Environmental Engineering Reference
In-Depth Information
The mean value for water table depth of the study area measured
in situ
was fluctuated
from 20.24 to 45.34cm with the highest value (47.70cm) reached in winter and the lowest
value (19.30cm) observed during monsoon. The high water run-off during the wet season and
the high evaporation during the dry season are the most important factors controlling the
difference in ground water (Chapman, 1976; Loon, 2005). In this study, water table depth in
the winter season was significantly greater than water table depth in the monsoon season due
to less water input and higher evaporation, whereas in the wet season, more water run-off
from higher elevations caused lower soil drainage. Generally, soil that is often inundated due
to low elevation has poor drainage, leading to differences in groundwater level (Day et al.
,
1987) and thus the water table depth was found to be significantly lower in monsoon rather
than winter in the present research.
Soil pH recorded in four seasons was almost neutral. Values obtained varied between
6.75 to 6.97 with minimum value (6.66) that was found during winter and maximum value
(7.90) that was recorded during premonsoon. Variation in soil pH of salt marsh bed was 6.10-
7.20 that was reported by Ihm and Lee (1998). It was found in this study that the soils of salt
marsh bed were almost neutral to slightly acidic, depending on soil moisture. In general, areas
with low elevation, high flooding frequency, and anaerobic conditions (Ponnamperuma,
1972) have near-neutral pH and others have suggested that most wetland soils have neutral
pHs (6.5 to 7.5) (Gambrell, 1994; Mitsch and Gosselink 2000) that agreed with the findings
of the present study.
Free soil water salinity variation was found to be distinct in the present study that was
ranged from 10.52 to 21.06‰ with a minimum concentration (5.33‰) recorded during
monsoon and the maximum concentration (24‰) observed during winter. Soil salinities in the
brackish water marshes were measured by Zieman and Odum (1977) from 15‰−20‰ that
agreed with present findings. The highest and the lowest soil salinities in the present study
were recorded during winter and monsoon periods since the soil salinity at any point of the
intertidal zone is directly related to salinity of tidal waters, time interval between inundations,
rainfall, the rate of evaporation and the retention properties of soil (Hutchings and Saenger,
1987). However, the salinity in soil water varies depending on various factors such as the
flooding frequency, precipitation, presence of tidal creeks, drainage gradient, water table
depth, and freshwater inflow (Mitsch and Gosselink, 2000; Mendelssohn and McKee,2000)
as the results found in the present investigation.
Soil organic carbon of
Porteresia
bed was fluctuated from 1.76 to 3.42% with a
minimum value (1.58%) during monsoon and the maximum value (4.57%) found during
winter. Similarly the soil organic matter ranged from 3.03 to 5.90% with a minimum value
(2.72%) found during monsoon and the maximum value (7.89%) found during winter. The
high percentage of organic carbon and organic matter was recorded in winter throughout this
study could primarily be attributed to input from the salt marsh in form of dead leaves and
decaying stem, roots. Mann (1982) as well as Smith (1996) stated that organic enrichment of
mangrove sediment in the intertidal zone is from leaf litter derived from mangrove trees and
from detritus. Variations of organic matter (2.60-4.90%) in salt marsh were noticed in a study
completed by Ihm and Lee (1998) which was coincided with this study. However organic
matter is known to affect other properties of soils (Brady, 1974). The highest organic matter
content found in winter had the highest field water capacity of soil but the reverse was the
case in monsoon, postmonsoon and premonsoon which recorded low percentages of organic
