Distribution, Transport, Adsorption, and Precipitation of Inorganic

32

D i s t r i b u t i o n , Transport, A d s o r p t i o n , a n d Precipitation of I n o r g a n i c P h o s p h o r u s in t h e G e n e s e e

River

M. M. REDDY

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: March 19, 1979 | doi: 10.1021/bk-1979-0093.ch032

State of New York, Department of Health, Albany, NY 12201

Understanding the f a t e of phosphorus i n a watershed i s c r i t i c a l f o r t h e development o f s t r a t e g i e s t o cope e f f e c t i v e l y w i t h e u t r o p h i c a t i o n ( 1 ) · Sediment-bound phosphorus i s c o n t r i b u t e d b y sewage, e r o d e d s o i l , p l a n t m e t e r i a l , and u r b a n r u n o f f . These s o l i d s a r e t r a n s p o r t e d as suspended sediment and as b e d l o a d . T r a n s p o r t o f phosphorus a s s o c i a t e d w i t h l a r g e r p a r t i c l e s i z e s e d iment o c c u r s o n l y d u r i n g p e r i o d s o f h i g h r i v e r d i s c h a r g e . Soluble phosphorus e n t e r i n g a watershed as r u n o f f or wastewater i n p u t s , on t h e o t h e r h a n d , i s a p p a r e n t l y s o r b e d on suspended p a r t i c l e s a n d / o r r e a c t s w i t h o t h e r water column c o n s t i t u t e n t s to form i n s o l u b l e s u b s t a n c e s w h i c h a r e t r a n s p o r t e d by w a t e r and e v e n t u a l l y d e p o s i t e d i n g r e a t e r abundance i n f i n e g r a i n e d s e d i m e n t . In l a k e s s o l u b l e phosphorus i n p u t s a r e t y p i c a l l y converted to b i o mass, r e c y c l e d through t h e water column, and e v e n t u a l l y d e p o s i t e d i n bottom sediments. E s t a b l i s h m e n t of r e a l i s t i c and s u c c e s s f u l s t r a t e g i e s f o r c o n t r o l l i n g phosphorus i n p u t s to the North American Great Lakes r e q u i r e s that p e r i o d s of i n t e n s e h y d r o l o g i c a l a c t i v i t y i n a b a s i n be c a r e f u l l y s t u d i e d and c h a r a c t e r i z e d . In t h i s paper , we s h a l l e x a m i n e s e v e r a l m o d e l c h e m i c a l r e a c t i o n s i n h a r d w a t e r s w h i c h may i n f l u e n c e p h o s p h o r u s c o n c e n t r a t i o n s i n t h e w a t e r c o l u m n and s e d i m e n t . Chemical r e a c t i o n s i n f l u e n c i n g phosphate d i s t r i b u t i o n i n t h e G e n e s e e R i v e r were i d e n t i f i e d u s i n g t h r e e s e p a r a t e techniques: 1) s e d i m e n t s a m p l e s c o l l e c t e d d u r i n g s y n o p t i c s u r v e y s were a n a l y z e d u s i n g a v a r i e t y o f s e l e c t i v e p h o s p h o r u s e x t r a c t i o n p r o c e d u r e s t o c h a r a c t e r i z e sedimenfebound p h o s p h o r u s ; 2) w a t e r column c h e m i c a l c o n c e n t r a t i o n s from samples o b t a i n e d c o n c u r r e n t l y w i t h t h e sediment samples were used t o c a l c u l a t e e q u i l i b r i a f o r the determination of i o n a c t i v i t y products of s e v e r a l mineral p h a s e s w h i c h may remove p h o s p h o r u s f r o m t h e w a t e r c o l u m n ; a n d 3) a s e e d e d c r y s t a l l i z a t i o n p r o c e d u r e was u s e d t o m o n i t o r t h e d i s t r i b u t i o n o f i n o r g a n i c phosphate between s o l u t i o n and s o l i d phases d u r i n g c a l c i t e p r e c i p i t a t i o n i n simulated n a t u r a l water. G e n e s e e R i v e r s a m p l i n g s i t e s a r e l i s t e d i n T a b l e I a n d a r e shown i n F i g u r e 1.

0-8412-0479-9/79/47-093-737$05.75/0 © 1979 American Chemical Society Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


Figure 1. Genesee River sampling sites

Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

32.

Inorganic Phosphorus in the Genesee River

REDDY

Table

I.

