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São conhecidos os impactos negativos da construção de grandes barragens no funcionamento de ecossistemas lóticos. No entanto, permanece por esclarecer a influência de pequenas obras de regularização em ecossistemas aquáticos de montanha, nomeadamente em vários rios do Nordeste Transmontano onde estão já implantados alguns Aproveitamentos Hidroelétricos, perspetivando-se, num curto prazo de tempo, a construção de mais alguns empreendimentos. O objetivo do presente trabalho consistiu na avaliação dos impactos dos Aproveitamentos Hidroelétricos das Trutas, Nunes, Torga e Rebordelo na qualidade ecológica dos cursos de água da bacia hidrográfica do rio Tua. Realça-se que os troços de cabeceira destes ecossistemas lóticos estão inseridos no Parque Natural de Montesinho, onde existem habitats singulares e espécies com elevado valor em termos de conservação.
Na avaliação dos impactos ecológicos recorreu-se a um conjunto de metodologias que permitiram caracterizar: 1) a componente abiótica, caso da qualidade físico-química da água e da condição dos habitats aquático e ribeirinho e 2) a componente biótica, baseada na amostragem das comunidades de macroinvertebrados e de peixes, que seguiram os protocolos emanados pela Diretiva Quadro da Água. Deste modo, na primavera/verão de 2012 e 2013 foi avaliada a integridade ecológica a montante e jusante de cada uma das Mini-Hídricas, mais propriamente em 11 locais de amostragem distribuídos pelos rios Tuela, Baceiro, Rabaçal e Mente. A análise integrada dos vários parâmetros abióticos e bióticos foi suficientemente sensível e permitiu detetar modificações na qualidade biológica global dos cursos de água, em particular nos locais situados a jusante das mini-hídricas. Contudo, as métricas responsivas (e.g. abundância e composição de espécies, índices bióticos e de diversidade) alertaram apenas para uma ligeira diminuição na integridade dos sistemas aquáticos, uma vez que a qualidade ecológica (avaliada em 5 classes: má, medíocre, razoável, boa e excelente) nunca registou uma classificação inferior ao estado ecológico de Bom. No entanto, apesar do estado global do ecossistema não revelar sinais de perturbação preocupante, registou-se um decréscimo de algumas espécies mais ameaçadas nos troços situados a jusante das Mini-Hídricas, caso de alguns núcleos populacionais de mexilhão de rio (Margaritifera margaritifera). Paralelamente, foi também detetada a presença de espécies exóticas, como o lagostim sinal (Pacifastacus leniusculus) que recentemente sofreu uma dispersão acentuada na bacia hidrográfica do rio Tua, pela ação deliberada do Homem.
A preservação dos habitats e das espécies autóctones requer, no futuro, uma vigilância continuada, a realizar através de programas de monitorização da qualidade da água, dos habitats e do biota e ainda o estabelecimento de medidas de gestão e ordenamento piscícola adequadas. Por fim, é ainda de realçar a necessidade de envolvimento das populações locais e dos visitantes da região, através da elaboração de programas de educação e sensibilização, de modo a garantir a conservação dos ecossistemas aquáticos do Nordeste Transmontano.
The negative impacts of big dams construction in the functioning of lotic ecosystems are relatively well known. However, it remains unclear the influence of small hydropower plants (SHP) in mountain aquatic ecosystems, namely in the Northeastern Portugal, where exist several SHP, and others are planned or in a construction phase. The aim of this work was to evaluate the impacts of 4 SHP, named Trutas, Nunes, Torga and Rebordelo on the ecological quality of the watercourses of the River Tua basin. It must be emphasized that these headstreams belong to Parque Natural de Montesinho, where there are unique habitats and species with high conservation. The ecological impact assessment was based on different methodologies that allowed to characterize: 1) the abiotic component, like physical and chemical water quality and thew condition of aquatic and riparian habitats, and 2) the biotic component, based on macro invertebrate communities and fish sampling, which followed the protocols issued by the Water Framework Directive. So, in the spring/summer of 2012 and 2013 it was evaluated the ecological integrity of the upstream and downstream of each SHP, more specifically in 11 sampling locations distributed across Tuela, Baceiro, Rabaçal and Mente streams. The integrated analysis of various abiotic and biotic parameters was sufficiently sensitive and allowed to detect changes in the overall biological quality of watercourses, particularly in locations located downstream of the SHP. However, responsive metrics (e.g. quantity and species composition, biotic and diversity index), only warned to a slight decrease in the aquatic systems integrity, since the ecological quality (evaluated in 5 classes: bad to excellent status) never decreased from the Good status. However, despite the good ecological condition of the ecosystems, there was a decrease of the most endangered species in the downstream sections of the SHP. As an example, the decreased in density of some freshwater pearl mussel populations (Margaritifera margaritifera) can be mentioned. At the same time, it was detected the presence of exotic species, such as the signal crayfish, (Pacifastacus leniusculus), which recently spread over the Tuela river by Human deliberate action. The preservation of habitats and native species requires, in the future, continued vigilance, to be achieved through the monitoring programs of water quality, habitat and biota and also the establishment of management measures. Finally, we also highlight the need to involve local people and visitors of the region through the development of education and awareness, to ensure the conservation of aquatic ecosystems of northeastern Portugal.
The negative impacts of big dams construction in the functioning of lotic ecosystems are relatively well known. However, it remains unclear the influence of small hydropower plants (SHP) in mountain aquatic ecosystems, namely in the Northeastern Portugal, where exist several SHP, and others are planned or in a construction phase. The aim of this work was to evaluate the impacts of 4 SHP, named Trutas, Nunes, Torga and Rebordelo on the ecological quality of the watercourses of the River Tua basin. It must be emphasized that these headstreams belong to Parque Natural de Montesinho, where there are unique habitats and species with high conservation. The ecological impact assessment was based on different methodologies that allowed to characterize: 1) the abiotic component, like physical and chemical water quality and thew condition of aquatic and riparian habitats, and 2) the biotic component, based on macro invertebrate communities and fish sampling, which followed the protocols issued by the Water Framework Directive. So, in the spring/summer of 2012 and 2013 it was evaluated the ecological integrity of the upstream and downstream of each SHP, more specifically in 11 sampling locations distributed across Tuela, Baceiro, Rabaçal and Mente streams. The integrated analysis of various abiotic and biotic parameters was sufficiently sensitive and allowed to detect changes in the overall biological quality of watercourses, particularly in locations located downstream of the SHP. However, responsive metrics (e.g. quantity and species composition, biotic and diversity index), only warned to a slight decrease in the aquatic systems integrity, since the ecological quality (evaluated in 5 classes: bad to excellent status) never decreased from the Good status. However, despite the good ecological condition of the ecosystems, there was a decrease of the most endangered species in the downstream sections of the SHP. As an example, the decreased in density of some freshwater pearl mussel populations (Margaritifera margaritifera) can be mentioned. At the same time, it was detected the presence of exotic species, such as the signal crayfish, (Pacifastacus leniusculus), which recently spread over the Tuela river by Human deliberate action. The preservation of habitats and native species requires, in the future, continued vigilance, to be achieved through the monitoring programs of water quality, habitat and biota and also the establishment of management measures. Finally, we also highlight the need to involve local people and visitors of the region through the development of education and awareness, to ensure the conservation of aquatic ecosystems of northeastern Portugal.
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Keywords
Biota Ecologia Impactos ecológicos Rios Bacia Hidrográfica do Rio Tua Bacia do Douro