Indian Journal of Marine Sciences Vol. 28, Decemb\!r 1999, pp. 345-354

Distribution of nutrients and major elements in riverine, estuarine and adjoining coastal waters of Godavari, Bay of Bengal

D Padmavathi & D Satyanarayana

Chemical Oceanography Division, School of Chemistry, Andhra University, Visakhapatnam 530 003, AP, India

Received 19 June 1998, revised 6 September 1999

Studies on the hydrographical parameters (salinity, temperature and dissolved oxygen) indicated distinct spati<ll and temporal variations. Nutrients (NO)-N, NH4-N, P04-P and Si04-Si) in general, exhibited a decreasing trend from riverine to estuarine and coastal region indicating their dominant occurrence with river water. This was also supported by relati vely higher levels in September (monsoon) when compared with January/February (postmonsoon) and May (premonsoon). Nutrients showed in general, an increasing trend from surface to the bottom particularly at farthest stations in the coastal region, which was due to their uptake at surface and remineralisation in the water column. All the nutrients exhibited distinct non-conservative behaviour with a net removal of 26-36% for silicon, 19-24% for ammonium, 14-16% for nitrate and 4-18% for phosphate. This was attributed to the combined effects of biological uptake by phytoplankton and desorption from the suspended particulates. Major elements (F, B, Ca and Mg) indicated an increasing trend from riverine to estuarine and shelf regions. They exhibited higher concentration in May followed by January/February and September and were predominanHn seawater. Fluoride showed non-conservative behaviour with a net removal of 13 'and 10% during September and May respectively and conservative behaviour in January/February. While the former was attributed to its adsorption on suspended solids in September and biological uptake in May, the latter was explained on the basis of simple physical mixing of seawater with fresh water. Boron showed non-conservative behaviour with a net removal of 12 to 19% which was attributed to its adsorption on to the suspended matter containing river borne clay minerals. Calcium and magnesium showed conservative behaviour in May and semi-conservative behaviour during September and January/February with a small net addition and removal respectively, in the latter. While the net addition in September may be due to their exchange with other cations during early stages of mixing, the removal during January/February is believed to be due to their involvement in the biological and/or geochemical processes. Estimation of nutrient and major elemental tluxes from Godavari river into the Bay of Bengal indicated their predominant input in monsoon (June-November) than non-monsoonal (December-May) period.

Estuaries constitute a major interface between land and the oceans and have been regarded as one of the most important aquatic systems. Distribution of chemical constituents in estuarine environment is controlled by physical, chemical and biological processes since they govern the fate and net fluvial transport of weathered material from continents to the oceans. Studies on the distribution and behaviour of dissolved constituents such as nutrients and major elements in riverine, estuarine and coastal regions are therefore important for assessing river inputs into the oceans. The Godavari river and its distributaries (Gauthami, Vainateyam and Vasishta) constitutes the second biggest river-estuarine system along the east coast of India, next only to the Ganga-Brahmaputhra river system. The Godavari drains over an area of 3.1x105 km2 and has a mean annual discharge at the delta apex! (Dowleswaram) of 1.05xlOI4 lit. Few physico-chemical studies such as salinity, temperature and current distribution2

-4, diurnal variation5.6

(salinity, temperature and nutrients), behaviour of silicon, calcium, magnesium and fluoride 7.8 in Gauthami, and seasonal variation of nutrients9

.lo in

Vasis~ta have been reported earlier in Godavari estuary. However, no systematic studies have been carried out so far on the hydrography, distribution and behaviour of nutrients and major elements in the riverine, estuarine and the adjoining coastal region of Godavari. In view of this a detailed study has been undertaken to assess their behaviour during estuarine mixing and to estimate their fluxes from Godavari river into the Bay of Bengal.

