i n t h i s per iod ; ( i i ) i n t he

i n t e r m ed i a t e s t ag e , an i n t e r m ed i a t e co n cen t r a t i o n

r ep r e s en t ed b y t h e d i u rn a l d a t a o f d ay 6 4 w as u s ed t o

ca l cu l a t e t h e co r r e s p o n d i n g f l u x e s f r o m t h e 6 t h t o t h e

10 th week ; ( i i i ) i n t he f i na l s t age , cond i t i ons f rom the

1 t h t o t h e 1 3t h w eek o f t h e cu l t u r e cy c l e w e r e a s s u m ed

t o p r ev a il , an d r ep r e s en t ed b y t h e d i u r n a l v a r i a t i o n d a t a

o f d ay 9 2 . T h e d a t a o b t a i n ed f r o m d ay 9 3 an d d ay 1 61

f o r t h e d r y an d r a i n y s ea s o n , r e s p ec t i v e ly , w e r e a s s u m ed

t o b e t y p i ca l o f p o n d d r a i n ag e v a l u e s , an d a f t e r th e i r

i nc lus ion , t he f l uxes o f nu t r i en t s , so l i d s ( t o t a l and

o r g an i c ) , ch l o r o p h y l l a , an d d i s s o l v ed o x y g en w e r e

ca l cu l a t ed co n s i d e r i n g each p a r am e t e r i n t h e w a t e r u s ed

to f i l l po nd s i n i t i a ll y (Tab le 3 ) . Fur th er de t a i l s on t he

ca l cu l a t i o n s a r e av a i l ab l e f r o m t h e au t h o r s o n r eq u es t .

D i s c u s s i o n

Chemical f luxe s

T h e a m o u n t o f w a t e r u s e d t o p r o d u c e a c r o p i n

p o n d s , v a r i ed d ep en d i n g o n t h e cu l t u r e cy c l e d u r a t i o n ,

p r o d u c t i o n an d t h e w a t e r ex ch an g e r a t e ; i n t h e d r y

s ea s o n ( 3 - 5 % d a i l y w a t e r ex ch an g e r a t e ) 9 . 0 ( p o n d 1 )

an d 1 7 . 3 m 3 ( p o n d 5 ) o f w a t e r w e r e d i s ch a r g ed p e r k i l o -

g r am o f w h o l e s h ri m p , w h i l e f o r t h e r a i n y s ea s o n ( 6 -

2 0 % d a i l y w a t e r ex ch an g e r a t e ) 1 1 . 5 ( p o n d 1 ) an d

T A B L E 3

T o t a l e s t i m a t e d a m o u n t s p e r h e c t a r e o f m a t e r i a l i n c o r p o r a t e d , d i s c h a r g e d a n d n e t l o a d i n g v i a w a t e r o n a s e m i - i n t en s i v e s h r i m p f a r m ( p o n d 1 ) d u r i n g

dr y ( 1991) and r a iny ( 1991 /1992) s easons . Va lues wer e c a lc u la ted c ons ider ing punc tua l measur emen ts ( method ( a ) , s ee tex t ) .

D r y s e a s o n R a i n y s e a s o n

I n l e t O u t l e t N e t I n l e t O u t l e t N e t

T o ta l suspend ed so l ids ( kg) 2958 4549

Or gan ic suspe nded so l ids ( kg) 441 640

Chlo r ophy l l a ( g ) 142 409

Dis so lved oxygen ( kg) 193 98

P- PO4 ( g ) 2886 995

N- N O2 ( g ) 133 198

N- N O3 ( g ) 178 541

N- NH 4 ( g ) 12971 9996

1591 2796 3686 890

199 323 704 381

267 202 1234 1032

- -9 5 - - - - - -

- 1 8 9 1 3 52 7 1 56 9 - 1 9 5 8

6 5 5 95 3 2 0 - 2 7 5

363 6137 365 - 5772

- 2 9 7 5 1 2 0 58 1 2 7 0 9 6 51

293

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2 1 .6 m 3 ( p o n d 5 ) o f w a t e r w e r e d i s c h a r g e d p e r k i l o g r a m

o f w h o l e s h r i m p . T h e s e v a l u e s f a ll c o n s i d e r a b l y b e l o w

t h e e s t i m a t e d w o r l d - w i d e r a n g e o f 3 9 - 1 9 9 m 3

w a t e r k g - 1 s h r i m p ( H o p k i n s a n d V i l l a l6 n , 1 99 2) .

