Water and organic carbon fluxes from an irregularly flooded brackish marsh on the upper Texas coast, U.S.A.

Estuarine,

Coastal and Shelf Science (1983)

16, 379-402

Water and Organic Carbon Fluxes from an Irregularly Flooded Brackish Marsh on the Upper Texas Coast, U.S.A.

R. B. Boreya, P. A. Harcombe Biology Department,

Rice University,

Received 23 September 1981

Keywords:

salt marshes; coastal plain

compounds;

and F. M. Fisher

Houston,

Texas

U.S.A.

77001,

and in revised form 27 July 1982

organic estuaries;

matter; flow Gulf of Mexico

rates;

dissolved

organic

Water ticulate periods

flows, concentrations of total (TOC), dissolved (DOC), and par(POC) organic carbon and seston were monitored for 52 die1 in the single creek draining a z7o-ha Spartina patens-Distichlis spicata marsh on the upper Texas coast. Rainfall, creek water flows, and water levels in the creek and on the marsh were measured by recording instruments. Rainfall accounted for most marsh flooding, and water outflow was significantly correlated with both rainfall and marsh water level. Creek flows were predominantly outward because microtopographic features and dense vegetation restricted overmarsh water flows and thereby reduced tidal flooding while extending the time of precipitation runoff. Concentrations of organic carbon in water leaving the marsh were highest in spring and summer and averaged 25.62, 21.41 and 3.35 mg 1-i of TOC, DOC and POC, respectively. These were 9.34, 9.93 and 0.04 mg I-‘, respectively, higher than bay water. Most POC was 0.3-28 pm in diameter. Seston ~28~ leaving the marsh was 95% amorphous material; the rest was plankton, grass particles and fecal pellets. Loss of organic carbon was directly correlated with net water flux, and thus rainfall accounted for most carbon loss. Net carbon loss averaged 196 kg TOC, ISO kg DOC and 32 kg POC per day. Net annual loss was ~.4--5*5~h of net aerial primary productivity (NAPP), or 21’55-30’09 g TOC me2 year-‘. Export from this marsh falls within the range found for other marshes and the data collectively indicate that coastal marshes are not losing as much organic carbon as has been suggested by indirect measurements. The discrepancy between potential and realized export is explained by the fact that export is not a simple removal of excess detritus by tidal action but is a more complicated process mediated by the interaction of additional factors such as rainfall, vegetation structure, microtopographic variation and decomposition, which can serve to reduce the amount and quality of NAPP exported.

Introduction There loss

is at present from

coastal

no consensus marshes.

Indirect

aPresent address: 1608, Port Arthur,

on the

general

estimates Texaco Texas

magnitude of marsh

U.S.A., Port 77640, U.S.A.

or significance export, Arthur

made Research

by

of organic

matter

measuring

major

Laboratories,

P.O.

Box

379 0272-7714i83/0403791-24

$3.00,‘0

8~3 1983

Academic

Press Inc.

(London)

Limited

380

R. B. Borey, P. A. Harcombe

& F. M. Fisher

energy sinks in the marsh or disappearanceof materials from the marsh surface, have indicated that as much as 45-70% of the net aerial primary production (NAPP) could potentially be exported to estuarinewaters (Teal, 1962; Day et al., 1973 ; Kirby & Gosselink, 1976). Realized export could fall substantially below these potential levels becauseall marsh consumptions cannot be measuredand tidal transport can never be completely efficient in removing excessdetritus. Nixon (1979) reviewed several studies and concluded that marsh export is not as large as previously believed and is not a significant contribution to bay secondary productivity. This view is supported by Haines (1977) whose study of carbon isotopes indicated most carbon in coastal waters does not originate in marshes,and by Howarth & Teal (1979) who suggestedthat anaerobic consumption may constitute a significant and previously unmeasured sink for carbon in marshes,thereby lowering potential export. Direct measurementsof marsh export made by monitoring detritus concentrations and water flows in tidal creeks have alsoshown that export from coastalmarshesis usually less than the potential indicated by indirect estimates,although theseresults indicate that export from individual marshescan vary from o-100% of NAPP (Sottile, 1973 ; Axelrad et al., 1974; Armstrong et al., 1975; Heinle & Flemer, 1976; Hackney, 1977; Settlemyre & Gardner, 1977; Woodwell et al., 1977). The methods utilized in these studiesare sufficiently similar that the variation in results probably arisesfrom differences in tidal action, geomorphology, vegetation structure, NAPP, climate, decompositionand other factors within the individual marshes.There has been very little researchon the effects of these factors, and their effect on export is largely a matter of speculation and intuition. The proximity of marsh grassto tidal waters and the intensity of tidal action are usually considered to be the dominant factors controlling export (Schelske & Odum, 1961; Odum et al., 1973). In any event, several studies have shown that the factors involved in the export processmay be selective in effect, and in order to calculate total net flux or to fully understand the process,all forms of organic carbon must be considered(Nadeau, 1972; Settlemyre & Gardner, 1977; Shisler& Jobbins, 1977; Woodwell et al., 1977). This researchwas undertaken to measureexport of organic materials from marshesand to examine possiblecontrolling factors. We chosea site on the Gulf coast, since it afforded the opportunity to observe export in a region in which tides, geomorphology, vegetation structure and climate differed from those in the better understood marshesof the Atlantic coast. Perhaps the most notable difference is that tides along the Atlantic coast are semidiurnal with amplitudes of 1-2 m, while those along the Gulf coast are diurnal with amplitudes lessthan 0.8 m. In addition, there is a tendency for winds and precipitation to influence bay water levels along the Gulf coast more than tides (Collier & Hedgpeth, 1950; Linton, 1968; Smith, 1974, 1977). If tidal action is a major factor affecting export, then reduction in tidal periodicity and heights along the Gulf coast might be expected to produce a corresponding reduction in export. It might also be expected that, under conditions of reduced tidal action, other factors would becomemore important in controlling export, and their effect could be more easily determined. These factors probably affect export in all marshes,but their effects may be maskedby high tidal ranges. Study area The marsh chosenfor study is located approximately 50 km east of Houston on the north shore of East Bay, the easternlobe of the Galveston Bay estuary on the upper Texas coast

Water and organic carbon jluxes

381

(Figure I). Almost 20% of the coastalmarshesof the Gulf Coast Prairie zone of Texas lie in the region immediately north and north-east of East Bay. Geology, vegetation and climate of the area north of East Bay are described by Rowe & Williams (1974). Pleistocene and Holocene surface sedimentsin the region form a broad, flat plain which gently slopesto the Gulf. Temperature rangesfrom -12 to 43 “C with an annual mean of 20 “C. Annual precipitation is approximately 132 cm and varies from 66 to 249 cm year-l.

Figure

I.

Location

of Coon

Creek

Marsh.

