River Mainstem Research Articles

Human-driven changes in sediment-water interactions may increase the degradation of ecosystem functioning in the Ganga River

While it is widely accepted that the magnitude of river water quality degradation depends upon the proportion of human interventions, the overall changes are ultimately the consequence of interconnected biogeochemical processes with poorly understood role of ecosystem feedbacks. Here, we conducted in situ and incubation experiments, considering a 620 km Ganga River main stem, two tributaries and two point source downstream locations for trajectory studies to analyze the human-driven changes in ecosystem feedback associated changes in ecosystem functioning of the Ganga River and its tributaries. The main stem coupled trajectory analyses show that benthic hypoxia/anoxia resulting from intensive human releases generates positive feedbacks (sediment-P and –metal release) to exacerbate the degradation of ecosystem functioning in the Ganga River and tributaries. We found 1.9 to 4.6 times higher rates of sediment-P release and about 1.1 to 3.7 times higher rates of sediment-metal releases at sites with DOsw < 2.0 mg/L. Excess release of phosphorus from sediment enhanced the eutrophy whereas sediment-metal release and bioavailability led to a sharp decline in microbial biomass and FDAase activity. The Carlson’s index, ecological response index, Dodds’s trophic state classification, and risk index support these results because the sites with benthic hypoxic/anoxic condition did show trophic state in eutrophic to hypereutrophic range and metal pollution in very high to extremely polluted and high risk category indicating significant effect of these drivers. The study, for the first time, showed that positive feedbacks exacerbate the degradation of ecosystem functioning in human-impacted large rivers. We suggest the need for increased efforts considering the magnitude and connectivity of positive feedbacks and associated repercussions for improving mechanistic understanding of their contributions to overall structural and functional shifts in the large rivers.

Tracing sources of stormflow and groundwater recharge in an urban, semi-arid watershed using stable isotopes

Study regionIn this study, we use stable isotopes of water to quantify the flow pathways delivering water to the tributaries, mainstem river and groundwater basin underlying urban San Diego. Information about sources of stormflow and recharge are necessary to maintain the health of waterways and aquifers, but studies of these processes are scarce in urban, semi-arid regions. Study focusIsotopic methods have been used in experimental or natural watersheds, but also have potential to quantify urban water cycling behaviour and water sources. We sampled baseflow, precipitation, and hourly stormflow from eight events with a range of antecedent conditions, and used end member mixing analysis to determine stormflow and groundwater sources. New hydrological insights for the regionOur results show that hydrologic connectivity controls stormflow sources. After a dry summer, and early in storm events, connectivity of pre-event water with the channel is low, so only new precipitation reaches the river. In wetter conditions, connectivity is higher and pre-event surface water mixes with infiltration-origin groundwater. Deeper groundwater composition mimics stormflow, a mix of stagnated river water and infiltration-origin water. The close connection between streamflow and groundwater implies that improving groundwater quality requires improvements to surface water quality. Average uncertainty in source fractions was ±8.0 %, suggesting that despite complex water pathways in urban, semi-arid environments, isotopic sampling is valuable for quantifying water sources.

Spatiotemporally varying inter-relationships between mainstem riverbed elevation and tributary sediment supply since the last interglacial in the upper Ara River, central Japan