T h e c h e m i c a l f l u x e s e s t i m a t e d f o r t h e p a r a m e t e r s

c o n s i d e r e d w e r e d i f f e r e n t b e t w e e n t h e t w o s e a s o n s

( T a b l e 3 ) . T h e r a i n y s e a s o n v a l u e s ( i n l e t a n d o u t l e t )

w e r e g e n e r a ll y h i g h e r t h a n t h o s e f o r t h e d r y s e a s o n , d u e

t o a l o n g e r c u l t u r e c y c l e d u r i n g t h e r a i n y ( 1 65 d a y s )

t h a n t h e d r y ( 9 5 d a y s ) s e a s o n . A d d i t i o n a l l y , o t h e r

f a c t o r s s u c h a s r a i n f a l ls a n d i n t e n s i ty o f s o l a r r a d i a t i o n ,

c o u l d a c c o u n t f o r o b s e r v e d d i f f e r e n c e s b e t w e e n s e a s o n s .

I n t h i s c o m p a r i s o n i t i s i m p o r t a n t t o c o n s i d e r t h a t t h e

s a m p l i n g s c h e d u l e w a s n o t t h e s a m e f o r b o t h c y c l e s .

D u r i n g t h e d r y s e a s o n , s a m p l e c o l l e c t i o n s w e r e m a d e a t

d a w n ( 0 3 0 0 - 0 5 0 0 h ) , w h e r e a s i n t h e r a i n y s e a s o n , t h e y

w e r e m a d e i n t h e a f t e r n o o n ( 1 5 0 0 - 1 6 0 0 h ) . I n t h i s t y p e

o f s h r i m p ( G u e r r e r o - G a l v ~ i n , 1 9 93 ) a n d f i s h p o n d ( e. g.

T u c k e r a n d B o y d , 1 98 5; K r o m

e t a l . ,

1 9 8 5 ; E r ez

e t a l . ,

1 9 9 0 ) , d i u r n a l v a r i a t i o n s t r o n g l y a f f e c t s d i s s o l v e d

o x y g e n , a m m o n i a a n d c h l o r o p h y l l a . T h e n e t f l u x o f

n i t r i t e , n i t r a t e a n d t o t a l a m m o n i a w e r e i n c o n s i s t e n t . I n

t h e r a i n y s e a s o n n i t r i t e a n d n i t r a t e s e e m s t o d r o p i n t h e

p o n d s ( n e g a t iv e f l u xe s ) , w h e r e a s i n t h e d r y s e a s o n a

c o n t r a r y t e n d e n c y i s n o t e d ( T a b l e 3 ) . F o r a m m o n i a , t h e

r e v e r s e w a s o b s e r v e d ; p o s s i b l y d u e t o t h e s e a s o n a l

i n f lu e n c e o r s i m p l y d u e t o t h e e f fe c t o f th e d i f f e r e n t

s a m p l i n g s c h e d u l e .

C h e m i c a l f l u x e s i n t h e d r y s e a s o n c a l c u l a t e d u s i n g

d i u r n a l d a t a ( m e t h o d b , T a b l e 4 ) w e r e c o n s i d e r a b l y

d i f f e re n t f r o m t h o s e c a l c u l a t e d u s i n g b i w e e k l y d a t a

( m e t h o d a , T a b l e 3 ) . I n f a c t , in t h e c a s e o f p h o s p h o r u s

T A B L E 4

Total estimated amoun ts per hec tare of m aterial incorporated,

discharged and net loading via water on a semi-intensiveshrimp farm,

during d ry season (1991). Values we re calculated considering diurnal

variations and the s tages of the culture cycle (method (b), see text).

