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Efeitos da intensificação agrícola na qualidade ecológica das linhas de água inseridas na rede secundária do Empreendimento de Fins Múltiplos de Alqueva
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Resumo(s)
A agricultura intensiva apresenta impactos significativos nos ecossistemas dulçaquícolas, sendo por isso
fundamental que em grandes projetos de irrigação se efetue a monitorização ambiental destes
ecossistemas. Este trabalho comparou os resultados das monitorizações de três elementos biológicos,
fauna piscícola, macroinvertebrados bentónicos e macrófitos, na rede secundária de rega do
Empreendimento de Fins Múltiplos de Alqueva, realizadas em 2016, 2019 e 2021, de acordo com a
Diretiva Quadro da Água (DQA). O objetivo foi compreender o impacto da agricultura intensiva sobre
estes elementos biológicos, realizando uma avaliação indireta com base em parâmetros físico-químicos
que podem ser afetados por este tipo de agricultura. Especificamente, procurou-se identificar os
principais fatores que influenciam a composição das comunidades biológicas ao longo do espaço e do
tempo, e as tendências de variação na qualidade biológica. Os resultados evidenciaram uma tendência
de dominância de taxa de elevada tolerância à degradação ambiental, tendo as comunidades biológicas
apresentado uma reduzida variação interanual, e não existindo tendências claras de diferenciação em
função da localização geográfica. Os taxa responderam diferenciadamente aos parâmetros físicoquímicos, tendo os taxa tolerantes sido mais abundantes na presença de elevados teores de nutrientes.
No caso da fauna piscícola, observou-se um número considerável de indivíduos de espécies exóticas. A
qualidade biológica apresentou uma ligeira pioria em 2019 face aos outros anos, que não foi claramente
acompanhada de variação sensível dos parâmetros físico-químicos, podendo resultar das condições
ambientais. Os resultados não evidenciaram uma relação entre a intensificação agrícola e a qualidade
biológica. A qualidade biológica quantificada com base nos macroinvertebrados bentónicos foi inferior
a “Bom” em todas as estações, não sendo atingidos os objetivos ambientais estabelecidos pela DQA.
Isto sugere que as medidas de mitigação dos impactos da agricultura intensiva podem estar a ser
insuficientes, e que esta situação deve ser analisada em maior detalhe no futuro.
Intensive agriculture has significative impacts on freshwater ecosystems, making it essential to implement environmental monitoring of the ecosystems in large irrigation projects. This work compared the results of the monitoring of three biological elements, fish fauna, benthic macroinvertebrates and macrophytes, in the secondary irrigation network of the Alqueva Multipurpose Project, carried out in 2016, 2019 and 2021, in accordance with the Water Framework Directive (WFD). The objective was to understand the impact of intensive agriculture on these biological elements, which was evaluated indirectly using physicochemical parameters that can be affected by this type of agriculture (e.g. total nitrogen concentration in water). Analyses aimed to identify the main factors associated with the composition of biological communities over time and across space, and variation tendencies in biological quality. Results showed a tendency for communities to be dominated by taxa that are tolerant to environmental degradation. Biological communities presented a low interannual variation, and there was no clear differentiation in relation to geographical location. Taxa showed different responses to physicochemical parameters, with tolerant taxa tending to be more abundant with high nutrient concentrations. Fish fauna, included a considerable number indviduals of exotic species. Biological quality showed a slight decrease in 2019 comparing with other years, which was not associated with physicochemical parameters, and could result from environmental conditions. Results did not demonstrate a relation between agricultural intensification and biological quality. Water quality assessed using benthic macroinvertebrates was below “Good” in all monitoring sites, not achieving the goals of the WFD. This suggests that intensive agriculture mitigation measures may not be having enough results, and this situation should be analysed in greater detail in the future.
Intensive agriculture has significative impacts on freshwater ecosystems, making it essential to implement environmental monitoring of the ecosystems in large irrigation projects. This work compared the results of the monitoring of three biological elements, fish fauna, benthic macroinvertebrates and macrophytes, in the secondary irrigation network of the Alqueva Multipurpose Project, carried out in 2016, 2019 and 2021, in accordance with the Water Framework Directive (WFD). The objective was to understand the impact of intensive agriculture on these biological elements, which was evaluated indirectly using physicochemical parameters that can be affected by this type of agriculture (e.g. total nitrogen concentration in water). Analyses aimed to identify the main factors associated with the composition of biological communities over time and across space, and variation tendencies in biological quality. Results showed a tendency for communities to be dominated by taxa that are tolerant to environmental degradation. Biological communities presented a low interannual variation, and there was no clear differentiation in relation to geographical location. Taxa showed different responses to physicochemical parameters, with tolerant taxa tending to be more abundant with high nutrient concentrations. Fish fauna, included a considerable number indviduals of exotic species. Biological quality showed a slight decrease in 2019 comparing with other years, which was not associated with physicochemical parameters, and could result from environmental conditions. Results did not demonstrate a relation between agricultural intensification and biological quality. Water quality assessed using benthic macroinvertebrates was below “Good” in all monitoring sites, not achieving the goals of the WFD. This suggests that intensive agriculture mitigation measures may not be having enough results, and this situation should be analysed in greater detail in the future.
Descrição
Relatório de estágio de mestrado, Ecologia e Gestão Ambiental, 2023, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Monitorização ambiental Ecossistemas dulçaquícolas Uso do solo Elementos de qualidade biológica Diretiva Quadro da Água Teses de mestrado - 2023