1Ude, Emmanuel Fame*, 1Ugwu,
Lawrence Larry Chukwuma, 2Mgbenka, Benard Obialor and 3Nwani,
Christopher Didigwu
1.
Department
of Fisheries and Aquaculture, Ebonyi State University, P. M. B. 053,
Abakaliki-Nigeria.
2.
Department
of Zoology, Fisheries and Aquaculture Unit,University of Nigeria Nsukka,
Nigeria
3.
Department
of Fisheries and Aquaculture, Ebonyi State University, P. M. B. 053,
Abakaliki-Nigeria.
ABSTRACT
A
baseline study of the limnological integrity of Ebonyi River, a tropical lotic
system in south-eastern Nigeria was conducted between September 2006 and
February 2008 to assess its potential in enhancing fisheries production for the
benefit of the rural poor, who depend on the resources of the river for
survival. The parameters measured were nitrate-nitrogen, nitrite-nitrogen and
phosphate-phosphorus.
Results show that nitrate varied between 40.43mg/L in
September 2006 and 1.73mg/L in December 2007, Showing significant difference
(P<0.01) among months. The values recorded for nitrites varied between
0.2mg/L in September 2006 and 0.4mg/L in February 2008, showing significant
(P<0.01) variation among months. Values recorded for phosphorus was highest
(0.05mg/L) in the month of October 2006 while the least mean value (0.32mg/L)
was recorded in the month of May 2007 and
showed significant (p<0.01) variation in monthly means. It was concluded
that the values of the measured parameters falls within tolerable range for
enhanced fisheries development in the area.
Key words: Limnology, Tropical, River
INTRODUCTION
Less than 0.01% of the Earth’s total
water resources occur in liquid form covering approximately 3% of the land
surface (Revenga and Kura, 2003).
Extreme variability in the spatial and temporal distribution of this
small amount of water, together with the large geomorphologic variability, has
resulted in a variety of water bodies – from ephemeral pools to large lakes and
mighty rivers. A significantly large
proportion of the Earth’s biodiversity representing nearly all kinds of
organisms – from microorganisms to mammals – inhabits inland waters (Revenga
and Kura, 2003).
The purpose of environmental assessment
and management is ultimately the maintenance of biological integrity. Fish needs certain optimum conditions for
feeding, breeding, respirations, growth and movement.
Recent evidence indicates that some
sedimentary rocks contain large amounts of fixed Nitrogen, and so weathering
may provide significant amounts of nitrate to running waters in some
circumstances (Holloway et al., 1998,
Thompson et al., 2001, Williard et al., 2005). Spatial variation in
stream water nitrate concentrations is influenced by nitrification in upland
soils, which affects the extent to which catchments retain or export nitrate
via stream flow (Likens and Bormann 1995, Bernhardt et al., 2005).
Principal anthropogenic inputs of
Nitrogen to streams include agricultural fertilizers, atmospheric deposition,
N-fixing crops, and human and animal wastes (Boyer et al., 2002). Nitrogen inputs often vary seasonally due to the
effects of the growing season and hydrology. Due to uptake of N by terrestrial
vegetation, stream water concentrations tend to be lower during the growing
season and higher during the dormant season (Vitousek et al., 1975). Although some fertilizer is assimilated by crops,
when applied at high levels, substantial amounts of N leach into surface and
groundwater, resulting in increases in river nitrate concentrations (Heathwaite
et al., 1996, Gachter et al., 2004)
Meybeck 1982 reported that major
forms of nitrogen found in natural waters appear as dissolved inorganic
nitrogen, nitrate (No3-), Nitrite (No2-), ammonium (NH4+),
dissolved organic Nitrogen. All these added together are referred to as total
dissolved nitrogen. Another form of Nitrogen in water is particulate organic
nitrogen. The entire forms of N summed up are known as total nitrogen.
