Sequeira, M.D.

Five surface water monitoring campaigns were conducted in the Mondego hydrological basin during the drought that affected Portugal in the hydrological year of 2021/2022. Sampling took place between March and November 2022. Measured water quality indicators were contrasted with a geochemical background created from open data. During the drought period, the water tends to become more alkaline, due to lower dilution and higher bicarbonate from groundwater waters, NO2 concentrations kept increasing, exceeding the background; despite the low runoff, most minor ions were undetectable. In the following hydrological year, with high rainfall events, an increased turbidity was verified, with values above the background, NO2 concentrations return to normal, and some of the minor ions (Al, As, Fe and Mn) were detectable, some passing the background in all watercourses. View more (in Portuguese)

Authors: Sequeira, M. D., Tavares, A. O., Castilho, A.

After the rural fires that affected Portugal in 2017, nine campaigns of surface water monitoring were conducted over a span of two years in 10 watercourses of the Mondego river basin. The results were analyzed alongside catchment basin characteristics and precipitation data to develop regression models for each water parameter. It was observed that precipitation introduced Al and NO3 to the surface waters, leading to increased turbidity while also exhibiting a dilution effect. Carbonate geology tended to elevate concentrations of Ca and HCO3 in the water, along with its alkalinity, whereas igneous geology influenced the content of As in the water. Agricultural usage appeared to manifest in Cl, K, Na, and electrical conductivity of the waters. The fire-affected artificial area proved to be the most impactful in the majority of models, seemingly responsible for a significant portion of As, NO3, SO4, Ca, K, and Mg, and consequently, for electrical conductivity. View more

Authors: Sequeira, M. D., Dinis, P., Castilho, A. Tavares, A. O.

As water is facing increasing pressures from population and economic growth and climate change, it becomes imperative to promote the protection, restoration and management of this resource and its watersheds. Since water quality depends on multiple factors both natural and anthropic, it is not easy to establish their influences. After the October 2017 fires that affected almost 30% of the Mondego hydrographic basin in Central Portugal, 10 catchments were selected for periodic physical-chemical monitoring. These monitoring campaigns started one month after the fires and lasted for two hydrological years, measuring the electric conductivity (EC), pH, dissolved oxygen (DO), turbidity (Turb), alkalinity (Alk), major and minor ions, and trace elements. The obtained data were then statistically analysed alongside the geomorphological characteristics of each catchment coupled with features of land-use and occupation. From the results, it was possible to establish that fire-affected artificial areas, through the atmospheric deposition and surface runoff of combustion products, had the most impact on surface water quality, increasing As, K−, Ca2+, Mg2+, NO3−, SO42− and Sr, and consequently increasing electrical conductivity. Agricultural land-use seems to play a major influence in raising the water’s EC, Cl, K− and Na2+. Regarding natural factors such as catchment geology, it was found that the extent of igneous exposures influences As, and the carbonate sedimentary units are a source of Ca2+ and HCO32− concentrations and impose an increase in alkalinity. Rainfall seems, in the short term, to increase the water concentration in Al and NO3−, while also raising turbidity due to sediments dragged by surface runoff. While, in the long-term, rainfall reduces the concentrations of elements in surface water and approximates the water’s pH to rainfall features. View more

Authors: Sequeira, M. D., Castilho, A., Tavares, A. O., Dinis, P.

International Journal of Environmental Research and Public Health: IF: 3.390; Q2: Pollution; H Index: 138