Coon Creek Marsh, named for its centrally located tidal creek, is located in the south-west corner of the Anahuac National Wildlife Refuge (Figure 2). The marsh is bordered on all sides by roads and levees constructed between 1952 and 1968. These prevent water from leaving or entering the marsh except through Coon Creek. The creek flows through two culverts in the south levee into East Bay. Coon Creek is 0.7 km long and attains a maximum width of 4 m and a depth of 1.2 m as it approachesthe south levee. The creek connects East Bay with three ponds located in the interior of the marsh. They cover approximately IO ha and represent the lowest marsh elevations, approximately IO cm above mean sea level (MSL). Elevations increaseoutward from this central region and reach a maximum height of 61 cm above MSL on the east and south (bay front) borders. Thus the natural exchange between the marsh and bay is via Coon Creek, so the surrounding levees have little hydrological effect asidefrom insuring isolation of the study area. The dominant plant speciesof the Coon Creek marsh are Spartina patens and Lktichlis spicata. Scirpusolneyi, S. maritimus,Juncusroemerianusand Spartina alternsj7oraalso occur in the marsh, but represent relatively minor components(Henderson & Harcombe, 1976). This assemblageis typical of the marshesof the upper Texas coast. Net aerial primary production, estimated by the standard IBP harvest method (Milner & Hughes, 1968), is x.1-1.8 kg m-2 of dry plant material per year. (C. A. Henderson,unpublished data). There is no significant peat formation, possibly becauseof rapid decomposition due to the mild

382

R. 3. Boxy,

climate or the routine and attract waterfowl.

practice

P. A. Harcombe

of periodically

& F. M. Fisher

burning

the wetlands

to improve

cattle grazing

Materials and methods Measurements were made of water levels, water flows, organic carbon and seston in the creek water, and precipitation. These were obtained either by unattended recording instruments or during 24-h site visits conducted approximately every two weeks.

EAST BAY

-

0

COOfl

Crack

A

Marsh

water

. . . . . Roads

with

Smoli

ditch

Apprortmott

Figure

z. Coon

level

recorders

dttcher and

and

levees

levee

elevotlons,

Creek

site

SOmpllng

cm

above

Marsh.

Water levels in Coon Creek were monitored by a staff gauge and a recorder located just inside the levee at the two culverts (Figure 2). Continuous water level recordings were made at two marsh sites (Figure 2) during the second year of study. Planimetry of a 1962 topographic map prepared by the U.S. Fish and Wildlife Service, showed that approximately 35% of the total marsh surface area lies below the elevation of the west recorder, 30.9 cm above MSL, and 30% of the marsh surface area is above the elevation of the east recorder, 38.2 cm, above MSL. The locations of the marsh recorders were chosen for their proximity to sampling sites of a concurrent NAPP study.

Water and organic carbon $uxes

383

Water velocities were determined with a flow meter (General Oceanics Model 2030) placed in one of the culverts for a timed interval. Unattended, long-term measurementsof water velocities and direction of flow were obtained with a General Oceanics Model 2040 Film Recording Velocity Meter mounted in one of the culverts. This recording velocity meter was used in conjunction with the creek water level recorder to provide two ot five week records of creek flows. Velocities were calculated from single I 5-min intervals every 2 h and net flow was calculated according to a formula similar to that usedto calculate net die1 water flux. Precipitation was measuredat the Coon Creek levee with a recording rain-gauge. Die1 sampling

Manual measurementsof creek flows and collections of water sampleswere carried out for 52 die1periods from May 1975to May 1977. A samplinginterval of 24 h waschoseninstead of the more common tidal cycle becausepreliminary work had shown that creek flows did not agreewell with predicted coastaltides. No advantage could be obtained from attempting to sampleonly during spring and neap tides becauseperiods of maximum and minimum creek flows and water levels were usually independent of lunar tidal influence. Therefore, sample days were more or lessrandom with respect to tidal regimes and were scheduled approximately every two weeks. Samplesand measurementswere taken every 2 h during die1periods for the first year and every 3 h for the secondyear. Sampleswere collected for analysisof total organic carbon (TOC), dissolved organic carbon (DOC) and seston. Measurements taken concurrently included salinity (YSI Co. Model 33 S-C-T Meter), water velocity and water level. Water and carbon jhx

calculations

Flux of water and organic carbon for each measurementand sample during a die1period were calculated by computing the cross-sectionalarea of water in the culverts (known diameter) from creek water level, and multiplying this by water velocity and then carbon concentration. Velocities were assignednegative or positive values to denote, respectively, ebb or flood flows. Net water and organic carbon fluxes for each die1sampling period wete determined by the appropriate trapezoidal rule formula: Net die1flux (1st year) = (1/2y1+y2+...+y~...+y12+1/2yIa) Net die1flux (2nd year) = (~/zy,+y,+...+y~...+y,

Z; Z = 7200s,

+r/2yg) Z; Z = IO 800 s,

where ye is the appropriate value in cubic meters of water ot kg organic carbon pet second for the ith measurementof the die1sampling period and Z is the number of secondsbetween those measurements. Appreciable differences in the heights of water at either end of the culverts were never observed. Therefore it was assumedthat the culverts had a negligible effect on creek water flows other than increasingthe velocity of water as it moved through theseconstrictions, a circumstance that made the detection and measurementof slow creek flows more accurate. Collection

and analysis of organic carbon samples

Water samplesfor analysisof organic carbon were taken 20 cm below the surface in r-pint masonjars. Subsampleswere withdrawn from each jar with an all-glasssyringe, forced through a glassfiber filter (Gelman Type A/E No. 61630), and collected in a borosilicate screw cap culture tube. These samplescontained only dissolvedorganic carbon (DOC) as

384

R. B. Borey, P. A. Harcombe& F. M. Fisher

defined by the 0.3 pm filter porosity (99.7% effi cient by DPP test), while the masonjar samplesrepresentedtotal organic carbon (TOC). The difference between the values found for the TOC and DOC representedparticulate organic carbon (POC) for the sample.Both TOC and DOC sampleswere preserved with concentrated sulphuric acid (z ml 1-l) and mercuric chloride (ca. 40 mg l-l), sealedwith linerlesspolypropylene closures,and placed on ice for transportation to the laboratory. In the laboratory, the masonjars were fitted with stainlesssteel blade kitchen blender assembliesand blended for several minutes. This procedure reduced particle sizes in the TOC samplesand insured a homogenoussuspension.A portion of eachTOC suspensionwas transferred to a culture tube, and then both TOC and DOC culture tubes were purged of COs by bubbling with nitrogen for several minutes. Evaporation during bubbling was minimized by passingthe nitrogen through low-carbon water prior to its introduction into the sample tube. If the samplescould not be analysed for organic carbon immediately, they were frozen until analysis could be performed, The TOC and DOC sampleswere analysed with a Beckman Total Organic Carbon Analyzer attached to a Model 215-A Non-dispersive Infrared Analyzer and a chart recorder. This method of collecting, preserving and analysing organic carbon is similar to that outlined in Methods for Chemical Analysis of Water and Wastes(EPA, 1971), and measures all forms of organic carbon, both living and dead, which can enter the 6-cm opening of the masonjar. All glassware,utensils and closureswere washedwith chromic acid, thoroughly flushed with tap water, and finally rinsed severaltimes with low-carbon water. Low-carbon water was produced by double distillation in an all-glass apparatus, acidification with 0.25 ml 1-l sulphuric acid, and purging with nitrogen to drive off CO,. This water was stored in an all-glasscontainer with an Ascarite CO, trap on the air inlet. The borosilicate culture tubes were heated for at least I h at 450~5ooC to remove any carbon contaminants. The glassfiber filters were free of organic binders and had been previously ignited by the manufacturer, but they were also reheated at 400-450 “C for I/Z h prior to their use. The delrin filter holders (Gelman No. 4320) and polypropylene closures were soaked in low carbon water when first obtained to remove any leachableorganic compounds. They were then washedby the above proceduresprior to eachuse. Collectionand analysisof sestonsamples Seston sampleswere taken every 6 h to determine the composition of detritus in the creek water and investigate its contribution to TOC. These sampleswere collected by pouring 15 1of creek water through a plankton net with a 28 pm mesh. The sampleswere preserved with formalin (working solution 3-5%) buffered with hexamine and refrigerated until analysed.Particles were visually identified and counted at IOO x magnification. Results Water jlux Flooding of the marshsurface. Since there were no upland water sourcesfor the Coon Creek Marsh, increasesin marsh water levels could only be causedby inputs from tidal flooding and/or precipitation. Decreasesin water levels were the result of lossesby evapotranspiration and surface drainage. The water levels registered by the east and west marsh water level recorders for the year May 1976 to May 1977 showed no daily tidal fluctuation at either location and, except for a few dry periods, water was continuously present on the marsh surface (Figure 3). Increasesin water level were very abrupt, while decreasesoccurred