Sampling

Si t e


location

Sites

739

on t h e G e n e s e e R i v e r , N . Y .

U.S.G.S. Miles st a t i ο η from mouth o f number Genesee

Latitude

Longi tude

Wei 1 s v i 11 e

137

04 - 2 2 1 0 - 0 0

42°07'20"

77°57'27"

Transit Br.

117

04 - 2 2 1 4 - 2 3

42°19'46"

78°04« 3 6 "

Portagevi11e

85

04 - 2 2 3 0 - 0 0

42°34'13"

78°02'33"

Mt.

62

04 - 2 2 7 5 - 0 0

42 44'00"

77°50'21"

35

04 - 2 2 8 5 - 0 0

42°55 04"

77°45'27"

5

04 - 2 3 2 0 - 0 0

43°10'50"

77°37'40"

Morris

Avon Rochester

o

,

P u b l i s h e d r e p o r t s d i s c u s s i n g the i n f l u e n c e of calcium c a r bonate s o l i d s u r f a c e s on the phosphate i o n c o n c e n t r a t i o n i n n a t u r a l water (2, 3) i n c l u d e : 1 ) s o l u b i l i t y product-based c a l c u l a t i o n s (4j 5) ; ΪΤ spontaneous p r e c i p i t a t i o n experiments from h i g h l y supersaturated s o l u t i o n s (6^ Ij 8, 9) ; 3) a d s o r p t i o n of phosphate onto calcium carbonate (10, 11, 12, 13). These exper iments have provided u s e f u l i n f o r m a t i o n , but s e v e r a l have not i n c l u d e d a c t i v i t y c o e f f i c i e n t or i o n p a i r c o r r e c t i o n s i n t h e i r analyses, s e r i o u s l y l i m i t i n g the a p p l i c a b i l i t y of the r e s u l t s . In other s t u d i e s , s o l u t i o n s of h i g h s u p e r s a t u r a t i o n were employed which y i e l d e d complex, p o o r l y defined s o l i d phases. The m u l t i p i c i t y o f complex c r y s t a l polymorphs and hydrates i n the calcium phosphate system i s now w e l l recognized and must be considered i n the i n t e r p r e t a t i o n o f experiments i n v o l v i n g the removal of phosphate from n a t u r a l waters (14, 15). Experimental Procedures Sample C o l l e c t i o n , Pretreatment, and A n a l y s i s . Sedimentbound phosphorus i n the Genesee R i v e r was s t u d i e d by sampling bottom sediment, f i n e - m a t e r i a l washed from bottom sediment, sus pended sediment, and water column p a r t i c u l a t e m a t e r i a l a t s i x s t a t i o n s on the r i v e r . The sampling program was planned to be s y n o p t i c w i t h complete chemical and h y d r o l o g i c a l parameters r e corded a t each s i t e . One k i l o g r a m s u r f i c i a l sediment samples were c o l l e c t e d i n midstream at most s i t e s during s i x f i e l d t r i p s



