Legacy Lead Stored in Catchments Is the Dominant Source for Lakes in the U.K.: Evidence from Atmospherically Derived...

There has been a considerable reduction in anthropogenic lead (Pb) emission in the atmosphere in recent decades. However, the reduction in Pb inputs in many lakes does not match this as the Pb stored in catchment upper soil layers, derived from previous deposition, has become an important source although it is difficult to assess quantitatively. This work uses atmospherically deposited ²¹⁰Pb as a tracer to track Pb movement, and so for the first time, we were able to calculate the relative Pb inputs from direct atmospheric deposition and catchment sources to lakes in the U.K. directly. Within individual lake sites, ratios of ²¹⁰Pb/Pb in the catchment terrestrial mosses were normally an order of magnitude higher than those in the catchment surface soils, trapped lake sediments, and the surface sediments in the lake bottom. Results suggest that the Pb isotope signatures in the mosses are close to or dominated by atmospheric depositions, and it is reasonable to use the ratios of ²¹⁰Pb/Pb in terrestrial mosses collected from the lake sites with a high annual rainfall over 2000 mm to represent those in atmospheric depositions. It reveals that after the reduction in Pb emissions, catchment Pb inputs now typically account for more than 95% of the total Pb entering the lakes.