{"id":24089,"date":"2025-12-05T15:52:01","date_gmt":"2025-12-05T14:52:01","guid":{"rendered":"https:\/\/www.mio.osupytheas.fr\/?p=24089"},"modified":"2025-12-05T16:56:29","modified_gmt":"2025-12-05T15:56:29","slug":"thesis-helene-plihon","status":"publish","type":"post","link":"https:\/\/www.mio.osupytheas.fr\/en\/these-helene-plihon\/","title":{"rendered":"Congratulations to H\u00e9l\u00e8ne Plihon who defended her thesis on Friday 5 December 2025 - La Garde Campus"},"content":{"rendered":"
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H\u00e9l\u00e8ne Plihon<\/a><\/strong> defended his thesis under the joint supervision of UTLN (MIO) and UFC (LABOMAR) on Friday 5 December 2025<\/strong> at 3.00 pm in Toulon in the amphitheatre Y.008 (Campus de la Garde), on the following topic: Parameters influencing the upstream-downstream distribution of metals and carbon storage in semi-arid mangroves in Cear\u00e1, north-east Brazil\/Par\u00e2metros que influenciam a ocorr\u00eancia de metais e o armazenamento de carbono ao longo de um gradiente montante-jusante em manguezais semi\u00e1ridos do Cear\u00e1, Nordeste do Brasil.<\/em><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Members of the Jury<\/strong><\/h4>
  • Ms Marie-No\u00eblle PONS, Director of Research-CNRS, University of Lorraine (France), Rapporteur<\/li>
  • Ms Patricia TURCQ-MOREIRA, Research Director, IRD -Toulouse (France), Rapporteur<\/li>
  • Mr Maxime BRIDOUX, Director of Research-HDR, CEA Saclay (France), Examiner<\/li>
  • Drude DE LACERDA, University Professor, CNPq - Universidade Federal do Cear\u00e1 (Brazil), Examiner<\/li>
  • Ms Rozane VALENTE MARINS, University Professor, Universidade. Federal do Cear\u00e1 (Brazil), Thesis co-director<\/li>
  • Mr St\u00e9phane MOUNIER, Senior Lecturer (HDR), University of Toulon (France), Thesis supervisor<\/li><\/ul>

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    Abstract<\/strong><\/h4>

    This thesis focuses on two semi-arid mangroves in north-east Brazil, Pacoti and Jaguaribe, crossed by the rivers of the same name and studied along a river gradient running from upstream to downstream. Pacoti, which was once impacted but is now protected, contrasts with the Jaguaribe mangrove, which has been subject to intensive aquaculture downstream and urban, agricultural and hydraulic pressures upstream for more than twenty-five years. Sediment cores (80 cm) were taken at three river positions (upstream, middle, downstream), with an additional point near the shrimp farms for Jaguaribe. At 5 cm intervals, the sediments were analysed for grain size (fine fraction, Al, Fe), organic matter (OM) characteristics (%LOI, %C, %N, C\/N, Rock-Eval\u00ae), total sulphur, trace metals (Zn, Co, Cr, Hg), and optical properties (UV-Vis spectroscopy and 3D fluorescence). Carbon and metal stocks, as well as pollution indices (PLI), were established for each core. For an equivalent organic matter content (~4 %), Pacoti sediments have an average carbon concentration (2.16 %) that is almost twice that of Jaguaribe (1.2 %). This difference reflects a different OM composition: in Jaguaribe, the OM is more nitrogenous (C\/N ~15) and more oxidised (134-285 mg CO\u2082-g-\u00b9 TOC) than in Pacoti (C\/N ~21.8; 118-130 mg CO\u2082-g-\u00b9 TOC). These signatures reflect mainly fluvial inputs (anthropogenic and natural) for Jaguaribe, whereas the OM in Pacoti comes essentially from the mangrove itself. This has a direct impact on carbon stocks and stability. Pacoti stores up to five times more carbon than Jaguaribe (85.83 versus 16.41 MgC-ha-\u00b9). The OM in Jaguaribe sediments is more labile and not very humified, suggesting a greater vulnerability to mineralisation. Interactions between OM, sulphur and metals also reflect these contrasts. In Jaguaribe, Hg and Zn are strongly correlated with the fine fraction (R > 0.9), OM (R > 0.87) and nitrogen (R > 0.82), while Co is associated with fine particles (R = 0.8). For Pacoti, the correlation of Hg with sulphur (R = 0.84) reflects an interaction typical of preserved mangroves. Despite the accumulation of OM, the low complexation of copper (LogK ~4.95) suggests limited metal retention. Spatially, Pacoti shows relative sediment homogeneity along the fluvial gradient, whereas Jaguaribe shows strong heterogeneity, with accumulation of fine particles, carbon and metals (PLI>1 for Zn, Co) downstream and near the shrimp farms, making these stocks vulnerable to erosion. This study shows that the capacity of mangroves to store carbon and metals depends closely on the nature of the organic matter, the granulometry and the uses of the catchment area.<\/p>


