Molecular evidence for recent land use change from a swampy environment to a pond (Lorraine, France)

• Published in: Organic geochemistry Vol. 50; pp. 1 - 10
• Main Authors: Bertrand, O., Mansuy-Huault, L., Montargès-Pelletier, E., Losson, B., Argant, J., Ruffaldi, P., Etienne, D., Garnier, E., Dezileau, L., Faure, P., Michels, R.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2012; Elsevier
• Subjects: dredging; Earth Sciences; Earth, ocean, space; Environmental Sciences; eutrophication; evolution; Exact sciences and technology; Geochemistry; Global Changes; land use change; macrophytes; Marine and continental quaternary; organic matter; palynology; Sciences of the Universe; sediments; Soil and rock geochemistry; sterols; Surficial geology; swamps; watersheds; France; Lorraine; Europe; Moselle France; Western Europe; France, Lorraine; ponds; upper Holocene; swamps; Quaternary; eutrophication; degradation; sterols; upper Quaternary; dredging; settlement; palynology; drainage basins; coupling; land use; management; organic materials; alteration; Cenozoic; Phanerozoic; Holocene; paleoenvironment; pond; Lansquenet (Lorraine)
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2012.06.004

► Sedimentary record was used to reconstruct the paleoenvironmental history of a pond. ► Sources of natural OM and changes in depositional conditions were identified from organic ratios. ► Recent land use changes were evidenced in catchment area from organic ratios and pollen. ► Fish ponds could be used to study environmental changes in a small watershed. Evidence of a changing environment in the catchment area of a small pond (Lansquenet, Lorraine, France) during the last millennium was provided by coupling palynology data and organic ratios [terrestrial to aquatic ratio: TAR(HC); the C29 vs. C27 sterols, C29/C27(ST); average chain length, ACL and aquatic/macrophytes ratio, Paq]. The depositional and alteration conditions of organic matter (OM) were provided by the 5α(H)-stanols/Δ5-sterols ratio. This study shows that quite simple organic ratios clearly allow identification of the different evolution steps of a watershed, from a swamp to the progressive settlement of a pond. During the swampy period, the C/N(at) (ca. 11.1), TAR(HC) (ca. 36.8), C29/C27(ST) (ca. 8.7) and Paq (<0.3) show a high contribution of allochthonous OM associated with the presence of particular aquatic and mesohygrophilous species. A woody level dated to the XIIIth century reflects the period of the settlement of the pond in a more oxic environment [5α(H)-stanol/Δ5sterol ratio <0.2]. Then, the progressive increase in aquatic input and the development of submerged and floating macrophytes are evidenced by low C/N(at) (<7.6), TAR(HC) (ca. 2.7), C29/C27(ST) (ca. 2) and high Paq (ca. 0.5), suggesting an increase in the water level and eutrophication of the pond. A second oxic event [5α(H)-stanols/Δ5sterols ratio averaging 0.16], associated with extensive OM degradation, corresponds to the most recent dredging in 2002 and reflects an important disturbance of sediments due to pond management.