Major forms of phosphorus found in
natural waters are present as dissolved inorganic phosphorus (PO4-3
orthophosphate or soluble reactive phosphorus). This is also known as total
dissolved phosphorus. It is also present as dissolved organic phosphorus and
particulate organic phosphorus. These are referred to as total organic
phosphorus. A combination of total dissolved phosphorus and total organic
phosphorus is known as total phosphorus (Meybeck, 1992).
Allan and Castillo (2007) reported
that Nitrogen and phosphorus are the major nutrients that have been found to
influence rates of primary production and the activity of heterotrophic
microbes. Research has shown that benthic algal productivity can be limited by
either N or P singly, be co-limited by both, or not be nutrient limited (Allan
and Castillo, 2007). Sources and supplies of N and P vary considerably with
geology, soils, climate, and vegetation, and their concentrations often are
substantially elevated owing to anthropogenic inputs.
Phosphorus in waters is present in
several soluble and particulate forms including organically bound phosphorus,
inorganic polyphosphates and inorganic orthophosphates (Lind, 1979). Adeniji
(1983) regarded phosphorus as a biologically active element which cycles
through many states in the aquatic ecosystem, and its concentration in any one
state depends on the degree of metabolic synthesis or decomposition occurring
in the aquatic system. Similarly, Cole (1983) observed that phosphorus is the
element most likely to cause a stimulation of plant production and is thus
often measured in relation to excessive production and problems of
eutrophication.
Phosphorus dynamics in streams is
influenced by physical, chemical and biological process. The principal biological process are
autotrophic and heterotrophic uptake of dissolved P and its assimilation into
cellular constituents , transfer of organic phosphorus through the food chain
and its eventual release and mineralization by excretion and the decomposition
of egested material. Algae and microbes
in biofilms likely obtain the majority of their P from the water column, but
rooted macrophytes and benthic algae can remove P from the sediments as well.
Phosphorus may be excreted or released following cell lysis directly as
dissolved inorganic P, which subsequently is mineralized to orthophosphate by
bacterial activity. The decomposition of
organic matter including feces, dead organisms and leaf litter also releases P
into the water column and sediment pore water (Mainstone and Parr 2002).
Ebonyi River is a freshwater river
system which opens into Cross River and subsequently the Atlantic Ocean. Thus ecological changes within the river are
of inter-regional concern. The river is
bounded by many communities in Ebonyi State. At the moment there seems to be no
published information on its physicochemical properties.
This study is considered important
because of the multiple uses of Ebonyi River. Apart from its relevance as
source of fish production it serves the people as source of portable water
supplied by the State Water Corporation after purification. It also provides
facilities for wildlife, transportation and vegetable irrigation farms for the
people. In view of the multipurpose use of the river, impacts of schemes that
change the form and function of the river and hydrograph on fish and fisheries
can be anticipated in project planning. Unfortunately in spite of the
recognized importance of the river and the various activities taking place in
and around it, little or no detailed scientific information on the river is
available.
MATERIALS
AND METHODS
Area of Study
The area of study is Ebonyi River
which is a freshwater system that has its source from lower Benue River and
opens into Cross River, but transverses the old Abakaliki Zone of Ebonyi State,
Nigeria. Abakaliki is situated between 060 19.370` North latitudes
and 0080 07.692` East longitudes. There are two distinct seasons
within the zone; a wet season which starts from April to August and the dry
season which starts from September to March. The research work covered the
period from September 2006 to February 2008.
Sampling
Locations: Sampling
locations were chosen after preliminary surveys of the river based on such
factors as representation of upstream, midstream and downstream, volume of
water, depth, activities taking place in and around the river and
accessibility. Four sampling locations were marked at intervals of 3.5 to 8km (Figure
1).
Location 1 is in Ebonyi Local
Government area. The area serves the locals as source of water for domestic use
as well as site for dry season irrigation farming for vegetables and fishing
amongst other uses.
