The effect of physicochemical parameters on the abundance of zooplankton of River Adada, Enugu, Nigeria

Figures & data

Figure 1. Map of River Adada indicating sampling stations. Station A (upstream or S1), station B (mid-stream or S2), station C (downstream or S3).

Table 1. From the total number of zooplankton, the rainy season had the highest number of encountered individuals. By stations and seasons, C had more number of individuals in the dry season, while station B in the rainy season (Table 1a). There was no significant difference in zooplankton abundance with seasons (Table 1 b). The multiple pairwise-comparison (Tukey contrasts) between different stations also found no significant difference in zooplankton abundance (table 1c). Significant term in bold.

(a) Seasonal abundance		Station A	Station B	Station C	Total
Dry		302 (32%)	216 (23%)	427 (45%)	945
Rain		292 (23%)	591 (46%)	391 (31%)	1,274
(b) Variables (Zooplankton)	Estimate	S.E	t	P
Intercept	12.08	0.82	14.66	0.01
Seasons	−1.05	1.16	−0.90	0.37
(c) Stations	Estimate	S.E	t	P
A - B	16.55	8.05	−2.05	−2.05
B - B	−2.05	8.06	−2.28	0.09
C - B	−17.75	8.05	−2.20	0.11
B - A	0.11	1.44	−1.26	0.56
C - A	0.56	1.40	−0.86	0.81
C - B	0.60	1.42	0.42	0.97

Table 2. Indicating that copepods (n = 798) were the most encountered zooplankton, followed by the rotifers (n = 564), cladocerans (n = 476) and Ostracods (n = 381). However, the cladocerans had more number of life forms (n = 10 species), followed by copepods (n = 8), rotifers (n = 7) and ostracods (n = 2).

Generic combination	Species	Abundance (%)
Copepods	Macrosetella gracilis	61 (8)
	Setella gracillis	102 (13)
	Diaptomus africanus	119 (15)
	Cryptocyclops bicolor	64 (8)
	Thermocyclops neglectus	149 (19)
	Centropages furcatus	110 (14)
	Copepod nauplii	75 (9)
	Harpacticoid nauplii	118 (14)
Cladocerans	Moina reticulate	15 (3)
	Euryalona orientalis	49 (10)
	Chydorus sphaericus	11 (2)
	Diaphanosoma excisum	88 (18)
	Moina micrura	67 (14)
	Bythosrephes longimanus	55 (12)
	Simocephalus expinous	73 (15)
	Bosmina longirostris	26 (5)
	Acroperus africanus sp. nov	21 (4)
	Alona costata	71 (15)
Ostracods	Parastenocypris unispinosa	152 (55)
	Cytheridella tepida sp. nov	122 (45)
Rotifers	Keratella cochlearis	97 (17)
	Brachionus angularis	63 (11)
	Lecane leontina	201 (36)
	Trichocerca cylindrica	44 (8)
	Keratella tropica	55 (10)
	Lophocharis oxysternon	90 (16)
	Brachionus caudatus	14 (2)
Insect larva	Chironomid imicola larva	31 (29)
	Parachironomus biannulatus larva	19 (18)
	Tanytarsus curticornis	42 (39)
	Chaoborus sp. larva	15 (14)

Table 3. Comparing values from the dry and rainy seasons, the mean water temperature in station A was high during dry season. Meanwhile, turbidity in station B, DO (station B), pH (station C), PO₄³⁻ (station B) and NO₃- (station A) were all high in the rainy season.

	Station A	Station B	Station C
Water properties (Dry season)
Temperature (°C )	21.32 ± 0.2	20.8 ± 0.01	21.00 ± 0.3
Turbidity (NTU)	4.18 ± 0.8	5.25 ± 0.1	5.17 ± 0.4
DO (mg/L)	3.86 ± 0.1	4.13 ± 0.4	3.54 ± 0.2
pH	6.35 ± 0.01	5.21 ± 0.3	5.92 ± 0.2
PO4^³⁻ (mg/L)	1.45 ± 0.2	1.32 ± 0.02	1.40 ± 0.5
NO3- (mg/L)	1.41 ± 0.5	1.18 ± 0.1	1.48 ± 0.1
Water properties (Rainy season)
Temperature (°C)	19.33 ± 0.04	20.77 ± 0.3	19.83 ± 0.01
Turbidity (NTU)	4.72 ± 0.7	7.25 ± 0.1	4.37 ± 0.01
DO (mg/L)	4.82 ± 0.3	8.13 ± 0.9	4.28 ± 0.3
pH	6.57 ± 0.1	7.19 ± 0.01	7.32 ± 0.1
PO4³⁻ (mg/L)	1.34 ± 0.02	1.88 ± 0.2	0.80 ± 0.5
NO3- (mg/L)	1.61 ± 0.8	1.54 ± 0.3	1.10 ± 0.3

