Energy Dynamics of Three Low-Order Southeast Alaska Streams: Allochthonous Processes

Allochthonous processes of three low-order southeast Alaska streams, exhibiting a range of riparian vegetation and successional stages occurring before and after logging, were compared. Leaf-litter traps were used to estimate annual litter input. Leaf processing rates were measured by confining known amounts of leaf material in litter bags. Instream woody debris and stored and transported organics were also estimated. Annual litter inputs ranged from 52 g AFDW-m−2 on a clearcut watershed to 295 g AFDW.m−2 on a logged and deciduously revegetated watershed. All deciduous species tested (red alder—Alnus rubra, black cottonwood—Populus trichocarpa, salmonberry—Rubrus spectabilis) had fast post-leaching processing rates (k > 0.01), while western hemlock (Tsuqa heterophylla) was processed slowly (k < 0.005). The logged watersheds contained the largest amount of woody debris. Stored particulate organic matter (POM) was generally 2 or more times greater in depositional than erosional areas. Seasonal changes in stored POM were most obvious in erosional areas. Transported POM was highest in a logged watershed revegetated with deciduous riparian species. The results of this study suggest that logged watersheds, with extensive riparian regeneration, potentially increase the allochthonous energy base of streams in southeast Alaska.