Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessment
Foraminiferal mudflat communities in the Auray estuary, located along the French Northwest Atlantic coast, were investigated in September 2020. Numerous living specimens of calcareous species showed marks of dissolution. The number of affected individuals, together with their dissolution degree, var...
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Académie des sciences
2024-07-01
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| Series: | Comptes Rendus. Géoscience |
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| Online Access: | https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.5802/crgeos.269/ |
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| author | Fouet, Marie Daviray, Maxime Geslin, Emmanuelle Metzger, Edouard Jorissen, Frans |
| author_facet | Fouet, Marie Daviray, Maxime Geslin, Emmanuelle Metzger, Edouard Jorissen, Frans |
| author_sort | Fouet, Marie |
| collection | DOAJ |
| description | Foraminiferal mudflat communities in the Auray estuary, located along the French Northwest Atlantic coast, were investigated in September 2020. Numerous living specimens of calcareous species showed marks of dissolution. The number of affected individuals, together with their dissolution degree, varied from one site to another. Moreover, pH profiles showed porewater acidification of the subsurface sediment at several stations. We propose two metrics quantifying the degree of dissolution: (i) the “Foraminiferal Test Dissolution” (FTD), based on binocular observations of the foraminiferal community, and (ii) the “Calcareous Test Preservation Ratio” (CTPR), surface ratio (0–0.5 cm) of total living foraminiferal densities (0–1 cm). In stations showing sediment acidification, the O2-pH profiles show the typical biogeochemical signatures of cable bacteria activity (pH increase in the oxic zone followed by strong acidification in the suboxic zone). This suggests that bacterial activity could be responsible for the strong pH decrease leading to corrosive porewaters affecting calcareous tests, hence severe FTD in the first centimetre of sediment leading to high CTPR. Furthermore, observations of FTD in other estuaries on the French Atlantic coast indicate that the phenomenon has become widespread. Re-investigated foraminiferal tests sampled in 1995–1996 in the Auray estuary show no dissolution marks, suggesting that the dissolution process observed in 2020 appeared over the last thirty years. Therefore, the FTD and CTPR could be used as rapid tools to establish the occurrence of dissolution processes, pending geochemical confirmation. The FTD could also be used as sediment acidification proxy in historical records, where geochemical analyses are not possible. |
| format | Article |
| id | doaj-art-1c51afa45c11481092eb2c6c2ac288ee |
| institution | Kabale University |
| issn | 1778-7025 |
| language | English |
| publishDate | 2024-07-01 |
| publisher | Académie des sciences |
| record_format | Article |
| series | Comptes Rendus. Géoscience |
| spelling | doaj-art-1c51afa45c11481092eb2c6c2ac288ee2025-02-07T10:41:12ZengAcadémie des sciencesComptes Rendus. Géoscience1778-70252024-07-01356G1839610.5802/crgeos.26910.5802/crgeos.269Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessmentFouet, Marie0https://orcid.org/0000-0002-6137-6349Daviray, Maxime1https://orcid.org/0000-0003-1422-3398Geslin, Emmanuelle2Metzger, Edouard3https://orcid.org/0000-0002-5838-4540Jorissen, Frans4https://orcid.org/0000-0002-9325-6085UMR EPOC, Université de Bordeaux, CNRS, UMR 5805, Station Marine d’Arcachon, 2 rue du Professeur Jolyet, 33120, Arcachon, FranceUniv Angers, Nantes Université, Le Mans Université, CNRS, LPG UMR 6112, F-49000 Angers, FranceUniv Angers, Nantes Université, Le Mans Université, CNRS, LPG UMR 6112, F-49000 Angers, FranceUniv Angers, Nantes Université, Le Mans Université, CNRS, LPG UMR 6112, F-49000 Angers, FranceUniv Angers, Nantes Université, Le Mans Université, CNRS, LPG UMR 6112, F-49000 Angers, FranceForaminiferal mudflat communities in the Auray estuary, located along the French Northwest Atlantic coast, were investigated in September 2020. Numerous living specimens of calcareous species showed marks of dissolution. The number of affected individuals, together with their dissolution degree, varied from one site to another. Moreover, pH profiles showed porewater acidification of the subsurface sediment at several stations. We propose two metrics quantifying the degree of dissolution: (i) the “Foraminiferal Test Dissolution” (FTD), based on binocular observations of the foraminiferal community, and (ii) the “Calcareous Test Preservation Ratio” (CTPR), surface ratio (0–0.5 cm) of total living foraminiferal densities (0–1 cm). In stations showing sediment acidification, the O2-pH profiles show the typical biogeochemical signatures of cable bacteria activity (pH increase in the oxic zone followed by strong acidification in the suboxic zone). This suggests that bacterial activity could be responsible for the strong pH decrease leading to corrosive porewaters affecting calcareous tests, hence severe FTD in the first centimetre of sediment leading to high CTPR. Furthermore, observations of FTD in other estuaries on the French Atlantic coast indicate that the phenomenon has become widespread. Re-investigated foraminiferal tests sampled in 1995–1996 in the Auray estuary show no dissolution marks, suggesting that the dissolution process observed in 2020 appeared over the last thirty years. Therefore, the FTD and CTPR could be used as rapid tools to establish the occurrence of dissolution processes, pending geochemical confirmation. The FTD could also be used as sediment acidification proxy in historical records, where geochemical analyses are not possible.https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.5802/crgeos.269/Benthic foraminiferaTest preservationCable bacteriaSediment acidification proxy |
| spellingShingle | Fouet, Marie Daviray, Maxime Geslin, Emmanuelle Metzger, Edouard Jorissen, Frans Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessment Comptes Rendus. Géoscience Benthic foraminifera Test preservation Cable bacteria Sediment acidification proxy |
| title | Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessment |
| title_full | Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessment |
| title_fullStr | Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessment |
| title_full_unstemmed | Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessment |
| title_short | Foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats: new perspectives for present and historical assessment |
| title_sort | foraminiferal test dissolution reveals severe sediment acidification in estuarine mudflats new perspectives for present and historical assessment |
| topic | Benthic foraminifera Test preservation Cable bacteria Sediment acidification proxy |
| url | https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.5802/crgeos.269/ |
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