Past and present mercury flux to a West African crater lake (Lake Bosomtwe/Bosumtwi, Ghana)

Lake sediment cores have been used to reconstruct mercury deposition patterns in many parts of the world; however, no studies to date have used these methods in West Africa, nor are there any published measurements of mercury deposition to this region. We measured mercury in a 210Pb dated sediment core from a meromictic crater lake in West Africa (Lake Bosomtwe, Ghana). Lake Bosomtwe has a very small catchment area to lake area ratio (1.1) and the sediment mercury profile is expected to reflect past and present atmospheric mercury deposition to the lake. Mercury concentrations in sediments as well as mercury flux to the sediments increased from the mid-1800s to latter half of the 1900s, however there has been a sharp decline in mercury flux to Lake Bosomtwe in recent decades. The recent decline in mercury flux to Lake Bosomtwe's sediments does not appear to be consistent with trends in local, regional or global mercury emissions, and may instead reflect declining global atmospheric mercury concentrations or declining European emissions, highlighting the importance of long-range atmospheric transport of mercury.

► We characterized mercury concentrations in and flux to the sediments of Lake Bosomtwe, West Africa.
► Mercury concentrations in and flux to the sediments peaked in the latter half of the 1900s.
► There has been a strong decline in Hg flux to Lake Bosomtwe's sediments in recent decades.
► This decrease may reflect declining atmospheric Hg deposition to the region.
► A long history of artisanal gold mining in this region may have led to pre-industrial Hg contamination.