U n i v e r s i t y o f Mary land Center f o r Environmental

and E s t u a r i n e S tud ies Chesapeake B i o l o g i c a l Labora to ry Sol ornons , MD 20688

UMCEES Ref. 740. 82-5 CBL

ENVIRONMENTAL IMPACT OF HYDRAULIC ESCALATOR

DREDGING ON OYSTER COMMUNITIES

F i n a l Repor t

January 27, 1982

Submi t ted t o t h e Department o f N a t u r a l Resources

Mary land T idewater F i s h e r i e s A d m i n i s t r a t i o n

Klaus G. Drobeck

Michael L. Johnston

TABLE OF CONTENTS

SECTION I - Broome I s l a n d Environmental Impact Study

S i t e Loca t i on

A b s t r a c t

Methods

F i e l d Work

Labo ra to ry Work

Sediment Traps

Seston

Cu r ren t V e l o c i t i e s and T i d a l Data

Phys i ca l Observat ions

Elemental Ana l ys i s

Benthic Communities

Concl us ions

Recornmen da t i o n s

L i t e r a t u r e C i t a t i o n and Review

SECTION I1 - Midd le Bay R e c l a s s i f i c a t i o n S i t e s

Chart I

, . ' s t a t i o n ~ o c a t i o n '

ABSTRACT

A study t o assess t h e e f f e c t s o f h y d r a u l i c esca la to r dredging on an

o y s t e r community was i n i t i a t e d a t t h e request o f t h e Department o f Na tu ra l

Resources, Mary1 and Tidewater F i she r ies Admin is t ra t ion . The purpose o f t he

work was t o reeva lua te a study done by Manning (1957). A s i t e i n the Patuxent

R ive r n o r t h o f Broome I s l a n d c l a s s i f i e d as o y s t e r bottom was se lec ted t o

conduct an i n - s i t u i n t e n s i v e experiment us ing the Manning s tudy as a frame-

work f o r p r o j e c t design. Clams and oys te rs were present i n the study area,

a l though o y s t e r popu la t i ons were l i m i t e d i n number.

Present data suggest t h a t t h e e f f e c t s o f heavy p a r t i c u l a t e s t o mature

o y s t e r s w i t h i n 15 f e e t o f t h e dredging opera t ion were minimal . Deposi t ion

r a t e a t t h i s 1 5 - f t s t a t i o n was equ iva len t t o approximately 1 /8" . Seston data

i n d i c a t e t h a t wind and t i dal-induced events may have a more profound e f fec t

on t o t a l suspended sediment l o a d a t t h i s s i t e i n the Patuxent R ive r than

does dredging. Post dredging v i s u a l examinat ion o f the bottom w i t h i n t h e

dredge zone revealed no o y s t e r s h e l l s a t t he subs t ra te i n t e r f a c e a l though

clam s h e l l s were i n evidence. D i f fe rences o f c o l o r and topography were

immediate ly ev iden t w i t h i n the conf ines o f t he dredged p l o t . Subst ra te sur -

face appeared much l i g h t e r i n c o l o r than the ad jacent und is turbed bottom and

was undu la t i ng and wavy across t h e dredge d i r e c t i o n a l a x i s .

Four a d d i t i o n a l ' s i t e s i n the middle Chesapeake es tua r ine system were

i n v e s t i g a t e d t o hydrograph ica l 1 y charac te r i ze the a reas and t o determine t h e

s t r u c t u r e and elemental composit ion o f the sediments. Oyster bar composit ion

and macro-benthic communities were a l s o described.

METHODS - BROOME ISLAND - FIELD WORK

On February 28, 1980, a dye study was performed a t t h e Chesapeake Bay

model a t Vattapeake t o determine prel imi nary current flow c h a r a c t e r i s t i c s of

two poss ible areas f o r t h e impact study. The two areas (one adjacent t o

Jacks Marsh i n t h e Patuxent River and one a t Buoy Rock in t he Chester River)

were t es ted during a period of maximum spring runoff . Dye was introduced

a t both flood and ebb t i d a l events a t each s i t e ; and flow d i r e c t i o n , dispersion

and dye t rave l were measured.

On October 13, 1980, an in-situ survey of th ree Patuxent River s i t e s was

performed using conventional grabs, sounders, and drogues t o determine bottom

composition, depth and current veloci ty and d i rec t ion . The determination was

t o l oca t e the dredge-impact study a t a locat ion north of Broome Island i n

approximately 8-10 f e e t of water. The s i t e , located w i t h i n t h e boundaries

of a c l a s s i f i e d natural oys te r ba r , supported both natural clam and oys te r

populations, was conve r~en t w i t h a commercially productive oyster reef and

was i n convenient proximal distance t o t h e Chesapeake Biological Laboratory.

On October 13, 1 4 , and 15, the s i t e boundary l im i t s were es tab l i shed ,

cizfined w i t h buoys, and t he pre-dredge environmental sampling was performed

(Fig . I3 , Table XV). A 1/10 square-meter hydraulical ly operated van Veen

grab was used fo r a l l the benthic samples col lec ted and a modified coring

device was used t o c o l l e c t sediment samples. The cores , approximately 15 t o

20 inches i n length , were frozen immediately upon co l l e c t i on . Benthic

macrofaunal samples were gently washed on a 0.5 mm screen and preserved in

formalin. Oyster populations were sampled by SCUBA divers using a square

meter frame a t random s i t e s w i t h i n the impact zone. The estimated number of

l i v e market s i z e was 2090 within the confines of t h i s p lo t . The pre-dredging

sampling exercise was followed by t h e implantation by the divers of sediment

t r ap s and sediment displacement stakes ( F i s . I Sediment ~ a t a ) .

On October 17 the research vessel was securely anchored i n the

middle of the impact zone. A current meter was s e t a t one meter from

the bottom a n d sample col 1 ect ions and envi ronmental measurements were

obtained on one-ha1 f hour in te rva ls . [Tabl e XV Environmental Data, 14

through 24). Dredging commenced when the t i de was considered r u n n i n g

a t fu l l ebb and was continued unt i l s lack, a period of four and one-

ha1 f hours.

On October 18 the sediment t raps were retrieved (see Sediment Data).

On October 21 the divers visual ly inspected the dredged plot and the

sediment displacement s takes . Cores were removed from the impact zone

and t reated as previously described (Fig. VI, Tables XVII - XVIII).

The experimental s i t e s were rev is i ted i n March, June and September

1981. In March the dredge and impact zones and adjacent control s i t e s

were sampled fo r benthic macrofauna. In June the dredge zone and

control s i t e s were sampl ed and the September samples included dredge,

impact and control . Environmental data was a l so collected on each

v i s i t a t i on (Fig. VII, VIII, IX) (Tables X X , XXII, XXIV).

