Major River Systems Research Articles

Increased Mercury and Reduced Insect Diversity in Linked Stream-Riparian Food Webs Downstream of a Historical Mercury Mine.

Historical mining left a legacy of abandoned mines and waste rock in remote headwaters of major river systems in the western United States. Understanding the influence of these legacy mines on culturally and ecologically important downstream ecosystems is not always straightforward because of elevated natural levels of mineralization in mining-impacted watersheds. To test the ecological effects of historic mining in the headwaters of the upper Salmon River watershed in Idaho (USA), we measured multiple community and chemical endpoints in downstream linked aquatic-terrestrial food webs. Mining inputs impacted downstream food webs through increased mercury accumulation and decreased insect biodiversity. Total mercury (THg) in seston, aquatic insect larvae, adult aquatic insects, riparian spiders, and fish at sites up to 7.6 km downstream of mining was found at much higher concentrations (1.3-11.3-fold) and was isotopically distinct compared with sites immediately upstream of mining inputs. Methylmercury concentrations in bull trout and riparian spiders were sufficiently high (732-918 and 347-1140 ng MeHg g-1 dry wt, respectively) to affect humans, birds, and piscivorous fish. Furthermore, the alpha-diversity of benthic insects was locally depressed by 12%-20% within 4.3-5.7 km downstream from the mine. However, because total insect biomass was not affected by mine inputs, the mass of mercury in benthic insects at a site (i.e., ng Hg m-2 ) was extremely elevated downstream (10-1778-fold) compared with directly upstream of mining inputs. Downstream adult aquatic insect-mediated fluxes of THg were also high (~16 ng THg m-2 day-1 ). Abandoned mines can have ecologically important effects on downstream communities, including reduced biodiversity and increased mercury flux to higher order consumers, including fish, birds, and humans. Environ Toxicol Chem 2022;41:1696-1710. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

A late 2nd/early 1st millennium BC interaction arc between Mainland Southeast Asia and Southwest China: Archaeometallurgical data from Hebosuo and Shangxihe, Yunnan

In this paper we use archaeometallurgical data from the Yunnanese Bronze Age sites of Hebosuo and Shangxihi, to examine the nature of early exchange networks within Yunnan, across southern China and into Mainland Southeast Asia (MSEA). Traditional perspectives on relations between China and MSEA were viewed from a Core-Periphery (C–P) perspective, derived from World Systems Theory (WST) but this area, though now divided by national borders, has shared ecological and cultural characteristics that allow its definition as the Southeast Asian Massif (SAM).The fourteen analysed samples were all unleaded copper or bronze, mostly as-cast and with some annealing. Their lead isotope signatures did not group at site level but showed broad consistency with the other, limited, signatures available from Yunnan, Sichuan and Guangxi. Critically, comparison with MSEA signatures revealed good isotopic consistency with key Bronze Age sites in Thailand, Myanmar and Vietnam, active within tight timeframes, and mostly lying on or near the path of major river systems that find their source in or via Yunnan. The picture we propose, based on current data, is one of a complex network of autochthonous SAM societies interacting at short (ca. 50 km), medium (ca. 300 km) and long (ca. 800–1600 km) ranges over mountainous and forested terrain.

Geographical Description of Kumadugu-Yobe River Basin of West Africa

Kumadugu-Yobe river basin is located in African sub-region within the boundary of Nigeria and Niger republic. The basin is drained by two major river systems; river Yobe and kumadugu gana. The Two major rivers empty their waters into Lake Chad. The basin falls within three major climatic belts, namely: the guinea savannah at the water head; Sudan at mid-stream and Sahel at downstream. The rainfall pattern varies from over 1200mm at the Jos plateau water head to less 400mm at downstream. The basin constitutes only 6% of the Lake Chad basin but accommodating more than 55% of the basin’s population and also providing livelihood means to over 15 million people, particularly farmers, pastoralists and fishermen. However series of impediments has been altering with hydrology of basin following the sahelian drought of 1970s and 1980s. The basin ecosystem is vital to not only the local population but to global community at large. The hadejia-Nguru wetlands of basin is the key host to wintering migratory birds from Europe and also one of the Ramsar wetland site of international importance.

