Publicação
Threats to the native fish community of the Vilariça River: agricultural activities and the Baixo Sabor Hydroelectric Scheme
| Resumo: | The freshwater biota in Mediterranean rivers is subject to impacts such as river fragmentation and eutrophication due to hydropower plants and intensive agriculture. The loss of fish biodiversity, whether potamodromous or diadromous, is a mirror of those impacts. Thus, it was selected as a case study of the Sabor River catchment, particularly the Vilariça River, in order to evaluate the effects of human activities, namely river regulation and agricultural activity, on river water quality and the health and life cycles of two target potamodromous species of the Douro River catchment: the Iberian barbel (Luciobarbus bocagei) and the Douro nase (Pseudochondrostoma duriense). The work was divided into three stages. In the first stage, the impact of river damming on water quality and aquatic fauna was assessed in the Sabor River (Chapter 2). Changes in water quality were marked by increases in temperature and electric conductivity downstream of dams and by the input of phosphorus and nitrogen into the two reservoirs, which triggered a growth of algae, an increase in chlorophyll-a, and a drop in water transparency. The consequences of water quality deterioration for aquatic fauna were severe, marked by abrupt declines of native fish species and the invasion of exotic species. The ecological status, determined from ecological quality ratios, changed from good-fair in the unaffected watercourses to fair-poor in the regulated streams. The second stage of the work, developed in the Vilariça River, consisted of relating water quality to agricultural practices and the health status of the fish (Chapters 3, 4, and 5). The water was classified as polluted and extremely polluted in summer and winter, respectively. In summer, the values of physicochemical parameters and metals in the water may be caused by less flow and excessive agricultural fertilization, which reached the river through irrigation and leaching, and in winter by the erosion of soil particles with associated metals. The pronounced and severe histopathological changes observed in both species, such as aneurism, exudate, and hypertrophy in the gills and biliary duct epithelial detachment, hyperplasia of the biliary epithelium, congestion of blood vessels, and degenerative vacuolization in the liver, were statistically related to the poor water quality. The Integrated Biomarker Response, computed from histopathological changes identified in the gonads, gills, and liver, showed higher values in the summer and in the middle and downstream sections of the river compared to the winter season and the upstream section, which is in agreement with the spatiotemporal distribution of concentrations of metals in the river water. In the third stage, also developed in the Vilariça River, the fluvial rehabilitation measures for the reproduction conditions of L. bocagei were evaluated (Chapter 6). The results showed that migration and spawning were improved with incremental flow from a bypass system created for this purpose. Installed submerged weirs also contributed to the success of spawning since they facilitated the upstream migration and the establishment of spawning and resting areas. Additionally, to assess the spawning activity of L. bocagei, a spawn-per-unit-effort (SPUE) methodology was developed. It was proposed to integrate this methodology into the monitoring plan of the compensatory measures of the Vilariça River because it will provide greater knowledge of the spawning activity of L. bocagei, which is essential for improving conservation efforts. In addition, it presents a set of mitigation and management measures directed to the conservation of fish communities in Mediterranean streams in order to reduce the negative impact of agricultural contamination on water quality and fish health, such as improving the irrigation methods, preserving the vegetation cover, promoting reforestation in degraded and burned areas, and improving the riparian vegetation. |
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| Autores principais: | Santos, Regina Maria Bessa |
| Assunto: | Sabor and Vilariça Rivers Potamodromous fish |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso restrito |
| Instituição associada: | Universidade de Trás-os-Montes e Alto Douro |
| Idioma: | inglês |
| Origem: | Repositório da UTAD |
| Resumo: | The freshwater biota in Mediterranean rivers is subject to impacts such as river fragmentation and eutrophication due to hydropower plants and intensive agriculture. The loss of fish biodiversity, whether potamodromous or diadromous, is a mirror of those impacts. Thus, it was selected as a case study of the Sabor River catchment, particularly the Vilariça River, in order to evaluate the effects of human activities, namely river regulation and agricultural activity, on river water quality and the health and life cycles of two target potamodromous species of the Douro River catchment: the Iberian barbel (Luciobarbus bocagei) and the Douro nase (Pseudochondrostoma duriense). The work was divided into three stages. In the first stage, the impact of river damming on water quality and aquatic fauna was assessed in the Sabor River (Chapter 2). Changes in water quality were marked by increases in temperature and electric conductivity downstream of dams and by the input of phosphorus and nitrogen into the two reservoirs, which triggered a growth of algae, an increase in chlorophyll-a, and a drop in water transparency. The consequences of water quality deterioration for aquatic fauna were severe, marked by abrupt declines of native fish species and the invasion of exotic species. The ecological status, determined from ecological quality ratios, changed from good-fair in the unaffected watercourses to fair-poor in the regulated streams. The second stage of the work, developed in the Vilariça River, consisted of relating water quality to agricultural practices and the health status of the fish (Chapters 3, 4, and 5). The water was classified as polluted and extremely polluted in summer and winter, respectively. In summer, the values of physicochemical parameters and metals in the water may be caused by less flow and excessive agricultural fertilization, which reached the river through irrigation and leaching, and in winter by the erosion of soil particles with associated metals. The pronounced and severe histopathological changes observed in both species, such as aneurism, exudate, and hypertrophy in the gills and biliary duct epithelial detachment, hyperplasia of the biliary epithelium, congestion of blood vessels, and degenerative vacuolization in the liver, were statistically related to the poor water quality. The Integrated Biomarker Response, computed from histopathological changes identified in the gonads, gills, and liver, showed higher values in the summer and in the middle and downstream sections of the river compared to the winter season and the upstream section, which is in agreement with the spatiotemporal distribution of concentrations of metals in the river water. In the third stage, also developed in the Vilariça River, the fluvial rehabilitation measures for the reproduction conditions of L. bocagei were evaluated (Chapter 6). The results showed that migration and spawning were improved with incremental flow from a bypass system created for this purpose. Installed submerged weirs also contributed to the success of spawning since they facilitated the upstream migration and the establishment of spawning and resting areas. Additionally, to assess the spawning activity of L. bocagei, a spawn-per-unit-effort (SPUE) methodology was developed. It was proposed to integrate this methodology into the monitoring plan of the compensatory measures of the Vilariça River because it will provide greater knowledge of the spawning activity of L. bocagei, which is essential for improving conservation efforts. In addition, it presents a set of mitigation and management measures directed to the conservation of fish communities in Mediterranean streams in order to reduce the negative impact of agricultural contamination on water quality and fish health, such as improving the irrigation methods, preserving the vegetation cover, promoting reforestation in degraded and burned areas, and improving the riparian vegetation. |
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