Land Use, Nutrient Yield, and Eutrophication in the Chowan River Basin

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REPORT NO. 205

LAND USE, NUTRIENT YIELD, AND EUTROPHICATION IN THE CHOWAN RIVER BASIN

Nancy J. Craig Edward J. Kuenzler

Department of Environmental Sciences and Engineering School of Public Health

University of North Carolina at Chapel Hill August 1983

Wal

er Resources Research

lnslilule

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Copies available from: Water Resources Research Institute of The University of North Carolina 124 Riddick Building

North Carolina State University Raleigh, North Carolina 27650

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LAND

USE, NUTRIENT YIELD, AND EUTROPHICATION

IN THE CHOWAN RIVER BASIN

Nancy

J.

Craig Research Assistant

Edward

J.

Kuenzler

Professor of Environmental Biology

Department of Environmental Sciences and Engineering University of North Carolina at Chapel Hill

Chapel Hill, North Carolina 27514

This research was supported in part by funds provided by the U.S.

Department of the Interior, Washington, D.C. through The University of North Carolina Water Resources Research Institute as authorized by the Water Research and Development Act of 1978.

Project No. B-127-NC(A) Agreement No. 14-34-001-027 4

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ACKNOWLEDGMENTS

Karen Stone and Chris Madden greatly assisted in the computer work necessary to complete the report. We wish to thank Drs. Wendell Gilliam, Frank Humenik, John Day, Eugene Turner, Hans Paerl, Charles Weiss, Curtis Richardson, and Ms. Beverly Young for their helpful

discussions of the problem and their criticism of the manuscript. The contributions and technical criticisms of those mentioned above are gratefully acknowledged, but responsibility for the conclusions and recommendations rests with the authors.

DISCLAIMERS STATEMENT

Contents of this publication do not necessarily reflect the views and policies of the U.S. Department of the Interior, nor does mention of trade names or commercial products constitute their endorsement or recommendation for use by the U.S. Government.

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ABSTRACT

Land u s e changes w i t h i n t h e Chowan R i v e r w a t e r s h e d o v e r t h e p a s t t h r e e d e c a d e s were d e t e r m i n e d t o a s s e s s p o t e n t i a l impact of t h e above changes on r e c e n t w a t e r q u a l i t y d e g r a d a t i o n and e u t r o p h i c a t i o n of t h e Chowan R i v e r . Although farm a c r e a g e h a s d e c r e a s e d , t h e amount of h a r v e s t e d c r o p l a n d h a s remained c o n s t a n t . Y i e l d s from a l l major c r o p s have i n c r e a s e d due t o g r e a t e r m e c h a n i z a t i o n and i n c r e a s e s i n f e r t i l i z e r usage (1957-1976). North C a r o l i n a ' s u s a g e of n i t r o g e n f e r t i l i z e r p e r a c r e of farmland i n t h e Chowan R i v e r w a t e r s h e d h a s been s i g n i f i c a n t l y h i g h e r t h a n V i r g i n i a ' s . There h a s been a n a p p a r e n t l a r g e i n c r e a s e i n a r t i f i c i a l d r a i n a g e on faxms from 1940 t o 1978, a p p r o a c h i n g 1 2 % a y e a r . Approximately 67% of t h e f a r m l a n d i n North C a r o l i n a i s now d r a i n e d v e r s u s 6% i n V i r g i n i a . A 30% d e c r e a s e i n oak-gum-cypress f o r e s t e d w e t l a n d h a s o c c u r r e d i n t h e North C a r o l i n a Chowan b a s i n w i t h i n a

t e n - y e a r p e r i o d (1964-1974).

C o n s t r u c t i o n of mass b a l a n c e models f o r a g r i c u l t u r a l l a n d , u p l a n d f o r e s t , and w e t l a n d f o r e s t p e r m i t t e d e s t i m a t i o n of n u t r i e n t y i e l d from d i f f e r e n t l a n d u s e s . Of t h e a n n u a l n i t r o g e n i n p u t s t o t h e Chowan R i v e r (6.94 x 106 kg N / y r ) , t h e models s u g g e s t e d t h a t a g r i c u l t u r e c o n t r i - b u t e s 6 2 % , f o r e s t and w e t l a n d s 21X, and p o i n t s o u r c e s 1 7 % . A g r i c u l t u r e c o n t r i b u t e s 72%, f o r e s t s and w e t l a n d s 22% and p o i n t s o u r c e s 6% of t h e a n n u a l p o t e n t i a l phosphorus i n p u t s (3.06 x 106 kg P / y r ) . Swamp

f o r e s t s were e s t i m a t e d t o remove 83% o f t h e t o t a l N and 51% of t h e t o t a l P i n s t r e a m s p a s s i n g through t h e s e w e t l a n d s .

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TABLE OF CONTENTS

p a g e LISTOFFIGURES

. . .

i x

. . .

SUMMARY. CONCLUSIONS. AND RECOMMENDATIONS x i i i INTRODUCTION

. . .

1

. . .

.

A S o u r c e s o f I n f o r m a t i o n

5 . . .

.

1 A g r i c u l t u r a l t r e n d s 5

. . .

2

.

D r a i n a g e d a t a 6

3

.

F o r e s t l a n d

. . .

6

. . .

4

.

Mass b a l a n c e models 8

. . .

5

.

C r o p l a n d 8

6

.

Animals: d a i r y cows. b e e f c a t t l e . hogs.

. . .

a n d c h i c k e n s

9 . . .

7

.

Swamp-forest s y s t e m

9 . . .

8

.

Upland f o r e s t 11

. . .

RESULTS 1 3

. . .

.

A A g r i c u l t u r a l Changes. 1950-1978 1 3

. . .

B

.

Changes i n Forest 1 7

. . .

C

.

Mass B a l a n c e Models 2 1

. . .

1

.

Major c r o p s 2 1

. . .

.

2 L i f e s t o c k models 23

. . .

3

.

Swamp f o r e s t model 3 5

. . .

.

4 Upland f o r e s t model 36

DISCUSSION

. . .

4 1

. . .

A

.

A g r i c u l t u r a l T r e n d s 4 1

. . .

.

B F o r e s t Changes 4 3

. . .

C

.

Mass B a l a n c e Models 4 4

. . .

1

.

A g r i c u l t u r e mass b a l a n c e model 44

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page

2 . Livestock mass balance model

. . .

52 3 . Swamp f o r e s t mass balance model

. . .

54 4 . Upland f o r e s t mass balance model

. . .

57

D.

Comparison of Non-Point Source Pollution from Mass

Balance Models

. . .

57

LITERATURE CITED

. . .

59

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LIST OF FIGURES

F i g u r e 1. 2. 3. 4. 5 . 6. 7. 8 . 9. 1 0 .

11.

1 2 .

1 3 .

14.

15.

The Chowan R i v e r d r a i n a g e b a s i n i n n o r t h e a s t e r n North

. . .

C a r o l i n a and s o u t h e a s t e r n V i r g i n i a

Change i n number o f farms and p e r c e n t a g e of a r e a i n

. . .

farms i n t h e Chowan R i v e r B a s i n , 1950-1978

Changes i n a r e a s of major a g r i c u l t u r a l l a n d u s e s i n

. . .

t h e Chowan B a s i n

Changes i n a r e a s d e v o t e d t o major c r o p s i n t h e chowan

. . .

B a s i n , 1950-1978

Changes i n y i e l d s of major c r o p s i n t h e Chowan B a s i n ,

. . .

1950-1978

Changes i n number of farm a n i m a l s i n t h e Chowan B a s i n ,

. . .

1950-1978

H i s t o r i c a l t r e n d of amounts of n i t r o g e n (N) and phospho-

. . . .

r u s ( P ) from f e r t i l i z e r used i n t h e Chowan B a s i n

C u r r e n t f e r t i l i z e r u s a g e i n Chowan Basin based on

. . .

f e r t i l i z e r s a l e s

Land a r t i f i c i a l l y d r a i n e d f o r a g r i c u l t u r e , 1940-1978

. .

Mass b a l a n c e models f o r c o r n f o r g r a i n and s i l a g e i n

. . .

North C a r o l i n a Chowan B a s i n

Mass b a l a n c e models f o r soybeans and p e a n u t s i n North

. . .

C a r o l i n a ChowanBasin

Mass b a l a n c e models f o r t o b a c c o and c o t t o n i n North

. . .