Water and organic carbon jhxes

385

more gradually. The pattern of water level changes was similar for both locations, but absolutewater level was consistently higher on the higher east marsh. To investigate the causesof marsh flooding, a determination was made as to whether increasesin water levels at both locations were associatedwith rainfall events or high tides. It was assumedthat a high tide, as indicated by the water level recorder at the entrance to Coon Creek, had to be above the marsh water level to produce an increase. However, precipitation of any amount was always considered to have the potential to increasewater levels. A review of the water level and precipitation records showedthat marsh water levels

20 M

J

J

A

s

0

N

Q

J

F

M

AM

Month

Figure 3. 31 and 38 recorders. subsurface

East and west water levels, May rg76-May 1977. Horizontal lines at cm are the respective surface elevations at the west and east water level Water levels below these elevations (i.e. August, September) indicate water level when the marsh was dry. -, East; -, west.

responded immediately to rainfall, but there was a lag of several hours before marsh water levels increasedin responseto high tides entering Coon Creek. In all, there was a combined total of 148 water level increasesat the two locations. Of these, 607’ were associatedsolely with precipitation, 16% solely with tidal flooding, and 24% with both precipitation and tides. An increasein marsh water level was consideredto be causedsolely by precipitation if it occurred during a rainfall event and the preceding creek high water level waslower than the marsh water level. There were 49 such increasesat the eastsite and 40 at the west site, and these increaseswere significantly related to rainfall at both sites (Figure 4, g2 = o-96 and 0.56). Water level increasesexceeded rainfall during periods of relatively low marsh water levels, probably due to runoff from higher unflooded marshareas(Figure 5). However, water level increaseswere less than rainfall during periods of relatively high marsh water levels (Figure 5), probably becausewater drainagefrom the marsh is more rapid than precipitation input when marsh water levels are relatively high. Multivariate regressionanalysesshowed that the increasedue to rainfall on the west side was also significantly related to water level prior to flooding (multiple r2 = o-81), thereby explaining someof the variation shown in Figure 4. The west marsh, being lower and more subject to the presenceand drainage of water, therefore showed better correlation among rainfall, marsh water level increase,and initial water level than the higher east marsh. An increase in marsh water level was attributed solely to tidal flooding when it was preceededby a creek high water level which exceededmarsh water level and there was no

386

R. B. Borey, P. A. Harcombe

8

& F. M. Fisher

I

I

I

I

I

1

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2

3

4

5

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6-

4-

$2 : $ ; .5

0

7

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pu.. 0

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5

(cm)

Figure 4. Relationship of marsh water level increase to precipitation. Numerals indicate number of overlapping points. (a) East marsh, r = 093,Y = -0.05 i- 1.06 (X). (b) West marsh, r = 0.75, Y = 0.32+0.79(X).

accompanying precipitation. There was only one such increase at the east recorder, but there were 22 at the lower west site. For the west site, there was a significant linear relationship between tidal head (difference in tidal height and initial marsh water level) and the water level increase produced (r2 = 0.81, Figure 6). The increases were about half of the tidal head, which suggests vegetation and geomorphic resistances reduced the potential amount of flooding. These resistances caused the marsh water level to begin to rise an average of 4.25 h after the creek water level exceeded the marsh water level and to continue to rise an additional average of 45 h after the creek water level fell below that of the marsh. A marsh water level increase was assumed to be caused by both tide and precipitation when it was associated with a rainfall event and a creek water level exceeding the marsh water level. There were II increases at the east site and 25 increases at the west site that met these criteria. Multivariate regression analyses showed that water level increases were significantly correlated with both tidal head and precipitation but not with initial marsh water level (Table I). Tidal head was more important than rainfall and explained 61% of the variation at the east site and 74% of the variation at the west site when it was considered as the sole independent variable. Comparison of the number of flooding events and total increases in water level attributable to the three flood-producing situations indicates that rainfall is the most important flooding

Water and organic carbon fluxes

Woter

level

ot

start

Figure 5. Effect of initial marsh precipitation. Numerals indicate T = -0.36, Y = 4+I5-o*088(X).

Tldol

Figure 6. Relationship Y = -1.56+0.53(X).

head

(cm)

387

of

precipltotlon

water

(tldol

MSL)

on marsh water level increase due to of overlapping points. (a) East marsh, marsh, T = -0.73, Y = 22.80-0.59(X).

number (b) West

of west marsh

(cm obove

level

height

water

-marsh

level

rater

level 1

increase

to tidal

head.

r = 090,

equation

EI = -3.43+(0.83)HE+ (1’73)RA EI = -6z.S+(r.~o)HE+ (2~08)RA+(1~30)IH WI = -3.20+(0.66)HE+ (o.83)RA WI = -8.31+(0.68)HE+ (0~81)RA+(o~13)IH

Regression

0.60 0.46 0.46

a.78 0.86 0.86

0.91

0.91

22

22

0.60

R4

Simple

0.93

HE

IO

T

coefficients r

-0.28’

-

- 0’45”

-

IH

of east and west marsh

0.78

Multiple

Correlation

analyses

0.90

of

regression

IO

No.

r. Multiple

nNot significant. Number of samples includes only increases with initial water cm; WI, west marsh water level increase in cm; HE, difference pitation; IH, initial water height in cm above MSL.