Em outubro de 2017, a região Centro de Portugal foi fortemente afetada por vários incêndios florestais. A bacia hidrográfica do Mondego foi afetada em quase 30% da sua extensão. Para compreender os impactes destes incêndios na qualidade das águas superficiais, foram realizadas campanhas de monitorização em dois anos hidrológicos. Em 10 pontos de monitorização foram analisados os parâmetros físico-químicos das águas superficiais. Usando dados de parâmetros físico-químicos dos últimos 30 anos foram criados fundos geoquímicos e determinados os impactes que os incêndios tiveram sobre as águas superficiais. Imediatamente após os incêndios florestais verificou-se um aumento muito superior ao fundo geoquímico dos teores de Cl, NO3, SO4, Al, As, Fe e Mn. O aumento de Cl, NO3, SO4, e Mn parece estar relacionado com a combustão de matéria orgânica. As altas concentrações de Al e Fe e um aumento da turbidez a par de uma baixa condutividade elétrica, nas campanhas de períodos com maior precipitação, sugerem que estes elementos possam estar relacionados com o transporte de sedimentos para as linhas de águas após a remoção da vegetação. No segundo ano hidrológico a maior parte das linhas de água regressaram aos valores normais por comparação ao do seu fundo geoquímico. No entanto, nas linhas de água em bacias localizadas em grandes áreas agrícolas verificaram-se concentrações acima dos fundos geoquímicos para NO3 e As, sugerindo que possam estar parcialmente associados às atividades agrícolas. View more

Authors: Sequeira, M. D., Castilho, A., Dinis, P., Tavares, A.

In October 2017, the Mondego hydrological basin was devastated by multiple wildfires. To understand the impacts that these had on surface water quality, monthly monitoring campaigns were implemented in the affected catchments. The campaigns oversaw the water’s physical characteristics and major, minor and trace constituents. Analysis of major changes was performed, as well as comparisons with geochemical backgrounds, determined using publicly available data collected prior to the fires. The backgrounds allowed us to verify which water parameters were most influenced by the fires. Wildfires were responsible for increasing turbidity on all watercourses, and electrical conductivity increased in watercourses with flatter, granitoid/sedimentary-dominated watersheds. Cl−, NO3−, and SO42− surpassed background values in most monitored basins. Changes in Al, Fe, Mn, As, Ba, and Zn concentrations were observed in all watercourses after the wildfires and decreases after intense rainfall. Background values were particularly exceeded for Al in all monitoring points and As in basins with extensive agricultural areas. Burnt plant material and organic matter partially account for the increases in Cl−, NO3−, SO42−, Al, As, Fe, and Mn content. High Al, Fe and Zn with low water conductivity suggests that these elements were associated with sediment loads after the removal of vegetation. View more

Authors: Sequeira, M. D., Castilho, A. M., Dinis, P. & Tavares, A. O.

Water: IF: 2.069; Q2: Water Science and Technology; H Index: 42

Following the major wildfires that affected the Central region of Portugal in 2017, a watercourse monitoring campaign was initiated in November 2017 to determine changes in water proprieties in a post-fire scenario, and establish the persistence of these effects. In the Mondego River basin, 10 points, from 6 watercourses, were chosen based on the size of the watershed and the percentage of burnt area. Monthly water monitorization featured in situ parameters and major ions analysis. A higher electrical conductivity was found in water in November 2017, before the first runoffs. Major ions have, in generally, decreased from December to January. However, the Cavalos brook showed an increase in NO3 concentration, and the downstream of Mondego River showing increase in Ca, HCO3 and NO3. View more

Authors: Sequeira, M. D., Castilho, A. M., Dinis, P. & Tavares, A. O.

Comunicações Geológicas: IF: 1.000; Q3: Environmental Science; H Index: 13

The wildfires of 2017 were responsible for vegetation clearance in a wide area of central Portugal, leaving the weathering profiles more exposed to erosive action. In the present research, suspended loads from a set of catchment areas affected by these fires with diverse geological and orographic features were periodically sampled to evaluate spatial and seasonal variability in sediment production. Bulk mineralogy reflected the geology of the source areas, but displayed high variability even for a single sampling site, which can be partially linked to the grain-size control on sediment composition. Clay mineralogy provided a better picture of the denudation at catchment scale. The predominance of detrital illite with low I5/I10 (ratio of the intensities at 5 Å (002) and 10 Å (001)) indicated very shallow weathering profiles. Chlorite was usually the second most common mineral, more common in metasedimentary-derived sediments, whilst kaolinite was detected only in less steep catchment areas with a predominance of granitic basement rocks or where previous-cycle depositional units are also present. Year-long shifts in clay assemblages were attributed to different spatial patterns of denudation. A depletion of kaolinite occurred in sampling sites mainly sourced by granitoids. An opposite trend was observed where areas with Meso-Cenozoic deposits, less affected by the wildfires than those with basement units, occupy significant proportions of the drainage basins. This trend was ascribed to the wearing out of the weathering profiles covering the basement. Regolith denudation was also testified by a progressive decrease in I5/I10. Shifts in clay mineralogy linked with progressive surface denudation were found to be limited in areas with shallow soils, but may complicate any paleoenvironmental reconstructions based on sediment composition when more evolved weathering profiles have been eroded. View more

