seasonal variations of organic-carbon and nutrient ... · degradation of doc and poc within the...

Seasonal variations of organic-carbon and nutrient transport through

a tropical estuary (Tsengwen) in southwestern Taiwan

J.-J. Hung1,2 & M.-H. Huang11Institute of Marine Geology and Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan, ROC2Author for correspondence (tel.:+886-7-5255147; fax:+886-7-5255130; e-mail: [email protected])

Received 17 April 2003; Accepted 15 June 2004

Key words: carbon and nutrients, estuarine budgets, fluvial fluxes, net nitrogen loss, net organic carbonproduction, sediment yield

Abstract

This paper reports the fluvial fluxes and estuarine transport of organic carbon and nutrients from a tropicalriver (Tsengwen River), southwestern Taiwan. Riverine fluxes of organic carbon and nutrients were highlyvariable temporally, due primarily to temporal variations in river discharge and suspended load. Thesediment yield of the drainage basin during the study period (1995–1996, 616 tonne km)2 year)1) was ca.15 times lower than that of the long-term (1960–1998) average (9379 tonne km2 year)1), resulting mainlyfrom the damming effect and historically low record of river water discharge (5.02 m3 s)1) in 1995. Theflushing time of river water in the estuary varied from 5 months in the dry season to >4.5 days in the wetseason and about 1 day in the flood period. Consequently, distributions of nutrients, dissolved organiccarbon (DOC) and particulate organic carbon (POC) were of highly seasonal variability in the estuary.Nutrients and POC behaved nonconservatively but DOC behaved conservatively in the estuary. DOCfluxes were generally greater than POC fluxes with the exception that POC fluxes considerably exceededDOC fluxes during the flood period. Degradation of DOC and POC within the span of flushing time wasinsignificant and may contribute little amount of CO2 to the estuary during the wet season and floodperiod. Net estuarine fluxes of nutrients were determined by riverine fluxes and estuarine removals (oradditions) of nutrients. The magnitude of estuarine removal or addition for a nutrient was also seasonallyvariable, and these processes must be considered for net flux estimates from the river to the sea. As a result,nonconservative fluxes of dissolved inorganic phosphorus (DDIP) from the estuary are )0.002, )0.09 and)0.59 mmol m)2 day)1, respectively, for dry season, wet season and flood period, indicating internal sinksof DIP during all seasons. Due to high turbidity and short flushing time of estuarine water, DDIP in theflood period may be derived largely from geochemical processes rather than biological removal, and thisDDIP should not be included in an annual estimate of carbon budget. The internal sink of phosphoruscorresponds to a net organic carbon production (photosynthesis–respiration, p–r) during dry(0.21 mmol m)2 day)1) and wet (9.5 mmol m)2 day)1) seasons. The magnitude of net production (p–r) is1.5 mol m)2 year)1, indicating that the estuary is autotrophic in 1995. However, there is a net nitrogen loss(nitrogen fixation–denitrification < 0) in 1995, but the magnitude is small ()0.17 mol m)2 year)1).

1. Introduction

The estuarine region is one of the most productiveareas in coastal systems. Primary productivity is

generally an order of magnitude greater in estu-aries than in the open ocean, as estuaries regularlyreceive allochthonous nutrients (Schlesinger 1991;Pernetta & Milliman 1995; Malone et al. 1996).

Environmental Geochemistry and Health 27: 75–95, 2005.� 2005 Springer. Printed in the Netherlands.

75

Estuaries may be regarded as sinks with respect toCO2 from the standpoint of high productivity.However, estuaries may act as traps for terrestrialorganic matter fueling biological respiration andprovide a source of CO2, although the fate of inputorganic matter in estuarine food webs is not wellunderstood (IGBP 1005; Smith & Hollibaugh1993; IGBP 1995; Kempe 1995).Smith & Hollibaugh (1993) stressed the use of

net organic metabolism (difference between grossprimary productivity and respiration) in de-termining the importance of coastal ocean relativeto anthropogenic perturbation of the global car-bon cycle. They also argued that the coastal oceanis a site of net organic oxidation from a long-termviewpoint, but recent evidence (see LOICZ web-site for biogeochemical budgets) and this papershow that many estuaries are sites of net organicmatter production. Apparently, different coastalecoystems may exhibit contrasting roles in influ-encing nutrient and organic metabolism (Smith2001).During recent decades, riverine discharges of

nutrients and organic matter have increasedsignificantly due to human intervention withinwatersheds (GESAMP 1987; Meybeck 1993;Howarth et al. 1996; Meybeck & Regu 1996). Aclose link is generally found between ecosystemmetabolism and terrestrially derived nutrients intemperate ecosystems (Borum 1996; Kemp et al.1997; Smith & Hollibaugh 1997). It remains dif-ficult to assess completely a function of estuarineecosystem in response to the input of terrestrialnutrients in tropical area largely because of con-founding physical and biogeochemical factors(Eyre & Ball 1999; Eyre & McKee 2002).Therefore, it is of interest to know whether ashallow coastal water body is a carbon source orsink (IGBP 1995), particularly in tropical areas.To assess carbon sources and sinks throughprocess studies is not a simple task, Gordon et al.(1996), however, proposed guidelines for theLand-Ocean Interactions in the Coastal Zone(LOICZ) programme to assess nonconservativenutrient fluxes and carbon budgets for wellboundary-defined coastal systems. This steady-state budgeting method provides an alternativemethod to evaluate the biogeochemical metabo-lism and fate of nutrients and carbon in coastalsystems when direct measurements of productiv-ity and respiration are not available. Net nutrient

fluxes in the coastal zone can be also determinedfrom budget calculations, which is essential toevaluate the effects of riverine discharges oncoastal function and carbon metabolism.Although the importance of small and medium

sizes of estuarine systems in determining coastalcarbon cycle has been studied (Smith et al. 1991;Smith & Hollibaugh 1997; Hydes et al. 1999;Swaney et al. 1999), experiments in these systemsare relatively rare in tropical areas such as islandsin Oceania. River discharges of water and sedi-ments from these islands are seasonally variableand dependent heavily on episodic short-livedstorms (Kao & Liu 1996; Liu et al. 1998). Milli-man & Syvitski (1992) reported that sediment in-put to coastal areas from such islands (e.g.Taiwan) is much higher than previous estimates(Milliman & Meade 1983). Biogeochemical pro-cesses of organic carbon and nutrients in this is-land’s estuaries could be quite different from thosein temperate regions.The purpose of this study is to evaluate seasonal

variations of river fluxes and estuarine budgets forcarbon and nutrients from a tropical river(Tsengwen) in southwestern Taiwan, from whichthe quantitative relationship of inputs, internalmetabolism and outputs of organic carbon andnutrients can be established. The C—N—P bud-gets in the tropical estuary may be also betterunderstood.

