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Avaliação do Efeito da Reabilitação de Rios Urbanos na Biodiversidade e Condição Ecológica: O caso do Rio Fervença (Bragança, NE Portugal)
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Advisor(s)
Abstract(s)
Diferentes atividades antrópicas estão na origem da degradação de ecossistemas
terrestres e em particular de água doce, entre os mais ameaçados, à escala mundial.
Com efeito, a fragmentação de habitats aquáticos e ribeirinhos, a poluição da água, a
introdução de espécies invasoras, a sobre-exploração de recursos e as alterações
climáticas têm contribuído para uma contínua perda de biodiversidade e integridade
ecológica. Nos rios urbanos a influência humana ainda é mais expressiva, tendo
justificado a implementação de muitos projetos de reabilitação fluvial, maioritariamente
orientados para a regulação e controlo de cheias e embelezamento de áreas marginais,
sem preocupação de garantir a biodiversidade e serviços de ecossistema associados.
Neste enquadramento, o presente estudo teve como objetivo avaliar os efeitos da
reabilitação na biodiversidade e qualidade ecológica do rio Fervença, em particular no
setor urbano - zona POLIS da cidade de Bragança (NE Portugal). Assim, no ano de
2024, foram amostrados, com periodicidade sazonal (inverno, primavera e verão), 14
locais de amostragem distribuídos pelos rios Fervença e Sabor (locais de referência).
Foram aplicadas as metodologias definidas pela Agência Portuguesa do Ambiente
(APA), no âmbito da Diretiva Quadro da Água (DQA), para avaliação dos elementos 1)
físico-químicos da água e 2) hidromorfológicos, de suporte aos elementos 3) biológicos,
caso das comunidades de macroinvertebrados e peixes. Consideraram-se 6 setores
correspondentes às seguintes tipologias: 1) RM - Referência montante (S1 e S2); 2) MR-
Montante rural (F1, F2); MU - Montante urbano (F3, F4); 4) RP - Reabilitado POLIS (F5
a F8); JU - Jusante urbano (F9, F10); e RJ - Referência jusante (S3 e S4). Os resultados
obtidos para a qualidade da água, baseados em análises de redundâncias (dbRDA, 71%
da variância explicada) e testes univariados (testes H Kruskall-Wallis, P<0,05),
evidenciaram diferenças significativas, nomeadamente entre os setores urbanos (RP e
JU) e de referência (RM), para as variáveis físico-químicos da condutividade, total de
sólidos dissolvidos, fosfatos, cloretos e acidez total. No que respeita aos habitats
aquáticos e ribeirinhos, os índices de modificação (HMS) e qualidade (HQA) do habitat
(River Habitat Survey, RHS) foram suficientemente sensíveis para detetar a degradação
aquática e ribeirinha nos setores urbanos, com especial destaque para a zona
reabilitada POLIS. Relativamente às respostas bióticas foram também encontradas
diferenças significativas (testes PERMANOVA 2-way, P<0,05), nomeadamente entre os
setores e as estações do ano para as comunidades de invertebrados e apenas entre
setores para as comunidades de peixes. Nas comunidades de invertebrados, a análise
multivariada (ordenação nMDS, testes ANOSIM e SIMPER) permitiu identificar famílias
e diferenciar comunidades euribiontes, típicas de zonas perturbadas (RP e RJ), das comunidades estenobiontes, presentes nas zonas de referência. Com efeito, apesar de
superior abundância de organismos, a diversidade (H’) e equitabilidade (J’) foi inferior
nas zonas perturbadas, concentrada no domínio avassalador de Crustacea (Asellidae)
e ainda de Gastropoda (Physidae, Lymnaeidae), Hirudinea (Erpodbdellidae,
Glossiphoniidae), Oligochaeta e Diptera (Chiroinomidae, Simuliidae). Registo ainda para
a presença assinalável de espécies invasoras, como o lagostim-sinal (Pacifastacus
leniusculus). Por sua vez, sobressaem nas comunidades dos locais de referência
táxones pertencentes aos Ephemeroptera (Ephemerellidae, Siphlonuridae), Plecoptera
(Leuctridae, Perlidae) e Trichoptera (Sericostomatidae, Calamoceratidae), indicadores
da saúde do ecossistema fluvial. No caso da comunidade piscícola, os resultados
obtidos evidenciaram, à semelhança das comunidades de invertebrados, uma
separação evidente entre comunidades de setores de referência relativamente a setores
urbanos. Registo para o crescente domínio de espécies exóticas, caso góbio (Gobio
lozanoi), gambúsia (Gambusia holbrooki) e perca-sol (Lepomis gibbosus) nos locais
mais antropizados (RP e JU), particularmente sob efeito da poluição e regularização
(e.g., açudes), em detrimento das espécies reófilas nativas, caso da truta-de-rio (Salmo
trutta), boga-do-norte (Pseudochondrostoma duriense), em maior abundância em locais
de boa integridade ecológica (RM, RJ). Ficou ainda evidente que o verão parece ser a
estação do ano mais crítica para as comunidades de invertebrados e menos para os
peixes, provavelmente pelas condições ambientais mais adversas, potenciadas pelos
caudais inferiores detetados ultimamente em função das alterações climáticas patentes.
