Dynamics of copper, cadmium, chromium, and lead storage in a subtropical forest headwater stream

Sediments and plant litter in forest headwater streams serve as vital repositories and carriers of elements, including heavy metals, that influence material cycling and energy flow of the forest ecosystem, but until now we know little about the dynamics of heavy metals in headwater streams. Here, we continuously monitored the storage and assessed the drivers of copper (Cu), cadmium (Cd), chromium (Cr), and lead (Pb) in sediments and plant litter from a subtropical forest headwater stream between March 2021 and February 2022. Results showed that (1) the total storage of Cu, Cd, Cr, and Pb in the sediments were 285.7, 10.4, 1084.7, and 4347.5 mg m⁻², respectively, while those in plant litter were 0.23, 0.02, 3.5, and 0.68 mg m⁻²; (2) the storage of Cu, Cd, Cr, and Pb varied between different sampling reaches, showing an overall decrease pattern from the source of the stream to the mouth; and (3) heavy metal storage was significantly higher in the reaches with than without tributaries and with mixed riparian forests than broad-leaved riparian forests, and was positively affected by rainfall intensity, stream water dissolved oxygen and alkalinity and water depth, but negatively by stream water pH and temperature. Our results suggest that forest headwater streams play an important role in heavy metal storage and flux, which will help to better understand the dynamics of heavy metals along with the hydrological process in forest ecosystems.