2. Materials and methods

2.1. Study area

The Tsengwen River is a mountainous river in thetropical zone of southwestern Taiwan. The river(length,139.5 km) originates in the WansuiMountain of Central Mountain Range (elevation,2440 m). It drains a watershed comprised of sub-urban, rural and agricultural zones with a totalarea of 1177 km2 (Hydrological Year Book ofTaiwan 1995). The drainage basin of the TsengwenRiver is composed of sedimentary rocks ranging inage from Late Miocene to Pleistocene. The majorrock types are mudstone and sandstone, with localconglomerates (Liu et al. 1998). Soil distribution isheterogeneous ranging from poorly developedyellow soils in the upper reach to noncalcareousalluvial soils in the coastal plain. The carbonate

J.-J . HUNG AND M.-H. HUANGJ.-J . HUNG AND M.-H. HUANG76

contents of surface layers of most soils are gen-erally less than 1% (Sheh & Wang 1989). The riverdischarges into the Taiwan Strait where waterdepth is generally <200 m. The estuarine zone,defined in this study by a salinity range due tomixing of river and sea waters, extends approxi-mately 10–25 km from the river mouth, dependingon river discharge. Therefore, the study area of theTsengwen Estuary is seasonally variable(Figure 1). The depth ranges approximately from1.5 to 4 m. The average annual rainfall for thedrainage basin is 2643 mm (Hydrological YearBook of Taiwan 1995). Average monthly rainfallrecorded from a weather station near the estuarygenerally exceeds 120 mm during the southwesternmonsoon (wet) season (May–September) andnormally is <50 mm during the northeasternmonsoon (dry) season (October–April) (data ofCentral Weather Bureau Taiwan 1995). As a re-sult, river discharge is high during the wet seasonand low during the dry season (Figure 2). Duringthe wet season, episodic floods from heavy mon-soon rains or typhoons are not unusual and criti-cally influence water discharge and suspendedload. Estuarine water temperature ranges from16 �C in winter to 33 �C in summer. The estuarywidth ranges from about 50 m in the upper estuary

to about 300 m in the river mouth. The depthranges from �1.5 m in the upper estuary (in dryseason) to �4 m near the estuarine mouth. Themean tidal range in this study area is about 1 m(Lin et al. 1999).

2.2. Sampling and analytical methods

Samples of river water were taken monthly from agauged station (Ma-Shan) in the lower reach fromJanuary 1995 to December 1996. Estuarine watersamples were collected upstream from the rivermouth on board a small vessel during the dry sea-son (January 10, 1995), flooding period (June 14,1995) and wet season (September 30, 1995). Toensure covering a wide range of salinity, the sam-pling stations were not fixed but determined fromsalinity spatial distribution because seawater in-trusion distance was different in each samplingperiod. At each sampling station, the water sampleswere collected from various (3–4) depths using ahome-made sampling system consisting of a peri-staltic pump and a silicone tube. Contaminationwas carefully avoided according to sampling pro-cedures by Hung & Shy (1995). Salinity, pH anddissolved oxygen (DO) were measured in situwith asalinometer (Hydro-Bios), a pH meter (Orion

Fig. 1. Map of the study area.

ESTUARINE TRANSPORT OF ORGANIC CARBON AND NUTRIENTSESTUARINE TRANSPORT OF ORGANIC CARBON AND NUTRIENTS 77

Research) and a DO-meter (YSI model 58), with aprecision about ±5, ±2 and ±7%, respectively.Salinity was determined via an Autosal salinometer(Guildline 8400B) in the laboratory again to gainmore precise (±0.002 psu) salinity values for de-riving water budgets. Four litres of each samplewas stored in a polyethylene bottle and broughtback the laboratory immediately. Next, the waterwas filtered through an acid-cleaned, dried and pre-weighed Nucleopore membrane filter to determinethe concentration of total suspended matter(TSM), dissolved and particulate trace metals.A subsample was filtered through a pre-com-

busted (at 450 �C, 4 h) GF/F filter to measure dis-solved inorganic nutrients (NO�3 þNO�2 ;NHþ4 ;PO3�

4 ; Si), dissolved organic carbon (DOC), organicnitrogen (DON) and organic phosphorus (DOP).Dissolved inorganic nitrogen (DIN) (NO�3 ;NO�2 ;NHþ4 ) and phosphate (PO3�

4 ) species weredetermined colorimetrically (Grasshoff et al. 1983)by using a flow injection analysis (Pai et al. 1990).Precision was generally better than 5%. DOC wasdetermined with the high temperature catalyticoxidation method (Shimadzu TOC 5000) (Hung &

Lin 1995) with precision better than 4%. Totaldissolved nitrogen (TDN) was measured with hightemperature oxidation and chemiluminescent de-tection (Antek N/S analyzer) with reproducibilitywithin ±8% for seawater (n ¼ 8). DON was cal-culated from the difference between TDNandDIN.DOP was also calculated from the difference be-tween dissolved inorganic phosphate (DIP) andtotal dissolved phosphorus (TDP), which was de-termined with UV-persulfate oxidation andcolorimetric method (Ridal & Moore 1990). epro-ducibility of TDP measurement in a seawater(n ¼ 8) is ±7%. The concentration of each speciesin a sample was averaged from three replicates.A DOC incubation experiment was conducted

to simulate the degradation rate of DOC in theestuary. Ten litres of river water from Ma-ShanStation were sampled and filtered through com-busted Whatman GF/C filters (�1.2 lm pore size).The filtered water was divided and stored in300 ml amber glass bottles tightened with glassstoppers. The bottles were wrapped with alumi-num foil and incubated in the dark at 25 �C up to150 days. Duplicate samples were extracted and

QP QE

4.72 -4.96

QR Qr

-13.8 13.8

Water Budget ( fluxes in 103m3d-1 )

SR QR Sr = 0

= - 0.365 Qr Sr = 0

S2 = 34

Qx 2 1

TsengwenEstuary

TsengwenEstuary

S1 =18.8

= 365Qx = 23.9

Salt Budget ( fluxes in 103 kg d ) -1

( S - S )

Fig. 2. Steady-state water and salt budgets for the Tsengwen estuary during the dry season. Qr, Qp, QE and QR represent river

discharge, precipitation, evaporation and residual flow, respectively. Sr, SR, S1 and S2 denote salinity in river water, residual flow,

estuary and ocean, respectively.

J . -J . HUNG AND M.-H. HUANGJ.-J . HUNG AND M.-H. HUANG78

opened for DOC determination after various per-iods of incubation. Degradation of DOC wasevaluated from the decrease of DOC concentra-tion with an increase of incubation time (Moranet al. 1999).Duplicate particulate-matter samples collected

on GF/F filters were used for analyses of parti-culate organic carbon (POC) and nitrogen (PON).POC and PON were then determined with a C/N/Sanalyzer (Fisons NCS 1500) after removing theinorganic carbon with hydrochloric acid (Hunget al. 1999). Finally, duplicate POC samples weresent to Europa Scientific’s ANCA-MS System inEngland for stable carbon isotope (13C) determi-nation with a C/N mass spectrometer (Tracermass,ANCA-MS). Reproducibility was reported to be±0.002 at.% 13C.

2.3. Biogeochemical modelling approach

The biogeochemical fluxes and metabolism of nu-trients and organic carbon in the estuary wereevaluated by using the LOICZ biogeochemicalbudget model (Smith et al. 1991; Gordon et al.1996). This biogeochemical budget model is asteady-state box model. According to LOICZBiogeochemical Modelling Guidelines (Gordonet al. 1996), nonconservative nutrient and organiccarbon budgets can be constructed from non-conservative distributions of substances and waterbudgets which in turn are constrained from the saltbalance under a steady-state assumption. Thenonconservative flux of a material is estimatedfrom the flux deviation between inputs and out-puts based on salt-water balances. The non-conservative flux of DIP is assumed to be anapproximation of net metabolism, because phos-phorus is apparently a limiting nutrient and is notinvolved in gas-phase reactions. Nitrogen andcarbon both have other major pathways such asdenitrification, nitrogen fixation, gas exchangeacross the air–sea interface, and calcification. Thechallenge of this central assumption arises fromthe fact that nonconservative DIP flux in a coastalsystem may be influenced and partially derivedfrom geochemical exchange between dissolved andparticulate phases via adsorption–desorption and/or oxidation–reduction reactions in sediment aswell as in the water column (Jensen et al. 1995). Inthis study system, such geochemical exchanges areconsidered to be minimum or equal between

adsorption and desorption during dry and wetseasons while the estuary is thoroughly oxygenatedin the water column. During the short period offlooding, the influence of geochemical processesmay not be negligible and may violet the centralassumption as the estuarine water is turbid andresuspension of bottom sediment can be sig-nificant. Therefore, nonconservative flux of DIPduring the flood period is excluded from annualbudget consideration. Those biogeochemicalpathways of carbon and nitrogen can be approxi-mated from nonconservative phosphorus flux andC—N—P stoichiometric ratios of reactive particlescoupled with measured flux for nitrogen in theestuary. Because of the distinct seasonal variabilityin river water and material inputs, water and nu-trient budgets estimated from a box model for theestuary can only be valid by assuming steady-state(the estuarine volume change with time is con-stant, dV/dt ¼ 0) within a season.Details of modelling can be found from the

