Macroinvertebrate communities were investigated over 1-yr period at three reference sites and at six impacted sites located upstream and downstream of a small dam located in the Simbrivio Stream (Tiber basin, Central Italy). Data on physicochemical, hydro-morphological and trophic variables were collected to assess possible dam effects on taxonomic composition, density, diversity and trophic structure of macroinvertebrate communities. Major changes in environmental variables occurred within the first three sites below the dam (distance<1km): alteration of flow regime (characterized by a constant, residual flow and, in rainy period, by short-term fluctuations), increase of epilithic biomass and, during spring period, decrease of the coarse and fine particulate organic matter associated with benthic samples. Water temperature, conductivity, pH, dissolved oxygen and nutrient concentrations (ammonium and soluble reactive phosphorus) were not affected by river regulation. The effect of the Simbrivio Dam on assemblages of macroinvertebrate communities was noticeable in the spring sampling, where the qualitative composition of benthic fauna below the dam differed from that above it. In this period, the dam produced an alteration of the taxonomic composition and a reduction of taxa richness of downstream sites, particularly in relation to stoneflies, caddisflies and mayflies (EPT taxa). Many taxa of stream insects disappeared at short or long-distance from the dam. Nevertheless, a few of these taxa (as Epeorus assimilis, Isoperla saccai, Rhithrogena gr. hybrida) were collected below the dam in the autumn sampling. Thus, the prevailing conditions of constant flow might favour the presence of these taxa but the sudden rises in river flow due to short-term fluctuations (in winter and spring) had a harmful interference on life cycles of some specific taxa. In this period, macroinvertebrate communities of boulders were the most affected by river regulation. On the contrary, in autumn, the results showed an increase of total and EPT taxa of downstream communities. The effect of the Simbrivio Dam on trophic structure of macroinvertebrate communities was evident on scrapers and collector filterers in spring period, and on shredders in autumn period. The analysis of environmental variables patterns along the watercourse suggested that the principal factors affecting the macroinvertebrate communities at downstream sites were alteration of hydrological conditions, epilithic development and heterogeneity and stability of substrata. In the present study, total densities and diversity indices are probably not the most appropriate macroinvertebrate community metrics for assessing the effects of stream regulation caused by a small dam. Taxonomic composition gives a better interpretation of the alteration of the biota. Finally, Plecoptera and Ephemeroptera Heptageniidae seem to be the most affected taxa to river regulation

De Cicco, M. (2008). Effects of a small headwater dam on macroinvertebrate communities and environmental variables in a Mediterranean stream.

Effects of a small headwater dam on macroinvertebrate communities and environmental variables in a Mediterranean stream

DE CICCO, MARCO
2008-04-18

Abstract

Macroinvertebrate communities were investigated over 1-yr period at three reference sites and at six impacted sites located upstream and downstream of a small dam located in the Simbrivio Stream (Tiber basin, Central Italy). Data on physicochemical, hydro-morphological and trophic variables were collected to assess possible dam effects on taxonomic composition, density, diversity and trophic structure of macroinvertebrate communities. Major changes in environmental variables occurred within the first three sites below the dam (distance<1km): alteration of flow regime (characterized by a constant, residual flow and, in rainy period, by short-term fluctuations), increase of epilithic biomass and, during spring period, decrease of the coarse and fine particulate organic matter associated with benthic samples. Water temperature, conductivity, pH, dissolved oxygen and nutrient concentrations (ammonium and soluble reactive phosphorus) were not affected by river regulation. The effect of the Simbrivio Dam on assemblages of macroinvertebrate communities was noticeable in the spring sampling, where the qualitative composition of benthic fauna below the dam differed from that above it. In this period, the dam produced an alteration of the taxonomic composition and a reduction of taxa richness of downstream sites, particularly in relation to stoneflies, caddisflies and mayflies (EPT taxa). Many taxa of stream insects disappeared at short or long-distance from the dam. Nevertheless, a few of these taxa (as Epeorus assimilis, Isoperla saccai, Rhithrogena gr. hybrida) were collected below the dam in the autumn sampling. Thus, the prevailing conditions of constant flow might favour the presence of these taxa but the sudden rises in river flow due to short-term fluctuations (in winter and spring) had a harmful interference on life cycles of some specific taxa. In this period, macroinvertebrate communities of boulders were the most affected by river regulation. On the contrary, in autumn, the results showed an increase of total and EPT taxa of downstream communities. The effect of the Simbrivio Dam on trophic structure of macroinvertebrate communities was evident on scrapers and collector filterers in spring period, and on shredders in autumn period. The analysis of environmental variables patterns along the watercourse suggested that the principal factors affecting the macroinvertebrate communities at downstream sites were alteration of hydrological conditions, epilithic development and heterogeneity and stability of substrata. In the present study, total densities and diversity indices are probably not the most appropriate macroinvertebrate community metrics for assessing the effects of stream regulation caused by a small dam. Taxonomic composition gives a better interpretation of the alteration of the biota. Finally, Plecoptera and Ephemeroptera Heptageniidae seem to be the most affected taxa to river regulation
18-apr-2008
A.A. 2006/2007
Ecologia
19.
river regulation; river dams
comunità macrobentoniche; Torrente Simbrivio; condizioni idrologiche
Settore BIO/07 - ECOLOGIA
English
Tesi di dottorato
De Cicco, M. (2008). Effects of a small headwater dam on macroinvertebrate communities and environmental variables in a Mediterranean stream.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/449
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