Hydrobiologia vol. 60, 3, pag. 203-211, 1978

SEASONAL FLUCTUATION OF WATER QUALITY (NUTRIENTS AND PIGMENTS) IN LOWER DELAWAREBAY

'Don MAURER, 2Les WATLING, 3Dan BOTTOM & 4Ann PEMBROKE

'College of Marine Studies, University of Delaware, Lewes, DE 19958; 2 Ira C. Darling Center, University of Maine, Wal-pole, ME 04573; 3 P.O. Box 3597, Coos Bay, OR 97420; 4 Pandullo, Quirk Associates, 545 Tilton Road, Northfield, NJ08225.

Received November 29, 1977

Keywords: water quality, nutrients, pigments, Delaware Bay

Abstract

Water quality samples were obtained monthly or bimonthly 17times from May 1974 to May 1975 at three stations in DelawareBay. In addition, two 12-hour cruises were also conducted at onestation in February and April 1975. Surface and bottom watersamples were taken. Measurements and analyses included tem-perature, salinity, dissolved oxygen, silicate, nitrate and nitrite,orthophosphate, ammonia, chlorophylls a, b, and c, phaeo-pigments, and carotenoids.

The annual pattern of temperature was typical of an estuary inthe mid-Atlantic Bight. Salinity and dissolved oxygen rangedfrom 22.9 to 29.7%o and from 4.53 to 8.53 ml/l, respectively.Nutrient and pigment values showed seasonal peaks. Silicate(30.3 ,pg-at/l) and orthosphate (1.59 g-at/l) were highest inSeptember. Highest concentrations of ammonia were common-ly measured in July (6.80 g-at/l) and September (5.13 /Ag-at/l),and peak concentrations of nitrate and nitrite were recorded inJanuary (24.27 g-at/l), February (8.2 pg-at/), and May (I6.37pg-at/). Peak concentrations of chlorophyll a were measured inAugust (17.2 g-at/l), October (5.70 g-at/l), and March (15.33pg-at/l). In general, the annual pattern for chlorophylls b and cwere similar to chlorophyll a. Comparison with other estuariesand bays (Narrangansett Bay, Long Island Sound, Raritan Bay,and Chesapeake Bay) indicated that concentrations of nutrientsand pigments in Delaware Bay were generally similar in magni-tude and seasonality. These are the first set of seasonal waterquality data for lower Delaware Bay.

Introduction

Water quality in the Delaware Estuary has been of con-siderable interest for some time (Cronin, 1967). On one

Dr. W. Junk b.v. Publishers - The Hague, The Netherlands

hand, fishing and recreation require one level of waterquality standards, and on the other hand, transportationand port activities require another level. Because of thesediverse activities, a variety of State, federal, and privateorganizations together with academic and research in-stitutions have studied water quality here. However, to agreat extent, these studies have been primarily restrictedto the upper bay and river (USGS, 1970) or data from thelower bay reside in unpublished reports. In the lower baymost water quality research has been conducted in saltmarshes. Here a major effort has been launched to studythe seasonal fluctuations of nutrients, their source, path-ways, and ultimate fate (Reimold & Daiber, 1970;Aurand & Daiber, 1973). In view of this heavy commit-ment to the marshes, it was surprising to find that therewere no published systematic studies of water quality inthe lower bay. A number of local studies contained dataon temperature, salinity, turbidity, dissolved oxygen, andmethods to monitor these. There was a single figure ofchlorophyll distribution in the lower bay based on a one-day multi-ship cruise, but there were no systematic sea-sonal data on nutrients and pigments (Cronin et al., 1962;Szekielda et al., I972; Klemas et al., 1973; Szekielda,1973; Haskin & Tweed, I976). This contrasted markedlywith extensive data from other large bodies of water(Narragansett Bay, Long Island Sound, Chesapeake Bay)on the northeastern coast of the United States (Kester &Courant, 1973). Consequently, during the course of abaseline study in lower Delaware Bay, the acquisition ofseasonal nutrient and pigment data was considered animportant first step in understanding the productivity ofan interesting and complex estuary. The purpose of thisaccount was to present these preliminary findings.