Materials and Methods Water samples were collected 111 May

(premonsoon), September (monsoon) and lanuarylFebruary (postmonsoon) during 1993-1995 in the riverine (sts. R1-R7), estuarine (Gauthami sts. E1-

E2 and E2A; Vainateyam sts.Er E4: Vasishta sts . ErE7) and coastal (Bhairavapalem sts. C I-C4:

346 INDIAN 1. MAR. SCI., VOL., 28, DECEMBER 1999

Vadalarevu sts. C5.C8; Antarvedi sts. C9-C 12) regions off Godavari (Fig. I). A large number of intermediate stations (not shown in the figure) were selected to follow the tidal influence on salinity and nutrients in the estuarine regions . On each coastal transect, water samples were collected at 10, 20, 30 and 50 m depth contours. Temperature and salinity were measured using Hydro-Bios in situ salinometer (T-S Bridge Type, MC5). Dissolved oxygen was fix:ed immediately after collection and then determined by modi'fied Winkler's method 1 I . Pi Itered sea water samples (Millipore, 0.45 !Jm dia.) were employed for estimation of nutrients and major elements. Nutrients (N03-N, NH4-N, P04-P and Si04-Si) were determined by standard photometric methods as described in Grasshoff'2 within 12 hours of the sample collection : Fluoride and boron were determined spectrophotometrically using lanthanum-alizarin comlexone l3 and curcumin l4 respectively. Total Ca and Mg were estimated by a complexometric titration with standard EDTA solution using Eriochrome Black-T as indicator. Calcium was then estimated separately with standard EGT A solution using Zincon as indicator'5. The EGTA titre value was corrected by multiplying with a factor of 0.989 in computing the Ca concentration. The amount of Mg was computed from the difference in the two titre values. The Mg value so obtained was corrected by multiplying with a factor of 1.6% in order to account for the error involved in the above method l5 as suggested by Carpenter & Manella'6. The precision obtained by replicate (six) analyses and expressed as standard deviation are nitrate : ±0.29; ammonium: ±0.08; phosphate: ±O.09; silicon: ±0.05 ; F: ±0.04; B: ±0.34; Ca and Mg: ±0.01.

Results and Discussion

Spatial and temporal variations Salinity (surface, bottom, overall) showed an

increasing trend from riverine to estuarine and coastal region during the study period (Fig. 2). The surface (average) salinity was higher in May than JanuarylFebruary and lower in September which was attributed to the combined effects of high insulation and cessation of river water influx in May and high river water influx coupled with intense precipitation in September. Further, it showed an increasing trend form surface to bottom in estuarine and coastal regions. The average surface to bottom gradient in the

17" 0 '

N

t

Fig. I-Station locations

estuarine region (sts. E 1-E7) was high in September (7 .78x 10-3

) than January/February (2. 73x I 0-1) and

May (2.l2x 10-3) . This can be attributed to fairly high

river discharge in September (161.26x 111(, I it.sec -I )

resulting in a partially mixed type of estuarine

systems. However, the river water discharge in January/February (14.32x 106 I it.sec -I) and May

(5.82xI06 lit.sec- I) decreases significantly and

becomes almost negligible leading to dominant tidal effect, thus making them well mixed type of estuaries'. This was also reflected on the total flushing time of fresh water in the estuaries which were computed from the salinity distribution data l7

.

The maximum (43.01, 4.05, 26.48 tidal cycles) and minimum (2.8, 0.78, 1.79 tidal cycles) flushing times obtained in the study area (Gauthami, Vainateyam and Vasishta estuaries) during May and September were in accordance with the minimum (5.8xI06

Iit.sec-') and maximum (161.26x 106 lit.sec- I) river

discharges during these two months respectively thus indicating an inverse relationship between total

flushing time and the river discharge4.

j

, I

)

\a

PADMA V ATHI & SA IT ANARA Y ANA: NUTRIENTS & ELEMENTS IN GODAVARI WATERS 347

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SURFACE MAY SEP JAN,ffEB MAY SEP JANjFEB

BOTTOM OVERALL

Fig.2-Temporal and spatial variation of temperature, salinity and dissolved oxygen in riverine, estu arine and coastal waters of Godavari .

Fluoride, B, Ca and Mg exhibited increasing trends from riverine to estuarine and to coastal waters like that of salini ty . The average (surface, bottom and overall) concentration of all of them in estuarine and coastal waters followed the order May > January/February > September in the study area (Fig. 3). Relatively high concentration levels during May was due to the negligible river discharge and intrusion of seawater into the estuary to a greater extent by tidal effect coupled with well-mixed conditions. However, the concentration levels of F, B, Ca and Mg remained almost same at surface and bottom waters in riverine region, reSUlting in no significant variation in their overall concentration (Fig. 3). Significant (probability, P<O.OOI) positive correlations obtained between chlorinity and major elements (Fig. 4) suggest that they were predominantly of marine origin . Lower concentration in September was due to the high influx of fresh water from the river. They showed an increasing trend from surface to bottom which indicates the effect of fresh water influx in the surface waters.