Location 2 is about 1.5km from the
faculty of Agriculture and natural resources Management campus of the State
University. The site is prominent
because, the pumping station of the State water corporation is located
there. This mini dam at this site ensures
availability of large volume of water all year round in the station allowing
for fishing activities, irrigation vegetable farming and other domestic uses
Location 3 is located at Onuebonyi,
500metres from Ebonyi State Fertilizer blending Industry. It is also a site for domestic water supply
to the rural dwellers within the vicinity.
Fishing and small scale irrigation activities also goes on around the
station.
Location 4 is located at Echara in
Ikwo local Government area. This is the
major source of water supply for the rural dwellers of the area. Artisanal fishing and river-side irrigation
vegetable farming are among the notable activities taking place in the station.
All analysis was done using the standard
methods described in APHA (1999) and Lind (1979). Water samples was collected fortnightly from
the chosen stations (1, 2, 3 and 4) using sampling bottles.
The analysis of phosphate-phosphorus was
by colorimetric method using HANNA analytical kit.
RESULTS
The monthly mean variation of nitrate-nitrogen
in relation to station in Ebonyi River is presented in table 1, it varied
between 40.43mg/L in September 2006 and 1.73mg/L in December 2007, Showing
significant difference (P<0.01) among months. The means of location 1 and 2 showed no significant
(P>0.05) from each other but varied significantly (P<0.01) from location
3 and 4 whose values are not significantly different from each other.
The result of monthly mean values of
Nitrite-Nitrogen in relation to locations is presented in table 2. The values varied between 0.2mg/L in
September 2006 and 0.4mg/L in February 2008.
It also showed significant (P<0.01) variation between seasons while
there was interaction in the values of December 2006 and March 2007. Similarly the mean values of December 2007
interacted with those of January and March 2008 Fig. 2 shows the monthly
variation of the values of nitrite-nitrogen in relation to stations.
The mean monthly variation of phosphate
phosphorus in relation to stations in Ebonyi River showed higher concentration
in the months of the end of rainy season, the highest mean value (0.05mg/L)
recorded in the study period was in the month of October 2006 while the least
mean value (0.32mg/L) was recorded in the month of May 2007. (Table 3)
variation in monthly mean values was significant (P<0.01) different
months. Location 1 and 4 were not
significantly different (P>0.05) from each other but varied significantly
(P<0.01) from locations 2 and 3 which are also significantly different
(P<0.01) other locations.
DISCUSSION
Nitrate nitrogen was found to exhibit
the pronounced seasonal variation of all other chemical parameters measured.
The mean values recorded in rainy season were higher than those recorded for
other months. The reason for this high concentration may be due to excessive
influx of nutrients from farm lands where fertilizer is used to boost crop
production particularly around the river environment as well as input through
runoff into the river. Nwoko (1991) had suggested that nitrate nitrogen could get
into the water through various sources such as cattle dung, fertilizer run-off
and leaching of leguminous farms. The decrease in concentration level of the
nitrate nitrogen in other months may be due to heterotrophic uptake by
micro-organisms, sediment adsorption and complete loss of some aquatic
macrophytes.
Phosphate phosphorus concentration values were higher in October, and
July than in other months. Olsen and Sommerfield (1977) associated phosphate
increase with phytoplankton standing crop increase. The recorded values
remained stable in most other months. Sandra (2000) reported that phosphorus is
the most important and limiting substance
controlling
organic production. Although the values of phosphate- phosphorus recorded in
this study differ from the range 3.8 - 6.30 observed by Beadle (1981) in some
productive African rivers and lakes, it agrees with the 20 -51mg/L range
recorded in Delimi River by Anadu and Akpan (1986). The sources of phosphorus
in the river during the study period may be due to intensive agricultural
activities around the river involving the use of fertilizers and pesticides to
produce dry season crops like vegetables and even Maize. Villagers were using
water from the river for domestic activities including washing of cloths with
detergents which increase phosphate level of the water. It is therefore concluded that the values of
the measured parameters falls within tolerable range for enhanced fisheries
development in the area if the integrity is enhanced or at least maintained.
