Changes in vegetation regeneration, species composition and diversity in a spent carbide waste polluted habitat.
Man's effort to improve his standard of living through the control of nature and development of new products; have resulted in the pollution or contamination of the environment. Much pressure is exerted on the ecosystems and most, if not all of these influences result in the release of substances otherwise known as pollutant. In the global world today, various types of activities, including agriculture, industry and transportation produce a large amount of wastes and new types of pollutants. The global environmental deterioration problem seems to be at its worst in Nigeria (Kinako and Zuofa, 1992). In addition, increase in human population, industrialization, and urbanization have also contributed their quota to the waste generation and drastic reduction in species diversity. Since antiquity, soil has been the repository of society's wastes (Evans, 1989). These pollutants directly or indirectly affect the growth and development of plant, animal and man. Pollutants can cause leaf injury, stomatal damage, premature senescence, decrease photosynthetic activities, disturb membrane permeability and reduce growth and yield in sensitive plant species (Tiwari et al., 2006). Pollutants have also been known to cause the alteration in the physical and chemical nature of the soil which consequently affects plants (Chronopoulos et al., 1997). This may invariably lead to reduction in height and biomass; or resulting in complete plant mortality (Tanee and Akonye, 2009, Anyanwu and Tanee, 2008; Tanee and Anyanwu, 2007; Pezeshki et al., 2000) Carbide waste like every other waste has been reported to be an impediment to most agricultural processes.
Carbide waste is a by-product produced from the use of calcium carbide to generate acetylene gas. The acetylene gas in combination with oxygen produced oxyacetylene flame used by panel beaters and welders for welding and fabrication work. This waste product is whitish or grayish in colour and has high pH (alkaline). After the welding work, these waste (carbide waste) are usually dumped carelessly in the environment especially in nearby forest and vegetation which sooner or later get incorporated into the soil.
Kinako and Amadi (1997) observed a significant adverse effect of dumped carbide on water infiltration, vegetation regeneration and biomass accumulation of plants. In a pot experiment conducted by Ahmed et al. (2006) to investigate the effect of calcium carbide on the growth and yield of rice, wheat and cotton, observed that encapsulated calcium carbide released large amount of acetylene that was slowly reduce to ethylene. This they observed slowed down the release of nitrate from the applied urea which might help in improving nitrogen use efficiency. Tanee and Ochekwu (2010) reported a reduction in the growth and yield of Zea mays (maize) and Arachis hypogea (groundnut) in carbide waste polluted soil especially at high concentration. Kathleen (1980) also reported that E. coli, S. cerevisiae and B. subtilis were inhibited within 15 minutes by the addition of 1% solution of carbide waste due to the increase in the pH of the medium.
Little attention is drawn to the adverse effect of the disposal of carbide waste on the environment especially as it affect plant regeneration and species diversity, hence the need for this research. It is expected that results obtained from this work will widen our knowledge on the effect of carbide waste on plant. This will also assist farmers, panel beaters/welders, sanitation authorities on the proper way(s) of disposal this waste without any harm to the environment.
Materials and Methods
The research work was carried out at vegetation at the back of the Faculty of Pharmaceutical Sciences, University of Port-Harcourt, Choba-Port Harcourt, Nigeria. It is situated in the Niger-Delta part of Nigeria, located within latitude 4[degrees] and 5[degrees]N; and longitude 6[degrees] and 7[degrees] 05'E (Fig.1). The area is characterized with high rainfall (2000-3000mm/year), high mean temperature range (between 23 [degrees]C-35 [degrees]C) and high relative humidity.
[FIGURE 1 OMITTED]
The carbide waste collected from a welding workshop at Choba-PortHarcourt was allowed to dry for some days to get rid of water inorder to obtain the real weight and grinded into powder for easy spread. A suitable site of 10m x 10m was required but a total area of 12m x 12m measured with a measuring tape was cleared and made barred through weeding with cutlass. The extra 2m became a boundary around the study site and separated it from the surrounding vegetations. Before clearing the dominant species on the site were identified. These were Tridax procumbense, Eleusine indica, Syndrella nodiflora, Mimosa pudica, Panicum maximum, Commelina benghalensis and Euphorbia hirta. 10 contiguous plots each measuring 40cm x 40cm were located within the 10m x 10m study site by random sampling approach. Each of the sample plots was separated into two subplots (treatment and control) with 5cm wide with a plank.
600 grams of carbide waste was applied to each treatment sub-plot by hand. The control sub-plot received no carbide waste. The experiment lasted for 123 weeks.