LABORATORY WORK

Benthic Col lections

The benthic sampl es were treated conventional ly. A1 1 sampl es were

careful ly washed, separated, species identified and numerated, a n d when

considered necessary s t a t i s t i c a l l y analyzed.

Sediment Sampl es

The sediment sampl es were thawed, homogenized a n d equally spl i t .

The portion for grain s ize analysis was washed with fresh water through

a 0.063 mm sieve, placed in a 9 0 ' ~ oven until completely dry ( 3 days) and

separated into various fractions by Ro Tap (12 minutes). Material larger

t h a n 2 m m , gravel and she l l , was discarded; the remaining fractions were

weighed. The s i l t - c lay suspension t h a t passed through the 0.063 mm sieve

was measured t o volume, thoroughly mixed, and a 100 a1 iquot sample

removed a n d f i l t e red on a 5.5 cm GFC Mill ipore f i l t e r . Material remain-

i n g in suspension a f t e r standing for two hours was considered the clay

fraction and treated identical ly in separation. The f i l t e r s containing

the samples were dried a t 90°c, allowed to cool t o room temperature in a

dessicator, weighed, a n d a l l fractions calculated t o percentage (Sediment

Fractions Analysis, a l l Tables).

The portion of the homogenized sample separated for elemental analysis

was washed with deionized water through a nitex screen (0.063 mm), the

c lay-s i l t fraction thoroughly mixed and portions ranging from 150 mls to

600 rnls were lyophilized. The dried powder was placed in plast ic v ia ls ,

stored in a dessicator a n d pelletized a t 5000 psi. The pel le ts , weighing

approximately 0.3 grams each, were glued t o carbon planchetts a n d analyzed

for elemental composition in a carbon carr ier system (Elemental analysis).

SEDIMENT TRAPS

Sediment t raps were deployed one day pr io r t o the planned dredging

exercise a t 15 f e e t , 35 f e e t , and 95 f e e t down current from the dredge zone

and 50 f e e t u p current from the dredge zone (Fig. 11). Cup attachment posi t ions

were adjusted t o correspond with depth var ia t ion. Although depth did not vary

s ign i f i can t ly throughout the study area , uniformity between s t a t i ons as t o cup

distance from the bottom and surface was considered e s sen t i a l . Display

suspensions were held ve r t i ca l l y i n the water column by the up1 i f t i n g force

of a large submerged buoy attached to the upper end of the cup 1 ine (Fig. I ) .

The lower end of the l i n e was attached t o a heavy weight (approx. 600 1 b . ) .

A small f l o a t at tached to the submerged buoy w i t h a l i g h t l i n e was used t o

locate the display posit ion. The cups were f i l l e d with tap water and capped

pr ior to deployment. Cups measured 22 centimeters deep and 7.62 centimeters

2 in diameter with an e f f ec t i ve catching area of 45.6 cm . The following day

jus t preceding the dredging the caps were removed and the t raps exposed f o r

a 24-hour period. The caps were then replaced, the cups re t r ieved and placed

separately i n p l a s t i c bags t o avoid accident ia l sp i l l age during t r a n s i t t o

the 1 aboratory .

Component separation included sand, s i l t s , and c lays . A1 1 material t h a t

washed through the .063 mm sieve was considered s i l t s and clays , while the

f ract ion t h a t remained i n the sieve was considered sand. The suspensions

containing the s i l t -c lay compdnents were thoroughly mixed, a 100-ml a1 iquot

removed and f i l t e r e d on a 5.5 cm GFC Mill ipore f i l t e r . Material remaining i n

suspension a f t e r a 2 - h r . period was considered clay and was t rea ted i den t i ca l l y

in separat ion. The col lected components were labeled and dr ied i n a 9 0 ' ~

oven, dessicated to room temperature, and weighed. Clay component weights

were sub t rac t ed from t h e t o t a l s i l t - c l a y component and t h e d a t a f o r a1 1

fractions recorded (Table I ) . The cont ro l sediment t r a p d i sp l a y deployed

t h r e e days a f t e r the dredging a c t i v i t i e s , kept in pos i t i on f o r a period of 10

days, was t r e a t e d i d e n t i c a l l y and then reduced t o a 24-hr average.

SEDIF/IEIJT TRAP CONSTITUENCY

A ) 15' -35 ' -95 ' downcurrent 24-hr s t a t i o n

1 ) I n i t i a l Dredge Plume

2) Secondary and l a t e n t dredge plumes

3) Background

B) 50' upcurrent 24-hr s t a t i o n

1) Secondary and l a t e n t dredge plumes

2 ) Background

C ) Control - 10-day - reduced t o 24 hrs.

1 ) Background

15"-35'- and 95' minus cont ro l =

1 ) I n i t i a l dredge plume

2) Secondary and l a t e n t dredge plumes

15 '-35 ' and 95 ' minus 50' dor~ncurrent =

1 ) I n i t i a l dredge plume

SEDII IENT TRAPS

Approximate Volume of Sand i n Sottom Cups

15-foot downcurrent 24-tir s tat ion

30 percent -.259 mrn - nediu~il s ize sand particles m i xed with shell

f rayinents

30 percent - .150 rmq sand

30 percent - .p75 mm s3nd

10 percent - smaller t h a n .075 sim sand

35-foot downcurrent 24-hr s t a t i ~ n

10 percent - -259 nrn shell frayinents

43 percent - .I50 m!n sand

40 percent - .075 : I ~ I sand

1.0 percent - smaller t h a n .075 mn sand

95 foot dov~ncurrent 24-hr station

19 percent - -25.1) rnm shell and chitin fragments

30 percent - -150 r:l:n sand

63 percent - .a75 rnril sand

Very srnall axount of sand - less t h a n .075 gl.iI

SO-foot upcurrent 24-hr station

15 percent - .259 ;nr;l large f l a t chitin ?art icles

2'3 percent - . I 3 3 rnnl s a n d

6d percent - .075 an sand

5 percen t - Less t h a n .075 n;il sand

Con t ro l - 13-day - reduced t o 24 h rs .

53 percent - ,253 l a r g e sand g ra ins and s h e l l f r a y e n t s

approx imate ly 15 percen t o f t h i s f r a c t i o n :+as s h e l l

f ragments

30 percen t - .I53 ~nn sand

15 percen t - .075 an sand

5 percent - l e s s t h a n .075 1i11n sand

Est imated volunes o f sand i n a l l bottoiq cups cons is ted o f f r a c t i o n s

rang ing frorn 0.253 rn111 t o 0.963 !ilm. The ! i i ghes t percentage o f t h e l a r g e r

g ranu les (0.23i) n!m) \rere i n t h e c o n t r o l and 1 5 - f t dosrncurrent hottor7 cups.