Water Pollution Control Policies and Laws in China and Suggestions for Vietnam

Water is an indispensable part of our environment. China is facing a serious water pollution situation. In order to reduce water pollution, China has implemented a wide range of policies to reduce and control water pollution. Vietnam is a country with remarkable similarities with China in terms of political institutions as well as economic development. Notably, two major river systems of Vietnam, the Red River and the Mekong River both originate from China and directly affect the water environment in Vietnam. Thus, the evaluation of China's water pollution control policies will provide helpful experiences and lessons to improve Vietnam’s policies and law on water pollution control.

A first calibration of culturable bacterial diversity and their dual resistance to heavy metals and antibiotics along altitudinal zonation of the Teesta River.

Culturable bacterial diversity and co-occurrence of heavy metal and antibiotic resistance were investigated from the water and sediments along the course of the Teesta River, in the Eastern Himalayas. Water and sediment samples collected from six sampling points during the monsoon and winter seasons were subjected to analysis of physico-chemical parameters, heavy metal contamination and antibiotic tolerance. The culturable bacterial diversity established by application of bacterial culture and 16S rRNA gene sequencing, ascertained the majority belonged to Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes and Deinococcus-Thermus. Among the 5 phyla, Proteobacteria and Actinobacteria were the dominant phyla present in both water and sediment samples, whereas Bacteroidetes, Firmicutes and Deinococcus-Thermus were unique to particular sites. The Shannon index indicated that the bacterial richness was more in the water column as compared to sediment. From the total of 245 isolates, 69 genera were identified. Heavy metal tolerance and antibiotic resistance profiles showed some isolates to be tolerant to high levels of heavy metals and multiple antibiotics indicating a major concern in terms of river ecosystem serving as a pool for dissemination of such resistant genes. The antibiotic resistance and heavy metal contamination diversified along the human-impacted downstream sites, endorsing the contribution of anthropogenic factors. The present report on bacterial diversity and the associated metal and antibiotics tolerance among bacteria is the first of its kind on Teesta River, the only major river system flowing through the state of Sikkim and parts of North Bengal.

Assessing the Invasion Risk of Humulus scandens Using Ensemble Species Distribution Modeling and Habitat Connectivity Analysis.

Given the rapid spread of invasive alien plant species in Europe and limited information regarding their distribution and dispersion patterns, we analyzed the invasive risk of Humulus scandens, a species with an increased invasive potential. We collected occurrence records from Romania within an EU funded project and literature data, in order to perform an ensemble distribution model. Environmental variables varied from downscaled topoclimatic continuous entries to categorical ones, such as soil class, texture, or land use. Results showed potential core areas of the species within the study region. By inverting the probability output of the models, we have created a resistance surface which helped us model its dispersion patterns. Further, we assessed the probability of invasion for each resulted corridor using the species dispersion ecology and created an invasion risk map. H. scandens is highly influenced by milder climates and areas with constant flooding events, thus we found that the Tisa basin and its tributaries can be under a high invasion risk, spreading through the entire catchment, in Central, Western, and Northern Romania, towards the Eastern Carpathians. The Danube acted as a dispersion corridor for major river systems in southern Romania, but the dispersion capability of the species dropped in steppe areas with higher aridity and limited water course network. This approach is useful for creating adequate action plans in relation to invasive alien plant species, and should urgently be regarded, as results show a potentially large distribution of H. scandens across entire water catchment areas, with devastating effects on natural ecosystems.

