Floods, major formative drivers of channel and floodplain structure and associated riparian and in-stream communities1,2, are increasing in intensity and magnitude with climate change in many regions of the world3,4. However, predicting how floods will affect stream channels and their communities as climate changes is limited by a lack of long-term pre-flood baseline data sets across different organismal groups. Here we show salmon, macroinvertebrate and meiofauna communities, monitored for 30 years in a system evolving owing to glacier retreat, were modified significantly by a major rainfall event that caused substantial geomorphic change to the stream channel. Pink salmon, reduced to one-tenth of pre-flood spawner densities, recovered within two generations. Macroinvertebrate community structure was significantly different after the flood as some pioneer taxa, which had become locally extinct, recolonized whereas some later colonizers were eliminated. The trajectory of the macroinvertebrate succession was reset towards the community structure of 15 years earlier. Meiofaunal abundance recovered rapidly and richness increased post-flood with some previously unrecorded taxa colonizing. Biotic recovery was independent of geomorphological recovery. Markedly different responses according to the organismal group suggest caution is required when applying general aquatic ecosystem theories and concepts to predict flood events.
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We thank those who have carried out research at WPC for long field seasons over the 34 years to develop the long-term record, including S. Conn, E. Flory, K. Monaghan, I. Phillips and A. Veal. We are grateful to Captain J. Luthy, of the MV Nunatak, who for many years supplied our remote field camp in Goose Cove and latterly to Captain J. Smith of the MV Capelin, who facilitated access to the stream. We are grateful to numerous others in the National Park Service, not mentioned above, for other logistic and field support. We are especially grateful to D. Lawson for supplying the rainfall data for the flood period and to R. Weingartner and G. Felder for constructing the rainfall intensity figure. Research has been supported by financial support from various bodies including NERC (GR9/2913, NE/E003729/1, NE/E004539/1 and NE/E004148/1), the Royal Society and the universities of Birmingham, Leeds and Roehampton. M.J.K was financially supported by a joint University of Birmingham/University of Worcester PhD scholarship.