Phosphorus Fractionation in Sediment and Agricultural Soils Surrounding Lake Toho in the Rainy Season

Abstract

In recent years, land use related to anthropogenic activities has contributed to high surface water contamination. During the last decade, Lake Toho, in the Republic of Benin, has suffered anthropogenic pollution by the use of fertilizers from farmers around the lake. We assessed the mobility and bioavailability of phosphorus in cultivated soils around the lake to detect the extent of the contamination. The results showed that the cultivated soils around Lake Toho are weakly acidic or even basic with water pHs between 6.25 and 8.3. The humidity of cultivated soils varies from 1% to 38% on different horizons. The content of organic matter is ranged from 40.30% to 49.70%. The total phosphorus concentration ranged from 1049.74 μg.g-1 to 28436.52 μg.g-1 with a high rate of enrichment at the 30 cm horizon. The high contents of total phosphorus recorded at the superficial horizon were due to the use of fertilizers to amend the soil. All forms of phosphorus are represented (P-L, P-Fe, P-Ca, P-Al, and P-OM). The organic fraction predominates on the upper layer of the soil except for sites located outside crop fields. The strong correlation between the Total phosphorus (TP), the (Pr), mobile phosphorus (P-L), and the to organic matter-bound Phosphorus (P-OM) showed that the high phosphorus contents at the upper horizon of the soil were due not only to the anthropogenic contribution but also to the source rock. The remarkable presence of phosphorus in the P-L and P-MO fractions poses a risk of phosphorus transport to the lake. This can lead to eutrophication which can cause the death of fish and harmful toxins development.