Assemblage of wetland bird Species in Purbasthali Oxbow Lake, West Bengal, India: Implications for Management

The present study attempts to assess the composition, abundance and diversity of avifauna with respect to their habitat in and around the Purbasthali wetland, based on both primary data collected through the point count method during 2017–2019 and literature data. Among the total 77 species (encompassing 10 orders and 19 families), 39 species are migrants, 18 are rare and 24 species show declining global trend. According to their habitat, they are sub-divided into three categories i.e. waterfowls (live in open water, 20 species), waders (live in bank areas/water edge area, 45 species) and wetland associated (live in nearby trees, 12 species). The Shannon-Wiener Diversity Index (H’) and the Evenness Index (E’) are used to examine the diversity within and between the habitats. The result reveals higher diversity and evenness of the waders in comparison to others. The maximum diversity (H′=3.02) and evenness (E′=0.79) has been recorded for the waders in 2019, whereas the least values (H′=1.02, E′=0.34) have been found in 2016 for the waterfowls. Relative Diversity Index affirms the dominance of the Anatidae family. The birds of the area have now been seriously threatened by human intervention.

Age and Palynological Characteristics of Floodplain Deposits of the Kolyma Lowland (North-East Siberia)

River floodplains, reaching several kilometers in width, are one of the main landscape features of the Kolyma Lowland. Their relationship with other forms of relief - yedoma, alasses, and fragments of river terraces - is seen clearly in the Bolshaya Kuropatoch'ya River basin, which is located in the Lowland between 156°30' E and 157°15' E. The first radiocarbon dating of the floodplain deposits of the Kolyma Lowland was undertaken in a study of an outcrop on the left bank of the Bolshaya Kuropatoch'ya River (71°40' N, 156°45' E). Here floodplain sediments, represented by the alternating layers of alluvial silt and peat with a total thickness of 5 m, were exposed along a steep bank of an oxbow lake. The radiocarbon results show that the formation of the modern floodplain of the Bolshaya Kuropatoch'ya River began at the end of the Middle Holocene and continued during the Late Holocene to the present. Since the vegetation cover of arctic and subarctic regions is characterized by low pollen productivity, the spore-pollen spectra of modern and fossil plant communities often include an increased amount of pollen from plant species exotic to the Arctic, brought to the site by long-distance wind transport. For a more reliable interpretation of the spore- pollen spectra of the floodplain sediments, an analysis of the modern vegetation in the Bolshaya Kuropatoch'ya River basin and in a coastal area bordering the East Siberian Sea (about 71°05' N) was carried out, accompanied by an herbarium collection. The radiocarbon-dated palynological data indicate the development of the modern Betula-Salix shrub-herbaceous tundra during the second half of the Holocene. The establishment of this vegetation community reflects the replacement of an earlier Betula forest-tundra, which had prevailed in the northern regions of Western Beringia during the Early Holocene and included Duschekia fruticosa and large shrub species of Salix. Such dramatic changes in the vegetation cover were associated with the rise in sea level about 7.000-6.000 years ago, when seas approached modern levels. This change, in turn, led to a decrease in the contrast of summer and winter temperatures and, thus, to a decrease in the continentality of the climate and a significant reduction in the growing season in the coastal regions of the East Siberian Sea.

Improving flood and drought management in agricultural river basins: an application to the Mun River Basin in Thailand

Agriculture productivity is regularly affected by floods and droughts, and the severity is likely to increase in the future. Even if significant efforts are spent on water development projects, ineffective project planning often means that they continue to occur or are only partly mitigated, for example, in the Mun River Basin, Thailand, where 1,000 s of water projects have been implemented. Despite this, the basin regularly experiences floods and droughts. In this study, an analysis of the adverse impacts of basin-scale floods and droughts on rice cultivation in the Mun River Basin is conducted, and an estimation of the coping capacity of existing measures. The results demonstrate that while the total storage capacity of in-situ and ongoing projects would be sufficient to tackle both hazards, it can only be achieved if the projects are effectively utilised. Based on this, proposed solutions for the region include small farm ponds, a subsurface floodwater harvesting system, and oxbow lake reconnections. The suggested measures are practicable, economical, environmentally low-impact, and their implementation (if executed with appropriate care) would reduce flood and drought problems in the basin. Notably, the measures and calculation methods proposed for this basin can also be applied to other crops and regions.

Changes in Algal Plankton Composition and Physico-Chemical Variables in a Shallow Oxbow Lake

In our work, we sought to answer whether we find differences among the various zones of an oxbow lake with different land uses based on physico-chemical variables and dominant algal plankton species. The two ends of the oxbow lake are bordered by settlements, and near them there are open water areas where fishing is the major utilization form. Between the two open water areas we find a protected area with a large aquatic plant coverage and two transition zones towards the open water areas. The oxbow lake receives periodic water replenishment only at one end from one of the open water areas. During summer—due to the lack of rain—the water of the oxbow lake is used for irrigation in the surrounding arable land, so the water level fluctuation can be significant in the riverbed. Our study was performed within a vegetation period of spring, early summer, mid-summer, and fall. In connection with the ecological classification of a smaller water body, studies on the physical and chemical properties of the water and the composition of the algal plankton are usually carried out in few places and relatively infrequently. The characteristics of a water body are also influenced by seasonal changes, which can be the changes in the extent of vegetation coverage, the way land is used and the possibility of water replenishment, to which the algal community usually responds with changes. Based on our study, it can be said that even in a relatively small water body, we found a large differences based on the chemical and physical properties of the water and the characteristic algal species. Open water zones, areas with large macrovegetation coverage, and the transition zones were separated from each other.

