Impact of the Climate Change and the Recent Development of an Artificial Tropical Estuary on the Mobility and Distribution of Phosphorus: Case of Vridi Channel (Côte d'Ivoire)

This study focused on the effects of the climate change and the recent modification of Vridi channel on the mobility and distribution of phosphorus (P) in its superficial sediments. To best estimate this fact, the annual mobility and distribution of P were followed and compared before and after this development during two different annual periods, marked differently by the climate change effects. The first annual period has covered the period from April 2014 to March 2015 and this channel presented its former hydromorphology, with hydroclimatic conditions very close to that normal of Abidjan district. The second period annual has covered the period from October 2018 to September 2019 and this channel presented its current hydromorphology and, characterized by a rainfall drop and high ambient air temperatures compared to that normal of Abidjan district.

A monthly sampling has been done at 5 cm below the surface sediment in this channel during each annual period. The mobility and distribution of P was assessed in the superficial sediments of this channel according two sequential extraction protocols: the modified Van Eck method and the modified Olsen method. Total phosphorus was assessed according AFNOR NF X31-147.

The total phosphorus contents and all P fractions contents of these superficial sediments assessed by these two sequential methods and obtained over the period from April 2014 to March 2015 are higher than those determined over the period from October 2018 to September 2019. Thus, the recent development of this estuary, with as a corollary the modification of the physical and chemical characteristics of its superficial sediments, would have had the effect of clearing P towards the Atlantic Ocean and/or accelerating its sedimentation; hence the reduction of eutrophication risk of this aquatic ecosystem.