Dissertations / Theses on the topic 'Peracid'

O sistema quimiluminescente peróxi-oxalato vem sendo estudado por diversos grupos de pesquisa ao redor do mundo desde os anos 60. Esse interesse em especial se deve ao fato de que em comparação com a maioria dos sistemas quimiluminescentes, que apresentam rendimentos quânticos da ordem de 1%, esse sistema apresenta rendimentos quânticos de emissão consideravelmente maiores, cerca de 30%. O sistema peróxi-oxalato consiste na reação de ésteres fenólicos substituídos derivados do ácido oxálico com peróxido de hidrogênio, catalisada por uma base e em presença de compostos aromáticos policondensados fluorescentes com baixo potencial de oxidação, chamados de ativadores (ACT). O mecanismo desta reação, apesar de intensamente estudado, ainda não se encontra completamente esclarecido. Especificamente, a estrutura do intermediário formado durante a reação, que é responsável pela quimiexcitação do ativador, não é conhecida ainda. No presente trabalho, foram completados estudos previamente efetuados no nosso grupo com derivados perácidos, intermediários na reação peróxi-oxalato. Foram sintetizados e caracterizados dois novos derivados perácido, o O,Ohidrogênio monoperóxi-oxalato de 3-clorofenila e o O,O-hidrogênio monoperóxioxalato de 3-nitrofenila. Dos estudos cinéticos da reação destes perácidos com imidazol, na presença de 9,10-difenilantraceno como ativador, foram obtidos constantes de velocidade de ciclização e rendimentos quânticos singlete. As constantes de velocidade determinadas, junto com os dados obtidos anteriormente no grupo, mostram correlação linear de energia livre com as constantes de substituintes de Hammett, obtendo-se um valor de = 2,18 ± 0,16, o que indica a formação de alta densidade de carga negativa no estado de transição do passo lento. A correlação linear entre as constantes de velocidade e os valores de pKa dos grupos de partida fenólicos levou à determinação do valor de βGP = -1,07 ± 0,08, indicando que a quebra da ligação para o grupo de partida é muito avançada no estado de transição no passo lento da reação. Os rendimentos quânticos singlete mostram dependência com as propriedades eletrônicas dos substituintes, aumentando inicialmente com o aumento das propriedades de atração de elétron do substituinte, porém, com substituintes mais atraentes que hidrogênio, observa-se uma leve diminuição no rendimento quântico. O conjunto de dados apresentados neste trabalho, junto com os resultados obtidos anteriormente pelo grupo, demonstra claramente que a reação de ciclização dos perácidos, catalisada por imidazol, deve ocorrer de maneira concertada, ou seja, a saída do grupo de partida fenólico ocorre em conjunto com o ataque nucleofílico do íon percarboxilato à função éster no passo lento da reação. Conseqüentemente, foram obtidas neste trabalho evidências experimentais fundamentadas para a ocorrência da 1,2- dioxetanodiona como intermediário de alta energia na reação peróxi-oxalato.