To ta l amounts :#ere, a t a l l l e v e l s and s t a t i ~ n s , g r e a t e r i n b o t t o ~ cups and

l e a s t i n t h e upper cups. Hpproxi:nately t i v i ce t h e anount of sand 5y w i g h t was

t rapped i n t h e hottoin cups w i t h i n each d i s p l a y w i t h t h e except ion o f t he 59 - f t

upcu r ren t d i sp l ay which was f o u r t irnes greater . Vol umes ;vere no t atte:n?ted

w i t h t h e sand cozponents o f t h e midd le and upper cups s i nce a i x u n t s c o l l e c t e d

were t o o l i rn i ted f o r re1 a t i v e separa t ion es t i na tes . She1 1 f ragaen ts coniposed

a s i g n i f i c a n t p o r t i o n o f t h e l a r g e r f r a c t i o n i n t h e c o n t r o l , t h e 1 5 - f t , and

t h e 3 5 - f t s t a t i o n s 8;ri t h arnounts dec l i n i n j v r i t h increased d i s t a n c e f r o n t h e

dredge zone. There Nere no obviorls s h e l l fragnlents i n t h e 5 9 - f t upcur ren t

s t a t i o n . i.luch o f t h e l a r g e r f r a c t i o n a t t h i s s t a t i o n :{as l i g h t , c h i t i n o u s

f l akes up t o t h r e e rnpi i n s ize . The sand g r a i n s conta ined i n t h e 3.250 !n:n

c o n t r o l f r a c t i o n \ .e re cons iderab ly 1 d r g x ;~!ien cocnp3red t o t h n sa-ne f r a c t i o n s

o f t h e o t h e r s t a t i o n s .

The weight in grams per square meter are indicated in Tab1 e 11. I t i s

assurned from t h i s data t h a t 551 grams of sand were deposited in the v ic in i ty

of the 15-ft dormcurrent station per m2 of bottom. T h i s is equivalent t o

approximately three t o four mm in height (1/8 inch). Since 99 percent of t h e

to ta l sediment trapped at the 15-ft station was sand (Table 111), t h 2 addit ion

of s i l t or clay i s not significant when considering burial of large oysters .

Deposition of sand a t the 35-ft downcurrent station was 91.58 g/n2,

approximately 13 percent of al l sand trapped by downcurrent displays in t h e

bottom cups. The amount of sand trapped a t the 35-ft downcurrent station was

reduced six times when compared t o the 15-ft downcurrent station (Table XI I I ) . Between the 35-ft and 95-ft downcurrent s tat ions the amount of sand trapped,

although n o t equivalent, \$as not significantly reduced. I t i s obvious from

the data tha t the majority of the heavy particulates in suspension a t the

15-ft station had fallen out before reaching the 35-ft s ta t ion- The t o t a l

percentage of the downcurrent samples represented by sand a t a l l levels

declined s l ight ly with increased distance from the dredge s i t e (Table 111).

The 50-ft upcurrent station had the least amount of sand per unit sanpl e whi 1 e

the control had the second greatest amount.

The amount of sediment trapped in the 24-hr exposure period resulting

d i rec t ly from the dredging p1 umes was determined by excluding the bzckground

(control ) figures. (Tables V , VI, VII, and VI I1 .) Percentage comparison

among stat ions shifted significantly toward t h e middle 2nd upper trzps a t t h e

35-ft and 95-ft s tat ions while there was no change i n the 15-ft station i n

t h i s regard. There was a noticeable shift of sand tovrard the midd le and upper

levels when comparing percentages among stations. '[here was a1 so a noticeabl e

s h i f t toward the 15- f t s t a t i o n a t a l l l e v e l s from t h e 35-f t and 95- f t

s t a t i o n s (Tables IX, X,I, XII) .

S i l t s and Clays

Comparing the 24-hour d isplays , the 15-foot s t a t i o n co l l ec ted the

g r e a t e s t amount of s i l t and c lay (Table IV). This conformed w i t h t he

r e s u l t s a s was evidenced by the sand c o l l e c t i o n s . Downcurrent from t h i s

s t a t i o n a t both t h e 35-foot and the 95-foot s t a t i o n s t h e amount of s i l t

co l l ec ted i n 24 hours was not i n any amount g rea te r than t h e thousandths

of a gram range a t the cup level and hundredths o f a gram t o t a l weight

within a d isplay (Table I ) . These two s t a t i o n s exhibi ted incons i s t en t

deposit ion r a t e s , p a r t i c u l a r l y noticeable a t the bottom cup 1 eve l s . Among

s t a t i o n s , the 35-foot d isplay exhibi ted a deposition r a t e t h a t i s approximately

equivalent a t a l l l e v e l s . The 95-foot s t a t i o n , al though, exhibi ted a

s i m i l a r i t y , a t the middle and top cup l e v e l s , t o the 35-foot s t a t i o n . Com-

pa ra t ive ly , the 50-foot upcurrent d isplay demonstrated the widest range of

variance between the top and bottom cups, a ninefold inc rease , and i n t o t a l

amount o f s i l t was s l i g h t l y more than double t h e control d isplay in amount

o f s i l t deposited. The control d isplay demonstrated uniformity, an approxi-

mate doubling o f deposition r a t e with each level change top t o bottom and

t o t a l amount percen tagewise corresponded favorably w i t h t he 15-foot down-

cur ren t s t a t i o n display .

The c lay co l l ec ted i n t h e 24-hour downcurrent d i sp lays demonstrated t h e

1 e a s t uniformity of the separa te ly estimated f r a c t i o n s . Total amount never

exceeded the thousandths o f a gram range in any of the d isplays and near ly hal f

of the up-curren t s t a t i ons demonstrated a reasonable uniformity in deposi-

t ion r a t e s among displays . The control trapped the l e a s t amount of s i l t

and c lay when compared t o t o t a l s of a1 1 displays , indicat ing t h a t sand was

a t a l l levels within t h i s display nearly equivalent t o the 15-foot s t a t i on

percentagewise (Table 111).

The i r r e g u l a r i t i e s expressed in the s i l t and clay f rac t ions probably

r e f l e c t wave f ron t suspensions of unique character . The p a r t i c l e s i z e ,

shape, aggregate composition, e t c . , i n combination w i t h current speed and

distance traveled from point source a f f e c t the s e t t l i n g r a t e and eventual

deposition. The suspension and/or resuspension of buried material by a

highly disrupt ive process may a1 so contribute t o deposition pecu la r i t i e s .

The l a t e n t dredge plume however resul ted in a cons i s ten t ly regular deposi-

t i o n r a t e a s demonstrated by the 50-foot upcurrent s t a t i o n . This l a t e n t

plume was manifest as an uninterrupted mass of discolored water while the

primary dredge plumes were successive waves of sediments of varying width

and colorat ion. The control display demonstrated the most uniform coll ec-

t ions of the s i l t s and clays w i t h approximate doubling e f f e c t s from top

to mid to bottom cups. The to ta l amount of these l i gh t e r par t i cu la tes

was a l so the l e a s t of a l l displays suggesting t h a t t he dredging process

disturbed and placed in to suspension a great deal of material when corn-

pared t o background. Since the control was deployed fo r a 10-day in t e rva l ,

i t was a l so r e a l i s t i c to suppose t h a t the t o t a l background l eve l s were

generally of unknown qua l i ty and may have or iginated from various sources,

among them possibly being hydraulic dredging.

