Effects Of Habitat Types On Leaf Litter Decomposition And Macroinvertebrates Colonization In A Headwater Stream Of Changbai Mountain In Winter

There are less natural algae and lower nutrient levels in headwater streams,which makes leaf litter become one of the main food sources to aquatic organism.As the middle part of food chain in freshwater ecosystem,macroinvertebrates play a critical role in leaf litter decomposition.According to River Continuum Concept,nutrients in headwater streams,such as organic detritus,can affect the ecological function of the whole river basins.As the sources of Songhua River in Northeast China,forest streams in Changbai Mountain have unique topography and climate characteristics.Hence,related ecological studies on these headwater streams are of great importance.In order to analyze the effects of habitat types on leaf litter decomposition and macroinvertebrates colonization,this paper focused on mass loss rates of Acer mono,Tilia amurensis,Quercus mongolica leaf litter and macroinvertebrates in riffles and pools in a headwater stream of Changbai Mountain in winter.1.Dry mass loss rates of three kinds of leaf litter in riffles were higher than in pools,which meant they were significantly affected by habitat types(P < 0.05).After 185 days of decomposition,the mean dry mass loss of the three were 12.73%(A.mono);15.71%(T.amurensis);22.84%(Q.mongolica)in riffles,and they were 22.93%;27.27%;37.40% respectively in pools.Besides,habitat types had no significant effect on the dry mass remaining of Q.mongolica leaf litter in the pre-freezing period,and the possible reason is the thick waxy layer on the leaf surface,which may reduce the rate of decomposition.2.During this study,7865 macroinvertebrates were collected from three kinds of leaf litter bags in riffles and pools,belonging to 5 class,10 orders,29 families,33 subfamilies and 55 genera(species),among which proportion of Insecta was 83.05%.Habitat types had no significant effect on the biomass,richness and biodiversity index of macroinvertebrates functional feeding-groups(P > 0.05),but there was a significant effect to the relative abundance of density of them(P < 0.05),especially the predators,whose relative abundance of density was higher in riffles than in pools.In the pre-freezing period,the relative abundance of density of shredders was higher in riffles than in pools,and when it came to the thawing period,it did the reverse.More collector-gatherers were found in pools,while more collector-filterers were in riffles.There were fewer scrapers than other groups during this study.3.In all leaf litter bags,predators,collector-gatherers and shredders were main functional feeding-groups,but different kinds of leaves affected the community structure of macroinvertebrates.The abundance of macroinvertebrates in A.mono bags and Q.mongolica bags in riffles presented an increasing trend over time in winter,but it changed in the opposite trend in Tilia amurensis bags.Hydropsyche sp.,Ephemerella sp.,Chironomidae sp.3,Orthocladiinae sp.2,Tanypodinae sp.and Gammarus sp.were all dominant groups in these bags.Xanthoperla sp.belonging to Chloroperlidae in A.mono and T.amurensis leaf litter bags was the abundant group,but it was the rare group in Q.mongolica leaf litter bags.