Terrigenous export and ocean currents' diffusion of organophosphorus flame retardants along China's adjacent seas

High demands for but strict regulatory measures on Organophosphorus Flame Retardants (OPFRs) have resulted in mainland China transitioning from the region that imports OPRFs to one that exports these substances. Simultaneously, large quantities of terrigenous OPFRs have been exported to adjacent seas by the major river systems, particularly the Yangtze River. This study examined the presence of ten OPFRs in China's adjacent seas. High levels of OPFRs were observed in seas south of mainland China, with Tris (2-chloroethyl) phosphate (TCEP) and Tris (1,3-dichloro-2-propyl) phosphate (TDCPP) dominant. The terrigenous OPFRs were redistributed by the ocean surface currents, with OPFRs tending to accumulate in regions with lower current speed. The producers of OPFRs are mainly distributed along the Haihe, Yellow, and Yangtze river systems. The application of OPFRs to electric vehicle charging stations, charging connectors, and 5G infrastructure in the Chinese mainland will likely drive rapid growth in OPFR related industry in the future. The diffusion trend map of OPFR indicated that the Bohai Sea and the central northern Yellow Sea are at high risk of ecological damage in the spring. The offshore region of the north of the South China Sea tended to aggregate more OPFRs in summer. Regions of the OPFR aggregation effect were at a higher risk of ecological damage.

Integrated System for Multi-Usage Reservoir Management in Sri Lanka

The Mahaweli Authority of Sri Lanka (MASL) is responsible for planning the water allocation across five major River systems in Sri Lanka. This includes providing water to the 15 major hydro plants and over 32 irrigation areas. MASL has been using computer models since the1980’s to meet the various water demands over the entire system and establish the right balance between the multiple stakeholders as part of the calculation of a seasonal plan (SOP). This includes an evaluation of the risk associated with water shortages for irrigation. As part of an on-going modernization effort, a fully integrated system for multi-use reservoir management (Vista DSSTM) has been developed and implemented to help produce the seasonal plan on an operational basis. It includes a multi objective long and shortterm optimization model, extensive data acquisition capability as well as inflow and irrigation water demand forecasting. The system has been designed to dynamically address changes in conveyance maximum capacities due to outages or other unplanned maintenance activities, along with changes in water supply due to expected near-term rain events. The new implementation has been in operation over the last 12 months and is expected to provide greater flexibility in conducting the various analyses, promote higher data integration, and further optimize the use of the country’s water resources.

Mamíferos do Estado de São Paulo: diversidade, distribuição, ecologia e conservação

Abstract Mammals are charismatic organisms that play a fundamental role in ecological functions and ecosystem services, such as pollination, seed dispersal, nutrient cycling, and pest control. The state of São Paulo represents only 3% of the Brazilian territory but holds 33% of its mammalian diversity. Most of its territory is dominated by agriculture, pastures, and urban areas which directly affect the diversity and persistence of mammals in the landscape. In addition, São Paulo has the largest port in Latin America and the largest offshore oil reservoir in Brazil, with a 600 km stretch of coastline with several marine mammal species. These human-made infrastructures affect the diversity, distribution, ecology, and the future of mammals in the state. Here, we answer five main questions: 1) What is the diversity of wild mammals in São Paulo state? 2) Where are they? 3) What is their positive and negative impact on human well-being? 4) How do mammals thrive in human-modified landscapes? 5) What is the future of mammals in the state? The state of São Paulo holds 255 species of native mammals, with four endemic species, two of them globally endangered. At least six species (two marsupials, Giant otter, Pampas deer, Brazilian dwarf brocket deer, and Giant armadillo) were extirpated from the state due to hunting and habitat loss. The intense human land use in the state forced many mammalian species to change their diet to cope with the intense fragmentation and agriculture. Large-scale monoculture has facilitated the invasion of exotic species such as wild boars (javali) and the European hare. Several “savanna-dwelling” species are expanding their ranges (Maned wolf, Brocket deer) over deforested areas and probably reflect changes towards a drier climate. Because the state has the largest road system, about 40,000 mammals from 33 species are killed per year in collisions causing an economic loss of 12 million dollars/year. The diversity of mammals is concentrated in the largest forest remnants of Serra do Mar and in the interior of the State, mainly in the regions of Ribeirão Preto and Jundiaí. Sampling gaps are concentrated throughout the interior of the state, particularly in the northwest region. Wild mammals play a fundamental role in many ecosystem services, but they can also be a concern in bringing new emergent diseases to humans. Although the taxonomy of mammals seems to be well known, we show that new species are continuously being discovered in the state. Therefore, continuous surveys using traditional and new technologies (eDNA, iDNA, drones), long-term population monitoring, investigation of the interface of human-wildlife conflict, and understanding of the unique ecosystem role played by mammals are future avenues for promoting sustainable green landscapes allied to human well-being in the state. The planting of forest or savanna corridors, particularly along with major river systems, in the plateau, controlling illegal hunting in the coastal areas, managing fire regimes in the Cerrado, and mitigating roadkill must be prioritized to protect this outstanding mammal diversity.