Severe Little Ice Age drought in the midcontinental United States during the Mississippian abandonment of Cahokia

Drought has long been suspected as playing an important role in the abandonment of pre-Columbian Native American settlements across the midcontinental United States between 1350 and 1450 CE. However, high-resolution paleoclimatic reconstructions reflecting local effective moisture (the ratio of precipitation to evaporation) that are located in proximity to Mississippi period (1050–1450 CE) population centers are lacking. Here, we present a 1600-year-long decadally resolved oxygen isotope (δ18O) record from Horseshoe Lake (Collinsville, IL), an evaporatively influenced oxbow lake that is centrally located within the largest and mostly densely populated series of Mississippian settlements known as Greater Cahokia. A shift to higher δ18O in the Horseshoe Lake sediment record from 1200 to 1400 CE indicates that strongly evaporative conditions (i.e., low effective moisture) were persistent during the leadup to Cahokia’s abandonment. These results support the hypothesis that climate, and drought specifically, strongly impacted agriculturally based pre-Columbian Native American cultures in the midcontinental US and highlights the susceptibility of this region, presently a global food production center, to hydroclimate extremes.

Late-Holocene palaeoenvironmental reconstruction from a lake in the Amazon Rainforest-Tropical Savanna (Cerrado) boundary in Brazil using a multi-proxy approach

As an ecotone, the region between the Amazon Rainforest and Tropical Savanna (Cerrado) biomes is, by definition, more susceptible to climate change. Therefore, understanding palaeoenvironmental dynamics is essential to address the future responses of such transition areas to climatic fluctuations. In this context, we present a new sediment record for the Late-Holocene retrieved from Barro-Preto, currently an oxbow lake located in an ecotone at the southern Brazilian Amazon border. Our multi-proxy data include carbon and nitrogen isotopes, as well as bulk TOC, chlorophyll derivatives, grain-size and microcharcoal analyses, all anchored on a radiocarbon-dated chronology. The sedimentary process recorded at the Barro-Preto Lake responded to both local and regional climate dynamics. It was influenced by river excursions associated to local responses to precipitation changes by the activation of the palaeochannel connecting the main-stem river and the Barro-Preto lake. This activation was evidenced by the presence of different colour lithology laminations accompanied by coarser sediments and also by climate conditions known to influence the Amazon region. Depositional processes linked to lake dynamics and different oxbow lake cycle stages were also important to explain the changes verified in the Barro-Preto record, endorsing the use of this lake formation for palaeoclimatic reconstructions. The record indicated a rising humidity trend, reflected by a progressive increase in lacustrine productivity, in accordance to other studies carried out in the Amazon region concerning the Late-Holocene, associated with a more southward displacement of the Intertropical Convergence Zone. Despite this rising humidity trend, dry episodic events during the Late-Holocene were evidenced by charcoal data, also coherent with regional Amazon studies, albeit exhibiting increased intensity, suggesting that the transitional nature of the environment might have influenced susceptibility to fires.

Contribution of archaeobotany to understand taphonomic phenomena. The case of a Preboreal oxbow lake of Autrecourt-et-Pourron (Ardennes, France).

By analyzing the mechanisms that govern the interactions between environmental factors and ecosystems, paleoecology refines our knowledge of the mechanisms that are structuring plant communities, helping us to understand the complexity of past environments. While undertaking palaeoecological analyses, it is necessary to analyze and to understand the taphonomic phenomena influencing plant macrofossil assemblages. Indeed, the evaluation of under- and over-representation of taxa makes it possible to judge the interest and quality of the retained data set as a source of paleo-ecological information. The French National Centre for Archaeological Research (CNRA) recommends "refining taphonomic modelling in different aspects: accumulation and modification processes by biological agents, natural ageing processes of taphocenoses" (National Research Programming 2016, p. 35). The inability to reconstruct the diagenetic history of sedimentary layers can sometimes lead to erroneous palaeoecological interpretations. Like all archaeological documents, macrofossil plant assemblages come to us distorted by the taphonomic processes involved in the formation of sediment layers. The study of waterlogged plant macrofossils preserved in the wet sediments of an oxbow lake of the river Meuse (Autrecourt-et-Pourron, Ardennes, France) aims to analyze these taphonomic processes. This archaeobotanical study focusing on a river wall dated to the Preboreal period (11.7 ̵ 10.7 ka BP) allows establishing a taphonomic reference frame. We applied a correspondence analysis to establish links between criteria preservation and the analyzed sediment samples. We observed differences in preservation conditions depending on the stratigraphy and nature of the sediments. Before conducting archaeobotanical studies in natural contexts, an assessment of the taphonomic state of the retrieved plant macrofossils is highly recommended.