HYDROLOGICAL STUDY OF COASTAL WATERS OF MANGALORE: PRE AND POST MONSOON SCENARIO.

IRJMST Volume 5 Issue 4 [Year 2014] Online ISSN 2250 - 1959

International Research Journal of Management Science & Technology http://www.irjmst.com Page 23

HYDROLOGICAL STUDY OF COASTAL WATERS OF MANGALORE:

PRE AND POST MONSOON SCENARIO.

1Madhavi.K and 2Gangadhara Gowda.

1 Assistant professor Department of Aquatic Environment Management,

College of Fishery Science, Muthukur, Andhra Pradesh, India -524344.

2 Professor and Head, Department of Aquatic Environment Management,

College of Fisheries, Mangalore, Karnataka, India – 575002

Abstract

Hydrological study of physico-chemical parameters are of utmost importance, as

it is having lot of influence on the composition, density and relative abundance of

planktonic communities which are finally going to decide the fate of productivity of

coastal waters. Air temperature, water temperature, pH, salinity, dissolved oxygen,

ammonium-N, nitrite-N, nitrate-N, phosphate-P and silicate-Si were observed and

analysed to understand the hydrology of Mangalore coastal waters during the pre-

monsoon (Feb. 2013 to May 2013) and post-monsoon (Oct.2013 to Jan.2014)seasons.

Introduction

Coastal ecosystems play an important role in the global biogeochemical cycles of

macronutrients. Despite their relatively small volume, they contribute disproportionately

to global primary production. Coastal margins that are influenced by major rivers are an

important source of dissolved and particulate material to the ocean and to global

biogeochemical fluxes. The Mangalore coast which is situated at the western part of the

Indian peninsula stretching to about 22 Kms of Coastal district of Dakshina Kannada,

Karnataka. Coastal waters off Mangalore provide for a multi-species fishery, and the area

is known as one of the largest upwelling systems in the world.


International Research Journal of Management Science & Technology http://www.irjmst.com 4

Materials and Methods

Regular monthly sampling of surface and subsurface (near bottom) waters was

carried out during the pre-monsoon (February 2013 to May 2013) and post-monsoon

(October 2013 to January 2014) at the old port of Mangalore, Karnataka (Lat. 120. 50

1.

69911

North & Long. 740. 48

1. 940

11 East). Water samples were collected using a clean

plastic bucket from the surface and by Nansen’s Reversing water sampler from the

subsurface.

Rainfall data was obtained from Agricultural Research Station, Kankanadi,

Mangalore. Atmospheric and surface water temperatures were measured using standard

mercury filled centigrade thermometer. Salinity was analysed in the laboratory by

following Mohr’s method (Strickland and Parsons, 1972). Dissolved Oxygen was

estimated by modified Winkler’s method (Strickland and Parsons, 1972). pH was

measured potentiometrically using digital pH meter (EUTECH instruments, pH/mv/0C/

0F

meter). For the analysis of nutrients, water samples were filtered using a Millipore

Filtering System (MFS) and analysed for dissolved inorganic phosphate, nitrite-nitrogen,

nitrate-nitrogen, ammonium-nitrogen and reactive silicate by adopting the standard

methods described by Strickland and Parsons, 1972.



Results and Discussion

Rainfall

It is the most important cyclic phenomenon in tropical countries as it brings

important changes in the hydrographical characteristics of an aquatic environment. The

total annual rainfall received in the study area was 3526 mm, minimum precipitation was

observed in the month of March (24.9 mm) and maximum in the month of June (1483.2

mm).

Air Temperature

The minimum air temperature of 25.90C was observed in the month of October

(post-monsoon), while a maximum temperature of 32.80C was recorded in the month of

May (pre-monsoon). The seasonal mean (Mean±SD) air temperature values for pre-

monsoon and post-monsoon seasons were found to be 31.15±1.49 and 27.23±1.13

respectively.

The fluctuation in the air temperature was closely related to the seasonal changes

in the insolation, wind and precipitation, so, highest temperatures were observed during

pre-monsoon and low values during monsoon post-monsoon.

Damotharan et al., 2010 observed air temperature in the range of 23.50C to 28.2

0C

in Point Calimere coastal waters.