740

CHEMICAL

MODELING IN AQUEOUS SYSTEMS

f r o m J u n e 1975 t o M a r c h 1 9 7 7 . B o t t o m s e d i m e n t s a m p l e s w e r e o b t a i n e d w i t h n o n m e t a l l i c e q u i p m e n t a n d most w e r e w e t - s i e v e d immediately through a 2-mmpolyethlyene s i e v e using r i v e r water. Sediment samples were f r o z e n on s i t e and s t o r e d f r o z e n u n t i l a n a l y s i s . Sample c o l l e c t i o n a n d p r e t r e a t m e n t p r o c e d u r e s ( 1 6 , 17) h a v e b e e n a d o p t e d f r o m t e c h n i q u e s e m p l o y e d b y t h e U. S. G e o l o g i c a l S u r v e y ( B . M a l o , U. S. G e o l o g i c a l S u r v e y , p e r s o n a l c o m m u n i c a t i o n , 1975). Suspended sediment samples were o b t a i n e d by c o n t i n u o u s h i g h - s p e e d c e n t r i f u g a t i o n o f l a r g e volumes o f r i v e r water, o r by c o l l e c t i n g t h e suspended sediment o b t a i n e d i n t h e f i e l d wets i e v i n g procedure. P a r t i c u l a t e m a t e r i a l i s defined as that which i s r e t a i n e d b y f i l t e r i n g a r i v e r w a t e r s a m p l e t h r o u g h a 0.45um M i l l i p o r e filter. T y p i c a l l y , two l i t e r s o f w a t e r w e r e f i l tered f o r particulate analysis. Suspended sediment measurements made a t t h e same t i m e , b y t h e U. S. G e o l o g i c a l S u r v e y , w e r e u s e d to c o n v e r t t h e p a r t i c u l a t e c o n c e n t r a t i o n s t o a d r y weight b a s i s . F r o z e n b o t t o m s e d i m e n t s a m p l e s w e r e thawed f o r a n a l y s i s , d r i e d a t 110*C, c r u s h e d a n d s i e v e d t h r o u g h a 100-mesh n y l o n s i e v e a n d d i g e s t e d w i t h HNO3-H2O2 a t 1 0 0 ° C f o r two h o u r s ( 1 8 ) , a n d / o r with a c i d - a l k a l i n e p e r s u l f a t e (19). Since s i l i c a t e minerals are not s o l u b i l i z e d i n these procedures the r e s u l t s a r e considered o n l y as an estimate o f t h e t o t a l a v a i l a b l e phosphorus. Suspended sediments were f r e e z e - d r i e d i n t h e l a b o r a t o r y b e f o r e a n a l y s i s . P a r t i c u l a t e m a t e r i a l was d i g e s t e d d i r e c t l y o n t h e f i l t e r u s e d f o r c o l l e c t i o n , employing t h e d i g e s t i o n t e c h n i q u e d e s c r i b e d above. F r a c t i o n a l a n a l y s i s p r o c e d u r e s were chosen f o r h i g h r e p r o d u c i b i l i t y and p r e c i s i o n . A phosphorus e x t r a c t i o n procedure e m p l o y i n g NaOH ( w i t h N a C l ) t o d e t e r m i n e o c c l u d e d p h o s p h o r u s was a d o p t e d from t h e work o f W i l l i a m s e t a l j (20, 2 1 ) . The sequence i n t h i s p r o c e d u r e was f i r s t e x t r a c t i o n w i t h NaOH a n d t h e n e x t r a c t i o n with d i l u t e hydrochloric a c i d , the residue being d i s carded. Work p e r f o r m e d i n t h i s l a b o r a t o r y (M. M. Reddy a n d E . S h p i r t , New Y o r k S t a t e D e p t . o f H e a l t h , u n p u b l i s h e d d a t a , 1976) and e l s e w h e r e ( 2 2 ) i n d i c a t e s t h a t t h e NaOH e x t r a c t a b l e p h o s p h o r u s i s a measure o f b i o a v a i l a b l e sediment phosphorus. Hydrochloric a c i d e x t r a c t a b l e p h o s p h o r u s , f o l l o w i n g NaOH e x t r a c t i o n , m e a s u r e s a p a t i t e p l u s phosphorus i n c o r p o r a t e d i n i r o n o x i d e s . T h e NaOH e x t r a c t o b t a i n e d i n t h i s s t u d y was n o t d i g e s t e d a n d r e f l e c t s o n l y i n o r g a n i c f o r m s o f p h o s p h o r u s . A d d i t i o n a l f r a c t i o n a t i o n m e t h o d s we u s e d t o i d e n t i f y e l e m e n t a l a s s o c i a t i o n between p h o s p h o r u s a n d hydrous m e t a l o x i d e s i n sediments. These e x t r a c t i o n p r o c e d u r e s are largely empirical. The p r o c e d u r e employed h e r e c o n s i s t e d o f one i n i t i a l e x t r a c t i o n b y h y d r o x y l a m i n e h y d r o c h l o r i d e - n i t r i c a c i d r e a g e n t ( 2 3 ) f o l l o w e d b y e x t r a c t i o n w i t h ammonium o x a l a t e - o x a l i c acid s o l u t i o n (24), the residue being discarded. The h y d r o x y ! a m i n e e x t r a c t i o n p r o c e d u r e was u s e d t o i d e n t i f y t h e manganese o x i d e - p h o s p h a t e r e l a t i o n s h i p , w h i l e ammonium o x a l a t e - o x a l i c a c i d removes amorphous i r o n o x i d e s a n d p h o s p h a t e a s s o c i a t e d w i t h t h e s e oxides. A d e t a i l e d d e s c r i p t i o n o f t h e procedures used i n t h i s s t u d y f o r water column a n a l y s i s has been p r e s e n t e d e l s e w h e r e (25,


32.