Os resultados baseados nos dados atuais e respetiva comparação com a situação de
pré-reabilitação, evidenciaram a inexistência de ganhos em termos de biodiversidade e
estado ecológico do rio Fervença, nomeadamente no setor urbano - zona POLIS, 20
anos após a execução das obras de reabilitação na cidade de Bragança. Neste sentido,
configura-se a necessidade de aplicar medidas/ações de melhoria do ambiente aquático
e ribeirinho, no sentido de recuperar serviços de ecossistema associados à valorização
da componente ecológica. Entre as ações sugerem-se a mitigação/minimização e/ou
eliminação de impactes negativos (e.g., inputs localizados de poluição), o recurso a
soluções baseadas na natureza (e.g., técnicas de engenharia natural nos habitats
degradados), a gestão eficiente da água (e.g., reuso de água da ETAR), a gestão
adaptativa às alterações climáticas (e.g., reforço de galerias ripícolas), com o intuito de
promover a recuperação e conservação do rio Fervença num quadro de sustentabilidade
ecológica.
Different human activities are responsible for the degradation of many ecosystems, with particular emphasis on freshwater systems, which are among the most threatened worldwide. Indeed, the fragmentation of aquatic and riparian habitats, water pollution, the introduction of invasive alien species, the overexploitation of resources and climate change have contributed to an ongoing loss of biodiversity and ecological integrity. In urban rivers, human influence is still more significant, justifying the implementation of many river rehabilitation projects, mainly aimed at regulating and controlling floods and beautifying marginal areas, without any concern for increasing biodiversity and associated ecosystem services. In this context, the present study aimed to evaluate the effects of the rehabilitation on the biodiversity and ecological quality of the Fervença River, particularly in the urban sector - POLIS zone of the Bragança city (NE Portugal). Thus, in 2014, 14 sampling sites distributed along the Fervença and Sabor (reference sites) rivers were sampled seasonally (winter, spring and summer). The methodologies defined by the Portuguese Environment Agency (APA), within the scope of the Water Framework Directive (WFD), were applied to assess 3 different elements: 1) physical- chemical water variables; and 2) hydromorphological evaluation supporting the 3) biological communities, namely macroinvertebrate and fish. Six sectors corresponding to the following typologies were also considered: 1) RM - Upstream reference (S1 and S2); 2) MR- Rural Upstream (F1, F2); MU - Urban Upstream (F3, F4); 4) RP - POLIS Rehabilitation (F5 to F8); JU - Urban downstream (F9, F10); and RJ - Downstream reference (S3 and S4). The results obtained for water quality, based on redundancy analysis (dbRDA, 71% of the variance explained) and univariate tests (Kruskall-Wallis H tests, P<0.05), showed significant differences, notably between sectors under urban influence (RP and JU) and reference (RM) condition, for the physical-chemical parameters of water conductivity, total dissolved solids, phosphates, chlorides and total acidity. Regarding aquatic and riparian habitats, habitat modification (HMS) and quality (HQA) indices (River Habitat Survey, RHS) were enough sensitive to detect