TABLE

increases

69.74 59’79

30.16

20.95

15’97

HE

F values

produced

46.47

13’37

14’44

Regression

level

9.76

0.41"

water level;

0.83

0.07

-

0.36

-

IH

and tide

level increase in RA, cm of preci-

0.31

0.31

0.80 10.48

0.55

0.90

2.99” 11.88

0.46

RA

0.68

HE

-

IH

Standardized regression coefficients

of precipitation

7.20

R4

by a combination

depth at or above surface elevation. EI, east marsh in cm between tidal height and initial marsh water

water

Water and organic carbon jfuxes

389

agent for the higher east marsh. On the east marsh, rainfall alone was responsiblefor 80% of the flood events as compared to 2% caused by the tides. The remaining 18% were produced by a combination of tides and precipitation. Tidal flooding was more prevalent in the lower west marsh, but rainfall alone still accountedfor 46% of the flood events while tides accounted for 25% of the flood events. In terms of total water level increase,rainfall alone produced 34% of the cumulative 155 cm of the yearly water level increaseon the east marsh as compared to 18% attributed to tides alone. Rainfall contributed 23% and tides contributed 24% of the cumulative 193 cm of yearly water level increaseon the west marsh. Water flux in CoonCreek. Flood, ebb and net water fluxes for Coon Creek were calculated for 52 sample days during the two year study. Winter was the period of least water flux 60 50 40

B 0 G 5-

30 20

J1JJASONDJFMAMJJASONDJFMAM 1975

Figure 7. Die1 flood, ebb and net water water flux; -, flood and ebb volumes.

1976

volumes,

1977

May

Ig75-May

1977. -,

Net

(Figure 7). All but seven sampledays had net water lossesand 22 sampledays had no flood flows at all. Average flood, ebb and net water volumes per die1period were 5498, 12 322 and 6824 m3, respectively. The most outstanding result of the die1water flux measurementsis the large discrepancy in ebb and flood volumes; that is, net water lossesoccurred on 87% of the sampledays. Continuous water flux records obtained by the recording flow meter in conjunction with the creek water level recorder for severalperiods over the two year study alsoindicated a general pattern of significant net water efflux. Creek water levels roseand fell with the tides on most sample days, but ebb and flood flows matching the tidal pattern were absent for 66% of the sample days. Observations revealed that the effect of most high tides was a slowing of ebb flow or a brief period of inflow. Most days with net imports were the result of strong flooding produced by unusually high bay levels brought on by strong onshorewinds and/or high river discharge into the bay. These observations, plus the results of the analysis of marsh water level changespresented above, indicate that rainwater was draining from elevations higher than most tides could penetrate.

R. B. Borey, P. A. Harcombe & F. M. Fisher

390

Water flux wasnot correlated with creek water levels or die1changesin creek water levels, but it wascorrelated with water level changesat both the eastand west marshsites(Figure 8, r2 = 0.72, 0.41). Most marsh water level changeswere negative, indicating a decreasein water level (i.e. there were few flood events). Multivariate regressionanalysisindicated that the east marsh water level changeswere the overall determinant of net creek water flux; inclusion of west marsh water level changesdid not significantly improve the correlation. (a)

o-

3

x

-20

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(cm)

Figure 8. Effect of marsh die1 water level change on net die1 water flux. Numerals indicate number of overlapping points. (a) East marsh, r = 0.85, Y = 0.86f24.28 (X). (b) West marsh, r = 0.64, Y = -7*78+8.23(X).

Water flux was alsosignificantly related to marshwater levels at the beginning of the die1 period (Figure 9, rs = 0.90, 0*85), and with precipitation recorded for the previous day (Figure IO, P = o-50). Both were probably due to greater runoff associatedwith higher marsh water levels. Such correlations were not significant for rainfall on earlier days or for weekly averages of rainfall, probably becauseefflux is greatest immediately following a rainfall event. Organic

carbon

The hydrological analysisindicated that most water draining from the marsh consistedof precipitation or a mixture of precipitation and an older tidal flood. Thus ebb flows from

Water and organic carbon jhxes

I

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t? x. -2

-20

-

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-

-60

-

-80

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42 1 MSL) Figure 9. Effect of initial marsh water level on net die1 water flux. Numerals indicate number of overlapping points. (a) East marsh, I = 0.95, Y = - 979.03 + 49.58(X) -0.63(Xs). (b) West marsh, I = 0.92, Y = -845.02+50.65(X) -0.75 (X2). 30

level

at start

of die1

period

40

(cm

above

40

20

“0 ; “E : E E P 5 : z”

0

-20

-40

-* 0

-60

-’

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0

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Figure number

10. Effect of of overlapping

1 3 durm~

1 4 prewur

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1 6

, 7

km)

on net die1 water flux. Numerals precipitation points. r = -0 ‘71, Y = -4.34 - I I .44(X).

indicate

R. B. Borey, P. A. Harcombe

392

& F. M. Fisher

Coon Creek had a relatively constant salinity that was usually lower and always different from that of flood water from the bay. By using salinity asa naturally occurring conservative indicator, the source of creek water, i.e. runoff or flood water from the previous tide, could thus be determined with someconfidence, at least for sampling days with well established creek flows of sufficient duration. Samplescollected from Coon Creek were then divided into marshwaters or bay watersfor determination of averageorganic carbon concentrations. Accurate interpretation could not be obtained from 16 sampledays with little or no water flux, so these days were not included in comparison of organic carbon in marsh and bay waters.

50

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MJJASONDJFMAMJJASONDJFMAM 1976

1975

Figure TOC;

II. Marsh o, DOC;

organic carbon A, POC.

concentrations,

1977

May ro75-May

1977.

0,

The averagedie1concentrations of total organic carbon (TOC), dissolvedorganic carbon (DOC) and particulate organic carbon (POC) in marsh water for samplingdays with reliable salinity profiles were higher in the warmer months (Figures II and 12). This seasonal variation in concentration of organic carbon for Coon Creek Marsh is generally consistent with results from other marshes(de la Cruz, 1965; Sottile, 1973 ; Settlemyre & Gardner, 1977; Woodwell et al., 1977). Average marsh organic carbon concentrations were 25.62 mg 1-l for TOC, x.41 mg 1-l for DOC, and 3.35 mg 1-l for POC. These were greater than those in the bay for the same day by 9.34, 9.93 and 0.04 mg 1-l, respectively, for TOC, DOC and POC. These differences are statistically significant for TOC and DOC according to a paired t-test. The averageconcentrations are not additive becauseDOC was not determined for the first five sampling days. POC in Coon Creek bay water had approximateIy the samerange asthat found in flood water of other marsh systemsbut DOC was generally higher for the Coon Creek Marsh (Table 2). DOC in Coon Creek bay water fell within the range for Texas bays (Wilson, 1963; Maurer & Parker 1972). DOC concentrations may be somewhat higher in the waters of Texas estuariesthan thoseof the Atlantic coast. For Coon Creek Marsh, the high concentration of DOC is remarkablein that it representsDOC almost entirely gained from the marsh

Water and organic carbon fluxes

393

30 (cl -

20

:

.

if

‘O

MJJASONDJFMAM Month

Figure 12. Annual variation in marsh organic carbon concentrations (best polynomial fit for two years of data). (a) TOC, Y = 0.86,Y = 1550+(1.32)X -(2.31 x IO -a)Xe+(~.48 x IO -a)X3 -(qo7 x IO -‘)X4+(4.07x IO -10)X5.(b) DOC, r = 0.54, Y = qyg--(1’15 X 1o-~)X+(3.21 x IO-~)X~. (c) POC, r = 0.66, Y = 4.92-t (7.85 x 1o-~)X-(1.41 x IO -3)X2+(6.28 x IO -B)X3-(8.39 x IO -O)X4.