C a r o l i n a Chowan B a s i n

Mass b a l a n c e model f o r wheat i n North C a r o l i n a Chowan B a s i n

. . .

Mass b a l a n c e models f o r c o r n f o r g r a i n and s i l a g e i n

V i r g i n i a C h o w a n Basin

. . .

Mass b a l a n c e models f o r soybeans and p e a n u t s i n V i r g i n i a C h ~ w a n B a s i n . . . ~

. . .

page

2 1 3 1 5 15 16 1 6 1 8 1 8 1 9 25 26 27 2 8 2 9

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F i g u r e

_page

16. Mass b a l a n c e models f o r tobacco and b a r l e y i n V i r g i n i a

Chowan Basin

. . . , . . .

31

1 7 . Mass balance model f o r wheat i n V i r g i n i a Chowan Basin

.

32

18. Mass b a l a n c e model f o r major c r o p s i n t h e t o t a l Chowan

Basin

. . .

33

19. Mass balance models f o r hogs, c h i c k e n s , d a i r y cows, and

beef c a t t l e i n V i r g i n i a Chowan Basin

. . .

34

20. Mass balance models f o r hogs, c h i c k e n s , d a i r y cows, and

beef c a t t l e i n North C a r o l i n a Chowan Basin

. . .

37

21. Mass balance model f o r swamp f o r e s t ecosystem i n t h e

t o t a l Chowan Basin

. . .

38 2 2 . Mass balance model f o r upland f o r e s t i n t h e t o t a l Chowan

Basin

. . .

39

2 3 . D i s t r i b u t i o n of n i t r o g e n and phosphorus i n p u t s t o t h e

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LIST OF

TABLES

T a b l e

page

1. E s t i m a t e d magnitude of non-point s o u r c e c o n t r i b u t i o n t o

s u r f a c e w a t e r s i n conterminous U.S.

. . .

3 2. P e r c e n t a g e of c o u n t y w i t h i n t h e Chowan R i v e r Basin

. . .

7 3. Annual N and P b a l a n c e s f o r l i v e s t o c k s y s t e m s

. .

,

. .

1 0 4. Average farm s i z e ( h e c t a r e s ) and p e r c e n t of t o t a l

c r o p l a n d t h a t was h a r v e s t e d i n t h e Chowan b a s i n ,

. . .

y e a r s 1950-1978 1 4

5. P e r c e n t of t o t a l number of farms i n which o p e r a t o r i s f u l l - o w n e r , part-owner, o r t e n a n t i n Chowan b a s i n ,

. . .

1950-1978 20

6. Land a r t i f i c i a l l y d r a i n e d by c o u n t y i n Chowan B a s i n a s

. . .

p e r c e n t of t o t a l l a n d and l a n d i n f a r m s , 1978 20 7. S o i l C o n s e r v a t i o n Watershed P r o j e c t s i n North C a r o l i n a

. . .

Chowan Basin completed t o d a t e 21 8. Change i n a r e a (103ha) of commercial f o r e s t l a n d t y p e

. . .

i n t h e Chowan B a s i n , 1964-1974 22

9 . P e r c e n t a g e of t o t a l commercial f o r e s t by f o r e s t t y p e s

. . .

i n Chowan B a s i n , 1974 23

1 0 . Area ( h e c t a r e s ) and p e r c e n t a g e o f t o t a l a r e a of

commercial f o r e s t l a n d by ownership c l a s s i n Chowan b a s i n ,

. . .

y e a r s 1964, 1974 24

11. N u t r i e n t y i e l d from c r o p l a n d b e f o r e swamp p r o c e s s i n g i n t h e Chowan B a s i n , 1972-1980, b a s e d on mass b a l a n c e

. . .

m o d e l s . . 35

1 2 . Amounts of n i t r o g e n and phosphorus a p p l i e d a n n u a l l y i n

. . . .

f e r t i l i z e r . . . 36 1 3 . Ranking of major c r o p s of p o t e n t i a l y i e l d s of n i t r o g e n

. . .

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Table

-

page

14. A comparison of nutrient y i e l d 8 from a g r i c u l t u r a l systems and f o r e s t e d watersheds

. . .

49

15.

Estimation of annual phosphorus l o s s from cropland due

t o e r o s i o n . .

. . .

51

16,

Total p o t e n t i a l and annual n i t r o g e n and phosphorus

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SUMMARY, CONCLUSIONS,

AND

RECOMMENDATIONS

The Chowan R i v e r h a s been e x p e r i e n c i n g blue-green a l g a l blooms s i n c e t h e e a r l y 1 9 7 0 ' s . Land use changes and i n t e n s i t y of l a n d u s e i n t h e Chowan w a t e r s h e d o v e r t h e p a s t t h r e e d e c a d e s were examined t o d e t e r m i n e i f t h e s e s i g n i f i c a n t l y c o n t r i b u t e t o t h e n u i s a n c e blooms.

The Chowan R i v e r b a s i n (12,650 kmz), l o c a t e d i n n o r t h e a s t e r n North C a r o l i n a and s o u t h e a s t e r n V i r g i n i a , i s p r e d o m i n a n t l y f o r e s t e d

( 7 6 % ) . F o r e s t t y p e s i n c l u d e l o b l o l l y and s h o r t l e a f p i n e , oak-pine, oak-hickory, oak-gum-cypress, and elm-ash-cottonwood, Most of t h e remaining 22% i s i n a g r i c u l t u r a l l a n d u s e ( e x c l u d i n g farm woodland); a small f r a c t i o n i s u r b a n i z e d . S e v e n t y - t h r e e p e r c e n t of t h e a g r i c u l t u r a l l a n d i s l o c a t e d w i t h i n t h e V i r g i n i a p o r t i o n of t h e Chowan w a t e r s h e d and 27% i n North C a r o l i n a .

S i n c e 1950 t h e number of f a r m s , a s w e l l a s farm a c r e a g e , w i t h i n t h e watershed h a s d e c r e a s e d . T h i s i s p r i m a r i l y due t o t h e d e c r e a s e i n farm woodland; p a s t u r e l a n d and h a r v e s t e d c r o p l a n d have remained

e s s e n t i a l l y t h e same i n a r e a . The p a t t e r n of change i s one o f fewer b u t l a r g e r f a r m s , t h a t have s u b s t a n t i a l l y i n c r e a s e d y i e l d s of t h e major c r o p s ( c o r n f o r g r a i n and s i l a g e , s o y b e a n s , p e a n u t s , t o b a c c o , w h e a t , c o t t o n , and b a r l e y ) . T h i s i n c r e a s e i n c r o p y i e l d i s due i n p a r t t o g r e a t e r farm m e c h a n i z a t i o n and i n c r e a s e s i n f e r t i l i z e r u s a g e from 1957-1976. North C a r o l i n a c o u n t i e s w i t h i n t h e Chowan B a s i n i n r e c e n t y e a r s h a v e u s e d r o u g h l y t h e same amount o f n i t r o g e n and phosphorus ( m e t r i c t o n s / y r ) a s V i r g i n i a ' s p o r t i o n of t h e w a t e r s h e d , a l t h o u g h V i r g i n i a c o n t r i b u t e d 66% o f t h e h a r v e s t e d c r o p l a n d . The number of l i v e s t o c k on farms h a s remained c o n s t a n t e x c e p t f o r c h i c k e n s

( l a y e r s d e c r e a s e d ; b r o i l e r s g r e a t l y i n c r e a s e d ) . The p e r c e n t a g e of f a r m e r s who both own and r e n t p a r t o f t h e i r farms h a s i n c r e a s e d s i g n i f i c a n t l y a t t h e expense of f u l l - o w n e r s and t e n a n t s .