Suspension reduction expressed as a to ta l of a l l f rac t ions indicate

no percentage change between the 15-foot and 35-foot s t a t i o n s when compared

t o to ta l sand and a s l i g h t percent reduction between the 35-foot a n d the

%-foot s ta t ions (Table XI1 I ) .

Graph 1 represents the estimated reduction r a t e i n sediment load

occurring between the 15 and %-foot s t a t i ons .

Total material in suspension between these s ta t ions was reduced by 86%.

The maximum reduction, however, 83% of the t o t a l , occurred between the 15-

foot and 35-foot s t a t i ons , a distance of 20 f e e t . The remaining sediment

load was fur ther reduced by 3% of the t o t a l between the 35-foot and 95-foot

s t a t i ons , a distance of 60 f ee t . Considering the suspension load between

the 35-foot and the 95-foot s ta t ions as a separate segment, the u n i t re-

duction was 19% of the t o t a l .

The aggregate suspended materials a t the three downcurrent s ta t ions

consisted of b o t h the material placed in suspension by the dredging operation

and the background suspension. A t the 15-foot s ta t ion s l i g h t l y more than 91%

of a l l materials in suspension resulted from the dredge plume and s l i g h t l y

l e s s than 9% was background. A t the 35-foot s t a t i on , 48% of suspended

material was dredge plume rela ted and 52% was background. A t the 95-foot

s ta t ion 36% of suspended material was dredge plume rela ted and 64% was back-

ground .

The sediment t raps simi 1 a r ly demonstrated the reduct ion in sediment

load with increased distance from the dredge zone. Trapped material decreased

by a fac tor of 11 times between the 15-foot a n d the 35-foot s ta t ions and 18

times between the 15-foot a n d the 95-foot s t a t i ons . As a separate segment

trapped material between the 35-foot a n d the 95-foot s t a t i ons was reduced

by 1 .6 times.

Fig. 11

DREDGE and IMPACT SlTE, PATUXENT RIVER, BROOME ISLAND BAR

Dredge Zone

P O S I T I O N S 0 NE

0- SED L X I ~ ~ . T TRAP and METERING STAKE-0

O n e sediment t r a p was p o s i t i o n e d 50 f e e t n o r t h of t h e dredge zone

75 ft.

I o # -

I 75 ft.

0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0

I ( Impact Zone

-

T 50 ft.

1 SW-

0 0 0 0 0 0 0 0 0

f - - - - - - - - 150ft. - --- - - ---4 SE

Table I SEDIMENT TRAPS

Weight i n grams i n sediment t r a p s

15 '+ 35'+ 95 I + 50'- Con t ro l

Sand T M B

T o t a l

S i l t T M B

T o t a l

Clay T M B

T o t a l

TOTALS 15 '+ 35'+ 95 '+ 50' - Con t ro l

TOP 1.1843 . I99 3 . I490 .0498 .0853

M i d 1.6366 .2941 .2420 ,0814 . I365

Bottom 2.574 .4229 3 5 73 .2090 .25 71

Table II

SEDIMENT TRAPS

Weight i n g r a m s / s q u a r e meter from sed imen t t r a p d a t a

no . x 219 .3

15'+ 35'+ 95'+ 50 ' - C o n t r o l

Sand T 257.0 42.22 31.34 M 355.0 63.38 52.24 B 551.0 91.58 75.81

T o t a l 1163.0 197.18 159.39

S i l t T 1 . 9 3 1 .12 - 8 8 M 2.72 0.88 .72 B 6 . 4 3 1 . 0 5 1 .97

T o t a l 11 .08 3.05 3.57

C l a y T .79 .37 .46 M .72 .24 .ll B .94 .11 .57

T o t a l 2.45 .72 1.14

T o t a l s - Sand, S i l t and Clay:

TOP 259.72 43.71 32.68

Mid 358.44 64.50 53.07

Bottom 558.37 92.74 78.35

Table 111

SEDIMENT TRAPS

Percen tage Comparison Among S t a t i o n s

% of T o t a l of (T,M,B) T,M,B

- - - - --

15 ' 35 ' 95 ' 50'- Con t ro l

Sand T M B

S i l t T M B

Clay T M B

Table IV SEDIMENT TRAPS

Percen tage comparison between s t a t i o n s

T o t a l Sand 15' 35' 95'

S i l t - T 3.93 M 4.32 B 9.45

Clay T 1.62

T o t a l - Sand, S i l t and Clay - Percen tage t o t a l r e p r e s e n t e d by sand

15' 35 ' 95' 50 ' - - Con t ro l

9 9 9 7 9 6 TOP 96 9 9

Mid 99 98 98 95 9 8

99 9 7 9 3 Bottom 99 98

Table V

SEDIMENT TRAPS

Weight i n grams i n sediment t raps minus c o n t r o l

Sand T M B

Tota l

S i l t T M B

Tota l

Clay T M B

TOTALS

Top

Mid

Bottom

Tab le V I

SEDIMENT TRAPS

Weight i n grams/square meter from sediment t r a p data minus control

no. X 219.3

15 '+ 35'+ 9 5 ' t 50 ' - Control

Sand T 238.58 M 325.86 B 496.01

Total 1060.45

S i l t T 1.69 M 2.24 B 5.33

Total 9.26

Clay T .75 M .66 B .83

Total 2.24

TOTALS

Bottom 502.17

Table VII

SEDIMENT TPAPS

Percentage compari s ion among s t a t i o n s

% of t o t a l minus con t ro l

Sand T

M

B

S i l t T

M

B

Clay T

M

B

Table VIII

SEDIMENT TRAPS

Percentage cornparision between s t a t i o n s

% o f t o t a l minus c o n t r o l

T o t a l 15 ' 35 ' 95'

Sand T

M

B

S i l t T

M

B

Clay T

M

B

TOTALS - Sand, S i l t and Clay: Percentage t o t a l represented by sand

15 ' 35 ' 95 '

T 9 9 9 5 93

M 99 9 8 99

B 99 99+ 94

Table IX

Sediment Traps

Weight i n grams i n sediment t r a p s minus the 50 ' up-current

s t a t i o n i n d i c a t e s t h e i n i t i a l plume plus 24 hour background l e v e l .

