Influence of mild to severe flow alterations on invertebrates in three mountain streams

Invertebrates were compared upstream versus downstream from diversions on three small, headwater streams in the central Rocky Mountains, USA. Flow alteration of these streams varied from mild (some aspect of all natural flow components was transferred downstream) to severe (nearly 100% of the flow was diverted for 10–11 months of the year). The analysis was separated into periods of frequent (diversion gates often opened and closed; April–October) and infrequent flow fluctuations (stable low flows due to constant diversion; November–March). Invertebrates appeared resilient to mild flow alterations as neither the abundance, diversity, nor spatial and temporal variation in abundance and diversity differed upstream versus downstream during either period. In severely diverted streams, however, total invertebrate density downstream from the diversion was only 50% of upstream. Invertebrate diversity was also reduced; ten taxa abundant upstream were absent in downstream sections. Chironomids, ostracods and Ameletus spp. comprised 80% of total invertebrate density during constant, low flow conditions in the severely diverted streams. Although all taxa in the severely diverted streams recovered (drift) during the period of frequent flow fluctuations, spatial and temporal variation (coefficient of variation) in both density and the number of taxa was significantly greater downstream. Depending on the frequency with which free-flowing conditions were re-established, many invertebrate populations (especially mayflies and some stoneflies) declined or were even locally extirpated (e.g. Hesperoperlapacifica, Megarcyssignata, Neothremmaalicia, Polyceliscoronata). Downstream communities in severely diverted tributaries appeared to fluctuate between two stable endpoints; a depauperate low-flow community dominated by chironomids and ostracods and a more abundant and diverse natural-flow community dominated by mayflies, chironomids, ostracods, stoneflies and caddisflies. Water abstraction (extent and timing of diversion) could be managed to minimize risks to downstream ecological resources.

[1]  R. Sparks,et al.  THE NATURAL FLOW REGIME. A PARADIGM FOR RIVER CONSERVATION AND RESTORATION , 1997 .

[2]  Stanley D. Smith,et al.  Functional Responses of Riparian Vegetation to Streamflow Diversion in the Eastern Sierra Nevada. , 1991, Ecological applications : a publication of the Ecological Society of America.

[3]  R. Rader.  A functional classification of the drift: traits that influence invertebrate availability to salmonids , 1997 .

[4]  P. Boon.  The impact of river regulation on invertebrate communities in the U.K. , 1988 .

[5]  D. Dudgeon.  Effects of water transfer on aquatic insects in a stream in Hong Kong , 1992 .

[6]  A. Boulton,et al.  The ecology of two intermittent streams in Victoria, Australia.: III. Temporal changes in faunal composition , 1992 .

[7]  Charles C. Coutant,et al.  A GENERAL PROTOCOL FOR RESTORATION OF REGULATED RIVERS , 1996 .

[8]  F. Hauer,et al.  Serial discontinuities in a Rocky mountain river. II. Distribution and abundance of trichoptera , 1989 .

[9]  J. Stanford,et al.  The Ecology of Regulated Streams , 1979, Springer US.

[10]  F. C. De Moor,et al.  Changes in the physico‐chemistry and benthic invertebrates of the great fish river, South Africa, following an interbasin transfer of water , 1988 .

[11]  M. Palmer,et al.  Ecological Heterogeneity in Streams: Why Variance Matters , 1997, Journal of the North American Benthological Society.

[12]  R. Rader,et al.  Effects of Ambient and Enhanced UV-B Radiation on Periphyton in a Mountain Stream , 1997 .

[13]  J. Lockwood,et al.  Effects of sediment and flow regime on the aquatic insects of a high mountain stream , 1990 .

[14]  G. Petts,et al.  Influence of water abstraction on the macroinvertebrate community gradient within a glacial stream system: La Borgne d'Arolla, Valais, Switzerland , 1994 .

[15]  D. Patten,et al.  Riparian vegetation instream flow requirements: A case study from a diverted stream in the Eastern Sierra Nevada, California, USA , 1990 .

[16]  Thomas A. McMahon,et al.  Stream Hydrology: An Introduction for Ecologists , 1997 .

[17]  B. Statzner,et al.  Stream hydraulics as a major determinant of benthic invertebrate zonation patterns , 1986 .

[18]  D. Messier,et al.  A review of the effects of water transfers in the La Grande Hydroelectric Complex (Québec, Canada) , 1989 .

[19]  Geoffrey E. Petts,et al.  WATER ALLOCATION TO PROTECT RIVER ECOSYSTEMS , 1996 .

[20]  Göran Englund,et al.  EFFECTS OF FLOW REGULATION, HABITAT AREA AND ISOLATION ON THE MACROINVERTEBRATE FAUNA OF RAPIDS IN NORTH SWEDISH RIVERS , 1996 .

[21]  David P. Braun,et al.  How much water does a river need , 1997 .

[22]  Carla M. Delucchi,et al.  Comparison of community structure among streams with different temporal flow regimes , 1988 .

[23]  J. Wright,et al.  Ecological effects of groundwater pumping and a natural drought on the upper reaches of a chalk stream , 1987 .

[24]  B. W. Sweeney,et al.  Geographic Analysis of Thermal Equilibria: A Conceptual Model for Evaluating the Effect of Natural and Modified Thermal Regimes on Aquatic Insect Communities , 1980, The American Naturalist.

[25]  J. Ward,et al.  Influence of regulation on environmental conditions and the macroinvertebrate community in the upper Colorado river , 1988 .

[26]  J. Stanford,et al.  Thermal Responses in the Evolutionary Ecology of Aquatic Insects , 1982 .