The Impact of Makeshift Oil Refineries on the Macro-Invertebrates of the Nun River Estuary, Niger Delta, Nigeria

¹GIJO AH, ²HART AI, ¹*SEIYABOH EI

Greener Journal of Biological Sciences, vol. 6, no. 5, pp. 112-119, December, 2016

¹Department of Biological Sciences, Niger Delta University, Wilberforce Island, P. M. B. 71, Yenagoa, Bayelsa State, Nigeria

²Department of Animal and Environmental Biology, University of Port Harcourt, P.M.B. 5323, Port Harcourt, Rivers State, Nigeria.

INTRODUCTION

Benthic organisms (or benthos) are organisms that inhabit the bottom of the rivers, streams or seas, whether in the intertidal region or below tidal marks (Tait 1982; Josiah 1997). They fall into two major categories, namely, the animal called zoobenthos and the plant component known as the phytobenthos (Holmes and McIntyre 1984). The zoobenthos which are essentially invertebrates are further distinguished into three groups: macro-benthos, meio-benthos and micro-benthos, according to the size of the organisms. The macro-benthic invertebrates (or macro- zoobenthos) are described as bottom dwelling animals that are big enough to be retained by a sieve with a mesh size of 1.0mm (Holmes and McIntyre, 1984; Day 1981 and 1982). Most macrobenthic organisms have intermediate planktonic larval phases, a few swim freely during a short breeding season before settling permanently on rocks, sediments, or mangroves to become adults. The most abundant macro-zoobenthos are often polychaetes, molluscs (both bivalves and gastropods), nematodes, isopods, ceridian and panaeid shrimps, crabs and echinoderms (Gijo, 2011). The intertidal macro- zoobenthos have been recognized to be economically important. For instance, benthic molluscs are important sources of calcium and protein in human diets and these are often found in the mangrove environment (Sasekumar, 1984; Josiah, 1997; Gijo, 2011). Also, the shells of the gastropod molluscs such as T. fuscatus and P. fusca are used extensively in some localities in building and construction works. Zoobenthos also serve as food to various species of birds and fishes like Fundulus heterodontus and Aplocheilichthyes spilauchena which feed on mangrove invertebrates such as molluscs, crustaceans and polychaetes (Sasekumar, 1984; Josiah, 1997; Gijo, 2011).

            A baseline ecological survey of the macro- invertebrates of the Nun River estuary was conducted from September, 2009 to July, 2010. Shortly after the research, makeshift oil  refineries  were  established  in  the  estuary and this resulted in frequent oil spills from 2011 till date, which seriously polluted the area. These events necessitated the current research.

            The aim of this project was to investigate the impacts of makeshift oil refining activities on the mangrove ecosystem and on the macro- invertebrates of the Nun River Estuary in Brass Local Government area, Bayelsa State, Nigeria. The specific objective of this research is:

            To determine the impacts of the crude oil spillages associated with the makeshift oil refining activities on the benthos of the area.

MATERIALS AND METHODS

Description of Study Area

The study area is the Nun River Estuary, which is situated around Akassa kingdom in Brass Local Government Area of Bayelsa State, Nigeria. Several creeks, inlets, and canals are connected to this estuary, which serve as navigational routes and drainages in the area. It is also connected to other estuaries through these channels. The Brass river estuary is situated towards the east while the Sangana river estuary is situated towards the west of the Nun River estuary. The Atlantic Ocean is connected to the Nun River estuary from the south.

Figure 1: Map of the Niger Delta, Nigeria

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Makeshift oil refineries (Kpo fire) are established in the area. Indigenous technologies used to distil locally made gin (ogogoro or kaikai) are employed to refine the crude oil into various petroleum products. Metal pipes and drums welded together are used- in which crude oil is boiled and the resultant fumes are collected, cooled and condensed in tanks to be used locally for lighting, energy or transport.

            The makeshift (local) oil refineries or Kpo fire have been in operation since 2011 and abated gradually early 2015. The study area was chosen because, in spite of the heavy aquatic pollution that the estuary has been subjected to, no research has been conducted in the area to ascertain the impacts on the macro benthic intertidal invertebrates.

Designation of Sampling Stations

Six sampling stations were chosen. The randomized block experimental design was used during the research. Two Six sampling stations were chosen. The randomized block experimental design was used during the research. Two of the sampling stations (stations 1 and 3) were established exactly on the makeshift oil refinery camps, which were designated the “highly impacted zones” and Station 2 was established in an area that is adjacent to station 1, which was designated as “partially impacted zone”. The remaining sampling stations (stations 4, 5, and 6) were the three sampling stations (Stations 1, 2, and 3), that were sampled during the base line study, respectively. The experimental design that was used during study was the randomized block design.

Field Sampling

This research was conducted for one year; from August, 2014 to July, 2015. A reconnaissance survey of the area was conducted prior to the main study. Benthos, water and soil were sampled once a month from the six sampling stations along a transect running from the low intertidal level (LTL) through the mid intertidal level (MTL) to the high intertidal level (HTL).

