Environmental Engineering Reference
In-Depth Information
The average value for water pH recorded in the four seasons of the study area was found
to be almost neutral throughout the study period with minimum value (6.79) during monsoon
and maximum value (7.22) during winter. Water pH in the vicinity of salt marsh bed was
found to be a range of 6.99-8.79, while Jagtap et al. (2006) conducted their research on the
ecology of salt marsh. The higher values found might the effect of higher salinity of their
research field. Generally, fluctuations in pH values during different seasons of the year is
attributed to factors like removal of CO
2
by photosynthesis through bicarbonate degradation,
dilution of seawater by freshwater influx, low primary productivity, fluctuations of salinity
and temperature and decomposition of organic materials as stated by Karuppasamy and
Perumal (2000) and Rajasegar (2003). High pH was recorded during winter seasons, which
might be due to the influence of more seawater penetration (Das et al.
,
1997) and due to the
presence of high photosynthetic activity in more transparent waters of the study area
(Subramanian and Mahadevan, 1999). The lower pH values of water influencing
Porteresia
beds in the present study found in monsoon period due to enormous volume of fresh water
inputs lead to dilution of salts. The fluctuation in pH values might also be due to the changes
in the sulphur oxidation state, resulting in strongly acidic conditions and high redox potentials
as in the case of mangrove ecosystem (Benmoussa et al.
,
1997). The higher pH values
recorded during the winter season reflect the buffer effect of the incoming seawater during
reduced river discharge. A similar pattern was recorded by Guimarães et al.
,
2009; Pereira et
al.
,
2010 and Sousa et al.
,
2009 in the estuarine and coastal areas.
The average value for water transparency recorded in and around the
P. coarctata
bed
ranged from 9.11cm to 19.22cm throughout the study period with a minimum value (6.67cm)
observed in monsoon and the maximum value (20.67cm) found in winter. Significant
variations in the range of water transparency level in different seasons were found in the
present study. Similar trend in the variations and values of water transparency levels in
different seasons in the coastal waters of Bangladesh were reported by Mahmood (1986) and
Chowdhury et al. (2010). Interactions between water tarnsparency and other factors like water
temperature, water salinity, dissolved oxygen, total suspended solids, tidal height, inundation
period, water table depth, soil temperature, soil salinity, soil organic carbon, organic matter,
soil texture (% sand & % clay), soil moisture, field water capacity, bulk density, particle
density, the exchangeable Ca, Mg, total N and the available P of soil were significant in the
present study. Water transparency and total suspended solids (TSS) are negatively interrelated
that depend on circulation pattern and freshwater discharge of coastal waters as reported by
Rashid (1999).
Variation in mean value of dissolved oxygen content in the present study was from
4.99mg/L to 5.96mg/L. Higher values of dissolved oxygen were recorded during monsoon
months and lower values were found during winter in the present investigation,. The highest
(5.64 ml/L) value of DO was found by Jagtap et al. (2006) in
Porteresia
beds as like as found
in the present study. The relatively higher (4.99-5.96ml/L) concentrations of DO in the waters
over
Porteresia
beds rather than mangrove environment (1.5-5.0 ml/L) could be due to the
relatively moderate decomposition activities in beds compared to the later (Jagtap, 1985).
Higher dissolved oxygen concentration observed during the monsoon season might be due to
the cumulative effect of higher wind velocity joined with heavy rainfall and the resultant
freshwater mixing (Das et al.
,
1997). Mitra et al. (1990) mainly attributed seasonal variation
of dissolved oxygen to freshwater flow and terrigenous impact of sediments. In the present