There h a s been a n i n c r e a s e i n a r t i f i c i a l d r a i n a g e on farms from

1940-78 which a p p r o a c h e s a 12% i n c r e a s e p e r y e a r . T h e r e e x i s t s a s i g n i f i c a n t amount of a r t i f i c i a l d r a i n a g e of a g r i c u l t u r a l l a n d i n t h e North C a r o l i n a p o r t i o n of t h e Chowan b a s i n . Approximately 67% o f t h e farm l a n d i n t h e North C a r o l i n a Chowan w a t e r s h e d i s d r a i n e d v e r s u s 6%

o f t h e f a r m l a n d i n t h e V i r g i n i a Chowan w a t e r s h e d . T h i s i s d u e , i n p a r t , t o t h e g r e a t e r amount of low-lying f a r m l a n d w i t h i n t h e C o a s t a l P l a i n i n North C a r o l i n a which c a n n o t b e r o u t i n e l y t i l l e d w i t h o u t

d r a i n a g e . The S o i l C o n s e r v a t i o n S e r v i c e h a s c h a n n e l i z e d a p p r o x i m a t e l y

22% of t h e s t r e a m m i l e s w i t h i n t h e North C a r o l i n a Chowan w a t e r s h e d , w h i l e i t h a s n o completed p r o j e c t s i n V i r g i n i a . T h i s i n c r e a s e i n d r a i n a g e of a g r i c u l t u r a l l a n d , p r i m a r i l y i n North C a r o l i n a , c o u l d c o n t r i b u t e s i g n i f i c a n t l y t o g r e a t e r n u t r i e n t i n p u t s i n t o t h e Chowan w a t e r s h e d . More w a t e r i s a b l e t o l e a v e t h e f i e l d s a t a f a s t e r r a t e , c a r r y i n g r e s i d u a l f e r t i l i z e r n u t r i e n t s . Much of t h i s d r a i n a g e , due t o c h a n n e l i z a t i o n , may bypass t h e swamp f o r e s t n u t r i e n t - r e m o v a l p r o c e s s , t h e r e b y i n c r e a s i n g t h e n u t r i e n t l o a d i n t h e r i v e r .

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F o r e s t l a n d a c r e a g e h a s i n c r e a s e d w i t h i n t h e Chowan watershed d u r i n g t h e y e a r s 1964-1974. A l l t y p e s o f f o r e s t , e x c e p t oak-pine, have i n c r e a s e d i n a r e a i n t h e t o t a l Chowan b a s i n , p r i m a r i l y i n V i r g i n i a . A s i g n i f i c a n t d e c r e a s e i n t h e oak-gum-cypress f o r e s t e d wetland h a s o c c u r r e d w i t h i n t h e North C a r o l i n a Chowan b a s i n , amounting t o a 30X d e c r e a s e w i t h i n t h e t e n y e a r period. Again, due t o t h e n a t u r e of t h e swamp f o r e s t ' s a b i l i t y t o a c t a s a n u t r i e n t s i n k (83% o f t o t a l N i n p u t s removed; 51X t o t a l P i n p u t s removed), t h i s d e c l i n e i n swamp a c r e a g e and f u n c t i o n i n g may c o n t r i b u t e t o t h e i n c r e a s e i n n u t r i e n t s a v a i l a b l e t o t h e Chowan R i v e r .

C a l c u l a t i o n s from mass b a l a n c e models f o r a g r i c u l t u r a l l a n d , upland f o r e s t , and wetland f o r e s t p r o v i d e e s t i m a t e s of t h e n u t r i e n t y i e l d from d i f f e r e n t l a n d u s e s (non-point s o u r c e s ) , According t o

t h e s e n u t r i e n t b u d g e t s , a g r i c u l t u r a l l a n d y i e l d s 62% of t h e a n n u a l n i t r o g e n i n p u t s (6.94

x

l o 6

k g l y r ) i n t o t h e r i v e r , w h i l e f o r e s t and w e t l a n d s c o n t r i b u t e 21%. By comparison, S t a n l e y and Bobbie (1977) c a l c u l a t e d a n n u a l n i t r o g e n i n p u t s t o be 7.0 x

lo6

k g l y r based on

a c t u a l c o n c e n t r a t i o n s i n t h e r i v e r and r i v e r f l o w . The remainder (17%)

i s due t o p o i n t s o u r c e s a l o n g t h e r i v e r . The a n n u a l phosphorus i n p u t s t o t h e r i v e r (3.06 x

lo6

k g l y r ) c o n s i s t of a g r i c u l t u r a l s o u r c e s , 72%; f o r e s t s and w e t l a n d s , 22X; and p o i n t s o u r c e s , 6%. These c a l c u l a t i o n s i n d i c a t e t h a t a g r i c u l t u r a l cropland i s t h e s o u r c e of most of t h e n i t r o g e n and phosphorus a v a i l a b l e t o t h e r i v e r . T h i s e s t i m a t e f o r phosphorus i s probably h i g h . A l a r g e p o r t i o n o f t h e phosphorus i s probably t i g h t l y bound, e s p e c i a l l y i n i n o r g a n i c s o i l s , and w i l l l e a v e predominately by e r o s i o n . That phosphorus which i s e r o d e d i s s u b j e c t t o s e d i m e n t a t i o n i n a g r i c u l t u r a l d i t c h e s , i n stream d e p o s i t s , on swamp f o r e s t f l o o r s , and on t h e bottom of t h e Chowan R i v e r , and t h e r e f o r e much of i t w i l l n o t r e a c h t h e r i v e r . A r e f i n e d e s t i m a t e o f phosphorus y i e l d i s 1.52 x

lo6

k g l y r .

Recommendations

Based on t h i s i n v e s t i g a t i o n and a review of o t h e r s t u d i e s , t h e f o l l o w i n g recommendations a r e made:

Because a g r i c u l t u r e i s t h e dominant non-point s o u r c e of n i t r o g e n and phosphorus, Best Management P r a c t i c e s d e s i g n e d t o r e d u c e n u t r i e n t and sediment l o s s e s from a g r i c u l t u r a l l a n d s h o u l d be adopted. These should i n c l u d e r e g u l a r s o i l t e s t i n g , t i m i n g and a p p l i c a t i o n r a t e s o f f e r t i l i z e r t o match s p e c i f i c c r o p needs; n o - t i l l o r c o n s e r v a t i o n t i l l a g e ; c o n t o u r and t e r r a c i n g p r a c t i c e s ; u t i l i z a t i o n of a n i m a l waste a s a r e s o u r c e ; and u s e of sediment b a s i n s and g r a s s e d waterways f o r sediment c o n t r o l (Loehr 1977; N.C. Dept. N a t u r a l Resources and Community Development, D i v i s i o n o f Environmental Manage- ment 1982a, 1982b.)

F u r t h e r wetland d r a i n a g e and c h a n n e l i z a t i o n s h o u l d c e a s e i n t h e North C a r o l i n a Chowan watershed. It h a s been demonstrated i n numerous s t u d i e s t h a t swamp-bottomland f o r e s t ecosystems remove n u t r i e n t s and s i l t from s t r e a m s , Channelized s t r e a m s which have l o s t c o n t a c t w i t h t h e swamp f o r e s t c a r r y g r e a t e r amounts of n u t r i e n t s t h a n n a t u r a l s t r e a m s which a c t i v e l y

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i n t e r a c t w i t h t h e f o r e s t e d wetland. I n c r e a s e d c h a n n e l i z a t i o n and d r a i n a g e bypass t h i s n a t u r a l system and s h u n t a g r i c u l - t u r a l w a s t e d i r e c t l y i n t o t h e Chowan R i v e r . A g r i c u l t u r a l d i t c h e s s h o u l d end a t t h e edge of t h e swamp f o r e s t and r u n o f f s h o u l d be d i v e r t e d t o move by s h e e t f l o w t h r o u g h t h e swamp i n s t e a d of d i s c h a r g i n g d i r e c t l y i n t o t h e s t r e a m . Water t a b l e s s h o u l d b e k e p t h i g h i n w i n t e r months i n low l y i n g f i e l d s t o i n c r e a s e d e n i t r i f i c a t i o n and d e c r e a s e n i t r a t e l o s s e s t o t h e r i v e r .

Due t o t h e importance of swamp f o r e s t s a s n u t r i e n t b u f f e r s f o r a g r i c u l t u r a l w a s t e , s p e c i a l p r o t e c t i o n s h o u l d b e g i v e n t o t h e s e a r e a s . It i s recommended t h a t no f u r t h e r r e d u c t i o n i n swamp f o r e s t o c c u r w i t h i n t h e North C a r o l i n a w a t e r s h e d . L a r g e t r a c t s i n c r i t i c a l l o c a t i o n s s h o u l d be purchased by t h e S t a t e o r by c o n s e r v a t i o n o r g a n i z a t i o n s , w i l d l i f e c l u b s , o r o t h e r o r g a n i z a t i o n s , and m a i n t a i n e d a s p r o d u c t i v e n a t u r a l w e t l a n d s . I n a d d i t i o n , t a x r e d u c t i o n s o r o t h e r i n c e n t i v e s which encour- a g e landowners t o keep bottomlands f u n c t i o n i n g a s n a t u r a l w e t l a n d s y s t e m s s h o u l d be g i v e n t o f a r m e r s and t i m b e r companies.