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Fig.3-Temporal and spatial variation or F. B. Ca anel Mg in riverine. estuarine. and coastal waters of Godavari.

Temperature, dissolved oxygen (~O) and nutrients showed a decreasing trend from riverine to estuarine and coastal regions (Figs 2, S) thus ex hibiting an inverse relationship to salinity . This was also reflected in the significant negati ve corre lations obtained between 0 0 and salinity in the study area (May: -0.60 at P=O.O I, September: -0.67 at P=O.OO I and January/February : -0.59 at P=O.O I, and between nutrients and chlorinity (Fig. 6) . Temperature was relatively high in May (coinciding with summer) and low in January/February (coinciding with winter) with intermediate values in September wh ich was in accordance with the vanat lon ' of atmospheric temperature9

• Temperature showed a decreasing trend from surface to bottom in May and September. However, in January/February it exhibited a decrease

348 INDIAN 1. MAR. SCI., VOL., 28, DECEMfJER 1999

® <e ® :::' 1280

SEP JAN/FEB , r=;/ Ol .::t:

. ~960

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-3 CHLORINITY ( X 10 )

0--0 GAUTAMI ~ VAINATEYAM lr-t!. VASISHTA

Fig.4--Relationship between chlorinity and F, B, Ca and Mg in Gauthami, Vainateyam and Vasishta estuaries.

from surface (24.5°C) to middle (24:2°C) followed by an increase to bottom (24.6°C) at Bhairavapalem (st. C, j,a decrease from surface (24.7°C) to middle (24.4°C) followed by an increase to bottom (24.6°C) at Vadalarevu (sts. C7 and Cg), and a continuous increase form surface (23.6°C) to bottom (24.2°C) at Antarvedi (sts. C" . and C12) transect, indicating thermal inversion which was attributed to advictive

processes. Such temperature inversion leadi ng to sinking of surface waters near the coast was reported

earlier off Visakhapatnam coast IX- 20. The average concentrations of DO were relati vely high in January/February followed by September and May (Fig. 2). While the former was attributed to the combined effects of winter cooling and high photosynthetic activity leading to increase in DO in

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PADMAVATi-li & SATY ANARAYANA: NUTRIENtS & ELEMENTS IN GODAVARI WATERS 349

;;' 45Q 'E ~ 360

~ 270 :1. Z 180

8 ...J 90

ill RIVER

~ 0 LJJ..I:a..Jw.:..,-""",,

.. ';'-6 5.5

~ 4.4

. ~ 3.3

~ 2.2

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~ 5.4

~ ~ 3.6 ;;;)

b 1.8

~ 0 LW!&.IJ.I!IIuwa

~ 7.5

ill ESTUARV I COAST

Fig.S-Temporal and spatial vari ation of nutrients in riverine, estuarine and coastal waters of Godavari .

January/February, the latter was due to the decrease of its solubility because of increase in temperature and salinity of the water column during May.

The average (surface, bottom and overall) concentration of nutrients followed the order September> January/February > May in the study area (Fig. 5) . Relatively high concentration in September can be attributed to the combined effects of precipitation and river runoff. Lowest

. concentration observed in May may be due to their utilisation by phytoplankton in estuarine and coastal waters. They exhibited a decreasing trend from head to the mouth of each estuary particularly during September indicating their predominant freshwater origin . The vertical distribution of nutrients in the coastal region particularly at the farthest stations, showed a decreasing trend from surface to mid depth (up to 20 m) followed by an increase up to bottom (50 m) . Surface depletion and bottom enrichment thus suggest their involvement in the biogeochemical

cycles namely uptake by phytoplankton during photosynthesis at surface and regeneration in the water column through combined effects of microbial decomposition, biochemical oxidation of organic matter, and remobilisation into the overlying waters from the sediment-water interface .

Behaviour of nutrients and major elements during estuarine mixing

Based on the concept of theoretical dilution line (TDL)21, the behaviour of dissolved nutrients and major elements in all the three estuarine systems of Godavari has been investigated in detail. All nutrients (NO.1-N, NH4-N, P04-P and SiOrSi) exhibited non­conservative behaviour in the three estuaries, where the experimental data points showed distinct deviations from TDL at all chlorinities (Fig. 6). The extent of removal or addition of the nutrients were calculated using the equation 22

.