Authors: Dinis, P., Sequeira, M. D., Tavares, A. O., Carvalho, J., Castilho, A. M. & Pinto, M. M.

Appl. Clay Sci.: IF: 4.180; Q1: Geology; H Index: 109

In October of 2017 a series of rural fires affected Portugal’s Central Region, leading to the destruction of 40–60% of the forest area in some districts. A monitoring program was initiated in 5 catchments of the Mondego drainage basin, in order to understand the temporal evolution of the water’s physical and chemical characteristics in a post-fire scenario. This monitoring program was implemented in catchments with sizes between 20 km2 and 160 km2 in areas 60%–99% burnt. For each catchment a gauging point was selected near the mouth of the river. These 5 gauging points were assessed monthly, starting one month after the fire, in November 2017, and ending in June 2018. In each campaign stream water was sampled for laboratory analysis and in-situ physical-chemical proprieties were measured. Major ions in water samples were determined through ion chromatography (IC) and molecular absorption spectroscopy, and inductively coupled plasma optical emission spectrometry (ICP-OES). Trace elements were evaluated through ICP-OES and inductively coupled plasma mass spectrometry. Total organic carbon and dissolved organic carbon were evaluated through the oxidation method and polycyclic aromatic hydrocarbons were determined by high-performance liquid chromatography. The data collected was crossed with the catchment’s morphometric, geological and land use data, including characteristics of the burnt area. Results showed that these fires affected the surface waters in the studied catchments, producing an increase in turbidity, and in the concentrations of Al, Fe, Mn and possibly NO3 and As. View more

Authors: Sequeira, M. D., Castilho, A. M., Tavares, A. O., & Dinis, P.

Ecol. Indicators: IF: 4.800; Q1: Ecology; H Index: 97

Os incêndios de 2017 que afetaram a Região Centro de Portugal provocaram impactos ambientais, sociais, económicos e institucionais. Um dos impactos reconhecidos no pós-evento foi nas propriedades das águas superficiais. Esta constatação levou a uma campanha de monitorização dos cursos de água para determinar as alterações nas propriedades da água, no âmbito das atividades do projeto INTERREG Risk AquaSoil. Para tal, na bacia do Rio Mondego, foram escolhidos 10 pontos de monitorização, particularmente de 6 cursos de água, com base nas dimensões da bacia de drenagem e percentagem de área ardida. A monitorização mensal contemplou análises in situ de parâmetros físico-químicos e determinação de iões maiores e menores, elementos traço, gases dissolvidos e outros compostos. Os resultados mostram um aumento de turbidez das águas, associado à presença de cinzas e sedimentos; a introdução de Al (alumínio), Fe (ferro) e Si (silício), através de processos de erosão; e de As (arsénio) através do transporte pelo escoamento superficial. Todos os cursos de água apresentaram valores de turbidez acima do regulamentado para consumo público e alguns valores de pH abaixo do estabelecido. Relativamente às concentrações de metais, o Rio Mondego e a Ribeira de Cavalos, apresentaram concentrações superiores ao legislado para consumo humano. View more (in Portuguese)

Authors: Sequeira, M. D., Tavares, A. O., Castilho, A. M., & Dinis, P. A.

Individuals play a crucial role in combating climate change, but high levels of acknowledgment and engagement are needed to lead to changes toward more sustainable behaviours. In this aspect, media plays an important role in shaping individuals' awareness about climate change. This study aims to analyse Iberian media coverage about climate change to further discuss its influence on the public's engagement with the subject. A total of 449 news were collected from Iberian newspapers. Their characteristics were analysed through quantitative content analysis. Data shows important journalistic bias toward a national framing, mainly focusing on drought and its impact on agriculture. The debate is focused on technological and political discourses. The gaps found on the Iberian media coverage may contribute to public's low levels of acknowledgement and engagement, not enhancing the possibility of change in individuals' behaviours for more sustainable actions. View more

Authors: Areia, N. P., Intrigliolo, D., Tavares, A., Mendes, J. M., & Sequeira, M. D.