The t r e n d f o r m a i n t a i n i n g upland f o r e s t s w i t h i n t h e e n t i r e w a t e r s h e d s h o u l d be c o n t i n u e d s i n c e t h e s e f o r e s t s a r e a

s o u r c e of h i g h q u a l i t y w a t e r .

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INTRODUCTION

The Chowan River watershed (12,650 km2), located in southeastern Virginia and northeastern North Carolina (Fig.

I),

is predominantly forested (76% of the area) but with an economically important agricultural region (22%). The watershed is sparsely populated (200,000 people) with most municipalities below 10,000 people. The Piedmont and Coastal Plain are the two major physiographic regions in the basin. Coastal Plain soils are generally either poorly drained or moderately well-drained sands, with some poorly drained peat soils along the lower river. Piedmont soils are nearly all loamy, well-drained soils (Humenik

- -

et al. 1980). For a detailed description of the Chowan River watershed see U.S. Department of Agriculture

(USDA

1981).

Since the early 1970's the Chowan River has been experiencing extensive summertime blue-green algal blooms, symptomatic of eutrophi-

cation, because of excessive nutrients (Rohlich 1969; Stanley and Hobbie 1977; Sauer and Kuenzler 1981; Balducci 1982; Kuenzler

- -

et al. 1982; Paerl 1982; Stone 1982). Eutrophication often results in

undesirable changes in water quality and in natural biological commu- nities, the advent of nuisance algal blooms and anoxic bottom-water conditions, and decreased commercial and recreational fish catches. Although much of the terminology and methodology developed for describing and studying eutrophication has come from the investigation of lakes, the same principles can be applied to the Chowan River. The prolonged effects of increased nutrient loading result in similar changes in rivers: changes in community structure, such as the development of large populations of blue-green phytoplankton and the

dominance of less desirable pollution-tolerant fish species.

Nutrients which cause eutrophication come from point sources such as municipal sewage and industrial wastes, non-point sources such as urban runoff and drainage from agricultural land, and natural sources such as runoff from forests, precipitation, and sediment recycling. This study will focus primarily on non-point source pollution.

According to Adamkus (1976), non-point sources of pollution (NPS) are :

1) discharges which enter surface waters in a diffuse manner and at intermittent intervals that are related mostly to the occurrence of precipitation events;

2 ) pollution sources which arise over an extensive area of land and most of which is in transit overland before it reaches surface water (although some may enter as groundwater);

3 ) sources which cannot be monitored at their point of origin (such as a drainage pipe), and the exact source of which is difficult to trace, and

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Within the United States, non-point sources contribute roughly

80% of the total nitrogen load and more than 50% of the total phospho-

rus load to receiving waters (Novotny and Chesters 1981).

The impact

of NPS on water quality depends on the distance of the source from the

nearest stream or river, and the overland flow process which occurs en

route. The most severe impact from NPS usually occurs during or

following a major storm event, when the highest loadings (and concen-

trations) of pollutants are measured (Novotny and Chesters 1981).

Within the Chowan River basin, the non-point sources are agricul-

tural runoff and erosion, and natural sources such as precipitation

and runoff from forests and wetlands. Agricultural runoff is a major

non-point source contributor throughout the United States (Table 1).

Fertilizer nutrients, sediment, and animal waste are generally the

most significant sources of nutrients in agricultural NPS pollution

(Loehr 1977).

The amount of nutrients in the runoff and the quantity

of that runoff depend on the type of farming, fertilizer practices,

and drainage practices of the area (Keeney and Walsh 1972).

In recent

decades throughout the U.S., agricultural production has become more

efficient due to greater mechanization and increased use of agricul-

tural chemicals, both pesticides and fertilizers. Natural sources are

generally considered background sources with which the natural river

system developed. Forest runoff is a source of this type. Runoff from

wetlands and the nutrient content of precipitation are natural sources

which can also have

a

cultural nutrient component (Loehr 1977).

Table 1. Estimated magnitude of non-point source contributions to

surface waters in conterminous U.S. (millions tons/year)

(from Novotny and Chesters, 1981)

Sediment

-

N

-

P

Cropland

1700

3.9

1.42 Pasture and range

1190

2.3

0.98 Forest

232

0.35

0.08

The objectives of this study were:

1) to determine land use changes within the Chowan River water-

shed which could affect NPS nutrient loading to the river.

2) to examine agricultural practices such as fertilizer applica-

tion rates, mechanization, livestock husbandry, and drainage

activities which may be related to the nutrient yield from

agriculture.

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Basin. By t h i s procedure, t h e r e l a t i v e c o n t r i b u t i o n , magnitude, and s i g n i f i c a n c e o f each NPS can be determined.

4 ) t o s u g g e s t management recommendations t h a t might a m e l i o r a t e poor water q u a l i t y i n t h e Chowan River.

T h i s r e p o r t t o Water Resources Research I n s t i t u t e i s s l i g h t l y m o d i f i e d from a t e c h n i c a l r e p o r t by Nancy J. C r a i g i n p a r t i a l

f u l f i l l m e n t of t h e r e q u i r e m e n t s f o r t h e Master o f S c i e n c e i n P u b l i c H e a l t h , Department of Environmental S c i e n c e s and E n g i n e e r i n g ,

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METHODS

S o u r c e s of I n f o r m a t i o n

A g r i c u l t u r a l t r e n d s

The primary s o u r c e of i n f o r m a t i o n f o r a g r i c u l t u r a l t r e n d s i n t h e Chowan Basin f o r t h e y e a r s 1950 t h r o u g h 1 9 7 8 was t h e U.S. Census of A g r i c u l t u r e , (U.S. Bureau of Census (U.S.B.C.) 1952, 1 9 6 1 , 1967, 1972, 1977, 1981). I n 1950 t h e d e f i n i t i o n of f a r m was a p l a c e o f t h r e e o r more a c r e s ( 1 a c r e = .405 h e c t a r e s ) o n which t h e v a l u e of a g r i c u l t u r a l p r o d u c t s s a l e s , e x c l u s i v e of home g a r d e n s , amounted t o $150 o r more. Farms were counted i n t h e c e n s u s i f t h e y were l e s s t h a n t h r e e a c r e s b u t had s a l e s of a g r i c u l t u r a l p r o d u c t s of $150 o r more (U.S.B.C. 1 9 5 2 ) . By 1959 t h e d e f i n i t i o n o f farm had changed t o i n c l u d e p l a c e s of l e s s t h a n 1 0 a c r e s i f s a l e s amounted t o a t l e a s t $250. P l a c e s of 1 0 o r more a c r e s were c o n s i d e r e d farms i f s a l e s amounted t o a t l e a s t $50 o r would normally be e x p e c t e d t o produce a g r i c u l t u r a l p r o d u c t s i n s u f f i - c i e n t q u a n t i t y t o meet t h a t r e q u i r e m e n t (U.S.B.C. 1 9 6 1 ) . I n 1974, t h e d e f i n i t i o n of farm had once a g a i n changed. A farm was t h e n c o n s i d e r e d a n y e s t a b l i s h m e n t which d u r i n g t h e c e n s u s y e a r had o r n o r m a l l y would have had s a l e s of a g r i c u l t u r a l p r o d u c t s of $1,000 o r more. The c r i t e r i o n f o r t h e minimum number of a c r e s i n t h e farm was d e l e t e d . The 1969, 1974, and 1978 c e n s u s e s were c o n d u c t e d by m a i l whereas e a r l i e r c e n s u s e s had been c o l l e c t e d by c e n s u s p e r s o n n e l . Due t o t h e change i n method of d a t a c o l l e c t i o n and f a r m d e f i n i t i o n , c e n s u s d a t a a r e n o t e x a c t l y comparable. However, t h e y a r e t h e most thorough and complete d a t a s o u r c e f o r b o t h North C a r o l i n a and V i r g i n i a c o u n t i e s w i t h i n t h e Chowan Basin.

