Flood and tides trigger longest measured sediment flow that accelerates for thousand kilometers into deep-sea

Here we document for the first time how major rivers connect directly to the deep-sea, by analysing the longest runout sediment flows (of any type) yet measured in action. These seafloor turbidity currents originated from the Congo River-mouth, with one flow travelling >1,130 km whilst accelerating from 5.2 to 8.0 m/s. In one year, these turbidity currents eroded 1-2 km3 of sediment from just one submarine canyon, equivalent to 14-28% of the annual global-flux from rivers. It was known earthquakes trigger canyon-flushing flows. We show major river-floods also generate canyon-flushing flows, primed by rapid sediment-accumulation at the river-mouth, but triggered by spring tides weeks to months after the flood. This is also the first field-confirmation that turbidity currents which erode can self-accelerate, thereby travelling much further. These observations explain highly-efficient organic carbon transfer, and have important implications for hazards to seabed cables, or how terrestrial climate change impacts the deep-sea.

Evaluation and Re-estimation of Instream Flow Considering the Water Quality and Aquatic Ecosystem of the Seomjingang River Watershed

In this study, the appropriateness of the current publicly announced and managed instream flow in the Seomjingang River watershed was evaluated based on the water quantity, water quality, and state of the aquatic ecosystem. The stream flow was evaluated based on the observed water flow rate at the Gurye-gun (Songjeong-ri) station that is the main point of the Seomjingang River flow management and located at the lowest downstream of the main stream of the Seomjingang River. Another important reason for choosing this station was that observational data from before the construction of the major dam to the present day were available. The water quality and aquatic ecosystem conditions were reviewed based on the data measured over the past 20 years, and the achievement ratio of instream flow was compared with that of stations in the other major river systems. Based on the evaluation result, the instream flow was re-estimated for the 11 important stations of the Seomjingang River and its two branches. Based on the currently permitted water use of the Seomjingang River, the amount of water required to supply for the instream flow deficit during dry seasons was predicted and presented as a reference for water management work.

Scratching the Surface(s): Examining the complexity of geological contexts for the Palaeolithic of the Sonar Basin, Madhya Pradesh

The Sonar River Valley is centrally located in Madhya Pradesh, flanked by rich Palaeolithic and fossiliferous localities in the Son and Narmada Valleys and has historically been overlooked in favour of the latter rivers, that tend to preserve well stratified Quaternary formations along varying portions of their length. Here an attempt is made to look at the Sonar basin through a broader lens, examining the various landforms found in the district of Damoh through which the Sonar flows before joining the Ken. The objective of this paper is threefold: to bring together the geomorphology of the area both in association with and as a result of fluvial action but also as a product of other geomorphic processes; to understand the consequence these processes have on the visibility of the prehistoric archaeological record within the region; and to look at this geoarchaeological relationship in the wider context of some of the major river basins in Madhya Pradesh, notably the Son and Narmada. Secondary sources on geology and geoarchaeology have been integrated with preliminary fieldwork in Districts Damoh and Narsinghpur, and to a smaller extent in Sagar, Chhatarpur and Panna. This work demonstrates the complexity of the South Asian Palaeolithic record that stretches beyond fluvial contexts, in turn helping to spatially expand our understanding of hominin behaviour beyond narrow riverine corridors.

Potential impacts of stratospheric aerosol injection on drought risk managements over major river basins in Africa

Most socio-economic activities in Africa depend on the continent’s river basins, but effectively managing drought risks over the basins in response to climate change remains a big challenge. While studies have shown that the stratospheric aerosol injection (SAI) intervention could mitigate temperature-related climate change impacts over Africa, there is a dearth of information on how the SAI intervention could influence drought characteristics and drought risk managements over the river basins. The present study thus examines the potential impacts of climate change and the SAI intervention on droughts and drought management over the major river basins in Africa. Multi-ensemble climate simulation datasets from the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) Project were analysed for the study. The Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) were used to characterize the upper and lower limits of future drought severity, respectively, over the basins. The SPEI is a function of rainfall and potential evapotranspiration, whereas the SPI is only a function of rainfall, so the difference between the two indices is influenced by atmospheric evaporative demand. The results of the study show that, while the SAI intervention, as simulated in GLENS, may offset the impacts of climate change on temperature and atmospheric evaporative demand, the level of SAI that compensates for temperature change would overcompensate for the impacts on precipitation and therefore impose a climate water balance deficit in the tropics. SAI would narrow the gaps between SPEI and SPI projections over the basins by reducing SPEI drought frequency through reduced temperature and atmospheric evaporative demand while increasing SPI drought frequency through reduced rainfall. The narrowing of this gap lowers the level of uncertainty regarding future changes in drought frequency, but nonetheless has implications for future drought management in the basins, because while SAI lowers the upper limit of the future drought stress, it also raises the lower limit of the drought stress.