741


REDDY

26).


During each a n a l y s i s , r e p l i c a t e s of samples c o l l e c t e d i n the Genesee R i v e r were analyzed as q u a l i t y - c o n t r o l check samples. The c o e f f i c i e n t s o f v a r i a t i o n f o r t o t a l phosphorus a n a l y s i s o f three sediments used as q u a l i t y - c o n t r o l check samples were 0.12 (n = 12), 0.16 (n = 11), and 0.13 (n = 11), w i t h means of 412, 487, and 758 ug P/g, r e s p e c t i v e l y . Seeded C r y s t a l l i z a t i o n Experiments. A d e t a i l e d d e s c r i p t i o n of the seeded growth technique has been p u b l i s h e d r e c e n t l y (27). The f o l l o w i n g summarizes the experimental procedure employed. Reagent grade chemicals; d i s t i l l e d , d e i o n i z e d , f i l t e r e d (0.22-urn M i l l i p o r e f i l t e r ) water; and grade A glassware were used i n a l l experiments. Supersaturated c a l c i u m carbonate s o l u t i o n s were prepared by drop-wise a d d i t i o n of 200 ml o f 5 χ 10~^ M calcium c h l o r i d e s o l u t i o n to 200 ml of 8 χ 10~3 M sodium bicarbonate s o l u t i o n i n a thermostated double-walled Pyrex g l a s s r e a c t i o n v e s s e l . S t a b i l i t y o f the supersaturated s o l u t i o n was v e r i f i e d by the constancy of pH f o r a t l e a s t one hour before the s t a r t o f each experiment. S o l u t i o n pH changes accompanying c a l c i t e growth a f t e r i n o c u l a t i o n of the s t a b l e supersaturated s o l u t i o n w i t h seed c r y s t a l were monitored w i t h a Corning pH meter and a s t r i p chart recorder. Calcium c o n c e n t r a t i o n i n s o l u t i o n during c r y s t a l l i z a t i o n was f o l l o w e d by a n a l y s i s o f s o l u t i o n f i l t r a t e s . An EDTA t i t r a t i o n procedure employing c a l c e i n i n d i c a t o r (28) w i t h a micrometer b u r e t t e was used t o determine c a l c i u m c o n c e n t r a t i o n i n the f i l t e r e d s o l u t i o n . T o t a l carbonate c o n c e n t r a t i o n was c a l c u l a t e d from a t i t r i m e t r i c a n a l y s i s of the f i l t r a t e u s i n g 0.01 _N s u l f u r i c a c i d and methyl P u r p l e i n d i c a t o r (pH range 4.8 - 5.4). A Ouantachrome Monosorb s u r f a c e area a n a l y z e r was used to measure seed c r y s t a l s u r f a c e area; a P h i l l i p s powder d i f f r a c t i o n ap paratus w i t h copper Ka r a d i a t i o n and a n i c k e l f i l t e r was employed f o r X-ray powder d i f f r a c t i o n v e r i f i c a t i o n o f seed c r y s t a l com p o s i t i o n . C a l c i t e seed c r y s t a l s were prepared by r a p i d l y adding 0.5 M C a C l s o l u t i o n t o 0.5 M Na2C0 s o l u t i o n at 5 C. The v i s c o u s suspension formed was g r a d u a l l y warmed t o 25°C, s t i r r e d o v e r n i g h t , then washed w i t h d i s t i l l e d water. Seed was aged i n d i s t i l l e d , d e i o n i z e d water 6 months before use. The seed c o n s i s t e d of uniform aggregates o f f l a t c r y s t a l s shown to be c a l c i t e by X-ray d i f f r a c t i o n , w i t h a s u r f a c e area of 1.71 m^/g. Seeded c r y s t a l growth experiments were performed i n s o l u t i o n s resembling n a t u r a l waters. I o n i c s p e c i e s c o n c e n t r a t i o n s were c a l c u l a t e d from measured s o l u t i o n pH and from t o t a l c a l c i u m and carbonate c o n c e n t r a t i o n s , using the mass a c t i o n and mass balance equations i n Table I I . C a l c u l a t i o n s were performed u s i n g s u c c e s s i v e approximations f o r i o n i c s t r e n g t h , I , (34) w i t h a Wang 720 C programmable c a l c u l a t o r . Ion a c t i v i t y c o e f f i c i e n t s were obtained from the m o d i f i e d Debye - Huckel equation proposed by Davies (36). Bicarbonate i o n was the predominant carbonate species i n the experimental s o l u t i o n s , accounting f o r more than 95% of the t o t a l carbonate 9