Recent f e r t i l i z e r t r e n d s were based o n s t a t e a g r i c u l t u r a l s t a t i s - t i c s (N.C. Department of A g r i c u l t u r e 1973-1981; V i r g i n i a Department of A g r i c u l t u r e and Commerce, D i v i s i o n o f P r o d u c t and I n d u s t r y R e g u l a t i o n 1956-1981). North C a r o l i n a h i s t o r i c a l f e r t i l i z e r t r e n d s were c o l l e c t e d from t h e U.S. Census of A g r i c u l t u r e due t o l a c k of r e p o r t i n g by t h e s t a t e a g e n c i e s i n t h e 1 9 6 0 ' s and 1 9 5 0 ' s . The f e r t i l i z e r d a t a i n North C a r o l i n a i s based on t o n s r e c e i v e d i n t h e c o u n t i e s from m a n u f a c t u r e r s f o r r e t a i l e r s and consumers. To c a l c u l a t e t h e amount of n i t r o g e n i n t h e f e r t i l i z e r s o l d , t h e p e r c e n t a g e of n i t r o g e n i n e a c h t y p e of

f e r t i l i z e r m a t e r i a l ( s u c h a s anhydrous ammonia, ammonia n i t r a t e , ammonia s u l f a t e , e t c . ) was d e t e r m i n e d and summed, The same p r o c e d u r e was f o l l o w e d f o r phosphorus i n f e r t i l i z e r m a t e r i a l s . The p e r c e n t a g e

of n i t r o g e n and phosphorus i n mixed f e r t i l i z e r tonnage was a l s o

c a l c u l a t e d . The sums of t o t a l N and t o t a l P ( a s e l e m e n t a l N and P) i n f e r t i l i z e r m a t e r i a l s and mixed f e r t i l i z e r e q u a l s t h e t o t a l amount of N

and P s o l d (and assumed a p p l i e d ) f o r t h e c o u n t i e s i n North C a r o l i n a . V i r g i n i a ' s s t a t i s t i c s a r e a l s o based on s a l e s and d i s t r i b u t i o n of f e r t i l i z e r . The s o u r c e of d a t a used f o r V i r g i n i a i s t h e p u b l i c a t i o n , F e r t i l i z e r Used and R e s u l t s of I n s p e c t i o n , and d a t a a r e p r e s e n t e d a s consumption by c o u n t i e s i n t o t a l m i x t u r e , t o t a l m a t e r i a l s , and t o t a l n u t r i e n t s of n i t r o g e n and phosphorus.

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and weighing maps of t h e t o t a l county and t h a t p o r t i o n o f t h e c o u n t y w i t h i n t h e Chowan Basin. ( S e e T a b l e 2). T h i s p r o c e d u r e assumed t h a t

farmland was e v e n l y d i s t r i b u t e d w i t h i n e a c h county.

Drainage d a t a

Data o n a r t i f i c i a l d r a i n a g e of a g r i c u l t u r a l l a n d s was o b t a i n e d from t h e U.S. Census of A g r i c u l t u r e S p e c i a l Reports: D r a i n a g e of A g r i c u l t u r a l Lands (U.S.B.C. 1942-1981). Land d r a i n e d r e f e r s t o a n

a r e a of a g r i c u l t u r a l l a n d b e n e f i t e d t o some e x t e n t by w a t e r removal t o improve t h e s o i l environment f o r p l a n t growth and i n c l u d e s s u r f a c e and s u b s u r f a c e d r a i n a g e ( d i t c h e s , s u b s u r f a c e d r a i n s , d i k e s , pumping p l a n t s , and l a n d g r a d i n g ) . Drainage t h a t i s p a r t of i r r i g a t i o n s y s t e m s i s e x c l u d e d (U.S.B.C 1981). I n some c o u n t i e s d r a i n e d l a n d may exceed l a n d i n farms due t o d r a i n a g e of woodlands o r o t h e r l a n d s which a r e n o t p a r t of a n a g r i c u l t u r a l o p e r a t i o n . I n most c o u n t i e s , however, d r a i n e d l a n d can b e r e l a t e d d i r e c t l y t o f i g u r e s f o r l a n d i n f a r m s (U.S.B.C. 1981).

I n t h e 1940 c e n s u s o f d r a i n a g e r e p o r t , a l l l e g a l l y o r g a n i z e d d r a i n a g e e n t e r p r i s e s r e g a r d l e s s of s i z e were covered. A d r a i n a g e e n t e r p r i s e was d e f i n e d a s t h e a r e a : ( 1 ) o r g a n i z e d i n one d r a i n a g e d i s t r i c t , ( 2 ) a s s e s s e d f o r t h e same p u b l i c d r a i n , o r ( 3 ) i n c o r p o r a t e o r p r i v a t e ownership d r a i n e d by works o p e r a t e d a s one u n d e r t a k i n g . The d a t a on d r a i n a g e by f a r m owners, i n d i v i d u a l l y o r c o o p e r a t i v e l y , w i t h o u t l e g a l o r g a n i z a t i o n were n o t c o l l e c t e d f o r 1940 f o r e n t e r p r i s e s of l e s s t h a n 500 a c r e s . The c e n s u s r e p o r t s t a t e s t h a t t h e e x c l u s i o n of t h e s e s m a l l e n t e r p r i s e s had a m a t e r i a l e f f e c t on t h e number of e n t e r p r i s e s c o v e r e d b u t had o n l y a minor e f f e c t on t h e amount of a r e a d r a i n e d (U.S.B.C. 1 9 4 2 ) , which was i m p o r t a n t f o r our purposes.

The 1959 and 1969 d r a i n a g e p r o j e c t s a l s o i n c l u d e o n l y t h o s e d r a i n a g e p r o j e c t s b e n e f i t i n g 500 o r more a c r e s (U.S.B.C. 1961, 1973). The 1978 a c r e a g e e s t i m a t e f o r a g r i c u l t u r a l l a n d a r t i f i c a l l y d r a i n e d s u b s t a n t i a l l y e x c e e d s e a r l i e r e s t i m a t e s . The r e p o r t s t a t e s t h a t t h i s r e s u l t s from c o l l e c t i o n of d a t a from s t a t e and c o u n t y S o i l C o n s e r v a t i o n S e r v i c e s o f f i c e s r a t h e r t h a n having i n d i v i d u a l f a n n e r s r e p o r t i t , a s was done p r e v i o u s l y . It f u r t h e r s t a t e s t h a t t h i s g r e a t l y improved t h e a c c u r a c y of t h e d a t a and p r e v i o u s y e a r s were u n d e r r e p o r t e d (U.S.B.C. 1 9 8 1 ) .

F o r e s t l a n d

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Table 2. P e r c e n t a g e of county w i t h i n t h e Chowan R i v e r Basin.

NORTH CAROLINA PERCENT

B e r t i e 2 8

Chowan 50*

G a t e s 7 1

Her t f o r d 1 0 0

Northampton 6 9

V I R G I N I A

Brunswick Dinwiddie G r e e n s v i l l e

I s l e of Wight Lunenburg Mecklenberg Not toway P r i n c e George Southamp t o n Suf f o l k S u r r y Suss ex

PERCENT

9 2

92

1 0 0

5 0 1 0 0

1 7

5 3

5 1 100 30 60 100

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1974).

The sampling procedures and methods of the U.S. Forest Service

(USFS) are designed to provide the most reliable atatistics at the

county and state levels (Cost 1975).

For the Chowan watershed, etatie-

tical analysis indicates a sampling error of

+0.5%

for estimates of

total commercial forest area. The possibilitF

for error increases as

the total is subdivided by forest type.

Mass balance models

Mass balance models for nitrogen and phosphorus were calculated

for agricultural cropland, animal systems, swamp forest, and upland

forest. In recent years, agricultural mass balance models have become

common in the literature (Frink 1969; Gilliam and Terry 1973; Fried et

-

al. 1976; Frissel 1978; Schueler and Kemp 1979; Correll 1981).

The

-

mass balance method attempts to identify all inputs, storages, and

outputs of a particular nutrient within a defined system at steady

state, assuming the storage pool (soil system, forest system) is not

changing (Frissel 1978).

This assumption may not be true for phos-

phorus as will be addressed later in the Discussion section.

In the agricultural system there will naturally be year-to-year

fluctuations but these tend to be cancelled if long-term values are

used as this report did. To calculate the nutrient budget for agri-

culture, farming operations were broken down into two components,

cropland and animal systems. Quantities are expressed in kg (1 kg

=

2.2 lb) of elemental nitrogen or phosphorus (not N20 or P205)

per year for the whole watershed or per unit area (hectare).