Spatial distribution of arsenic in groundwater in the northwestern Hanoi

Arsenic contamination in groundwater is commonly found in alluvial plains of major river basins, in which the Red river delta has also been reported to be contaminated with high levels of arsenic. In this study, groundwater from 50 household wells was collected to study the spatial distribution of arsenic in northwestern Hanoi. The results showed that arsenic concentration in groundwater varied in a wide range of less than 5 to 334 μg/l, of which up 62% of the wells exceeded the WHO guideline value of 10 μg/l for arsenic content in drinking water. Arsenic groundwater in this area is unevenly distributed throughout the area, high arsenic concentrations are found in a narrow band between Red river and Day river. This pattern of arsenic distribution is strongly related to the sediment age, sedimentary processes, and it is also modified by local groundwater flow parts and the occurrence of hydraulic connection between aquifers, which are observed in the study area. Arsenic is released into the groundwater during the reductive dissolution of arsenic-bearing minerals under the presence of organic matter.

Spatial and Temporal Variations of Freezing and Thawing Indices From 1960 to 2020 in Mongolia

Mongolia is one of the most sensitive regions to climate change, located in the transition of several natural and permafrost zones. Long-term trends in air freezing and thawing indices can therefore enhance our understanding of climate change. This study focuses on changes of the spatiotemporal patterns in air freezing and thawing indices over Mongolia from 1960 to 2020, using observations at 30 meteorological stations. Our results shows that the freezing index ranges from −945.5 to −4,793.6°C day, while the thawing index ranges from 1,164.4 to 4,021.3°C day over Mongolia, and their spatial patterns clearly link to the latitude and altitude. During the study period, the trend in the thawing index (14.4°C-day per year) was larger than the trend in the freezing index (up to −10.1°C-day per year), which results in the net increase of air temperature by 2.4°C across Mongolia. Overall, the increase in the thawing index was larger in the low latitudes and altitudes (e.g., the Gobi-desert, steppes, the Great lake depression and major river valleys) than in high latitudes and altitudes (mountain regions), while it was the opposite for the freezing index. The highest values for both thawing index and freezing index (i.e. the least negative values) have occurred during the last 2 decades. As the trends in the freezing and thawing indices and mean annual air temperature confirm intensive climate warming, increased permafrost degradation and shallower seasonally frozen ground are expected throughout Mongolia.

MtDNA species-level phylogeny and delimitation support significantly underestimated diversity and endemism in the largest Neotropical cichlid genus (Cichlidae: Crenicichla)

Crenicichla is the largest and most widely distributed genus of Neotropical cichlids. Here, we analyze a mtDNA dataset comprising 681 specimens (including Teleocichla, a putative ingroup of Crenicichla) and 77 out of 105 presently recognized valid species (plus 10 out of 36 nominal synonyms plus over 50 putatively new species) from 129 locations in 31 major river drainages throughout the whole distribution of the genus in South America. Based on these data we make an inventory of diversity and highlight taxa and biogeographic areas worthy of further sampling effort and conservation protection. Using three methods of molecular species delimitation, we find between 126 and 168 species-like clusters, i.e., an average increase of species diversity of 65–121% with a range of increase between species groups. The increase ranges from 0% in the Missioneira and Macrophthama groups, through 25–40% (Lacustris group), 50–87% (Reticulata group, Teleocichla), 68–168% (Saxatilis group), 125–200% (Wallacii group), and 158–241% in the Lugubris group. We found a high degree of congruence between clusters derived from the three used methods of species delimitation. Overall, our results recognize substantially underestimated diversity in Crenicichla including Teleocichla. Most of the newly delimited putative species are from the Amazon-Orinoco-Guiana (AOG) core area (Greater Amazonia) of the Neotropical region, especially from the Brazilian and Guiana shield areas of which the former is under the largest threat and largest degree of environmental degradation of all the Amazon.

Identifying the World’s Most At-Risk River Basins

Major river basins around the world, including the Amazon, may be hot spots for ecological shifts as the planet warms.