PA / PR = 100 [( (Pm / Pth) -I )]

where PA / PR = percentage addition / percentage removal of the constituent, Pm = measured concentration of the constituent and Pth = theoretical concentration of the constituent obtained from regression equation . The extent of (net) removal of nutrients varied from 26 to 36% for silicon , 19 to 24% for ammonium, 14 to 16% for nitrate and 4 to 18% for phosphate in different months. While the removal of nutrients in general , was attributed to their biological uptake.23

.24 and adsorption on suspended

solids25.26

, the addition was attributed to their mineralisation in the water column and transport across the sediment-water interface17

. Higher percentage removal of silicon observed in the present study, during May and September than January/February can be attributed to its uptake by organism (diatoms) and adsorption on suspended solids. Earlier investigations on the behavior of silicon indicated its non-conservati ve behavior with a net removal of 1 1-41 % in Gauthami Godavari which was attributed to its biological uptake7

.x. Similar non­

conservative behavior with significant removal of silicon was reported in Vellar2~ , Mandovi-Zuari ]') , Cochin backwaters.1

O, Mahanadi1 1, Ganges 32 and

RushikulyaJ.1 estuaries. The extent of removal of NH4-

N was relatively high in May (24%) than September and January/February which may be due to the high standing crop of phytoplanktonJ4

• The net removal of

350 INDIAN J. MAR. SCI., VOL., 28, DECEMBER 1999

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b:1 0.045

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CHLORINITY ( X 1 O~3 )

o 5 10 15 20

0----<) GAUTAMI ~ VAINATEYAM fr--t:. VASISHTA

Fig.6-Relationship between chlorinily and nutrients in Gauthami , vainateyalll and Vasishta estuaries,

NOrN was relatively high (14-16%) at low

chlorinites (O-lOx 1 0-3) due to its uptake by

phytoplankton during primary production. However, addition of NOrN was observed at high chlorinities

(l2-18xI0-3) which can be attributed to its

remineralisation in the water column or desorption from the bottom sediments. A non-conservative behaviour with a net loss of 14-32% of nitrate was

d · Md ' Z .19 I ' M I d ·1s reporte 111 an OVt- uan- ane In a lana r ' estuaries which was attributed to its biological utilisation. Relati vely high (percentage) removal of P04-P in January/February observed during the

present study may be due to the combined effects of desorption from suspended particulates and its greater utilisation by phytoplankton . Greate r extent of removal of P04-P in low chlorinity regIOn

(0-llxlO-3) was attributed to its ad sorption on

sediment particulates2s. However, enrichment of

PO.j-P. in the high chlorinity (12-18x I0- ' ) region was believed to be due to its desorption from the bottom sediments . Removal of P04-P in May and September and addition in January/February was reported in Mandovi and Zuari estuaries2

,) whic h was attributed to the combined effects of uptake by phytoplankton

•

, --

~

PADMAVATHI & SATY ANARA YANA: NUTRIENTS & ELEMENTS IN GODAVARI WATERS 351

and adsorption on suspended particulates in the fonner. Extensive removal of P04-P in the low salinity upstream region and substantial addition in the high salinity lower reaches reported in Mahanadi estuary35 was attributed to its adsorption on suspended particulates and desorption from the bottom sediment respectively.

The range and average nutrient (N03-N, NH4-N, P04-P and Si04-Si) concentrations and nutrient to chlorinity ratios in different chlorinity ranges in the study period (Table 1) indicate a decreasing trend with increase in chlorinity. The overall nutrient to chlorinity ratios computed in the chlorinity range 15 to 19x1O-3 were found to be 3.46 ± 0.41xl0-5

, 0.128 ±0.015xlO-5

, 0.140 ± 0.007xlO-5 and 0.145 ±O.062xlO-5 for silicon, nitrate, ammonium and phosphate respecti vel y.

Variation of major element concentrations with

chlorinity (Fig. 4) indicates different patterns. For example, flouride indicated conservative behavior in January/February where the data points fall on or near to the TDL, and non-conservative behavior during May and September, where the data points showed distinct deviations from the TDL, indicating removal in the chlorinity range 8 to 14xlO-3 during May, and 12.5 to 19x 1 0-3 range during September. The net removal of flouride varied from 10 and 13% during May and September respectively which was attributed to the combined effects of its adsorption . on suspended solids and its biological uptake. Significant negative correlations between dissolved flouride and total suspended matter, TSM (September: -0.47 at P<0.05; May: -0.69 at P<O.OO I) and between dissolved flouride and particulate organic carbon, POC (September: -0.64 at P<O.O I, May: -0.89 at P<O.OOI) also lend support to this view.