203

NEW JERSEY

HYDROGRAPHICAND

PLANKTONSTATIONS

MAUICERIVER

SFPILULONRIVER

DELAWARE

KILESBR50 0

Fig. . Map of Delaware Bay showing location of hydrographic stations.

204

CaEK

Methods

Water quality data were obtained monthly or bimonthly17 times from May , 1974 to May 28, 1975 alwaysat high

slack tide at three stations (Fig. ). Stations were selected

because they represented a rapid horizontal gradient

from shallow to deep water in the lower bay. Station I

was 20.8 m deep and Stations II and III were 6. m deep.

Moreover, the study area is near an important anchorage

site for oil lightering. In addition, two 12-hour cruises

were also conducted at Station 11 on February 20 and

April 14, 1975. Surface and bottom water samples were

taken at all stations.

Temperatures were measured with standard reversing

thermometers. Salinities were measured in the laborato-

ry with a Beckman 6320N laboratory salinometer. Sam-

ples for nutrient analysis were stored frozen in plastic con-

tainers to await analysis. All samples for pigment analysis

were filtered immediately aboard ship using Whatman

GF/C glass fiber filters. The filters were then frozen and

stored in a dessicator until analyzed. Concentrations of

dissolved oxygen, silicate, nitrate and nitrite, orthophos-

phate, ammonia, chlorophylls a, b, and c, phaeopig-

ments, and carotenoids were analyzed according to pro-

cedures in Strickland & Parsons (1968). Pigment analyses

followed the acetone extraction technique, and extinc-tion coefficients were measured on a D.U. spectrophoto-meter. Concentrations were estimated using the SCOR/UNESCO formulae.

Results and discussion

All raw data were presented in tables and figures in Wat-ling & Maurer (1976). Emphasis was placed on surfacedata. Based on variance ratios, F values were computedfor the hydrographic data per station. Except for chloro-phyll, there were no statistically significant (p < 0.05) dif-ferences among surface data. Consequently, surfacevalues were pooled, and their mean value per samplingperiod was presented in Table . When F values werecomputed between surface and bottom data, there weresome statistical differences. These differences togetherwith chlorophyll data will be cited when appropriate.

Temperature, salinity, oxygen

The annual pattern of surface temperature was typical ofan estuary in the Mid-Atlantic Bight. Lowest and highest

ble 1

Mean values of water quality data for lower Delaware Bay.

Date

May 1, 1974May 9May 22June 13June 20July 19Aug. 1Aug. 21Sept. 17Oct. 15Oct. 30Nov. 14Dec. 13Jan. 16, 1975Feb. 20*March 18April 14*May 9May 28

Temp. Sal. Dissolved Silicate Ortho P04 NH3 -N NO3 & NO2 CHa

"C 0/00 02 m/t pg-at/z ig-at/z wg-at/t og-at/z mg/m3

14.213.317.221.321.823.425.423.922.517.114.113.26.14.53.65.56.3

13.218.2

24.227.725.822.927.128.428.329.128.528.227.629.728.7

23.325.526.724.824.9

6.836.956.254.795.424.694.744.814.536.045.615.737.10

8.488.538.406.875.72

1.603.34.213.9612.917.9011.2330.36.13.9

12.69.1

12.613.71.201.400.871.88

0.060.060.090.060.180.771.090.881.590.480.260.940.640.570.360.00.060.030.17

1.330.631.231.471.636.802.331.305.131.031.232.22.773.637.40.00.70.01.97

16.371.805.40

11.330.533.106.409.67

12.479.773.833.03

14.4324.2718.2010.2010.802.376.27

10.636.508.83

13.878.67

17.23.9011.9315.701.935.53

5.515.338.46.05.97

CHb

mg/m3

1.871.601.301.701.472.000.530.871.230.370.67

0.41.170.500.430.73

CHc

mg/m3

4.231.772.675.672.907.101.835.036.700.531.17

1.93.371.801.101.20

*12-hour study at Station II

205

temperatures were recorded in February and early Au-gust, respectively (Table I). In the fall and winter therewas little or no vertical temperature stratification, where-as in the spring and summer bottom waters were gener-ally cooler than surface waters (Watling & Maurer, 1976).