Sci. Total Envi.: IF: 6.551; Q1: Env. Chemistry; H Index: 205

Authors: Areia, N. P., Sequeira, M. D., Mendes, J. M. & Tavares, A. O.

Following the major wildfires that affected the Central region of Portugal in 2017, an environmental monitoring campaign was initiated in November of 2017. Among other environmental issues, the program aims to understand the shifts in sediment production. Mineralogical data obtained so far indicate a progressive decrease in kaolinite and increase in feldspar contents in most sampling sites. These trends point to a strong erosion in the areas affected by the wildfires during the high rainfall events of late 2017 and early 2018.

Dinis, P., Sequeira, M. D., Tavares, A. & Castilho, A.

The Portuguese Central Region was affected, in 2017, by major series of wildfires that contributed to the largest burnet area of the last 10 years. After a wildfire, the loss of vegetation might lead directly to soil erosion and subsequently contamination of superficial water. The reduction, or elimination, of the vegetative cover diminishes evapotranspiration and rain drop’s interception, exposing soil and increasing run-off, which associated with a decreased rugosity, due to the loss of organic matter and soil debris, increases its erodibility. During the combustion phase, condensation of volatile organic compounds in sublayers of the soil might lead to a hydrophobic soil. With the first rains it is expected an increase in run-off which introduces sediments, ashes and other debris in the watercourses, leading to an increase in turbidity, and diminished dissolved oxygen. Ashes transported by the run-off carry nitrates and phosphates leading to an increased content of algae and water eutrophication. The combustion of bioaccumulating species could lead to elevated concentrations of metals and metalloids, dangerous for their toxicity and persistence. During a wildfire, polycyclic aromatic hydrocarbon (PAH) could be formed, despite their insoluble nature, these can be found on soil or watershed sediments, and pose a major concern due to their cancerogenic effects. To compare water proprieties before and after the first run-offs and the water quality in subsequently months, understanding what are the effects of the run-off in a post-fire scenario, and, if any, determine the persistence of these same effects, a watercourse monitoring campaign was initiated in November of 2017 in the Mondego River basin, which was affected with approximately 30% of burnt area. For this, 10 monitoring points, from 6 watercourses, were chosen based on the size of the watershed and the percentage of burnt area. The monthly water monitorization feature in situ analysis and laboratory analysis of major anions, major and metallic cations, Total Organic Carbon (TOC), Dissolved Organic Carbon (DOC) and PAHs. Due to their close relation between suspended sediments and water characteristics and composition, a mineralogical analysis for these was also considered, as well as a chemical and granulometric analysis in some cases. Bottom sediments are collected in the beginning and the end of the major pluviosity period, and submitted to a granulometry and mineralogic analysis, to perceive changes in erosion and transport of watercourses. Data obtained so far shown a higher electric conductivity in the November, which could be associated with ashes presence in the water, before the first run-offs, with a decreasing trend in the next months. This is also supported in the lower pH values, in December, and a return to values similar to November, in January. Most of the monitoring points have shown a decrease in concentration of Cl, Na, K, Mg, Ca and SO4 from December to January, which might be related to a high mineralized run-off. Also, the majority of the waters of the monitoring points changed their hydrochemical facies, for the same time period, with a decrease in their chlorinate content. View more

Sequeira, M. D., Castilho, A., Dinis, P. & Tavares A.

