Paleohydrological changes in an Amazonian floodplain lake: Santa Ninha Lake

Abstract

Holocene environments have been reconstructed by sedimentological, mineralogical and organic geochemical analysis of a 270-cm core from Santa Ninha Lake, a floodplain lake in lower Amazonia. Dated by fourteen AMS-radiocarbon dates, the sediment core has a basal age of 5,600 cal years BP and different sedimentary units were identified. These units document various hydrologic phases in the evolution of this lake. Reduced Amazon River influence, with reduced high-water levels of the river, characterized the period between 5,600 and 5,100 cal years BP. Comparison with other Amazonian and Andean paleoclimate studies point to a dryer climate during this phase. After 5,100 cal years BP coarse sediments and quartz increase which suggest a higher inflow of the Amazon River. Between 5,000 and 2,300 cal years BP the coarse sediments and quartz remain high but the organic carbon showed the lowest values. The riverine inflow caused dilution of the organic material produced in the lake and consequently low rates of carbon flux in these phases were recorded. These results show that the hydrodynamics of the Amazon River strongly influence the behavior, productivity and consequently the sedimentation process in the floodplain lakes.

Palaeofires in Amazon: Interplay between land use change and palaeoclimatic events

“…Temperature increases related to the Holocene Thermal Maximum are characterised by relatively warm climates between 11,000 and 5000 years BP as indicated by numerous proxy records (Renssen et al, 2012). The temperature increases during early to middle Holocene are associated with major changes in the precipitation/evaporation balance that are considered responsible for regional decrease in hydrological balance recorded by low lake levels during the mid-Holocene in Amazonia (Baker et al, 2001;Cordeiro et al, 2008;Moreira et al, 2012Moreira et al, , 2013aTurcq et al, 2002a,b) and an increase in fire occurrences. Melo and Marengo (2008) reconstructed high temperature and low precipitation in Amazonia sectors based on model simulations of mid-Holocene conditions.…”

“…Whitlock et al (2010), based on statistical modelling of global fire patterns, suggest that the distribution of fire is related to net primary productivity, because of the importance of burnable biomass. Increasing human population in the Amazon most likely made forest fires more common primarily after 3000 cal years BP, even taking into account that the climate during the late Holocene was wetter than during the mid/late Holocene as indicated by high lake levels in different neotropical sectors (Martins, 2012;Behling et al, 2001;Turcq et al, 2002a;Cordeiro et al, 2008;Moreira et al, 2012;Moreira et al, 2013a,b). Even assuming a higher lake level related to a wetter climate in the late Holocene, dry events related to human occupation in Amazonia are evidenced in the last 2000 years.…”

Contamination status of dioxins in sediment cores from the Three Gorges Dam area, China

“…It has been proved that hydrodynamics could strongly influence the sedimentation process. Sedimentation process in Santa Ninha Lake was influenced markedly by hydrodynamics (Moreira et al 2012). Without high water velocity, no strong mixing occurred in Taihu lake and Chaohu lake, two big lakes in the middle and lower reaches of Yangtze River basin.…”

A 2700calyr BP extreme flood event revealed by sediment accumulation in Amazon floodplains

“…All these authors highlight the importance of these floodplain lakes to sediment accumulation. Sediment storage can occur at different timescales (from hundreds to thousands of years) (Dunne et al, 1998;Behling and Costa, 2000;Moreira-Turcq et al, 2004), and it is strongly influenced by the hydrodynamics of the Amazon River (Irion et al, 2006(Irion et al, , 2010Moreira et al, 2012Moreira et al, , 2013. Mertes et al (1996) estimated that 80% of the material being transported by the Amazon passes through the floodplain lake systems.…”