Water Temperature

It is well known that water temperature influences organisms directly on the

physiological parameters and indirectly through change in the physicochemical properties

of water. Therefore, water temperature becomes an important factor to record in the

environmental studies. In surface waters, the minimum water temperature of 26.80C was

observed in the month of October- (post-monsoon), while a maximum temperature of

31.60C was recorded in the month of May (pre-monsoon). In subsurface waters, a

minimum of 26.70C was observed in the month of October (post-monsoon) and a

maximum of 31.30C in the month of May. The seasonal mean (Mean±SD) surface water



temperature values for pre-monsoon and post-monsoon seasons were found to be

30.70±0.98 and 28.00±1.10 respectively. The seasonal mean (Mean±SD) subsurface

water temperature values pre-monsoon and post-monsoon seasons were found to be

30.40±0.93 and 27.73±0.93 respectively.

The temperature values for the entire period of observation reflect to a great

extent the climatic variations. A trend in temperatures of Air > Surface > Subsurface

(Pre-monsoon) and Surface > Subsurface > Air (Post-monsoon) was observed. The

recorded high pre-monsoon and low monsoonal and post-monsoonal values can be

ascribed to meteorological phenomenon i.e high solar radiation and precipitation

respectively. In Kalpakkam coastal waters, Sahu et al., 2012 observed, surface water

temperature in the range from 26.00C (august) to 31.8

0C (May) indicated an annual

variability of about 5.80C.

Damotharan et al., 2010 observed water temperature in the range of 24.00C to

29.50C in Point Calimere coastal waters. Santhosh Kumar and Perumal (2012) in

Ayyampattinam coastal waters reported the water temperature in the range of 25.50C to

33.40C.

pH

pH is known as master variable in water, since many properties, processes and

reactions are pH dependent. In surface waters, the minimum pH of 7.45 was observed in

the month of November (post-monsoon), while a maximum pH of 8.31 was recorded in

the month of May (pre-monsoon). In subsurface waters, a minimum of 7.82 was observed

in the month of October and a maximum of 8.38 in the month of May. The seasonal

mean (Mean±SD) pH values of surface waters for pre-monsoon and post-monsoon

periods were found to be 8.26±0.04 and 7.82±0.33 respectively. The seasonal mean

(Mean±SD) pH values of subsurface waters for pre-monsoon and post-monsoon periods

were found to be 8.33±0.05 and 8.06±0.19 respectively.



The bottom water pH was found to be, by and large higher than that of the surface

water. By and large, the marginal change observed in pH of coastal waters from one

month to the other may be due to the excessive buffering activity of sea water.

The observed pre-monsoon maximum pH could be attributed to high rate of

evaporation under high temperature conditions. The observed post-monsoon minima can

be ascribed to rainfall, resultant freshwater mixing.

Damotharan et al., 2010 observed pH in the range of 7.8 to 8.3 in Point Calimere

coastal waters. Santhosh Kumar and Perumal (2012) in Ayyampattinam coastal waters

reported the pH in the range of 7.8 to 8.2.

Salinity

Salinity is a dynamic indicator of the nature of the exchange system. The salinity

distribution with in coastal water ways reflects the relative influx of fresh water supplied

by rivers. In surface waters, minimum salinity of 9.12 psu was observed in the month of

October- (post-monsoon), while a maximum pH of 34.36 psu was recorded in the month

of May (pre-monsoon). In subsurface waters, a minimum of 27.12 psu was observed in

the month of October and a maximum of 34.99 psu in the month of May. The seasonal

mean (Mean±SD) salinity values of surface waters for pre-monsoon and post-monsoon

periods were found to be 33.15±0.88 and 19.47±10.29 respectively. The seasonal mean

(Mean±SD) salinity values of subsurface waters for pre-monsoon and post-monsoon

periods were found to be 33.90±0.79 and 29.43±1.73 respectively. The recorded higher

values during pre-monsoon season could be attributed to low amount of rainfall, higher

rate of evaporation. Damotharan et al., 2010 recorded salinity in the range of 26 to 35 psu

in Point Calimere coastal waters. Smitha et al. (2010) observed an annual variation of

24.45 to 36.72 ppt in coastal waters of Kalpakkam. Santhosh Kumar and Perumal (2012)

in Ayyampattinam coastal waters reported the salinity in the range of 23 ppt to 35 ppt.

Dissolved Oxygen (DO)



Dissolved oxygen is an important characteristic of water and its concentration in

water is an indicator of prevailing water quality and ability of water body to support a

well-balanced aquatic life.

In surface waters, the minimum dissolved oxygen content of 4.52 mg/L was

observed in the month of May (pre-monsoon), while a maximum of 6.52 mg/L was

recorded in the month of November (post-monsoon). In subsurface waters, a minimum of

3.92 mg/L was observed in the month of December and a maximum of 5.94 mg/L in the

month of November. The seasonal mean (Mean±SD) DO content of surface waters for

pre-monsoon and post-monsoon periods were found to be 5.23±0.60 and 5.69±0.61

respectively. The seasonal mean (Mean±SD) DO content of subsurface waters for pre-

monsoon and post-monsoon periods were found to be 4.59±0.55 and 5.09±0.85

respectively.

