Influence of drought on algal biofilms and meiofaunal assemblages of temperate reservoirs and rivers |
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Authors: | Maria-José Caramujo Carlos Rafael B Mendes Paulo Cartaxana Vanda Brotas Maria-José Boavida |
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Institution: | (1) Dept. Biologia Animal, Faculdade de Ciências, Centro de Biologia Ambiental, Universidade de Lisboa, Campo Grande C2, 1749-016 Lisbon, Portugal;(2) Faculdade de Ciências, Instituto de Oceanografia, Universidade de Lisboa, Campo Grande, 1749-016 Lisbon, Portugal;(3) Faculdade de Ciências, Laboratório Marítimo da Guia, Universidade de Lisboa, Estrada do Guincho, 2750-374 Cascais, Portugal |
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Abstract: | The role of hydrological droughts in shaping meiofauna abundance through alterations in biofilm biomass and composition was
investigated. In January 2005, continental Portugal was under a moderate to severe drought resulting from a 40% to 60% decrease
in rainfall during the previous 12 months relative to the long-term average (1961–1990). Reservoir capacity was reduced by
30–50% relative to average values and the width of streams was reduced by 20–80% in the Zêzere River Basin (central Portugal).
Algal biomass and algal class composition of biofilms was assessed through quantification of algal pigments in three reservoir
and six river locations. During drought, habitat alterations are expected to be sharp in rivers while, in the absence of water
quality deterioration, the habitat characteristics of reservoirs are expected to remain fairly unaffected. Chlorophylls and
carotenoid pigments were extracted from biofilm samples and analysed using high performance liquid chromatography (HPLC).
In the winter of 2003, during the period of average rainfall, biofilm biomass did not exceed 5 μg chlorophyll a cm−2 at any location. River biofilm biomass was roughly half of that measured in the reservoirs. In the winter of 2005 (drought),
biofilm biomass increased by more than 5-fold in river locations and remained low or decreased in the reservoirs. Algal biofilms
were either dominated by Bacillariophyceae or by Chlorophyceae regardless of the existence of drought. The relative contribution
of Bacillariophyceae to total biofilm biomass was higher during the drought than under average hydrological conditions. The
abundance of harpacticoids, cladocerans and ostracods was favoured by the drought only in the reservoirs where an increase
in diatom proportion in biofilms was observed. The increase in the abundance of cyclopoid copepods, turbellarians, nematodes
and chironomids in rivers during the drought could be explained by algal class composition and biomass of biofilms and environmental
variables (organic matter sediment content, phosphorus availability content and sediment granulometry). The hydrological drought
appears to regulate meiofauna abundance only in river locations, possibly through the promotion of the growth of biofilms
and the availability of organic matter deposited in rivers during the drought.
Handling editor: D. Ryder |
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Keywords: | Carotenoid pigments Mediterranean climate Meiofauna Micro-crustaceans Microalgae Periphyton |
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