aquatic and riparian degradation in urban sectors, with special emphasis on the POLIS rehabilitated area. Relatively to the biotic responses, significant differences were also found (2-way PERMANOVA tests, P<0.05), namely between sectors and seasons for invertebrate communities and only between sectors for fish communities. Regarding invertebrate communities, multivariate analysis (nMDS ordination, ANOSIM and SIMPER tests) allowed the identification of families and the differentiation of eurybiont communities, typical of disturbed areas (RP and RJ), from stenobiont communities, present in reference areas. In fact, despite the higher abundance of organisms, diversity (H’) and equitability (J’) were lower in disturbed areas, concentrated in the overwhelming dominance mainly of Crustacea (Asellidae) but also of Gastropoda (Physidae, Lymnaeidae), Oligochaeta, Hirudinea (Erpodbdellidae, Glossiphoniidae) and Diptera (Chiroinomidae, Simuliidae). Also noteworthy is the notable presence of invasive species, such as the signal crayfish (Pacifastacus leniusculus). In contrast, taxa belonging to the Ephemeroptera (Ephemerellidae, Siphlonuridae), Plecoptera (Leuctridae, Perlidae) and Trichoptera (Sericostomatidae, Calamoceratidae) stand out in the communities of the reference sites, being indicators of the health of the river ecosystem. In the case of the fish community, the results obtained showed, similarly to the invertebrate communities, a clear separation between communities in reference sectors in relation to urban sectors. It must be highlight the dominance of exotic species, such as Pyrenean gudgeon (Gobio lozanoi), mosquito-fish (Gambusia holbrooki) and pumpkinseed (Lepomis gibbosus) in the most anthropized sites (RP and JU), particularly under the effect of pollution and regulation of weirs, to the detriment of native rheophilic species, such as brown trout (Salmo trutta), northern straight-mouth nase (Pseudochondrostoma duriense), in greater abundance in reference sites of good ecological integrity (RM, RJ). It was also evident that summer appears to be the most critical season for invertebrate communities and less for fish, probably due to more adverse environmental conditions, exacerbated by the lower flows, detected more recently, due to evident climate changes. The results obtained, based on current data and comparisons with the pre-rehabilitation situation, showed the lack of gains in terms of biodiversity and ecological state of the Fervença river, particularly in the urban sector - POLIS zone, 20 years after the execution of the rehabilitation works in Bragança. In this sense, there is a need to apply measures/ actions to improve the aquatic and riparian environment, to recover associated ecosystem services with the valorization of the ecological component. The suggested actions include mitigation/ minimization and/or elimination of negative impacts (e.g., point-source pollution), the use of nature-based solutions (e.g., natural engineering techniques in degraded habitats), efficient water management (e.g., reuse of water from the WWTP), adaptive management of climate change (e.g., reinforcement of riparian galleries), with the aim of promoting the recovery and conservation of the Fervença river, within a framework of ecological sustainability.