Inlet Outlet Net

Tota l suspe nded solid s (kg) 2303 3605 1302

Organic suspe nded solid s (kg) 261 730 469

Chlorop hyll a (g) 47 407 360

Dissolved oxyge n (kg) 78 163 85

P-P O4 (g) 1467 1987 520

N -NO 2 (g) 179 436 257

N -NO 3 (g) 176 322 146

N-NH 4 (g) 8519 52 74 -324 5

Marine Pollution Bulletin

a n d d i s s o l v e d o x y g e n , t h e s i g n o f t h e n e t f l u x d i f f e r e d

b e t w e e n m e t h o d s . T h i s i n d i c a t e s t h e i m p o r t a n c e o f

d i u r n a l f l u c t u a t i o n s ( 2 4 h s a m p l i n g p e r i o d ) o f t h e s e

p a r a m e t e r s w h i c h s h o u l d b e c o n s i d e r e d i n t h e e s t i m a -

t i o n o f c h e m i c a l f l u x es .

N e t f l u xe s c a lc u l a t e d i n t h i s s t u d y a r e m u c h l es s t h a n

t h o s e r e p o r t e d f o r i n t e n s i v e s h r i m p p o n d s i n S o u t h

C a r o l i n a , U S A ( H o p k i n s

e t a l . ,

1 9 9 3 ) a n d , i n a d d i t i o n ,

d u r i n g t h e d r y s e a s o n , s e m i - i n t e n s i v e s h r i m p p o n d s

a p p e a r t o c o n s u m e a m m o n i a ( n e g a t i v e n e t f l u x ) . F o r

t o t a l s u s p e n d e d s o l i d s , t h e s e m i - i n t e n s i v e p o n d s

o p e r a t e d w it h a m e a n w a t e r e x c h a n g e o f 3 - 5 % d a y - l ,

h a d a n e t fl u x b e t w e e n 8 90 a n d 1 59 0 k g h a - t c r o p - i .

F o r i n t e n s i v e p o n d s , o p e r a t e d w i t h a w a t e r e x c h a n g e o f

0 - 2 5 % , t h e n e t f l u x w a s o f 5 5 5 4 a n d 11 2 8 9 k g h a - 1

c r o p - l . T h e r e ac t iv e p h o s p h a t e v a l u es d e t e r m i n e d i n

t h e p r e s e n t s t u d y a r e a l s o s e v e r a l t i m e s l e s s t h a n t h o s e

r e p o r t e d b y H o p k i n s

e t a l .

( 1 9 93 ) , ( 3 8 .6 k g h a - l f o r

p o n d s s t o c k e d 4 4 P L m - 2 a n d o p e r a t i n g w i t h a d a i l y

w a t e r e x c h a n g e o f 2 5 % ) . H o w e v e r , t h e fe e d r a te s w e r e

7 - 1 5 t h a - t c r o p - ~ , a s o p p os e d t o 2 . 2 - 3 . 8 t h a - I

c r o p - ~ i n t h e p r e s e n t s t u d y .

M a s s b a l a n c e s

U s i n g t h e s t r a te g y p r o p o s e d b y T u c k e r a n d B o y d

( 1 9 8 5 ) a f ir s t m a s s b a l a n c e f o r t h e f a t e o f n u t r i e n t s i n

f e e d a d d e d t o s h r i m p p o n d s w a s d e v e l o p e d b a s e d o n

e s t i m a t e s o f fe e d c o n v e r s i o n , t h e a m o u n t o f fe e d

a d d e d , t h e d r y w e i gh t c o n c e n t r a t i o n o f n i t ro g e n a n d

p h o s p h o r u s a n d t h e m o i s t u re c o n t e n t , o f fe e d a n d

s h r i m p . S i n c e s h r i m p c o m p o s i t i o n w a s 3 1 % d r y

m a t t e r , 8 . 9% n i t ro g e n a n d 0 . 3 % p h o s p h o r u s

( T a b l e 5 ), a b o u t 4 6 . 7 % a n d 7 . 4 % o f t h e n i t r o g e n

a n d p h o s p h o r u s r e s p e c t i v e l y , o r i g i n a l l y c o n t a i n e d i n

t h e f e e d , w a s r e m o v e d f r o m t h e p o n d w h e n s h r i m p

w e r e h a r v e s t e d . T h e r e m a i n i n g w a s l o s t t o t h e w a t e r

a s d e c o m p o s i t i o n o r e x c r e t o ry p r o d u c t s a n d e v e n t ua l l y

i n c o r p o r a t e d i n n a t u r a l c y c l e s .