The following parameters were assessed: plant regeneration, plant height, percentage frequency of occurrence, species diversity, above-ground weight (fresh and dry weight). The plant regeneration was done by counting the number of rooted plants in each sample plot on weekly basis. The vegetation height was obtained by taken the average height of the measurement of ten plants in each sample plot on weekly basis. The percentage frequency of occurrence was calculated using the formula:
% frequency of occurrence = n/N x100/1
Where n = number of sample plot in which the species occurred; N = total number of sample plots used for the exercise.
At the termination of the experiment, the plant species in each sample plot were identified and number (species content) recorded. The population density per metre-square for each species was calculated. The species diversity was also calculated using Shannon-Wiener diversity index (1949) which states thus:
H = -[summation](pi(log pi)};
Pi = ni/N
Where; ni= number of individual of the ith species; and N= total number of individual of all species.
The above-ground biomass of rooted plants in each sample plot were harvested with a cutlass and immediately taken to the laboratory to avoid water loss. These were weighed on a weighing balance (Meter Toledo model) to obtain the fresh weights. The dry weight was obtained by wrapping the harvested plant from each sub-plot in aluminum foil and dried in Fanem drying and sterilizing oven at 80 [degrees]C for 72 hours and then weighed on the same weighing balance.
All data collected were subjected to statistical analysis such as mean, standard deviation and standard error mean (SEM). Students' t-test was employed to determine the level of significant between means @p=0.05.
Carbide waste adversely affected the rate of vegetation regeneration (Table 1). It was observed that the rate of vegetation regeneration was significantly depressed by the addition of carbide waste. The vegetation regeneration was very scanty at the treatment sub-plots. Similar result was also recorded for the vegetation height (Table 2) in which the vegetation heights in the carbide waste treatment sub-plot were significantly lower than that in the control.
Table 3 showed the percentage frequency of occurrence of the various species encountered in the experimental site (treatment and control). The percentage frequencies of occurrence of the species in the control were higher than that in the carbide waste treatment sub-plot. Only Panicum maximum and Ageratum conyzoides recorded equal percentage frequency of occurrence in both the treatment and control sub-plots. Similar trend were observed for the population density (Table 4). The population densities of all the 8 species recorded was higher in the treatment than that in the control. Mimosa pudica was completely eliminated in the carbide waste treatment plot. Despite the fact that control sub-plots have a higher species content of the different species as against the treatment sub-plots, there was no difference between the species diversity in both the treatment and control sub-plots using Shannon-Wiener diversity index (Table 5).
Figs. 2 and 3 showed the mean vegetation above-ground fresh weight and dry weight yields respectively in both the treatment and control sub-plots. Result showed a significant (p=0.05) reduction in both the vegetation above-ground fresh weight and dry weight yields in the carbide waste treatment sub-plots as against the control.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Result obtained from this study is in agreement with Tanee and Ochekwu (2010) who observed that high concentration of spent carbide waste significantly affects the growth and yield of plants especially maize and groundnuts. Odjegba and Sadiq (2002) observed that anything that interfere with nutrient and water absorption by plant will definitely affects normal growth and development of plants. It might therefore, be suggested that carbide waste interference with water absorption by plant leading to reduction in germination/sprouting and subsequent growth. This suggestion is true since Kinako and Amadi (1997) reported a reduction in water infiltration in carbide waste polluted soil due to the blocking of soil pores by the carbide waste particles. An increase in soil pH in spent carbide waste polluted environment has been reported by Kathleen (1980) and Tanee and Ochekwu (2010). This might also be responsible for the scanty regeneration and the poor growth in the carbide waste polluted soil since most plants grow best at pH close to neutrality (Purseglove, 1985a & b).
Results showed significant increments in the species percentage frequency of occurrence, population density and species numbers in the control than in the polluted habitats except Ageratum conyzoides in which the above parameters were higher in the treatment than the control. Mimosa pudica was completely eliminated from the ecosystem. The phytotoxicity of the spent carbide waste might have imposed some environmental stress on the plants thereby leading to the reduction in their numbers. The total absence of Mimosa pudica plant in the carbide waste polluted sub-plots is an indication of the plant sensitivity to pollution stress showing that the plant cannot withstand pollution stress and can therefore easily go extinct in pollution prone environment. Drastic reduction in the above-ground fresh weight and dry weights in the carbide waste polluted soil as compared to the control is in line with Tanee and Ochekwu (2010) and Kinako and Amadi (1997) who independently also reported a reduction in total plant biomass in carbide waste polluted habitats. The delay in the germination/sprouting and subsequent reduction in growth of the plant species in the carbide waste treated plots might have contributed to the reduction in the aboveground biomass of the vegetation species. It is possible that the toxicity of the carbide waste could have interfere with the plant metabolic activities leading to poor growth and development (Achuba, 2006). It is observed that the different species responded differently especially in their growth performances to the carbide waste application indicating the different adaptations of the species to pollution stress in terms of tolerance and sensitivity.