2

3


742

CHEMICAL

MODELING IN AQUEOUS

Table II. Equations Used f o r C a l c u l a t i o n of Species at 25°C and 1 Atm Pressure Equation* Mass

Reference

_ .35

(29)

-10.33

(30)

= 10-14-00

(31)

3

1 0

6

[H C0 ] Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: March 19, 1979 | doi: 10.1021/bk-1979-0093.ch032

constant

3

2. [H ] [ C 0 - ] 2

+

3

=

1 0

[HCO3-] 3. [H ] [OH"] +

4.

Ionic

action

1-[H*][HC0 -] __ 2

for

SYSTEMS

[CaC0 ] 3

103.2

(32)

1.3

(33)

[Ca2 + ] 0 2 - ] [ C

3

+

5.

[CaHC0^ ]

=

1 0

[ C a ] [HCO3-] z+

[CaQH ]

6.

= 10 · 1

+

4

(34)

[Ca ][OH"] 2+

7. ( [ C a 2 + ]

[ C

0 2-]) 3

= 10 -8.4

c a l c i t e

(35)

Mass balance"'' 8.

T

C a

=

[Ca ] f 2+

+

[CaOH ] +

+

+

[ÇaHC0-, 3

+

[CaC0 °] 3

2

9

·

T

C0 = [ 3^"] C 0

o

[HC0 "1] 3

[H C0 2

3 ]

[CaHC0 +] 3

+ (CaC0 Q) 3

fo *

Bracketed solution.

terms denote thermodynamic a c t i v i t i e s

t The term f denotes the a c t i v i t y of charge z . z

coefficient

for


in ion

32.

REDDY


743

c o n c e n t r a t i o n . Calcium carbonate and b i c a r b o n a t e i o n - p a i r concen t r a t i o n s were considered i n s o l u b i l i t y c a l c u l a t i o n s . The i n f l u e n c e o f phosphate i o n - p a i r formation on the c r y s t a l l i z a t i o n r e a c t i o n was examined and found t o be n e g l i g i b l e (27) a t the phosphate c o n c e n t r a t i o n l e v e l s employed.


R e s u l t s and D i s c u s s i o n s Phosphorus D i s t r i b u t i o n . The major sediment phosphorus f r a c t i o n i s that e x t r a c t e d by h y d r o c h l o r i c a c i d (Table I I I ) . Ammonium o x a l a t e - o x a l i c a c i d s o l u t i o n e x t r a c t s somewhat l e s s phosphorus than h y d r o c h l o r i c a c i d , w h i l e sodium hydroxide as w e l l as hydroxylamine e x t r a c t much l e s s . Phosphorus e x t r a c t e d from sediment by NaOH has been r e l a t e d to non-occluded, surface-exchangeable, b i o a v a i l a b l e forms (22). H y d r o c h l o r i c a c i d e x t r a c t i o n y i e l d s occluded phosphorus i n c o r porated i n hydrous metal o x i d e s , carbonate and phosphate m i n e r a l s of sediment. Hydroxylamine reagent s p e c i f i c a l l y removes hydrous manganese o x i d e s , w h i l e amorphous hydrous oxides of i r o n and aluminum are removed by the o x a l a t e reagent. T o t a l a v a i l a b l e sediment phosphorus analyses i n c l u d e s sediment organic phosphorus components i n a d d i t i o n t o the i n o r g a n i c p o r t i o n determined by the s e l e c t i v e e x t r a c t i o n procedures. The v a r i a t i o n i n t o t a l a v a i l a b l e sediment phosphorus con c e n t r a t i o n among the three sediment types shown i n Table I I i s c l e a r . A s t a t i s t i c a l a n a l y s i s of t h i s data shows that both the suspended sediment and p a r t i c u l a t e t o t a l phosphorus concentra t i o n s are g r e a t e r than the bottom sediment v a l u e a t the 99% con f i d e n c e l e v e l . Phosphorus content i n c r e a s e s i n the sequence; bottom sediment, suspended sediment, and p a r t i c u l a t e m a t e r i a l i n accordance w i t h the i n c r e a s e i n surface area (M. M. Reddy, New York State Dept. of H e a l t h , unpublished data, 1977). High surface area sediment components may adsorb phosphorus-containing substances,from the water column, i n c r e a s i n g t h e i r phosphorus con c e n t r a t i o n . Another p o s s i b l e e x p l a n a t i o n i n c l u d e s d i l u t i o n o f bottom sediment by r e l a t i v e l y i n e r t primary m i n e r a l s i n the sand and s i l t s i z e f r a c t i o n s . Phosphorus Transport. Sediments are recognized as a major t r a n s p o r t medium f o r phosphorus to the North American Great Lakes. Phosphorus t r a n s p o r t i n watersheds such as the Genesee occurs i n l a r g e p a r t during r a i n f a l l and snow^-melt discharge events. The t r a n s p o r t o f elements from a watershed can be ex pressed as instantaneous u n i t l o a d . This q u a n t i t y i s defined as the amount of m a t e r i a l c a r r i e d by a r i v e r a t a given p o i n t d i v i d e d by the area drained by the r i v e r above that p o i n t . For the s y n o p t i c s t u d i e s described here, the instantaneous u n i t loads are expressed as grams o f phosphorus per second per acre (Figure 2 ) . The major component o f the phosphorus load transported by the Genesee R i v e r d u r i n g the two sampling periods discussed here