Table 4. Zooplankton abundance in station A in relation to physical and chemical indices of River Adada. Indicating that zooplankton abundance in the river was not only affected by seasons, pH, turbidity, PO₄³⁻, and DO but the joint interactive effect of temperature on DO, PO₄³⁻, and pH as well. Significant terms are in bold, while insignificant terms are not included in the table. Insignificant predictors may not be statistically significant, but had a joint significant effect in the presence of another predictor (temperature), thus, included in the table.

Variable (station A)	Estimate	SE	z	P
Intercept	0.31	2.80	0.11	0.91
Seasons (Rain)	0.20	0.08	2.53	0.01
pH	0.63	0.28	2.25	0.02
Temperature	0.08	0.12	0.62	0.53
Turbidity	0.20	0.04	4.64	0.01
PO4^³⁻	−1.24	0.57	−2.17	0.03
DO	−0.77	0.39	−1.97	0.04
Temperature × DO	0.04	0.02	2.03	0.04
Temperature × PO4³⁻	0.05	0.03	1.97	0.04
Temperature × pH	−0.03	0.01	−2.58	0.01

Table 5. Zooplankton abundance in station B in relation to physical and chemical indices of River Adada. Indicating that zooplankton abundance in the river is not only affected by seasons, turbidity, PO₄³⁻, NO₃-, and DO but the joint effect of temperature on DO, and NO₃-. Significant terms are in bold, while insignificant terms are not included in the table. Insignificant predictors may not be statiscally significant, but had a joint significant effect in the presence of another predictor (temperature), thus, included in the table.

Variable (station B)	Estimate	SE	z	P
Intercept	1.41	1.80	0.79	0.43
Seasons (Rain)	−0.55	0.10	−5.34	0.01
pH	0.06	0.03	1.91	0.06
Temperature	0.06	0.08	0.68	0.50
Turbidity	−0.08	0.04	−2.19	0.03
PO4^³⁻	0.12	0.04	3.26	0.01
NO3-	−1.35	0.35	−3.89	0.01
DO	1.13	0.43	2.65	0.01
Temperature × DO	−0.05	0.02	−2.67	0.01
Temperature × NO3-	0.06	0.02	3.86	0.01

Table 6. Zooplankton abundance in station C in relation to physical and chemical indices of River Adada. Indicating that zooplankton abundance in the river is not only affected by temperature, turbidity, PO₄^³⁻, NO_3-, and DO but the joint effect of temperature on DO, and PO₄^³⁻. Significant terms are in bold, while insignificant terms are not included in the table. Insignificant predictors may not be statiscally significant, but had a joint significant effect in the presence of another predictor (temperature), thus, included in the table.

Variable (station C)	Estimate	SE	z	P
Intercept	3.14	0.74	4.23	0.01
Temperature	−0.01	0.03	−0.05	0.96
Turbidity	−0.07	0.03	−2.04	0.04
PO4^³⁻	0.94	0.32	2.95	0.01
NO3-	0.08	0.03	3.19	0.01
DO	−0.08	0.03	−3.07	0.01
Temperature × PO4^³⁻	−0.04	0.01	−2.83	0.01

Figure 2. Zooplankton in relation to temperature (°C) in station A, n = 594.

Figure 3. Zooplankton in relation to DO (mg/L) in station A, n = 594.

Figure 4. Zooplankton in relation to phosphate in station A, n = 594.

Figure 5. Zooplankton in relation to pH in station A, n = 594.

Figure 6. Zooplankton in relation to turbidity in station A, n = 594.

Figure 7. Zooplankton in relation to pH in station B, n = 807.

Figure 8. Zooplankton in relation to temperature in station B, n = 807.

Figure 9. Zooplankton in relation to turbidity in station B, n = 807.

Figure 10. Zooplankton relation to phosphate in station B, n = 807.

Figure 11. Zooplankton relation to nitrate in station B, n = 807.

Figure 12. Zooplankton in relation to DO in station B, n = 807.

Figure 13. Zooplankton in relation to temperature in station C, n = 818.

Figure 14. Zooplankton in relation to turbidity in station C, n = 818.

Figure 15. Zooplankton in relation to phosphate in station C, n = 818.

Figure 16. Zooplankton in relation to nitrate in station C, n = 818.

Figure 17. Zooplankton in relation to DO in station C, n = 818.