Specific Diversity and Dynamics of the Phytoplankton Population in a Pond Fertilized with Chicken Droppings in the West Highlands Cameroon

Area and Period of Study

The test was carried out at the Aquaculture Station of the Application and Research Farm (F.A.R) of the University of Dschang (North Latitude: 5°44’-5°36’ and Est Longitude: 10°06’-9°85’, altitude: 1392 -1396 m) located in the West Cameroon highlands agro-ecological zone. This zone is characterized by a short dry season (mid-November to mid-March) and a long rainy season (mid-March to mid- November). Annual rainfall varies between 1500 and 2000 mm and temperatures range between 14°C (July-August) and 25°C (February).

Obtaining and Conditioning of Chicken Droppings

In order to avoid variability in chemical composition, hen droppings were collected from the same farm and stored at room temperature. A sample was taken to determine the concentration of dry matter, total nitrogen and total phosphorus. The mean values of the dropping characteristics were as follows: dry matter (80.2 ± 3.33%), total nitrogen (2 ± 0.14%) and total phosphorus (1.5 ± 0.06%).

Experimental Ponds

The test was carried out inside 9 diversion ponds with the same surface area (5.7 x 5.7 m) and a depth of 1 m with a flow rate of 3.23 liters per minute. In order to eliminate undesirable organisms (fish) and increase the alkalinity of the environment, the ponds were dewatered for a period of 7 days and limed with quicklime at a dose of 400 kg/ha. Mesh size net (1.5 mm) was attached to the inlet pipe of each pond to prevent fish intrusion from the reservoir. Each of the three treatments consisting of 0; 800 and 1000 kg/ha of chicken droppings was applied in one of the ponds randomly. Each treatment was repeated three times.

Conduct of the Trial and Data Collection

Pond Fertilization: In order to control phytoplankton production, chicken droppings were applied to the ponds by spreading once a week for a period of 6 months. For this purpose, the fertilizer doses were weighed with an electronic precision scale 0.1g each time before application. Sampling of Phytoplankton Organisms: Phytoplankton sampling was carried out on a biweekly basis for 6 months. Sampling was carried out at 20 different points in the water column of each pond using a calibrated polyethylene container with a capacity of 1 liter, i.e. a total volume of 20 liters/pond filtered through a 40 µm mesh plankton sieve. A volume of 350 ml of concentrated phytoplankton was recovered, fixed by the addition of 5% formaldehyde and kept in plastic bottles for quantitative and qualitative analyses. Determination of the Physico-Chemical Characteristics of Water: The Secchi disc transparency, temperature, pH, dissolved oxygen and electrical conductivity were measured directly in the field using a ballasted Secchi disc attached to a graduated string, Thermo-Conductimeter, Thermo- PH meter, pH meter, Thermo-Oxymeter and Thermo- Conductimeter from HANNA respectively. Nitrite, nitrate and total phosphates were determined by spectrophotometry (spectrophotometer HACH DR/2000) according to Apha techniques [8]. Qualitative and Quantitative Analysis of Phytoplankton: Each previously filtered sample (350ml) was left to rest for a minimum of 24 hours to allow for phytoplankton sedimentation. A volume of 300ml of water was then removed above the phytoplankton residue by siphoning and the concentrated phytoplankton samples were kept in beakers. The qualitative analysis of the phytoplankton was carried out according to the method described by Nguetsop, et al. [9]. Thus, after homogenization, two drops (10 μl) of each concentrated phytoplankton sample were taken with a pipette, mounted between slide and slide and observed using an Olympus optical microscope (×40 objectives), model BH- 2, equipped with a nomarski lens. For each sample, three slides were prepared to ensure reproducibility of the slides [9].

The identifications were made using the keys of Bourelly and Manguin [10]; Compère [11]; Couté and Rousselin [12], Compère [13, 14]; Gasse [15]; Iltis [16]; Gasse [17]; Krammer and Lange-Bertalot [18].

