Distribution Characteristics And Seasonal Dynamics Of Litter In A Headwater Stream Bed Of The Changbai Mountains

Litter distributed in stream beds provides a considerable amount of food and living space for aquatic organisms to live in headwater streams.The characteristics of how litter is distributed directly break the structure and functions of headstream stream ecosystem.It is noteworthy that in northern cold regions,the accumulation and composition of stream bed litter critically impact the vital stream ecological process(e.g.,the survival of organisms in winter and the decomposition of litter),whereas this topic has been rarely discussed.This study took a 200 meters natural reach of a headwater stream in the Changbai Mountains as the object.The distribution characteristics and seasonal dynamics of litter in the stream bed were determined with in-situ sampling method.After 230 days of research,the major results were drawn as follows:(1)Pool and riffle were the main habitat types in the headwater stream of the experimental region.Pool and riffle exhibited significantly different physical characteristics.For instance,riffle achieved significantly higher amount,total length and average velocity than pool.(2)The litter patches in the experimental stream bed were classified into litter patches trapped by stone,litter patches trapped by wood and litter patches sinking in pools,which exhibited significant differences in accumulation and composition among the accumulated types.It was found that litter patches sinking in pools exhibited significantly larger accumulated area and water depth than those of litter patches trapped by stone and litter patches trapped by wood,while their current velocity was noticeably less than that of the latter two types of litter patches;Litter patches trapped by wood displayed significantly larger accumulated height than litter patches trapped by stone and litter patches sinking in pools.Litter patches trapped by stone and litter patches trapped by wood primarily consist of leaves,followed by leaf fragments and the least branches and trunks.Except autumn,litter patches sinking in pools were mainly composed of leaf fragments and branches and trunks,with fewer leaves.(3)The distribution of litter patches exhibit significant seasonal dynamics.Litter patches in melting period in winter exhibited significantly larger accumulated height than in other periods.Litter patches in spring displayed significantly smaller accumulated area than in other periods,and the water depth displayed significantlylarger than in other periods.The proportion of leaves in litter patches trapped by stone tended to decrease,and that of leaf fragments was elevated gradually;Litter patches sinking in pools exhibited gradually increasing proportions of branches and trunks over time.(4)Water depth displayed positive correlations with accumulated height of all kind of litter patches.However,it displayed negative correlations with dry weight of leaf fragments in litter patches trapped by stone and litter patches trapped by wood.The distribution characteristics of litter in the stream bed of headstream stream should have obviously spatial and temporal differences.The accumulation of litter can be made more efficient by adding intercepting structures such as fallen wood to ensure that aquatic organisms have a stable food source at different times.