Historical Fluxes of Metal and Metalloids in an Aquatic Ecosystem Affected by Land-Use Change and Mining Activities in Northwestern Mexico

Freshwater reservoirs are essential owing because of their ecological,economic,and social importance.They are particularly vulnerable to contamination,as of metal and metalloids,derived from anthropo-genic activities like mining.The temporal variations in trace element concentrations(arsenic(As),mercury(Hg),chromium(Cr),copper(Cu),nickel(Ni),lead(Pb),and zinc(Zn)),enrichment,fluxes,and possible sources were evaluated by studying two sediment cores from the La Angostura(ANG)Reservoir(northwest Mexico),using 210Pb geochronology.The enrichment factors showed from null to minor enrichment for most elements,but moderate to severe enrichment of mercury(Hg).Most trace element concentrations had a detrital origin,and notable Hg concentration increases since the past decade were associated with severe drought periods,likely resulting from wildfires.The observed sediment con-centrations of As and Hg can cause adverse effects on biota in the ecosystem since they are above the probable effect level(PEL).Development of strategies for metal attenuation in this reservoir is recom-mended and metals should be controlled until specific ecotoxicological studies are performed.