LOICZ web site (http://www.nioz.nl/loicz/). Brief-ly, using salt as a conservative tracer, the waterbudget from the Tsengwen estuary can be derivedfrom the balance of salt transported through theestuary (Figure 2). Dissolved nutrient budgets areestimated from water budgets and nutrient con-centrations in each compartment. The nutrientbudgets are derived from dissolved inorganic (i.e.DIP and DIN) and organic (i.e. DOP and DON)materials but both are constrained independently.Nonconservative fluxes of DIP (DDIP) and DOP(DDOP) can be derived from the following equa-tions:

DDIP¼�ðRDIPoutflux�RDIPinfluxÞ¼�½QRDIPRþQXðDIP1�DIP2ÞþQrDIPr�;

ð1Þ

where QR and QX values are negative and Qr valueis positive in the budget calculation for theTsengwen estuary. DIPr, DIP1, DIP2 and DIPR

denote mean DIP concentration in the river runoff,estuary, Taiwan Strait and residual-flow bound-ary, respectively. According to Gordon et al.(1996), DIPR can be adopted as 1/2(DIP1+ DIP2).The DDIP was used to derive net ecosystem

metabolism (p–r) according to the following re-lationship:

½p–r� ¼ �DDIC0 ¼ DDIP�ðC:PÞparticulate: ð2Þ


The Redfield ratio (106) was used for stoichio-metric calculation because phytoplankton is theprimary producer (Wong, S.-L., personal com-munication) in the estuary. The in- situ particulateC/P ratio was remarkably affected by detrituscontribution and was not adopted for calculation.Meanwhile, the nitrogen metabolism (nfix)denit)can be derived from the difference between non-conservative nitrogen flux and expected nitrogenremoval through biological uptake

½nfix�denit� ¼DNobserved�DNexpected

¼DNobserved�DP �ðN:PÞparticulate: ð3Þ

The Redfield N:P ratio (16) is also applied for thecalculation.

3. Results and discussion

3.1. Seasonal variability of river discharge andsediment load

In the Tsengwen drainage basin, more than 80% ofannual precipitation falls between May and Sep-tember, mostly from monsoon rain and typhoonstorms (Hydrological Year Book of Taiwan 1995).The river water discharge generally increases fromMay to August and then decreases to near zeroafter October (Figure 3). As a result, river waterdischarge in August is about 2–3 times discharge inJuly or September (Figure 3). The summed dis-charge of July and August accounts for 81% of the

annual discharge. River water discharges in recentyears (1995 and 1996) are lower than the long-termaverage (1982–1994), with the exception of August1996 due to heavy typhoons. The annual meandischarge in 1995 (5.02 m3 s)1) is the lowest level inhistorical records largely due to lack of typhoons inthe summer season (Figure 4(a)). The typhoons‘‘Gloria’’ and ‘‘Herb’’ produced high rainfall dur-ing 28 July–8 August 1996 and the monthly dis-charge peaked in August (Figures 3 and 5).The annual sediment load at the gauged station

(Ma-Shan Station in the lower reach) was a sum ofmonthly sediment loads that were calculated bysumming up daily sediment loads. The daily sedi-ment loads were estimated according to the em-pirical relationship (Ls ¼ 10aQb, Crawford 1991)between daily sediment load (Ls (tonne/day)) anddailymean discharge (Q (m3 s)1)). After logarithmictransformation, this empirical relationship becomeslinear between Ls and Q (log Ls ¼ a + b log Q),where a and b are the intercept and slope of therating curve. Data of Ls andQ were extracted froma long-term database established by the Water Re-sources Bureau, Taiwan (TWRB). The TWRBmeasured water discharge (Q) every day but sedi-ment load (Ls) only 3–4 days per month; therefore,the rating curvewas constructed by using the data ofmultiple years. Because the gauged station wasmoved from Hsi-kang Station up to Ma-shan Sta-tion after 1982, three rating curves (Figure 6) wereestablished from 1960 to 1972 (before damming)at Hsi-kang Station, from 1974 to 1981 (after

J F M A M J J A S O N D

0

30

60

90

120

150

Ma-Shan St. 1982-1994 1995 1996

Dis

char

ge (

m s

ec )

3-1

Time (month)

Fig. 3. Monthly discharge of the Tsengwen river water at the Ma-shan Station.


damming) at Hsi-kang Station, and from 1982 to1998 atMa-shan Station. The annual sediment loadbetween 1960 and 1998 was estimated by using the

three rating curves, and the long-term variation ofsediment load was compared to that of river waterdischarge (Figures 4 (a) and (b)).

1960 1965 1970 1975 1980 1985 1990 1995

0

20

40

60

80

100D

isch

arge

(m

s )

3-1

1960 1965 1970 1975 1980 1985 1990 1995

0

1x107

2x107

3x107

4x107

Sed

imen

tload

(to

n yr

) -1

1960 1965 1970 1975 1980 1985 1990 1995

0

10000

20000

30000

Time (yr)

Sed

imen

t yie

ld (

ton

km y

r )

-2-1

(a)

(b)

(c)

Fig. 4. The long-term (1960–1998) distributions of river discharge (a), sediment load (b), and sediment yield (c) from the gauged

stations (His-kang and Ma-shan) in the lower reach of Tsengwen river.


The slope of rating curve increases slightlyfrom 1.867 during 1960–1972 to 1.935 during1974–1981, and from 1.935 to 2.02 during 1982–1998, which may indicate the increase of soilerodibility in the lower watershed since 1960. Thismay be attributed to the intensive farming andland-use change due to economic growth duringrecent decades. Because there is no gauged stationon the upper range of main channel, it is hard toevaluate the direct effect of damming on sedimentload recorded downstream. The reduced sedimentload due to damming may be partially compen-sated by the increase of soil erosion in middle-lower watersheds during last decades. However,the averaged sediment load is 1.52 · 107 tonneyear)1(1960–1972), 1.16 · 107 tonne year)1(1974–1981) and 5.92 · 106 tonne year)1 (1982–1998),respectively, for periods before damming, afterdamming at His-kang and after damming at Ma-shan Station. It is observed that the sedimentload has decreased since the construction of theTsengwen Dam at 1973. Liu et al. (1998) alsoreported that a large amount of sediment mayhave accumulated in the Tsengwen Reservoir

after the construction of the Tsengwen Dam. Thedecrease of sediment supply have resulted in thelandward shift of the coastline around the rivermouth (Liu et al. 1998).The monthly suspended sediment load during

the study period was estimated using the ratingcurve for 1982–1998. The higher load is observedbetween May and September (Figure 7(b)) be-cause rainfall intensity causes rock denudation andsoil erosion (Degens 1989). The total suspendedload between July and August 1996 accounted forapproximately 73% of annual load. During thedry season, discharges of river water and sus-pended sediment decline dramatically as a result ofvery low sediment yield.Sediment yield (616 tonne km)2 year)1) from the

total drainage area for the period 1995–1996 ismuch lower than the long-term (1960–1998, Figure4(c)) record (9379 tonne km)2 year)1) that can beregarded as the long-term average yield for thiswatershed. The low sediment yield of 1995–1996 isprimarily due to very low water discharge(5.02 m3 s)1) during 1995. However, this year’s re-cord is still 4 times greater than the global mean

