A mineralogical and organic geochemical overview of the effects of Holocene changes in Amazon River flow on three floodplain lakes

A synthesis of the impacts of the Amazon River hydrological changes on the sedimentation process of organic matter (OM) in three different floodplain lakes (Santa Ninha, Maracá, and Comprido lakes) is presented in this study. Today the Santa Ninha and Maracá lakes are directly and permanently connected with the main channel of the Amazon River, in contrast to Comprido Lake, which is indirectly and periodically influenced by the Amazon River due to its greater distance from the main channel. All three lake sediment records showed a reduced river inflow due to dry climatic conditions during the early and middle Holocene followed by an increased fluvial input during the wetter late Holocene. In Santa Ninha and Maraca Lakes, the reduced river inflow period was recorded by sediments with a low abundance of smectite (on average ~ 20 wt.%), a clay mineral mainly transported by the fluvial system, high total organic carbon (TOC) contents (on average ~ 8.2 wt.%), and a predominantly acidic soil OM input evidenced by high concentrations (on average 180 µg gTOC- 1) of branched glycerol dialkyl glycerol tetraethers (GDGT). During the late Holocene, a higher smectite abundance (on average ~ 43 wt.%) and a lower TOC content (on average ~ 1.4 wt.%) pointed to greater dilution by riverine lithogenic matter. This change was accompanied by a proportional increase in the aquatically produced crenarchaeol, suggesting a higher lake water level. In Comprido Lake, a sedimentation gap occurred during the early and middle Holocene. The wetter late Holocene, since 3000 cal years BP, was characterized by high TOC values (on average ~ 9 wt.%) and a sharp increase in soil OM input as recorded by an increase in branched GDGT concentrations (on average ~ 81 µg gTOC- 1), but the smectite content was low (on average ~ 14%). This combination suggests that the soil OM input to Comprido Lake from the local catchment area became dominant during the wet-climate late Holocene due to the large distance of the lake from the Amazon River main channel. Consequently, our study shows that the sedimentation processes of OM in Amazonian floodplain lakes were strongly influenced by variations in the hydrodynamic regime of the Amazon River during the Holocene. However, the impacts of the variations on the three floodplain lakes were different depending on the distance of each lake from the main channel of the Amazon River

5. Impacto del cambio climático en la sedimentación y en la acumulación de carbono en los lagos de la Amazonia peruana

Los suelos, las aguas y los sedimentos de la cuenca amazónica son importantes compartimentos del ciclo de carbono, el cual se encuentra parcialmente almacenado en los bosques inundables y en los lagos de inundación de la región (20% de la superficie total de la cuenca). Estudiar los procesos de sedimentación lacustres a diferentes escalas espaciales y de tiempo permite mejorar le estimación del balance biogeoquímico del carbono (uno de los gases de efecto Invernadero responsable del cambio climático actual, el CO2). Las tasas de sedimentación en las áreas de inundación dependen de varios factores, como el tipo de agua de los lagos y del tipo de conexión que tienen con los ríos. El análisis en laboratorio de muestras de sedimentos, que mantienen la secuencia de deposición, sirve para determinar las condiciones geológicas, meteorológicas, los cambios en el ecosistema e incluso acciones de origen humano que pueden haber afectado los regímenes de sedimentación y la composición de los sedimentos a lo largo del tiempo.Les sols, les eaux et les sédiments du bassin amazonien sont des compartiments importants du cycle du carbone, qui est partiellement stocké dans les forêts et les lacs inondés dans la région (20% de la superficie totale du bassin). Connaître les processus de sédimentation lacustres à différentes échelles spatiales et temporelles permet d'améliorer l'estimation de l'équilibre biogéochimique du carbone (un des gaz responsables du changement climatique actuel, CO2). Les taux de sédimentation dans la plaine inondable dépendent de plusieurs facteurs, y compris le type d'eau des lacs et le type de connexion avec les rivières. Les analyses de laboratoire des échantillons de sédiments, qui maintiennent la séquence de dépôt, sont utilisées pour déterminer les caractéristiques géologiques, les conditions météorologiques, les changements dans l'écosystème et même les actions humaines qui peuvent avoir une incidence sur les régimes de sédimentation et la composition des sédiments au fil du temps.The soils, waters and sediments of the Amazon basin are important compartments of the carbon cycle, which are partially stored in flooded forests and lakes of flooding in the region (20% of the total basin area). The study of lacustrine sedimentation processes at different spatial and temporal scales allows improving the estimation of biogeochemical carbon balance (one of the greenhouse gases responsible for the current climate change, CO2). Sedimentation rates in flood areas depend on several factors, such as the type of water from lakes and the type of connection this water has with rivers. The laboratory analysis of sediment samples, which maintain the deposition sequence, is used to determine geological and meteorological conditions; as well as changes in the ecosystem, even actions arising from humans that may have affected the sedimentation regimes and sediment composition along the time

Spatial and seasonal contrasts of sedimentary organic matter in floodplain lakes of the central Amazon basin

In this study, we investigated the seasonal andspatial pattern of sedimentary organic matter (SOM) in fivefloodplain lakes of the central Amazon basin (Cabaliana,Janauaca, Canaçari, Mirituba and Curuai) which have differentmorphologies, hydrodynamics and vegetation coverages.Surface sediments were collected in four hydrologicalseasons: low water (LW), rising water (RW), high water(HW) and falling water (FW) in 2009 and 2010.We investigatedcommonly used bulk geochemical tracers such as theC V N ratio and the stable isotopic composition of organic carbon(?13Corg/. These results were compared with lignin phenolparameters as an indicator of vascular plant detritus andbranched glycerol dialkyl glycerol tetraethers (brGDGTs) totrace the input of soil organic matter (OM) from land to theaquatic settings. We also applied the crenarchaeol as an indicatorof aquatic (rivers and lakes) OM. Our data showed thatduring the RW and FW seasons, the surface sediments wereenriched in lignin and brGDGTs in comparison to other seasons.Our study also indicated that floodplain lake sedimentsprimarily consisted of allochthonous, C3 plant-derived OM.However, a downstream increase in C4 macrophyte-derivedOM contribution was observed along the gradient of increasingopen waters – i.e., from upstream to downstream. Accordingly,we attribute the temporal and spatial difference inSOM composition to the hydrological dynamics between thefloodplain lakes and the surrounding flooded forests

