Influence of lacustrine food-web structure and organic matter imputs on the biochemical composition of pelagic compartments and on the biodegradability of sedimented organic matter

Within lakes, carbon and nutrient cycles are partly controlled by sedimentation, allochthonous inputs, food-web structure and interactions between these compartments and/or processes. As sources of organic matter and nutrients for aquatic ecosystems, sediments and terrestrial materials can exert a bottom-up forcing on pelagic communities. Top-predators control carbon and nutrient transfers within aquatic food webs, which changes the sedimentation process and nutrient cycles. This study showed that the indirect control exerted by predators on primary producers changed the stoichiometry and the biochemical composition (polyunsaturated fatty acids, sterols, chlorophyll degradation products, proteins and sugars), and the biodegradability of recently sedimented organic matter through a trophic cascade. These modifications of sediment biodegradability led to a bottom-up forcing on seston, zooplankton and fish biomass. Autochthonous and allochthonous organic matters used in this study had contrasted effects on the stoichiometry of seston, zooplankton and recently deposited sediment but weak effects on their composition of lipid biomarkers. Finally, bottom-up effects induced by organic matter inputs, as sediment or soil, on pelagic compartments seemed minor compared to the top-down effects induced by the trophic cascade.Les cycles du carbone et des nutriments des lacs sont en partie contrôlés par la sédimentation, les apports de matières terrestres, les réseaux trophiques et les interactions entre ces compartiments et processus. Les sédiments et les matières terrestres sont des sources de matière organique et de nutriments pour les écosystèmes aquatiques qui peuvent avoir un effet ascendant sur les communautés pélagiques. Les prédateurs de sommets de chaînes exercent quant à eux un contrôle descendant sur le cycle des nutriments aquatiques et sur le processus de sédimentation, via la modification des transferts de matière au sein des réseaux trophiques. Cette étude a permis de montrer que la structure du réseau trophique, en modifiant le contrôle des producteurs primaires par leurs consommateurs, influe sur les compositions élémentaire et biochimique (acides carboxyliques polyinsaturés, stérols, dérivés de la chlorophylle, protéines et sucres) de la matière organique qui sédimente et sur sa biodégradabilité. Cette modification de biodégradabilité influence en retour les biomasses du seston, du zooplancton, ou des poissons. Les matières organiques d'origines différentes (autochtone et allochtone) étudiées ont des effets contrastés sur les compositions élémentaires du seston, du zooplancton et des sédiments récemment déposés, mais très peu d'impact sur la composition des biomarqueurs lipidiques de ces compartiments. Les effets ascendants sur la structure des réseaux trophiques pélagiques des apports de matière organique sous forme de sédiment ou de terre se sont avérés assez mineurs comparés à ceux induits par la modification de la structure des réseaux trophiques aquatiques

Influence de la structure des réseaux trophiques lacustres et des apports de matière organique sur la composition biochimique des compartiments biotiques et sur la biodégradabilité de la matière organique sédimentée