-1 0 1 2 3 4 5 6 7 8 9 10 11

0

200

400

600

800

1000

1200

1400

1600

HerbGloria

Typhoon

Dis

char

ge (

m s

ec )

3

-1

Time after Gloria typhoon (day)

Fig. 5. Discharge of Tsengwen riverwater at the Ma-shan Station during the typhoon periods. Data are adapted from the Hydrological

Year Book of Taiwan, 1997.


value (152 tonne km)2 year)1, Milliman & Meade1983). The long-term sediment yield is ca. 60 timeshigher than the global mean value, conforming thatthe sediment yield of Taiwan Island may be largest

in the world (Milliman & Syvitski 1992). The veryhigh sediment yieldmay be attributed to anomalousdenudation rates and soil erosion (Li 1976; Youet al. 1988) that are determined from high mean

1 10 100 1000

100

101

102

103

104

105

106

107

198

1960-1972, Hsi-Kang

1 10 100 1000100

101

102

103

104

105

106

107

1974-1981, Hsi-Kang

Log(S. load)= 0.247 + 1.935LogQR=0.929, p<0.0001

Sed

. loa

d (t

onda

y )

-1

1 10 100 1000

100

101

102

103

104

105

106

107

Log (S.load)=0.037 +2.02LogQR=0.908, p<0.0001

Sed

. loa

d (t

on d

ay-1

)

Q (m s )3 -1

Log(S. load) =0.531 + 1.867LogQR=0.924, p<0.0001

Sed

. loa

d (t

on d

ay )-1

(a)

(b)

(c)

Fig. 6. The empirical rating curves between sediment load (Ls) and river discharge (Q) for periods from 1960 to 1972 at His-kang

gauged station (a), from 1974 to 1981 at His-kang gauged Station (b), and from 1982 to 1998 at Ma-shan gauged Station (c).


elevation, intensive farming, lower vegetative cov-erage and concentrated rainfall in a short period onTaiwan Island.

3.2. Seasonal variations of carbon and nutrientfluxes

Fluxes of organic carbon and nutrients areestimated from the river water discharge andconstituent concentrations at Ma-shan Station.Although the concentration decreases with an in-

crease of water discharge for most dissolved con-stituents, the monthly flux of a constituent islargely proportional to water discharge(Figure 7(a)). A difference of approximately threeto four orders of magnitude was observed for anyone of the dissolved nutrient and DOC fluxesbetween the highest and lowest (Figure 7(a)).Nearly 75% of annual DOC and nutrient fluxesinto the estuary occurred during the high-flowperiod of July–August. Nitrate and nitrite aremajor nitrogen species in the dry season while

103

104

105

106

107

108

109

10-2

10-1

100

101

102

103

104

105

106

Sept/1995 - Aug/1996

AJJMAMFJDNOS

Sus

pend

ed lo

ad (

ton

mon

th )-1

Time (month)

19961995

AJJMAMFJDNOS

Sept./1995 - Aug./1996

DIN PO

4

SiO4

DOC POC

Flu

x (m

ole

mon

th )-1

(a)

(b)

Fig. 7. Temporal variations of constituent fluxes (a) and suspended load (b) at the gauged station (Ma-shan) in the lower reach of

Tsengwen river.


ammonium is the major nitrogen species in wetand flood seasons. In contrast to higher con-centration of nitrate in temperate rivers (e.g. De-laware River) during the warm season partly dueto higher nitrification rate (Church 1986), theTsengwen River transports more nitrogen parti-cularly as ammonium during the wet and flood(warmer) seasons. This may be due to productionof inorganic nitrogen in the watershed, particu-larly for ammonium from fertilizers and pointsources, during the dry season and flushing intothe river during the wet and flood seasons.Anthropogenic inputs of nutrients from wa-

tershed into river water are significant as nutrientconcentrations are much higher in the TsengwenRiver than those reported from worldwide un-polluted rivers (Meybeck 1982). The elementalratios between DIN and DIP are lower in the dryseason (DIN/DIP = 10–54) than in wet and floodseasons (DIN/DIP = 74–232). The DIN/DIP ra-tio of river water may be related to nutrientsources. Billen et al. (1991) reported that the meanDIN/DIP ratio of river water is generally around100 if DIN and DIP are derived from agriculturalwatersheds, but this ratio may approach to bearound 10 if DIN and DIP are derived from ur-banized and/or industralized watersheds. Intensivefarming, heavy use of fertilizers and release ofuntreated wastewater from middle and lower wa-tersheds are probably responsible for high fluxes ofnutrients and DOC during wet and flood seasons.Despite lower fluxes of nutrients and DOC duringthe dry season, their high concentrations andlower DIN/DIP ratios in river water are likelyderived largely from the discharge of untreatedwastewater from rural and suburban areas. Duringthe wet season, the relatively high DIN/DIP ratiosin river water may result mainly from larger out-put of DIN over DIP from the agriculture-domi-nated watershed.Fluxes of POC are primarily determined by

magnitudes of sediment loads, although POCweight concentrations decrease with the increase ofTSM. Seasonal variations of POC fluxes are sig-nificant (Figure 7(a)) due to much greater sedi-ment loads in the wet season than in the dryseason. The flux of POC during the high-flowperiod of July–August accounts for >85% of theannual flux. Fluxes of POC decreased from Sep-tember to January and then increased to a max-imum in August. In general, POC fluxes are

comparable with DOC fluxes during most seasons,but POC fluxes are greater than DOC fluxes dur-ing the period (July–August) of peak flow (Figure7(a)). Meybeck (1982) reported that the [DOC]/[TOC] ratio generally falls between 0.6 and 0.8 inlowland rivers, but is lower than 0.5 in highlandriver. Our results show that the ratio ([DOC]/[DOC+POC]) is approximately 0.5 during the dryseason (lower TSM) but lower than 0.5 during thewet and flood seasons (higher TSM). Our data alsosupport previous other reports showing a generallyhigher DOC/POC ratio in low TSM rivers andestuaries and lower DOC/POC ratio in high TSMsystems (Ittekkot & Laane 1991; Abril et al. 2002).High concentrations of DOC (149–684 lM) and

POC (142–1529 lM) suggest that both are moreprobably derived from agricultural soils than fromalpine plants, since DOC concentrations observedfrom mountainous streams in southern Taiwan aregenerally less than 60 lM (Hung J. J., unpublisheddata) during most seasons of a year. DOC con-centrations in river water are much lower in a steepwatershed than a flat watershed, resulting fromrelatively low water residence time in a steep wa-tershed (Ludwig & Probst 1996). Kao (1995) alsofound that annual POC flux was largely controlledby soil erodibility from Lanyang river in north-eastern Taiwan.

