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A material flux study in the Karnaphuli River estuary has been started and expected to be carried

out for at least two consecutive seasonal cycles covering premonsoon, monsoon and postmonsoonseasons. This paper presents interim budgets of water, salt and nutrients for this estuary for the

late monsoon season using the LOICZ Biogeochemical Modelling Guidelines (Gordon et al,1996) based on preliminary field work and analyses accomplished so far.

A 17.5 km2 segment of the estuary with an average depth of about 10m is selected for the present

study (Figure 1).

Sampling and analysis

Inner and outer segments of the Karnaphuli River estuary were sampled during the late monsoonof 2002 for nutrients (NO3

-, NO2-, NH4

+, PO4- and SiO2

-) and other water quality parameters as a

part of an ongoing material flux study. Water samples were collected, preserved, transported andanalyzed following standard procedure (Barnes, 1959; Strickland and Parsons, 1965; Parsons and

Stickland, 1968; APHA, 1975; Jin-Eong et al, 1985). Average from several samples for eachparameter was used in this budgeting exercise. Rainfall data were collected from Bangladesh

Meteorological Department and discharge values were interpolated from a previous work in thesame estuary (Monwar, 2001). Evaporation was calculated from other atmospheric data. Rainfall,estimated evaporation and interpolated discharge were 83.52, 34.26 and 6.47 million m3/day

respectively. Groundwater exchange and outfall were assumed to be negligible. Salinity andnutrient data used in this budgeting exercise are shown in Table 1.

Table 1: Chemical composition of water samples from Karnaphuli river estuary

Salinityppt

DIPmmol/m3

NO3-

mmol/m3NO2

-

mmol/m3NH4

+

mmol/m3DIN

mmol/m 3

Inner segment 3.92 293.92 4.93 0.73 1.71 7.37

Outer segment 17.9 179.44 6.16 0.44 1.04 7.64

Water and salt budget

No significant vertical stratification in salinity was observed and a single layer system is

conceived. Results of the water and salt budgeting are shown in Figure 2.

Figure 2: Water and salt budget for the Karnaphuli River estuary

VSyst = 175

VP = 4.85VE = -1.58

VQ = 0.003

VG = VO = 0

(assumed)

VR = -3.28 SSyst = 3.92SOuter = 17.9SQ = 0

VGSG = 0

VX(SOuter-SSyst) = +35.7VX = 2.56

VRSR = -35.7

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NP budget

The one layer single box DIP and DIN budgets for the Karnaphuli River estuary system are

shown in Figure 3.

Figure 3: DIP (left) and DIN (right) budget for the Karnaphuli River estuary (fluxes in 106

mmol/day)

DIP Syst=293.92 mmol/m

DIPatm = 0 (assumed)

DIP Q = 0VQ DIPQ = 0

VG DIPG =VQ DIPQ = 0(assumed)

VR DIPR = -775

3

DIPOuter = 179.44DIP R = 236.68

VX(DIPOuter- DIPSyst)= -293

DIP = +1,070

DINSyst=7.37 mmol/m

DINatm = 0 (assumed)

DIN Q = 0VQ DINQ = 0

VG DING =VQ DINQ = 0(assumed)

VR DINR = -24.6

3DINOuter = 7.64

DINR = 7.51

VX(DINOuter- DINSyst)= 0.69

DIN = +23.9

Stoichiometric calculations of aspects of Net System Metabolism

Positive P values could be attributed to a net production of DIP within the system and suggests

that the estuary is mainly heterotrophic. Based on Redfield N:P ratio of 16:1, DINexp and (nfix-

denit) was calculated. Table 3 summarizes the ecosystem metabolism. High negative values of

(nfix-denit) suggests an actively denitrifying system in the Karnaphuli River estuary.

Table 3: Estimated rates of nonconservative DIN fluxes and (nfix-denit)

DIP DINobs DINexp (nfix-denit)

mmol/m2 /day 61.03 1.37 976.48 -975.11

106

mol/day 1.07 0.0239 17.12 -17.06

References

APHA 1975. Standard Methods for the examination of water and waste water, 14th ed. AmericanPublic Health Association, Washington D.C., 1193pp.

Barnes H. 1959. Apparatus and Methods of Oceanography (Chemical). Vol.1. London and N.Y.,

Acad. Press.341pp.

Gordon, D.C.,Jr., Boudreau, P.R., Mann, K.H., Ong, J.E., Silvert, W.L., Smith, S.V.,

Wattayakorn, G., Wulff, F. and Yanagi, T. 1996. LOICZ Biogeochemical ModellingGuidelines. LOICZ Reports and Studies 5. 96pp.

Jin-Eong, O., Wooi-Khoon, G., Chee-Hoong, W. and Din, Z.B.H. 1985. Productivity of the

Mangrove Ecosystem: a Manual of Methods. Mangrove Ecosystem Research Group,Universiti Sains Malaysia. 117pp.

Monwar, M. 2001. Flow and discharge characteristics in the Karnaphuli River estuary. In-term

Research Paper. Institute of Marine Sciences, Chittagong University, Bangladesh.

Parsons, J.D.H. and Strickland, T.R. 1968. A practical hand book of Sea water Analysis. Bull.Fish. Res. Bd. Com. 167-311p.

Strickland, J.D.H. and Parson, T.R. 1965. A Manual of Sea water analysis. Bulletin No.125. Fisheries Res. Board of Canada, Ottawa.