Finally,

note that the term "yield" has two common meanings, (1) the amount of

crop harvested from farmland, and (2) the amount of nutrient carried

away by runoff from the land.

Cropland

The mass balance for cropland has as its primary inputs fertil-

ization of the field, precipitation, and sometimes nitrogen-fixation

by legumes. The principal outputs are denitrification, harvested plant

biomass, leaching, surface runoff and erosion of soil. To arrive at

these numbers the following assumptions and calculations were made:

1)

The amount of fertilizer applied annually to a specific crop

was the average amount recommended by the state's agricultural exten-

sion agency.

2)

The average amount of nitrogen and phosphorus from precipi-

tation falls equally on the entire watershed. (Precipitation values

were calculated from Gambell and Fisher 1966; Kuenzler et al. 1977).

--

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l i e d

4 ) D e n i t r i f i c a t i o n r a t e s were assumed t o be 15% of t h e app f e r t i l i z e r n i t r o g e n ( F r i s s e l 1978).

5 ) The amount h a r v e s t e d was d e t e r m i n e d by m u l t i p l y i n g t h e

n u t r i e n t c o n t e n t by t h e a v e r a g e a n n u a l y i e l d s (e.g., b u s h e l s l a c r e y r ) of t h e major c r o p s (Romaine 1965). Average y i e l d s were c a l c u l a t e d f o r y e a r s 1972-1980 f o r a l l major c r o p s i n V i r g i n i a and North C a r o l i n a

(N.C. Crop l a n d L i v e s t o c k R e p o r t i n g S e r v i c e 1972-1981, V i r g i n i a Department of A g r i c u l t u r e , D i v i s i o n of Chemistry and Foods, 1973-81.) According t o F r i s s e l ( 1 9 7 8 ) , t h i s i s a r e l i a b l e method t o c a l c u l a t e n u t r i e n t removals by c r o p s .

6 ) A p o r t i o n of t h e a g r i c u l t u r a l n u t r i e n t y i e l d ( e . g . , kg N/ha y r ) from major c r o p s i s removed by swamp f o r e s t s . To d e t e r m i n e t h i s amount w e assumed t h a t t h e h y d r o l o g i c i n p u t s p e r h e c t a r e i n t o t h e swamp system of t h e Chowan B a s i n a r e t h e same a s f o r C r e e p i n g Swamp, North C a r o l i n a , f o r which t h e r e i s e x t e n s i v e d a t a . We made t h i s a s s u m p t i o n because b o t h w a t e r s h e d s have t h e same p r o p o r t i o n s o f a g r i - c u l t u r e and upland f o r e s t s . I t was d e t e r m i n e d from t h e mass b a l a n c e models t h a t 86% of t h e h y d r o l o g i c i n p u t s i n t o t h e swamp s t r e a m s b a s i n were a g r i c u l t u r a l i n o r i g i n and 14X was due t o r u n o f f from f o r e s t s and w e t l a n d s . E i g h t y - s i x p e r c e n t of t h e n i t r o g e n and phosphorus i n p u t s i n t o t h e swamps were t h e r e f o r e s u b t r a c t e d from t o t a l n i t r o g e n and phosphorus y i e l d s from a g r i c u l t u r a l c r o p s , t o c a l c u l a t e t h e r e d u c t i o n i n n u t r i e n t y i e l d s from c r o p l a n d due t o removal by t h e swamp. Swamp p r o c e s s i n g removes 83% of t h e t o t a l N and 51% of t h e t o t a l P from w a t e r p a s s i n g t h r o u g h t h e swamp. ( S e e D i s c u s s i o n : Swamp Mass Balance Model.)

7 ) The amount a v a i l a b l e t o t h e r i v e r i n s u r f a c e r u n o f f and l e a c h i n g from s o i l s i s t h e d i f f e r e n c e between o u t p u t s and i n p u t s .

Each mass b a l a n c e model was c a l c u l a t e d i n k g l h a a y r f o r e a c h

major c r o p w i t h i n t h e b a s i n , s e p a r a t i n g North C a r o l i n a and V i r g i n i a f o r comparative purposes. T o t a l i n p u t s , o u t p u t s , and e x c e s s e s ( l o 6 k g l y r ) were c a l c u l a t e d by m u l t i p l y i n g v a l u e s i n k g l h a _{y r by} t h e a v e r a g e a c r e a g e of t h a t c r o p (1972-1980).

Animals: d a i r y cows, beef c a t t l e , h o g s , and c h i c k e n s

Mass b a l a n c e s f o r n i t r o g e n and phosphorus i n t a k e s , p r o d u c t s , and e x c r e t a were determined f o r d a i r y cows, b e e f c a t t l e , h o g s , and c h i c k e n s w i t h i n t h e Chowan b a s i n . These were c a l c u l a t e d by u s i n g v a l u e s i n T a b l e 3 and a n e i g h t y e a r a v e r a g e f o r t h e number of a n i m a l s i n e a c h g r o u p i n g . B r o i l e r c h i c k e n numbers f o r V i r g i n i a a r e o n l y f o r t h e y e a r 1978 (U.S.B.C. 1981). F i v e p e r c e n t of t h e n i t r o g e n and phosphorus e x c r e t e d by a n i m a l s was assumed a v a i l a b l e t o s t r e a m s (Robbins e t a l e

--

1972; F r i s s e l 1978).

swam^-forest system

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Table

3.

Annual N and P balances for livestock systems

(adapted from Frissel 1978)

N (kglhead)

P (kg/head)

Class of Livestock Intake Product Excreted Intake Product Excreted

Cattle

Dairy cows

166

4

6

120

28

8

20 Beef

48

12

36

7

3

4 Chickens

Broilers

0.82

0.43

0.39

0.21

0.09

0.12 Layers

1.10

0.28

0.83

0.27

0.03

0.24 Hogs

8.7

2.6

6.1

1.80

0.28

1.53 precipitation, other hydrologic inputs such as streams and rivers, and

nitrogen fixation. The outputs were harvesting of timber, denitri-

fication, and outflow of swamp water carrying nutrients from the

sediment-water storage. Phosphorus sedimentation onto the swamp

forest floor and nitrogen and phosphorus accumulation in wood incre-

ment were also calculated. To derive the values for these inputs,

outputs, and cycles the following assumptions were made:

1) Precipitation values were the same as for major crops.

2) Hydrologic inputs, other than precipitation, were based on

the nitrogen and phosphorus inputs into Creeping Swamp, North Carolina,

(Neuse River drainage), and extrapolated for the entire Chowan River

watershed. This extrapolation is reasonable because the proportion of

agricultural land to forest in the Creeping Swamp watershed closely

match those proportions in the Chowan watershed. These inputs include

drainage from agriculture, upland forest and swamp forest (~arbro

_-

et

al. 1981).

-

3) The amount of nitrogen fixation occurring due to alder and

bacterial metabolism is unknown. According to Kadlec and Kadlec

(1978) the contribution of nitrogen fixation to the nitrogen budget of

a

freshwater wetland has never been studied.

4 )

The amount of nitrogen loss was based on values by Brinson

(1981) of 75% removal of NH4 and 94% removal of NO3 by the swamp

system. Assuming NH4 is 17% of TN and NO3 is 43% of TN (Kuenzler

et al. 1977), the amount of total nitrogen loss was calculated.

--

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f o r e s t t r e e s p e c i e s (M. Messina, Department of F o r e s t r y , North C a r o l i n a S t a t e U n i v e r s i t y , p e r s o n a l communication).

6) The amount h a r v e s t e d i n d r y w e i g h t was c a l c u l a t e d by m u l t i - p l y i n g t h e a n n u a l amount removed i n growing s t o c k (USFS 1974) by t h e a v e r a g e s p e c i f i c g r a v i t y of swamp f o r e s t s p e c i e s (.58 gm/cm3) a f t e r c o n v e r t i n g from f t 3 t o cm3. N i t r o g e n and phosphorus h a r v e s t e d was determined by m u l t i p l y i n g t h e d r y w e i g h t by t h e a v e r a g e p e r c e n t of n i t r o g e n and phosphorus i n t h e stem of swamp f o r e s t s p e c i e s (.24% N,

.03% P of d r y w e i g h t ) (M. Messina, p e r s o n a l communication).

