Major River Systems Research Articles

Brown watersnakes (Nerodia taxispilota) as bioindicators of mercury contamination in a riverine system

Mercury (Hg) is a contaminant that enters the environment through natural or anthropogenic means. Ecological risk assessments have examined Hg bioaccumulation and effects in many taxa, but little is known about Hg dynamics in reptiles, or their potential use as bioindicator species for monitoring Hg in aquatic systems. Numerous snake species, like North American watersnakes (Nerodia spp.), are piscivorous and are exposed to Hg through their diet. The purpose of this study was to identify factors associated with Hg accumulation in a common watersnake species and compare Hg concentrations of the snakes to those in fish occupying the same habitats. To this end, we sampled brown watersnakes (Nerodia taxispilota) from the Savannah River, a major river system in the southeastern U.S., and compared N. taxispilota Hg accumulation trends to those of bass (Micropterus salmoides), catfish (Ictalurus and Ameiurus spp.), and panfish (Lepomis and Pomoxis spp.) collected from the same reach. Total Hg (THg) in N. taxispilota tail tips ranged from 0.020 to 0.431 mg/kg (wet weight; mean: 0.104 ± 0.008). Snake tail THg was significantly correlated with blood THg, which ranged from 0.003 to 1.140 mg/kg (0.154 ± 0.019). Snake size and site of capture were significantly associated with tail THg. Snake tail THg increased at sites along and downstream of the area of historic Hg pollution, consistent with fish THg. Snake muscle THg was predicted based on tail THg and ranged from 0.095 to 1.160 (0.352 ± 0.022). To gauge Hg biomagnification in N. taxispilota, we compared predicted snake muscle THg concentrations to THg in fish of consumable size. Average biomagnification factors for THg in N. taxispilota were 3.1 (panfish) and 5.4 (catfish), demonstrating N. taxispilota likely biomagnify Hg through their diet. These results reveal N. taxispilota to be an effective bioindicator species for monitoring Hg in aquatic environments.

Systematics of a Neotropical clade of dead-leaf-foraging antwrens (Aves: Thamnophilidae; Epinecrophylla)

The stipple-throated antwrens of the genus Epinecrophylla (Aves: Thamnophilidae) are represented by eight species primarily found in the lowlands of the Amazon Basin and the Guiana Shield. The genus has a long and convoluted taxonomic history, with many attempts made to address the taxonomy and systematics of the group. Here we employ massively parallel sequencing of thousands of ultraconserved elements (UCEs) to provide both the most comprehensive subspecies-level phylogeny of Epinecrophylla antwrens and the first population-level genetic analyses for most species in the genus. Most of our results are robust to a diversity of phylogenetic and population genetic methods, but we show that even with thousands of loci we are unable to fully resolve the relationships between some western Amazonian species in the haematonota group. We uncovered phylogenetic relationships between taxa and patterns of population structure that are discordant with both morphology and current taxonomy. For example, we found deep genetic breaks between taxa in the ornata group that are currently regarded as species, and in the haematonota and leucophthalma groups we found paraphyly at the species and subspecies levels, respectively. As has been found in many Amazonian taxa, our phylogenetic results show that the major river systems of the Amazon Basin appear to have an effect on the genetic structure and range limits within Epinecrophylla. Our population genetics analyses showed extensive admixture between some taxa despite their deep genetic divergence. We present a revised taxonomy for the group and suggest areas for further study.

Assessment of Morpho-Dynamics through Geospatial Techniques within the Padma-Meghna and Ganges-Jamuna River Confluences, Bangladesh