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Table III. S t a t i s t i c s f o r Phosphorus A n a l y s e s f o r Several Sediment Types C o l l e c t e d i n the Genesee R i v e r Watershed, New Y o r k , (ug/g) Sample

x"

Range

σ

CV

Ν


Bottom Sediment Total A v a i l a b l e 560 NaOH E x t r a c t a b l e 58 HC1 E x t r a c t a b l e 398 NH 0H E x t r a c t a b l e 74 (NH ) C 0 Ex185 tractable 2

4

2

2

4

330 5 177 6 49

-

980 410 731 313 453

140 62 99 63 93

0.25 1.07 0.25 0.86 0.50

99 98 98 98 83

390 19 258 3 119

- 2020 360 - 1000 232 - 664 109 - 385 102 - 1110 222

0.46 1.43 0.21 1.46 0.47

46 17 17 17 17

0.70

61

Suspended Sediment* Total Available 770 NaOH E x t r a c t a b l e 163 HC1 E x t r a c t a b l e 528 NH 0H E x t r a c t a b l e 70 ( N H ) C 0 4 Ex474 tractable 2 2

4

2

2

Particulate Total

Analysis

Analysis

910

400 - 3000 640

Suspended sediment samples were o b t a i n e d by c o n t i n u o u s high-speed c e n t r i f u g a t i o n of l a r g e volumes of r i v e r w a t e r , or by c o l l e c t i n g the suspended sediment o b t a i n e d in the f i e l d w e t - s i e v i n g p r o c e d u r e . P a r t i c u l a t e m a t e r i a l i s d e f i n e d as t h a t which i s r e t a i n e d by f i l t e r i n g a r i v e r water sample through a 0.45-ym M i l l i p o r e f i l t e r .



32.