Assessment of Groundwater Potential Zones across Katrol Hill Fault, Kachchh, Western India: A Remote Sensing and GIS Approach

The present study focuses on the use of remote sensing and geographical information system tools for morphometric and geomorphic analysis of major river basins across the Katrol Hill Fault, which makes drainage divide. It aims to find groundwater potential for the management and planning of groundwater resources. The study area consists of 6 major watersheds of major river systems namely Bhurud, Khari, and Pat flowing north of the major divide, while Rukmawati, Nagavanti, and Bhukhi are southerly flowing rivers. Based on linear, areal, and geomorphic aspects, a watershed with excellent groundwater potential was found. The highest order in the area is the 5th order stream. Appropriate drainage network characteristics, elongated shape, and permeable lithological formation with low relief among all the watersheds made WS3 be excellent potential for groundwater. The statistical analysis, where Cp value was computed, showed the potential groundwater zone to be in WS3 followed by WS2 and WS5. These results were even verified with field data, collected from well-inventory and that too favored WS3 as an excellent groundwater potential.

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.

Life-Long Learning Know-How Transfer Centers for Flood Risk Assessment in Romania and Hungary

The sector affected by surplus or scarcity of water requires proper understanding of river and landscape system behavior, what is possible to be done to prevent potential damages and losses need skilled professionals, who are familiar also with the newest IT based hydroinformatic tools and technological achievements to find the best possible solutions. An extensive programs of Water Authorities in Romania and in Hungary have been running to provide flood risk maps in all the main river basins including also those which across the both countries. The obtained results will be contribute to the better understanding and general prediction of flooding on the major river systems and assist the governments to act (in real time and space) in accordance with contingency planning based on flood risk management plans, moreover future development plans of regions and cities will get a proper guidance and platforms for future feasibility studies. However Flood Directive implementation has been ongoing in Romania and Hungary, `bridging and direct trainings` for relevant sectors as it is planned in this project have not been provided and have not been planned for future in Romania and Hungary. Based on these needs in 2011 was initiated and organized an international cooperation project financed by the European Union with the theme: “Development of knowledge canters for life-long learning by involving of specialists and decision makers in flood risk management using advanced Hydroinformatic tools” [1]. In this paper we give a brief overview of the main objectives proposed, a description of the partners and some aspects of the activities developed in the project and some of the results obtained

Genetic diversity and population structure of Salix alba across river systems in Turkey and their importance in conservation management

ABSTRACT Background Salix alba is a pioneer species of river ecosystems throughout Turkey. Its genetic diversity and population structure across these ecosystems is currently unknown. Aims We investigated genetic diversity in Turkish S. alba to assess factors likely to shape the genetic structure of the species and to assist with conservation recommendations. Methods Six hundred and forty-six individuals from 10 major river systems in Turkey were genotyped using 15 microsatellite markers. Between one and five sub-populations were sampled from each river system with 23 sub-populations sampled in total. Results Populations contained moderately high levels of genetic diversity. Five genetic groups were detected by Bayesian clustering, with samples from particular river systems mainly assigned to particular genetic groups. This revealed a geographic structure, also detected by principal coordinate analysis, showing that particular river system populations in different parts of Turkey were genetically similar to each other but different from those in other parts of the country. Conclusion Genetic isolation caused by geographic distance (in part) and natural barriers among river systems appear to have shaped the genetic structure of populations. The results have important implications for the conservation of genetic resources within S. alba and restoration of degraded Turkish populations of the species.