Bangladesh is a low-lying riverine country with the mighty Ganges–Brahmaputra–Meghna (GBM) major river system including their abundant tributaries and distributaries. Land erosion–accretion is a very common phenomenon in this riverine country. This process extensively erodes huge productive landmasses at the river confluence zones every year. The main objective of this study was to understand the confluence morpho-dynamics and identify the vulnerable areas near the Padma–Meghna Confluence (PMC) and Ganges–Jamuna confluence (GJC) due to confluence shifting and erosion–accretion phenomenon of those rivers. The present study utilized multi-temporal Landsat satellite images from 1972 to 2019 approximately ten years of interval. Results showed that the PMC indicated frequent variation in migration trend towards NW from 1972 to 1980, SE from 1980 to 2010, and then reversed towards NW direction from 2010 to 2019. On the other hand, the GJC confluence point moved NW direction (2.37 km) from the year 1972 to 1980, but from 1980 to 2019, the confluence shifted towards the SE direction. Due to the migration dynamics, huge changes happened in width and sand bars area of both confluences. In PMC, confluence width increased remarkably indicating erosive flow during 1972–1980, then progressively shortened up to 2019, indicating accretion. In contrast, GJC shows a significant accretional trend over the 47 years. The sand bar area of the PMC increased about 147.09 km2 throughout the study period. But, GJC shows an opposite scenario where the total sand bar area decreased about 51.02 km2 in the same period. From the vulnerability study of erosion–accretion scenarios, it is predicted that Paturia Ferry Ghat area, Aricha Ferry Ghat area, Arua, Baruria, Dashkin Saljana, Bhadiakola, Masundia, Khanganj and Nyakandi areas near GJC and Chandpur sadar, Srimandi, Sakhua, Bilaspur and char Atra near PMC are highly vulnerable zones. The outputs of the study will enable policy makers to take necessary measures to reduce the erosional severity on both confluence zones and could also provide a basis for proper land management.

Differential changes in precipitation and runoff discharge during 1958–2017 in the headwater region of Yellow River of China

Maintenance of steady streamflow is a critical attribute of the continental river systems for safeguarding downstream ecosystems and agricultural production. Global climate change imposes a potential risk to water supply from the headwater by changing the magnitude and frequency of precipitation and evapotranspiration in the region. To determine if and to what extent the recent climate changes affected streamflow in major river systems, we examined the pattern of temporal variations in precipitation, temperature, evapotranspiration and changes in runoff discharge during 1958–2017 in the headwater region of the Yellow River in northeastern Tibetan Plateau. We identified 1989 as the turning point for a statistically significant 14% reduction in streamflow discharge (P < 0.05) for the period 1989–2017 compared with 1958–1988, approximately coinciding with changes in the monthly distribution but not the interannual variations of precipitation, and detected a mismatch between precipitation and runoff after 2000. Both annual precipitation and runoff discharge displayed four- and eight-year cyclic patterns of changes for the period 1958–1988, and a six-year cyclic pattern of changes for the period 1989–2017, with two intensified two-year cyclic patterns in the changes of precipitation and a three-year cyclic pattern in the change of runoff further detected for the later period. Our results indicate that the temporal changes in runoff are not strictly consistent with the temporal variations of precipitation in the headwater region of Yellow River during the period 1958–2017. In particular, a full recovery in annual precipitation was not reflected in a full recovery in runoff toward the end of the study period. While a review of literature yielded no apparent evidence of raised evapotranspiration in the region due to recent warming, we draw attention to increased local retention of rainwater as a possible explanation of differential changes in precipitation and runoff.

The use of sedimentary metal data in predictive modelling of estuarine contamination, assessment of environmental condition and pollutant source identification (Narrabeen Lagoon, Sydney, Australia).

Narrabeen Lagoon is recognized as an Intermittently Closed and Open Lake or Lagoon (ICOLL) and is the largest coastal lagoon (2.2km2) in the Sydney metropolitan region. The catchment (53km2) supports five major river systems, and land use comprises of 56% residential, 42% parkland and 2% light industry, commercial, hospital and education. An initial screening environmental assessment was undertaken using sedimentary metals to determine the magnitude of anthropogenic change and level of ecological risk posed by these contaminants. Results illustrated an unusual example of an estuary significantly influenced by human-induced change, but exhibiting minimal ecological risk. This anomaly was due to high anthropogenic metal concentrations in the fine fraction of surficial sediment, which was considerably diluted by abundant metal-poor coarse material resulting in reduced adverse ecological impact for total sediment. Predictive modelling to 2020 suggested that Pb concentrations will decline and Cu and Zn levels will increase slightly. Modelling of river discharge and analyses of fluvial sedimentary metals suggested stormwater derived from the most urbanized catchments and a major roadway combined with poor flushing explained surficial sediment metal distributions in the lagoon.

First description of neonate Batagur trivittata (Testudines: Geoemydidae).