Sand T

M

8

Total

S i l t T

M

B

Total

Clay T

M

B

Tota 1

TOTALS Sand, Si 1 t and Clay

15 ' 35' - -

To P 1 .I345 .I495

M i d 1 -5542 -21 27

Bottom 2.3380 -2283

Table X

Sediment Traps

Weight in grams/square meters minus the 15' up-current s t a t i o n

no. X 219.3

Sand T 346.45

b? 338.36

B 508.49

1193.30 Total

S i l t T

M

B

Total

Clay T

H

B

Total

TOTALS - Sand, S i l t and Clay

To P 348.79

Mid 340.84

Bottom 512.72

Table XI

Sediment Traps

Percentage Comparison among s t a t i o n s

% o f t o t a l minus t h e 50' up-current s t a t i o n

Sand T

M

B

S i l t T

M

B

Clay T

M

B

Tab le XI1

Sediment Traps

Percentage comparison between s t a t i o n s

% o f t o t a l minus 50 ' up -cu r ren t s t a t i o n

To ta l 15'+ 35'+ 95 ' +

Sand T

M

B

S i l t T

M

B

C lay T

M

B

TOTALS -Sand, S i l t and Clay. Percentage t o t a l represented by sand.

15 '+ 35 ' + 95 ' + - TOP 9 9 9 7 9 6

Mid

Bottom

Table XI11

Sediment Traps

Percentage comparison of sand between t h e 15' and 35'

s t a t i o n s and the 35' and 95' s t a t i o n s weight i n

grams/square meters - no. x 219.3

15 ' minus 35'

- - -

35' minus 95'

Top - Of t h e es t imated sand i n suspension between t h e 15'

s t a t i o n and t h e 35' s t a t i o n , 84% had e i t h e r d i spe r sed

o r had i n a l l p r o b a b i l i t y f a l l e n out of t h e top l e v e l .

The % r a t e of f a l l o u t between t h e 35' s t a t i o n and t h e

95' s t a t i o n was 26% of t h e t o t a l amount i n suspension.

Mid - Of t h e es t imated sand i n suspension between t h e 15'

s t a t i o n and t h e 35' s t a t i o n , 82% had i n a l l p r o b a b i l i t y

f a l l e n out . The % f a l l o u t r a t e between t h e 35' s t a t i o n

and t h e 95' s t a t i o n was 18% of t h e t o t a l amount i n

suspension.

Bottom - Of t h e es t imated sand i n suspension between t h e 15 '

s t a t i o n and t h e 35' s t a t i o n , 83% had i n a l l p r o b a b i l i t y

f a l l e n out . The % f a l l o u t r a t e between t h e 35' s t a t i o n

and t h e 95' s t a t i o n was 1 7 % of the t o t a l amount i n

suspension.

Seston

The sediment i n suspension i n t h e wa te r column ( s e s t o n ) averaged an

i n c r e a s e w i t h dep th i n t h e samples c o l l e c t e d on t h e 1 3 t h , 14 th , and 1 5 t h

o f October and averaged a decrease w i t h depth i n t h e samples c o l l e c t e d on

t h e 1 7 t h o f October (Tab le XIV). T o t a l amounts o f ses ton p e r s t a t i o n

were a l s o g r e a t e r i n t h e c o n t r o l c o l l e c t i o n s (1 3 th , 1 4 t h , 1 5 t h ) t han

t h o s e o b t a i n e d j u s t p r i o r t o and d u r i n g d redg ing ( 1 7 t h ) . Seston a l s o

averaged an i n c r e a s e d u r i n g d redg ing when compared t o t h e sample taken

j u s t p r i o r t o d redg ing . Heavy nor thwes t winds p r e v a i l e d d u r i n g t h e

i n i t i a l c o n t r o l samp l ing which c o u l d conce i vab l y r e s u l t i n t h e h i g h

l e v e l s o f suspended m a t e r i a l i n t h e wa te r column. The winds d i m i n i s h e d

d u r i n g t h e course o f t h e f o l l o w i n g days ' c o l l e c t i o n s and i n c r e a s e d some-

what d u r i n g t h e d redg ing phase c o l l e c t i o n s p o s s i b l y a f f e c t i n g t h e t o t a l

ses ton l o a d i n g (Tab le X V , Env i ronmenta l Data). The ses ton data, how-

ever , suppo r t s t h e t u r b i d i t y c a l c u l a t i o n s a t an approx imate 60% i n c i d e n c e

and i s i n a l l p r o b a b i l i ty n o t c o r r e l a t e d s i g n i f i c a n t l y . Seston sarnpl i n g

i s a h i g h l y mani pu l a t i v e techn ique f o r e s t i m a t i n g t h e amount o f m a t e r i a l

suspended i n t h e wa te r column w h i l e m o n i t o r i n g t u r b i d i t y i s e s s e n t i a l l y

a simp1 e mechanica l o r i n s t r u m e n t a l procedure.

The data (Tab le x IV ) i n d i c a t e s t h e apparen t ses ton i n c r e a s e i n t h e

wa te r column was s l i g h t c o n s i d e r i n g t o t a l suspension l e v e l s d u r i n g t h e

s i n g u l a r d redg ing o p e r a t i o n . The consol i d a t i n g e f f e c t o f s e v e r a l dredges

o p e r a t i n g s i m u l t a n i o u s l y i n a comparable area however c o u l d e l e v a t e t o t a l

suspension l e v e l s h i g h enough t o depress o y s t e r pumping r a t e s and e f f e c t

t he development o f o y s t e r eggs and l a r v a e . Loosaaoff and Tommers

(1948) demonst ra ted t h e e f f e c t o f s i l t c o n c e n t r a t i o n s on o y s t e r f e e d i n g

a c t i v i t y and conc luded t h a t pumping r a t e s were c o n s i d e r a b l y reduced a t

O.lg/l. Davis and Hidu (1969) indicated a s ignif icant decrease in the

percentage of oyster eggs developing normally when subjected to 0.188g/l

of s i l t . Survival and growth of oyster larvae was also reduced progressively

as s i l icon dioxide par t ic le s ize was decreased. The substrate in the

dredge zone a t Broome Island averaged less than five percent s i l t and back-

g r o u n d levels of seston probably resulted from several untraced sources.

Oyster tongers and clam dredgers were b o t h operating in a f fec t ive proximity.

Increased potential for water column loading by a l l sources would be magnified

considerably in areas containing large percentages of s i l t as was demonstrated

by the Manning study. The current, the sa l in i ty , and the physical condition

of the disturbed sediment a f f ec t the density and length of period in suspen-

sion considerably. The e f fec t , par t icular ly on sedimentary f i l t e r feeding

organisms, i s related t o tu rb id i ty density, par t ic le s i z e and shape, season,

species and adaptation.

Current veloci t ies a t the Broome Island s tat ion (Table XIVd) ranged

from .02 t o .27 knots on an ebb t i d e . These values compared favorably with

resu l t s of the dye study conducted a t the Chesapeake Bay model in Mattapeake.