3.3. Seasonal patterns of estuarinehydrogeochemistry

Figure 8(a)–(c) shows the distributions of salinityprofiles in the Tsengwen estuary during dry, floodand wet seasons, respectively, in 1995. Seawaterintrusion reached approximately 22 km from theestuarine mouth upstream during the dry seasonwith very low flow. This distance was approxi-mately twofold that in the flood season whenseawater was pushed downstream and confined toa lower portion of the water column. Riverwatermixed fairly well with seawater in the estuaryduring the dry season, but was only partiallymixed during the flood period and wet season.Therefore, the flushing time of river water in theestuary, derived from the fraction of freshwatermethod (Asselin & Spraulding 1993), was sig-nificantly longer in the dry season (150 days) thanin the flood period (<1 day) and wet season(>4.5 days). Variable flushing time may influenceestuarine biogeochemistry as well. The estuary was


Fig. 8. Salinity profiles in the Tsengwen estuary during the dry season (a), flood season (b) and wet season (c) in 1995. The difference of

bathymetric patterns is caused from different sampling locations in different seasons.


generally in an oxygenated condition with dis-solved oxygen exceeding 150 lM. Sulfate reduc-tion may not be important in affecting the carbon

budget of the estuarine water. It should be noted,however, that sulfate reduction may be importantin the sediments of this estuary.

Fig. 9. TSM profiles in the Tsengwen estuary during the dry season (a), flood season (b) and wet season (c) in 1995.


Distributions of TSM also display contrastingpatterns according to seasons. The horizontalconcentration gradient increases toward the tur-bidity maximum from upstream and then de-creases away from it towards the river mouthduring the dry season (Figure 9(a)). The hor-izontal TSM distributions, however, indicate thatno turbidity maximum occurs during the flood(Figure 9(b)) and wet (Figure 9(c)) seasons, duringwhich the TSM generally decreases first down-stream and then increases again towards the rivermouth. As a result, TSM and POC are non-conservative in the estuary and significant portionsof TSM and POC are removed before they areexported out of the estuary.

3.4. Nutrient and organic carbon behaviors in theestuary

Because of the seasonal variations of flushing timeand elemental distribution, the behavior andtransformation of nutrients and organic carbon inthe estuary appear to vary seasonally. Distribu-tions of NH4

+ are apparently nonconservativeduring all seasons (Figure 10(a)). Distributions ofnitrate and nitrite also appear to be non-conservative but exhibit different patterns duringdifferent seasons (Figure 10(b)). Biological utili-zation would be principally responsible for es-tuarine removal of NH4

+ due to preferentialuptake of NH4

+ over nitrate. Nitrification may bealso important for NH4

+ removal in the estuary.This may also account for a slight production of(nitrate+nitrite) in the estuary during the dryseason. Significant nitrification may offset thebiological utilization and lead to an addition pat-tern in the estuary. However (nitrate+nitrite) ap-pears to be significantly and slightly removed,respectively, during wet and flood seasons, prob-ably due to biological uptake in the estuary, as theconcentration is lower in wet and flood seasonsthan in the dry season. DON distributions are alsoapparently nonconservative during all seasons(Figure 10(c)). Complete sets of DON distribu-tions in estuaries are rarely found for comparison,particularly in tropical regions. However, in thissystem biological utilization of DON may be re-latively small when DIN is abundant in the es-tuary.Both DIP and DOP behave nonconservatively

in the estuary, but nonconservative removals are

less distinct for DOP than for DIP (Figures 11(a)and (b)). As phytoplankton is a vital primaryproducer in this estuary (Wong S.-L, personalcommunication), variable levels of phosphorusremoval may occur in the estuary during variableseasons. Nonconservative DIP removals may in-dicate that the removals occur primarily throughbiological activity in addition to the mixing be-tween river water and seawater during dry and wetseasons. However, geochemical removal may belargely responsible for the significant DIP removalas estuarine water was very turbid and pro-ductivity was very low during the flood period.The increase of pH in the estuarine water may alsoenhance DIP adsorption. Another possibility isthat large input of organic matter may fuel themicrobial production and remove DIP sig-nificantly. Also, very short flushing time of freshwater in the estuary may lead to very low rate ofbiological carbon uptake during the short periodflood season. Smith (2001) pointed out that DDIPmay not be used as a proxy for net carbon flux forturbid estuaries where DIP adsorption onto theparticulate materials or desorption from them canbe significant. Nonconservative DIP flux in theflood period is excluded to reduce the uncertaintyof annual DIP budget. Phosphate removal is ofparticular interest as it is the likely limiting nu-trient as reflected from DIN/DIP ratios rangingfrom 16–45 in the estuary mouth to 75–225 in theupper estuary. Meanwhile, dissolved DIP removaldoes not take place in gas-phase exchange.Therefore, the nonconservative DIP removal isdue to biological metabolism and applied to cal-culate C—N—P biogeochemical budgets in theestuary during dry and wet seasons discussed inthe following section.DOC distributions display a quite conservative

behavior in the estuary (Figure 12(a)). DOC con-centrations range from 680 to 100 lM in the dryseason and are greater than those during flood andwet seasons (298–150 lM), likely resulting fromdifferent degrees of dilution by river water andseawater. This conservative behavior resemblesthose found in other estuaries in Taiwan (Hung1995) and those estuaries in temperate areas(Sharp et al. 1982; Mantoura & Woodward 1983;Norredin & Courtot 1989). The conservative be-havior suggests that the mixing process primarilycontrols DOC distributions in the Tsengwen es-tuary. Biological production and degradation of

J.-J . HUNG AND M.-H. HUANGJ.-J . HUNG AND M.-H. HUANG88

DOC may not be ruled out but may be on thesame magnitude.Degradation of labile DOC estimated from the

incubation experiment (data not shown for brev-ity) displays that less than 7% of DOC degradeswithin the flushing time of wet (4.5 days) and flood(1 day) seasons, but nearly 30% of DOC degradeswithin the flushing time (150 days) of the dryseason. Little biological removal and productionmay lead to a conservative distribution of DOC inwet and flood seasons. However, during the dry

season DOC is more labile and up to 30% may bebiologically consumed and supplied con-temporaneously to meet conservative distributionin the estuary. It is noteworthy that total DOCinflux is much smaller in the dry season thanin flood and wet seasons due to large differencein water discharge. The extent of POC degradationin the estuary is hard to evaluate but is expected tobe small during flood and wet seasons, as sus-pended sediment was transported out of the es-tuary within a short time. The ratio of DOC/DON

0 5 10 15 20 25 30 35

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30 35

0

20

40

60

80

100

120

140

wetflood

dry

Nitr

ate+

Nitr

ite (

µM)-

dry

0

4

8

12

16

20 Nitrate+

Nitrite (µM

)- flood & w

et

0 5 10 15 20 25 30 35

0

20

40

60

80

dry flood wet

DO

N (

µM)

Salinity

dry flood wet

NH

+ 4 (µM

)

(a)

(b)

(c)

Fig. 10. Distributions of NH4+ (a), nitrate (b) and DON (c) in the Tsengwen estuary during all seasons in 1995.


in the estuary varies only slightly over each season,ranging from ca. 9.5 at the river end-member to ca.8.0 at the estuarine mouth. As DOC is con-servative and DON is nonconservative in the es-tuary, estuarine DOC/DON ratios appear to bedetermined by mixing process between Tsengwenriver water (DOC/DON >10) and associatedcoastal seawater (DOC/DON <8) and by pro-cesses controlling DON distribution.Particulate organic carbon (POC) was trans-

ported nonconservatively in the estuary during allseasons (Figure 12(b)) because the heterogenousdistribution of TSM determines the distribution ofPOC. Estuarine POC concentrations markedlyexceed those in the coastal ocean, ranging from660 to 30 lM in the dry season, from 200 to60 lM in the flood period, and from 150 to 50 lMin the wet season. POC is more enriched in TSMduring the dry season (1.6–17%) than during theflood (0.57–4.6%) and wet (1.6–5.6%) seasons.