Fig. 1: Map of Ebonyi Basin showing Sampling Locations
Table 1: The
Monthly Mean Values of Nitrate Nitrogen Concentrations (mg/L)
in Relation to Locations in Ebonyi River
|
|
Locations
|
|
||||||
|
Months
|
1
|
2
|
3
|
4
|
Mean
|
|||
|
September 2006
|
41.140
|
40.260
|
39.810
|
40.490
|
40.425a
|
|||
|
October 2006
|
13.405
|
14.020
|
14.370
|
14.515
|
14.078g
|
|||
|
November 2006
|
6.710
|
5.985
|
7.570
|
5.730
|
6.499i
|
|||
|
December 2006
|
1.585
|
1.325
|
1.435
|
1.665
|
1.503l
|
|||
|
January 2007
|
1.895
|
1.470
|
1.630
|
1.815
|
1.703l
|
|||
|
February 2007
|
1.715
|
1.485
|
1.805
|
2.015
|
1.755l
|
|||
|
March 2007
|
1.660
|
1.475
|
1.890
|
1.895
|
1.730l
|
|||
|
April 2007
|
20.605
|
21.630
|
22.610
|
23.625
|
22.117f
|
|||
|
May 2007
|
28.895
|
28.985
|
29.640
|
29.755
|
29.319e
|
|||
|
June 2007
|
33.590
|
35.145
|
35.605
|
36.205
|
35.136d
|
|||
|
July, 2007
|
36.110
|
37.060
|
37.045
|
37.340
|
36.889c
|
|||
|
August 2007
|
36.135
|
36.270
|
36. 715
|
37.530
|
36.663c
|
|||
|
September 2007
|
37.980
|
38.225
|
39.000
|
39.570
|
38.694b
|
|||
|
October 2007
|
12.580
|
12.060
|
12.830
|
12.735
|
12.551h
|
|||
|
November 2007
|
3.425
|
3.535
|
4.670
|
3.480
|
3.777j
|
|||
|
December 2007
|
1.610
|
1.655
|
1.965
|
1.670
|
1.725l
|
|||
|
January 2008
|
2.005
|
2.000
|
2.035
|
2.010
|
2.012k
|
|||
|
February 2008
|
2.015
|
2.015
|
2.045
|
2.025
|
2.025k
|
|||
|
Mean
|
15.726b
|
15.811b
|
16.259a
|
16.337a
|
|
|||
|
|
|
|
|
|
|
|||
|
F- LSD (p< 0.05):
|
Locations = 0.3029**;
|
Months = 0.6426**;
|
Locations x Months
= NS
|
|||||
|
|
|
|
|
|||||
|
Levels of significance: ** = p<0.01 and NS = non
significant
|
|
|||||||
Means
followed by the same latter(s) are not significantly different
|
Table 2: The Monthly Mean values of Nitrite Nitrogen
Concentrations (mg/L) in Relation to
Locations in Ebonyi River
|
|
|
Locations
|
|
||||||
|
Months
|
1
|
2
|
3
|
4
|
Mean
|
|||
|
September 2006
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
October 2006
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
November 2006
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
December 2006
|
0.3000
|
0.3000
|
0.4000
|
0.3000
|
0.3250cd
|
|||
|
January 2007
|
0.4000
|
0.4000
|
0.4000
|
0.4000
|
0.4000a
|
|||
|
February 2007
|
0.4000
|
0.4000
|
0.4000
|
0.4000
|
0.4000a
|
|||
|
March 2007
|
0.2000
|
0.4000
|
0.4000
|
0.4000
|
0.3500bc
|
|||
|
April 2007
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
May 2007
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
June 2007
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
July, 2007
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
August 2007
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