The Burmese Roofed Turtle (Batagur trivittata Duméril Bibron, 1835) is a large (straight-line carapace length [CL] to 620 mm; Platt et al., 2019), aquatic, herbivorous turtle endemic to the major river systems of Myanmar (Smith 1931; TTWG 2017). Although historically widespread and apparently abundant, long-term population declines resulted from chronic egg collecting, subsistence harvesting of adults, and loss of critical nesting habitat (Platt et al. 2017a). By the late 1990s B. trivittata was considered a candidate for Extinct status (Bhupathy et al. 2000) until a living specimen purchased in a Chinese wildlife market came into the possession of an American turtle collector in the early 2000s (Platt et al. 2005; W.P. McCord, pers. comm.). Shortly thereafter, field surveys "rediscovered" two remnant populations in the Dokhtawady and upper Chindwin Rivers (Platt et al. 2005; Kuchling et al. 2006). Intense ex- and in-situ recovery efforts were launched shortly thereafter and continue today (Kuchling Tint Lwin 2004; Çilingir et al. 2017).

Spatiotemporal Changes of Riverbed and Surrounding Environment in Yongding River (Beijing section) in the Past 40 Years

Abstract Yongding River is one of the five major river systems in Beijing. It is located to the west of Beijing. It has influenced culture along its basin. The river supports both rural and urban areas. Furthermore, it influences economic development, water conservation, and the natural environment. However, during the past few decades, due to the combined effect of increasing population and economic activities, a series of changes have led to problems such as the reduction in water volume and the exposure of the riverbed. In this study, remote sensing images were used to derive land cover maps and compare spatiotemporal changes during the past 40 years. As a result, the following data were found: forest changed least; cropland area increased to a large extent; bareland area was reduced by a maximum of 63%; surface water area in the study area was lower from 1989 to 1999 because of the excessive use of water in human activities, but it increased by 92% from 2010 to 2018 as awareness about protecting the environment arose; there was a small increase in the built-up area, but this was more planned. These results reveal that water conservancy construction, agroforestry activities, and increasing urbanization have a great impact on the surrounding environment of the Yongding River (Beijing section). This study discusses in detail how the current situation can be attributed to of human activities, policies, economic development, and ecological conservation Furthermore, it suggests improvement by strengthening the governance of the riverbed and the riverside. These results and discussion can be a reference and provide decision support for the management of southwest Beijing or similar river basins in peri-urban areas.

Comammox Nitrospira within the Yangtze River continuum: community, biogeography, and ecological drivers

The recent discovery of comammox Nitrospira as complete nitrifiers has fundamentally renewed perceptions of nitrogen cycling in natural and engineered systems, yet little is known about the environmental controls on these newly recognized bacteria. Based on improved phylogenetic resolution through successful assembly of ten novel genomes (71–96% completeness), we provided the first biogeographic patterns for planktonic and benthic comammox Nitrospira in the Yangtze River over a 6030 km continuum. Our study revealed the widespread distributions and relative abundance of comammox Nitrospira in this large freshwater system, constituting 30 and 46% of ammonia-oxidizing prokaryotes (AOPs) and displaying 30.4- and 17.9-fold greater abundances than canonical Nitrospira representatives in water and sediments, respectively. Comammox Nitrospira contributed more to nitrifier abundances (34–87% of AOPs) in typical oligotrophic environments with a higher pH and lower temperature, particularly in the plateau (clade B), mountain and foothill (clade A) areas of the upper reach. The dominant position of planktonic comammox Nitrospira was replaced by canonical Nitrospira sublineages I/II and ammonia-oxidizing bacteria from the plateau to downstream plain due to environmental selection, while the dissimilarity of benthic comammox Nitrospira was moderately associated with geographic distance. A substantial decrease (83%) in benthic comammox Nitrospira abundance occurred immediately downstream of the Three Gorges Dam, consistent with a similarly considerable decrease in overall sediment bacterial taxa. Together, this study highlights the previously unrecognized dominance of comammox Nitrospira in major river systems and underlines the importance of revisiting the distributions of and controls on nitrification processes within global freshwater environments.

Analysis and Prevention of Urban River Pollution

According to the principle of “nearby discharge” of waste-water treatment, with the progress of industry, the amount of pollutants discharged into urban rivers keeps increasing. Under the requirements of limited river pollution and environmental carrying capacity, the pollution situation of urban rivers needs to be explored and the ways of pollution control need to be explored. At present, most of China’s rivers are polluted, and none of the seven major river systems has been spared. The pollution sources of urban rivers include industrial pollution sources, domestic pollution sources, agricultural pollution sources, oil tankers and other pollution sources. The pollutants in urban rivers include organic pollutants, inorganic pollutants, plant nutrients and heavy metals in water. Pollution prevention and control measures of urban rivers: pollution source control, adhere to the income reduction; physical method, chemical method, biology - ecological method. In a water basin of Guangdong province as an example, some indexes because of pollution in urban river “surface water environment quality standard GB 3838-2002” V class level, basic use as mentioned in the measures for prevention and control of pollution of rivers.