Within lakes, carbon and nutrient cycles are partly controlled by sedimentation, allochthonous inputs, food-web structure and interactions between these compartments and/or processes. As sources of organic matter and nutrients for aquatic ecosystems, sediments and terrestrial materials can exert a bottom-up forcing on pelagic communities. Top-predators control carbon and nutrient transfers within aquatic food webs, which changes the sedimentation process and nutrient cycles. This study showed that the indirect control exerted by predators on primary producers changed the stoichiometry and the biochemical composition (polyunsaturated fatty acids, sterols, chlorophyll degradation products, proteins and sugars), and the biodegradability of recently sedimented organic matter through a trophic cascade. These modifications of sediment biodegradability led to a bottom-up forcing on seston, zooplankton and fish biomass. Autochthonous and allochthonous organic matters used in this study had contrasted effects on the stoichiometry of seston, zooplankton and recently deposited sediment but weak effects on their composition of lipid biomarkers. Finally, bottom-up effects induced by organic matter inputs, as sediment or soil, on pelagic compartments seemed minor compared to the top-down effects induced by the trophic cascade.Les cycles du carbone et des nutriments des lacs sont en partie contrôlés par la sédimentation, les apports de matières terrestres, les réseaux trophiques et les interactions entre ces compartiments et processus. Les sédiments et les matières terrestres sont des sources de matière organique et de nutriments pour les écosystèmes aquatiques qui peuvent avoir un effet ascendant sur les communautés pélagiques. Les prédateurs de sommets de chaînes exercent quant à eux un contrôle descendant sur le cycle des nutriments aquatiques et sur le processus de sédimentation, via la modification des transferts de matière au sein des réseaux trophiques. Cette étude a permis de montrer que la structure du réseau trophique, en modifiant le contrôle des producteurs primaires par leurs consommateurs, influe sur les compositions élémentaire et biochimique (acides carboxyliques polyinsaturés, stérols, dérivés de la chlorophylle, protéines et sucres) de la matière organique qui sédimente et sur sa biodégradabilité. Cette modification de biodégradabilité influence en retour les biomasses du seston, du zooplancton, ou des poissons. Les matières organiques d'origines différentes (autochtone et allochtone) étudiées ont des effets contrastés sur les compositions élémentaires du seston, du zooplancton et des sédiments récemment déposés, mais très peu d'impact sur la composition des biomarqueurs lipidiques de ces compartiments. Les effets ascendants sur la structure des réseaux trophiques pélagiques des apports de matière organique sous forme de sédiment ou de terre se sont avérés assez mineurs comparés à ceux induits par la modification de la structure des réseaux trophiques aquatiques

Influence de la structure des réseaux trophiques lacustres et des apports de matière organique sur la composition biochimique des compartiments biotiques et sur la biodégradabilité de la matière organique sédimentée

Within lakes, carbon and nutrient cycles are partly controlled by sedimentation, allochthonous inputs, food-web structure and interactions between these compartments and/or processes. As sources of organic matter and nutrients for aquatic ecosystems, sediments and terrestrial materials can exert a bottom-up forcing on pelagic communities. Top-predators control carbon and nutrient transfers within aquatic food webs, which changes the sedimentation process and nutrient cycles. This study showed that the indirect control exerted by predators on primary producers changed the stoichiometry and the biochemical composition (polyunsaturated fatty acids, sterols, chlorophyll degradation products, proteins and sugars), and the biodegradability of recently sedimented organic matter through a trophic cascade. These modifications of sediment biodegradability led to a bottom-up forcing on seston, zooplankton and fish biomass. Autochthonous and allochthonous organic matters used in this study had contrasted effects on the stoichiometry of seston, zooplankton and recently deposited sediment but weak effects on their composition of lipid biomarkers. Finally, bottom-up effects induced by organic matter inputs, as sediment or soil, on pelagic compartments seemed minor compared to the top-down effects induced by the trophic cascade.Les cycles du carbone et des nutriments des lacs sont en partie contrôlés par la sédimentation, les apports de matières terrestres, les réseaux trophiques et les interactions entre ces compartiments et processus. Les sédiments et les matières terrestres sont des sources de matière organique et de nutriments pour les écosystèmes aquatiques qui peuvent avoir un effet ascendant sur les communautés pélagiques. Les prédateurs de sommets de chaînes exercent quant à eux un contrôle descendant sur le cycle des nutriments aquatiques et sur le processus de sédimentation, via la modification des transferts de matière au sein des réseaux trophiques. Cette étude a permis de montrer que la structure du réseau trophique, en modifiant le contrôle des producteurs primaires par leurs consommateurs, influe sur les compositions élémentaire et biochimique (acides carboxyliques polyinsaturés, stérols, dérivés de la chlorophylle, protéines et sucres) de la matière organique qui sédimente et sur sa biodégradabilité. Cette modification de biodégradabilité influence en retour les biomasses du seston, du zooplancton, ou des poissons. Les matières organiques d'origines différentes (autochtone et allochtone) étudiées ont des effets contrastés sur les compositions élémentaires du seston, du zooplancton et des sédiments récemment déposés, mais très peu d'impact sur la composition des biomarqueurs lipidiques de ces compartiments. Les effets ascendants sur la structure des réseaux trophiques pélagiques des apports de matière organique sous forme de sédiment ou de terre se sont avérés assez mineurs comparés à ceux induits par la modification de la structure des réseaux trophiques aquatiques