surface, while part of the DOC in ebb waters of other marshesconsists of that already contained in the flooding water. POC was made up of extremely small and highly decomposedparticles. The organic sestonsamplesconsistedof grassparticles, fecal material, plankton and amorphousdetrital material; the latter made up almost 95% of the organic seston in both marsh and bay waters. There was slightly more amorphous detrital material in marsh waters than bay waters, but the difference was not statistically significant by a grouped t-test. Comparisons of POC values with organic seston numbers and cross-sectionalareaswere significant only for marsh water samples,and even so, net sestonlarger than 28 pm accounted for lessthan 20% of the POC variation in marsh water samplesaccording to regressionanalysis. This suggeststhat most of the POC consistedof particles lessthan 28 pm in diameter, the mesh size of the plankton net, but larger than 0.3 Frn, the pore size of the glassfiber filter. The POC determination did not include large grasspieceswhich could have significantly

R. B. Borey, P. A. Harcombe

394

TABLE

Type of Water

Location Coon Creek, TX Texas (Wilson, 1963 ; Maurer & Parker, 1972) Swan Lake, TX (Armstrong et al., 1975) Barataria Bay, LA (Happ et al., 1977) Catfish Bayou, MS (Hackney, 1977) Sapelo Island, GA (de la Cruz, 1965 ; SOttik!,

Dill

2. Approximate

1973)

Creek, SC (Settlemyre & Gardner, 1977)

Ware Creek, VA (Axelrad et al., 1974) Carter Creek, VA (Axelrad et al., 1974) Gott’s Marsh, MD (Heinle & Flemer, 1976) Nacote Creek, NJ (Nadeau, 1972) Tuckerston, NJ (Shisler & Jobbins, 1977)

Flax Pond, NY (Woodwell et a/., 1977) Great Sippewissett Marsh, MA (Valiela et al., 1978)

aOrganic

&f F. M. Fisher

ranges

of organic

mg TOC

Marsh Bay

Ebb Flood

Bay

carbon

1 -l

in marsh

mg DOC

9.4-58.2

10.1-38.4

4%-91'0 10.0-63.0 3.0-57'0

0.9-39.1

1 -r

2~6-10~2

3'~

-

Flood Ebb Flood Ebb Flood Ebb Flood Ebb Flood Ebb

3’0-31.0

z.o-Ig’o

Flood Ebb Flood

3.0-12.0 -

2.0-

7'0

1.5-

2.6

1’5-

2.4

5'5-13'3 3‘3-13'3 2’3-17’0 2.4-10.5

-

plant

2.0 1’0 0.5

-10.4” - 3.7a -29.3”

0.2 0.8 0.4 0’3 0’4 2’1

-17.8~ - 7.1 -10.4 -23’9 -12.5 - 8.8

1.9

-

0.8

o-8 2.0

dry

1.3

-1o.o= - 3.8"

1'0

1'3-12'2 1.3-12.2

by dividing

-

8.0

Ebb Flood Ebb

estimated

-

1 -l

-

-

-

carbon

mg POC 0-12.4

Ebb Flood

Ebb Flood

systems

weight

9'9 4'3 6.8 -17.0

2.0 0.2 0.2

- 6.0 - 1.6 - 2.4

0’1 0’1

- 2’2 - 2’2

by two.

increasedthe POC fraction of the TOC. To investigate the amount of large grassparticles leaving Coon Creek, a I x 1.5 mm mesh screen was placed over the culverts on six occasions.Grass pieceslonger than the 6 cm (diameter of samplebottle mouth) were collected, dried and weighed. By assumingthat half of the dried weight was organic carbon, it was determined that the flux of theselarge pieceswas lessthan 0.017’ of the TOC flux. Two of the six sampleswere particularly notable in that they were taken after a higher than normal tide and rainfall. Loss of large and floating material would have been greatest at that time, but there wasstill no significant lossof large plant material. Net die1 flux of organic carbon. Net flux of TOC per day ranged from a loss of 2546 kg in

April to a gain of 554 kg in June (Figure 13). Average net die1organic carbon fluxes for the two years were lossesof 196 kg TOC, 150kg DOC and 32 kg POC. The TOC loss is the averageof all 52 sampling days while the DOC and POC fig ures were calculated from only 47 samphng days because DOC was not measured for the first five sampling days. The net die1 TOC fluxes (Figure 13) closely resemble net die1 water fluxes (Figure 7), and the relationshipsof all carbon components(TOC, DOC and POC) with net die1water fluxes were significant (rz = 0.96, 0.96, 0’55). As water flux varied much more than carbon concentrations in the water, net organic carbon flux was primarily determined by the net

Water and organic carbon jluxes

395

1975

Figure

13. Net

die1TOC flux, 14

1976

May

1975-13

1977

May

1977.

water flux. Not surprisingly, there was also a significant correlation between rainfall and net organic carbon flux, due to the influence of rainfall on net water flux (Figure IO). of organic carbon. Accurate estimatesof annual TOC flux are difficult to obtain becauseof the complexity of marsh systemsand the difficulty of obtaining sufficient data. The specific method employed depends on the characteristics of the individual system, the amount of data available, and the judgment of the investigator basedon his experience with the system. Several methods of calculating annual flux of organic carbon can be used for Coon Creek Marsh (Table 3). The simplestestimateof annual net TOC flux is obtained by multiplying averagenet die1 TOC flux (-196.03 kg) by the number of days in a year. The result is 71 551 kg TOC lost per year from the Coon Creek Marsh, but the 95% confidence interval of &117*05 kg for the daily average is large becauseof the seasonalvariation. Also, seasonalitymay have biasedthe yearly estimateof net TOC lossbecausesampledays were not evenly distributed. A better estimate of export is made by assumingeach die1sampleis representative only of the period in which it was obtained. This assumptionwas supported by the long-term flow measurementswhich showedthat consecutive days were generally similar with respect to water flows. The following trapezoidal rule equation wasused: Annualflux

kg TOC year-l = I/2(Yl+Yz)~,,,+I/2(Y2+Y3)~*,3+...+1/2(Y51+Y52)~51,52 2 years where yt is the net export for the ith die1sampling period and &+r is the number of days between die1 sampling periods i and i+ I (total number of days = 730 = z years). Net TOC flux calculated with this equation was 58 193 kg TOC year-‘, 19% lower than that obtained using the unweighted die1 average. Another estimateis obtained by integrating values under polynomial curves derived from the combined die1 TOC fluxes (Figure 14). This tends to minimize effects of short-term fluctuations, and perhaps produces a more general result. The value obtained using this method is 62 892 kg TOC year-l. Net annual TOC flux can alsobe estimated from measurementsof factors affecting water

396

R. B. Borey, P. A. Harcombe & F. M. Fisher

-0.5

-

-1.0

-*

-1.5

-

-2.5

-

.

