Drought and post-drought recovery cycles in an intermittent Mediterranean stream: structural and functional aspects

ACUNA, V.; MUÑOZ, I.; ADONIS GIORGI; OMELLA, M.; SABATER, F.; SABATER, S.

JOURNAL OF THE NORTH AMERICAN BENTHOLOGICAL SOCIETY

Allen Press

Año: 2005 vol. 24 p. 919 - 933

0887-3593

Macroinvertebrate community structure and stream ecosystem metabolism were studied in an intermittent forested Mediterranean stream during seasonal summer droughts from 2001 to 2003 to see the effects that the intensity of the seasonal drought had on the stream ecosystem. Stream metabolism was profoundly affected by stream intermittency because of organic matter accumulation during the dry period and the consequent enhanced ER during the post-drought recovery. The relationship between water level and habitat heterogeneity and biotic diversity during the contraction-expansion cycles was attempted and maximal biotic diversity was reported at low water levels during contraction. Macroinvertebrate community response to drying exhibited a ‘stepped’ response apparently defined by thresholds. Flow cessation involved a threshold with considerable changes in the community structure and watercourse desiccation induced a discontinuity in the stream system, as the macroinvertebrate community after the dry period markedly differed from that previous to desiccation. Resumption of flow in autumn led the macroinvertebrate composition to a state similar to before the onset of flow in the wetter year. As few taxa demonstrate resistance to drying, resilience to drying is the dominant response to disturbance in the Fuirosos.The influence of drought on the macroinvertebrate community differed across substrata. Drying led to considerable changes in density on cobbles and leaves, but not on sand. Drying resulted in an increase in density that peaked in pools soon after flow ceased, but then rapidly decreased because of the physicochemical changes associated with fragmentation of the stream continuity.