The annual range of surface salinity at the study areawas 6.8%o (Table ). Delaware Bay is generally polyhaline(I8-30%o) from its mouth up to the Leipsic River. Croninet al. (962) showed that haline stratification was strongonly in the winter and spring. At Station I there was evi-dence to suggest stratification in the spring and earlysummer (Watling & Maurer, 1976). Mean bottom sa-linity here was greater (p < 0.05) than all other mean sur-face and bottom salinities. Polis and Kupferman (1973)noted that yearly changes in river flow can drasticallyalter the salinity structure of the lower bay. This pattern isfurther complicated by horizontal salinity gradients of4%o in one meter (Szekielda et al., 1972).

Absolute values of dissolved oxygen were lower insummer than winter as would be expected (Table ). Thewater was consistently fully saturated only during the latewinter to early spring; otherwise, full saturation occurredonly after mid-October.

35

30

0

wCI

0

-j(I,

25

20

15

I0

5

0

Nutrients

Silicate values showed seasonal peaks, the highest ofwhich occurred in September (Table ). Decreases insilicate were measured in August, October, and March(Fig. 2).

The pattern for orthophosphate was very similar to sili-cate, in particular from June to December (Fig. 3). How-ever, orthophosphate declined rapidly after February andwas not detectable in March and remained low in theearly spring.

Highest concentrations of ammonia were measured inJuly, September, and a single high at Station II in Febru-ary with low concentrations during the other samplingperiods (Table ). Ammonia values changed rapidlyduring the summer and fall, but varied more graduallyin the winter until a sudden decrease in March (Fig. 4).Values were slightly higher in bottom water than surfacewater (Watling & Maurer, 1976), but the differences werenot statistically significant. Ammonia values in May1975 did not reach the May values of 1974.

Highest concentrations of nitrate and nitrite wererecorded in January, February, and May (Table ). Sur-

SURFACE SILICATE

STA I o-o

STA Ti --

STA m

/974 1975SAMPLING DATE

Fig. 2. Seasonal cycle of silicate concentrations in surface samples at hydrographic stations.

206

I

SURFACE ortho-P0 4

o o STA. I~O- STA.I

_-- STA.TII· .--STA.ITI

/974 /975

SAMPLING DATEFig. 3. Seasonal cycle of orthophosphate concentrations in surface samples at hydrographic stations.

SURFACE NH3 -N0- STA.I

-u STA.I--.- STA.Tr

May J J A S 0 N D J F M A May

/974 /975SAMPLING DATE

Fig. 4. Seasonal cycle of ammonia concentrations in surface samples at hydrographic stations.

207

1.7

1.61.51.4

1.31.2

o 1.0: 0.9

i. 0.80a 0.7

0.6

_ 0.5o 0.4

0.3

0.20.1

0.0

10a

zIn

Iz

1.0

-- A

SURFACE N0 3 + NO2

STA I o-oSTA II a---&

STA m a.--

May J J A S 0 N D J F M A May

/974 /975SAMPLING DATE

Fig. 5. Seasonal cycle of nitrate and nitrite concentrations in surface samples at hydrographic stations.

I 'I tI-

SURFACETOTAL CHLOROPHYLL-a

STA I o-o

STA h---.

STA m -.

A '

May J J A

/"

9

?74

0 N D J F M A May

/975SAMPLING DATE

Fig. 6. Seasonal cycle of total chlorophyll a concentrations in surface samples at hydrographic stations.