A m a s s b a l a n c e m o d e l w a s d e v e l o p e d f o r n i t r o g e n

a n d p h o s p h o r u s u s i n g d i u r n a l d a t a c a l c u l a t e d w i t h

m e t h o d b , a n d m a s s b a l a n c e d a t a f r o m T a b l e 5 ( F i gs 2

a n d 3 ). I n p u t d a t a i n c l u d e d t h e a m o u n t o f f e e d

s u p p l i e d , n u m b e r o f s h r i m p s t o c k e d , f e r t il i z a ti o n ,

r e a c t i v e a n d o r g a n i c s u s p e n d e d p h o s p h a t e , i n o r g a n i c

n i t r o g e n s p e c ie s ( a m m o n i a + n i t ri t e + n i t r a te ) a n d

o r g a n i c s u s p e n d e d n i t r o g e n o f i nl e t w a t e r d u r i n g f il li ng

a n d i n ef f lu e n t d u r i n g w a t e r e x c h a n g e , a n d a t h a r v e s t

T A B L E 5

Balance for nitrogen and ph osphorus in a semi-intensiveshrimp culture pond, used to grow 1822 kg shrimp ha -J at a feed conversion atio of 1.2.

Shrimp: 31% dry matter, 8.9% N , 0.3% P; feed: 88% dry m atter, 5.6% N, 1.2% P. Nitrogen and p hospho rus contents are on a dry w t basis.

Removed in shrimp

A d d e d

in feed Lost to water

(kg) (kg) (% in feed) (kg)

N itrog en 107.7 50.3 46.7 57.4

Phosp horus 23. 1.7 7.4 21.4

2 9 4

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Volume 34/Number 5/May 1997

Inlet water

25.3 Kg N

(17.8 )

Ammonia Shrimp

Shdmp foo d volat i l izat ion ha rves t

Shrimp 107.7 kg N 38.8 kg N 50.3 kg N M ac ro fau na

stocked (76.0 ) (27.4 ) (35.5 ) associated

<0.1 kg N

i - - ,', ~ \

0.6 kg N

( < o .1 ) i 7 , ( o . 4 0 , o

Fertilization~ ~ ~ I ~ ~ /

8.8 kg N

(6.2 ) _ j j ~

r--~_ Se dimen t Outlet water

Lz-'-> accum ulation ?) 52,1 kg N

(36.7 )

External food

Fig . 2 N i t ro g en mass b a l an ce pe r 1 ha o f po n d (1 82 2 k g sh r imp

harvested) in the semi-intensiveshrimp farm for the dry season

(water exchange, 3-5 ). Unquantified arrows represent

processes that may constitute possible sources of error in the

mass balance (see text). Percentages are of total nitrogen

input to pond.

Shrimp

stocked

<0.1 kg P

(<0.4 )

F ertiliza tion ' ~

0.9 kg P

(3.2 ) ~

Inlet water

3.7 kg P

(13.4 )

External food

Shrimp food

23.1 kg P

(83.4 )

Shrimp

harvest

1.7kg P

(6.1 )

Sediment

accumulation

17.6 kg P

(63.5 )

i

Macrofauna

associated

<0.1 kgP

(~/0.4 )

/

Outlet water

_ _ 8.4 kg

(30.3 )

Fig . 3 Pho spho ru s mass b a l an ce pe r 1 ha (18 2 2 k g sh r imp ha rve s t ed )

in t he semi - in t en s ive sh r imp fa rm fo r t he d ry sea so n (wa te r

exchange, 3--5%). Unquant i f ied arrows represent processes tha t

may constitute possible sources of error in the mass balance

(see text). Percentages are of total phosphorus input to

pond.

nitrogen and phosphorus associated with the shrimp

produced. Nitrogen export ed by ammonia volatilization

and nitrogen or phosphorus adsorbed by sediments

were calculated by difference.

