Environmental Engineering Reference
In-Depth Information
from 7.67 in September to 8.98 during May. By
and large, the pH values were lower in initial
stations and gradually increased downstream.
Also the summer values were in general highest
and the post-monsoon values were the lowest
(Table
6.10
).
that the river water nearly becomes devoid of any
dissolved oxygen in the downstream direction at
stations IV and V, causing anoxic conditions.
Total Suspended Solids
Much variation in the levels of TSS was recorded
from all the stations (Table
6.12
). Stations I and II
had relatively low levels of TSS as compared to
stations III, IV, and V. The values of TSS increased
from station I to station V (Table
6.12
). Thus,
station I recorded the lowest values of TSS, while
the highest values were met with at station V. The
post-monsoon season recorded the highest values
of suspended solids (Table
6.12
) from all the
stations. The highest mean value of 685.20 mg/L
was recorded from station V in the month of
August. The lowest value recorded at this station
was in the month of December (Table
6.12
).
Overall the winter season had the least values of
suspended solids (Table
6.12
). The mean summer
values were just a little higher than the winter
values and thus ranged between the winter and
the summer levels.
Dissolved Oxygen
The levels of dissolved oxygen fl uctuated from
season to season at all the sampling stations.
During the sampling period, mean DO values, as
low as 0 mg/L to as high as 7.8 mg/L, were
obtained (Table
6.11
). On the whole, however,
stations I, II, and III showed fairly good amount
of dissolved oxygen, while stations IV and V had
very low levels of oxygen throughout the year
(Table
6.11
). As expected the dissolved oxygen
levels were highest during the winter season at
almost all the stations (Table
6.11
) except at sta-
tion V. Station III had the highest mean value
(7.8 mg/L) of DO in the month of January. The
lowest levels at all the stations were encountered
during the hot summer season (Table
6.11
).
In fact during the month of April, stations IV and
V had mean DO levels equal to 0.48 mg/L and
0 mg/L, respectively. Station II had dried up com-
pletely by the summer season. Station III showed
fairly good amount (3.79 mg/L) of DO even in
summer. Though station I had the highest dissolved
oxygen values for the early summer season, it
dried up by the end of April. Owing to the proper
mixing of water during the post-monsoon period,
most stations showed reasonably good amount of
dissolved oxygen (Table
6.11
). In fact highest
mean value (1.44 mg/L) of dissolved oxygen for
station V was recorded during the post-monsoon
season in the month of August (Table
6.11
).
Similarly the other stations also showed good
amount of dissolved oxygen during this period.
The DO values must also be seen in comparison
with the BOD values. As the DO values fall, there
is a concomitant rise in the BOD levels. This is
clearly seen in (Table
6.16
). Since biologically
degradable organic matter constitutes 7 % of
sewage, it has a direct infl uence on the dissolved
oxygen content of the water (Hynes
1978
) result-
ing in the “oxygen-sag curve.” As indicated in
Table
6.11
, the DO levels fall to such an extent
Chlorophyll-a
The chlorophyll-a content varied throughout the
study period with the maximum being recorded
during the post-monsoon period and the mini-
mum in summer at all the stations (Table
6.13
).
Stations IV and V showed very low chlorophyll-a
content throughout the year, while stations I, II, and
II had a good level of chlorophyll-a (Table
6.13
).
The mean chlorophyll-a values at station IV ranged
from 4.20 in April to 21.90 in October
(Table
6.13
). Similarly the mean chlorophyll-a
content at station V ranged from 6.10 in April to
22.10 in October (Table
6.13
). Stations I and III
showed drastic fl uctuations in the level of
chlorophyll-a throughout the year (Table
6.13
).
Total Reactive Phosphate
Stations I and II showed low levels of total
reactive phosphate in comparison to station IV
and V (Table
6.14
). Station III showed moderate
values of total reactive phosphate. Throughout
the year, highest values were obtained in summer,
while the lowest during the post-monsoon season
at all the stations (Table
6.14
).
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