The peroxyoxalate chemiluminescence has been intensely studied since the sixties by several research groups all around the world. This interest is mainly due to the fact that the peroxyoxalate system is highly efficient, showing quantum yields of around 30 %, much higher than other well known chemiluminescence reactions which commonly show quantum yields of around 1% or less. The peroxyoxalate system consists in the base catalyzed reaction of activated oxalate esters with hydrogen peroxide in the presence of highly fluorescent polycondensed aromatic hydrocarbons with low oxidation potentials, called activators (ACT). Although intensely investigated, the mechanism of this complex transformation is still not yet completely clarified. This is true specifically for the structure of the high-energy intermediate, formed during the reaction sequence, which is responsible for chemiexcitation, not known at all up to now. In the present work, former studies of our group on peracid derivatives, intermediates in the peroxyoxalate reaction, were completed. Two new peracid derivatives, 3-chlorophenyl O,O-hydrogen monoperoxyoxalate and 3- nitrophenyl O,O-hydrogen monoperoxyoxalate were synthesized and characterized. Kinetic studies on the reaction of these peracid derivatives with imidazole, in the presence of 9,10-diphenylanthracene as activator, led to the determination of cyclization rate constants and singlet quantum yields. These rate constants, together with data formerly obtained by our group, show linear free-energy correlation with the Hammett substituent constants, resulting in a reaction constant of = 2,18 ± 0,16, that indicates the formation of a high negative charge density in the transition state of the rate-limiting step. Similarly, the linear correlation of the rate constants with the pKa values of the phenolic leaving groups leads to the determination of a value βGP = -1,07 ± 0,08, indicating a high degree of leaving group bond cleavage in the transition state of the rate-limiting step. The singlet quantum yields also show dependence on the electronic properties of the substituents, initially increasing with the increase in the electron withdrawing nature of the substituent, however, a slight decrease in the quantum yields is observed with substituents more electron withdrawing than hydrogen. The data accumulated in this work, together with results earlier obtained in our group, clearly demonstrate that the cyclization reaction of the peracid derivatives, catalyzed by imidazole, proceeds in a concerted manner, i.e. the phenolic leaving group departure occurs together with the nucleophilic percarboxylate attach to the ester function in the rate-limiting reaction step. Consequently, it was possible to obtain in this work solid experimental evidence for the occurrence of 1,2-dioxetandione as the high-energy intermediate in the peroxyoxalate reaction.

In recent years, polymer-assisted solution-phase synthesis has become a prevalent method because of its various advantages over conventional solution-phase chemistry, such as the ease of separation of the supported species from a reaction mixture by filtration and washing, the opportunity to use an excess of the reagent to force the reaction to completion, and the adaptability to continuous-flow processes. Peroxycarboxylic acids are common oxidants in a wide range of chemical transformations, but their use is often limited because of the associated handling risks. Some relatively stable peracids, such as meta-chloroperoxybenzoic acid, are commercially available, but quenching of unreacted species followed by extractions and/or chromatography separation is often required. The immobilisation of this type of reagent on a solid support can offer distinct advantages with respect to handling and stability. Carboxylic ion-exchange resins, such as acrylic macroporous matrix, can be oxidised to give highly functionalised supported peroxycarboxylic acids. The polymer-supported peracid generated from Dowex MAC-3^® proved to be the best in terms of oxidation capacity among the supports and reaction conditions tested. The new high-loading polymer-supported peracid was stable under standard laboratory practice, also when it was crushed or heated, and it was used successfully in the oxidation of sulfides, alkenes, and pyridines, giving the products with high yields and purities without the need for any additional purification step.

L'etude realisee entre dans le cadre de la recherche de nouveaux reactifs non chlores pour le blanchiment papetier. Deux peroxyacides ont ete evalues : l'acide peroxyacetique et l'acide peroxymonosulfurique. La premiere partie a ete consacree a l'optimisation des procedes de blanchiment. Differents aspects de l'usage de ces reactifs en application au blanchiment des pates a papier chimiques kraft ont ete envisages. Ces travaux montrent que les peroxyacides sont des agents de blanchiment efficaces pouvant etre utilises pour la delignification de pates cellulosiques a fortes teneurs en lignine, comme pour parfaire la decoloration de pates comportant de faibles taux de lignine residuelle. Une application industielle a pu voir le jour decoulant de ces travaux. La seconde partie, a developpe l'etude de la caracterisation de lignines residuelles issues de pates traitees par les peroxyacides. Ce travail constitue en fait une reponse a des travaux anterieurs a cette these, sur l'effet activateur des peroxyacides. Les resultats obtenus par mesure en rmn#1#3c montrent que, contrairement au modele propose pour interpreter cet effet, les lignines issues des pates traitees ne presentent pas un enrichissement en unites phenoliques. En revanche, une reduction sensible de la teneur en unites aromatiques totales, assortie d'une conservation du ratio groupements phenoliques / groupements aromatiques totaux a ete note. Par ailleurs, les lignines residuelles se sont enrichies en groupements carboxyliques. Enfin, la troisieme partie, a etudie l'action de certains cations metalliques sur les peroxyacides. Ainsi, les peroxyacides sont decomposes catalytiquement par les metaux les plus couramment rencontres dans les pates, tels le fer ou le cuivre. De plus, les mecanismes de decomposition peuvent conduire a la generation de radicaux hydroxyles nefastes pour la qualite de la cellulose. D'autre part, l'etude de l'influence du cobalt s'est averee interessante, dans la mesure ou ce metal decompose efficacement les peroxyacides en conduisant a la generation d'especes sans consequence pour la cellulose, mais tres actives pour oxyder des molecules modeles de lignine. Ce point ouvre un champ d'applications potentiel des peroxyacides en blanchiment, en presence d'activateurs tels le cobalt ou encore les complexes de celui-ci.