The contrasting estuarine geochemistry of rare earth elements between ice-covered and ice-free conditions

Rare Earth Elements, including the lanthanide series and Y (REYs), are important tracers and paleo-proxies of biogeochemical processes, water mass transport and oceanic mixing. At the interface between the continents and oceans, the geochemical behaviour of REYs in estuarine environments is generally described as being non-conservative, with large-scale removal by particle scavenging. This conventional interpretation stems from observations carried out in tropical or sub-tropical estuaries. However, major river systems in the mid- and high latitude regions are subjected to winter conditions when a frozen watershed and an ice cover may affect the continental input of particles and the REY geochemistry. Here, we investigate the geochemical behaviour of REYs in the Estuary and Gulf of St. Lawrence (EGSL) in spring 2003 as well as winter and summer 2020. In contrast to the ice-free seasons, REYs and Fe behave conservatively in the estuary during the winter. In addition, we observed a higher REY affinity toward particle surfaces and fractionation in REE patterns in the hypoxic deep waters of the estuary. The latter observation may reflect enhanced REY sorption to mineral-carrier surfaces exposed upon the remineralization of organic coatings on settling particles and to manganese oxides of benthic origin. Computed partition coefficient (Kd) values and strong correlations between Y/Ho, Er/Nd and Ce anomalies with dissolved oxygen concentrations support this hypothesis. The estimated annual dissolved load of REYs from the EGSL to the ocean ranges from 0.4 to 75 tons per year, thus contributing significantly to the global marine budget. The global river loading of dissolved Nd to the ocean was also revised to 4000 tons per year based on data available for 21 river systems.

Bioindicator snake shows genomic signatures of natural and anthropogenic barriers to gene flow.

Urbanisation alters landscapes, introduces wildlife to novel stressors, and fragments habitats into remnant 'islands'. Within these islands, isolated wildlife populations can experience genetic drift and subsequently suffer from inbreeding depression and reduced adaptive potential. The Western tiger snake (Notechis scutatus occidentalis) is a predator of wetlands in the Swan Coastal Plain, a unique bioregion that has suffered substantial degradation through the development of the city of Perth, Western Australia. Within the urban matrix, tiger snakes now only persist in a handful of wetlands where they are known to bioaccumulate a suite of contaminants, and have recently been suggested as a relevant bioindicator of ecosystem health. Here, we used genome-wide single nucleotide polymorphism (SNP) data to explore the contemporary population genomics of seven tiger snake populations across the urban matrix. Specifically, we used population genomic structure and diversity, effective population sizes (Ne), and heterozygosity-fitness correlations to assess fitness of each population with respect to urbanisation. We found that population genomic structure was strongest across the northern and southern sides of a major river system, with the northern cluster of populations exhibiting lower heterozygosities than the southern cluster, likely due to a lack of historical gene flow. We also observed an increasing signal of inbreeding and genetic drift with increasing geographic isolation due to urbanisation. Effective population sizes (Ne) at most sites were small (< 100), with Ne appearing to reflect the area of available habitat rather than the degree of adjacent urbanisation. This suggests that ecosystem management and restoration may be the best method to buffer the further loss of genetic diversity in urban wetlands. If tiger snake populations continue to decline in urban areas, our results provide a baseline measure of genomic diversity, as well as highlighting which 'islands' of habitat are most in need of management and protection.