Apparently, the contribution of autochthonousPOC is more pronounced in the dry season than inflood and wet seasons. Using 29 and 19.5&(Schlesinger 1991) as terrestrial and marine end-members d13C values, respectively, the contribu-tion of autochthonous sources to total POC in theestuary amounts up to 70% during the dry season(Figure 12(c)). Despite failure in d13C determina-tion during sample pre-treatment, the contributionof autochthonous POC would be small duringflood and wet seasons as POC concentration (%)and POC/PN values (8.5–17) approach the rangesfound from agricultural soils in the Tsengwenwatershed.

3.5. Water and nutrient budgets in the estuary

The Tsengwen Estuary is a semi-enclosed systemwhere the Tsengwen river water meets and mixeswith seawater from the Taiwan Strait. Application

0 5 10 15 20 25 30 35

0.0

0.4

0.8

1.2

1.6

2.0

0 5 10 15 20 25 30 35

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0 dry flood wet

DO

P (

µM)

Salinity

dry flood wet

PO

3- 4 (

µM)

(a)

(b)

Fig. 11. Distributions of DIP (a) and DOP (b) in the Tsengwen estuary during all seasons in 1995.


of the LOICZ biogeochemical model for assess-ment of carbon metabolism in the estuary showsstrong seasonal variations in estuarine waterbudgets during 1995 (Table 1). The variable waterbudgets would result in significant variations ofcarbon and nutrient budgets.

DDIP are all negative and vary seasonally in 1995(Table 1). This indicates that DIP is removed fromthe estuary corresponding to nonconservative dis-tribution patterns during all seasons. The extent ofremoval is equivalent to 36% ()8.48 mol day)1),33% ()1185 mol day)1) and 32% ()226 mol -

0 5 10 15 20 25 30 35

100

200

300

400

500

600

700

c

0 5 10 15 20 25 30 35

-30

-28

-26

-24

-22

-20

δ C

(‰)

13

Salinity

0.0

0.2

0.4

0.6

0.8

1.0

ft

C- 13

f t

0 5 10 15 20 25 30 35

0

100

200

300

400

500

600

700 dry flood wet

PO

C (µ

M)

dry flood wet

DO

C (

µM)

(a)

(b)

(c)

Fig. 12. The abundance of DOC (a) and POC (b) in the Tsengwen estuary during all seasons in 1995. The distribution of d13C and the

fraction of terrestrial origin (ft = terrigenous POC/total POC) of POC during the dry season also displays in the figure 9c. The ft is

derived from measured riverine and marine end-member d13C values (d13Cmeasured = [d13Criver · ft] + [d13Cmarine · (1 ) ft)]).


day)1) of total inputs in dry, flood and wet seasons,respectively. The DDIP normalized by area are)0.002, )0.59 and )0.09 mmol m)2 day)1, respec-tively, for dry, flood and wet seasons. The largernegative value implies a larger internal sink, and theextent is apparently proportional to the extent ofriverine input. Because DDIP in the flood periodcan be largely derived from geochemical processesdiscussed in the preceding section, we do not applyDDIP data in (p)r) derivation for the flood period.Although the flood period is short (14 days), it mayincrease the uncertainty of annual (p)r) if a largeDDIP in the flood period ()0.59 mmol m)2 day)1)is considered for the annual budget. Nevertheless,DDIP in the flood period should be accounted for inthe estimate of annual net DIP flux out of the es-tuary which may be critical in determining coastalnet productivity. Following the same procedures,the nonconservative DOP flux is )0.005 (dry),+0.14 (flood) and )0.12 mmol m)2 day)1 (wet),suggesting the importance of DOP involved inbiological metabolism. Under the assumption oflow primary production, a positive DDOP in theflood season means that a significant DOP may bederived from the transformation of particulate or-ganic phosphorus (POP) buried in sediments.Nonconservative fluxes are different in value

and direction between DIN and DON during all

seasons (Table 1). During the dry season, DIN isadded to the estuary in addition to riverine inputwhile DON is removed from the estuary.Transformation between DON and NH4

+ in theestuary is possible. This results in a net internalsource of total dissolved nitrogen (DTDN =0.27 mmol m)2 day)1) in the estuary. During theflood and wet seasons, DIN is removed but DONis added to the estuary. This may be due to re-latively larger DIN and TSM (PON) fluxes in theflood and wet seasons than in the dry seasonfrom the river, and larger PON deposited in es-tuarine sediments during the flood and wet sea-sons than in the dry season. Subsequently, PONis decomposed and DON is released from sedi-ments. However, DIN and DON combinationsresult in net internal sinks of TDN for both floodand wet seasons.

3.6. Stoichiometric calculations of C-N-P budgets

The internal removal of DIP during dry and wetseasons suggests that a net DIC removal (seeEq. (2)) occurs if DDIP is assumed to transforminto POP completely. The particulate organic C:Pratio in the Tsengwen estuary was not measured,and the Redfield ratio (106) is adopted forstoichiometric calculation because phytoplankton

Table 1. Measured water, nitrogen and phosphorus budgets in the Tsengwen estuary during 1995.

Dry season (240 days) Flood season (15 days) Wet season (135 days)

Estuarine area (106 m2) 3.8 2.0 2.5

Qr (runoff) m3 day)1 13824 1956960 411264

QR(residual flow) (m3 day)1) )13 824 )1956960 )411264

Qx(exchange flow) (m3 day)1) )23 960 )2523448 )668304

DIP removal (mmol day)1) )8480 )1184476 )226000

DIP removal (% input) )36 )33 )32

DDIP (mmol m)2 day)1) )0.002 )0.59 )0.09DOP removal (mmol day)1) )19 917 +273974 )308963

DOP removal (% input) )50 +6.2 )29

DDOP (mmol m)2 day)1) )0.005 +0.14 )0.12

DIN removal (mmol day)1) +1299057 )62972000 )13097216

DIN removal (% input) +109 )22 )38

DDIN (mmol m)2 day)1) +0.34 )32 )5.2

DON removal (mmol day)1) )299937 +36900000 +412806

DON removal (% input) )23 +17 +0.75

DDON (mmol m)2 day)1) )0.08 +18 +0.17

P–r (DDICO) (mmol m)2 day)1) 0.21 – 9.5

nfix–denit (mmol m)2 day)1) 0.37 – )1.7

J. -J . HUNG AND M.-H. HUANGJ.-J . HUNG AND M.-H. HUANG92

is the primary producer in the estuary (WongS.-L., personal communication). The net DIC re-moval from the water column of estuary is esti-mated to be 0.21 and 9.5 mmol m)2 day)1,respectively, for the dry and wet seasons in 1995.Experimental results also show that there is a netnitrogen fixation (0.37 mmol m)2 day)1) duringthe dry season but a net denitrification during thewet ()1.7 mmol m)2 day)1) season in 1995. Theestuarine (nfix)denit) appears to vary with theinput of total inorganic nitrogen; greater nitrogeninput may result in higher denitrification rate.Annual budgets of )DICo (1.5 mol m)2 year)1)and net denitrification (0.17 mol m)2 year)1) in1995 are calculated from daily budgets and timespan in each season.The net ecosystem metabolism (p)r) is

