Effects of a multi-year experimental flood regime on macroinvertebrates downstream of a reservoir

Abstract

Abstract.We examined the response of stream macroinvertebrates to a multiple-year experimental flood regime downstream of a large reservoir. Benthic samples were collected from the River Spöl prior to the initial flood (1999) and at periodic intervals before and after eight floods from 2000 through 2002. Three artificial floods occurred each in 2000 and 2001, and two floods were implemented in 2002. We also sampled macroinvertebrates in an adjacent tributary (Val da l'Aqua) on the same dates as in the Spöl to assess the natural temporal variability in assemblage structure. The regulated baseflow discharge in the Spöl was < 2.5 m 3 /s, whereas the floods ranged from 10 m 3 /s to over 25 m 3 /s with some flood peaks reaching > 40 m 3 /s for a short period. Repeated measures ANOVA indicated that the floods significantly reduced macroinvertebrate densities in the Spöl, although recovery to pre-flood densities occurred within a matter of weeks to densities found in 1999. A principal components analysis revealed that assemblage composition shifted in Aquat. Sci. 65 (2003) 210-222 1015-1621/03/030210-13 DOI 10.1007/s00027-003-0663-8 © EAWAG, Dübendorf, 2003 Aquatic Sciences response to the recurring floods, first from 1999 to 2000 and then from 2000 to 2001/2. Taxa that decreased in abundance due to the floods included the Gammaridae (Gammarus fossarum) and Turbellaria (Crenobia alpina). Taxa that increased in abundance included Baetidae, Chironomidae, and Simuliidae. Some Plecoptera, Trichoptera, and Heptageniidae that were negatively impacted by the floods in 2000, subsequently increased in abundance. Our data suggest that the response of macroinvertebrates to experimental floods occurs over a period of years rather than months, as species composition adjusts to the new and more variable habitat template. Future changes are expected as additional species begin to colonize the river from adjacent sources. The results clearly show that the experimental flood regime should be maintained if resource managers wish to sustain the development of a more natural macroinvertebrate assemblage.

Recovery of stream invertebrates after catastrophic flooding in southeastern Minnesota, USA

“…Baetidae mayflies and Chironomidae midges recovered very quickly post-flood, a result generally attributed to the mobility of their adult stages (Robinson et al 2003). Blackflies also typically return quickly (Robinson et al 2003), although their recovery was very protracted in both Trout Run and the Middle Branch in the present study. The larger Ephemerellidae mayflies and Hydropsychidae caddisflies were greatly reduced in the Middle Branch and virtually absent from Trout Run for a year after flooding.…”

“…It required over a year for amphipod densities in Trout Run to reach normal levels, but Middle Branch numbers remained at minimal levels nearly 2 years post-flood. Reduced taxa richness and changes in community structure are typical of benthic invertebrate assemblages subjected to severe flooding (e.g., Hynes 1970;Lytle 2000;Robinson et al 2003;Snyder and Johnson 2006;Elzinga et al 2009). In the streams of Whitewater State Park, taxa were lost and community structure modified, but only in the smaller systems.…”

Spatial and temporal variation of benthic macroinvertebrates in the Nam Gnom Basin receiving discharged waters from the Nam Theun 2 Reservoir (Lao PDR)

“…Flow regime has a strong influence on the biodiversity of rivers and importance of keeping the flow as close as possible to the natural regime is attested (Stanford et al, 1996;Poff et al, 1997) and confirmed by the interest in restoring natural flow regime to recover biotic integrity all around the world (Sparks, 1995;Petts, 1996;Galat et al, 1998;Sparks et al, 1998;Dudgeon, 2000;Robinson et al, 2003;Attwood & Cottet, same issue).…”

Use of protected areas for freshwater biomonitoring – case studies in Switzerland

“…Slides for diatoms are examined using a Nikon microscope (Eclipse 600) and, when necessary, by scanning electron microscopy (SEM; JEOL JSM 35 CF). A minimum of 250 diatom valves are counted and identified along random transects from each slide based on the keys of Krammer & LangeBertalot (1991, 1999a, b, 2000, Round et al (1990), Lange-Bertalot & Moser (1994), and Lange-Bertalot & Metzeltin (1996).…”