Upland f o r e s t

A mass b a l a n c e model was a l s o c a l c u l a t e d f o r upland f o r e s t . The

USFS 1974, 1976a, and 1976b a c r e a g e f o r a l l t y p e s of upland f o r e s t were summed f o r t o t a l a c r e a g e . The o n l y i n p u t i n t o t h e system was assumed t o be p r e c i p i t a t i o n . Although some w e a t h e r i n g may o c c u r , t h i s v a l u e was undetermined. Outputs were t i m b e r h a r v e s t i n g and r u n o f f . The f o l l o w i n g assumptions were made f o r t h e upland f o r e s t model:

1) P r e c i p i t a t i o n i n p u t v a l u e s were t h e same a s major c r o p s .

2 ) N u t r i e n t o u t p u t s were c a l c u l a t e d from l i t e r a t u r e v a l u e s o f a n

a n n u a l y i e l d of 1.12 kg N/ha and .56 kg P/ha (Loehr 1974; N.C.

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(31)

RESULTS

A g r i c u l t u r a l Changes, 1950-1978

Over t h e p a s t t h r e e decades s i g n i f i c a n t changes have o c c u r r e d i n a g r i c u l t u r a l l a n d u s e and p r a c t i c e i n t h e Chowan River Basin. The number of farms i n t h e b a s i n h a s d e c r e a s e d from 20,562 i n 1950 t o 5,403 i n 1978 ( F i g . 2 ) r e s u l t i n g i n a d e c r e a s e i n t o t a l farm a c r e a g e . The

FARMS

CHOWAN

RIVER BASIN

t ~ 3 2o 0 PERCENTAGE

2 a

8

LL

80

0 15 v,

m

E

CI

60 z

LL

5

cn

3

1

0

40 z

0 I-

I

Z

I-

20

8

[r

W

5

o

a

0

F i g u r e 2. Change i n number of farms and p e r c e n t a g e of a r e a i n farms i n t h e Chowan Basin,1950-1978.

p e r c e n t a g e o f t o t a l l a n d a r e a i n t h e w a t e r s h e d devoted t o f a r m i n g h a s d e c r e a s e d from 63% t o 41% ( F i g . 2). The a v e r a g e f a r m s i z e h a s more t h a n doubled, however, i n t h i s same t i m e p e r i o d ( T a b l e 4 ) . The change i n l a n d u s e on farms (1950-1978) shows a s i g n i f i c a n t d e c r e a s e i n farm woodland w i t h a s l i g h t d e c r e a s e i n t o t a l c r o p a c r e a g e and p a s t u r e l a n d ( F i g . 3 ) . Harvested c r o p l a n d h a s s t a y e d r o u g h l y t h e same d u r i n g t h i s time p e r i o d ( F i g . 3 ) . The a r e a devoted t o seven major c r o p s w i t h i n t h e b a s i n ( F i g . 4 ) c o n s t i t u t e s most o f t h e h a r v e s t e d c r o p l a n d ( F i g .

3 ) . Corn, soybeans, and peanuts were t h e dominant c r o p s i n terms o f

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Table 4. Average farm s i z e ( h e c t a r e s ) and p e r c e n t of t o t a l c r o p l a n d t h a t was h a r v e s t e d i n t h e Chowan b a s i n , y e a r s 1950-1978,

( U . S . B . C . Census of A g r i c u l t u r e 1952, 1961, 1967, 1972, 1977, 1981)

Average s i z e farm % t o t a l c r o p l a n d Year ( h e c t a r e s ) h a r v e s t e d

T o t a l Chowan 1 9 50 1959 1964 1969 1974 1978

North C a r o l i n a 1950 1960 1964 1969 1974 1978

V i r g i n i a 1950 1959 1964 1969 1974 1978

decreased. Harvest y i e l d s of f i v e major c r o p s a l l showed modest t o marked i n c r e a s e s from 1950 t o 1978 ( F i g . 5 ) .

Change i n t h e number of farm a n i m a l s w i t h i n t h e time p e r i o d examined does n o t appear t o be l a r g e , e x c e p t f o r t h e i n c r e a s e i n

number of b r o i l e r c h i c k e n s ( F i g . 6 ) . The number of commercial b r o i l e r s o v e r t h e p a s t decade has d r a s t i c a l l y i n c r e a s e d from .06 x 106 t o

14.5 x

lo6,

a 74-fold i n c r e a s e (B. Young, Department o f B i o l o g i c a l and A g r i c u l t u r a l Engineering, p e r s o n a l communication). The number of farm machines used i n t h e watershed h a s n e a r l y t r i p l e d from 1950-1978 ( n o t shown) t o a t o t a l of approximately 5500.

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CHOWAN RIVER BASIN

AREAS IN MAJOR L A N D USED

8

FARM w O ~ U ~

11

HARVESTED CROPLAND

1 1 ! I I L I ,

5 0 55 60 65 70 75 80

YEAR

F i g u r e 3 . Changes i n a r e a s of major a g r i c u l t u r a l l a n d u s e s i n t h e Chowan B a s i n .

CHOWAN RIVER BASIN

AREAS PLANTED

-

MAJOR CROPS

22

k

i

55

CORN

-

GRAIN

I'0

I

I I I I I I I

50 55 60 65 70 75 80

YEAR

F i g u r e 4. Changes i n a r e a s d e v o t e d t o major c r o p s i n t h e Chowan

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YIELDS OF MAJOR CROPS

CHOWAN RIVER BASIN

YEAR

F i g u r e 5. Changes i n y i e l d s of major c r o p s i n t h e Chowan Basin

1950-1978.

LIVESTOCK NUMBERS CHOWAN RNER BASIN

500

YEAR

F i g u r e

6 .

Changes i n number of farm a n i m a l s i n t h e chowan B a s i n

1950-1978.

(35)

t o n n a g e d o u b l e d from 1957 t o 1976 i n V i r g i n i a and t h e n d r o p p e d t o t h e 1957 v a l u e , w h i l e p h o s p h o r u s f e r t i l i z e r t o n n a g e r e m a i n e d c o n s t a n t . Commercial f e r t i l i z e r u s a g e i n N o r t h C a r o l i n a h a s remained e s s e n t i a l l y s t a b l e o v e r t h e p a s t s i x t e e n y e a r s (1958-1974) w i t h a s l i g h t i n c r e a s e i n m e t r i c t o n s / h e c t a r e o f c r o p l a n d , C u r r e n t f e r t i l i z e r u s a g e (1973- 1 9 8 0 ) i n t h e w a t e r s h e d h a s a l s o remained f a i r l y c o n s t a n t w i t h a p e a k o c c u r r i n g i n 1976 ( F i g . 8 ) .

Ownership p a t t e r n s o f f a r m s changed from 1950-1978 ( T a b l e 5 ) .

Full-owners a r e t h o s e who own l a n d a n d d o n o t r e n t from o t h e r s . P a r t - owners own some l a n d and r e n t some, a n d t e n a n t s r e n t e n t i r e l y f r o m o t h e r s . The p e r c e n t a g e s o f f u l l - o w n e r s a n d t e n a n t s h a v e d e c r e a s e d w h i l e p e r c e n t a g e o f p a r t - o w n e r s h a s more t h a n d o u b l e d .

Land a r t i f i c i a l l y d r a i n e d f o r a g r i c u l t u r e i n t h e w a t e r s h e d o v e r t h e p a s t 30 y e a r s h a s i n c r e a s e d e x p o n e n t i a l l y from 905 h e c t a r e s i n 1 9 4 0 ( p r i m a r i l y i n G a t e s County, NC) t o 1 2 4 , 0 3 5 h e c t a r e s i n 1 9 7 8

( F i g . 9 ) . A p p r o x i m a t e l y 31X o f t o t a l l a n d and 67% o f l a n d i n f a r m s o f t h e N o r t h C a r o l i n a s e c t i o n o f t h e Chowan R i v e r w a t e r s h e d i s a r t i f i - c i a l l y d r a i n e d ( T a b l e 6 ) . Much l e s s d r a i n a g e h a s t a k e n p l a c e i n V i r g i n i a ; a p p r o x i m a t e l y 2% o f t h e t o t a l l a n d a n d 6% o f f a r m l a n d i s a r t i f i c i a l l y d r a i n e d . For t h e t o t a l Chowan R i v e r w a t e r s h e d , a b o u t 9.7% o f t h e t o t a l l a n d a n d 2 3 . 6 % o f f a r m l a n d i s a r t i f i c i a l l y d r a i n e d ( T a b l e 6 ) . The amount o f l a n d d r a i n e d i n S o i l C o n s e r v a t i o n S e r v i c e (S.C.S.) p r o j e c t s i n N o r t h C a r o l i n a i s 4.5 x

lo4

h e c t a r e s by t h e c h a n n e l i z a t i o n o f 1 0 0 km o f s t r e a m s ( T a b l e 7 ) . No c o m p l e t e d S.C.S. w a t e r s h e d d r a i n a g e p r o j e c t s were r e p o r t e d i n t h e V i r g i n i a w a t e r s h e d .