Influence de la structure des réseaux trophiques lacustres et des apports de matière organique sur la composition biochimique des compartiments biotiques et sur la biodégradabilité de la matière organique sédimentée

Les cycles du carbone et des nutriments des lacs sont en partie contrôlés par la sédimentation, les apports de matières terrestres, les réseaux trophiques et les interactions entre ces compartiments et processus. Les sédiments et les matières terrestres sont des sources de matière organique et de nutriments pour les écosystèmes aquatiques qui peuvent avoir un effet ascendant sur les communautés pélagiques. Les prédateurs de sommets de chaînes exercent quant à eux un contrôle descendant sur le cycle des nutriments aquatiques et sur le processus de sédimentation, via la modification des transferts de matière au sein des réseaux trophiques. Cette étude a permis de montrer que la structure du réseau trophique, en modifiant le contrôle des producteurs primaires par leurs consommateurs, influe sur les compositions élémentaire et biochimique (acides carboxyliques polyinsaturés, stérols, dérivés de la chlorophylle, protéines et sucres) de la matière organique qui sédimente et sur sa biodégradabilité. Cette modification de biodégradabilité influence en retour les biomasses du seston, du zooplancton, ou des poissons. Les matières organiques d origines différentes (autochtone et allochtone) étudiées ont des effets contrastés sur les compositions élémentaires du seston, du zooplancton et des sédiments récemment déposés, mais très peu d impact sur la composition des biomarqueurs lipidiques de ces compartiments. Les effets ascendants sur la structure des réseaux trophiques pélagiques des apports de matière organique sous forme de sédiment ou de terre se sont avérés assez mineurs comparés à ceux induits par la modification de la structure des réseaux trophiques aquatiques.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Stanols as a tool to track the origin of microbial contamination of oysters, Crassostrea gigas, in shellfish areas.

International audienceRunoff of cattle manures (cows, pigs, sheeps) or discharge of effluent from wastewater treatment plants (WWTP) into aquatic ecosystems can lead to microbiological contamination of waters and living organisms. In coastal ecosystems and particularly in shellfish harvesting areas, the presence of pathogen microorganisms in waters induces fecal contamination of filter feeding bivalves (oysters, mussels, scallops...), therefore leading to human health risks associated to the consumption of these contaminated organisms. Watershed management plans that aim at limiting these risks require the development of tools able to identify fecal contamination sources. The fecal indicator bacteria used in the regulations to determine fecal contamination are not source specific since they are found in the feces of most warm-blooded animals. Thus, microbiological biomarkers have been developed in association with chemical biomarkers as Microbial Source Tracking (MST) methods. Fecal stanols, by-products of sterols obtained by human and animal microbial gut flora, are found in considerable amounts in feces with different relative proportions depending on their animal or human source. Recently, in association with microbiological biomarkers, the stanol fingerprint of contaminated waters has been successfully used to determine the main source of fecal contamination (cow, pig or human sources) in rural watersheds (Brittany, France). Up to now, the use of the stanol fingerprint to track the fecal contamination in shellfish tissues, especially bivalves, has been limited to the analysis of coprostanol, a stanol commonly associated to human contamination. Therefore, whether the stanol fingerprint can be used as a MST method in bivalves or not is still unknown. The first aim of this study was to compare several organic extraction procedures of stanols in the oyster Crassostrea gigas to determine a reliable method for stanol fingerprint analysis in bivalves. Solvent extraction and purification steps have been carried out with attention as they are critical for stanol quantification. Secondly, the evolution of the stanol fingerprint of oysters with time was evaluated during 6 days by artificially contaminating microcosms with two concentrations of a WWTP effluent. In the microcosms, the fingerprint of stanols as a chemical biomarkers of fecal (human) contamination was compared to counts of Escherichia coli, a commonly used microbial indicator. In association with microbial markers, the method developed from the two previous steps will be applied at the watershed scale in order to identify sources of fecal contamination in Brittany and Normandy (France)

