Dynamics of heavy metals in the fine sediments from a subtropical forest headwater stream during a rainy season

Abstract

ABSTRACT Headwater streams, as the capillaries of rivers, largely control the functional integrity of the entire river network. Headwater stream sediments, especially fine sediments, are essential ecosystem components and dominant reservoirs for heavy metals, with these reservoirs significantly affecting their cycling in streams. However, the dynamics of heavy metals in headwater stream sediments are not well assessed in the literature. Here, we assessed the temporal and spatial storage dynamics of several common heavy metals (i.e., Mn, Zn, Cu, Cr, Cd, and Pb) in the fine sediments from a typical subtropical forest headwater stream during the rainy season of 2021 (Mar–Aug). We found that (1) the mean storage of fine sediment of heavy metals was ordered Mn (21.57 g m−2) > Pb (2.53 g m−2) > Zn (2.27 g m−2) > Cr (0.66 g m−2) > Cu (0.12 g m−2) > Cd (0.006 g m−2); (2) their storage had a transient increase during the rainy season, followed by a decrease, but storage of both Zn and Cr was unevenly distributed from stream source to mouth; and (3) the key factors controlling heavy metal storage were water alkalinity, temperature, and pH, as well as monthly precipitation. These findings suggest that forest headwater streams can store heavy metals, but the amounts vary across temporal and spatial scales. Our results help us better understand the role of headwater streams in storing and transferring materials in forest ecosystems.