Age determination and the petrogenesis of the granitic rocks of Portugal, especially of the north and center, have been subjects of research and debate by groups of geologists, mainly in the last decades of the 20th century. First, they were considered as a single intrusion, which was reflected in the geological maps of Portugal, where all the granitoids were represented by the same symbol. Reflecting the advances in the methods of radiometric dating and in the geological knowledge, it is recognized today a range of ages to the granitoid rocks of northern and central Portugal going from the Neoproterozoic to the late Paleozoic times. As examples of these studies, we considered the granitic and gneissic rocks outcrop in the center of Portugal, in the region between Coimbra and Nisa, in the vicinity of two firstorder tectonic accidents: the Porto-Tomar-Ferreira do Alentejo shear zone (ZCPTFA) and the Tomar-Badajoz-Cordoba shear zone (ZCTBC). These structures represent a border between two geotectonic zones of the Iberian Massif: the Central Iberian Zone (ZCI) and the Ossa Morena Zone (ZOM). The aim of this study was to sketch the evolution of the representation of these granitic and gneissic bodies in the geological maps of Portugal, scales 1:500.000 and 1:1.000.000, from the nineteenth century to the present day, and compare this representation with the advances of geological knowledge. Granites and gneisses, in the geological maps at 1:1.000.000 scale, are included in large groups and it is not possible to distinguish the different bodies in respect to its nature and age, with only some differentiation for the gneisses represented in the 2010 edition. This distinction is achieved in the geological maps at 1:500.000 scale, especially, in the 1972 and 1992 editions. The evolution of the cartographic representation and maps legends reflect the advancement in the application of K-Ar and Rb-Sr radiometric methods of dating, in the eighties and nineties of the 20th century, and U-Pb dating in early years of the 21st century. It also points out the advances in petrography and geochemistry, which are also crucial to the edition of numerous geological maps of Portugal, at a scale of 1:50.000. According to the available data, these rocks represent evidence of magmatism during Neoproterozoic and Cambric-Ordovician times. It is concluded that there are significant mismatches between the recent geological knowledge and the representation of these rocks in the last editions of the geological maps of Portugal, thus justifying new maps editions, in particular, at a scale of 1:500.000. View more (in Portuguese)

Authors: Gomes, E. M., Silva, M. M. V., Sequeira, M., & Lopes, F. C.

Mem. Real Sociedad Española de Historia Natural: IF: 0.201; Q2: Earth and Planetary Sciences; H Index: 8

Authors: Gomes, E. M. C., Silva, M. M. V. G., Sequeira, M. D. & Lopes, F. C.

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Authors: Volpe, L., Garcia, A., Gómez, M. P., Sequeira, M., Török, Á., Vattai, A. & Vaccaro, C.

The old Escádia Grande gold mine, located in the Góis region, was exploited during the roman occupation in the Iberian Peninsula, and again between 1939 and 1952, having been abandoned ever since. The area is predominantly constituted by the “Complexo Xisto Grauvaquico” (CXG), consisting of phyllites and metagraywackes, with intrusions of stockwork type veins that where explored. The mine has four entrances to the galleries that are sealed, with drains at the bottom that pour mining drainage, as well as two tailing occupying a total area of 25,000 m2, which are a mixed of the sterile material and the discarded materials from the process of ore treatment. The presented study describes and evaluates the environmental changes that have been generated by the mining activity and its abandonment in terms of water, stream sediments and soils. The waters that travel through the mining area show a contamination that extends up to 1.5 km South, with high levels of As, Cu, Pb and SO4, associated with a decrease in pH and an increase in electrical conductivity. Due to the low pH values, and high concentrations of arsenic and nickel, the water becomes unfit for human consumption, being, however, acceptable for irrigation. The stream sediments are under the direct influence of the mine, presenting high geoaccumulation indexes of Ag, As, Au, Fe, Pb, Sb and Zn, being the highest preoccupation the water line that crosses the mining area, with high geoaccumulation of arsenic, antimony, silver and gold, occurring smaller contaminations of lead, iron and zinc. The mining area and mineralized veins area present, generally, acid soils with low electric conductivity. The Southern tailings causes, in the surrounding soils, an increase in concentrations of As, Au, Cu, Mn, Ni, Pb, Sb and Zn, being the main focus of soil contamination. The Northern tailings causes an increase of Cu and Ni concentrations in the nearby soils. While the mineralized veins increase the concentrations of Ag, Au and Sb. View more (in Portuguese)

Authors: Sequeira, M.