Sampling of intertidal benthic macro invertebrates

Different sampling methods were used in the collection of faunal samples. These methods included the use of quadrats, Visual counts (Okon, 2005), collections (Hanley, 1993; Okon, 2005), and burrow counts (Mc Guinness, 1992, 1993). Sampling of the macro invertebrates of the area was done monthly with a quadrat of size 0.5m2 (50cm x 50cm) at the ebb of the spring tide in each of the stations. The benthos covered by the quadrat was excavated with the aid of a spade to the depth of about 20cm, digging below 20cm will produce a strong smell and only few animals are found beyond that depth (Sesarkuma, 1984). Prior to the excavation, all juvenile crabs, and gastropod molluscs crawling within the quadrat were hand- picked and put into a labeled wide mouthed bottle containing 10% formalin and 0.1% of the vital stain, Rose Bengal (Mason and Yevich 1967; Frigelos and Zenetos 1988). The excavated samples were kneaded and then washed with several runs of water through a 1mm mesh sieve (Holland et al., 1977). Where the substratum was sticky and muddy, it was broken up in small bits and macro fauna sorted out by hand picking. After washing, the mangrove residue, the macrofauna retained in the sieve were transferred into the bottle containing Rose-Bengal in formalin (10%).

Sorting and Identification of Benthos

The preserved zoobenthic samples were examined in the laboratory and the infauna present were isolated. Initially, each sample was washed to remove the formaldehyde which would otherwise cause a choking smell and discomfort. The samples were then placed on a white surgical tray and pink stained animals were removed with a pair of forceps and were preserved in 50% alcohol. By means of an illuminating dissecting microscope the infauna were sorted and identified to the lowest possible taxonomic level using the keys of Day (1967).

The number of species in each sample and station were recorded. Some components of the macro fauna notably, the polychaetes, oligacheates and crustaceans were fragmented during the process of washing, hence only heads were counted (Ankar and Jansson, 1973; Gijo, 2011).

For the calculation of density, the formula that was used was:

= Total number of animals

    Total Area of quadrat

The density of the major macrofauna was estimated by counting the number of organisms present in each sample, and values were approximated to the nearest whole number.

The percentage frequency of occurrence was calculated with the formula:

=Number of occurrence of species in sample thrown X 100

Total Number of throws                          1

PAST (a statistical package) was used to calculate the dominance, evenness, and the Shannon- Weaver’s, Simpson’s, and Margalef’s diversity indices.

RESULTS

The checklist of the intertidal benthic macro invertebrates is presented in Table 1. A total 18 species distributed among 14 genera and 9 families were recorded during the study. Also, a total of 2, 942 individual organisms were collected in which 41 belonged to the Class Polycheata, 684 belonged to the Class Decapoda (subphylum crustacea), and 2, 217 belonged to the Class Gastropoda (Table 1).

As the margalef values show (Table 2) species richness was highest at station 4 and lowest at stations 1 and 3. Community diversity (Shannon- Weaver) was in the sequence: 4>2>6>5>1=3. The species are more evenly distributed at station 2 and Simpson’s dominance peaked at station 2. The monthly diversity indices (Table 3) revealed that, based on margalef values, species richness was highest in September, 2014 and  lowest  in  January , 2015. Community diversity (Shannon- Weaver) also had the highest value in September, 2014 and lowest in June, 2015. The species were more evenly distributed in January, 2015 and Simpson’s dominance peaked in June, 2015.

Table 1: A Checklist of benthic macro invertebrates collected from the Nun River Estuary

Figure 2: Percentage composition of each class of benthic macro invertebrates of the Nun River Estuary during the current study

Figure 3: Percentage composition of each class of benthic macro invertebrates of the Nun River Estuary during the baseline study in 2009- 2010

Table 2: Diversity indices across the stations

Table 3: Monthly diversity indices (August, 2014- July, 2015)

DISCUSSION

The data obtained during this study indicated that the makeshift oil refining activities had a tremendous impact on the benthos. The impact of the illegal oil refineries affected both the density and distribution of the biota. 30 species of benthic macro invertebrates were identified during the baseline study, whereas, only 18 species were recorded in the current study. About 12 species were absent during the current study. The species that were absent include Marphysa sp., Marphysa sanguinae, Notomastus latericeus, Lumbrinereis sp., Marianida pinniger, Lillyalla sp., Mandippi sp., Littorina anguilifera, Neritina owenensis, Pachymelania aurita, Pachymelania bryonensis, and Crassostrea gasar. The organisms that were recorded during the baseline study belonged to 15 families; unlike those of the current study that had just 10 families. Also, the total of number of individual organisms were higher in the baseline study than the current study. 3,052 individual organisms were collected during the baseline study while only 2, 942 individual organisms were obtained during the current study. The 3,052 individual organisms were collected from only 3 sampling stations and the samples were collected for only 6 months out of one year; unlike the current study that had up to 6 sampling stations and the samples were collected for 12 months.