L’étude est consacrée au groupe religieux des Pérates, décrit dans la « Refutatio omnium haeresium V, 12-18 » et autrement peu connu. La thèse est partagée en trois parties : une première concernant l’exégèse du groupe, basée sur des « testimonia crucis et ligni » et sur le renversement de plusieurs figures bibliques négatives (Caïn, Esaü, Nimrod), une procédure appelée « Protestexegese » ; une analyse des matériaux païens recueillis par la secte parmi les cultes à mystères ou polythéistes, surtout en rapport avec l’adoration du serpent et l’astrologie ; une tentative de situer le groupe en Asie Mineuse et d’en offrir une perspective sociologique. Les résultats de la recherche permettent d’en montre l’origine chrétienne, même si les éléments chrétiens ont été mélangés d’une façon syncrétiste avec la philosophie grecque, les cultes à mystères, l’astrologie et d’autres composantes ; la connaissance de l’exégèse et de la culture juive par les appartenants au groupe permet de montrer une probable origine à l’intérieur des églises chrétiennes de la disapora, entre Ier et IIème siècles
This work studies the sect of the Perates, which is described in the Refutatio omnium haeresium V, 12-18 and which is otherwise very little known. The study is divided into 3 main parts : an assessment of the exegesis of the group, founded on a series of “testimonia crucis et ligni”, and on the reversal of some negative figure of the Bible (Cain, Esau, Nimrod), a procedure usually called Protestexegese ; an analysis about the materials gathered by the sect in heathen cults and religions, above all the adoration of the serpent and astrology ; a trial to place the group in the “milieu” of Asia Minor and of a sociological assessment. The results of the research allow to point to a Christian origin of the sect, even if the Christian elements have been syncretistically mixed with Greek philosophy, mystery cults, astrology, and other components ; the knowledge of Jewish exegesis and culture by the sectarians shows a likely origin inside the Christian churches born in the Diaspora among Ist and IInd centuries

This Master Thesis deals with the world-renowned pianist Murray Perahioa and his contribution to the pianist. It describes his life and introduces readers to his views on music. It is analyzing his recordings and focuses on his editorial activity also. Analysis of the recordings is centered on important works of the Baroque and Classica era. Analysis of editorial work is conceived as another way to understand the weork of the extraordinary pianist.