Different human activities are responsible for the degradation of many ecosystems, with particular emphasis on freshwater systems, which are among the most threatened worldwide. Indeed, the fragmentation of aquatic and riparian habitats, water pollution, the introduction of invasive alien species, the overexploitation of resources and climate change have contributed to an ongoing loss of biodiversity and ecological integrity. In urban rivers, human influence is still more significant, justifying the implementation of many river rehabilitation projects, mainly aimed at regulating and controlling floods and beautifying marginal areas, without any concern for increasing biodiversity and associated ecosystem services. In this context, the present study aimed to evaluate the effects of the rehabilitation on the biodiversity and ecological quality of the Fervença River, particularly in the urban sector - POLIS zone of the Bragança city (NE Portugal). Thus, in 2014, 14 sampling sites distributed along the Fervença and Sabor (reference sites) rivers were sampled seasonally (winter, spring and summer). The methodologies defined by the Portuguese Environment Agency (APA), within the scope of the Water Framework Directive (WFD), were applied to assess 3 different elements: 1) physical- chemical water variables; and 2) hydromorphological evaluation supporting the 3) biological communities, namely macroinvertebrate and fish. Six sectors corresponding to the following typologies were also considered: 1) RM - Upstream reference (S1 and S2); 2) MR- Rural Upstream (F1, F2); MU - Urban Upstream (F3, F4); 4) RP - POLIS Rehabilitation (F5 to F8); JU - Urban downstream (F9, F10); and RJ - Downstream reference (S3 and S4). The results obtained for water quality, based on redundancy analysis (dbRDA, 71% of the variance explained) and univariate tests (Kruskall-Wallis H tests, P<0.05), showed significant differences, notably between sectors under urban influence (RP and JU) and reference (RM) condition, for the physical-chemical parameters of water conductivity, total dissolved solids, phosphates, chlorides and total acidity. Regarding aquatic and riparian habitats, habitat modification (HMS) and quality (HQA) indices (River Habitat Survey, RHS) were enough sensitive to detect aquatic and riparian degradation in urban sectors, with special emphasis on the POLIS rehabilitated area. Relatively to the biotic responses, significant differences were also found (2-way PERMANOVA tests, P<0.05), namely between sectors and seasons for invertebrate communities and only between sectors for fish communities. Regarding invertebrate communities, multivariate analysis (nMDS ordination, ANOSIM and SIMPER tests) allowed the identification of families and the differentiation of eurybiont communities, typical of disturbed areas (RP and RJ), from stenobiont communities, present in reference areas. In fact, despite the higher abundance of organisms, diversity (H’) and equitability (J’) were lower in disturbed areas, concentrated in the overwhelming dominance mainly of Crustacea (Asellidae) but also of Gastropoda (Physidae, Lymnaeidae), Oligochaeta, Hirudinea (Erpodbdellidae, Glossiphoniidae) and Diptera (Chiroinomidae, Simuliidae). Also noteworthy is the notable presence of invasive species, such as the signal crayfish (Pacifastacus leniusculus). In contrast, taxa belonging to the Ephemeroptera (Ephemerellidae, Siphlonuridae), Plecoptera (Leuctridae, Perlidae) and Trichoptera (Sericostomatidae, Calamoceratidae) stand out in the communities of the reference sites, being indicators of the health of the river ecosystem. In the case of the fish community, the results obtained showed, similarly to the invertebrate communities, a clear separation between communities in reference sectors in relation to urban sectors. It must be highlight the dominance of exotic species, such as Pyrenean gudgeon (Gobio lozanoi), mosquito-fish (Gambusia holbrooki) and pumpkinseed (Lepomis gibbosus) in the most anthropized sites (RP and JU), particularly under the effect of pollution and regulation of weirs, to the detriment of native rheophilic species, such as brown trout (Salmo trutta), northern straight-mouth nase (Pseudochondrostoma duriense), in greater abundance in reference sites of good ecological integrity (RM, RJ). It was also evident that summer appears to be the most critical season for invertebrate communities and less for fish, probably due to more adverse environmental conditions, exacerbated by the lower flows, detected more recently, due to evident climate changes. The results obtained, based on current data and comparisons with the pre-rehabilitation situation, showed the lack of gains in terms of biodiversity and ecological state of the Fervença river, particularly in the urban sector - POLIS zone, 20 years after the execution of the rehabilitation works in Bragança. In this sense, there is a need to apply measures/ actions to improve the aquatic and riparian environment, to recover associated ecosystem services with the valorization of the ecological component. The suggested actions include mitigation/ minimization and/or elimination of negative impacts (e.g., point-source pollution), the use of nature-based solutions (e.g., natural engineering techniques in degraded habitats), efficient water management (e.g., reuse of water from the WWTP), adaptive management of climate change (e.g., reinforcement of riparian galleries), with the aim of promoting the recovery and conservation of the Fervença river, within a framework of ecological sustainability.
Description
Keywords
Rios urbanos Macroinvertebrados Peixes Integridade ecológica Reabilitação ambiental