REDDY


745

(December 14, 1975 and March 13, 1976) i s that a s s o c i a t e d w i t h the suspended sediment. D i s s o l v e d phosphorus i n the water column during these p e r i o d s was t y p i c a l l y l e s s than h a l f o f the t o t a l water column c o n c e n t r a t i o n . U n i t loads v a r i e s w i d e l y (Figure 2 ) . A f l o o d c o n t r o l im poundment, l o c a t e d j u s t upstream of the Mount M o r r i s sampling s t a t i o n , markedly i n f l u e n c e s the Genesee R i v e r discharge and suspended sediment concentrations a t the downstream s t a t i o n s . Three sampling s t a t i o n s upstream of the Mount M o r r i s impoundment ( W e l l s v i l l e , T r a n s i t Br., and P o r t a g e v i l l e ) show a smooth and systematic i n c r e a s e i n the phosphorus u n i t load w i t h i n c r e a s i n g discharge. I n c o n t r a s t , u n i t loads a t the mid-basin s i t e s show much l a r g e r abolute values and f l u c t u a t i o n s than the other s t a t i o n s . These s t a t i o n s e x h i b i t l a r g e v a r i a t i o n s i n discharge and t h e r e f o r e i n suspended sediment c o n c e n t r a t i o n s . M i n e r a l S a t u r a t i o n i n the Genesee R i v e r . The importance o f heterogeneous e q u i l i b r i a i n r e g u l a t i n g d i s s o l v e d i n o r g a n i c phosphorus concentrations i n the Genesee R i v e r was examined by c a l c u l a t i n g the i o n a c t i v i t y products of s e v e r a l m i n e r a l phases using the WATEQF (37) chemical model and/or mass a c t i o n and mass balance equations w i t h a s m a l l l a b o r a t o r y computer. During h i g h discharge periods i n December and March there i s extensive unders a t u r a t i o n i n the water column w i t h respect t o calcium carbonate and phosphate phases, w h i l e during August 1976, a r e l a t i v e l y lower-flow p e r i o d , the f i r s t f o u r downstream sampling s t a t i o n s i n the Genesee showed s a t u r a t i o n o r s u p e r s a t u r a t i o n w i t h respect to c a l c i t e (Figure 3 ) . Thus, during the summer,it appears t h a t i n the lower reach o f the Genesee R i v e r c a l c i t e p r e c i p i t a t i o n l i m i t s the c o n c e n t r a t i o n o f d i s s o l v e d calcium. S a t u r a t i o n l e v e l s f o r the thermodynamically s t a b l e calcium phosphate m i n e r a l , h y d r o x y a p a t i t e , are 1 0 ^ below the e q u i l i b r i u m values f o r the Genesee R i v e r S t a t i o n s during the high f l o w sampling periods of December and March. P r e c i p i t a t i o n of hydroxyapatite o r other calcium phosphate phases does not occur so these s o l i d phases do not r e g u l a t e phos phate c o n c e n t r a t i o n i n the subsaturated r i v e r water. F e r t i l i z e r a p p l i e d t o calcareous s o i l s produces minerals such as hydroxyapatite (13). When such s o i l s a r e eroded, and subsequently c a r r i e d t o the Genesee R i v e r , t h i s m i n e r a l phase w i l l be i n a markedly subsaturated s o l u t i o n and w i l l tend t o d i s s o l v e , r e l e a s i n g i n o r g a n i c phosphate t o the water column. Two major sub-basins i n the Genesee R i v e r watershed have d i f f e r e n t c a l c i t e s a t u r a t i o n l e v e l s . Oataka Creek sub-basin, a predom i n a t e l y a g r i c u l t u r a l r e g i o n , had c a l c i t e s a t u r a t i o n values much c l o s e r t o e q u i l i b r i u m than those found f o r the Genesee R i v e r on the sampling dates. Canasaraga Creek sub-basin, an area l e s s i n t e n s i v e l y c u l t i v a t e d than Oataka Creek sub-basin, e x h i b i t e d s a t u r a t i o n o r supersaturâtion i n August but was subsaturated i n December 1975 and March 1976. From these data, i t can be hy pothesized that there are higher sediment phosphorus contents i n


746

CHEMICAL MODELING IN AQUEOUS SYSTEMS

60

• December 14, 1975


• March 13,1976 to Ο

50

Ω 30

CO Ζ)

tr ο χ

20

CL CO

Ο

χ

CL

10

J

140

I

ι L

J

120 100

1

1

80

l _ l

60

I

I

ι I

40

I

ι

20

ι

0

MILES ABOVE MOUTH OF GENESEE RIVER Figure 2. (a, above) Total phosphorus unit load (g Ρ/sec/acre), (B, top right) percent unit load as dissolved phosphorus, and (c, bottom right) discharge (cfs) plotted as a function of sampling point distance from Lake Ontario. Samples represent dates preceeding and following the snow melt runoff event in 1976.



32.

REDDY


140

120 100 80

60

40

20

747

0

MILES ABOVE MOUTH OF GENESEE RIVER

140

120 IO0

80

60

40

20

0

MILES ABOVE MOUTH OF GENESEE RIVER

American Chemical Society Library

Jenne; Chemical Modeling Aqueous Systems ί 155 16thinSt. N. W. ACS Symposium Series;Mfafthinntnn American Chemical Society: Washington, DC, 1979. Π P onnoe