In addition to nitrogen lost from the system with

discharged phytoplankton, there is significant organic

nitrogen in the form of suspended microbial/detrital

complexes. In this model, the amount of nitrogen and

phosphorus in the particulate material was calculated

using the measurements of organic suspended solids

(Table 4) and considering the Redfield ratio of 106:16: I

for C:N:P. This ratio was used to estimate the input and

output of suspended nitrogen and phosphorus during

water exchange, filling and draining.

295

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P r o ce s s e s o t h e r t h an t h o s e d e s c r i b ed i n t h e m as s

b a l an ce s ( F i g s 2 an d 3 ) m i g h t ad d o r r em o v e n i t r o g en

a n d p h o s p h o r u s f r o m t h e s h r i m p p o n d . P l a n k t o n a n d

d e t r i t a l m a t e r i a l a r e t r an s p o r t ed w i t h t h e w a t e r p u m p ed

f r o m t h e l a g o o n s y s t e m t o t h e p o n d s a n d m a y a c t a s

ex t erna l food fo r t he sh r imp . Det r i t a l aggregat es ,

m i c r oa l g ae , c o p e p o d s , a m p h i p o d s , p o l y c h a e t es a n d

m o l l u s c s , w h i ch g r o w an d co m e w i t h w a t e r ex ch an g es ,

h a v e b e e n c o n s i d e r ed a n i m p o r t a n t p a r t o f th e d i e t o f

s h r i m p cu l t u r ed i n s em i - i n t en s i v e p o n d s ( C h o n g an d

S as ek u m ar , 1 9 8 1 ; G l ea s o n an d W e l l in g t o n , 1 9 8 8 ).

H o w ev e r , t h i s is p r o b ab l y a m i n o r s o u r ce o f n i t r o g en

a n d p h o s p h o r u s i n th e m a s s b a l a nc e s , b e c a u s e o f th e

r e l a ti v e l y s m a ll f l ux e s o f p h y t o p l a n k t o n i c b i o m as s ( a s

ch l o r o p h y l l a , s ee T ab l e s 3 an d 4 ) in co m p a r i s o n t o t h e

s u p p l y o f s h r im p f eed an d t h e p l an k t o n an d d e t r it a l

m a t e r i a l g en e r a t ed in s i tu i n t h e p o n d w a t e r . In s i tu

p r o d u c t i o n o f n a tu r a l f o o d w a s s t i m u l a t e d m a i n ly f r o m

t h e i n p u t o f n i t r o g en a n d p h o s p h o r u s , v i a fe r t il i za t i on ,

f eed an d i n l e t w a t e r . N - f i x a t i o n b y b l u e - g r een a l g ae w as

n o t t ak en i n t o a cco u n t b y t h e m o d e l , an d t h e s i g n i f i c -

an ce o f th i s co n t r i b u t i o n i s u n k n o w n .

R e m o v a l o f n i tr o g e n a n d p h o s p h o r u s f r o m t h e p o n d s

a l s o co u l d h av e o ccu r r ed t h r o u g h g r az i ng o f o t h e r s m a l l

o r g an i s m s t h a t en t e r ed t h e p o n d b y p a s s i n g t h r o u g h t h e

po nd f i lt e rs a t t he ga t es (300 l am) as l a rva l s t ages . Thes e

o r g a ni s m s m i g h t h a v e g r o w n a n d c o m p e t e d f o r s p a c e

an d f o o d w i t h t h e s h r i m p . D u r i n g 1 99 3/ 19 9 4 a t t h e

s am e s h r i m p f a r m u t i l i z ed f o r t h e p r e s en t s t u d y , t h e

