Environmental Engineering Reference
In-Depth Information
porosity, and volumetric water and air relations (Humberto et al.
,
2006). Like bulk density
and particle density, the porosity of soil varied slightly in different seasons that were ranged
from 53.00 to 56.29% with a minimum value (51.39%) measured in postmonsoon and a
maximum value (58.86) observed in premonsoon. Variations in the range of bulk density and
porosity of salt marsh sediment were reported by Bradley and Morris (1990) that agreed with
present findings. Particle density of soil in the
Porteresia
bed was observed to increase with
an increase in bulk density; while porosity of the sediment increased with a decrease in bulk
density that agreed with findings of Ansa and Francis (2007). Characteristically, winter was
different from all other seasons by having the lowest average bulk density (1.22gcm
-3
) and a
very high porosity (56.29%). The high porosity ensured that more pore spaces were occupied
by air and water when compared to the other sediment collected in other seasons. The low
particle density found in winter could be attributed to the high organic matter content of the
soil, since organic matter weighs less than an equal volume of soil (Brady, 1974). High
particle density with low organic matter content was recorded during premonsoon, monsoon
and postmonsoon. As expected, an inverse relationship was observed between porosity and
bulk density with the latter increasing as the former decreased that coincide the result
obtained by Ansa and Francis (2007).
Total N found in the soil of salt marsh bed was- 0.08 to 0.14% with lower values (0.06%)
recorded during winter and higher values (0.15%) recorded during postmonsoon whereas
available P measured from the present research field was- 3.92 to 12.00µg/g with the lowest
value (3.00µg/g) found during winter and the highest value (14.00µg/g) recorded during
postmonsoon. However, total nitrogen in salt marsh communities was 0.14-0.65mg/g
recorded by Ihm and Lee (1998) that might be slightly higher from the present study. Total N
is determined by the amount of litter fall and the rate of litter decomposition. The amount of
litter fall and the rate of litter decomposition are affected by flooding frequency and the
intensity of tidal flushing, which in turn affect total N in soil. In other words, total N is
lessened through the daily tidal flushing of organic matter that derives from autochthonous
litter fall (Tam and Wong, 1997). The quantity and quality of litter decomposition on the soil
surface of areas with lower elevation are strongly affected by tidal activity (Twilley et al.
,
1986). The higher values for total N and available P in the present observations were found
during postmonsoon which coincide the finding of Tan Lee (2008) as he mentioned that total
and available P remain high in the wet seasons in areas with high reducing conditions and
high organic matter content. Available P was negatively correlated with soil moisture since
soil with high moisture becomes reduced, lowering the organic matter decomposition rate
which could then lead to low available P as it was found in the present and the previous study
(Tan Lee, 2008).
R
EFERENCES
Abu Hena, M. K., Short, F. T., Sharifuzzaman, S. M., Haque, M. N., Hasan, M., Rezowan, M.
& Ali, M. (2007a). Salt marsh and seagrass communities of Bakkhali estuary, Cox's
Bazar, Bangladesh.
Estuarine Coastal and Shelf Science
,
75
, 72-78.