748

CHEMICAL

MODELING IN

AQUEOUS

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the a g r i c u l t u r a l sub-basin because of carbonate mediated phos phorus m i n e r a l i z a t i o n . In support of this hypotheses, Oataka b a s i n sediments are the Genesee watershed sediments w i t h the g r e a t e s t h y d r o c h l o r i c a c i d e x t r a c t a b l e phosphorus content. Release of phosphorus from a g r i c u l t u r a l l y d e r i v e d s o i l s and sediments during h i g h discharge p e r i o d s may be counteracted by r u n o f f d i l u t i o n . Data r e p o r t e d by the U. S. G e o l o g i c a l Survey f o r the S t . Lawrence and Lake Ontario b a s i n s , f o r the p e r i o d con s i d e r e d here,show phosphorus c o n c e n t r a t i o n i n r a i n w a t e r to be 0.010 mg P / l (38). T h i s c o n c e n t r a t i o n i s much l e s s than the s o i l water phosphorus c o n c e n t r a t i o n . Base f l o w Genesee R i v e r d i s s o l v e d i n o r g a n i c phosphorus c o n c e n t r a t i o n s are 0.004 mg P / l , w h i l e peak f l o w v a l u e s are approximately 0.011 mg P / l . Since recent e v i dence (39) i n d i c a t e s that l e s s than 25% of r a i n w a t e r phosphorus i s d i s s o l v e d i n o r g a n i c phosphorus, these r e s u l t s support the suggestion t h a t some form of s o l i d d i s s o l u t i o n i s i n v o l v e d i n the r e g u l a t i o n of the water column phosphorus c o n c e n t r a t i o n . D i s s o l v e d metals other than c a l c i u m have a minor e f f e c t on the d i s t r i b u t i o n of phosphorus between the water column and sed iment i n t h i s f l u v i a l system. The two p r i n c i p a l metals of poten t i a l i n t e r e s t , i r o n and aluminum, are present i n Genesee R i v e r water almost e n t i r e l y i n the p a r t i c u l a t e phase (40). D i s s o l v e d c o n c e n t r a t i o n s of these metals are below the d e t e c t i o n l i m i t ( l e s s than 50 ug/1). I r o n and aluminum minimum d e t e c t a b l e d i s s o l v e d c o n c e n t r a t i o n s were used t o estimate the s a t u r a t i o n l e v e l s of the corresponding phosphate m i n e r a l s . These c a l c u l a t i o n s suggest that both i r o n and aluminum phosphate m i n e r a l s are sub s t a n t i a l l y below s a t u r a t i o n l e v e l s . The s o l i d s u r f a c e s e x h i b i t e d by i r o n and aluminum hydrous oxides (as p a r t i c u l a t e m a t e r i a l i n the water column) undoubtedly serve as s i t e s f o r phosphorus a d s o r p t i o n and i n c o r p o r a t i o n i n the f l u v i a l system. Data p r e sented f o r the o x a l a t e e x t r a c t i o n procedure i n Table I I I demon s t r a t e the importance of phosphorus b i n d i n g by hydrous metal oxides. Nriagu (Canadian Center f o r Inland Waters, unpublished d a t a , 1975) has proposed that b a s i c metal phosphates are important s i n k s f o r heavy metals i n the environment. In most n a t u r a l waters of New York S t a t e , d i s s o l v e d b a s i c metals i n c l u d i n g Pb, Cu, and Zn are a t low c o n c e n t r a t i o n s (below 10 ug/1), and these metals would not be expected to be a major f a c t o r governing phosphorus d i s t r i b u t i o n . Phosphate D i s t r i b u t i o n During C a l c i t e C r y s t a l l i z a t i o n . The c r y s t a l l i z a t i o n r a t e data i l l u s t r a t e d i n F i g u r e 4 f o l l o w a r a t e equation dN / dt = k s N

2

(1)

where Ν i s c a l c i u m carbonate (mol / 1) at time t to be p r e c i p i t a t e d from s o l u t i o n before e q u i l i b r i u m i s a t t a i n e d ; k i s the


32.


REDDY

749

A u g u s t i , 1976

- K P = 8.34 "(t = 25 °C) P

S

M a r c h 13, 1976

_ p K = 8.05 -(t = 2 ° C ) S P


—I

1I

L_

D e c e m b e r 14, 1975

-pK p-8.05 -(t = 2 ° C ) S

140 MILES

Figure 3.

120

100

ABOVE

80 MOUTH

60

40

20

OF GENESEE

0 RIVER

Ion activity product of calcite plotted as a function of sampling point distance from Lake Ontario

8.8 f-

8.7

-12.4 _

x

Ο

Q.

2.2

„

2.0

ο

8.6 1.8

_i

Distribution, Transport, Adsorption, and Precipitation of Inorganic

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