Moving beyond the riverine barrier vicariant paradigm.

One of the main goals of evolutionary biology is to understand the processes behind current patterns of biodiversity. Shared geographic distributions among unrelated species may result from a common history, providing a unique opportunity to assess the evolution of the landscape and the origins of biodiversity. Until recently, vicariance prevailed as the main evolutionary model to be tested, and the riverine barrier hypothesis the null model for taxa with river-bounded distributions. In recent years, however, multispecies comparative approaches have unveiled idiosyncratic scenarios among codistributed species, suggesting that rivers may or may not play a role in the speciation process. In a From the Cover article in this issue of Molecular Ecology, Kopuchian et al. (2020) explore predictions of the riverine barrier hypothesis in a major subtropical river system, evaluating the degree of mitochondrial and nuclear genomic differentiation in seven bird species with allegedly morphological differentiation across the Paraná-Paraguay river system. The authors show that in only one case, the genetic differentiation was concordant with the river. Interestingly, pairs presented disparate divergence times and/or distinct demographic histories. In most cases, putative contact zones broadly coincided with the transition of different ecoregions, such as the Espinal/Chaco ecological ecotone. These findings argue against the role of the Paraná-Paraguay river system as a major biogeographic barrier and highlight the need to explore the role of ecology in species diversification. Here, we feature different perspectives for studying the processes governing species divergence and suggest a basic protocol to advance the study of riverine barriers.

The sedimentological evolution and petroleum potential of a very thick Upper Cretaceous marine mudstone succession from the southern high latitudes—a case study from the Bight Basin, Australia

During IODP Expedition 369, a 690 m thick succession of silty claystone spanning the early Turonian to the late Santonian was encountered at Site U1512 in the Bight Basin, offshore southern Australia. Stacking patterns, sedimentary facies and palynological assemblages reveal that the succession was rapidly deposited with hyperpycnal and hypopycnal flows in a marine prodelta setting, which was subject to basin restriction. The dominance of clay-rich facies and phytoclasts in the succession was likely the result of a major river system delivering a high sediment load into the Bight Basin when a warm, wet climate prevailed. A combination of high sedimentation rates (19–272 m/Myr) and accelerated subsidence prevented the delta from rapidly prograding into more distal regions of the basin. The complete Turonian to Santonian mudstone succession yields low total organic carbon (~1 wt%) and Type IV kerogens. However, palynofacies assemblages become progressively marine in character and total organic carbon values vary between 1 and 1.5 wt% with depth. This may indicate that the base of the hole at Site U1512 was close to potential organic-rich black shales associated with Ocean Anoxic Event 2. Low amplitude and irregular reflections on seismic data and disparities between biostratigraphic zonations suggest the upper 350 m of the Turonian to Santonian succession may represent a mass movement that happened during the Pleistocene. This study reveals that Site U1512 material likely represents a near-stratigraphically complete marine mudstone succession from high paleolatitudes, as well as the only depositional record that was fully cored from the Bight Basin.

Temperate freshwater soundscapes: A cacophony of undescribed biological sounds now threatened by anthropogenic noise.