positive but smaller in Tsengwen Estuary(1.5 mol m)2 year)1) than in Tokyo Bay(4.85 mol m)2 year)1, Yanagi 1999) and HakataBay (10.1 mol m)2 year)1, Yanagi 1999) in Japanand the Lingayen Gulf (6 mol m)2 year)1, Dupraet al. 2000) in Philippines, but the (p)r) is higher inTsengwen Estuary than in Bandon Bay(0.02 mol m)2 year)1, Wattayakorn et al. 2001) inThailand. Many environmental factors (e.g. annualtemperature, water residence time, nutrient andorganic matter loads) may affect the magnitude ofpositive (p)r) value in various systems. In general,the tropical system with large inputs of nutrientsand organic matter and relatively short residencetime tend to possess a small value of (p)r) as thehigh productivity rate is usually accompanied by ahigh respiration rate. On the other hand, our resultsare opposite to those observations from TomalesBay ()6.06 mol m)2 year)1, Smith et al. 1991) inUSA and Manila Bay ()2 mol m)2 year)1, Dupraet al. 2000) in Philippines. The Manila Bay is actu-ally separated into inner and outer bays. The innerbay is autotrophic (+6 mol m)2 year)1) and outerbay is heterotrophic ()8 mol m)2 year)1 ). It ap-pears that the organic matter produced in the innerbay supports the decomposition of organic matterin the outer bay. Additional organic matter may bederived from sediment for decomposition (Dupraet al. 2000). Relatively high value of net respirationrate for the Tomales Bay may be supported bysufficiently exogenous supply of organic matter,slow water exchange between bay and ocean, andsignificant sulfate reduction rate in the bay (Smithet al. 1991). As the Tsengwen estuary is oxygenated

throughout the year, the contribution of sulfate re-duction to nonconservative flux of total dissolvedinorganic carbon (DDICt) in the water column canbe regarded as minimal, although the sulfate re-duction could be an important process in anaerobicsediments. Theuptake rate of atmosphericCO2maybe estimated as the rate of 17.8 g C m)2 year)1 in1995 provided the chemical dissolution of carbo-nate is negligible in the estuary. The net deni-trification rate is smaller than those in Tomales Bay,Hakata Bay and Manila Bay listed in Table 2. Thiscould be due to shorter inwater residence time in thewet season with abundant DIN input for theTsengwen estuary than inTomales Bay,Hakata bayand Manila Bay.

4. Conclusions

(i) Riverine fluxes of organic carbon and nu-trients are highly seasonally variable; pri-marily due to seasonal variations of waterdischarge and sediment load. The long-termaverage sediment yield in the drainage basin ishigh (9379 tonne km)2 year)1) but the sedi-ment yield decreases after dam construction.Relatively low sediment yield during the studyperiod (616 tonne km)2 year)1) is causedfrom damming effect and a very low waterdischarge (5.02 m3 s)1) in 1995.

(ii) Removals and/or additions of sediment, or-ganic carbon and nutrients from the estuaryare also seasonally variable. Despite a largeextent of DDIP in the estuary occurs duringthe flood period, this DDIP is not included inthe annual (p)r) calculation primarily due toits derivation mainly from geochemical pro-cesses. Microbial uptake and rapid particlescavenging and deposition in sediments maybe responsible for DIP removal.

(iii) About 30% of riverine DIP was removed fromthe estuary during all seasons. The DDIP is)0.002 and )0.09 mmol m)2 day)1, respec-tively, for the dry and wet season; the estuar-ine system is apparently autotrophic andannual (p)r) is 1.5 mol m)2 year)1 in 1995.

(iv) Both DIN species and DON behave non-conservatively in the estuary. Denitrificationgenerally exceeds nitrogen fixation in 1995()0.17 mol m)2 year)1).


Acknowledgements

The authors would like to thank reviewers for theconstructive comments and the National ScienceCouncil of Republic of China for the financialsupport of this study under Contract NOs. NSC85-2621-P-110-03, NSC 86-2621-P-110-005 andNSC 87-2621-P-110-002. We are also grateful forF. Kuo and H.-J. Chang in sampling and analy-tical assistance.

References cited

Abril GM, Nogueria M, Etcheber H, Cabecadas G, Lemaire E,

Brogueira MJ. 2002 Behavior of organic carbon in nine

contrasting European estuaries. Estuarine, Coastal and Shelf

Science 54, 241–262.

Asselin S, Spraulding ML. 1993 Flushing times for the

providence river based on tracer experiments, Estuaries 16,

830–839.

Billen G, Lancelot C, Meybeck M. 1991 N, P, and Si Retention

along the Aquatic Continuum from Land to Ocean, in:

Mantoura RFC, Martin, J.-M. and Wollast R. (eds), Ocean

Margin Processes in Global Change,Wiley, NewYork, pp. 19–

44.

Borum J. 1996 Shallow water and land/sea boundaries, in:

Jorgensen BB. and Richardson K. (eds), Eutrophication in

shallow coastal marine ecosystems, American Geophysical

Union, pp. 179–203.

Church TM. 1986 Biogeochemical factors influcening the

residence time of microconstituents in a large tidal estuary,

Delaware Bay, Marine Chemistry 18, 393–406.

Crawford CG. 1991 Estimation of suspended-sediment rating

curves and mean suspended sediment loads, Journal of

Hydrology 129, 331–348.

Degens ET. 1989 Perspectives on Biogeochemistry, Springer-

Verlag, Berlin.

Dupra V, Smith SV, Crossland Marshall JI, Crossland CJ. 2000

Estuarine systems of the South China Sea region: carbon,

nitrogen and phosphorus fluxes, LOICZ Reports & Studies

No. 14, LOICZ, Texel, The Netherlands.

Eyre BD, Ball PW. 1999 A comparative study of nutrient of

nutrient processes along the salinity gradient of tropical and

temperate estuaries. Estuaries 22, 313–326.

Eyre BD, McKee LJ. 2002 Carbon, nitrogen, and phosphorus

budgets for a shallow subtropical coastal embayment

(Moreton Bay, Australia), Limnology and Oceanography 47,

1043–1055.

GESAMP. 1987 Land/sea boundary flux of contamintants:

Contributions from rivers. GESAMP Reports and Studies No.

32, Unesco.

Gordon DC, Boudreau PR, Mann KH, Ong J.-E, Silvert WL,

Smith SV, Wattayakorn G, Wulff F, Yanagi T. 1996 LOICZ

Biogeochemical Modelling Guidelines. LOICZ Reports &

Studies No.5, LOICZ, Texel, The Netherlands, 96 pp.

Grasshoff K, Ehrhardt M, Kremling K. 1983 Methods of

Seawater Analysis, 2nd ed, Chemie: Verlag, 419 pp.

Howarth RW, Billen G, Swaney D, Towsend A, Jawarski N,

Lajtha K, Downing JA, Elmgren R, Caraco N, Jordon T,

Berendse F, Freney J, Kudeyarov V, Murdoch P, Zhu ZL.

1996 Regional nitrogen budgets and riverine N&P fluxes

for drainage to the North Atlantic Ocean: Natural and

human influences, Biogeochemistry 35, 75–139.

Hung JJ. 1995 Terrigenous inputs and accumulation of trace

metals in the southeastern Taiwan Strait, Chemistry and

Ecology 10, 33–46.

Hung JJ, Lin PO. 1995 Distribution of dissolved organic carbon

in the continental margin off northern Taiwan, Terrestrial,

Atmospheric and Oceanic Sciences 6, 13–26.

Hung JJ, Shy CP. 1995 Speciation of dissolved selenium in the

Kaoping and Erhjen rivers and estuaries, southwestern

Taiwan, Estuaries 18, 234–240.

Hung JJ, Lin CS, Hung GW, Chung YC. 1999 Lateral

transport of lithogenic particles from the continental margin

of the southern East China Sea, Estuarine, Coastal and Shelf

Science 49, 483–499.

Hydes DJ, Kelly-Gerreyn BA, Le Gall A, Proctor R. 1999 The

balance of supply of nutrients and demands of biological

production and denitrification in a temperate latitude shelf

sea- A treatment of southern north sea as an extended

estuary, Marine Chemistry 68, 117–131.

Hydrological Year Book of Taiwan. 1995 Water resources

planning commission, 400 pp.

