| Resume |
This work presents recent data on the physico-chemical properties and the trophic
status of Kpassa reservoir at eighteen locations from August 2014 to February 2015.
Seventeen physico-chemical parameters were measured and data obtained were statistically
analyzed. The descriptive statistics showed their variations (minima-maxima)
as follows: pH (4.65 - 7.30), temperature (25.1˚C - 29.9˚C), dissolved oxygen (1
- 5.79 mg/L), oxydability (0.32 - 10.88 mg O2/L), electrical conductivity (55 - 77
μS/cm−1), TDS (76 - 94 mg/L), turbidity (15.70 - 274.40 NTU), transparency (0.24 -
1.55 m), suspended matter (3 - 92 mg/L), total phosphorus (0.25 - 1.90 mg/L), orthophosphate
(0.08 - 0.61 mg/L), nitrate (undetected 5.50 mg/L), nitrite (undetected
0.79 mg/L), ammonia (undetected 0.36 mg/L), chlorophyll a (7.20 - 2334.6 μg/L), silica
(4.34 - 15.67 mg/L) and N/P ratio (0.08 - 42.62). These parameters were mainly
influenced by agricultural activities and climatic conditions. The restriction or the
removal of the use of chemical fertilizers in agricultural activities in Kpassa reservoir
basin was recommended. The highest values of Pearson and Spearman correlations
were observed across TDS and conductivity (0.967; 0.951), turbidity and oxydability
(0.924; 0.665), turbidity and chlorophyll a (0.884; 0.663), turbidity and suspended
matter (0.982; 0.793), suspended matter and transparency (−0.781; −0.819), suspended
matter and nitrate (−0.813; −0.839), suspended matter and oxydability
(0.919; 0.602) and suspended matter and chlorophyll a (0.879; 0.656). Carlson’s
trophic state index (TSI) values varied between 36 and 66 showing that Kpassa reservoir
was eutrophic in August and mesotrophic to oligotrophic during the other
months of the sampling period. ANOVA and Kruskal-Wallis test indicated that there
were no significant differences between sampling stations. |