Changes i n F o r e s t

The a r e a o f commercial f o r e s t l a n d i n t h e Chowan w a t e r s h e d h a s i n c r e a s e d i n t h e y e a r s 1964 t o 1974 ( T a b l e 8). For t h e t o t a l b a s i n t h e r e was a n i n c r e a s e i n l o b l o l l y - s h o r t l e a f p i n e , o a k - h i c k o r y , oak- gum-cypress, a n d elm-ash-cottonwood f o r e s t , a n d a small d e c r e a s e i n o a k - p i n e f o r e s t . However, i n t h e N o r t h C a r o l i n a Chowan w a t e r s h e d t h e r e h a s been a n e t d e c r e a s e o f 9 x

lo3

h e c t a r e s o v e r t h e t e n y e a r p e r i o d . A l l f o r e s t t y p e s i n North C a r o l i n a e x c e p t f o r o a k - h i c k o r y h a v e d e c r e a s e d b u t t h e l a r g e s t d e c r e a s e (-21.3 x

l o 3

h e c t a r e s ) was

i n oak-gum-cypress, which i s f o r e s t e d w e t l a n d . T h i s amounts t o 302 l e s s o f t h i s t y p e o f f o r e s t i n N o r t h C a r o l i n a s i n c e 1 9 6 4 a n d a 24%

oak-gum-cypress d e c r e a s e f o r t h e t o t a l w a t e r s h e d . I n t h e V i r g i n i a p o r t i o n of t h e w a t e r s h e d t h e r e h a s b e e n a n i n c r e a s e i n e a c h o f t h e f o r e s t t y p e s f r o m 1964-1974 ( T a b l e 8 ) . Bottomland t y p e s (oak-gum- c y p r e s s and elm-ash-cottonwood) c o n s t i t u t e d 2 7 % o f t h e c o m m e r c i a l f o r e s t i n N o r t h C a r o l i n a a n d 1 0 % i n V i r g i n i a ( T a b l e 9 ) .

Ownership p a t t e r n s o f commercial f o r e s t i n t h e b a s i n t h r o u g h t h e y e a r s 1964-1974 h a v e n o t changed s f g n i f i c a n t l y . F a r m e r s own r o u g h l y h a l f , a n d t h e f o r e s t i n d u s t r y r o u g h l y a q u a r t e r of t h e c o m m e r c i a l f o r e s t . The r e m a i n d e r i s owned by m i s c e l l a n e o u s c o r p o r a t i o n s and i n d i v i d u a l s , t h e s t a t e , a n d c o u n t i e s and m u n i c i p a l i t i e s . T h e r e i s n o n a t i o n a l f o r e s t w i t h i n t h e r i v e r b a s i n ( T a b l e 1 0 ) .

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z

I I I

57 60

I 65

I

70 75 80

YEAR

F i g u r e 7. H i s t o r i c a l t r e n d o f amounts of n i t r o g e n (X) and p h o s p h o r u s (P) from f e r t i l i z e r u s e d i n Chowan E a s i n .

FERTILIZER

22 ₍ CHOWAN RIVER BASIN

(37)

YEAR

(38)

T a b l e 5. P e r c e n t o f t o t a l number o f farms i n which o p e r a t o r was a f u l l - o w n e r , part-owner, o r t e n a n t i n Chowan

b a s i n . 1950-1978. (U.S.B.C. Census o f A g r i c u l t u r e 1952 1961, 1967, 1972, 1 9 7 7 , 1981)

Year

-

Full-owner X Part-owner % Tenant %

1950 4 6 ₂₃ _{3 2}

1 9 5 9 4 3 ₃₄ _{2 1}

1 9 64 3 3 ₃₉ _{1 8}

1 9 6 9 3 9 _{4 1} _{1 2}

1974 3 3 ₄₉ _{1 2}

1978 28 ₅₅

₉

T a b l e 6. Land a r t i f i c i a l l y d r a i n e d by c o u n t y i n Chowan B a s i n a s p e r c e n t o f t o t a l l a n d and l a n d i n f a r m s , 1978. (U.S.B.C. Census of A g r i c u l t u r e 1981)

B e r t i e Chowan G a t e s H e r t f o r d Northampton TOTAL

VIRGINIA

Brunswick Dinwiddie G r e e n v i l l e

I s l e o f Wight Lunenburg Mecklenburg Nottoway P r i n c e George Southamp t o n Sur r y

S u s s e x Suf f o l k

CHOWAN BASIN TOTAL 1 2 4 , 0 3 5 9.7 23.6

(39)

Table 7. S o i l C o n s e r v a t i o n Watershed P r o j e c t s i n North C a r o l i n a Chowan Basin completed t o d a t e . (U.S.D.A., S o i l Conser- v a t i o n S e r v i c e (1977), U.S.D.A, S o i l C o n s e r v a t i o n S e r v i c e

(1981)).

Watershed

Date Drainage Channels

Completed Area ( h a ) C o n s t r u c t e d (km)

-

Ahoskie Creek 6/30/67 1 9 , 5 0 1 48.8 Burnt Mill Creek 11/02/62 4,251 5.2 Cutawhiskie Creek 6/22/66 12,049 33.5 Horse Swamp F l a t Swamp 10/08/64 3,779 16.2

P o l l o c k Swamp 04/30/66 5,862

-

13.4

TOTAL 45,442 1 0 9 . 1 k

*23% s t r e a m l e n g t h s c h a n n e l i z e d by SCS

i s due t o p r a c t i c e s such a s mechanical s i t e p r e p a r a t i o n ( i n c l u d i n g chop and burn, r o o t r a k e and bed, and b u l l d o z i n g ) , l o g d e c k s , and w i l d f i r e (Burns 1977).

Mass b a l a n c e Models

Major c r o p models. A mass balance model was c a l c u l a t e d f o r each major c r o p of North C a r o l i n a ( c o r n f o r g r a i n , c o r n f o r s i l a g e ,

soybeans, peanuts, tobacco, c o t t o n , and wheat) and V i r g i n i a ( c o r n f o r g r a i n , c o r n f o r s i l a g e , p e a n u t s , soybeans, wheat, tobacco, and b a r l e y )

( F i g s , 10-17). Mass b a l a n c e models of n i t r o g e n and phosphorus f o r t h e major c r o p s i n t h e Chowan watershed i n c l u d e a l l known s i g n i f i c a n t i n p u t s and o u t p u t s f o r t h e agro-ecosystem. T o t a l i n p u t s of n i t r o g e n f o r e a c h c r o p i n c l u d e f e r t i l i z e r , p r e c i p i t a t i o n , and n i t r o g e n -

f i x a t i o n ; t o t a l i n p u t s of phosphorus i n c l u d e f e r t i l i z e r and p r e c i p i - t a t i o n . The o u t p u t s a r e t h e amount of n i t r o g e n and phosphorus

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Table 8. Change i n a r e a (103 h a ) of commercial f o r e s t l a n d t y p e i n t h e Chowan Basin, 1964-1974. (USDA, F o r e s t S e r v i c e 1974, 1976a, 1976b)

TOTAL CHOWAN BASIN County

NORTH CAROLINA :

B e r t i e Chowan

Gates

Hertf o r d Northampton TOTAL h, VIRGINIA: Brunswick Dinwiddie G r e e n v i l l e I s l e o f Wight Lunenburg Mecklenberg No t toway P r i n c e George Southampton Suf f o l k S u r r y Sussex TOTAL

a l l g r o u p s

-0.62 -2.33 -1-18 -3.25 -1.75 -9.13 +1.82 +go. 50

-.02 +11.00

+3.60 -.09 +1. 04 +1.50 +74