Plant Debris Storage Characteristics In Alpine Forest Headwater Streams In The Upper Reaches Of Mingjiang River

Plant debris, mainly found in the forms of woody debris (fallen wood, branches and root, etc.) and non-woody debris (leaf, bark, flower, fruit and twigs, etc.), can enter into headwater streams and rivers because of natural debris fall, soil floor runoff, wind and other powers. The plant debris does not only play an essential ecological component in the forest aquatic ecosystems, but also displays an important linkage role in transferring energy and nutrients from forest to water ecosystems. The characteristics of plant debris are directly related to the headwaters quality environment and the output structure of carbon and nutrients in alpine forest ecosystem. In addition, nitrogen, phosphorus and heavy metals would gradually release along with the output and decomposition proceeding of plant debris in the aquatic ecosystems, thus these released elements would affect the ecological safety of the water environment in forest and downstream ecosystems. Therefore, in order to understand the storage characteristics of plant debris in alpine forest aquatic ecosystems,12 streams from head to end and a river were selected through quadrat sampling method in an alpine primary forest in western Sichuan in in the upper reaches of Mingjiang River at August,2013. Sampling quadrats were setted up as the 1 meter long and stream width in every 10 meter for every stream from end to source; 3 sampling quadrats were setted up as 5 meter long and river width in every 300 meter for the investigation of the river. And then, all the plant debris in all the quadrats were collected, and divided them into different components of woody and non-woody debris, calculating their existing storage. We investigated carbon, nitrogen, phosphorus and 7 heavy metal elements storage of plant debris and their distribution patters in diameters and decay classes in each streams and in the river.The results showed that the present total storage of woody debris and non-woody debris were 694.10 g/m2 and 499.45 g/m2 in streams, respectively; and which were 2630.72 g/m2 and 60.66 g/m2 in river, respectively. The woody debris with 1-2.5 cm and 2.5-5 cm accounted for 86.91% of total woody debris in the streams, and woody debris bigger than 10 cm diameter accounted for the least, only 1.22% of total storage in the investigated 12 streams. Woody debris in decay class â…¤ accounted for 66.57% of total storage in the alpine forest streams, which in decay class â…£ accounted for 25.17%, and which in decay class â…¡ and â…¢ accounted for 5.02% and 3.24%, respectively. Moreover, the non-woody debris less than 1 cm for 69.76% of total non-woody debris in the 12 streams, and leaf occupied the least with only 9.33%. There were obvious differences of the storage and distribution pattern of woody or non-woody debris between 12 headwater streams. Nevertheless, the woody debris bigger than 10 cm exhibited the largest proportion (88.23%) of total storage in the river, but 1-2.5 cm diameter woody debris occupied the least with only 1.20%. In contrast, woody debris in decay class â…¢ and â…£ occupied 68.20% of total storage of woody debris, although which in decay class â…¤ showed the least with only 5.60% of total storage. The reason is that more coarse woody debris left in the river, even if a few quantities, they contributed bigger to the woody debris storage than fine woody debris, and the decomposition rate of coarse woody debris was more slowly than fine woody debris. Moreover, the non-woody debris less than 1 cm twigs, leaves and barks were occupied for 74.42%,1.22% and 24.36% of total non-woody debris in the river, respectively. But which storage less than non-woody debris in streams obviously.Carbon, nitrogen and phosphorus storage of plant debris were directly related to its existing storage, but there were still some differences, because of the tree species, characteristics of aquatic and the own features of plant debris. Carbon, nitrogen and phosphorus storage of plant debris were 510.58 g/m2,1678.06 mg/m2 and 263.77 mg/m2, respectively, in the 12 headwater streams; And Carbon, nitrogen and phosphorus storage of woody debris occupied for 61.22%,48.27% and 43.19% of total plant debris in streams; In addition, Carbon, nitrogen and phosphorus storage of plant debris were 1096.62 g/m2, 1874.85 mg/m2 and 323.13 mg/m2 in the river, respectively; And Carbon, nitrogen and phosphorus storage of non-woody debris accounted for 1.00%,3.81% and 14.18%. Carbon, nitrogen and phosphorus storage of each components of woody debris and non-woody debris in accordance with the existing storage distribution characteristics within the streams and river, a slight difference. The major is related to its existing reserves directly, at the same time under the influence of tree species, and the streams or rivers characteristics, the nutrient concentration differences in the degradation process.Different organs had different enrichment of heavy metal elements along with the growth process of plant, and different adsorption or precipitation of heavy metal elements due to plant debris own characteristics and the aquatic environment they stayed, thus the plant debris heavy metal elements storage characteristics were different from their existing storage in the forest aquatic ecosystems. The heavy metal elements storage of woody debris and non-woody debris in streams were Mn> Zn> Cr> Cu> Pb> Ni> Cd. In generally, heavy metal elements storage of non-woody debris were higher than the woody debris in the headwater streams, the mainly reason why leaves and barks contain higher content of heavy metal material is that the leaves and barks were exposed to air, they could adsorb the metal elements in the atmospheric particulate matter, and which structure, function and physiological activity were different from the xylem. The heavy metal elements storage of woody debris in river were Zn> Mn> Cr> Pb> Cu> Ni> Cd, and of non-woody debris in river were Cr> Mn> Zn> Pb> Ni> Cu> Cd.These results here could not only provide the basic data in understanding the carbon, nitrogen and phosphorus and heavy metal elements output potential by plant debris in headwater streams and river in the alpine forest ecosystems, but also offer the new thought and efficient scientific evidences in managing the environment of the alpine forest in the upper of Mingjiang River, even the whole Mingjiang river basin.