Abstract This thesis examines three different areas of water treatment technology: the application of organic peracids in wastewater treatment; the removal of organic residues from boiler make-up water; and the use of geopolymers as sorbents. The main advantages of peracids as alternative wastewater disinfectants are their effective antimicrobial properties and high oxidation power, as well the absence of harmful disinfection by-products after their use. Performic, peracetic and perpropionic acids were compared in laboratory-scale disinfection, oxidation and corrosion experiments. From the techno-economical point of view, performic acid proved to be the most effective disinfectant against E. coli and fecal enterococci. However, in the bisphenol-A oxidation experiments, no advantages compared to hydrogen peroxide use were observed. It was also determined that corrosion rates on stainless steel 316L were negligible, while carbon steel seemed unsuitable in terms of corrosion for use with peracids even in low concentrations. Organic compounds in the boiler plant water-steam cycle thermally decompose and form potentially corrosive species. Activated carbon filtration was confirmed to be a suitable method for the removal of organic residue from deionized boiler make-up water. No significant differences in terms of treatment efficiency between commercial activated carbons were observed. However, acid washing as a pre-treatment reduced the leaching of impurities from new carbon beds. Nevertheless, a mixed-bed ion exchanger was required to remove leached impurities, such as silica and sodium. Geopolymers, or amorphous analogues of zeolites, can be used as sorbents in the treatment of wastewater. Metakaolin and blast-furnace-slag geopolymers showed positive potential in the treatment of landfill leachate (NH4+ ) and mine effluent (Ni, As, Sb)
Tiivistelmä Tämä väitöskirja käsittelee kolmea erillistä vedenkäsittelyteknologian osa-aluetta: orgaanisten perhappojen käyttöä jäteveden käsittelyssä, orgaanisten jäämien poistoa suolavapaasta kattilalaitoksen lisävedestä ja geopolymeerien sovelluksia vedenkäsittelysorbentteina. Orgaanisten perhappojen pääasialliset edut verrattuna kilpaileviin tekniikoihin ovat hyvä desinfiointiteho, korkea hapetuspotentiaali ja desinfioinnin sivutuotteiden muodostumattomuus. Permuurahais-, peretikka- ja perpropaanihapon vertailu osoitti permuurahaishapon olevan kemikaaleista tehokkain E. coli - ja enterokokkibakteerien inaktivoinnissa kustannus- ja teknisistä näkökulmista. Hapetuksessa, jossa käytettiin bisfenoli-A:ta malliaineena, ei kuitenkaan havaittu etua verrattuna edullisempaan vetyperoksidiin. Ruostumattoman teräksen (316L) pinnalla ei havaittu merkittävää korroosiota, kun taas hiiliteräs ei sovellu käytettäväksi perhappojen kanssa. Orgaaniset jäämät kattilalaitoksen vesi-höyrykierrossa hajoavat termisesti pienen moolimassan hapoiksi ja aiheuttavat korroosioriskin. Aktiivihiilisuodatuksen todettiin olevan soveltuva menetelmä orgaanisten jäämien poistoon lisävedestä. Aktiivihiililaatujen välillä ei havaittu merkittäviä eroja, mutta happopesu aktiivihiilen esikäsittelynä vähensi hiilestä liukenevien epäpuhtauksien määrää. Geopolymeerit ovat zeoliittien amorfisia analogeja ja niiden ioninvaihtokykyä voidaan hyödyntää vedenkäsittelysovelluksissa. Metakaoliini- ja masuunikuonapohjaisten geopolymeerien todettiin olevan lupaavia materiaaleja malliliuosten, kaatopaikan suotoveden ja kaivoksen purkuveden käsittelyssä poistettaessa ammoniumia, nikkeliä, arseenia ja antimonia

