103
lower than 616 Mg km
−2 year
−1 reported from a
watershed in south Sikkim (Rai and Sharma
1998) and 500–1,000 Mg km
−2 year
−1 reported
from other Himalayan region (Milliman and
Meade 1983).
Further, it may be noted here that the soil and
nutrient loss from the watershed has led to the
annual deposition of 1.42 Mg of total nitrogen,
0.31 Mg of total phosphorus and 6.88 Mg of
organic carbon to the lake. The sediments and
nutrients from the watershed were fi lling up the
lake gradually leading to decrease in the depth
and proliferated growth of vegetation; the peat
land, for example, had increased by 33 % in little
more than four decades reducing the open-water
surface of the lake and forming a kettle hole bog.
The radiocarbon dating of the peat samples
revealed that the peat had been deposited since
3,500 years and the recent formations were
encountered near the lake water periphery. The
peat land was, possibly, acting as a fi ltering
interface for the sediments and nutrients.
However, its intensity was rather limited especially during the rainy seasons. This view has
also been supported by Buttery et al. (1965) and
Gosselink and Turner (1978).
Most of the precipitation was received in the
rainy season that forced higher overland fl ow and
nutrients peaked in the lake during this season.
Notwithstanding the above, the transparency of
the lake generally decreases during the monsoon
season with increase in conductivity values.
Notably, most of the rains occur during the rainy
season. Concomitantly, aquatic biodiversity also
usually depicts seasonal fl uctuations in the lake
and bog as that of nutrients (Jain et al. 2005b).
The chlorophytes and rotifers, amongst the
plankton, portray abundance. The planktonic
productivity depicted 247 mgC m
−2 day and
respiration of 189 mgC m
−2 day in the lake during
warmer months (Jain et al. 1999). However, the
rate of primary production was within the range
of 7 to 3,000 mgC m
−2 day for Himalayan lakes
(Kaul 1977). The density and diversity of the
plankton revealed that the lake was enriched by
nutrients, possibly, from the upland watershed
during the rainy season. In fact, the physicochemical and biological characteristics of the
lake revealed its oligo-mesotrophic nature.
However, if the anthropogenic pressure continues
at the current rate, then the lake may be totally
derelicted in near future.
However, the process of lake fi lling could be
retarded and the lake longevity may be
increased by integrated management approach
where human interference is minimised; and
the resource extraction in the surrounding
watershed is rationalised. Some of the other
measures could be as follows:
(a) Restriction of fi rewood and timber collection, especially the canopy species from the
lake watershed. It is because exploitation of
the canopy species may cause imbalance
amongst the species that led to dominance by
secondary species reducing the fi rewood
biomass and quality of the forest.
(b) Dense mixed forest cover is to be maintained
on the ridges of the lake watershed to regulate
stream fl ow and reduce erosion process.
(c) Livestock grazing needs to be controlled in
the lake watershed to minimise soil loss.
(d) Trampling in the bog area needs to be
stopped completely as it leads to the sliding
down of peat into the water and making the
lake shallow.
(e) Animal wastes also enrich the lake with nutrients which, in turn, accelerates eutrophication
process. Recovery of the Sphagnum mats
takes at least two years after damage from
trampling. It may be noted here that Sphagnum
mats have important fi ltering interface role in
this lake where sediment load from the watershed was very high.
(f) Few native rhizomatous species such as
Alocasia may be grown at the forest edge
of lake to restrict the sediments from entering the bog.
(g) Successional process in the bog area should
be arrested by minimising sediment accretion from the watershed. This can be achieved
by reducing grazing intensities and fi rewood
extraction.
(h) Further, agricultural practice in the lake watershed was, perhaps, the main contributor of
sediment and nutrient load in the lake. It should
be taken care of. Conversely, agroforestry
6.9 High Altitude (HA) Lentic Bodies
lower than 616 Mg km
−2 year
−1 reported from a
watershed in south Sikkim (Rai and Sharma
1998) and 500–1,000 Mg km
−2 year
−1 reported
from other Himalayan region (Milliman and
Meade 1983).
Further, it may be noted here that the soil and
nutrient loss from the watershed has led to the
annual deposition of 1.42 Mg of total nitrogen,
0.31 Mg of total phosphorus and 6.88 Mg of
organic carbon to the lake. The sediments and
nutrients from the watershed were fi lling up the
lake gradually leading to decrease in the depth
and proliferated growth of vegetation; the peat
land, for example, had increased by 33 % in little
more than four decades reducing the open-water
surface of the lake and forming a kettle hole bog.
The radiocarbon dating of the peat samples
revealed that the peat had been deposited since
3,500 years and the recent formations were
encountered near the lake water periphery. The
peat land was, possibly, acting as a fi ltering
interface for the sediments and nutrients.
However, its intensity was rather limited especially during the rainy seasons. This view has
also been supported by Buttery et al. (1965) and
Gosselink and Turner (1978).
Most of the precipitation was received in the
rainy season that forced higher overland fl ow and
nutrients peaked in the lake during this season.
Notwithstanding the above, the transparency of
the lake generally decreases during the monsoon
season with increase in conductivity values.
Notably, most of the rains occur during the rainy
season. Concomitantly, aquatic biodiversity also
usually depicts seasonal fl uctuations in the lake
and bog as that of nutrients (Jain et al. 2005b).
The chlorophytes and rotifers, amongst the
plankton, portray abundance. The planktonic
productivity depicted 247 mgC m
−2 day and
respiration of 189 mgC m
−2 day in the lake during
warmer months (Jain et al. 1999). However, the
rate of primary production was within the range
of 7 to 3,000 mgC m
−2 day for Himalayan lakes
(Kaul 1977). The density and diversity of the
plankton revealed that the lake was enriched by
nutrients, possibly, from the upland watershed
during the rainy season. In fact, the physicochemical and biological characteristics of the
lake revealed its oligo-mesotrophic nature.
However, if the anthropogenic pressure continues
at the current rate, then the lake may be totally
derelicted in near future.
However, the process of lake fi lling could be
retarded and the lake longevity may be
increased by integrated management approach
where human interference is minimised; and
the resource extraction in the surrounding
watershed is rationalised. Some of the other
measures could be as follows:
(a) Restriction of fi rewood and timber collection, especially the canopy species from the
lake watershed. It is because exploitation of
the canopy species may cause imbalance
amongst the species that led to dominance by
secondary species reducing the fi rewood
biomass and quality of the forest.
(b) Dense mixed forest cover is to be maintained
on the ridges of the lake watershed to regulate
stream fl ow and reduce erosion process.
(c) Livestock grazing needs to be controlled in
the lake watershed to minimise soil loss.
(d) Trampling in the bog area needs to be
stopped completely as it leads to the sliding
down of peat into the water and making the
lake shallow.
(e) Animal wastes also enrich the lake with nutrients which, in turn, accelerates eutrophication
process. Recovery of the Sphagnum mats
takes at least two years after damage from
trampling. It may be noted here that Sphagnum
mats have important fi ltering interface role in
this lake where sediment load from the watershed was very high.
(f) Few native rhizomatous species such as
Alocasia may be grown at the forest edge
of lake to restrict the sediments from entering the bog.
(g) Successional process in the bog area should
be arrested by minimising sediment accretion from the watershed. This can be achieved
by reducing grazing intensities and fi rewood
extraction.
(h) Further, agricultural practice in the lake watershed was, perhaps, the main contributor of
sediment and nutrient load in the lake. It should
be taken care of. Conversely, agroforestry
6.9 High Altitude (HA) Lentic Bodies