TITLE:
Physico-Chemical Features of the Kpassa Reservoir, Northern Benin, with Emphasis on Its Trophic State: A Preliminary Study
AUTHORS:
Ousmane Touré Boukari, Daouda Mama, Youssouf Abou, Moctar Limam Bawa
KEYWORDS:
Physico-Chemical Features, Trophic State, Kpassa Reservoir, Okpara River, Benin
JOURNAL NAME:
Journal of Environmental Protection,
Vol.7 No.13,
December
26,
2016
ABSTRACT: 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), 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
(.781; .819), suspended matter and nitrate (.813; .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.