2. Cambios climáticos del Holoceno

Existe una variabilidad natural del clima. Se debe tanto a factores externos (como el cambio de la órbita de la Tierra) como internos (como erupciones volcánicas o movimientos tectónicos entre otros). Los paleo-climatólogos estudian los cambios del clima del pasado a través de complejos análisis de sedimentos de lagos, de testigos de hielo de los glaciares o también de estalagmitas de las cavernas. Estos registros son como libros donde está escrita la historia del clima de la Tierra. Usando estos marcadores ambientales y gracias a los modelos climáticos a diferentes escalas espaciales y de tiempo, los investigadores buscan discriminar cual es la parte natural del cambio climático actual de la parte debida a la actividad humana y disminuir las incertidumbres en las proyecciones futuras del clima.Il existe une variabilité climatique naturelle. Elle est due aussi bien à des facteurs externes (comme le changement d’orbite de la Terre) qu’internes (comme les éruptions volcaniques ou les mouvements tectoniques entre autres). Les paléo-climatologues étudient les changements du climat du passé en réalisant des analyses complexes de sédiments de lacs, de carottes glaciaires ou encore de stalagmites des grottes. Ces registres sont comme des livres où est écrite l’histoire du climat de la Terre. A partir de ces marqueurs environnementaux et des modelés climatiques à différentes échelles d’espace et de temps, les chercheurs cherchent à connaître quelle part du changement climatique actuel est naturelle et quelle part est liée à l’activité humaine et réduire les incertitudes dans les projections climatiques.There is natural climate variability. It ¡s due to both external factors (such as changes in Earth’s orbit) as well as internal factors (such as volcanic eruptions and tectonic movements among others). Paleoclimatologists study historic climate changes performance by complex analysis of lake sediments, ice cores or stalagmite caves. These records are like books in where the history of Earth’s climate has been written. Thanks to these environmental markers and the climate models at different scales of space and time, researchers seek to differentiate which part of the current climate change is natural and which part is due to human activity, in order to reduce uncertainties in future climate projections

4. HYBAM: un observatorio para medir el impacto del Cambio Climático sobre la erosión y los flujos de sedimentos en la zona Andino-Amazónica

La cuenca Amazónica es la más grande del mundo. La instalación del observatorio HYBAM con una amplia red de estaciones hidrológicas ubicadas desde el piedemonte andino hasta el océano Atlántico permite, desde el 2003, la generación de registros periódicos y confiables (nivel del agua, caudal, concentración de sedimentos y otros parámetros físico-químicos de la calidad del agua) a lo largo de toda la cuenca. Hoy en día, el desarrollo de técnicas satelitales, como la altimetría, permite completar eficientemente los datos obtenidos por las redes de medición en los ríos. El recrudecimiento de eventos extremos en la Amazonia (Inundaciones, sequias,) por efecto del cambio climático actual asociado a un cambio acelerado de ocupación de los suelos (deforestación, prácticas agrícolas), tiene una incidencia directa sobre la producción sedimentarla. Conocer los flujos de materiales transportados por los ríos es esencial tanto para la navegación fluvial como para guiar la explotación de los recursos naturales (agua, petróleo, minerales), para conocer el transporte de partículas contaminantes o para diseñar infraestructuras.Le bassin de l’Amazone est le plus grand du monde. La mise en œuvre de l’observatoire HYBAM avec un vaste réseau de stations hydrologiques situées sur les contreforts des Andes jusqu’á l’océan Atlantique permet de générer, depuis 2003, des données régulières et fiables tout le long du bassin (hauteur d’eau, débit, concentration de sédiments et d’autres paramètres physico-chimiques de qualité de l’eau). De nos jours, la mise au point des techniques par satellite, tels que l’altimétrie, permet de compléter efficacement les données obtenues par les réseaux de mesure dans les rivières. L’intensification des événements extrêmes dans la région amazonienne (inondations, sécheresses), liés au changement climatique actuel associé á un changement rapide de l’utilisation des terres (déforestation, pratiques agricoles), ont un impact direct sur la production de sédiments. Connaître les flux de matières transportés par les rivières est essentiel pour la navigation fluviale ainsi que pour guider l’exploitation des ressources naturelles (eau, pétrole, minéraux), connaître le trajet de particules polluantes ou concevoir des infrastructures.The Amazon basin is the largest basin in the world. The implementation of the HYBAM observatory, which has installed a large network of hydrological stations located from the Andean foothills down to the Atlantic Ocean, allows since 2003, generate periodical and reliable records (such as water level, flow, sediment concentration and other physicochemical parameters of water quality) along the entire basin. Nowadays, the development of satellite techniques, (such as altimetry), makes it possible to efficiently complete the data obtained by the measurement networks in rivers. The intensification of extreme events in the Amazon region (floods, droughts) occurred as a result of the current Climate Change associated with a more rapid change of land use (deforestation, agricultural practices) have a direct impact on sediment production. It is essential to know the flows of the materials transported by rivers, both for river navigation as well as to guide the exploitation of natural resources (water, oil, minerals), to know the transport of particulate pollutants, or to design infrastructures