Effect of removal of wood on streambed stability and retention of organic matter

We tested the hypothesis that wood influences stream channel morphology, sediment composition, retention, and storage of organic matter by experimentally removing all wood from 2 first-order reaches (ca 90 m length) of 2 neighboring tributaries (Salderrey and Cuchillo streams) in the Agüera catchment (Basque Country, Spain). We established 2 control reaches upstream from these treatment reaches. We completed maps of substrate, fill/scour transects, and wood surveys in 1997 (prior) and 1998 (after) wood removal. We measured monthly inputs of fine wood to the treatment reaches. In addition, we measured seston every 2 wk, benthic coarse organic particulate matter (CPOM) every 2 mo, and the retention capacity of reaches every 3 mo. All reaches were scoured during the study period, but the volume of sediment lost was higher in the treatment reaches (53 m3) than in the controls (14.2 m3 in Salderrey, 2.7 m3 in Cuchillo). As a result, the area of coarse substrate increased in the treatments, but remained unaltered in the controls. The capacity of the reaches to retain CPOM decreased after the treatment, but affected neither seston concentration nor the benthic storage of CPOM. Wood is an important constituent of Basque streams, and removal of wood significantly impacts channel structure and organic matter storage.