The cell counts were performed using an inverted

microscope, ZEISS 47 12 02 with the ×40 objective as recommended by Lund, et al. [19]. After homogenization, 10 ml of the sample was taken with a calibrated pipette, placed in a settling cup and allowed to settle for 10 min. Counts were made on six fields taken randomly from the cup. The minimum number of units (cell, filament, cenobe or colony) counted per replicate of a sample was set at 400, in order to have an accuracy of ± 10 to 95% confidence interval.

Statistical Analyses

The collected data were subjected to the one-factor analysis of variance (ANOVA 1). In the case of significant differences between the means, the Duncan’s test was applied to separate them at the 5% significance level. SPSS 20.0 (Statistical Package for Social Sciences) was used for these analyses.

Effects of Chicken Droppings Dose on Phytoplankton Species Richness and Distribution

The composition of the phytoplankton stand summarized in Table 1 shows that, independently of the doses of chicken droppings, a total of 237 species grouped in 6 phytoplankton phylum were recorded.

The distribution of phytoplankton species shows that of the 237 species identified, 164 are represented in unfertilized ponds, i.e. a proportion of 61.19%. As regards fertilized ponds, a total of 121 species or 51.05% were represented in ponds having received 800kg of dropping and 109 species representing 46% in 1000kg. From Table 1 summarizing the distribution of species, it can be seen that 83 out of 237 species were represented only in unfertilized ponds. The dominant species in these ponds are Merismopedia elegans, Mycrocystis aeruginosa, Nostoc entophytum.

In the fertilized ponds, the species specifically represented in the 800kg treatment were the highest (23 species out of 237) compared to those recorded with the 1000kg of chicken droppings dose (23 species). It should be noted that 66 species (i.e. 27.84% of the total species recorded) were represented transversally in all three treatments (0; 800 and 1000 kg).

The Pyrrophyte phylum is only represented in the ponds fertilized with the highest dose of chicken dropping, whereas the Rhodophyte phylum is only represented in the treatment with 800 kg/ha of chicken dropping.

Phylum Distribution of Phytoplankton Species as a Function of Dropping Dose

Figure 1 illustrates the distribution of species by phylum as a function of dropping dose. Overall, in unfertilized ponds, the algal flora is dominated by species belonging to the Bacillariophytes phylum (34%) whereas ponds fertilized at 800 and 1000 kg were dominated by Charophytes at 42 and 30% respectively.

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Dynamics of Phytoplankton Density as a Function of Dropping Dose

The evolution of phytoplankton density as a function of manure dose is illustrated in Figure 2, which shows that the trend, profile and rate of change in density were generally comparable between treatments.

Regardless of the test period, the lowest phytoplankton density values were observed in unfertilized ponds and the highest in ponds fertilized with the highest dose of chicken dropping (1000 kg/ha).

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Statistical analysis conducted on phytoplankton density showed that there was no significant difference (p < 0.05) between ponds fertilized at the 800 and 1000 kg of chicken droppings (Figure 3).

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a, b; bars with the same letter are not significantly different (p > 0.05); ind : individual, l : liter Figure 3: Comparison of phytoplankton density in ponds as a function of droppings dose.

Phytoplankton Diversity Index

The index Shannon & Weaver diversity and equitability summarized in Table 2 showed a decrease with increasing fertilizer dose. Thus, the highest values of Shannon’s index and equitability were recorded in unfertilized ponds and the lowest in ponds fertilized with the 1000 kg of chicken droppings.

Correlation between Physicochemical Characteristics of Water and Phytoplankton Density as a Function of Fertilizer Dose: Correlations between physicochemical characteristics of water and phytoplankton density (Table 3) showed that phytoplankton density is negatively and highly correlated (p < 0.01) with electrical conductivity, pH, dissolved oxygen, nitrite and nitrate in the control treatment. Conversely, phytoplankton density is positively and strongly correlated to transparency, dissolved oxygen and pH in the treatment at the dose of 800 kg/ha chicken droppings.

**: significant correlation p < 0.01 (bilateral); Table 3: Correlation between physicochemical characteristics of the water and phytoplankton density.