JAYACHANDRAN P.R. & S. BIJOY NANDAN

DEPARTMENT OF MARINE BIOLOGY, MICROBIOLOGY & BIOCHEMISTRY

SCHOOL OF MARINE SCIENCES

PRIMARY PRODUCTION PATTERN AND ITS INFLUENCE ON A MESOHALINE

MICROTIDAL TROPICAL ESTUARY

Introduction

q According to Pritchard (1967), an estuary is a semi-enclosed coastal body of water, which has a freeconnection with the open sea and within which seawater is measurably diluted with freshwater derivedfrom land drainage

q Estuaries have for long been important to mankind,as locations of coastal fisheries & navigation

q Estuaries are heterotrophic systems, in whichconsumption exceeds production, and it is theoverall organic loading that controls primary andsecondary production (Heip et al. 1995).

Objectives

q To assess primary production (PP) pattern in relationto hydrography in Kodungallur-Azhikode Estuarinesystem (KAE)

q To evaluate the influence of hydrographic variabilityon PP

q Role of allochthonous & autochthonous nutrients on PP

Study area

Ø Kodungallur - Azhikode estuary (KAE)-700 ha

Ø Important area for fishery

Ø Permanent connection with Sea at Munambam

Ø Two rivers, Karuvannur river & Chalakkudy river emptying into estuary

Ø KAE Connected to COE with a narrow channel at southern side

Period of study : July 2009 to June 2010

ST. COORDINATES IMPORTANCE

1 10 11'2.83''N and 76 10'15.89''E

Mouth of estuary, MunambamHarbour

2 10 11'27.13''N and 76 11'49.13''E

Intensive sand mining

3 10 11'48.01''N and 76 12'49.14''E

Confluent zone of two rivers

4 10 12'13.21''N and 76 13'18.70''E

Major fishing zone

5 10 12'41.65''N and 76 13'1.63''E

Cage culture of Lates calcarifer

6 10 11'26.63''N and 76 12'42.84''E

High water current with river discharge, ferry service

7 10 11'9.28''N and 76 13'13.98''E

River head, ferry service

Materials and Methodsv The Secchi disc transparency were measured on field

vTemperature by centigrade thermometer

v Dissolved oxygen (Winkler’s method; APHA, 2005)

v pH (Systronics pH meter)

v Carbon dioxide, alkalinity, hardness and BOD (APHA, 2005)

v Turbidity, TDS and salinity (Systronics water analyser model no.317)

vAmmonia, nitrite, phosphate, silicate , nitrate by (Grasshoff et al. 1983 & Zhang and Fischer, 2005)

vChlorophyll a, acetone extraction method (Parsons et al, 1984)

v Primary production - by in situ using the light and dark bottle oxygen method (Strickland and Parsons, 1972; Quasim et al, 1969)

Results and Discussion

• The average depth of estuary 3.6 m, maximum at Station I (4.3 m)

• Tidal variations in this part of coast under microtidal range (65 - 90cm)

• Average water temperature 28.9 C was observed during the study period PRE(30.4 C), POM (28.7 C) MON (27.5 C)

• Av: pH 7.36 with lowest of 6.89 (MON). Bottom water showed slightly higher pH

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Av. Turbidity 9.8 NTU, peak during mon.(av:20.2 NTU). Highest at mouth (St. I; av: 13.1NTU). The heavy river influx, fishing boatmovements and intense sand & clamshell mining activities could be reason forhigher turbidity

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• Mean TDS value observed in the KAE was 14.7‰. comparatively high inmon.(av: 18.6 ‰) followed by PRE(13.4‰ ) & POM (av: 11.4‰)

• Av. transparency- 1 ± 0.4 m, lowest in MON - 0.6 m. spatially lowest av. inSt.V (0.8 m) & highest in St. VI (av.1.1 m)

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The CO2 was high in POM (av: 6.9 mgL-1) as compared to MON (av: 6 mgL-1) & PRM(av: 6.3 mgL-1).could be due to allocthonus organic loading in the estuary.The av. BOD was 2.6 mgL-1, highest at St. I (av: 3.1 mgL-1).Clear stratification observed in salinity. BOT salinity (av.16.9±8.9‰ ) higher than SUR(12.4‰). MAX. at St.I (av: 18.9‰) & MIN. St. VII (av: 10.2‰)The salinity values showed a definite trend; it decreased from mouth to head.During MON., it was very low (5.4‰)

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qAv. DO of 5.1 ± 1mgL-1 . Spatially It rangedfrom av.4.7 mgL-1 St. I to av.5.9 mgL-1 St. VI.

