Environmental Engineering Reference
In-Depth Information
(1991) in coastal waters of Bangladesh and other parts of the world. The water and soil
temperature correlated significantly with water transparency, dissolved oxygen, total
suspended solids, tidal height, inundation period, water table depth, soil temperature, soil
organic carbon & organic matter, soil texture (% sand, silt & clay ), soil moisture, field water
capacity, bulk density, particle density, the exchangeable Ca & total N of soil in the present
study. Many studies have shown that water and soil temperature greatly influences the
organic matter decomposition (Howard and Howard, 1993). The loss of moisture by
evaporation is greatest in soil where temperature is high (Underwood and Chapman, 1993). It
is well known that the temperature and salinity affect the dissolution of oxygen (Vijayakumar
et al.
,
2000).
The mean values for water salinity recorded in monsoon (4.17‰), postmonsoon
(12.35‰), winter (19.01‰) and premonsoon (17.11‰) were varied significantly in the
present study. The minimum value (0‰) was measured in monsoon while the maximum
value (21.56‰) was found during premonsoon. Therefore a gradual increase of salinity
values from the monsoon to premonsoon was noticed in the present study. It is evident from
the previous studies that the changes in the salinity in the brackish water habitats such as
estuaries, backwaters, mangrove and salt marshes are due to the influx of freshwater from
land run off, caused by monsoon or tidal variations. As a results the most notable feature of
the hydrology of the estuarine and coastal waters of Bangladesh is the presence of a
prolonged low salinity (<15‰) period mostly during the monsoon and certain period of post-
monsoon (Mahmood, 1986; FAO, 1984). (Boaden and Seed, 1985) also reported that the
average salinity in the overlying water of salt marshes, was in the range of 5-38‰. The
salinity of surface and soil water varies depending on a number of factors such as rainfall,
fresh water input, tidal flooding, evapotranspiration, soil type and vegetation (Vernberg,
1993). Similar trend in salinity fluctuations were noticed in the present study. Higher salinity
values during winter could be attributed to the low amount of rainfall, higher rate of
evaporation and also due to sea water dominance in the study area (Sampathkumar and
Kannan, 1998; Govindasamy et al.
,
2000; Gowda et al.
,
2001; Rajasegar, 2003). During the
monsoon season (0‰), the rainfall and the freshwater inflow from the land in turn moderately
reduced the salinity (McLusky, 1989; SaiSastry and Chandramohan, 1990; Mitra et al.
,
1990;
Satpathy, 1996). The salinity values fluctuated from 0‰ to 35.65‰ was measured by Jagtap
et al. (2006) during monsoon to premonsoon period. They also reported that
Porteresia
beds
though commonly confined to polyhaline (18-30‰) zones, could survive in the wide (0-
35.65%) salinity range. Salinity of the waters gradually increases from September onwards
reaching at its peak during the month of May. Excessive evaporation due to high temperature
during premonsoon cause increased salinity in the
Porteresia
beds that coincides the findings
of the present study. The water salinity was significantly correlated (p<0.01) with other
hydropedological factors like water transparency, dissolved oxygen, total suspended solids,
inundation period, water table depth, soil salinity, soil organic carbon & organic matter, soil
texture, soil moisture, field water capacity, bulk density, particle density, exchangeable Ca,
Mg and total N of soil in the present study. From the previous studies it was proved that
enhanced saltwater intrusion from the rising sea levels and salinity of tidal waters have led to
an increase in surface soil salinity in the salt marshes (Day et al.
,
1995; Hutchings and
Saenger, 1987). Water salinity in salt marshes also interrelated with tidal flooding and
inundation of sea water (Adam, 1990).