Hydrological Year Book of Taiwan. 1997 Water resources

planning commission, 416 pp.

Table 2. Comparison of annual carbon and nitrogen budgets between the Tsengwen estuary (1995) and other reported estuarine

systems.

Variable Location Reference

p–r (mol C m)2 year)1) nfix–denit (mol N m)2 year)1)

+1.5 (1995) )0.17 (1995) Tseng wen estuary This study

)6.06 )1.42 Tomales Bay, USA Smith et al. (1991)

+10.1 )0.27 Hakata Bay, Japan Yanagi et al. (1999)

+0.5 +0.07 Spencer Gulf Australia Gordon et al. (1996)

+6 +0.5 Lingayen Gulf, Philippines Dupra et al. (2000)

)2 )1.1 Manila Bay, Philippines Dupra et al. (2000)

+0.02 +0.08 Bandon Bay, Thailand Wattayakorn et al. (2001)


IGBP. 1995 Land-ocean Interactions in the coastal zone:

Implementation plan, IGBP Report No. 33, Stockholm.

Ittekkot V, Laane RWPM. 1991 Fate of riverine particulate

organic matter, in: Degens ET, Kempe S, Richey JE. (eds),

Biogeochemistry of Major World Rivers, John Wiley, New

York, pp. 233–234

Jensen HS, Mortensen PB, Andersen FO, Rasmussen E, Jensen

A. 1995 Phosphorus cycling in a coastal marine sediment,

Aarhus Bay, Denmark, Limnology and Oceanography 40(5),

908–917.

Kao S.-J. 1995 The Biogeochemistry of Carbon on an Island of

High Denudation Rate: a Case Study of the Langyang His

Watershed, Ph.D. Thesis, National Taiwan University,

Taiwan.

Kao S.-J., Liu K.-K. 1996 Particulate organic carbon export

from a subtropical mountainous river (Langang His) in

Taiwan, Limnology and Oceanography 41(8), 1749–1757.

Kemp WM, Smith EM, Marvin-DiPasquale M, Boynton WR.

1997 Organic carbon balance and net ecosystem metabolism

in Chesapeake Bay,Marine Ecology Progress Series 150, 229–

248.

Kempe S. 1995 Coastal seas: a net source or sink of

atmospheric carbon dioxide. LOICZ Reports & Studies

No.1. LOICZ, Texel, The Netherlands.

Li YH. 1976 Denudation in Taiwan island since the pliocene

epoch, Journal of Geology 4, 105–107.

Lin H.-J., Shao K.-T., Kuo S.-R., Hsieh H.-L., Wong S.-L.,

Chen I.-M., Lo W.-T., Hung J.-J. 1999 A trophic model of a

sandy barrier lagoon at Chiku in southwestern Taiwan.

Estuarine, Coastal and Shelf Science 48, 575–588.

Liu JT, Yuan PB, Hung JJ. 1998 The coastal transition at the

mouth of a small mountainous river in Taiwan, Sedimentol-

ogy 45, 803–816.

Ludwig W, Probst J.-L. 1996 Predicting the oceanic input of

organic carbon by continental erosion, Global Biogeochemical

Cycles 10, 23–41.

Malone TC, Conley DJ, Fisher TR, Glibere PM, Harding

LW.Jr., Sellner KG. 1996 Scales of nutrient-limited phyto-

plankton productivity in Chesapeake Bays, Estuaries 19, 371–

385.

Mantoura RFC, Woodward EMS. 1983 Conservative behavior

of riverine dissolved organic carbon in Severn Estuary:

Chemical and geochemical implications. Geochimica Cosmo-

chimica Acta 47, 1293–1309.

Meybeck M. 1982 Carbon, nitrogen, and phosphorus

transport by world rivers. American Journal of Science

282, 401–450.

Meybeck M. 1993 C, N, P and S in rivers: from sources to

global inputs, in: Wollast, R. Mackenzie, F.T., Chou, L.

(eds), Interactions of C, N, P and S Biogeochemical Cycles and

Global Change, Springer-Verlag, Berlin, pp. 163–191.

Meybeck M, Ragu A. 1996 River discharge to the oceans: an

assessment of suspended solids, major ions, and nutrients,

UNEP/WHO, Environment of Information and Assessment

Div., UNEP, Nairobi, 245 pp.

Milliman JD, Meade RH. 1983 World-wide delivery of river

sediments to the oceans, Journal of Geology 91, 1–21.

Milliman JD, Syvitski PM. 1992, Geomorphic/tectonic control

of sediment discharge to the ocean: the importance of small

mountainous rivers, Journal of Geology 100, 525–544.

Moran MA, Sheldon WM. Jr., Sheldon JE. 1999 Biodegrada-

tion of riverine dissolved organic carbon in five estuarine of

the southeastern United States, Estuaries 22, 55–64.

Norredin S, Courtot P. 1989 Conservative behavior of humic

substance (DHS) in a macrotidal estuary. Composition of

particulate and dissolved phases, Oceanologica Acta 12, 381–

393.

Pai SC, Yang CC, Riley JP. 1990 Formation kinetics of the

pink azo dye in the determination of nitrite in natural waters,

Analytica Chimica Acta 232, 345–349.

Pernetta JC, Milliman JD. (eds). 1995 Land-Ocean Interactions

in the Coastal Zone Implementation Plan, IGBP Report No.

33, Stockholm, Sweden, 215 pp.

Ridal JJ, Moore RM. 1990 A re-examination of the measure-

ment of dissolved organic phosphorus in seawater, Marine

Chemistry 29 19–31.

Schlesinger WH. 1991, Biogeochemistry: an analysis of global

change. Academic Press, San Diego, pp. 226–297.

Sharp JH, Culberson CH, Church TM. 1982 The chemistry of

the Delaware estuary. General considerations, Limnology and

Oceanography 27, 1015–1020.

Sheh C.-S., Wang M.-K. 1989 An Introduction to the Soils of

Taiwan, National Chung-Hsing University, Taichung, Tai-

wan, 205 pp.

Smith SV, Hollibaugh JT, Dollar SJ, Vink S. 1991 Tomales Bay

metabolism: C-N-P stoichiometry and ecosystem heterotro-

phy at the land-sea interface, Estuarine, Coastal and Shelf

Science 33, 223–257.

Smith SV, Hollibaugh JT. 1993 Coastal metabolism and the

oceanic organic carbon balance, Reviews of Geophysics 31,

75–89.

Smith SV, Hollibaugh JT. 1997 Annual cycle and interannual

variability of ecosystem metabolism in a temperate climate

embayment, Ecological Monograph 67, 509–533.

Smith SV. 2001 Carbon-nitrogen-phosphorus fluxes in the

coastal zone: the LOICZ approach to global assessment, and

scaling issues with available data. LOICZ Newsletter No. 21,

LOICZ, Texel, The Netherlands.

Swaney DP, Howarth RW, Butler TJ. 1999 A novel approach

for estimating ecosystem production and respiration in

estuaries: application to holigohaline and mesohaline Hud-

son River, Limnology and Oceanography 44:1509–1521.

Wattayakorn G, Prapong P, Noichareon D. 2001 Biogeochem-

ical budgets and processes in Banton Bay, Suratthani,

Thailand, Journal of Sea Research 46, 133–142.

Yanagi T. 1999 Seasonal variations in nutrient budgets of

Hakata Bay, Journal of Oceanography 55, 439–448.

You C.-F., Lee T, Brown L, Jiusan J, Chen JC. 1988, 10Be study

of rapid erosion in Taiwan, Geochimica Cosmochimica Acta

52, 2687–2691.


seasonal variations of organic-carbon and nutrient ... · degradation of doc and poc within the...

Documents