Rainy Season Dynamics of Phosphorus Fractions in Lake Toho Sediments and Surrounding Agricultural Soils
Lyde Tometin *
Kabba Laboratory for Research in Chemistry and Applications (LaKReCa), École Normale Supérieure (ENS) of Natitingou, National University of Sciences and Technologies, Engineering and Mathematics (UNSTIM), Benin, Research Unit of Inorganic Chemistry, Materials Engineering and Environment, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin and Laboratory of Applied Hydrology (LHA) of the National Water Institute (INE) at the University of Abomey-Calavi, P.O. Box 526 Cotonou, University of Abomey-Calavi, Benin.
Jacques Kouazounde
Research Unit of Inorganic Chemistry, Materials Engineering and Environment, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin and Laboratory of Applied Hydrology (LHA) of the National Water Institute (INE) at the University of Abomey-Calavi, P.O. Box 526 Cotonou, University of Abomey-Calavi, Benin.
Nafiou E. Chitou
Research Unit of Inorganic Chemistry, Materials Engineering and Environment, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin.
Waris K. Chouti
Research Unit of Inorganic Chemistry, Materials Engineering and Environment, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin.
Mathias O. Dakpo
Kabba Laboratory for Research in Chemistry and Applications (LaKReCa), École Normale Supérieure (ENS) of Natitingou, National University of Sciences and Technologies, Engineering and Mathematics (UNSTIM), Benin and Research Unit of Inorganic Chemistry, Materials Engineering and Environment, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin.
Marius Dannon
Kabba Laboratory for Research in Chemistry and Applications (LaKReCa), École Normale Supérieure (ENS) of Natitingou, National University of Sciences and Technologies, Engineering and Mathematics (UNSTIM), Benin and Laboratory of Applied Hydrology (LHA) of the National Water Institute (INE) at the University of Abomey-Calavi, P.O. Box 526 Cotonou, University of Abomey-Calavi, Benin.
Fidèle Suanon
Laboratory of Applied Hydrology (LHA) of the National Water Institute (INE) at the University of Abomey-Calavi, P.O. Box 526 Cotonou, University of Abomey-Calavi, Benin.
Nicaise Yalo
Laboratory of Applied Hydrology (LHA) of the National Water Institute (INE) at the University of Abomey-Calavi, P.O. Box 526 Cotonou, University of Abomey-Calavi, Benin.
Daouda Mama
Laboratory of Applied Hydrology (LHA) of the National Water Institute (INE) at the University of Abomey-Calavi, P.O. Box 526 Cotonou, University of Abomey-Calavi, Benin.
Limam M. Bawa
Water Chemistry Laboratory (LCE), Faculty of Sciences (FS), University of Lomé (UL), BP 1515, Lomé, Togo.
*Author to whom correspondence should be addressed.
Abstract
Phosphorus enrichment in cultivated soils adjacent to surface waters can increase nutrient transfer and eutrophication risk, especially during rainy periods. This study evaluated the mobility and bioavailability of phosphorus in soils surrounding Lake Toho, southern Benin. Samples were collected from 13 sites and analysed for pH, moisture, organic matter, total phosphorus and operationally defined phosphorus fractions. Soil water pH ranged from 6.25 to 8.30, indicating weakly acidic to weakly basic conditions. Moisture varied from 1% to 38%, while organic matter ranged from 40.30% to 49.70%. Total phosphorus concentrations ranged from 1,049.74 to 28,436.52 µg g⁻¹ and were generally higher in the upper horizons. Phosphorus occurred as labile, iron-bound, aluminium-bound, calcium-bound, organic and residual fractions. Organic and residual phosphorus were the dominant forms overall, whereas labile and other potentially mobile fractions were detected across the sampled horizons. Correlation and principal component analyses indicated relationships among total phosphorus, residual phosphorus, labile phosphorus, organic matter, moisture and pH-related calcium associations. The results suggest that cultivated soils around Lake Toho contain substantial phosphorus stocks influenced by agricultural inputs, parent material and soil properties. During rainfall and runoff events, part of these stocks may be transferred towards the lake. Continued seasonal monitoring and improved nutrient management are therefore needed to reduce potential phosphorus losses while maintaining soil fertility. PCA confirms the consistency of the results and effectively synthesizes the key agronomic and environmental indicators essential for sustainable nutrient management. This analysis structures data variability by highlighting the predominant yield factors.
Keywords: Bioavailability, cultivated soils, Lake Toho, mobility, phosphorus