Les mecanismes de decomposition thermique des peracides ont ete largement etudies; l'etape d'amorcage de ces processus est la rupture homolytique de la liaison o-o du peracide. La nature des produits formes depend de la structure de peracide (aliphatique ou aromatique), de la nature du solvant (donneur d'hydrogene ou non) et de la temperature. Il a ete montre que le radical acylperoxyle est vraisemblablement implique dans ces processus. Dans le but d'identifier ce radical, nous avons montre que l'utilisation du peroxydicarbonate de di(4-tert-butyl) cyclohexyle (bchpc) comme source de radicaux (alcoxycarbonyl) oxydes, tres electrophiles, permet d'induire la decomposition d'un peracide (acides peroxybenzoique et peroxydecanoique) par arrachement de l'hydrogene peroxydique et cela a une temperature suffisamment basse pour que la decomposition auto-induite du peracide soit particulierement lente. La presence du radical acylperoxyle comme intermediaire du processus de decomposition induite a ete etablie sans ambiguites par piegeage du radical sur le cis-stilbene et identification de l'epoxyde trans resultant de la reaction d'epoxydation radicalaire du cis-stilbene par le radical acylperoxyle

Les vitesses de coupure esterolytique du p-nitrophenyldiphenylphosphate, pris comme modele de compose organophosphore, par differents nucleophiles alpha peroxygenes ont ete mesurees a un ph voisin de 9 en milieu micellaire avec l'acetate de cetyltrimethylammonium comme tensioactif. Des temps de demi-reaction tres courts ont ainsi ete obtenus avec l'anion perhydroxyle (20s), le perborate (5s) et le monoperphtalate de magnesium, mmpp, (0,2s). L'analyse des effets cinetiques des concentrations du tensioactif et du nucleophile a ete realisee en adaptant le modele de pseudophase et d'echange d'ions. Dans le cas du mmpp, qui en milieu aqueux se degrade plus vite qu'il ne reagit avec l'ester, on montre que les accelerations exceptionnelles observees en milieu micellaire (km/kw = 350 000m) resultent a la fois de fortes concentrations du nucleophile a l'interface micellaire et d'une reactivite km particulierement grande (km = 35 1/s). Ce resultat spectaculaire decoule en partie du choix de la glycine, plutot que du carbonate ou du borate, pour tamponner le milieu. En outre, une methode originale de mesure de constantes d'echange d'anions non chromophores a la surface micellaire, et qui utilise les variations de ph de la phase aqueuse provoquee par l'addition de tensioactif a ete proposee

Etienne Dupérac est un artiste français de la seconde moitié du XVIe siècle qui fut à la fois peintre, aquafortiste, architecte et spécialiste des jardins. Il a commencé sa carrière à Venise et à Rome où il séjourna pendant environ vingt ans (vers 1560-1578), avant de rentrer en France où il devint vers 1596 l’un des architectes d’Henri IV. Nous avons cherché à reconstituer l’ensemble de l’œuvre de Dupérac, qui était mal connu, mais aussi la complexité de son parcours, caractérisé par une forte ascension sociale. Notre thèse met l’accent sur la polyvalence de l’artiste, sa connaissance de l'antique et l’originalité de ses estampes - en particulier les vues de ruines, les planches d’architecture et les restitutions antiques. Elle montre que l’historien Onofrio Panvinio a joué un rôle déterminant dans son initiation aux sciences antiquaires. Elle suggère enfin l’existence d’un lien étroit entre ses restitutions archéologiques et son œuvre architectural, profondément influencés par les travaux de Pirro Ligorio
Etienne Dupérac is a French artist of the second half of the sixteenth-century, who was active as a painter, an etcher, an architect and a specialist of garden design. He began his career in Venice and Rome, where he passed nearly twenty years (ca. 1560-1578), then he turned back to France where he became, about 1596, one of Henri IV’s court architects. In our study, we tried to describe the whole work of Dupérac, which was quite unknown, but also the different stages of his life and of his social ascent. We have emphasized Dupérac’s versatility, his knowledge of roman antiquities and the interest of his prints, especially his views of roman ruins and modern buildings. And his reconstruction drawings of roman scenes and monuments. We proved that the historian Onofrio Panvinio played a major role in Dupérac’s initiation to antiquarian studies. We have also compared his architectural projects with his reconstruction drawings, which are very influenced by the work of Pirro Ligorio