.208

30

-S

001

1-

0z

z

25

20

15

I0

5

0

i 30E

E 25

0

- 20-J

O- 15O0

-JI 10O

5

0

3

3

SURFACE CHLOROPHYLL- b

STA I ; I STA 1' ---

STAm -- .

I..I ..

I.-!4 ! P: ~.! ,~ ~~ P; . ' '

P,* ,..o ·r

May J J A S 0 N D

/974SAMPLING DATE

Fig. 7. Seasonal cycle of total chlorophyll b concentrations in surface samples at hydrographic stations.

I

I · I

,., . iI. . i

'I I

SURFACE CHLOROPHYLL-cSTA I o-o

STAII ---STA m -- e

.. 0

May J J A S 0 N D J F M A May

1974 /975SAMPLING DATE

Fig. 8. Seasonal cycle of total chlorophyll c concentrations in surface samples at hydrographic stations.

\iEE

E

-

Ia-o0

0-JI

3.0

2.5

2.0

1.5

1.0

0.5

0

J F M A May

/975

14

12

E 0

E8

U

I

0g 4

I0 2

0

209

face values at Station I were normally higher than anyother measurements, but the differences were notstatistically significant. There was a sharp decrease innitrate and nitrite concentrations in the June 20 sample(Fig. 5). Such a reduction was not recorded in the concen-trations of any of the other nutrients for the same timeperiod.

Pigments

Peak concentrations of chlorophyll a were measured inAugust, October, and March (Table ). Surface andbottom values were highest at Station III and were sta-tistically different from those at Station I. Mean values atStation III were I 1.7 mg/m3, whereas they were 6.0 and5.6 mg/m3 at Station I (Watling & Maurer, 1976). Ingeneral, the annual pattern for chlorophylls b and c weresimilar to chlorophyll a (Figs. 6-8). Mean values ofchlorophylls b and c were higher at Station III than theother two stations. Both mean surface (1.45 mg/m 3)and bottom values of chlorophyll b (.49 mg/m 3) werestatistically different from the 0o.73 mg/m3 and 0.70mg/ 3 at Station I and the I.I mg/m 3 and 1.3 mg/m 3 atStation II. The mean surface value of chlorophyll c atStation III was statistically different from the value atStation 1.

Discussion

There was some association between nutrient values ob-tained in the lower bay and adjacent marshes. In studiesaround the Broadkill and Murderkill marshes nitrate andnitrite values were higher in the winter and fall and inor-ganic phosphorus and ammonia was highest in the sum-mer (Reimold & Daiber, 1970; deWitt, 197I; Aurand &Daiber, 1973). Thus, seasonal values in the bay reflectedseasonal patterns in the marshes. Work in progress byDelaware's Sea Grant marsh group indicated that sea-sonal peaks in nutrient concentration were not always thesame between marsh systems and that the main flow ofnutrient exchange between marshes and the lower baywas not always predictable.

Nutrient values for Delaware Bay were compared withother estuarine systems: Narragansett Bay, Long IslandSound, Raritan Bay, and Chesapeake Bay (Kester &Courant, 1973). All the systems were similar to the regionof Delaware Bay examined here in having low values of

dissolved oxygen in the summer and high values in thewinter. Moreover, there was evidence for Raritan Bay,Long Island Sound, Chesapeake Bay, and Delaware Bayhaving dissolved oxygen levels undersaturated duringsummer months.

In Long Island Sound, Narrangansett Bay, Chesa-peake Bay, and Delaware Bay inorganic phosphate val-ues were low in the spring and high in the summer exceptLong Island Sound which was high in the winter. Con-centrations ranged from o.o to < 2.0 Mg-at/l in the springto I.o to 5.0 g-at/l in the summer or .0-3.0 g-at/l inthe winter in Long Island Sound. In Raritan Bay whichJeffries (1962) suggested was a strongly polluted estuary,inorganic phosphorous values were near 6 ug-at/l inOctober and then decreased to levels between 2 and 3 g/at/l from April through the summer. Values for lowerDelaware Bay were closest to those of Chesapeake Bay.