ab u n d an c e an d d i v e r s i t y o f m a c r o f au n a ( fi sh e s an d

d ecap o d c r u s t a cean s ) w e r e d e t e r m i n ed d u r i n g t w o

s ea s o n s ( H en d r i ck x et al . , 1996) . B iomass t o t a l l ed

ab o u t 1 15 k g o f fr e s h w e i g h t ( 0 . 3 - 0 . 9 % o f s h r i m p

harves t ) . F i sh r ep rese n ted 90- -94% of t h i s t o t a l f r esh

w e i g h t. D o m i n an c e r e fl e c ted t h e i m p o r t an c e o f t w o fi sh

spec i es P o m a d a s y s m a c r a c a n t h u s a n d C y n o s c i o n x a n t h u -

lus. T h e b l u e c r a b Cal l inec tes arcua tus w as t h e o n l y

d e c a p o d c r u s t a c e a n h a r v e s te d . I n t h e p r e p a r a ti o n o f t h e

m as s b a l an ce , t h e f l u x e s o f n i t r o g en an d p h o s p h o r u s

a s s o c i a t ed w i t h m ac r o f au n a w e r e ca l cu l a t ed co n s i d e r i n g

t h e co r r e s p o n d i n g f r e s h w e i g h t (4 . 0 k g h a - b a s fi sh

b i o m a s s . A c o m p o s i t i o n o f 2 5 % d r y m a t te r , 8 %

n i t r o g en ( d r y w t ) , an d 1 . 5% p h o s p h o r u s ( d r y w t ) w as

a s s u m ed ( T u ck e r an d B o y d , 1 9 8 5 ) .

T h e ca l cu l a t ed n e t lo ad i n g o f s u s p en d ed o r g an i c

m a t t e r i s 4 6 9 k g h a - 1 o f p o n d w a t e r , ap p r o x i m a t e l y

2 1 . 3 % o f th e s h r i m p f eed s u p p li ed . T h e l a r g e s t s o u rce o f

n i t r o g en ( 7 6 . 0 %) an d p h o s p h o r u s ( 8 3 . 4 %) i s t h e r e s u l t

o f ap p l i ed f eed . S h r i m p h a r v e s t i n g a c co u n t ed f o r o n l y

3 5 .5 % a n d 6 . 1 % o f t h e t o ta l n i tr o g e n a n d p h o s p h o r u s

i n p u t i n t o t h e p o n d s . O u t l e t w a t e r r em o v ed s i g n i f i c an t

q u an t i t ie s o f n i t r o g en ( 3 6 . 7 %) an d p h o s p h o r u s ( 3 0 .3 %) .

D en i t r i f i c a t i o n , am m o n i a v o l a t i l i z a t i o n an d o r g an i c

n i t r o g en an d p h o s p h o r u s w e r e n o t d i r e c t l y ev a l u a t ed

i n t h i s s t u d y b u t , b ecau s e 2 7 . 4 % o f th e n i t ro g en w as

u n ac co u n t ed f o r i t w as a s s u m ed t o b e lo s t t h r o u g h t h e s e

p a t h w ay s . S i m i l a r ly , i t w as d ed u ced t h a t 6 3 . 5 % o f t h e

p h o s p h o r u s w a s a s s o c i a t e d w i t h t h e p o n d b o t t o m

296

Marine Pollution B ulletin

s ed i m en t s an d s u s p en d ed o r g an i c m a t t e r . T h e p r o ce s s e s

o f d en it r if i c a ti o n , am m o n i a v o l a t i li z a t io n , an d p h o s -

p h o r u s ad s o r p t i o n b y s ed i m en t s , s e r v e t o m o d e r a t e an d

r eg u l a t e t h e i r co n cen t r a t i o n s i n t h e w a t e r co l u m n

( T u ck e r an d B o y d , 1 9 8 5 ) . H o p k i n s et al . (1993) could

n o t a cc o u n t f o r 1 3 - 4 6 % o f n i t r o g en i n p u t i n in t en s iv e

s h r i m p p o n d s an d ex p l a i n ed t h i s l o s s t h r o u g h d en i -

t r if i c a ti o n an d a t m o s p h e r i c d i f fu s i o n o f u n - i o n ized

am m o n i a . B o y d (1 9 8 5) r ep o r t ed t h a t 5 7 % o f n i t ro g en

i n p u t s i n f r e s h w a t e r c a t f i s h p o n d s w e r e l o s t t h r o u g h

d en i t r i f i c a t i o n an d am m o n i a d i f f u s i o n an d t h a t 5 6 % o f

t h e p h o s p h o r u s w as l o s t t h r o u g h u p t ak e b y s ed i m en t s .