With increasing anthropogenic threats to the marine environment, it has become a priority to improve our understanding and conservation of marine fauna. In Antarctic waters, a rich and diverse benthic fauna thrives. However, the relative isolation of these organisms and their adaptation to the unique Antarctic environment potentially heightens their vulnerability to environmental change. Thorough research on the genetic and ecological structure of Antarctic benthic invertebrate populations is lacking, particularly for some of the most dominant taxa, such as the Amphipoda. This study investigated genetic structure, diversity and population ecology in some common Antarctic benthic amphipod species, to build a more rigorous understanding of the Antarctic benthos that will aid in future management planning. Genetic structure was explored over a circum-Antarctic scale in the widespread amphipod species Eusirus perdentatus and Eusirus giganteus from the continental shelf, using DNA sequences of two mitochondrial regions (COI and CytB) and one nuclear region (ITS2). Phylogenies and haplotype networks provided strong evidence that E. perdentatus harbours two previously undetected cryptic species, and E. giganteus harbours at least three, highlighting our current misunderstanding of Antarctic benthic diversity. There were clear differences in the distribution, genetic diversity and connectivity of populations within each cryptic species, and it is proposed that this reflects different modes of post-glacial recolonisation of the continental shelf. Within one cryptic species, high genetic population differentiation (FST > 0.47, p < 0.01) suggested a potential allopatric speciation process at play. Genetic connectivity was explored over large (1000km) to very fine (100m) distances in the ubiquitous nearshore amphipod Orchomenella franklini, using seven highly polymorphic microsatellite markers. Genetic diversity differed significantly among populations, potentially reflecting local environmental conditions including anthropogenic pollution. Hierarchical AMOVA revealed marked genetic subdivision (FST = 0.16, p < 0.001) across the largest geographical scale and evolutionary isolation of these populations was inferred. Furthermore, three loci showed signs of selection across this scale, providing evidence of locally adapted populations. Gene flow was also restricted at smaller scales, indicating a stepping-stone mode of dispersal consistent with the brooded development of amphipods. The ecology of O. franklini was investigated through length measurements, sex and reproductive status of > 6000 individuals, spatial and temporal patterns in abundance, and corresponding relationships with environmental data. The life history of O. franklini revealed several traits that exemplify adaptation to the polar environment, including delayed reproduction, longevity (> 2 years), and seasonal breeding linked to the summer phytoplankton bloom. There was preliminary evidence of inter-annual and spatial fluctuations in reproductive timing, potentially reflecting local sea-ice conditions. O. franklini was found to reach astounding densities (> 65,000/m2) and abundance was highly heterogeneous in space and time. The distribution of O. franklini was related to various sediment properties although the relationship differed with geographic region, highlighting a close association to the local environment as well as broader Antarctic conditions. This study has provided significant insight into the dynamics of Antarctic benthic amphipod populations over a range of scales. Together the results emphasise a considerable degree of heterogeneity largely overlooked in Antarctic benthic organisms (from the taxonomy of entire species down to local-scale intraspecific population dynamics), and thereby support predictions of their vulnerability to anthropogenicinduced change. Results also shed light on speciation processes in Antarctic waters, and will ultimately help inform future planning decisions regarding spatial management of the Antarctic benthic ecosystem.

