Carbon,nitrogen and phosphorus storage of woody debris in headwater streams in an alpine forest in the upper reaches of Mingjiang River

Woody debris,an essential component in headwater streams in the forest,plays an important linkage role in material cycling and the flow of energy between the ecosystems of the land and water. As the decomposition proceeds,carbon,nitrogen,phosphorus,and other elements in the woody debris are gradually released into the streams. These released elements,especially nitrogen and phosphorus,are not only an important contribution into the forest ecosystems but also affect the water environment of the forest streams and the downstream ecosystems. However,little information has been available on the storage of carbon,nitrogen,and phosphorus in woody debris in the forest streams. Therefore,for this study in August,2013,we selected 12 headwater streams,in the upper reaches of the Mingjiang River,located in an alpine primary forest in western Sichuan. In each stream,we investigated the carbon,nitrogen,and phosphorus storage of the woody debris,as well as their distribution patterns,pertaining to the diameters and the decay classes,from the head to the end,in the woody debris. The Akaike information criterion,corrected for sample size( AIC_C),was used for the selection of the optimum linear fit model to evaluate the total carbon,nitrogen,and phosphorus storage of woody debris in the headwaterstreams of the area of investigation. The results showed that the carbon,nitrogen,and phosphorus storages of woody debris per unit area of streams were 312.1 g / m~2,809.5 mg/m~2,and 110.9 mg/m~2,respectively,in these alpine forest headwater streams. Large variations were observed among the headwater streams pertaining to the carbon,nitrogen,and phosphorus storage of the woody debris. Moreover,both the woody debris diameter and the decay class could affect the storage of the carbon,nitrogen,and phosphorus. Woody debris at diameters of 1-2.5 cm and 2.5-5 cm contributed significantly more carbon( 86.71%),nitrogen( 87.20%),and phosphorus( 84. 55%) storage to the total storage,compared with those at other diameters. Woody debris at a diameter of >10 cm contributed the least and accounted for only 1.17%,0.94%,and1.56% of the total carbon,nitrogen,and phosphorus storage,respectively. In contrast,the woody debris of decay class Vshowed the highest contribution to carbon,nitrogen,and phosphorus storage; which were 65.86%,67.86%,and 60.31%,respectively,of the total carbon,nitrogen and phosphorus storage. However,the woody debris of decay classes and IIIaccounted for only 8.14%,8.70%,and 8.9