Leaf and twig litter decomposition of main species in different forests along the north slope of Changbai Mountain, northeast China Abstract From 2001 to 2003, the litter decomposition dynamics of dominant tree species were conducted using a litterbag burying method in the broadleaf-Korean pine forest, spruce-fir forest and Ermans birch forest, which represents three altitudinal belts in Changbai Mountain, northeast China. The spatial and temporal dynamics of litter decomposition and the effects of litter properties were examined. Furthermore, the decomposition trend of different species was simulated by the Olson model, and results showed that annual mass loss rates increased over time, but was not significantly correlated. Leaf decomposition rates increased after decomposing for 638 days (1.75 years), and the order of dry weight remaining rates of leaf litter for different species is: Asian white birch (Betula platyphylla) (24.56%)Asian white birch (0.624)>Korean pine (0.441)> spruce (0.406)>fir (0.397)>Ermans birch (0.385); in twig, it ranged from 7.8 to 29.3 years, and k follows the order: Amur linden (0.391)>fir (0.204)>Korean pine (0.176)> spruce (0.157)>Asian white birch (0.148)>Ermans birch (0.102). In general, the differences of decomposition rate are evident between leaf and twig litter and among species, and were higher in broad-leaved species compared with coniferous species at the same elevation, and decreased with the ascending of elevation.

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Under the influence of human activities, surface water quality has been significantly affected, which threatens human health and sustainability. In order to clarify the potential risks of heavy metal pollution to human health in river water, two tributaries of the Tumen River with significant differences in human activity interference were selected for investigation. Comparative analysis of the contents of chromium (Cr), cuprum (Cu), arsenic (As), cadmium (Cd), mercury (Hg), and plumbum (Pb) in the surface water of the two tributaries showed that the concentrations of As and Hg in some sampling sites exceeded the pollution standard values, and the Buerhatong River had a higher pollution level. Further analysis of the health risks revealed that the hazard quotient values of Cr, Cu, As, Cd, Hg, and Pb were <1, but the cumulative risk value of the Buerhatong River was higher than 1 for children, indicating adverse effects on human health. The As levels under the fish ingestion scenario had unacceptable carcinogenic risks, while the Cr in the Buerhatong River for adults and Cr and Pb in the Buerhatong River and Hunchun River for children had acceptable carcinogenic risks. Moreover, the As in the incidental water ingestion scenario also had acceptable carcinogenic risks. Therefore, the increase in human activity intensity can promote the increase in the health exposure risk of heavy metals in river water, and fish ingestion was the main exposure pathway, while children had higher exposure risks than adults.

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