Limited Co- existence of Native Unionids and Invasive Dreissenid Mussels more than 30 Y Post Dreissenid Invasion in a Large River System

There are serious concerns for native freshwater mussel survival (Bivalvia: Unionidae) in the Laurentian Great Lakes region after populations were seemingly pushed to the brink of extirpation following the introduction of dreissenid mussels (Dreissena polymorpha and D. rostriformis bugensis) in the mid-1980s. The Detroit River was the first major river system in North America to be invaded by dreissenids, and unionids were considered extirpated from the river by 1998. Since then several unionid refuges (areas with relatively low dreissenid impact and surviving unionids) have been found in coastal areas of lakes St. Clair and Erie, but no documentation exists in the Detroit River. To assess dreissenid presence and potential unionid persistence, a mixture of stratified random, historical, and potential refuge sites were surveyed during summer 2019 in the Detroit River. Unionid and dreissenid habitat use was further investigated with analysis of variance and classification tree analyses. Of the 56 sites surveyed, only five sites had live unionids totaling 220 animals of 11 species. More than 2000 unionid shells of 31 species were collected from 39 sites, confirming the large and diverse unionid populations that existed prior to the dreissenid invasion. Ninety-eight percent of live unionids found showed evidence of past or present dreissenid attachment. Estimated dreissenid densities were highly variable with river location and ranged from 0 to 5673 live individuals per m2, with the largest densities concentrated in the upstream half of the Detroit River. Despite their previously assumed extirpation from the Detroit River, live unionids were found during this comprehensive survey. Although only 40% of the historical species within the unionid assemblage remains, our results suggest, in the right conditions, some coexistence is possible among some species of unionids and dreissenids in this large river system.

Influences of natural salinity sources and human actions on the Shapour River salinity during the recent streamflow reduction period.

The Shapour River, with a catchment area of 4254 km2, is a major river system in southern Iran. While the upstream river flow (the upper Shapour River) is fresh, it becomes extremely salinized at the downstream confluence of the Shekastian saline tributary and the entering nearby Boushigan saline spring. Then, the river passes via the Khesht plain and finally discharges into Raeisali-Delvari storage dam which went into operation in 2009. Over the 2006-2019 period, reduced precipitation and over-utilization of freshwater resources resulted in ~ 72% streamflow reduction in the Shapour River. Due to not using the saline waters for irrigation, drinking, and industrial purposes, the ratio of saline-outflow of Shekastian tributary and Boushigan spring to fresh-outflow of upper Shapour River increased by ~ 3 times; consequently, river salinity fluctuation domain at the Khesht plain inlet dramatically increased from 2.1-4.0 dS m-1 to 3.7-26.0 dS m-1. It resulted in major economic damages to the agricultural sector of middle Shapour River. On the seasonal timescale, consecutive processes of salt accumulation during irrigation season of the Khesht plain date orchards and then salt drainage during the rainy season have adjusted salinity fluctuation domain from 3.7-26.0 dS m-1 at the plain inlet to 5.2-8.9 dS m-1 at the plain outlet. In the lower Shapour River, storage/mixing of fresh/saline inflow waters in the Raeisali-Delvari reservoir has adjusted strong river salinity fluctuation domain from 0.9-10.7 dS m-1 at the reservoir inlet to 3.6-5.5 dS m-1 at the reservoir outlet. The success of the Raeisali-Delvari reservoir for salinity adjustment is due to its suitable location on the Shapour River, by being situated downstream of all main river tributaries with natural saline/fresh sources of water.

Twenty-year trends in antimicrobial resistance from aquaculture and fisheries in Asia

Antimicrobial resistance (AMR) is a growing threat to human and animal health. However, in aquatic animals—the fastest growing food animal sector globally—AMR trends are seldom documented, particularly in Asia, which contributes two-thirds of global food fish production. Here, we present a systematic review and meta-analysis of 749 point prevalence surveys reporting antibiotic-resistant bacteria from aquatic food animals in Asia, extracted from 343 articles published in 2000–2019. We find concerning levels of resistance to medically important antimicrobials in foodborne pathogens. In aquaculture, the percentage of antimicrobial compounds per survey with resistance exceeding 50% (P50) plateaued at 33% [95% confidence interval (CI) 28 to 37%] between 2000 and 2018. In fisheries, P50 decreased from 52% [95% CI 39 to 65%] to 22% [95% CI 14 to 30%]. We map AMR at 10-kilometer resolution, finding resistance hotspots along Asia’s major river systems and coastal waters of China and India. Regions benefitting most from future surveillance efforts are eastern China and India. Scaling up surveillance to strengthen epidemiological evidence on AMR and inform aquaculture and fisheries interventions is needed to mitigate the impact of AMR globally.