The observed high post-monsoonal values might be due to the cumulative effects

of higher wind velocity, increased turbulence coupled with heavy rainfall during

monsoon. High biological activity during pre-monsoon can lead to low dissolved oxygen

concentration, besides, low solubility of dissolved oxygen under high temperature and

salinity conditions.

Damotharan et al., 2010 recorded oxygen in the range of 3.15 to 5.24 mg/L in

Point Calimere coastal waters. Santhosh Kumar and Perumal (2012) in Ayyampattinam

coastal waters reported the salinity in the range of 3.6 ml/L to 5.2 ml/L.

Ammonium-nitrogen

In surface waters, the minimum ammonium-N content of 1.26 µg-at/L was

observed in the month of April (pre-monsoon), while a maximum of 10.56 µg-at/L was

recorded in the month of December (post-monsoon). In subsurface waters, a minimum of

0.70 µg-at/L was observed in the month of January and a maximum of 8.14 µg-at/L in

the month of November. The seasonal mean (Mean±SD) ammonium-nitrogen content of

surface waters for pre-monsoon and post-monsoon periods were found to be 1.61±0.38

and 7.03±3.01 respectively. The seasonal mean (Mean±SD) ammonium-nitrogen content



of subsurface waters for pre-monsoon and post-monsoon periods were found to be

1.87±0.75 and 5.74±3.48 respectively.

The observed low ammonium-nitrogen values during pre-monsoon could be due

to the uptake by phytoplankton. The observed high values during post-monsoon might be

due to influx of nutrient laden terrestrial and river run-off, besides higher dissociation rate

of total ammonia at relatively low pH during this season.

Damotharan et al., 2010 recorded ammonium-N in the range of 0.016 to 85 µM in


coastal waters reported the ammonium-N in the range of 0.05 µg/L to 0.32 µg/L.

Nitrite-nitrogen

Among the three nitrogenous nutrients, nitrite-nitrogen is considered to be a very

unstable component being an intermediary stage in the nitrogen cycle. In surface waters,

the minimum nitrite-N content of 0.23 µg-at/L was observed in the month of February

(pre-monsoon), while a maximum of 1.80 µg-at/L was recorded in the month of October

(post-monsoon). In subsurface waters, a minimum of 0.27µg-at/L was observed in the

month of February and a maximum of 1.57 µg-at/L in the month of January. The

seasonal mean (Mean±SD) nitrite-nitrogen content of surface waters for pre-monsoon

and post-monsoon periods were found to be 0.40±0.19 and 1.06±0.73 respectively. The

seasonal mean (Mean±SD) nitrite-nitrogen content of subsurface waters for pre-monsoon

and post-monsoon periods were found to be 0.77±0.43 and 0.90±0.54 respectively.

The observed high values during monsoon/post-monsoon seasons could be due to

oxidation of ammonia, reduction of nitrate, and also due to the formation as intermediate

compound during the decomposition of autochthonous and allochthonous (that entered in

to these waters through land run-off during monsoon season) organic matter.

Damotharan et al., 2010 recorded nitrite-N in the range of 0.28 to 0.98 µM in


coastal waters reported the nitrite-N in the range of 0.74 µg/L to 0.896 µg/L.

Nitrate-nitrogen



In surface waters, the minimum nitrate-N content of 1.17µg-at/L was observed in

the month of February (pre-monsoon), while a maximum of 20.93 µg-at/L was recorded

in the month of November (post-monsoon). In subsurface waters, a minimum of 0.96µg-

at/L was observed in the month of February and a maximum of 5.98 µg-at/L in the

month of November. The seasonal mean (Mean±SD) nitrate-nitrogen content of surface

waters pre-monsoon and post-monsoon periods were found to be 2.17±1.10 and

8.42±8.44 respectively. The seasonal mean (Mean±SD) nitrate-nitrogen content of

subsurface waters pre-monsoon and post-monsoon periods were found to be 2.80±1.52

and 4.38±1.85 respectively.

The recorded high values of nitrate during post-monsoon season could be mainly

due to the organic materials received from the catchment area, by way of terrestrial and

river run-off. The recorded low values of nitrate during pre-monsoon season could be

attributed to phytoplankton growth, sedimentation and denitrification.

