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The Jizera River in Czechia is a typical mid‐sized Central European watercourse. Its floodplain shows a morphological contrast between the laterally stable low‐sinuous current channel and preserved palaeomeanders. The aim of this paper was to date and explain the obvious metamorphosis of the channel pattern from meandering to low‐sinuous. We analysed the morphology of the lower river reach using a digital terrain model (DTM) and historical maps from the 1840s. Furthermore, the floodplain architecture was described based on the DTM, geophysical imaging (ground penetrating radar, GPR), sediment lithology and anthropogenic contamination using geochemical proxies, and optically stimulated luminescence (OSL) dating. The geochemical proxies were processed using log‐ratio methods from the compositional data analysis toolbox. According to our results the Jizera River showed signs of systematic lateral floodplain reworking during the Late Holocene with only minor aggradation, although parts of the catchment are covered by easily erodible loess. Interestingly, vertical aggradation did not show a significant increase during the last millennium. In the main study area, this limited vertical aggradation resulted in the preservation of palaeomeander fragments and palaeochannel belts with 100–200 m mean width in the 300–600 m wide floodplain, which are recognisable in the topography and in subsurface GPR imaging. This channel meandering took place between around 4 and 1.2 ka, and the transition towards the laterally stable modern channel with low sinuosity occurred around 1.2 ka. This timing indicates a climatic rather than anthropogenic impact, which was rather weak around that time. One likely cause for this transition was the influx of material from ravines incised into the sandstone valley edges during past climatic extremes. Subsequently, the re‐establishment of a meandering pattern was possibly prevented by a combination of low fluvial activity and the construction of weirs that reduced stream power. [ABSTRACT FROM AUTHOR]

Packages of fluvial systems in the Lower Ganga plains (LGP) archive the changes in stratigraphic architecture induced by perturbations in the climatic system. In some parts of this landscape, where the fluvial sequences predominate, the role of climate in landsculpting is strongly indicated by the presence of sediment architecture. The present study is focused on the formation of alluvial plains of the Ajay River in the Rarh region that represent a region's environmental templates for understanding the landscape of LGP. The sedimentological, geomorphological, and optically stimulated luminescence (OSL) chronological investigations were attempted to document sedimentation patterns and the timing of deposition. The stratigraphic data from two exposed cliff sections and three boreholes are compared with proxy records to understand the Indian Summer Monsoon (ISM) controls on alluvial sedimentation for the last ~2.4 ka. The fluvial packages in the study area correspond to two significant channel phases: Period‐I (2.4–1.3 ka) and Period‐II (800–200 years ago). Period‐I is characterized by the episodes of floodplain development and lateral migration of the trunk river during Marine Isotope Stage (MIS) I, especially around 2 ka corresponding to the Roman Warm (RW) period in the Indian subcontinent. The sediment filling was high during ~2.4 ka due to ISM intensification, but in the later stage, the sedimentation was at a fairly steady rate. Conversely, Period‐II is characterized by flooding phenomena and aggradation of channel bodies across much of the present valley area during the last 800 years. The distinct flood events occurred during the times of significant shifts in ISM, from fluvial dormancy to sudden outbursts of monsoons (end of Little Ice Age [LIA] ~ 19th century), indicating that climatic patterns can be associated with the occurrences of abrupt flood events. The alluvial records fit well with the historical, instrumental, and published proxy data on the ISM validating the chronology and the potential of sedimentary archives for further studies related to the palaeoenvironment and palaeogeography. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to describe the late Holocene behaviour of rivers using an interdisciplinary approach combining fluvial geomorphology and subfossil trunk dendrochronology. The subfossil wood material collected along the rivers was investigated for dendrometric and dendrochronologic parameters. The research methods in these fields helped us to understand the effect of the fluvial environment on riparian trees and their records and helped in reconstructing the riparian palaeoenvironment. The study area consists of two rivers with different typologies but comparable sizes: the Moldova River, which features a braided to wandering channel in its lower reach, and the Siret River, which features a sinuous-meandering channel. Along the 100-km-long floodplain of the former and the 144-km-long floodplain of the latter, we found and sampled 77 subfossil trunks, of which 26 were subjected to 14 C dating. The resulting data consist of floodplain facies mapping data, electric resistivity measurements, absolute dates, and dendrometric and dendrochronologic data. The results indicate that during a 100-year period, the two rivers were sensitive to climate change and anthropogenic effects, particularly a narrowing of the active channel by 76% in the braided channel and 38% in the sinuous-meandering channel. During the past 3300–3000 YBP, the Moldova River maintained its braided style, whereas the sinuous-meandering style has been characteristic of the Siret River for the previous 6800–4600 YBP. The two distinct fluvial environments are recorded in the dendrometric structure of the trunks buried in the channel-fill sediments. The braided fluvial environment was more effective in uprooting riparian trees and incorporating them in the floodplain deposits, whereas the sinuous-meandering style of stream effectively buried tree trunks in lateral accretion lobes. Absolute and dendrochronologic dating allowed for the reconstruction of timelines of the felling of the trees and estimates of the magnitude of the responsible hydrological event. The flood events on the Siret River with a recurrence interval of 200 years ( Q max ~ 2500–2800 m 3 /s) were those most effective in destroying riparian forests, and the events on the Moldova floods with a 100-year recurrence interval ( Q max ~ 1200–1400 m 3 /s) were the most effective. Dendrochronology allowed for identification of wet phases (i.e., 3500–2900 YBP, 2200–2075 YBP, and 1000–800 YBP) and dry phases (e.g., 3200–3150 or 2775–2700 YBP, 1400 YBP). Finally, we draw attention to the potential for creating a highly replicable dendrochronological series spanning at least 7000 YBP. [ABSTRACT FROM AUTHOR]