Despite the fact that carbide waste affected the other measured parameters, it did not have any significant effect on the species diversity in both the treatment and control.
In conclusion, it is obvious that spent carbide waste drastically reduced vegetation regeneration and changed vegetation structure in terms of species composition and development. Therefore, better ways of disposing spent carbide waste should be sort out rather than dumping it indiscrimately on the nearby vegetations. Means of recycling this used product should be developed.
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Department of Plant Science and Biotechnology
University of PortHarcourt, Rivers State, Nigeria
Table 1: Changes in Rate of Vegetation Regeneration in spent carbide waste polluted habitat. Time (Weeks) Control Treatment t-test 1 10.3 [+ or -] 1.38 1.2 [+ or -] 0.6 7.32 * 2 15.8 [+ or -] 1.84 2.6 [+ or -] 0.6 7.62 * 3 23.7 [+ or -] 3.4 2.6 [+ or -] 0.6 6.89 * 4 31.2 [+ or -] 3.2 2.6 [+ or -] 0.6 10.19 * 5 36.0 [+ or -] 2.9 2.6 [+ or -] 0.6 11.04 * 6 39.2 [+ or -] 2.9 3.2 [+ or -] 0.39 11.88 * 7 42.4 [+ or -] 3.91 3.2 [+ or -] 0.39 11.33 * 8 44.4 [+ or -] 3.18 3.7 [+ or -] 0.39 12.50 * 9 47.4 [+ or -] 3.20 3.7 [+ or -] 0.36 13.50 * 10 48.0 [+ or -] 3.18 3.7 [+ or -] 0.36 14.38 * 11 53.9 [+ or -] 3.13 3.7 [+ or -] 0.36 15.94 * 12 57.6 [+ or -] 2.19 3.7 [+ or -] 0.36 18.25 * Values represent mean [+ or -] SEM * = significant @ p=0.05 Table 2: Changes in Vegetation Height (cm) in spent carbide waste polluted habitat. Time (weeks) Control Treatment t-test 1 0.8 [+ or -] 0.08 0.45 [+ or -] 1.08 3.44 * 2 2.25 [+ or -] 0.10 1.19 [+ or -] 0.22 2.73 ns 3 3.01 [+ or -] 0.10 1.65 [+ or -] 0.28 3.64 * 4 3.74 [+ or -] 0.12 2.07 [+ or -] 0.35 3.88 * 5 4.44 [+ or -] 0.15 2.39 [+ or -] 0.40 4.19 * 6 4.68 [+ or -] 0.12 2.78 [+ or -] 0.27 5.62 * 7 4.84 [+ or -] 0.12 2.93 [+ or -] 0.26 5.82 * 8 5.13 [+ or -] 0.02 3.05 [+ or -] 0.27 5.97 * 9 5.22 [+ or -] 0.10 3.79 [+ or -] 0.65 6.16 * 10 5.58 [+ or -] 0.48 3.46 [+ or -] 0.26 6.44 * 11 5.86 [+ or -] 0.12 3.63 [+ or -] 0.32 7.08 * 12 6.13 [+ or -]0.10 3.70 [+ or -] 0.32 8.00 * Values represent mean [+ or -] SEM * = significant @p=0.05 ns = not significant @ P= 0.05 Table 3: Changes in Species Percentage Frequency of Occurrence in spent carbide waste polluted habitat. Species Control (%) Treatment (%) Euphorbia hirta 70 40 Syndrella nodiflora 100 60 Eleusine indica 80 70 Panicum maximum 80 80 Ageratum conyzoides 10 10 Commelina benghalensis 40 20 Tridax procumbense 50 30 Mimosa pudica 10 0 Table 4: Changes in Population Density ([m.sup.-2]) in spent carbide waste polluted habitat. Species Control Treatment Euphorbia hirta 1512.5 165 Syndrella nodiflora 3435 215 Eleusine indica 1887.5 200 Panicum maximum 2555 200 Ageratum conyzoides 12.5 22.5 Commelina benghalensis 250 20 Tridax procumbense 1552.5 77.5 Mimosa pudica 92.5 -- Table 5: Changes in species number and diversity in spent carbide waste polluted habitat. Species Control Treatment Euphorbia hirta 605 66 Syndrella nodiflora 1,374 86 Eleusine indica 755 80 Panicum maximum 1,022 80 Ageratum conyzoides 5 9 Commelina benghalensis 100 8 Tridax procumbense 621 31 Mimosa pudica 37 -- Total 4519 360 Mean 564.84 51.428 Species diversity 0.726 0.743 (Shannon-Wiener index)