Environmental Engineering Reference
In-Depth Information
temperature and negative correlations with water and soil salinity. It is well known that the
temperature and salinity affect the dissolution of oxygen significantly (Vijayakumar et al.
,
2000).
A clear seasonal pattern of total suspended solids (TSS) was observed in water collected
from the vicinity of salt marsh bed of Fauzderhat coastal area during the study period.
Average TSS value ranged from 159.17 to 1096mg/L along with a minimum level (130mg/L)
found during winter and a maximum level (1145mg/L) recorded during monsoon. A
significant difference in the seasonal data was observed by Rashid (1999) in the Bakkhali
river estuary. The higher ranges (159.17 to 1096) recorded in the present observations as
compared to the ranges (91.17-213.25 mg/L) found by Rashid (1999) might be the resultant
of higher turbulence and velocity of water in the shallow ground of the study area where the
coarser sediment particle can easily accumulate in the surface of vegetation during low tide
and it can re-entered in to the solution during high tide.
Tidal height range in the study area was 1.10 to 2.66m with a minimum value (0.90m)
found during winter and a maximum value (2.85m) recorded in monsoon that was varied
significantly in different seasons of the year. The tides in the coastal and estuarine areas are
semi-diurnal with two high and two low periods per day and have maximum amplitude of 3-4
m at spring tide (Mahmood, 1986). The Bangladesh Inland Water Transport Authority
(BIWTA, 1978) recorded 4.27 m neap tides and 6.10 m spring tides in the coastal area of
Sandwip Island, Chittagong. In 24 years of tidal study, Chowdhury (1992) observed that the
monthly mean tidal range varies from 1.48 to 4.90 m with the mean value of 3.84 m in the
coastline adjacent to the Karnaphuly River estuary. Similar nature of tide and the tidal height
variation in different lunar phase was noticed in the present study. The variation of tidal
height was slightly lower than previous studies might be the effect of existing pattern of land
topography of Fauzderhat coastal area since the variation of tide level in the coastal areas is
highly attributed to the depth of the bay and varying topography of coastal water (Hossain,
2001).
The study area inundated throughout the year at different length of time was recorded
from 1.42 to 4.57 hour with a minimum value (1.25hr.) measured in winter and a maximum
value (4.95hr.) recorded during monsoon. Seneca et al. (1985) reported that
Spartinaalterniflora
exhibited luxuriant growth in the 4-7 hour inundation zones that was
mostly agreed with the present findings. Earlier studies (Niedowski, 2000) concluded that
tidal inundation is the primary physical characteristic of a salt marsh. Lack of inundation will
cause marsh substrates to dry out, changing the chemical properties of these substrates and
increasing erosion by wind, rain and terrestrial runoff (Burdick et al.
,
1997). Reduction of
tidal range in a salt marsh lowers the water table, and surface substrates become dry. In
addition to drying, the oxygen content of these substrates increases that can influence the rate
of organic matter decomposition, decrease in substrate pH to highly acidic conditions.
MacLeod et al. (1999) also showed that the main effect of tidal inundation was the
enrichment by marine associated metals (Ca, K, Mg and Na). The concentrations of soil
organic matter, total nitrogen, phosphorus, calcium, magnesium and potassium were found to
be high in landward sites and decreased gradually along tidal gradients, whereas pH and
salinity increase with distance from landward to seaward sites (Tam and Wong, 1997).
Similar results were found in the present investigations as the water and soil salinity decreases
significantly during monsoon and postmonsoon while the tidal height and inundation period
increases notably in the study site.