Tropical peatlands are an important carbon reservoir; however, they are vulnerable to climate change, fire events, and human disturbances, and may become a significant carbon source if degraded. In this paper, we investigated the late Holocene record of vegetation change, peatland evolution, and C accumulation based on analysis of a sediment core through a Mauritia-flexuosa palm dominated swamp (locally called " aguajal ") in the Madre de Dios region in southern Peru to better understand tropical peatland dynamics. Sedimentation commenced within shallow water, ponded on an impervious substrate, perhaps within an abandoned river channel or oxbow lake (1380–820 cal yr BP) located adjacent to a steep escarpment with terra firme (upland) rainforest above and lateral to floodplain forests. This was followed by the development of marsh (820–640 cal yr BP). A closed-canopy Mauritia flexuosa -dominated palm swamp was subsequently established (640300calyr BP) which later changed into an open canopy and mixed Mauritia - Hedyosmum palm swamp (300 cal yr BP to present). Two major changes in peat and C accumulation rates were observed: (1) onset of peat and C accumulation at 820 cal yr BP and (2) decrease of peat and C accumulation after 520 cal yr BP. Comparisons of our results with palaeoecological records from aguajales in northern Peru suggest that the dynamics were different in this region. The peat and C accumulation rates in our study core in southern Peru were ca. 4 mm yr−1 and ca. 200 g m−2 yr−1 faster, similar to a few sites in northern Peru. Aguajales in Madre de Dios region in southern Peru are an important carbon sink. Analyzing the dynamics of aguajales which are a kind of typical peatlands in Amazonia and comparing among different sites allows exploration and prediction of regional peatlands' development under the potential future impact of natural changes. • First study of a palm peatland (aguajal) development in Madre de Dios region, southern Peru • This study includes late Holocene vegetation dynamics, peat and C accumulation of the aguajal • Controlling factors in the dynamics are fluvial changes and climate • Comparisons with northern Peru suggest different vegetation succession • Peat and C accumulation rates in Madre de Dios were faster, similar to a few sites in northern Peru [ABSTRACT FROM AUTHOR]

Organic and inorganic geochemical analyses on sediments from Preto Lake, a central Amazon basin floodplain water body, were used to document hydrological changes of the Solimões River during the late Holocene. Between 3600 and 400 cal yr BP, Preto Lake received smectite-rich sediment from the Solimões River, with high concentrations of Al (~ 53 × 103 ppm) and Si (~ 210 × 103 ppm). The high detrital input suggests there was a direct connection between Preto Lake and the main river channel. High river inflow maintained lake stage and was responsible for the contribution to sediments of phytoplankton-derived organic matter. Low sediment organic carbon concentrations characterized this period (mean ~ 3.8 wt%), probably because of dilution by river-borne lithogenic matter. Although the river inputs remained high, abrupt increases in TOC content around 1800 and 1200 cal yr BP suggest brief increases in fluvial nutrient supply to Preto Lake. During the last 400 cal yr, substantial declines in smectite (mean 40%), Al (~ 29 × 103 ppm) and Si (138 × 103 ppm) suggest the establishment of a semi-isolated lake, with reduced river inflow. A large proportion of C3-plant-derived organic matter, supplied by runoff from the kaolinite-rich watershed, was observed during this period, and was accompanied by high autochthonous primary production, driven by development of an aquatic macrophyte community. This change in sediment organic matter source accounted for the greater TOC content (~ 20%) of sediments deposited during this period. Although Holocene climate change was an important control on fluvial sediment supply to upper and lower Amazon Basin floodplain lakes, sedimentation processes in Preto Lake can also be linked to changes in the river's course. The transition to a semi-isolated lake could have been a consequence of lateral and vertical sediment accretion, which formed a natural levee that blocked fluvial input to Preto Lake. [ABSTRACT FROM AUTHOR]