Broome I s l a n d Impact Study. Phys i ca l Observa t ions

Dredge Zone

V i s u a l obse rva t i ons d u r i n g d redg ing i n d i c a t e d s u b s t a n t i a l amounts o f

s h e l l b o t h on and i n t h e dredge zone s u b s t r a t e . Cons iderab le q u a n t i t i e s

o f s h e l l , p redomina te ly o y s t e r s h e l l were observed pass ing o v e r t h e e s c a l a t o r

and on s e v e r a l occas ions were so numerous t h a t t h e dredge became c l ogged

and ceased o p e r a t i n g . Random p re -d redg ing coun ts o f o y s t e r s bo th i n t h e

2 dredge and impac t zones y i e l d e d a mean d e n s i t y o f two oys te rs /m .

Three days a f t e r d redg ing an " i n s i t u " i n s p e c t i o n o f t h e s t udy a rea

was per fo rmed by scuba d i v e r s . T h i s pos t -d redg ing exam ina t i on o f t h e bot tom

r e v e a l e d no o y s t e r s h e l l a t t h e s u b s t r a t e i n t e r f a c e a l t h o u g h clam s h e l l s

were i n ev idence. D i f f e r e n c e s o f c o l o r and topography were immed ia te ly

e v i d e n t w i t h i n t h e c o n f i n e s o f t he dredged p l o t . The s u b s t r a t e su r face

appeared much l i g h t e r i n c o l o r than t h e a d j a c e n t u n d i s t u r b e d bottom.

Troughs and r i d g e s c o u l d be observed t h roughou t t h e area, an obv ious r e -

s u l t o f t h e dredge c u t s as was t h e c o l o r a t i o n change.

As w i t h t h e Manning s tudy, o y s t e r m o r t a l i t i e s w i t h i n t h e dredge p l o t

appeared t o be 100% due t o b u r i a l . Oys te rs and s u i t a b l e c u l t c h m a t e r i a l s

were absent f rom t h e s u b s t r a t e i n t e r f a c e w i t h t h e e x c e p t i o n o f a few s c a t t e r e d

clam s h e l l s . The b i o l o g i c a l i m p l i c a t i o n s concern ing o y s t e r p ropaga t i on i n an

a rea t h a t has been h y d r a u l i c a l l y dredged suggest a s u b s t a n t i a l r e d u c t i o n i n

r e c r u i t m e n t p o t e n t i a l due t o t h e l a c k o f spawning s t o c k as w e l l as s u i t a b l e

c u l t c h . R e c l a s s i f i c a t i o n f rom o y s t e r t o clam bot tom imp1 i e s a profound,

l o n g - t e r m a1 t e r a t i o n o f s u b s t r a t e m a t e r i a l and w o u l d r e q u i r e an i n t e n s i v e

management e f f o r t t o r e e s t a b l i s h o y s t e r commun i t i es .

I m p a c t Zone

Downstream f r o m t h e a r e a o f t h e dredge o p e r a t i o n no a l t e r a t i o n s i n

b o t t o m t o p o g r a p h y were e v i d e n t . M e t e r i n g s t a k e s imp1 a n t e d on t h e b o t t o m

i n d i c a t e d no s i g n i f i c a n t a c c u m u l a t i o n s o f d i s p l a c e d dredged m a t e r i a l i n t h e

i m p a c t zone. Sed iment d e p o s i t i o n as measured b y sed imen t t r a p s i s d i s c u s s e d

i n a n o t h e r s e c t i o n o f t h i s r e p o r t . O y s t e r s and c u l t c h m a t e r i a l rema ined un-

b u r i e d i n c l o s e p r o x i m i t y ( a p p r o x i m a t e l y 1 5 f t . ) d o w n c u r r e n t f rom where t h e

dredge had o p e r a t e d .

Manning (1957) r e p o r t e d sed imen t a c c u m u l a t i o n s o f o v e r one i n c h t w e n t y -

f i v e f e e t downstream f r o m h i s dredge zone and o v e r one-ha1 f i n c h f i f t y f e e t

downcur ren t from h i s dredge zone. T h i s a c c u m u l a t i o n o f d i s p l a c e d d redged

m a t e r i a l r e s u l t e d i n s i g n i f i c a n t m o r t a l i t i e s o f b o t h a d u l t and j u v e n i l e

o y s t e r s . M a n n i n g ' s work was c a r r i e d o u t i n a muddy s u b s t r a t e i n a s h a l l o w

c r e e k where c u r r e n t v e l o c i t i e s were c o m p a r a t i v e l y s t r o n g , a p p r o a c h i n g one

k n o t . I n c o n t r a s t , t h e Broome I s l a n d i m p a c t s t u d y was p e r f o r m e d i n a sandy

s u b s t r a t e where c u r r e n t v e l o c i t i e s n e v e r exceeded o n e - t h i r d o f a k n o t n e a r

t h e s u b s t r a t e i n t e r f a c e .

The a u t h o r s o f t h i s s t u d y do n o t d i s p u t e t h e f i n d i n g s o f t h e Manning

s t u d y e i t h e r i n method employed o r da ta g e n e r a t e d . However, p h y s i c a l c o n d i -

t i o n s o f s u b s t r a t e and c u r r e n t v a r y c o n s i d e r a b l y between g e o g r a p h i c r e g i o n s

t h r o u g h o u t t h e Bay. D e c i s i o n s t o r e - c l a s s i f y b o t t o m s h o u l d be based n o t o n l y

on b i o l o g i c a l a s p e c t s b u t s h o u l d c o n s i d e r s i t e - s p e c i f i c sed imen t t r a n s p o r t

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

ELEMENTAL ANALYSIS

The s i g n i f i c a n t e lementa l components r e p r e s e n t i n g each p a n - s i l t - c l ay

f r a c t i o n (.063mm): a r e r a t i o s d e r i v e d f rom bu l k mode e x c i t a t i o n a n a l y s i s p e r -

formed i n a scann ing e l e c t r o n mic roscope equipped w i t h an e n e r g y - d i s p e r s i v e

spec t romete r . ~o l ybdenum, i n h e r e n t i n t h e b u l k mode a n a l y s i s t echn ique , was

s t a t i s t i c a l l y reduced t o a coun t o f one i n each s a m p l e - t o p r o v i d e a t ime -

energy l e v e l emiss ion s tandard . A l l t h e e lements d e t e c t e d i n each sample

were s i m i l a r l y reduced i n t o t a l emiss ions so as t o c o r r e l a t e t h e s i g n i f i c a n t

e l ements w i t h t h e p rede te rmined t i m e scan program. The e lementa l r a t i o s

i l l u s t r a t e d i n t h e h is tograms a r e t h e r e f o r e d e r i v e d f rom t h e reduced t o t a l

molybdenum emiss ions w i t h t h e background r a d i a t i o n e l im ina ted .

