International Journal of Aquaculture 2013, Vol.3, No.2, 4
-
7
http://ija.sophiapublisher.com
5
1
Results
Five taxonomic groups consisting of forty-one species
were discovered from Ogun River (Table 1).
Chrysophyta
was represented by 15 species consisting
of 36.6%,
Chlorophyta
with 14 species consisting of
34.1%,
Cyanophyta (7 species) consisting of 17.1%,
Euglenophyta
with 3 species consisting of 7.3% and
Pyrrophyta
with 2 species consisting of 4.92%. The
abundance of phytoplankton species is presented in
Figure 1 and Table 2.
Cyanophyta
was the most
abundant with 41%. This was followed by
Chrysophyta
(31.4%),
Chlorophyta
(23.6%),
Euglenophyta
(2.5%)
and
Pyrrophyta
(1.5%).
Table 1 Number of species in each taxonomic group of
phytoplankton sampled (December, 2011 – June, 2012)
Taxonomic group
Total No. of species
Percentage (%)
Chrysophyta
15
36.6
Chlorophyta
14
34.1
Cyanophyta
7
17.1
Euglenophyta
3
7.3
Pyrrpphyta
2
4.9
Total
41
100.0
Figure 1 Taxonomic group abundance of phytoplankton in
River Ogun (December, 2011 - June, 2012)
2
Discussion
Cyanophyta
(
also known as Blue green algae,
Cyanobacteria
and
Myxophyceae
)
surpassed the
phytoplankton in terms of abundance while
Chrysophyta
surpassed in terms of number of
species/genus. The dominance of
Cyanophyta
has
been observed by several authors among which are:
Sekadende et al., (2004) who observed
Cyanophyta
dominance in Lake Victoria basin, Ogato, (2007) who
observed dominance of
Cyanophyta
in Lake Bishoftu,
Deng et al., (2007) who reported dominance of
Cyanobacteria
in summer and autumn in Lake
Chaohu; Shakila and Natarajan (2012) who also
observed dominance in the Temple Pond of Thiruporur,
Chennai. The abundance of
Cyanophyta
observed in
this study must have been caused by the polluted
nature of the water due to the anthropogenic activities
carried out around its shores. The dominance of
Cyanophyta
is a signal that the river is polluted.
Consequently, there is therefore need to regulate the
amount of pollutants discharged into the river so as to
avoid total ecological collapse and extinction of the
populace. It is hereby recommended that relevant laws
in respect to sustainability of the river should be
implemented.
3
Materials and Methods
3.1
Geography of the river
Ogun State is a state in the South-western region of
Nigeria. It has boundary with Lagos State to the South,
Oyo and Osun states to the North, Ondo State to the east
and the republic of Benin to the west. Abeokuta is the
capital and largest city in the state (NBS, 2012). River
Ogun is one of the main rivers in the southwestern part
of Nigeria with a total area of 2.24×10
6
m
2
and a fairly
large flow of about 393 m
3
secG1 during the wet season
(
Oketola et al., 2006). It is 3°28'E and 8°41'N from its
source in Oyo state to 3°25'E and 6°35'N in Lagos where
it enters the Lagos lagoon (Ayoade et al., 2004). Two
seasons are distinguishable in Ogun river basin, a dry
season from November to March and a wet season
between April and October. Mean annual rainfall ranges
from 900 mm in the north to 2 000 mm towards the
south. The estimates of total annual potential
evapotranspiration have been put between 1 600 mm and
1 900
mm (Bhattacharya and Bolaji, 2010). The water is
used for agriculture, transportation, human consumption,
various industrial activities and domestic purposes.
Along its course, it constantly receives effluents from
breweries, slaughterhouses, dyeing industries, tanneries
and domestic wastewater before finally discharging to
Lagos lagoon (Ayoade et al., 2004; Oketola et al., 2006).
A 100 square kilometer area around River Ogun has an
approximate population of 3 637 013 (0.03637 persons
per square meter) and an average elevation of 336 m
above the sea (Travel Journals, 2012). Numerous human
activities such as bathing, washing of clothes, fishing,
locust bean processing, mangrove cutting, and
transportation were noticed. These are potential sources
of pollution to the environment. Indiscriminate dumping
of human excreta was observed at two of the sampling
stations. Four sampling stations were established along
the length of Ogun River.