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Proposta de requalificação fluvial de zonas degradadas do Rio Angueira (NE de Portugal)
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Abstract(s)
São muitas as ameaças e pressões a que estão sujeitos os cursos de água, maioritariamente pela ação humana. A poluição e eutrofização da água, a fragmentação e degradação de habitats aquáticos e ribeirinhos, a dispersão de espécies invasoras, a sobrepesca e pesca ilegal e as alterações climáticas estão na origem, à escala mundial, da degradação de muitos ecossistemas fluviais. Neste enquadramento, o presente estudo teve como objetivo avaliar zonas alteradas por ação do homem, no Rio Angueira (NE de Portugal), pela presença de açudes e por cortes excessivos/degradação da galeria ripícola e contribuir para a sua requalificação através da elaboração de propostas de reabilitação fluvial. Assim, foram selecionados 4 locais de amostragem em cada uma de 3 zonas identificadas com sinais de degradação, , i.e., A1 e A2 - situados a jusante da barreira/açude, A3 - sob influência da albufeira e A4 - localizado numa zona lótica a montante (referência). A amostragem foi realizada em 2 estações do ano, inverno de 2024 e primavera de 2025. Para avaliação da qualidade ecológica recorreu-se aos protocolos da Agência Portuguesa do Ambiente, baseados na Diretiva-Quadro da Água, para caracterização de elementos físico-químicos gerais (água), hidromorfológicos (habitats) e biológicos (peixes) das águas superficiais. Os resultados obtidos revelaram uma boa qualidade da água, embora para um número exíguo de parâmetros, sendo essencial expandir a análise ao período estival, onde as condições ambientais costumam ser mais stressantes. Na qualidade hidromorfológica, a metodologia do River Habitat Survey permitiu classificar os habitats como significativamente modificados (e.g. baseado no índice HMS) associados, entre outras pressões, às albufeiras de açudes, ambientes tipicamente limnófilos, onde se verificou predominarem espécies exóticas invasoras. Nestas zonas lênticas do Rio Angueira observou-se um domínio de Lepomis gibbosus, cujo reflexo negativo no F-IBIP, índice piscícola oficial de Portugal, é evidente pela atribuição da classificação de MAU a todos os locais A3 das 3 zonas modificadas.
Complementarmente, a análise PERMANOVA (2way, P< 0,05), identificou diferenças significativas entre locais de amostragem e entre zonas de estudo e os testes emparelhados de análise de similaridades (ANOSIM 1way, P<0,05) confirmaram que essas diferenças ocorrem apenas entre os locais regularizados (A3) versus locais sob influência lótica, situados a montante (A4) e jusante (A1 e A2) das respetivas albufeiras. Tal facto, configura a importância da manutenção de zonas lóticas de elevada integridade ecológica como uma estratégia vital para a conservação de espécies ameaçadas. De facto, no rio Angueira subsiste Achondrostoma asturicense uma espécie endémica ameaçada “Em Perigo” (EN), de distribuição restrita em Portugal, cujas populações estão em declínio, face às pressões identificadas na bacia hidrográfica. É uma espécie de pequeno porte, cujo comprimento máximo (Lmáx) não ultrapassou 13,5 cm, um crescimento que oscilou entre isométrico, na zona de montante (Z1, b = 3,01) e alométrico negativo nas 2 restantes zonas (Z2, Z3; b < 3) e ainda diferenças significativas na condição corporal (0,75 < K < 0,84) e na estrutura populacional (detetadas todas as classes de tamanho/idade), baseada na distribuição de frequências de comprimento. Ficou ainda explícita a preferência de A. asturicense por habitats tipicamente reófilos, com sucessão de riffles e pequenos pools naturais, substratos compostos por gravilha, pedras pequenas e grandes, diversidade de velocidades da corrente e cobertura proporcionada, maioritariamente, pelas margens e raízes salientes, pedras e especialmente por macrófitos aquáticos submersos, dominados por Ranunculus sp.