Windows i n which s i g n i f i c a n t e lements were d e t e c t e d were sodium,

magnesium, s i l i c o n , a1 uminum, s u l phur, c h l o r i n e , potassium, ca l c i um , t i t a n i u m ,

i r o n , copper, z i n c , and n i c k e l . Concen t ra t i ons o f i r o n were g e n e r a l l y p r e -

dominant i n e v e r y sample. Calc ium, c h l o r i n e , s i l i c o n and copper i n d i c a t e d a

c o n s i s t e n t f requency o f abundance i n most sampl es . Unders tandab ly c h l o r i n e

and sodium shou ld be p r e s e n t .in any mar ine env i ronment . The e s t u a r i n e s e d i -

ments s h o u l d a l s o c o n t a i n p l e n t i f u l amounts o f ca l c i um . Most o f the:remain-

i n g e lements a r e p resen t i n t h e e 6 t u a r i n e sed iments o r i n t h e a s s o c i a t e d l i f e

forms. The e l emental a n a l y s i s i n d i c a t e s a p o t e n t i a l f o r i n c r e a s e d concen t ra -

t i o n s o f p a r t i c u l a r heavy me ta l s i n t h e fil t e r f e e d i n g organisms s i m p l y because

t h e y a r e a v a i l a b l e . I t appears u n l i k e l y t o pose a problem i n t h e a reas sampled

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

d i s t r i b u t i o n . I n source areas o f h i g h c o n c e n t r a t i o n s o f p o t e n t i a l l y harmful

e lements o r substances however, b i o c o n c e n t r a t i o n i n animal spec ies c o u l d

d i r e c t l y r e s u l t f rom e q u i l i b r i u m p a r t i t i o n i n g p a r t i c u l a r l y among r a p i d l y

d e v e l o p i n g egg o r l a r v a 1 s tages . T h i s c o n d i t i o n response would be a f f e c t e d

by seasonal variation i n a species, the duration and magnitude of the dredg-

i n g operation, and the part icular elemental species or combinations avai lable .

Oysters, f o r exampl e , as facul t a t ive anaerobes a re re1 a t ive ly inactive

metabolically i n cold winter seasons and have reduced act ive environmental

contact. Therefore they would l e s s l i kely be adversely affected by pol 1 utants

in t h i s condition.

B e n t h i c Sampl i ng -

The o r i g i n a l sampl ing des ign c a l l e d f o r a s e r i e s o f samples t o be t aken

i n t h e dredge and impact areas as we l l as ad jacen t c o n t r o l s i t e s . However,

due t o b o t h t h e l a r g e amount o f m a t e r i a l t o be processed i n each sample and

t h e observed l i m i t e d t r a n s p o r t o f sediment i n t o t h e impact zone, sampl ing i n

t h e months of March and June was con f i ned t o t h e Dredge and C o n t r o l s i t e s .

W i lhm (1967) o r i g i n a l l y i n d i c a t e d t h a t t h e s t r u c t u r e o f communit ies o f b e n t h i c

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

frat1 env i ronmenta l change. Due t o t h e i r sedentary n a t u r e t h e y a f f o r d us an

o p p o r t u n i t y t o sample a p o p u l a t i o n which i s r e l a t i v e l y immobi le and

access ib le . S i g n i f i c a n t v a r i a t i o n s i n spec ies d i v e r s i t y and t o t a l numbers o f

organisms a r e sometimes use fu l i n de te rm in i ng t h e impact o f an env i r o m e n t a l

p e r t u r b a t i o n . Maximum d i v e r s i t y r e s u l t s i f i n d i v i d u a l s a re equal l y

d i s t r i b u t e d among species. D i v e r s i t y i s m in ima l i f a1 1 i n d i v i d u a l s a r e o f one

species. The concept o f d i v e r s i t y i s p a r t i c u l a r l y impo r tan t because it i s

c a n m n l y cons idered an a t t r i b u t e o f a n a t u r a l o r o rgan ized community ( H a i r s t o n

1964). Two d i v e r s i t y i n d i c e s were chosen f o r t h i s study.

The Shannon-Wiener i n f o r m a t i o n - t h e o r e t i c a l measure o f mean spec ies

d i v e r s i t y per i n d i v i d u a l (ti') i s s e n s i t i v e t o b o t h r i c h n e s s and t h e spec ies

f requency d i s t r i b u t i o n . T h i s index

where H i s t h e i n f o r m a t i o n con ten t o f t h e sample ( b i t s / i n d i v i d u a l ), S = number

of spec ies, and P i i s t h e p r o p o r t i o n o f t h e t o t a l sample be long ing t o t h e i t h

spec ies. Va lues range f rom a m-inimum of 0 t o a maximum o f 3.

Simpson's (1949) index i s t h e sun o f t h e squares o f t h e p r o p o r t i o n s of

t h e component species. Domi nance c o n c e n t r a t i o n can be de te rmi ned f rom t h i s

index. It i s n o t g r e a t l y dependent on sample s i z e and i t i s no t necessary t o

a d j u s t t o c o n s t a n t e f f o r t b e f o r e c a l c u l a t i n g t h i s index. Values range f r a n 1,

i f a l l o f t h e i n d i v i d u a l s a r e o f one spec ies t o (1) i f t h e y a re e q u a l l y S

d i v i d e d among t h e spec ies ( S ) . It approaches O as S -> N and as S i n c reases .

The b i o l o g i c a l i ndex va l ue (B. I. va lue) f o r de te rm in i ng spec ies dominance

(Wade 1972) was a l s o u t i l i z e d . The B.I. va lue i s c a l c u l a t e d by ass i gn ing a

va l ue o f 10 t o t h e most abundant spec ies a t each sample s t a t i o n , 9 t o t h e

second rnost abundant species, e t c . The i n d i v i d u a l va lues a r e t h e n t o t a l l e d

f o r a l l s t a t i o n s and t h e i n d i v i d u a l s w i t h t h e h i g h e s t va lues a r e dec la red t o

b e t h e dani nant species.

Sediment c m p o s i t i o n and s a l i n i t y a r e t h e p r imary env i rormenta l f a c t o r s

govern ing s p a t i a l v a r i a t i o n o f b e n t h i c communit ies i n many areas o f Chesapezke

Bay. The b e n t h i c p o p u l a t i o n a t t h e Broorne I s l a n d s i t e i s a f a i r l y homogeneous

one due t o t h e l a c k o f v a r y i n g s u b s t r a t e t ypes and s t a b l e s a l i n i t y p a t t e r n s .

The sma l l phys i ca l s i z e o f t h e area sampled \.;as a l s o r e s p o n s i b l e f o r t h e

homogeneity.