The soundscape composition of temperate freshwater habitats is poorly understood. Our goal was to document the occurrence of biological and anthropogenic sounds in freshwater habitats over a large (46,000 km2) area along the geographic corridors of five major river systems in North America (Connecticut, Kennebec, Merrimack, Presumpscot, and Saco). The underwater soundscape was sampled in 19 lakes, 17 ponds, 20 rivers and 20 streams, brooks and creeks that were grouped into broad categories (brook/creek, pond/lake, and river). Over 7,000 sounds were measured from 2,750 minutes of recording in 173 locations over a five-week period in the spring of 2008. Sounds were classified into major anthropophony (airplane, boat, traffic, train and other noise) and biophony (fish air movement, also known as air passage, other fish, insect-like, bird, and other biological) categories. The three most significant findings in this study are: 1) freshwater habitats in the New England region of North America contain a diverse array of unidentified biological sounds; 2) fish air movement sounds constitute a previously unrecognized important component of the freshwater soundscape, occurring at more locations (39%) and in equal abundance than other fish sounds; and 3) anthropogenic noises dominate the soundscape accounting for 92% of the soundscape by relative percent time. The high potential for negative impacts of the anthropophony on freshwater soundscapes is suggested by the spectral and temporal overlap of the anthropophony with the biophony, the higher received sound levels of the anthropophony relative to the biophony, and observations of a significant decline in the occurrence, number, percent time, and diversity of the biophony among locations with higher ambient received levels. Our poor understanding of the biophony of freshwater ecosystems, together with an apparent high temporal exposure to anthropogenic noise across all habitats, suggest a critical need for studies aimed at identification of biophonic sound sources and assessment of potential threats from anthropogenic noises.

Phylogeography, genetic diversity, and population structure of Nile crocodile populations at the fringes of the southern African distribution.

Nile crocodiles are apex predators widely distributed in sub-Saharan Africa that have been viewed and managed as a single species. A complex picture of broad and fine-scale phylogeographic patterns that includes the recognition of two species (Crocodylus niloticus and Crocodylus suchus), and the structuring of populations according to river basins has started to emerge. However, previous studies surveyed a limited number of samples and geographical regions, and large areas of the continent remained unstudied. This work aimed at a fine scale portrait of Nile crocodile populations at the fringes of their geographic distribution in southern Africa. Wild and captive individuals were sampled across four major river systems (Okavango, Lower Kunene, Lower Shire and Limpopo) and the KwaZulu-Natal region. A multi-marker approach was used to infer phylogeographic and genetic diversity patterns, including new and public mitochondrial data, and a panel of 11 nuclear microsatellites. All individuals belonged to a phylogenetic clade previously associated with the C. niloticus species, thus suggesting the absence of C. suchus in southern Africa. The distribution of mitochondrial haplotypes indicated ancestral genetic connectivity across large areas, with loss of diversity along the north-south axis. Genetic variation partitioned the populations primarily into western and eastern regions of southern Africa, and secondarily into the major river systems. Populations were partitioned into five main groups corresponding to the Lower Kunene, the Okavango, the Lower Shire, and the Limpopo rivers, and the KwaZulu-Natal coastal region. All groups show evidence of recent bottlenecks and small effective population sizes. Long-term genetic diversity is likely to be compromised, raising conservation concern. These results emphasize the need for local genetic assessment of wild populations of Nile crocodiles to inform strategies for management of the species in southern Africa.

High prevalence of non-native fish species in a remote region of the Mamberamo River, Indonesia

Indonesian freshwater fish diversity is threatened by human activities such as logging, land clearing, pollution and introduction of non-native species. The latter may pose serious threats to endemic freshwater fauna even in relatively pristine and isolated habitats. One such area, West Papua in the island of New Guinea, is one of the least studied regions in the world and a biodiversity hotspot. The Mamberamo River contains the highest proportion of non-native fish compared to other major river systems in New Guinea. To document this, we conducted a field study to validate and further temporally characterise the fish biodiversity to ascertain its current status. Since the last ichthyological survey 15 years ago, we detected two additional non-native species (Leptobarbus melanopterus and Oreochromis niloticus) that have established in the river system. Moreover, our survey revealed that non-native fish are extremely common in the mid reaches of the Mamberamo River, comprising 74% of total catch, with non-native Barbonymus gonionotus (family Cyprinidae) now established as the dominant species. The biomass of non-native B. gonionotus now exceeds that of all native fish combined in the main river channel. These results highlight the serious threat of invasive species in remote regions that support high levels of endemic biodiversity. Plans for containment, prevention through education programmes, and management are urgently required.

