Carbon storage in mountainous headwater streams: The role of old‐growth forest and logjams

Abstract

AbstractWe measured wood piece characteristics and particulate organic matter (POM) in stored sediments in 30 channel‐spanning logjams along headwater streams in the Colorado Front Range, USA. Logjams are on streams flowing through old‐growth (>200 years), disturbed (<200 years, natural disturbance), or altered (<200 years, logged) subalpine conifer forest. We examined how channel‐spanning logjams influence riverine carbon storage (measured as the total volatile carbon fraction of stored sediment and instream wood). Details of carbon storage associated with logjams reflect age and disturbance history of the adjacent riparian forest. A majority of the carbon within jams is stored as wood. Wood volume is significantly larger in old‐growth and disturbed reaches than in altered reaches. Carbon storage also differs in relation to forest characteristics. Sediment from old‐growth streams has significantly higher carbon content than altered streams. Volume of carbon stored in jam sediment correlates with jam wood volume in old‐growth and disturbed forests, but not in altered forests. Forest stand age and wood volume within a jam explain 43% of the variation of carbon stored in jam sediment. First‐order estimates of the amount of carbon stored within a stream reach show an order of magnitude difference between disturbed and altered reaches. Our first‐order estimates of reach‐scale riverine carbon storage suggest that the carbon per hectare stored in streams is on the same order of magnitude as the carbon stored as dead biomass in terrestrial subalpine forests of the region. Of particular importance, old‐growth forest correlates with more carbon storage in rivers.