Tese de doutoramento em Biociências, no ramo de especialização de Ecologia Marinha , apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra
O principal objetivo do trabalho apresentado nesta tese é aumentar o conhecimento do estado ecológico e funcionamento de praias arenosas expostas na costa Atlântica Portuguesa. Os invertebrados bentónicos são estrutural e funcionalmente importantes nestes ecossistemas (e.g. reciclagem de nutrientes, relações tróficas), deste modo esta avaliação foi baseada na estrutura, composição e adaptações das comunidades macrobentónicas ao ambiente da praia. No contexto do crescente aumento de pressões humanas a atuar nestes ecossistemas, foi avaliado o uso de espécies chave como potenciais indicadores de distúrbios ambientais. Deste modo, este trabalho centra-se particularmente na avaliação do estado ecológico de praias arenosas sujeitas a pressões humanas (Capítulo I), na análise das estratégias de segregação de nichos em crustáceos (Capítulo II) e nas adaptações comportamentais de anfípodes Talitridae sujeitos a diferentes cenários ambientais (Capítulo III). No último capítulo (IV) é proposto um potencial bioindicador de impactos antropogénicos nos ecossistemas duna-praia. O Capítulo I avalia se alterações nas comunidades macrobentónicas foram indicador de pressões humanas a longo prazo (atividades de turismo e obras de engenharia) na praia do Cabedelo, em comparação com uma praia de referência em Quiaios. Neste sentido, o ambiente físico e a estrutura das comunidades macrofaunais foram comparadas entre praias em 1999−2000 e 2010−2011. As alterações detetadas na macrofauna (diminuição da abundância do anfípode Talitrus saltator e do isópode Tylos europaeus) foram consistentes com a interpretação do aumento das pressões humanas na praia do Cabedelo. Em contraste, na praia em Quiaios foi descrito um padrão semelhante na estrutura ecológica nos períodos considerados. No entanto, apesar do padrão encontrado na praia do Cabedelo ser sugerido como resultado de pressões humanas, este resultado salienta a necessidade de posteriores avaliações ecológicas efetivas. O Capítulo II descreve as estratégias de segregação de nichos em três crustáceos Peracarida nas praias de Cabedelo e Quiaios, que possuem diferentes disponibilidades de alimento (macroalgas, restos animais, plantas dunares). Neste sentido, foram efetuadas análises de isótopos estáveis de consumidores primários e potenciais fontes de alimento e o padrão de distribuição dos consumidores foi analisado no verão e inverno. Os resultados das dietas e da distribuição das espécies revelaram diferenças na segregação espacial e temporal dos nichos dos consumidores. Em Quiaios, as condições de inverno e a pouca disponibilidade de alimento, induziu à segregação dos nichos dos consumidores, pelo contrário, a maior disponibilidade de alimento na praia de Cabedelo permitiu uma dieta generalista destes crustáceos. Deste modo, a partição de recursos alimentares efetuada por estas espécies pode variar com a disponibilidade de alimento mas também com as condições ambientais. No Capítulo III, foram avaliadas as adaptações comportamentais de anfípodes Talitridae em cenários ecológicos distintos. No primeiro caso, o comportamento (orientação solar) e distribuição de duas espécies simpáticas foram analisados na praia de Quiaios. Apesar das condições estáveis oferecidas por esta praia mesotidal, cada espécie apresentou uma estratégia comportamental diferente. Talorchestia brito apresentou uma orientação solar definida e ocorreu principalmente na zona intertidal, enquanto que T. saltator apresentou uma distribuição e orientação mais flexíveis. Este estudo sugere que as restrições no habitat e as tolerâncias individuais de cada espécie podem determinar diferente flexibilidade comportamental no mesmo local. No segundo estudo do capítulo III, o comportamento (orientação e ritmos endógenos de locomoção) de T. saltator foi analisado numa praia recentemente restaurada (Leirosa) para testar as suas adaptações comportamentais à nova paisagem - duna frontal artificial. Os resultados revelaram uma orientação precisa para esta espécie que usa a bússola solar e indicações visuais (paisagem) para alcançar a zona óptima na praia, e um ritmo endógeno bem definido (com a componente de maré), o que sugere um comportamento estável desta população na praia da Leirosa. Por fim, no Capítulo IV, a estrutura e composição das comunidades macrofaunais na zona de duna artificial foi comparada com a de uma zona de duna natural na mesma praia (Leirosa). A densidade total, a riqueza específica e diversidade da macrofauna foram semelhantes entre as duas zonas, no entanto, na zona artificial foram registadas as mais baixas densidades de T. saltator, que coincide com a zona artificial dos geotêxtis na praia. Deste modo, esta espécie foi sugerida como bioindicador de perturbações no sistema dunar. A seção final de discussão geral sintetiza e discute o uso de comunidades macrobentónicas para avaliação do estado ecológico e funcionamento de praias arenosas expostas, com sugestões para futuros desafios científicos.