Are fecal stanols suitable to record and identify a pulse of human fecal contamination in short-term exposed shellfish? A microcosm study

In this study, the capacity of oysters to bioaccumulate fecal stanols and to record a source-specific fingerprint was investigated by the short-term contamination of seawater microcosms containing oysters with a human effluent. Contaminated oysters bioaccumulated the typical fecal stanols coprostanol and 24-ethylcoprostanol and their bioaccumulation kinetics were similar to that of the Fecal Indicator Bacteria Escherichia coli used in European legislation. Although stanol fingerprints of contaminated water allowed the identification of the human specific fingerprint, this was not the case for oysters. This discrepancy is attributed to (i) high concentrations of endogenous cholestanol and sitostanol, responsible for “unbalanced” stanol fingerprints, (ii) different accumulation/depuration kinetics of fecal coprostanol and 24-ethylcoprostanol and (iii) the limits of the analytical pathway used. These results show that fecal stanols bioaccumulated by oysters are useful to record fecal contamination but the usefulness of stanol fingerprints to identify specific sources of contamination in shellfish currently seems limited

Shifting Sands and Climate Change : Modalities of Dwelling at Yarte, Yamal, Siberia

Peer reviewedPostprin

Preserved lipid signatures in palaeosols help to distinguish the impacts of palaeoclimate and indigenous peoples on palaeovegetation in northwest Siberia

Arctic reindeer herders demonstrate resilience to climate fluctuations by adjusting their pastoral practices to changing environments. The multiple phases of occupation at one of the oldest identified reindeer-herding sites, I͡Arte 6 on the I͡Amal peninsula, northwest Siberia, are thought to be linked to its local vegetation cover. Here we provide information on local palaeovegetation and climate shifts which occurred between the 7th and the 11th century CE based on lipid biomarkers. Aliphatic compounds, pentacyclic triterpenoids, branched glycerol dialkyl glycerol tetraethers (brGDGTs) and other lipids were analysed in four separate palaeosols from two loess-palaeosol sequences at the site. Based on different indices, the impact of human- or root-derived lipids and post-depositional microbial degradation on the signature of the studied pedosequences seem limited, which indicates that palaeobiomarkers are well preserved and representative of the analysed compounds. n-Alkanes, n-carboxylic acids, n-aldehydes and pentacyclic triterpenoids point to the progressive colonization of grasses, sedges and herbs at the site, which can be attributed to the regional decrease in temperature suggested by bacterial-derived brGDGTs. During the last phase of occupation, however, when proxies point to increasing temperatures, and shrubs would normally be expected to return, the shrub cover continued to decrease, probably due to the impact of camping and holding reindeer at the site. The decoupling trends observed for particular pentacyclic triterpenoids as potential dwarf birch biomarkers could suggest a preferential shift of species within shrubs, probably influenced by human activities. Multi-family lipid biomarker analysis therefore made it possible to distinguish anthropogenic impacts on the local vegetation cover from regional climatic changes, and show how significant the impacts of humans on local vegetation can be, even in extreme environments where such activities are limited

Faecal biomarkers can distinguish specific mammalian species in modern and past environments

Identifying the presence of animals based on faecal deposits in modern and ancient environments is of primary importance to archaeologists, ecologists, forensic scientists, and watershed managers, but it has proven difficult to distinguish faecal material to species level. Until now, four 5β-stanols have been deployed as faecal biomarkers to distinguish between omnivores and herbivores, but they cannot distinguish between species. Here we present a database of faecal signatures from ten omnivore and herbivore species based on eleven 5β-stanol compounds, which enables us to distinguish for the first time the faecal signatures of a wide range of animals. We validated this fingerprinting method by testing it on modern and ancient soil samples containing known faecal inputs and successfully distinguished the signatures of different omnivores and herbivores