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WOS:000684005500003; International audience; Coastal habitats are interlinked by ecological connectivity, defined as the exchange of organic matter or organisms between habitats. The degree of this connectivity will depend in particular on the geometric properties of the landscape. The increasing anthropogenic alterations in estuaries therefore raises the need to understand how their morphological characteristics influence fluxes between habitats. We used stable isotopes to investigate the variability of ecological connectivity between three estuaries and their adjacent coastal areas by tracking the origin of the organic matter (estuarine vs coastal) underlying the diet of the migrant species Eucinostomus argenteus. The chosen estuaries were geomorphologically distinct, exhibiting, in particular, differences in their degree of connection to the sea, corresponding to the morphological features (shape, mouth width) controlling key physico-chemical variables in this habitat (e.g. salinity). The sampling of the basal food sources contributing to the food web was performed in the three estuaries and in their adjacent coasts. The variability in stable isotope ratios between estuaries was examined for both fish and sources of organic matter. In the three estuaries, Bayesian models were applied for each season (dry and rainy) to quantify the relative contribution of sources from estuarine and coastal environments supporting the diet of the silver mojarra. The share of coastal organic matter increased with the degree of sea connection, indicating that the properties of the seascape can regulate the intensity of interactions between ecosystems. Variations in ecological connectivity are likely to affect the functioning of ecosystems as they influence trophic pathways and energy flows between adjacent habitats. Morphological modifications could thus significantly disturb ecosystems by altering the structure of food web, thereby affecting certain ecosystem services such as the availability of living marine resources.

Deforestation associated with the initial settlement of New Zealand is a dramatic example of how humans can alter landscapes through fire. However, evidence linking early human presence and land-cover change is inferential in most continental sites. We employed a multi-proxy approach to reconstruct anthropogenic land use in New Zealand’s South Island over the last millennium using fecal and plant sterols as indicators of human activity and monosaccharide anhydrides, polycyclic aromatic hydrocarbons, charcoal and pollen as tracers of fire and vegetation change in lake-sediment cores. Our data provide a direct record of local human presence in Lake Kirkpatrick and Lake Diamond watersheds at the time of deforestation and a new and stronger case of human agency linked with forest clearance. The first detection of human presence matches charcoal and biomarker evidence for initial burning at c. AD 1350. Sterols decreased shortly after to values suggesting the sporadic presence of people and then rose to unprecedented levels after the European settlement. Our results confirm that initial human arrival in New Zealand was associated with brief and intense burning activities. Testing our approach in a context of well-established fire history provides a new tool for understanding cause-effect relationships in more complex continental reconstructions.

International audience; The origin of perylene, a five-ring polycyclic aromatic hydrocarbon (PAH), in sediments has been a matter of constant debate and its formation mechanisms remain unclear. A perylene record in sediment was described and could support a clear link between perylene and terrigenous organic matter (OM) input. The distributions of PAHs, the variations of organic proxies such as the ratio of terrigenous to aquatic n-alkanes (TAR(HC)) and 5a(H)-stanols/D5-sterols ratio in sediments have been investigated. Sediments were sampled from a pond artificially created during the Middle Ages from a swampy area. In the period prior to the pond creation, for which high contributions of terrigenous OM were evidenced, perylene was found to be the predominant PAH. Furthermore, perylene content was shown to increase in response to the establishment of more reducing conditions. This result supports the common idea that the main source of perylene is natural and derives from biogenic precursors under reducing conditions. The creation of the pond in this wetland is marked by the deposition of a wood rich level characterized both by more oxygenated conditions and higher concentrations of perylene. These high concentrations could result from the introduction of high concentrations of biogenic precursors of perylene under oxidative conditions. Subsequently, the progressive burial of the woody level could have allowed the establishment of oxygen depleted conditions and the formation of perylene. These results validate the use of perylene as a paleoenvironmental marker of terrigenous sources but it must be carefully used as a marker for syn- or post-depositional oxygen depleted conditions in lacustrine environments