A Study on the Distribution and Utilization of Recreational Resources Along the Grand Canal Culture Belt

With the construction of Grand Canal Culture Belt being upgraded to a national strategy, the authors used GIS and other analytical techniques to give an overview of 2,834 recreational resource points distributed in 49 prefecture-level administrative units of eight provinces or cities along the Grand Canal Culture Belt, analyzed the features of their quantitative and spatial distribution, finding that: (i) the recreational resources along the Grand Canal are spatially related to the major river systems, lakes and arteries of communication; (ii) the recreational resources along the Grand Canal are generally distinguished by a spatial agglomeration of “two poles and two sub-centers”, in which the natural recreational resources are distributed in the pattern of “three points and one line” while the cultural recreational resources are distributed with a notable feature of polarization. On that basis, the authors proposed several suggestions about the utilization of recreational resources along the Grand Canal Culture Belt: (i) Establishing a system of diversified recreational products by adapting to local conditions; (ii) building national scenic byways along the Grand Canal by relying on major river systems and arteries of communication; (iii) giving priority to the development of four recreational sections of the Grand Canal and foster core growth poles.

Dilution and propagation of provenance trends in sand and mud: Geochemistry and detrital zircon geochronology of modern sediment from central California (U.S.A.)

Integrated, multi-method provenance studies of siliciclastic sedimentary deposits are increasingly used to reconstruct the history of source-to-sink transport, paleogeography, and tectonics. Invariably, analysis of large-scale depositional systems must confront issues regarding how to best sample the system and adequately cope with the details of sediment mixing. Potential biases including variations in grain size, sediment flux, and mineral concentration may cause provenance tracking tools to misrepresent the contributions of source-areas that contribute to large drainage networks. We have acquired U-Pb detrital zircon data from modern sand and whole-rock geochemistry from mud sampled from the Sacramento-San Joaquin drainage of central California to elucidate conditions that can skew provenance trends along the course of a major river system. This drainage network is fed by headwaters that tap the Mesozoic pluton-dominated southern Sierra Nevada, the Paleozoic-Mesozoic wallrock and volcanic-dominated northern Sierra Nevada, the ultramafic-dominated eastern Klamath Mountains, and the intermediate to mafic Cascades volcanic arc. Analysis of the results indicates that detrital zircon provenance trends effectively record source variations for the southern, granite-dominated portion of the drainage network where contrasts in lithology and inferred zircon fertility are relatively minor. In these circumstances, mixture modeling of U-Pb detrital zircon data calibrated with a measure of zircon fertility approximates relative sediment flux contributed by individual drainages. Alternatively, in the northern parts of the system, source regions underlain by ultramafic and/or volcanic rocks are poorly represented, or entirely missing, in downstream detrital zircon records. In some cases, mud geochemistry data more faithfully represent sediment provenance trends. Sampling performed at the confluence of the Sacramento, American, Mokelumne, and San Joaquin Rivers within the Sacramento-San Joaquin Delta region yields a detrital zircon age distribution that is indistinguishable from that of an independently established database of Sierra Nevada batholith crystallization ages. However, when the combined river flows along a recently established passage to the Pacific through the San Francisco Bay region, dredged sediment is found to be significantly contaminated by locally eroded material from the Franciscan Complex and other rocks that crop out within the Coast Ranges. Large variation of Zr concentrations measured throughout the Bay area document that significant hydrodynamic fractionation impacts sediment delivery through this segment of the system. The more Sierra Nevada-like detrital zircon age distribution yielded by a piston-core sample from the continental slope may be explained by either early-stage unroofing of the Coast Ranges or more efficient sand delivery from the delta to the Pacific by a free-flowing river driven by a low stand in sea level.

Impact of hydraulic sorting and weathering on mica provenance studies: An example from the Yangtze River

Detrital muscovite and biotite 40Ar/39Ar analyses are useful tools for studying regional tectonic histories, sediment provenances and paleo-drainage reconstructions. During transport and recycling of detrital micas physical and chemical weathering occurs. This process effects the grain size and age populations ultimately found in river sediments, but is often ignored in provenance studies. Here, we present detrital muscovite and biotite 40Ar/39Ar results of 15 modern sediments from the Yangtze River to address the impact of grainsize on provenance age populations. The beam intensities of 39Ar, formed from 39K by neutron capture reaction during sample irradiation, have been used as an index for grain size. We found that relatively older detrital mica ages of the Yangtze River are often characterized by small 39Ar signals (i.e., grain sizes), and large grain sizes correspond to younger grains. This observation is also revealed by reanalysis of previously reported detrital mica studies in other major river systems (Red and Brahmaputra rivers) and sediments (Scotian Basin, Canada and Antarctic) and probably results from physical and chemical weathering during transport and recycling. Our Yangtze results indicate that detrital muscovite and biotite ages of grainsize ranging from 100 to 1000 μm cover all age components as identified in all dated grains (with a size of >100 μm), and thus indicate that detrital mica 40Ar/39Ar analyses should include also small grains from >100 μm to reduce the effects of hydraulic sorting and weathering. Grainsizes smaller than 100 μm have not been tested in this study, but will be more difficult to date due to both smaller beam intensities and possible recoil effects.