    Resumo<\/strong><\/h4>

    Esta tese analisa duas manguezais semi\u00e1ridas do nordeste do Brasil, Pacoti e Jaguaribe, atravessadas por seus respectivos rios ep\u00f4nimos e estudadas ao longo de um gradiente fluvial que se estende do trecho superior ao inferior. O estuario do Pacoti, historicamente impactado mas atualmente protegido por lei, contrasta com o do Jaguaribe, submetido h\u00e1 mais de vinte e cinco anos \u00e0 aquicultura intensiva no estuario e a press\u00f5es urbanas, agr\u00edcolas e hidrol\u00f3gicas nas partes superiores. Testemunhos de sedimentos (80 cm) foram coletados nas zonas a montante, intermedi\u00e1ria e a jusante, com um adicional pr\u00f3ximo a efluentes de fazenda de camar\u00f5es no estuario Jaguaribe. As an\u00e1lises sedimentares inclu\u00edram granulometria (fra\u00e7\u00e3o fina, Al, Fe), caracter\u00edsticas da mat\u00e9ria org\u00e2nica (MO) (%LOI, %C, %N, C\/N, Rock-Eval\u00ae), enxofre total, metais tra\u00e7o (Zn, Co, Cr, Hg) e propriedades \u00f3pticas (espectroscopias UV-Vis e de fluoresc\u00eancia 3D). Os estoques de carbono e metais, os \u00edndices de polui\u00e7\u00e3o (PLI), foram determinados para cada testemunho a cada 5 cm. Para um teor semelhante de mat\u00e9ria org\u00e2nica (~4%), os sedimentos do Pacoti apresentam concentra\u00e7\u00e3o m\u00e9dia de carbono (2,16%) quase duas vezes maior que a do Jaguaribe (1,2%). Essa diferen\u00e7a reflete composi\u00e7\u00f5es distintas da MO: no Jaguaribe, a MO \u00e9 mais rica em nitrog\u00eanio (C\/N ~15) e mais oxidada (99-206 mg O2.g-1 TOC) do que no Pacoti (C\/N ~21,8; 89-99 mg O2.g-1 TOC). Essas assinaturas indicam aportes predominantemente fluviais (antropog\u00eanicos e naturais) no Jaguaribe, enquanto a MO do Pacoti tem origem principalmente autoctone, produzida pela pr\u00f3pria vegeta\u00e7\u00e3o do manguezal. This difference has a direct impact on carbon balance and stability. O Pacoti armazena at\u00e9 cinco vezes mais carbono do que o Jaguaribe (85,83 contra 16,41 MgC-ha \u00b9). A MO dos sedimentos do Jaguaribe \u00e9 - mais l\u00e1bil e pouco humificada, sugerindo maior vulnerabilidade \u00e0 mineraliza\u00e7\u00e3o. As intera\u00e7\u00f5es entre MO, enxofre e metais tamb\u00e9m refletem esses contrastes. No Jaguaribe, Hg e Zn est\u00e3o fortemente correlacionados com a fra\u00e7\u00e3o fina (R > 0,9), com a MO (R > 0,87) e com o nitrog\u00eanio (R > 0,82), enquanto o Co est\u00e1 associado \u00e0s part\u00edculas finas (R = 0,8). No Pacoti, a correla\u00e7\u00e3o entre Hg e enxofre (R = 0,84) reflete intera\u00e7\u00f5es t\u00edpicas de manguezais preservados. Apesar da acumula\u00e7\u00e3o de MO, a fraca complexa\u00e7\u00e3o do cobre (LogK ~4,95) sugere uma capacidade limitada de reten\u00e7\u00e3o de metais. Espacialmente, o Pacoti apresenta relativa homogeneidade sedimentar ao longo do gradiente fluvial, enquanto o Jaguaribe mostra forte heterogeneidade, com ac\u00famulo de part\u00edculas finas, carbono e metais (PLI > 1 para Zn e Co) nas \u00e1reas inferiores e pr\u00f3ximas \u00e0s fazendas de camar\u00e3o, tornando esses estoques vulner\u00e1veis \u00e0 eros\u00e3o. Este estudo demonstra que a capacidade dos sedimentos de manguezais de armazenar carbono e metais depende estreitamente da natureza da mat\u00e9ria org\u00e2nica, da granulometria e do uso do solo na bacia hidrogr\u00e1fica. Key words : estoque de carbono, metais, mat\u00e9ria org\u00e2nica, manguezais semi\u00e1ridos, nordeste do Brasil, contamina\u00e7\u00e3o, complexa\u00e7\u00e3o<\/p>

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    Key words<\/strong><\/h4>

    carbon storage, metals, organic matter, semi-arid mangroves, north-east Brazil, contamination, complexation.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>","protected":false},"excerpt":{"rendered":"

    H\u00e9l\u00e8ne Plihon a soutenu sa th\u00e8se en co-tutelle entre l’UTLN (MIO) et l’UFC (LABOMAR), le vendredi 5 d\u00e9cembre 2025 \u00e0 15h00 \u00e0 Toulon dans l’amphith\u00e9\u00e2tre Y.008 (Campus de la Garde), […]<\/p>\n","protected":false},"author":319,"featured_media":24090,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[17,1,26],"tags":[],"class_list":["post-24089","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-a-la-une","category-actualites","category-theses"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/posts\/24089","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/users\/319"}],"replies":[{"embeddable":true,"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/comments?post=24089"}],"version-history":[{"count":22,"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/posts\/24089\/revisions"}],"predecessor-version":[{"id":24304,"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/posts\/24089\/revisions\/24304"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/media\/24090"}],"wp:attachment":[{"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/media?parent=24089"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/categories?post=24089"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.mio.osupytheas.fr\/en\/wp-json\/wp\/v2\/tags?post=24089"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}