No presente estudo, foi ainda considerada a propagação seminal de espécies lenhosas, arbóreas e arbustivas, nomeadamente de Alnus lusitanica, Fraxinus angustifolia, Prunus spinosa, Crataegus monogyna, Jasminum fruticans. Os testes de germinação mostraram taxas de germinação assinaláveis (> 50%), encorajadoras da criação ex situ de pools génicos. Para cada uma das 3 zonas degradadas foram apresentadas propostas de requalificação ao nível do canal e da zona ribeirinha. Na permeabilidade dos obstáculos físicos (açudes), atualmente intransponíveis pela fauna aquática, foram feitas propostas diferenciadas que incluíram a construção de escadas de peixes (bacias sucessivas) (Z1 - Angueira), uma rampa lateral naturalizada (Z2 - Serapicos) e uma rampa no canal fluvial principal, de declive suave, com melhoramento do canal de irrigação anexo (Z3 - São Joanico). Na zona ribeirinha as propostas incidiram no reforço dos estratos arbóreo, responsável pelo incremento do ensombramento da massa hídrica, mas também do estrato arbustivo, de modo a incrementar a diversidade da flora. Face à quebra de conectividade fluvial e degradação de zonas ripárias em todo o Rio Angueira, assume carácter estratégico a elaboração de projetos de requalificação fluvial e sua posterior implementação, tendo em conta os valores naturais e necessidade da sua preservação.
There are many threats and pressures affecting freshwater ecosystems, mostly due to human action. Water pollution and eutrophication, fragmentation and degradation of aquatic and riparian habitats, the spread of invasive species, overfishing and illegal fishing, and climate change are the causes of the degradation of many river ecosystems on a global scale. In this context, the present study aimed to evaluate modified zones by human action in the Angueira River (NE Portugal), due to the presence of weirs and excessive cutting/degradation of the riparian gallery, and to contribute to their requalification through the development of river rehabilitation proposals. Thus, 4 sampling sites were selected in each of the 3 areas identified with signs of degradation, i.e. A1 and A2 - located downstream of the barrier/weirs, A3 - under the influence of the reservoir, and A4 - located in the lotic zone upstream (reference sites). Sampling was carried out in two different seasons, winter 2024 and spring 2025. To assess ecological quality, protocols from the Portuguese Environment Agency, based on the Water Framework Directive, were used to characterize general physical-chemical (water), hydromorphological (habitats) and biological (fish) elements of surface waters. The results revealed good water quality, although based on a small number of parameters. For these reasons it is essential to expand the analysis to the summer period, when environmental conditions tend to be more stressful. In terms of hydromorphological quality, the River Habitat Survey methodology allowed the classification of habitats as significantly modified (e.g. based on the HMS index), associated, among other pressures, with weir reservoirs, typically limnophilic environments, where exotic species predominate. In these lentic areas of the Angueira River, a dominance of Lepomis gibbosus was observed, whose negative impact on the F-IBIP, the Portuguese official fish index, is evident by the attribution of the BAD classification to all A3 sites (e.g., artificial reservoirs) in the 3 modified zones by human action. In addition, the PERMANOVA analysis (2-way, P < 0.05) identified significant differences between sampling sites and between study zones, and the paired similarity analysis tests (ANOSIM 1-way, P < 0.05) confirmed that these differences occur only between regulated sites (A3) versus lotic sites, located upstream (A4) and downstream (A1 and A2) of the respective weirs. This fact demonstrates the importance of maintaining lotic zones with high ecological integrity as a vital strategy for the conservation of endangered species. In fact, Achondrostoma asturicense, an endemic threatened species with “Endangered” (EN) status, survives in the Angueira River, whose populations are in decline, given the pressures identified in the river basin. This is a small species, with a maximum length (Lmax) not exceeding 13.5 cm, and with a growth that oscillated between isometric, in the upstream zone (Z1, b=3.01) and negative allometric in the remaining 2 zones (Z2, Z3; b < 3) and also with significant differences in body condition (0.75 < K < 0.84) and in the population structure (all size/age classes detected), based on the length frequency distribution. The preference of A. asturicense for typically rheophilic habitats was also explicit, with a succession of riffles and natural pools, substrates dominated by gravel, small and large cobbles, diversity of current velocities and the presence of cover, provided mainly by the banks and protruding roots, cobbles and especially by aquatic macrophytes, dominated by Ranunculus sp. In this study, the seed propagation of woody plants, arboreal and shrub species, namely Alnus lusitanica, Fraxinus angustifolia, Prunus spinosa, Crataegus monogyna, Jasminum fruticans, was also considered. Thus, the germination tests carried out showed remarkable germination rates (> 50%), encouraging the ex-situ creation of gene pools for further restocking. Proposals for requalification of the canal and riparian zones were presented for each of the 3 degraded areas. In the permeability of the physical obstacles (weirs) currently insurmountable by aquatic fauna, different proposals were made, including the construction of fish ladders (successive basins) (Z1 - Angueira), a lateral naturalized ramp (Z2 - Serapicos) and a ramp in the main river channel, with a gentle slope, with improvement of the adjacent channel, i.e., for irrigation purposes (Z3 - São Joanico). In the riparian zone, the proposals are focused on strengthening the tree strata, responsible for increasing the shading of the watercourse, but also the shrub strata, to increase the diversity of the riparian ecosystem.