Sixty years since the creation of Lake Kariba: Thermal and oxygen dynamics in the riverine and lacustrine sub-basins.

The current boom of dam construction at low latitudes endangers the integrity and function of major tropical river systems. A deeper understanding of the physical and chemical functioning of tropical reservoirs is essential to mitigate dam-related impacts. However, the development of predictive tools is hampered by a lack of consistent data on physical mixing and biogeochemistry of tropical reservoirs. In this study, we focus on Lake Kariba (Southern Africa), the largest artificial lake in the world by volume. Kariba Dam forms a transboundary reservoir between Zambia and Zimbabwe, and therefore its management represents a socio-politically sensitive issue because the Kariba Dam operation completely changed the downstream hydrological regime. Although Lake Kariba represents a unique and scientifically interesting case study, there is no consistent dataset documenting its physical and chemical behaviour over time. This limits the scope for quantitative studies of this reservoir and its downstream impacts. To address this research gap, we aggregated a consistent database of in situ measurements of temperature and oxygen depth profiles for the entire 60 years of Lake Kariba’s lifetime and performed a detailed statistical analysis of the thermal and oxygen regime of the artificial lake to classify the different behaviours of the lake’s sub-basins. We demonstrate that the seasonal stratification strongly depends on the depth of the water column and on the distance from the lake inflow. Satellite data confirm these spatiotemporal variations in surface temperature, and reveal a consistent longitudinal warming trend of the lake surface water temperature of about 1.5°C from the inflow to the dam. Finally, our results suggest that the stratification dynamics of the lacustrine sub-basins have the potential to alter the downstream Zambezi water quality. Future research should focus on assessing such alterations and developing strategies to mitigate them.

Cryptic species and co‐diversification in sand scorpions from the Karakum and Kyzylkum deserts of Central Asia

AbstractLittle is known about species diversification within the deserts of Central Asia. For example, the degree of lineage divergence and timing of population differentiation, as well as potential biogeographic barriers driving diversification, are nearly unknown. Here, we analysed a multi‐locus data set for a widespread sand scorpion (Mesobuthus gorelovi) to evaluate cryptic species diversity and phylogeographic patterns across the Karakum and Kyzylkum deserts. We also combined these data with previously published sequence data to test for a signal of co‐diversification. A consensus species delimitation approach indicated that the widespread M. gorelovi is likely composed of up to five distinct species that began to diversify at the Miocene–Pliocene boundary. We observed shared patterns of lineage divergence across the Amu Darya River region in three scorpion taxa and found support for a shared history of assemblage diversification across this biogeographic barrier. Thus, major river systems appear to facilitate diversification among desert scorpions.

Evaluation of Bacteriological Quality Characteristics of Drinking Waters of few Village Sources in Coastal Areas of Bhimavaram region at West Godavari District, India

The essential requirement for human life to exist is water. After to the air, the other It has in various sources such as canals, ponds, rivers, lake, streams, reservoirs and etc. human settlers on the banks of major river systems at the earliest and has need water for drinking, bathing, cooking, laundering, and many more. But with the advancement of civilization the demand of water supply grately increased and now has such a stage to come that without well organized public water supply scheme, it is not possible to move the present human life and the develop the towns. Earlier has importance on quantity. And now today importance of quality comes to be recognized gradually in the later days. In this present study, numbers of water samples were collected various water supply schemes from 20 villages of bhimavaram region, West Godavari district, Andhra Pradesh. The drinking water samples are analyze its biological quality and it was found that some of the samples in the study area are exceeds or above the standard limit or permissible limit. On over all based on biological quality few drinking water sources located in and around different areas of Bhimavaram was seriously polluted by harmful bacteria and must need few treatment methods. So that need of attention not to use of supplied water and need to give suggestions and remedial measures to concerned local authorities of various disinfection treatment technologies or control measure to make supplied water free from pathogenic Bactria. Quality Assessment of drinking water from various sources (S Malhotra, S.K., Sndhu (2015), especially bacteriological quality should be periodically planned regularly to avoid and control waterborne diseases