Table I-Range and average concentrations of nutrients and nutrientlchlorinity ratios in the estuarine and coastal waters of Godavari

Number of Chlorinity Range Average

samples (X I 0-3) Nutrient NutrientlCI Nutrient Nutrient/Cl concentration ratio concentration ratio (X I 0-5)

(mg. kg-I) (x 10-5) (±SE) (±SE)

Silicon

87 0.0-1.0 5.40-12.9 779-7588 9.31±0.560 4386±830

24 1.0-5.0 5.23-8.69 105-594 6.97±O.872 270±131

28 5.0-10.0 2.71-6.88 29.2-128 4.82±O.725 68.4±15.1

53 10.0-15.0 0.52-6.08 3.55-56.4 2.51±0.517 20.7±5.09

134 15.0-19.22 0.19-1.93 0.90-6.63 0.58±O.139 3.46±0.41

Ammonium

87 0.0-1 .0 0.023-0.125 4.17-73.53 0.067±O.00 I 32.31 ±9.43

24 1.0-5.0 0.022-0.068 0.38-4.28 0.045±O.004 1.74±0.264

28 5.0-10.0 0.014-0.055 0.150-1.16 0.036±O.002 0.52±O.292

52 10.0-15.0 0.011-0.050 0.080-0.486 0.031 ±0.003 0.239±0.022

133 15.0-19.22 0.004-0.046 0.021-0.301 0.022±O.OO2 0.128±0.0 15

Nitrate

87 0.0-1.0 0.010-0.110 5.88-64.71 0.071 ±0.003 33. 16±1.875

24 1.0-5.0 0.021-0.097 0.630-6.30 0.058±0.004 2.411±0.294

28 5.0-10.0 0.019-0.074 0.191-1.16 0.044±O.003 0.635±O.058

53 10.0-15.0 0.014-0.052 0.094-0.447 0.032±O.OO I 0.257±0.0 13

134 15.0-19.22 0.003-0.062 0.0 I 6-0.352 0.024±O.00 I 0.140±O.007

Phosphate

87 0.0-1.0 0.035-0.282 7.64-165.9 0.086±O.0 18 34.96± 11.65

24 1.0-5.0 0.026-0.112 0.645-6.1 I 0.06 I ±0.007 2.490±0.838

28 5.0-10.0 0.023-0.094 0.268-1 .26 0.040±O.0 15 0.662±O.220

53 10.0-15.0 0.020-0.102 0.150-0.917 0.037±O.005 0.292±O.051

134 15.0-19.22 ND-0.064 0.053-0.373 0.035±O.0 19 0.145±0.O62

SE= Standard error, N.D= Non-detectable

352 INDIAN J MAR. SCI., VOL., 28, DECEMBER 1999

This is also in agreement with the earlier reports of high TSM in monsoon36 and high standing crop of phytoplankton in premonsoon34 season in the Godavari estuary. Earlier reports on flouride revealed conservative behavior during postmonsoon and non­conservative behavior during premonsoon (leading to its removal) in Gauthami Godavari8 and Mandovi­Zuari estuaries37. The average concentration of flouride and F/CI ratio (Table 2) computed in the present study (1.22 ± O.Olmg.kg-l, 7.10 ± 0.029xlO-5

respectively in the chlorinity range 15.0 to 19.22 xlO-3)are slightly lower and higher respectively than the average flouride concentration (1.30 mg.kg- I

) and F/CI ratio (6.7xlO-5

) for normal seawater38 of chlorinity 19.374xlO-3. However, the F/CI ratio obtained in the present study is in agreement with the earlier reports on Gauthami Godavari8 (7.05xlO-5

)

and Puma estuary39 (6.9 to 7.2xlO-5).