The number of species that were collected in the current study are also fewer than those recorded by other researchers in the Niger Delta. For instance, Josiah (1997) recorded 23 species; Zabbey (2002) recorded 30 species; Hart (1994) recorded 43 species; Mansi (1997) recorded 44 species and Zabbey (2011) recorded 65 species of macro-zoobenthos (18 species of epifauna and 47 species of infauna). However, Woke (2004) recorded just 14 species, fewer than those recorded  in the current study.

The results also show that the class Gastropoda, made up of 1 family and 2 species had the highest percentage composition (75.36%) and are the most dominant species of the area, followed by the class Decapoda (22.5%), Class Polychaeta (1.39%), and Class Bivalvia (0.57%), respectively (Table 1 and Figure 2). In the baseline study, the percentage composition of the Class Gastropoda was 64.1% (against 75.36% in the current study), followed by the Class Decapoda (Crustacea) which had a percentage composition of 15.37% (against 22.5% in the current study), and then Class Bivalvia which had a percentage composition of 11.99% (against 0.57% in the current study), and Class Polychaeta, which had a percentage composition of 8.55% (against 1.39% in the current study)- figure 3. Various results from studies on benthic macro invertebrates in the Niger Delta showed remarkable variation of dominant groups. According to Woke (2004) organisms of the Classes Gastropoda and Insecta were dominant in his study in terms of species composition and number of families. Conversely, Akani (1994), Mansi (1997), and Zabbey (2002) all reported that the polychaetes were the most dominant benthos. Also, Ewa-Oboho and Oladimej (1999) reported that Polychaetes and crustaceans dominated by species and number (31.2%, 55.6%) and (20.8%, 28.9%), respectively, followed by molluscs (16.9%). In addition, Zabbey (2002) reported that the Class Oligachaeta was the second most dominant benthos in terms of species composition and number of families followed by the Class Crustacea. Snowden and Ekweozor (1990) also reported that the polychaetes and the fiddler crab (Uca tangeri) were the most abundant.

Among all the organisms, Pachymelania fusca of the class Gastropoda was the most abundant, having about 2, 213 individual organisms out of the 2, 942 organisms that were collected during the study. Pachymelania fusca occurred only at the Mid and High intertidal zones of sampling station 6, unlike the baseline study in which the organism occurred in large numbers in at the low, mid and high intertidal zones of station 1 (current station 4) and the low and mid intertidal zones of stations 2 (current station 5) and 3 (current station 6). Decapod crustaceans had the highest number of families (7) and species (15) with the family Grapsidae being the most dominant. The polychaetes consisted of about 3 species from 2 families with the family Nereidae being the most abundant.

The results also indicated that the benthic macrofauna of stations 1 and 3 (the illegal oil refinery camps) were completely destroyed, except for station 3 that had just one species of Sesarma huzardi.  Station 1 had THC, pH, temperature, and salinity of 1881.79 mg/l, 5.54, 28.83oC, and 7.87%o, respectively. Similarly, Station 3 had THC, pH, temperature, and salinity of 1907.89mg/l, 5.47, 28.73oC, and 7.92%o, respectively.  The high THC in the illegal oil refinery camps coupled with the acidic pH (5.47 and 5.54) and low DO may have caused the elimination of the macrofauna in these stations. The intertidal benthic macro invertebrates of station 2 were also very few, compared to stations 4, 5, and 6. Station 2 had THC, pH, temperature, and salinity of 1810.43mg/l, 5.47, 28.68oC, and 7.9%o, respectively.  In a related study, Ekweozor, et al., (1989) undertook a baseline survey of the intertidal macrofauna of the Bonny Estuary and found that Port Harcourt and Okrika sites located in the central portion of the estuary had very low polychaete and total faunal densities with Okrika having a particularly lower number of species in comparison with the other sites, with Capitella capitata being dominant. These low faunal densities were ascribed to pollution of soil (Spies and Davies, 1979; Dauvin, 1982; McLusky, 1982). Levels of total oil and grease in the sediment at the Okrika site were found to: range from 0.13- 0.58g/l00g-1 at the least oiled and most oiled stations respectively, values which Ekweozor, et al., (1989) pointed out, far exceeded background levels found in other areas.

CONCLUSIONS

The study revealed that the persistent environmental pollution (specifically, oil spillages) that were caused by the makeshift oil refining activities have adversely affected the macro zoobenthos of the area, with overall negative effects on the sustainability in the Nun river estuary and the Niger Delta environment as a whole. Therefore, it is reasonable to conclude that the makeshift oil refineries and related activities that were condoned in Akassa kingdom, around the River Nun estuary, are detrimental to the environment.

RECOMMENDATIONS

The results of this study have shown the imminent problems that arise from the pollution of the water and sediments of the Nun River estuary. Based on the findings of this research, it is, therefore, recommended that:

1.   Makeshift oil refineries should be discouraged or, if they will be allowed to operate, proper measures should be put in place to prevent environmental pollution.

2.   Oil pollution in the estuary and other water bodies receiving effluents should be constantly monitored and properly controlled in order to forestall cumulative effects of pollution in the river.

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