There are many threats and pressures affecting freshwater ecosystems, mostly due to human action. Water pollution and eutrophication, fragmentation and degradation of aquatic and riparian habitats, the spread of invasive species, overfishing and illegal fishing, and climate change are the causes of the degradation of many river ecosystems on a global scale. In this context, the present study aimed to evaluate modified zones by human action in the Angueira River (NE Portugal), due to the presence of weirs and excessive cutting/degradation of the riparian gallery, and to contribute to their requalification through the development of river rehabilitation proposals. Thus, 4 sampling sites were selected in each of the 3 areas identified with signs of degradation, i.e. A1 and A2 - located downstream of the barrier/weirs, A3 - under the influence of the reservoir, and A4 - located in the lotic zone upstream (reference sites). Sampling was carried out in two different seasons, winter 2024 and spring 2025. To assess ecological quality, protocols from the Portuguese Environment Agency, based on the Water Framework Directive, were used to characterize general physical-chemical (water), hydromorphological (habitats) and biological (fish) elements of surface waters. The results revealed good water quality, although based on a small number of parameters. For these reasons it is essential to expand the analysis to the summer period, when environmental conditions tend to be more stressful. In terms of hydromorphological quality, the River Habitat Survey methodology allowed the classification of habitats as significantly modified (e.g. based on the HMS index), associated, among other pressures, with weir reservoirs, typically limnophilic environments, where exotic species predominate. In these lentic areas of the Angueira River, a dominance of Lepomis gibbosus was observed, whose negative impact on the F-IBIP, the Portuguese official fish index, is evident by the attribution of the BAD classification to all A3 sites (e.g., artificial reservoirs) in the 3 modified zones by human action. In addition, the PERMANOVA analysis (2-way, P < 0.05) identified significant differences between sampling sites and between study zones, and the paired similarity analysis tests (ANOSIM 1-way, P < 0.05) confirmed that these differences occur only between regulated sites (A3) versus lotic sites, located upstream (A4) and downstream (A1 and A2) of the respective weirs. This fact demonstrates the importance of maintaining lotic zones with high ecological integrity as a vital strategy for the conservation of endangered species. In fact, Achondrostoma asturicense, an endemic threatened species with “Endangered” (EN) status, survives in the Angueira River, whose populations are in decline, given the pressures identified in the river basin. This is a small species, with a maximum length (Lmax) not exceeding 13.5 cm, and with a growth that oscillated between isometric, in the upstream zone (Z1, b=3.01) and negative allometric in the remaining 2 zones (Z2, Z3; b < 3) and also with significant differences in body condition (0.75 < K < 0.84) and in the population structure (all size/age classes detected), based on the length frequency distribution. The preference of A. asturicense for typically rheophilic habitats was also explicit, with a succession of riffles and natural pools, substrates dominated by gravel, small and large cobbles, diversity of current velocities and the presence of cover, provided mainly by the banks and protruding roots, cobbles and especially by aquatic macrophytes, dominated by Ranunculus sp. In this study, the seed propagation of woody plants, arboreal and shrub species, namely Alnus lusitanica, Fraxinus angustifolia, Prunus spinosa, Crataegus monogyna, Jasminum fruticans, was also considered. Thus, the germination tests carried out showed remarkable germination rates (> 50%), encouraging the ex-situ creation of gene pools for further restocking. Proposals for requalification of the canal and riparian zones were presented for each of the 3 degraded areas. In the permeability of the physical obstacles (weirs) currently insurmountable by aquatic fauna, different proposals were made, including the construction of fish ladders (successive basins) (Z1 - Angueira), a lateral naturalized ramp (Z2 - Serapicos) and a ramp in the main river channel, with a gentle slope, with improvement of the adjacent channel, i.e., for irrigation purposes (Z3 - São Joanico). In the riparian zone, the proposals are focused on strengthening the tree strata, responsible for increasing the shading of the watercourse, but also the shrub strata, to increase the diversity of the riparian ecosystem.
Description
Keywords
Achondrostoma asturicense River monitoring Natural engineering techniques Propagation of riparian species Proposals for river requalification