Boron exhibited a non-conservative behavior (Fig. 4) during the entire study period where the data points showed distinct deviations from TDL. Deviations of boron from TDL were significant particularly in the chlorinity range 6 to 14x10-3

during May and 0 to 18x 10-3 in September and January/February leading to its removal. The net removal of boron (May: 19%, September: 15%, January/February: 12%) can be attributed to its adsorption onto the suspended matter containing river borne clay minerals. Significant negative correlations between dissolved boron and TSM observed in the present study (May: -0.49 at P<0.05; September: -0.51 at P<0.05; and January/February: -0.87 at P<Q.OO1) also lend support to this view. Levinson & Ludwick40 suggested that formation of a precipitate phase in which colloidal co-precipitation of boron with silica occurs on suspended solids in estuaries. Further, the ionic strength of the medium, particle size and the nature of clays also play an important role in its adsorption41. The net removal of boron obtained in the present study (12 to 19%) generally agrees with the earlier reports on other Indian

. I Pu 22 M' d I 42 M d ·43 d estuanes name y rna, In 0 a, an OVI an Hooghly44. Though the average concentration of boron (3.86 ± 0.029 mg.g- I

) was lower, the ratio of B/CI (0.23 ± 0.00IxlO-3, Table 2) was in good agreement with normal seawater l2 (cone: 4.5 mg.kg- I

,

ratio: 0.232xlO-3). Further, the B/CI ratio obtained in the present study agrees with those of earlier reports

on Mindola42 (0.24xlO-3), and Hoogl/4 (0.231

± 0.1 15xlO-3) estuaries. Cakium and magnesium showed conservative

behavior in May where the data points fall on or close to TDL, and semiconservative behaviour III

September and J anuary/February where the data points scatter on either side of the TDL. A net addition of 8% and 5% observed for Ca and Mg respectively (particularly in the chlorinity range 2 to 8xlO-3

) in September is attributed to the ir release from the exchangeable sites of majority of riverine clays with other cations in the early stages of estuarine mixing. While a net removal in January/February, ofCa (10%) in the chlorinity range 5 to 13xlO-3 may be mainly due to its invo lvement in the biogeochemical cycles such as its uptake by phytoplankton, a net removal of Mg (8 %) particularly in the higher chlorinity range of 12 to 18x I 0-3 can be attributed to its involvement in the geochemical process such as adsorption on fine grained suspended particles and its incorporation to varying amounts, as calcite and aragonite by the organisms which secrete carbonate skeletons45 . Significant negative correlations of dissolved Ca and Mg witl1 TSM (May : -0.51, -0.48 at P<0.05; September: -0.49, -0.48 at P<0.05, and January/February: -0.74, 0.78 at P<O.OOI), and dissolved Ca with POC (May: -0.95 at P=O.OOI; September: -0.63 at P<O.O I; and January/February : -0.94 at P=O.OOI) observed in the present study also support this view. The results obtained in the present study on the behaviour of Ca and Mg generally agree with earlier reports on Indian estuaries such as Puma22

, Mindola42, Mandovi-Zuari46

and Hooghl/7. The average ratios (Table 2) of CaiCI (0.022 ± 0.0001) and Mg/CI (0.066 ± 0 .0001 ) obtained in the present study (in the chlorinity range 15-19 .22x 10-3) agree with the normal sea water l) (Ca: 0.02126 ± 0.0025; Mg: 0.06692 ± 0 .00(04), and with those reported for other Indian estuaries such as Mindola42 (Ca: 0.0225 ± 0.0006; Mg: 0 .066 ), Purna2

}

(Ca: 0.0225 ± 0.0006; Mg: 0 .066) and coastal waters of Goa48 (Ca: 0.0213 ± 0.00007 ; Mg: 0.06641 ± 0.00028).

ELementaL fluxes A knowledge of elemental fluxes from rivers to the

oceans is essential for calculating material balance for various elements, and to find out their possible sinks and sources. It has been realised in recent years that estuaries play an important role in modifying the river

PADMAVATHI & SATY ANARA YANA: NUTRIENTS & ELEMENTS IN GODAVARI WATERS 353

Table2-Range and average concentration of major elements and their ratios with chlorinity in the estuarine and coastal waters of Godavari

Number Chlorinity Range Average

of samples (xl 0-3) Element Element/CI Element Element/CI

concentration ratio concentration ratio (mg kg-I) (±SE) (±SE)

