MSc

Forest vegetation and water are two valuable resources for mankind, and
both the resources influence each other. It is important to understand the interrelationship between forest vegetation and hydrology.
The present study was undertaken in Irumbupalam and Mayiladumpara
watersheds in Peechi-Vazhani wildlife sanctuary, Thrissur, Kerala. The aim of the
study was to identify and quantify the hydrological differences between these
watersheds and assess the extent to which these differences are related to vegetation
characteristics. Mayiladumpara watershed comprised of eight different land use
classes of which mixed crops and trees accounts highest (27.91%) area whereas
Irumbupalam comprised of three land use classes, of which, reserved forest
occupied the highest (67.74%) of area. Within each watershed, twenty-two, 10 m x
10 m sample plots were laid out for detailed enumeration of vegetation and soil
parameters. The Irumbupalam harbored a greater number of tree species (38)
compared to the Mayiladumpara (28). The mean tree density ha-1 was higher in
Mayiladumpara (586 individuals ha-1
) compared to Irumbupalam (509 individuals
ha-1
). Similarly, the mean tree basal area was greater in Mayiladumpara (45.48 m2
ha-1
) as compared to Irumbupalam (13.97 m2
ha-1
). The tree diversity was found to
be maximum in Irumbupalam watershed.
Physico- chemical properties of soil viz. soil pH, organic carbon, water
holding capacity, soil moisture and soil porosity showed showed higher values for
Irumbupalam watershed. There were differences in terms of soil physico- chemical
properties in watersheds between pre-monsoon and monsoon season. The highest
values for soil pH (5.87-7.05), C (2.12-6.61%), porosity (41.42-44.95 %), WHC
(41.85-72.92 %), SM (9.2- 44.07 %) was recorded in Irumbupalam. Whereas, BD
(0.74-1.64 gm cm-3) values were higher in Mayiladumpara than Irumbupalam.
Canonical correspondence analysis (CCA) showed a complex interrelationship
amongst species clustering, site and soil properties.
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Mean annual precipitation for both watersheds were recorded. Stream flow
measurements were taken monthly for stream depth and stream velocity using float
method. Groundwater levels observations was taken monthly from selected wells.
Water quality parameter was assessed monthly from upstream, mid-stream and
downstream points for both watersheds. Mean rainfall for Irumbupalam and
Mayiladumpara for the period (2017-21) was 457 mm and 514.8 mm respectively
in the pre-monsoon season, and 1555.5 mm and 1567.7 mm in the monsoon season.
Mayiladumpara's monthly streamflow was always higher than Irumbupalam. The
pre-monsoon water yield of well was higher in Irumbupalam as compared to
Mayiladumpara. The Irumbupalam watershed always had a higher water table than
the Mayiladumpara watershed. Stream water temperature (WT), total dissolved
solids (TDS), electrical conductivity (EC), turbidity, nitrate (NO3- ) were
significantly (p<0.05) higher in Mayiladumpara Irumbupalam. In contrast,
dissolved oxygen (DO) and pH of water was significantly higher (p<0.05) in the
Irumbupalam. Seasonal variation was observed in the physico-chemical properties
of stream water both in watersheds over the study period of eight months.
Pearson correlation coefficient revealed that canopy closure was
significantly related to some hydrological parameters. Canopy closure was
significantly correlated with four water physico-chemical parameters (p<0.05) viz.,
dissolved oxygen (DO), temperature, electrical conductivity (EC), (NO3-). This
indicated that canopy closure is related to water quality. Canopy cover was
positively correlated (p<0.05) with DO and negatively correlated with nitrate
(NO3- ) (p<0.05). Quantitative as well as qualitative hydrological differences was
observed between these watersheds. The physico-chemical parameters of stream
water like Dissolved oxygen, Electrical conductivity, Water temperature, Nitrate
was found to be influenced by canopy closure of watersheds.
The Canopy closure was significantly and positively correlated with soil
water holding capacity, soil moisture and soil organic carbon. Soil water holding
capacity was found to be significantly and positively correlated with soil porosity,
soil moisture soil organic carbon and negatively correlated with soil bulk density.
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Soil porosity was positively correlated with soil moisture and soil organic carbon
and negatively correlated with soil bulk density. Soil moisture was positively
correlated with the soil organic carbon and negatively with soil bulk density. Soil
bulk density was negatively correlated with the soil organic carbon
More extensive study covering a range of added parameters should be
conducted to understand the function of different forest ecosystems in maintaining
hydrological processes. The hydrological characteristics should be researched for
two or more annual cycles to get a comprehensive understanding. The results of this
study also point to an imperative necessity of longer duration studies covering (premonsoon, monsoon, and post-monsoon) seasons for more complete view of the
hydrological functions of a forest watershed.