September 2007
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
October 2007
|
0.2000
|
0.2000
|
0.2000
|
0.2000
|
0.2000e
|
|||
|
November 2007
|
0.2000
|
0.2000
|
0.4000
|
0.4000
|
0.3000d
|
|||
|
December 2007
|
0.3000
|
0.4000
|
0.4000
|
0.4000
|
0.3750ab
|
|||
|
January 2008
|
0.4000
|
0.4000
|
0.4000
|
0.4000
|
0.4000a
|
|||
|
February 2008
|
0.4000
|
0.4000
|
0.4000
|
0.4000
|
0.4000a
|
|||
|
Mean
|
0.2556c
|
0.2722b
|
0.2889a
|
0.2833a
|
|
|||
|
|
|
|
|
|
|
|||
|
F- LSD (p< 0.05):
|
Locations = 0.01566**;
|
Months = 0.03322**;
|
Locations x Months = 0.06645**
|
|||||
|
|
|
|
|
|||||
|
Level of significance: ** = p<0.01
|
|
|
||||||
|
Means followed by the same latter(s) are not significantly
different
|
||||||||
|
Table 3: The
Monthly Mean Values of Phosphate Phosphorus Concentrations (mg/L) in Relation to Locations in Ebonyi
River
|
|
|
Locations
|
|
||||||
|
Months
|
1
|
2
|
3
|
4
|
Mean
|
|||
|
September 2006
|
0.036000
|
0.043000
|
0.043000
|
0.038000
|
0.040000f
|
|||
|
October 2006
|
0.044000
|
0.056000
|
0.056500
|
0.044500
|
0.050250a
|
|||
|
November 2006
|
0.038000
|
0.043000
|
0.041000
|
0.036000
|
0.039500f
|
|||
|
December 2006
|
0.038000
|
0.043000
|
0.043000
|
0.036000
|
0.040000f
|
|||
|
January 2007
|
0.038000
|
0.047000
|
0.045000
|
0.036000
|
0.041500e
|
|||
|
February 2007
|
0.035000
|
0.049000
|
0.048000
|
0.035000
|
0.041750de
|
|||
|
March 2007
|
0.035000
|
0.049500
|
0.048000
|
0.036000
|
0.042125d
|
|||
|
April 2007
|
0.032000
|
0.042000
|
0.042000
|
0.032000
|
0.037000j
|
|||
|
May 2007
|
0.030000
|
0.037000
|
0.032000
|
0.030500
|
0.032375l
|
|||
|
June 2007
|
0.030000
|
0.040000
|
0.040000
|
0.036000
|
0.036500k
|
|||
|
July, 2007
|
0.038000
|
0.050000
|
0.049000
|
0.044000
|
0.045250c
|
|||
|
August 2007
|
0.035000
|
0.040000
|
0.038000
|
0.038000
|
0.037750i
|
|||
|
September 2007
|
0.035500
|
0.041500
|
0.039000
|
0.038000
|
0.038500h
|
|||
|
October 2007
|
0.044500
|
0.053000
|
0.053000
|
0.043000
|
0.048375b
|
|||
|
November 2007
|
0.038000
|
0.045000
|
0.041000
|
0.035500
|
0.039875f
|
|||
|
December 2007
|
0.038000
|
0.044000
|
0.041000
|
0.034000
|
0.039250g
|
|||
|
January 2008
|
0.037000
|
0.046000
|
0.044000
|
0.031000
|
0.039500fg
|
|||
|
February 2008
|
0.035000
|
0.049000
|
0.048000
|
0.037000
|
0.042250d
|
|||
|
Mean
|
0.036500c
|
0.045444a
|
0.043972b
|
0.036694c
|
|
|||
|
|
|
|
|
|
|
|||
|
F- LSD (p< 0.05):
|
Locations = 0.000293**;
|
Months = 0.000622**;
|
Locations x Months
= 0.001243**
|
|||||
|
|
|
|
|
|||||
|
Levels of significance: ** = p<0.01
|
|
|
||||||
|
Means followed by the same latter(s) are not significantly
different
|
||||||||
|
|
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