Fluoride

73 0.0 - 1.0 0.11-0.3S 30.9 - 177xlO-5 0.2I±O.068 97.4±3.733xI0-5

22 1.0-S.0 0.27-0.S7 8.43-27. Ix 10-5 0.39±O.014 16.1 ± 1.289x I 0-5

26 S.O-IO.O 0.48-0.78 6.03-10. 7x I 0-5 0.S9±0.0IS 8.24±O.219x I 0-5

49 1O.0-IS.0 0.60-1.14 S.79-9.96xlO-5 0.94±0.021 7.38±0.126x'1O-5

92 IS.0-19.22 1.04-1.37 6.SI-7.64xlO-5 1.22±O.01O 7. I 0±0.029x I 0-5

Boron

72 0.0-1.0 0.06-0.26 0.22-0.86xlO-3 0.12±0.OO8 O.SI ±O.O 17x I 0-3

22 I.O-S.O 0.23-1.36 O.14-0.40x I 0-3 0.7 I ±O.079 0.2S±0.014xI0-·'

26 S.O-IO.O 0.92-2.18 0. IS-0.28xI0-3 I.S2±O.066 0.21 ±O.OOSx I 0-3

49 1O.0-IS.0 1.80-3.83 0.18-0.27xlO-3 2.93±O.077 0.23±O.OO7x I 0-3

92 IS.0-19.22 3.36-4.S0 0.21-0.24xI0-3 3.86±O.029 0.23±O.00IxI0-3

Calcium

73 0.0-1.0 18.1-38.1 0.049-0.189 2S.8±O.S7 0.IIS±O.0034

22 I .O-S .O 40.0-149 0.01 9-0.0S9 93.7±6.43 0.036±0.0023

26 S.0-1O.0 128-226 0.018-0.031 I 79±6.42 0.02S±O.OOOS

49 1O.0-IS.0 164-363 0.016-0.026 290±6.23 0.023±0.0003

92 IS .0-19.22 31S-422 0.020-0.024 378±2.30 0.022±O.OOO I

Magnesium

73 0.0-1.0 11.9-48.3

22 I.O-S .O 84.0-381

26 S.O-IO.O 3S6-720

49 10.0-IS.0 S99-1067

92 IS.0-19.22 977-1264

SE= Standard error

inputs to oceans. Keeping this in view, an attempt has .. ' been made to compute the net annual fluxes of

nutrients and major elements to the Bay of Bengal from the Godavari river. For flux calculations the average river concentrations derived from the regression equations at zero chlorinity, annual river discharge, and the net (percentage) removal or addition of elements were taken into account. The annual (average) fresh water discharge of the Godavari river at Dowleswaram Barrage during the study period (1993 to 1995) was recorded as 1.07xlOI4lit (unpublished data from Godavari Head Works Division, Dowleswaram). Out of this about 2.2% (O.02xlOI4Iit) accounts for the non-monsoonal (December to May) and 97.8% (1.05x1014Iit) for the monsoonal (June to November) discharge respectively. The data on nutrients and major elemental fluxes thus computed are incorporated in

0.036-0.148 20.90±0.773 0.087±0.002S

0.OS2-0.117 206.1±2S.01 0.072±O.004S

0.057-0.076 496.2±16.3S 0.008±0.OO 13

0.059-0.073 8S3.8±18.S3 0.067±O.00 13

0.060-0.070 1122±16.24 0.066±0.00OI

Table 3-Nutrient and major elemental tluxes (xIO'Jg) from Godavari river into the Bay of Bengal

Nutrient Non-monsoon Monsoon Net tlux (December-May) (June-November) (annual)

Silicon 12 716 728

Nitrogen 0.2 IS.4 15.6

(N03-N+NH4-N)

Phosphorus 0.1 10.8 10.9

Fluoride 0.3 20.4 20.7

Boron 0.1 6.9. 7.0

Calcium 60 2820 2880

Magnesium 30 IS10 IS40

Table.3. It is evident from the data that the monsoonal, non-monsoonal and total (annual) fluxes of silicon obtained in the present study broadly agree with the earlier reports of nonmonsoonal

354 INDIAN 1. MAR. SCI., VOL., 28, DECEMBER 1999

(O.83x1011g)7, monsoonal (4.7xlOllg)8 and annual (4.7x1011 g)49 fluxes of silicon from Godavari river into the Bay of Bengal. The non-monsoonal and annual calcium and magnesium fluxes broadly agree with those of the earlier reports of non-monsoona( (Ca: 1.8x1011 g; Mg: l.Oxl0 11 g) and annual49 (Ca: 27.4x10 11 g; Mg: 64x1011 g) fluxes from the Godavari river into the Bay of Bengal.

Acknowledgement One of the authors (D P) thanks the Department of

Ocean Development (DOD), New Delhi, for the award of a research fellowship .

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