5 x ‘h z 0z

l

0.5 (b)

MJJASONDJFMAM Month Figure 14. Annual variation in net die1 TOC, DOC and POC flux (best polynomial fit for two years of data). (a) TOC, I = 0.37, Y = -464.69+5.01(X) -0~or4(~~). (b) DOC, r = 0.32, Y = -aaox5+a~g~(X) -oooo83(Xa). (c) POC, I = 0.34, Y = -74’51+0,74(x) -0*0020(x~).

flux. Net die1 TOC flux was significantly correlated with precipitation and therefore net annual TOC flux could be determined from the daily record of the Coon Creek precipitation recorder by using the rainfall and carbon flux regressionpreviously discussed.There were 165 days in which rainfall occurred during the two-year study and these yielded a total of 221*04 cm of precipitation. Applying the regressionfor each day and summingresulted in an estimated net annual flux of 81 238 kg TOC, 12--28% higher than the other estimates (Table 3). It may reflect the addition of unsampled days with higher than normal TOC lossesbecauseof faster runoff rates following precipitation. All but seven of the 52 sample days fell more than one day after a precipitation event and so missedthesepotentially high runoff days. However, the standard error of estimatefor this regressionis 282.04, due largely to the large variation betweendays following periodsof no rainfall, and therefore the accuracy of this prediction of annual TOC lossmust be suspect.The utility of this method lies in its potential application to this and similar marsheswhen actual measurementof TOC flux is lacking but rainfall data are available.

Water and organic carbon jluxes

TABLE

3. Estimates

of net annual

397

TOC

Unweighted die1 average Interval weighted die1 average Polynomial regression Precipitation regression

4. Comparsion

of export

from

Coon Creek, TX Sapelo Island, GA (Teal, 1962) (de la Cruz, 1965) (SOttile,

et al.,

g TOC m -* year-l

“/; NAPP

62 829

23’27

2.6-4.2

81 238

30’09

3.3-5.5

marshes Export as gTOCm-s year -l 21.6-30.1

2’4-5‘5

408a~~ IjrIb,c

45a z.Ib

Od

1974)

40

1x4

1974)

50

140

1973)

382”*C

5@ 7@

1976)

412”~~

1976)

7.3b ob

ob

1977)

Creek, SC (Settlemyre & Gardner, Flax Pond, NY (Woodwell et al., 1977) Great Sippewissett, MA (Valiela et al., 1978)

Marsh

2.9-4’8 2’4-3’9

Od

(Kirby & Gosselink, Gott’s Marsh, MD (Heinle & Flemer, Catfish Bayou, MS (Hackney,

Creek

26.50 2x.55

1973)

Ware Creek, VA (Axelrad et al., Carter Creek, VA (Axelrad et af., Barataria Bay, LA

Coon

71551 58 193

Export as y/b NAPP

Marsh

(Day

from

kg TOC year -r

Method

TABLE

export

Dill

1977)

aIndirect measurement. bOnly POC considered. COrganic carbon estimated by dividing dry dOnly DOC considered. eAssuming 9 kcal g -i of organic carbon.

-53

0

74b

40b

plant

weight

by two.

NAPP for the Coon Creek Marsh is 1.1 to 1.8 kg m-2 of dry plant material per year (G. A. Henderson, unpublished data). Assuming soa/0 of this is organic carbon, the various calculations indicate the 270 ha Coon Creek Marsh is exporting 2*4-5.5% of its NAPP, or 21.55-30.09 g m-2 year-’ (Table 3). Discussion This study indicates that export from Coon Creek Marsh is 2 to 6% of NAPP and that tides play a relatively minor role in the transport of organic carbon. Instead, there is an almost constant efflux of water that results in transport of organic carbon to East Bay and a net loss from the marsh system. This efflux is principally determined by precipitation and internal resistances to water flows. The existence of rainfall as the major cause of marsh flooding in Coon Creek Marsh is quite different from the situation in Atlantic coastal

398

R. B. Borey, P. A. Harcombe

& F. M. Fisher

marsheswhere tides dominate and flooding from precipitation is thought to be lessimportant (Linton, 1968). The reduction in tidal flooding can be partially attributed to the small range of the Gulf tides, but vegetation and microtopographic resistancesto water movement may also be important. Many tides higher than marsh water levels do not produce a marsh level increasepresumably becauseof theseresistances. The amounts and types of organic carbon in runoff water from Coon Creek Marsh are probably determined by an interaction between marsh hydrology, vegetation structure, and decomposition processes.Marsh water levels rarely exceed the vegetation height, and so large plant piecesmust be reduced to smaller sizeswhich can move through the grassin runoff. Spar&a patens and Distichlis spicita tend to recline and form a horizontal, interwoven mat of live and dead culms in the Coon Creek Marsh. Upon death, the largest plant pieces fall to the top of this mat and gradually move vertically downward into layers of smaller piecesas they break up. Thus, there is a very densemat of vertically graded layers of dead plant piecesin various stagesof decomposition.A similar graded structure hasbeendescribed by Blum (1968) for a Cape Cod S. patens marsh. Grass particles are still retained when they reach the marsh surface becausethe dense vegetation continues to hold small floating pieces and the overmarsh water flows are not conducive to suspensionof small particles. Thus most of the organic carbon leaving the marsh would have to be extremely small particles or in dissolved form. This was precisely the composition of organic carbon found in water draining from the Coon Creek Marsh. Most of the organic carbon in marsh water was DOC and the largest portion of the POC were particles 0.3-28 pm in diameter. Almost all of the larger particles were amorphous detrital material that indicated a high degreeof previous decomposition. The decomposition of marsh grass into small particles and dissolved compounds is a poorly understood processthat progressesto completion over an indefinite period of time (Darnell, 1967; de la Cruz & Gabriel, 1974; Gosselink& Kirby, 1974). Coon Creek Marsh efficiently retains both water and grassparticles long enough that organic carbon in water draining from the marsh is primarily highly decomposedsmall particles and dissolved compounds. Micro-organisms rapidly consume dissolved labile material in the marsh environment and will probably maintain very low aquatic concentrations of rapidly assimilated and metabolized materials(Parsons& Takahashi, 1973 ; Gallagher et al., 1976; Pomeroy et al., 1976; Gallagher & Pfeiffer, 1977). Overmarsh water flows are probably not so rapid asto allow dissolvedcompoundsto escapebefore they can be utilized by microbial populations. Thus, most of the DOC in marsh runoff may be refractory compoundsthat are not nutritionally useful or rapidly utilized by the microbial community. If this is true, then much of the organic carbon contributed to East Bay from Coon Creek Marsh also will not be nutritionally useful to bay organisms. A concept of refractory compounds in marsh waters agreeswith Sottile’s (1973) results which indicate that the flood and ebb water of SapeloIsland marshesmostly contain DOC which is not readily utilized by micro-organisms. It is alsoconsistentwith Nixon’s (1979) calculationsshowing that marshesare not necessarily associatedwith increasedbay productivity. Coon Creek Marsh retains detritus and maintains a relatively slow efflux of water which minimizes export and maximizes utilization of fixed carbon within the marsh system. Unlesstides are of sufficient height and/or vigorous flow, it would be reasonableto assume that other marshesmight behave in a similar manner. A comparison of export studies (Table 4) suggeststhat marshesfall into three groups in terms of export: thosethat approach or exceed 50% of NAPP, those which fall closer to 0% of NAPP, such as Coon Creek Marsh, and those which have a net annual import. The marshesin Table 4 with the highest