To ta l nurr~ber of spec ies c o l l e c t e d each n o n t h showed 1 i ttl e temporal

v a r i a t i o n a l though changes i n number o f i n d i v i d u a l s were ev i den t . Twen ty - f i ve

s p e c i e s were i d e n t i f i e d f rom t h e Oc tober p r e - d r e d g i n g sampl es t a k e n

i n t h e impac t , c o n t r o l and dredge zones ( T a b l e X X V I ) . T a b l e X I X i n -

d i c a t e s s p e c i e s dominance i n each zone, as c a l c u l a t e d b y t h e b i o l o g i c a l

i n d e x v a l u e f o r t h e month o f Oc tober . T h i s t a b l e i n d i c a t e s t h a t t h e r e

was 1 i t t l e v a r i a t i o n i n dominance between sampled s i t e s . A m a j o r i t y

o f t h e s p e c i e s found t o be dominant i n t h e impac t , d redge and c o n t r o l

zones a r e t y p i c a l l y found a s s o c i a t e d w i t h s h e l l s u b s t r a t e . N e r e i s

succ inea , an a n n e l i d worm, was found t o be t h e most dominant s p e c i e s

i n a l l t h r e e zones due t o t h e l a r g e amount o f o y s t e r s h e l l p r e s e n t .

O t h e r spec ies wh ich a r e s h e l l - s u b s t r a t e a s s o c i a t e d and were f o u n d t o

be dominant i n c l u d e d B. r e c u r v u s , - C. l a c u s t r e , 5. p a l u s t r i s , - - M. man-

h a t t e n s i s and - D. 1 euco lena. P o p u l a t i o n s o f t h e s o f t - s h e l l e d c lam,

Mya a r e n a r i a were r e l a t i v e l y l o w i n a l l zones sampled d u r i n g t h e month

o f Oc tober . P a t c h i n e s s was e v i d e n t i n a l l a reas sampled. Numbers o f

2 j u v e n i l e Mya t a k e n b y van Veen g r a b ranged f rom a h i g h o f 23/m on

Z s t a t i o n 10 i n t h e i m p a c t zone t o a l o w o f O/m on s e v e r a l s t a t i o n s i n

t h e dredge, impac t and c o n t r o l zones.

P o s t d r e d g i n g samples t a k e n i n March i n d i c a t e a r a p i d r e e s t a b l i s h -

ment o f t h e b e n t h i c p o p u l a t i o n i n t h e dredge zone. Twenty-one s p e c i e s

were i d e n t i f i e d f r o m s t a t i o n 4 i n t h e dredge zone, more t h a n any o t h e r

s t a t i o n i n c l u d i n g t h e two c o n t r o l s t a t i o n s . D i v e r s i t y v a l u e s were

u n i f o r m l y h i g h i n b o t h t h e dredge and c o n t r o l a reas . N e r e i s s u c c i n e a

was once a g a i n t h e most dominant s p e c i e s i n a l l a reas sampled ( T a b l e

X X I ) . O v e r a l l , 2 4 s p e c i e s were i d e n t i f i e d f r o m b o t h t h e dredge and

c o n t r o l samples w i t h t h e s h e l l s u b s t r a t e spec ies c o m p r i s i n g t h e m a j o r i t y

o f t h e dominant s p e c i e s . P o p u l a t i o n s o f t h e s o f t - s h e l l c lam i n c r e a s e d

s i g n i f i c a n t l y a t b o t h c o n t r o l and dredge s i t e s f o r t h e mon th o f

March. These j u v e n i l e mya were most l i k e l y t h e r e s u l t o f t h e p r e v i o u s f a 1 1 ' s

se t . Mean numbers/m2 i n t h e dredge zone ranged f r om a h i g h o f 450 t o a l ow of

150. The number o f rnya i d e n t i f i e d f rom t h e samples t aken on t h e two c o n t r o l

s t a t i o n s was cons ide rab l y h i g h e r w i t h 633/m2 on one s t a t i o n and 1,367/m2 on

t h e o t h e r .

Heterornastus f i l i f o r m i s , a s o f t s u b s t r a t e burrower, wasrnost dominant i n

t h e dredge and c o n t r o l zone samples taken i n June. Ne re i s succ inea, which had

been dan i nant i n t h e p r e v i o u s month 's sampling, was t h e second most d m i n a n t

spec ies. Garr~marus p a l u s t r i s , a gammarid arnphipod, was most abundant

numer ica l l y , hav i ng recorded 2,639 i n d i v i d u a l s on one s t a t i o n i n t h e c o n t r o l

zone. D i v e r s i t y values were u n i f o n n on a l l s t a t i o n s except f o r s t a t i o n 6, a

c o n t r o l s t a t i o n . Here, a l ow d i v e r s i t y va l ue ( H ' = 2.09) was ob ta ined due t o

t h e l a r g e c o n c e n t r a t i o n o f gammarus. Conversely t h e va lue ob ta i ned f o r

Simpson's index was h i g h (S.I . = .41464) i n d i c a t i n g t h i s p a r t i c u l a r spec ies

doninance o f t h e b e n t h i c p o p u l a t i o n o f t h i s s t a t i o n . Mya popu la t i ons were

once aga in h i gh when c m p a r e d t o t h e October samples. Values ob ta i ned f o r t h e

two c o n t r o l s t a t i o n s were 1,130/rn2 and 403/m2. I n t h e dredge zone t h e va lues

ranged f r a n a low o f 217/rn2 t o a h i gh o f 553/rn2. O v e r a l l , 23 spec ies were

i d e n t i f i e d f rom t h e samples taken i n t h e dredge and c o n t r o l zones f o r t h e

month o f June. C o n t r o l s t a t i o n s recorded a g r e a t e r number o f spec ies t h a n t h e

d r e d g ~ zone s t a t i o n s . Th i s was due t o t h e absence i n t h e dredge zone o f

Crassos t rea v i r g i n i ca , t h e American oys te r , Rhi thropanopeus h a r r r i s s i , a

p o r t u n i d c rab f r e q u e n t l y found on o y s t e r So t t on and Plolgula manhat tens is , a

s e s s i l e t u n i ca te .

I n September, samples were once aga in t aken i n t h e dredge, impact and

c o n t r o l zones. Heteromastus f i l i f o r m i s was found t o be t h e most dominant

spec ies i n a l l t h r e e zones. D i v e r s i t y va lues (HI) were u n i f o r m l y low on a l l

s t a t i o n s i n t h e dredge and impact zones. Values recorded on t h e two c o n t r o l

s t a t i o n s were s l i g h t l y h igher . O v e r a l l , t o t a l numbers of i n d i v i d u a l s were

depressed on a l l s t a t i o n s i n t h e t h r e e zones most l i k e l y t h e r e s u l t o f t h e

annual summer d i e - o f f o f t h e ben th i c community. Popu la t i ons o f Flya a r e n a r i a

were down s i g n i f i c a n t l y i n a l l areas sampled. Mya were most abundant on t h e

two c o n t r o l s t a t i o n s (23/m2 and 3/m2) and l e a s t abundant i n t h e impact zone

where none were found. Only one s t a t i o n i n t h e dredge zone recorded any Mya

(3 /&) . As was t h e case th roughout t h e e n t i r e study, t h e September samples

were dominanted by t h e s h e l l s u b s t r a t e assoc ia ted organisms.