Hydrological Connectivity in a Permafrost Tundra Landscape near Vorkuta, North-European Arctic Russia

Hydrochemical and geophysical data collected during a hydrological survey in September 2017, reveal patterns of small-scale hydrological connectivity in a small water track catchment in the north-European Arctic. The stable isotopic composition of water in different compartments was used as a tracer of hydrological processes and connectivity at the water track catchment scale. Elevated tundra patches underlain by sandy loams were disconnected from the stream and stored precipitation water from previous months in saturated soil horizons with low hydraulic conductivity. At the catchment surface and in the water track thalweg, some circular hollows, from 0.2 to 0.4 m in diameter, acted as evaporative basins with low deuterium excess (d-excess) values, from 2‰ to 4‰. Observed evaporative loss suggests that these hollows were disconnected from the surface and shallow subsurface runoff. Other hollows were connected to shallow subsurface runoff, yielding d-excess values between 12‰ and 14‰, close to summer precipitation. ‘Connected’ hollows yielded a 50% higher dissolved organic carbon (DOC) content, 17.5 ± 5.3 mg/L, than the ‘disconnected’ hollows, 11.8 ± 1.7 mg/L. Permafrost distribution across the landscape is continuous but highly variable. Open taliks exist under fens and hummocky depressions, as revealed by electric resistivity tomography surveys. Isotopic evidence supports upward subpermafrost groundwater migration through open taliks under water tracks and fens/bogs/depressions and its supply to streams via shallow subsurface compartment. Temporal variability of isotopic composition and DOC in water track and a major river system, the Vorkuta River, evidence the widespread occurrence of the described processes in the large river basin. Water tracks effectively drain the tundra terrain and maintain xeric vegetation over the elevated intertrack tundra patches.

Quantile regression illuminates the successes and shortcomings of long-term eutrophication remediation efforts in an urban river system

Despite massive financial investment in mitigation, eutrophication remains a major water quality problem and management priority. Eutrophication science—well established for lakes—is not as well developed for rivers, and scientific understanding of how rivers respond to eutrophication management is far more limited. Long-term data are required to evaluate progress, but such datasets are relatively rare for rivers. We analyzed 23 years of water quality data for the Charles River, a major urban river system in the northeastern U.S.A., to examine nutrient and phytoplankton biomass (chl-a) responses to decades of phosphorus (P) management. Using the more novel and robust approach of quantile regression, we identified statistically and ecologically significant declines in both total phosphorus (TP) and chl-a over time, but only for middle percentiles. Statistically high concentrations of TP and chl-a persist—the segments of the data of greatest concern to managers and the public—and yet this critical result is concealed by statistical tests often employed in eutrophication studies that only evaluate mean changes. TP, temperature, precipitation, and river segment jointly explain the most chl-a variation observed at the decadal scale. Spatial variation is also considerable: despite a significant decline in TP, the impounded lower river exhibits no long-term trend in chl-a and continues to experience annual blooms of harmful cyanobacteria—a lagging response comparable to that of a recovering eutrophic lake. Despite long-term successes in reducing P, chl-a, and cyanobacteria in the Charles River system, we did not detect any significant, long-term change in the attainment of statutory compliance, illustrating the protracted and complex nature of the river's response. Our analysis demonstrates the need for high-frequency, long-term water quality data to evaluate the progress of eutrophication management in urban rivers, and the utility of quantile regression for detecting critical trends in the occurrence of statistically low-frequency but ecologically high-impact events, including blooms of harmful cyanobacteria.