Water and organic carbon jhxes

399

export are regularly well flooded. Values for two of these, Sapelo Island marshes(Ted, 1962) and Barataria Bay marshes(Day et al., 1973; Kirby & Gosselink 1976),were indirect estimatesand consequentlyonly indicate the potential export. It is unlikely that this potential could be completely met and it is interesting to note that direct measurementsmade in Sapelo Island marshesby de la Cruz (1965) and Sottile (1973) suggestthat actual export may be half of the estimated potential. Great Sippewisett Marsh (Valiela et al., 1978) may export 40% of the NAPP, but a portion of this could be contributed from grounds-ater inputs. Calculations by Settlemyre & Gardner (1977) indicate that aimual export from Dill Creek Marsh, South Carolina, may exceed the yearly NAPP of the marsh. This may be due to an innaccurate hypsometric model and/or NAPP estimate used for the study. Export from Ware and Carter Creek marshesin Virginia (Axelrad et af., 1974) has also been calculated to be very high. Haines (1977) has suggestedthat some of this export is allochthonous carbon entering from the surrounding region. It should alsobe pointed out that all measurementsin thesetwo marshes were obtained during spring tides when losseswould be expected to be greatest. Axelrad et al. (1974) assumedthat export was proportional to tidal volume and applied appropriate corrections for the smaller volumes of other tides when they calculated annual export. However, de la Cruz’s (1965) data indicate that the instantaneousflux of particulate matter can be more than four times greater on spring tides than neap tides while water flux is only twice aslarge. This is not surprising, since more material should be removed per volume of water during spring tides due to the contribution of organic matter which accumulated in the higher, unflooded marsh areasbetween spring tide periods. If this relationship applies for Ware and Carter Creek marshes,then the yearly estimate of annual export basedon spring tidal flows will be too high in spite of the corrections applied by Axelrad et al. (1974). The marsh with lowest annual export, Gott’s Marsh (Heinle & Flemer, 1976), is similar to Coon Creek Marsh in that it experiencesweak tidal flooding. In addition, Gott’s Marsh has a creek heavily lined with Spartina cynosuroides which prevents dead grassfrom easily washing out of the marsh. The minimal flooding in this marsh and the consequentialretention of dead material increasesthe opportunity for excessNAPP to be consumed in the marsh, and hence reducesthe amount of export as comparedto more tidal marshes.Export from Gott’s Marsh is lessthan that from Coon Creek Marsh (Table 4), but the data include only particulate organic matter. Had dissolved organic matter been included, the total may have been closer to that of Coon Creek Marsh. Only Flax Pond Marsh (Woodwell et al., 1977)and Catfish Bayou Marsh (Hackney, 1977) fall into the last category of marsheswith a net import (Table 4). Catfish Bayou Marsh is a Gulf coast marsh with an import of particulate matter amounting to less than 1% of its NAPP. Considering the amount of dissolved material being lost from Coon Creek Marsh, it is quite possiblethat Catfish Bayou Marsh is losingmore than I o/oof its NAPP in dissolved form and may actually have a low net export. On the other hand, Flax Pond Marsh is somethingof an enigmabecauseit is a regularly well flooded S. alternsjlora marshsimilar to Sapelo Island marshesand should therefore have a relatively large export. The creek which drains Flax Pond Marsh, as well as a large depression in its interior, are anthropogenic (Woodwell & Pecan, 1973). It is reasonableto suspect that these features significantly alter the normal transportation of materials into and out of the marsh. Rapid filling of these areaswould be a natural consequence,and there appears to be sedimentation taking place in this marsh (Armentano & Woodwell, 1975; Muzyka, 1976; Flessaet al., 1977; Richard, 1978). Indeed, calculations by Woodwell et al. (1977) suggestthat there is a general loss of DOC from the Flax Pond Marsh but a

R. B. Borey, P. A. Harcombe

400

& F. M. Fisher

much larger gain of POC which results in an overall net gain of TOC to the system. Thus Flax Pond Marsh might have a relatively large export were it not for sedimentation, although POC uptake by musselsin the creek bed has alsobeen suggested(Nixon, 1979). From this review of marsh studies it can be concluded that coastal marshesin general are sourcesof organic carbon for bay systems, although most are probably not losing as much as has been assumed.In fact, it appearsthat relatively few marshesapproach the widely accepted loss of 50% of NAPP and most marsheswill have a significantly lower export due to the interaction of severalfactors affecting the transport process.The Coon Creek Marsh study has indicated that rainfall, vegetation structure, microtopographic variation, and decompositionmust be consideredin addition to tidal fluctuation when evaluating the export potential of a coastalmarsh. Acknowledgements Mr RusselClapper, manager of the Anahuac National Wildlife Refuge, provided the study site and assistanceover the courseof this research;TOC analyseswere done in the laboratory of Dr Ernst Davis, University of Texas School of Public Health, Houston, Texas, with the help of Mr Jim Bishop and Mr Jim Petros. MS Georgia Henderson supplied NAPP data from researchundertaken at Rice University, Houston, Texas. This project was supported in part by NSF grants OCE 75-19633 and DES 75-17184 and by an NIH Biomedical Research Support Grant awarded to Rice University. The senior author wassupported by fellowships from Rice University, including the Eleanor and Miles Bennet Fellowship in Hydrology. This study was part of a Ph.D. thesis by the senior author. References Armentano, T. V. & Woodwell, G. M. 1975 Sedimentation rates in a Long Island marsh determined by Pb-rzo dating. Limnology and Oceanography ~0,452-456. Armstrong, N. E., Hinson, M. 0. Jr., Collins, J. H. & Fruh, E. G. 1975 Biogeochemical cycling of carbon, nitrogen, and phosphorous in seawater marshes of Lavaca Bay, Texas. Technical Report EHE-75-02, CRWR-121. Center for Research in Water Resources, The University of Texas, Austin, Texas. Axelrad, D. M., Bender, M. E. & Moore, K. A. 1974 Function of marshes in reducing eutrophication of estuaries of the middle Atlantic region. Publication PB-231767 Virginia Institute of Marine Science, Gloucester Point, Virginia. Blum, J. L. 1968 Salt marsh spartinas and associated algae. Ecological Monographs 38, 199-221. Collier, A. & Hedgpeth, J. W. 1950 An introduction to the hydrography of tidal waters of Texas. Publications of the Institute of Marine science of the University of Texas I, 125-194. Darnell, R. M. 1967 Organic detritus in relation to the estuarine ecosystem. In Estuaries (Lauff, G. H., ed.), Publication 83, American Association for the Advancement of Science, Washington, D.C. PP.

Day,

376-382.