The primary goal of the research presented in this thesis is to provide a deep knowledge of the ecological status and functioning of exposed sandy beaches on the Portuguese Atlantic coast. Because benthic invertebrates are structurally and functionally important in beach ecosystems (e.g., nutrient cycling, trophic links), this assessment was based on macrobenthic communities’ structure, composition and adaptations to the beach environment. In the context of the increasingly human pressures on the sandy beach ecosystems, the use of key species as potential indicators of environmental changes was also evaluated. For this purpose, this work specifically focuses on the assessment of ecological status of sandy beaches subjected to long-term human pressures (Chapter I), on the analyses of niche segregation strategies of crustaceans (Chapter II) and on the behavioural adaptations of talitrid amphipods under different environmental scenarios (Chapter III). The last Chapter (IV) proposes a potential bioindicator of anthropogenic impacts on beach-dune ecosystems. Chapter I evaluates whether changes in the macrobenthic communities were a response indicator of ten years of increased human pressures (tourism activities and engineering actions) at Cabedelo beach, by comparing it with an undisturbed reference beach in Quiaios. In this sense, the physical environment and the macrofaunal communities’ structure at both beaches in 1999−2000 and 2010−2011 were compared. The detected faunal changes (decrease in the abundance of the talitrid Talitrus saltator and the tylid Tylos europaeus) were consistent with an interpretation of increased human pressures at Cabedelo beach. In contrast, Quiaios beach presented a similar pattern in key ecological measures in the two periods considered. The observed trends in Cabedelo are suggested to be an effect of human pressures, however, our findings emphasises the need of further effective ecological impact assessments. Chapter II describes the niche segregation strategies of three peracarid crustaceans from Cabedelo and Quiaios beaches, which are characterised by contrasting food availabilities, i.e. wrack (macroalgae, carrion and dune plants). To attain this goal, stable isotopic analyses of primary consumers and potential food sources were performed and the zonation patterns recorded for the winter and summer conditions. The results of the diets and distribution of these peracarid species revealed spatio-temporal differences in consumers’ niches. In Quiaios, winter and wrack-limited conditions allowed for niche segregation of primary consumers, in contrast, at Cabedelo beach, higher beach-wrack deposits induced generalist diets of the three crustaceans studied. Therefore, partitioning of forage resources by these species may vary according to food availability and also environmental constraints. In Chapter III, the behavioural adaptations of talitrid amphipods were assessed in two different ecological scenarios. In the first case, the behaviour (sun orientation) and distribution of two sympatric talitrids were analysed under the undisturbed environment described at Quiaios beach. Despite the stable conditions offered by this mesotidal beach, different behavioural strategies were described for each species. Talorchestia brito showed a precise sun orientation and occurred mainly on the intertidal area, while T. saltator revealed a more flexible distribution and orientation. The study suggested that individual habitat requirements and tolerances of these species might be reflected in their behavioural flexibility in a specific environment. In the second study comprehended in Chapter III, the behaviour (orientation and locomotor endogenous rhythms) of T. saltator were investigated at a recently restored beach (Leirosa) to test their behavioural adaptations to the new landscape - the artificial foredune. The results revealed a precise orientation of these talitrids, which use the sun compass and visual cues (landscape) to find the optimal zone on the beach, and a well defined free running rhythm (with a tidal component), suggesting a stable behaviour of this population at Leirosa beach. Finally, in Chapter IV, the composition and structure of the macrofaunal community in the artificial dune zone were compared with that in a natural dune in the same beach (Leirosa). The total density, taxa richness and diversity of macrofauna were similar between sites, but the artificial zone harboured a significantly lower density of T. saltator, coinciding with the zone where the geotextiles were placed in the beach. Therefore, this species was suggested to be a suitable bioindicator of disturbances on coastal dunes. A general discussion section synthesised and discussed the thesis contribution to understanding the use of macrobenthic communities to assess ecological status and functioning of exposed sandy beaches, suggesting future research challenges.