B r i gg s an d F u n g e - S m i t h ( 19 9 4) r ep o r t ed t h a t 3 1 % o f

n i t ro g en an d 8 4 % o f t h e p h o s p h o r u s w e r e r e t a i n ed in

t h e s ed i m en t s o f in t en s iv e m ar i n e s h r i m p p o n d s i n

T h a i l an d . C o m p ar ab l e p e r cen t ag e s r ev ea l t h a t r a t e s o f

d en i t r i f i c a t i o n an d am m o n i a d i f f u s i o n a r e co m p a r ab l e

be tween hyper sa l i ne ( average sa l i n i t y o f 47 .2 -48 .3 ) ,

m a r i n e s h r i m p an d f r e s h w a t e r p o n d s .

E n v i r o n m e n t a l a n d b i o g e o c h e m i c a l i m p l i c a t i o n s

T h e en v i r o n m en t a l l o ad p e r h ec t a r e o f s h r i m p p o n d

d u r i n g t h e g r o w i n g s ea s o n w as ca l cu l a t ed u s i n g t h e

d iu rna l d a t a (m etho d b ) : 257 g o f N-n i t r i te , 146 g o f N -

n i t ra t e , 5 20 g o f P - p h o s p h a t e , 4 6 9 k g o f s u s p en d ed

o r g an i c m a t t e r , 3 60 g o f ch l o r o p h y l l a an d 8 5 k g o f

d i s s o l v ed o x y g en . C o n s i d e r i n g t h e l o s s o f d i s s o l v ed

o x y g en an d i ts k n o w n e q u a t i o n f o r t h e o x i d a t i o n o f

o r g an i c m a t e r ia l ( S t u m m an d M o r g an , 1 9 81 ), i t c an b e

ca l cu l a t ed t h a t s i n ce 8 5 k g o f d is s o l v ed o x y g en w as l o s t,

68 .3 kg o f o rgan i c m ater i a l was ox id i zed . Th erefo re t he

n e t d i s ch a r g e o f s u s p en d ed o r g an i c m a t e r i a l w as

ad jus t ed t o 400 .7 kg .

T h e t o t a l e f f lu en t l o s s o f p h o s p h o r u s i n p o n d s

(def ined as t he phosphorus i npu t w i th f eed , f e r t i l i zer ,

i n l e t w a t e r an d s t o ck ed an i m a l s an d l o s s e s f r o m

r em o v a l o f s h r i m p a t h a r v e s t an d p o n d s ed i m en t

accu m u l a t i o n ) f o r e ach t o n n e o f p r o d u c t h a r v e s t ed i s

v a r i ab l e , d ep en d i n g o n t h e cu l t u r e s y s t em an d t h e

s p ec i es in v o l v ed . F o r e ach t o n n e o f ch an n e l c a t f is h

p r o d u ced i n q u a s i - s t a t i c p o n d s an am o u n t o f 1 . 5 k g o f

p h o s p h o r u s i s l o s t ( e s t i m a t ed f r o m B o y d , 1 9 8 5 an d

T u c k e r a n d B o y d , 1 9 8 5 ) . T o p r o d u c e o n e t o n n e o f

s h r i m p (P . vannamei ) i n s em i - i n t en s i v e p o n d s 4 . 6 k g o f

p h o s p h o r u s w as e s t i m a t ed t o b e l o s t t o t h e en v i r o n m en t

i n t h e p r e s en t s t u d y . I n cag e f a r m s , p h o s p h o r u s l o s s

es t imates r ange f rom 9 .4 kg (Ackefor s and Enel i , 1990)

t o 1 9 . 6 -2 2 . 4 k g ( H o l b y an d H a l l , 1 9 9 1) p e r t o n n e o f f i s h

p r o d u c e d .