J. W., Jr., Smith, W. G., Wagner, P. R. & Stowe, W. C. 1973 Community structure and carbon budget of a salt marsh and shallow bay estuarine system in Louisiana. Publication No. LSU-SG72-04. Center for Wetland Resources, Louisiana State University, Baton Rouge, Louisiana. de la Cruz, A. A. 1965 A study of particulate organic detritus in a Georgia salt marsh-estuarine ecosystem. Ph.D. thesis, University of Georgia, Athens, Georgia. I IO pp. de la Cruz, A. A. & Gabriel, B. C. 1974 Caloric, elemental, and nutritive changes in decomposing runcus roemerianus leaves. Ecology 55, 882-886. EPA 1971 Methods for Chemical Analysis of Water and Wastes. National Environmental Research Center Analytical Quality Control Laboratory, Cincinnati, Ohio. 312 pp. Flessa, K. W., Constantine, K. J. & Cushman, M. K. 1977 Sedimentation rates in a coastal marsh determined from historical records. Chesapeahe Science 18, 172-176. Gallagher, J. L. & Pfeiffer, W. J. 1977 Aquatic metabolism of the communities associated with attached dead shoots of salt marsh plants. Limnology and Oceanography 22, 562-565.

Water and organic carbon jluxes

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Gallagher, J. L., Pfeiffer, W. J. & Pomeroy, L. R. 1976 Leaching and microbial utilization of dissolved organic carbon from leaves of Spartina alternifora. Estuarine and Marine Coastal Science 4,467-47x. Gosselink, J. G. 8c Kirby, C. J. 1974 Decomposition of salt marsh grass, Spartina alterniflora. Limnology and Oceanography x9,825-832. Hackney, C. T. 1977 Energy flux in a tidal creek draining an irregularly flooded Juncus marsh. Ph.D. thesis, Mississippi State University, Mississippi State, Mississippi. 83 pp. Haines, E. B. 1977 The origins of detritus in Georgia salt marsh estuaries. Oihos 29, 254-260. of organic carbon in a Happ, G., Gosselink, J. G. & Day, J. W. J r. 1977 The seasonal distribution Louisiana estuary. Estuarine and Coastal Marine Science 5, 695-705. Heinle, D. R. & Flemer, D. A. 1976 Flows of materials between poorly flooded tidal marshes and an estuary. Marine Biology 35, 359-373. Henderson, G. A. & Harcombe, P. A. 1976 Net primary productivity of the Chambers County marshes. In Environmental Analysisfor Dwelopment Planning, Chambers County, Texas, vol. 7. Environmental Analysis Case Study Applications and Selected Technical Papers (Rowe, P. G. & Williams, D. L., eds). Rice Center for Community Design and Research, Houston, Texas. pp. 139-r 51. Howarth, R. W. & Teal, J. M. 1979 Sulfate reduction in a New England salt marsh, Limnology and Oceanography 24, 999-1013. Kirby, C. J. & Gosselink, J. G. 1976 Primary production in a Louisiana Gulf coast Spartina alterni’ora marsh. Ecology 57, 1052-1059. Linton, T. L. 1968 A description of the South Atlantic and Gulf coast marshes and estuaries. In Proceedings of the Marsh and Estuary Management Symposium (Newsom, J. D., ed.). T. J. Moran’s Sons, Baton Rouge, Louisiana. pp. 15-32. Maurer, L. G. & Parker, P. L. 1972 The distribution of dissolved organic matter in the near-shore waters of the Texas coast. Contributions in Marine Science 16, 109-124. Milner, C. & Hughes, R. E. 1968 Methods for the measurements of the primary production of grassland. IBP Handbook No. 6. Blackwell Scientific, Oxford. 70 pp. Muzyka, L. J. 1976 Pb-zro chronology in a core from the Flax Pond marsh, Long Island. M.S. thesis, S.U.N.Y., Stony Brook, New York, 73 pp. Nadeau, R. J. 1972 Primary production and export of plant materials in the salt marsh ecosystem. Ph.D. thesis, Rutgers University, New Brunswick, New Jersey. 167 pp. Nixon, S. W. 1979 Between coastal marshes and coastal waters-a review of twenty years of speculation and research on the role of salt marshes in estuarine productivity and water chemistry. In Estuarine and Wetland Processes: With Emphasis on Modelling (Hamilton, P. & MacDonald, K. B., eds). Plenum Press, New York. pp. 437-525. Odum, W. E., Zieman, J. C. & Heald, E. J. 1973 The importance of vascular plant detritus to estuaries. In Proceedings of the Coastal Marsh and Estuary Management Symposium (Chabreck, R. H., ed.). Louisiana State University, Baton Rouge, Louisiana. pp. 91-1r4. Parsons, T. R. & Takahashi, M. 1973 Biological Oceanographic Processes. Pergamon Press, Oxford. 186 pp. Pomeroy, L. R., Bancroft, K., Breed, J., Christian, R. R., Frankenberg, D., Hall, J. R., Maurer, L. G., Wiebe, W. J., Wiegert, R. G. & Wetzel, R. L. 1976 Flux of organic matter through a salt marsh. In Estuarine Processes, vol. II. Circulation, Sediments, and Transfer of Material in the Estuary (Wiley, M., ed.). Academic Press, New York. pp. 270-279. Richard, G. A. 1978 Seasonal and environmental variations in sediment accretion in a Long Island salt marsh. Estuaries I, 29-35. Rowe, P. G. & Williams, D. L. (eds) 1974 Environmental Analysis for Development Planning, Chambers County, Texas, vol. I. An Approach to Natural Environmental Analysis. Rice Center for Community Design and Research, Houston, Texas. 531 pp. Schelske, C. L. & Odum, E. P. 1961 Mechanisms maintaining high productivity in Georgia estuaries. Gulf and Caribbean Fisheries Institute Proceedings 14, 75-80. Settlemyre, J. L. & Gardner, L. R. 1977 Suspended sediment flux through a salt marsh drainage basin. Estuarine and Coastal Marine Science 5, 653-663. Shisler, J. K. & Jobbins, D. M. 1977 Tidal variations in the movement of organic carbon in New Jersey salt marshes. Marine Biology 40, 127-134. Smith, N. P. 1974 Intracoastal tides of Corpus Christi Bay. Contributions in Marine Science r&206-219. Smith, N. P. 1977 Meteorological and tidal exchanges between Corpus Christi Bay, Texas, and the northwestern Gulf of Mexico. Estuarine and Coastal Marine Science 5, 5 I 1-520. Sottile, W. S. II 1973 Studies of microbial production and utilization of dissolved organic carbon in a Georgia salt marsh-estuarine ecosystem. Ph.D. thesis, University of Georgia, Athens, Georgia. I53 PP. Teal, J. M. 1962 Energy flow in the salt marsh ecosystem of Georgia. EcoZogy 43, 614-624. Valiela, I., Teal, J. M., Volkmann, S., Shafer, D. & Carpenter, E. J. 1978 Nutrient and particulate fluxes in a salt marsh ecosystem: tidal exchanges and inputs by precipitation and groundwater. Limnology and Oceanography 23,798-812.

402

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P. A. Harcombe

@ F. M.

Fisher

Wilson, R. F. 1963 Organic carbon levels in some aquatic ecosystems. Publications of the Institute of Marine Science of the University of Texas 9, 64-76. Woodwell, G. M. & Pecan, E. V. 1973 Flax Pond : an estuarine marsh. Brookhaven National Laboratory Technical Report BNL 50397. 7 pp. Woodwell, G. M., Whitney, D. E., Hall, C. A. S. & Houghton, R. A. 1977 The Flax Pond ecosystem study: exchanges of carbon in water between a salt marsh and Long Island Sound. Limnology and Oceanography tz,833-838.