Influence of Inorganic Substrata Size, Leaf Litter and Woody Debris Removal on Benthic Invertebrates Resistance to Floods in Two Contrasting Headwater Streams

Abstract

We studied the influence of inorganic substrata size, leaf litter and woody debris removal on the resistance of benthic invertebrates to floods in two contrasting forested headwater streams of the Aguera basin (northern Spain): Cuchillo stream (stream bed dominated by cobbles and pebbles) and Salderrey stream (stream bed dominated by bedrock and boulders). Generally, floods had a greater effect on benthic invertebrates resistance in the Salderrey stream, apparently due to the high presence of loose substrata overlaying bedrock and the higher scouring of sediment in this stream. Unlike Salderrey stream total number of individuals of Simuliidae, Echinogammarus tarragonensis and Protonemura spp. in riffles greatly increased at the reach scale in the Cuchillo stream after two floods, suggesting that Cuchillo was more retentive than Salderrey. A positive relationship between substrata size and invertebrate resistance to floods was found in the Cuchillo stream but not in the Salderrey stream. It appears that the flood disturbances in the Salderrey stream were too strong to find an increase in resistance as substrata size increased. Invertebrate resistance on leaf litter and resistance predictability were also higher in the Cuchillo stream; the former result suggests that retention of leaf packs was greater in the Cuchillo stream. The lack of a statistically significant effect of woody debris removal may imply that the composition and stability of inorganic substrata have more influence on invertebrate resistance to floods than woody debris at the reach scale in these headwater streams dominated by relatively stable substrata. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)