Nitrate levels in Long Island Sound ranged from < .0to 5.0 ,ug-at/l during March through August and thenincreased to 12.0 to 20.0 Mzg-at/l from September toFebruary. Nitrate concentrations were < 2.0 g-at/lduring August in Narragansett Bay. Values in RaritanBay were again higher and ranged from 15.0 to 37.0 ,ug-at/I in the winter and spring and .0 to 5.0 ,ug-at/l in thesummer. Concentrations near 20.0o tg/at/l were recordedin Chesapeake Bay during thespring and decreased to lessthan 5 ig-at/l in the summer and fall. Highest concen-trations of nitrate and nitrite in lower Delaware Bay oc-curred during winter month (14.4-24.27 ,ug-at/l) with

occasional high values in the spring (16.37 gig-at/l). Thesemeasures of nitrogen were most similar to those in midChesapeake Bay.

Concentrations of pigment were similar among sever-al systems, but seasonal peaks differed. Long IslandSound had a spring peak of chlorophyll (> 25 mg/m3),Chesapeake Bay had summer (18-22 mg/m3 ) and fallpeaks (10-25 mg/m3), and Delaware Bay had summer(13.8-17.2 mg/m 3), fall (5.7 mg/m 3), and spring peaks

(15.3 mg/m).The relationship between nitrogen and phosphorus in

coastal systems and the use of nitrogen-phosphorus(atoms) ratios as measures of eutrophic conditions hasbeen thoroughly discussed (Jeffries, 1962; Ryther & Dun-stan, 971; Banse, 1974). This ratio was approximately8 : I throughout the year in Long Island Sound, variedfrom 35: I to .3: in Raritan Bay (highest in March andApril, lowest in July and August), and ranged betweepgo : I (spring) to 2.5 : I (fall) in Chesapeake Bay. In lowerDelaware Bay this ratio averaged 200: I in May and June

210

and approximately 20: throughout the summer andwinter months. Of the estuarine systems considered, onlyLong Island Sound did not have a strong input of riverwater nor is it surrounded by large salt marshes. Long Is-land Sound was also the only system where the nitrateand phosphate cycles were in near perfect correspon-dence. In the other areas, including lower Delaware Bay,nitrate values varied randomly in relation to phosphatewhich suggested that the major river and/or marshes andtidal creeks (Aurand & Daiber, 1973) may be responsiblefor the wide range of nitrate-phosphate ratios in thesesystems.

Ketchum (967) noted earlier experiments had dem-onstrated that available nitrogen was probably the nutri-ent limiting algal growth and that high concentrations ofinorganic phosphorus in the water reflected the excess ofthat element above the requirements of the phytoplank-ton. Thus, phosphorous concentration could be used as apollution index. Based on this, Long Island Sound, mid-Chesapeake Bay, and lower Delaware Bay did not showexcess nutrient pollution as did Raritan Bay.

This study has revealed a representative view of season-al fluctuation of nutrients in a small area of lower Dela-ware Bay. Future studies of nutrients should feature abaywide survey including seasonal differences betweensurface and bottom water and nutrient transfer betweenthe upper estuary and the lower bay and between thesurrounding marshes and the lower bay.

Summary

The first set of seasonal data on water quality for lowerDelaware Bay indicated that concentrations of nutrientsand pigments reflected to some degree seasonal nutrientpatterns in the marshes. However, there are times whenthe main flow of nutrient exchange between marshes andthe lower bay is not always predictable.

