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

We tested the hypothesis that wood influences stream channel morphology, se diment composition, retention, and storage of organic matter by experimenta lly removing all wood from 2 first-order reaches (ca 90 m length) of 2 neig hboring tributaries (Salderrey and Cuchillo streams) in the Aguera catchmen t (Basque Country, Spain). We established 2 control reaches upstream from t hese treatment reaches. We completed maps of substrate, fill/scour transect s, and wood surveys in 1997 (prior) and 1998 (after) wood removal. We measu red monthly inputs of fine wood to the treatment reaches. In addition, we m easured 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 h igher in the treatment reaches (53 m(3)) than in the controls (14.2 m(3) in Salderrey, 2.7 m(3) in Cuchillo). As a result, the area of coarse substrat e increased in the treatments, but remained unaltered in the controls. The capacity of the reaches to retain CPOM decreased after the treatment, but a ffected neither seston concentration nor the benthic storage of CPOM. Wood is an important constituent of Basque streams, and removal of wood signific antly impacts channel structure and organic matter storage.