A discernible trend was observed in the DOregime, SUR water with higher DO than theBOT (av: 5.6 mgL-1)(av: 4.7 mgL-1)

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Inorganic nitrate constituted the major fraction of total DIN (av: 58%) in the surface and bottom waters Silicate was highly varied during the study (av: 49.1 ± 28.7 µML-1) Seasonal av. Showed slight increase during MON (52.7µML-1) & POM (av:56.4 µML-1). Silicate is an essential nutrient for diatoms

High NO3-N during SW. MON (av: 19.1 ± 19.4 µML-1) whereas, NO2-N highestduring PRM (0.4 µML-1). PO4-P av. of 1 ± 1.3 µML-1 in the KAE with highest duringPRM (av: 2 ± 2.1 µML-1). Comparatively high PO4-P observed in BOT (av: 1.3 µML-1)when compared to SUR (av: 0.8 µML-1). Av: DIN in the water column 15 ± 12.1µML-1

with highest peak observed during SW. MON (24.2 µML-1)

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GPP-B (mg C m-3d-1)

GPP showed an av. of 1580 mgC m-3d-1

Highest during PRM (av: 1785) followed byPOM (av:1589) &MON (av: 1517). GPP highin the SUR (av:1702 ) compared to BOT (av:1500), comparatively less variation wasnoticed during MON due to well mixing ofwater column. Generally, increased GPPnoticed in the St’s nearby estuarine mouth (St.I; av: 1625), St. II (av: 1750) & St. III (av:1750) respectively. GPP displayed -vecorrelation with NO3-N (r = -.297)

Av: NPP was 790 mgC m-3d-1 with Highest

av: of 1035) (POM) followed by MON (av:828) & PRM (av: 585) respectively. NPP washigh in the SUR (av: 845) compared to BOT(av: 766). Relatively high NPP wasobserved in St. III (av: 921) and slightlylower values observed in St. VI (av: 588).NPP showed +ve correlation with PO4-P (r =0.167) 0.000

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• Bray-Curtis similarity index of GPPshowed 91.8% similarity BW St. IIand III in the SUR, BOT showed96.3% similarity BW St. IV and VI.month wise highest similarity of SURwas 94.7% B/W Jan (10) and July(09). Bottom showed highestsimilarity of 91.5 BW April (10) andJul (09)

• NPP showed 90.1% similarity BW St.I &VII in the SUR waters

• BOT showed 83.8% similarity B/W St.I & II. Bottom water showed highestsimilarity of 89.7 between April (10)and February (10)

Linear correlation BW salinity, pH & Eh was found to be more significant with Chl-a

Water temp. & CO2 showed less significance with Chl-a

Similarity index of Chl-a showed 90.6 % similarity BW St. I and III in the SUR water

The month wise highest similarity of SUR showed 91.6% during the months POM

Av: Chl-a content of KAE was moderatelyless compared to COE. Highest Chl-aduring PRM (av: 10.89 mgm-3) thendecreased in to av. of 5.16 mg m-3 duringthe MON. During PRM, Slight temporalvariations observed in water column, withhighest in SUR(11.04mgm-3), compared toBOT(9.04 mgm-3) but conditions wereamend during MON and POM due to wellmixing. Peak value of Chl-a was noticedduring April-10 (av. 11.65 mgm-3)

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Conclusion

vIntensive sand mining, poor agricultural practices and failures inurban planning resulted in an excessive sediment transfer andindustrial-sewage discharge to the basin of the estuary reducedthe light penetration and PP during monsoon

vSolar illumination, freshwater flow & turbidity played crucial role in PP

vNPP increased from 525 mgC m-3d-1 (CIFRI, 2005) to 790 mgC m-3d-1.This increased carbon fixation can be attributed to climaticvariations and increased nutrient loading

vQuantity and quality of primary production and hydrography in theKAE will be an important factor that controls the biotic potentialof estuary

THANK YOU

This work forms a part of research project entitled, Ecologyand fish production potential of the Kodungallur –Azhikode back water ecosystem sponsored by the KeralaState Council for Science, Technology & Environment andwe are thankful for their financial assistance