Damotharan et al., 2010 recorded nitrate-N in the range of 3.54 to 7.05 µM in


coastal waters reported the nitrate-N in the range of 3.21 µg/L to 6.34 µg/L.

Phosphate-phosphorus

Phosphate concentration in coastal waters depend upon its concentration in the

freshwater that mixed with the seawater with in the sea-land interaction zone,

phytoplankton uptake, addition through localized upwelling and replenishment as a result

of microbial decomposition of organic matters. In surface waters, the minimum

phosphate content of 0.51 µg-at/L was observed in the month of February (pre-monsoon),

while a maximum of 1.83 µg-at/L was recorded in the month of November (post-

monsoon). In subsurface waters, a minimum of 0.51µg-at/L was observed in the month of

February and a maximum of 3.52 µg-at/L in the month of November. The seasonal mean

(Mean±SD) phosphate-phosphorus content of surface waters for pre-monsoon and post-

monsoon periods were found to be 0.80±0.39 and 1.24±0.51 respectively. The seasonal

mean (Mean±SD) phosphate-phosphorus content of subsurface waters for pre-monsoon

and post-monsoon periods were found to be 1.04±0.51 and 1.97±1.22 respectively.



The observed higher monsoonal values can be attributed to regeneration and

release of total phosphorus from bottom mud (which is the major source of this nutrient)

in to the water column by turbulence and mixing due to the impact of precipitation.

Damotharan et al., 2010 recorded phosphate-P in the range of 0.2 to 2.8 µM in


coastal waters reported the phosphate-P in the range of 0.22 µg/L to 1.16 µg/L.

Silicate-silicon

The spatio-temporal variation of silica in coastal water is influenced by several

factors, more importantly the proportional physical mixing of sea water with freshwater,

adsorption of reactive silicate onto sedimentary particles, chemical interaction with clay

minerals, co-precipitation with humic compounds, and biological removal by

phytoplankton, especially by diatoms and silicoflagellates. The entry of silicate mainly

takes place through land drainage rich with weathered silicate material.

In surface waters, the minimum silicate content of 21.67 µg-at/L was observed in

the month of April (pre-monsoon), while a maximum of 165.00 µg-at/L was recorded in

the month of October (post-monsoon). In subsurface waters, a minimum of 19.85µg-at/L

was observed in the month of May and a maximum of 78.20 µg-at/L in the month of

March. The seasonal mean (Mean±SD) silicate-silicon content of surface waters for pre-

monsoon and post-monsoon periods were found to be 42.47±30.73 and 88.00±62.06

respectively. The seasonal mean (Mean±SD) silicate-silicon content of subsurface waters

for pre-monsoon and post-monsoon periods were found to be 35.93±28.27 and

31.98±14.91 respectively.

The observed high post-monsoonal values may be due to heavy inflow of

monsoonal freshwater derived from land drainage carrying silicate leached out from the

rocks. Further, due to the turbulent nature of water, during monsoon season, the silicate

from the bottom sediment might have been exchanged with overlying water. The minimal



values of silicate observed during pre-monsoon can be attributed to the outburst of

diatoms.

Damotharan et al., 2010 recorded silicate-Si in the range of 19.96 to 53.32 µM in


coastal waters reported the silicate-Si in the range of 24.85 µg/L to 61.92 µg/L.

Graphical representation of the parameters

0

5

10

15

20

25

30

35

F M A M O N D J

Pre monsoon Post monsoon

Air

Te

mp

. (0 C

)

Months

S

24

25

26

27

28

29

30

31

32

F M A M O N D J


Wat

er

Tem

p.(

0 C)

Months

S

SS

6.8

7

7.2

7.4

7.6

7.8

8

8.2

8.4

8.6

F M A M O N D J


pH

Months

S

SS

0

5

10

15

20

25

30

35

40

F M A M O N D J


Salin

ity

Months

S

SS



0

1

2

3

4

5

6

7

F M A M O N D J


DO

(m

g/L)

Months

S

SS0

2

4

6

8

10

12

F M A M O N D J


Am

mo

niu

m-N

Months

S

SS

00.20.40.60.8

11.21.41.61.8

2

F M A M O N D J


Nit

rite

-N

Months

S

SS0

5

10

15

20

25

F M A M O N D J


Nit

rate

-N

Months

S

SS



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0

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1.5

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4

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Ph

osp

hat

e-P

Months

S

SS0

20406080

100120140160180

F M A M O N D J


Silic

ate

-Si

Months

S

SS



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HYDROLOGICAL STUDY OF COASTAL WATERS OF MANGALORE: PRE AND POST MONSOON SCENARIO.

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