The to t a l e f f l uen t l o ss o f n i t rogen in ponds (def ined as

the n i t rogen inpu t w i th f eed , f e r t i l i zer , i n l e t water and

s t o ck ed an i m a l s m i n u s n i t r o g en r em o v a l w i t h h a r v e s t ,

m ac r o f au n a a s s o c i a t ed an d p o n d v o l a t i l i z a t i o n ) f o r e ach

t o n n e o f s h r i m p p r o d u ced i n s em i - i n ten s i v e p o n d s w as

e s t i m a t ed t o b e i n t h e o r d e r o f 2 8 .6 k g . T h i s v a l u e is

i n t e rm ed i a t e b e t w een t h e 1 2 k g t - t d ed u ced f r o m

T u c k e r an d B o y d ( 19 85 ) f o r c a t fi s h an d 7 8 k g t - I

r ep o r t ed b y A ck e f o r s an d En e l l ( 1 9 90 ) f o r c ag e cu lt u r e .

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V o l u m e 3 4 / N u m b e r 5 / M a y 1 9 9 7

S i m i l a r l y , d i f f e r en ce s i n a ccu m u l a t ed p h o s p h o r u s i n

s ed i m en t s am o n g t h e t h r ee d i f f e r en t cu l t u r e s y s t em s

w er e 6 3 . 5 an d 5 6 % i n t h e s h r i m p an d ca t f i s h p o n d s

(Tucker and Boyd , 1985) , r espec t i ve ly . In cage cu l tu re ,

w h e r e m o r e s t u d i e s h av e b een co n d u c t ed ( e . g . A ck e f o r s

an d En e l l, 1 9 9 0 ; H o l b y an d H a l l , 1 9 9 1 an d c i te s h e re i n ),

t h e v a l u e s d e t e r m i n ed r an g ed f r o m 3 8 t o 6 6 % ( v a l u e s

a r e in p e r c e n ta g e o f to t a l p h o s p h o r u s i n p u t t o p o n d o r

cage) .

T h e m e a n d i s c h a rg e o f p h o s p h o r u s a n d s u s p e n d e d

s o l id s f r o m s ew ag e w o r k s , c a l cu l a t ed i n te r m s o f g r am s

p e r p e r s o n p e r d ay , c an b e u s ed t o ex p r e ss t h e m as s f lo w

o f aq u acu l t u r e f a r m e f fl u en ts in p o p u l a t i o n eq u i v a l en t s

(P i l l ay , 1992) . Us ing t he popu la t i on equ iva l en t s o f

n i t r o g en an d p h o s p h o r u s g i v en b y B e r g h e im an d

S e l m er - O l s en ( 1 9 7 8 ) an d a s s u m i n g t h a t a l l t h e s h r i m p

f a r m s i n S i n a l o a s t a t e ( M ex i co ) o p e r a t e a s d e s c r i b ed

h e re , t h e 8 10 2 h a o r 8 6 10 t o f p r o d u c t i o n ( S E M A R N P ,

1995) , fo r sh r imp f arms in S ina loa r ep resen t a l oad

co r r e s p o n d i n g t o t h e u n t r ea t ed s ew ag e g en e r a t ed b y

56 200 to 192 750 and 43 500 to 149 170 peo p le i n t e rm s

o f n i t r o g en an d p h o s p h o r u s , r e s p ec t iv e l y , d i s ch a r g ed

p e r y ea r . T h i s h a s i m p o r t an t i m p l i ca t i o n s f o r s h r i m p

p o n d m an ag em en t w h i ch s h o u l d a i m t o r ed u ce e f f l u en t

i m p ac t o n ad j acen t w a t e r s , an d t o d e t e r m i n e t h e f a t e

an d m ech an i s m s o f a s s i m i l a t io n o f th e s e n u t r ien t s .

T h e a u t h o r s t h a n k H . B o j 6 r q u e z L e y v a a n d A . N f i fi e z - Pa s t r n f o r h i s

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s u p p o r t e d b y a r e s e a r c h g r a n t f r o m t h e C o n s e j o N a c i o n a l d e C i e n c i a y

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