Nutrient values for Delaware Bay were compared withother estuarine systems: Narragansett Bay, Long IslandSound, Raritan Bay, and Chesapeake Bay. All systemshad high dissolved oxygen in the winter with most havingdissolved oxygen levels undersaturated during summermonths. Inorganic phosphate values were low in thespring and high in the summer, except Long IslandSound which was high in the winter. Concentrations forlower Delaware Bay were closest to those of ChesapeakeBay. This also applied to levels of nitrate and nitrite. Con-centrations of pigment were similar among these sys-tems, but seasonal peaks differed. Based on nitrogen/

phosphorous ratios as measures of eutrophic conditions,lower Delaware Bay did not show excess nutrient pol-lution as did Raritan Bay.

References

Aurand, D. & Daiber, F. C. 1973. Nitrate and nitrite in the surfacewaters of two Delaware salt marshes. Ches. Sci. 4: Io5-I I .

Banse, K. 974. The nitrogen-phosphorus ratio in the photic zoneof the sea and the elemental composition of the plankton.Deep-Sea Res. 21: 767-771.

Cronin, L. E. 1967. The role of man in estuarine processes. In:Estuaries (G. H. Lauff, ed.). A.A.A.S. Publication 83, Wash-ington D.C.

Cronin, L. E., Daiber, J. C. & Hulburt, E. M. 1962. Quantitativeseasonal aspects of zooplankton in the Delaware River estuary.Ches. Sci. 3 (2): 63-93.

deWitt, W. I971. Water quality variations in the Broadkill Riverestuary. Ph. D. dissertation, University of Delaware, 127 pp.

Haskin, H. H. & Tweed, S. 1976. Oyster setting and early spatsurvival at critical salinity levels on natural seed oyster seedbeds of Delaware Bay. Final Report Water Resources ResearchInstitute Rutgers University, 66 pp.

Jeffries, H. P. 962. Environmental characteristics of RaritanBay, a polluted estuary. Limnol. Oceanogr. 7: 21-31.

Kester, D. R. & Courant, R. A. 1973. Chemical Oceanography,In: S. B. Saila (Ed.), Coastal and Offshore EnvironmentalInventory, Cape Hatteras to Nantucket Shoals. Marine Publ.Ser. No. 2, Univ. Rhode Island, Kingston, Rhode Island.

Ketchum, B. H. 1967. Phytoplankton nutrients in estuaries. pp.329-335. In: G. H. Lauff (Ed.), Estuaries. Amer. Assoc. Adv.Sci. Publ. 83, Washington, D.C.

Klemas, V., Otley, M., Wethe, C. & Rogers, R. 1973. Monitoringcoastal water properties and current circulation with space-craft. Presented at 2nd Joint Conference on Sensing of Envi-ronmental Pollutants, Washington, D.C., Dec. 10-12, 1973,343-354.

Reimold, R. J. & Daiber, F. C. I970. Dissolved phosphorousconcentrations in a natural salt marsh of Delaware. Hydro-biologia 36 (3-4): 361-371.

Ryther, J. H. & Dunstan, W. M. I1971. Nitrogen, phosphorus, andeutrophication in the coastal marine environment. Science171: I008-1013.

Strickland, J. D. H. & Parsons, T. R. 1968. A practical handbookof seawater analysis. Fish. Res. Bd. Canada, Bull. 167: I-31 I.

Szekielda, K. H. 1973. Chemical oceanography, 145-170 pp. In:Delaware Bay Report Series Vol. 4, College of Marine Studies,University of Delaware.

Szekielda, K. H., Kupferman, S. L., Klemas, V. & Polis, D. F.1972. Element enrichment in organic films and foam asso-ciated with aquatic frontal systems. J. Geophys. Res. 77 (27).

U.S.G.S. 1970. Water quality of the Delaware River Estuary Julythrough December 1967. United States Geological Survey inCooperation with the Delaware River Basin Commission-Open File Report, 83 pp.

Watling, L. & Maurer, D. (Eds.). 1976. Ecological Studies onBenthic and Planktonic Assemblages in Lower Delaware Bay.Report to National Science Foundation Research Applied toNational Needs Program, College of Marine Studies, Univer-sity of Delaware, 634 pp.

211