The dynamics of sediment transport processes over millennial time scales in mountain river valleys remain poorly understood, limiting our overall understanding of sediment routing through river basins. Here, we reconstruct changes of the mainstem riverbed elevation, tributary sediment supply processes, and their inter-relationships since the last interglacial in the upper Ara River valley, central Japan. Aggradation of the mainstem river valley began before 100–95 ka and terminated by 41–40 ka. Then, the elevation of the mainstem floodplain remained stable until ~15 ka. Lateral erosion by the mainstem river, and intermittent periods of incision, continued until 5 ka, after which the mainstem river began actively incising. Aggradation of the mainstem riverbed before 41–40 ka elevated tributary junctions, decreasing the slopes of tributaries. Using reconstructed slope changes, and assuming sediment transport by debris flow in tributaries with slopes steeper than 8% and by traction in shallower tributaries, we classified the tributaries into three types: Type-A, with sediment supply by debris flow since the last interglacial; Type-B, with sediment supply by traction during the last glacial period and afterwards by debris flow; and Type-C, with sediment supply by traction since the last interglacial. Based on the relation between relief ratio and drainage area, we subdivided Type-C tributaries into those that plotted along (Type-C1) or markedly below (Type-C2) the regression line of the mainstem river and Type-A and -B tributaries. During aggradation of the mainstem river, sediments supplied by debris flow from Type-A and -B tributaries accumulated around junctions, interfingering with mainstem deposits. During this period, the junctions of Type-C1 tributaries were elevated almost synchronously with mainstem aggradation, while the junctions of Type-C2 tributaries were blocked by mainstem river deposits, forming blocked-valley lakes. Around 30 ka, Type-A and -B tributaries formed fans around their junctions that were subsequently truncated by lateral erosion by the mainstem river during the late glacial period and early Holocene, forming toe-cut terraces. Tributary deposits that had accumulated around the junctions were then reworked while maintaining a dynamic equilibrium state with the mainstem river. We infer that the responses of tributary landforms and sediment supply processes to the changing elevation of the mainstem riverbed during glacial and interglacial cycles varied depending on the drainage area and relief of each tributary. Considering the river basin as a whole, however, tributary deposits stabilized the elevation of the mainstem floodplain.

Safeguarding Free-Flowing Rivers: The Global Extent of Free-Flowing Rivers in Protected Areas

Approximately one-third of long rivers remain free-flowing, and rivers face a range of ongoing and future threats. In response, there is a heightened call for actions to reverse the freshwater biodiversity crisis, including through formal global targets for protection. The Aichi Biodiversity Targets called for the protection of 17% of inland water areas by 2020. Here, we examine the levels and spatial patterns of protection for a specific type of inland water area—rivers designated as free-flowing. Out of a global total of 11.7 million kilometers of rivers, 1.9 million kilometers (16%) are within protected areas and 10.1 million kilometers are classified as free-flowing, with 1.7 million kilometers of the free-flowing kilometers (17%) within protected areas. Thus, at the global level, the proportion of rivers in protected areas is just below the Aichi Target, and the proportion of free-flowing rivers within protected areas equals that target. However, the extent of protection varies widely across river basins, countries, and continents, and many of these geographic units have a level of protection far lower than the target. Further, high discharge mainstem rivers tend to have lower extent of protection. We conclude by reviewing the limitations of measuring river protection by the proportion of river kilometers within protected areas and describe a range of mechanisms that can provide more effective protection. We also propose a set of recommendations for a more comprehensive quantification of global river protection.

Tracing the almost extinct mayfly Prosopistoma pennigerum (Müller, 1785) – an eDNA approach

The rare mayfly Prosopistoma pennigerum was once widely distributed across Europe and occurred virtually in every large river. Today, it holds fast against the ever-growing destruction of its habitat with a few relic populations remaining. Preliminary data and information on its congeners suggest that free-flowing rivers with near-natural hydrodynamics are its primary habitat. Rivers where the species currently occurs should be primary targets for large-scale landscape conservation and protection. According to the Water Framework Directive, achieving longitudinal and lateral connectivity is a priority target, and occurrence and viability of Prosopistoma pennigerum populations could be an indicator of restoration success. We developed and validated a targeted qPCR protocol to detect this mayfly and applied it to standardized water samples filtered for eDNA analysis from the Vjosë (Albania) and Volga (Russia), two rivers with extant populations of P. pennigerum. In the Vjosë river, 45 sampling sites were sampled three times in 2018 and 2019. In the Volga river, we focused on a site with &amp;gt;15 years of continuous records of P. pennigerum at Rzhev and two downstream locations, where eDNA samples were collected in 2017. At each sampling site in the Vjosë, eDNA samples were collected by filtering 0.5 L of stream water through each of two 0.45 µm Sterivex filters. In the Volga, 2 L of stream water were filtered through a total of eight 0.7 µm glass fibre filters. Filters were stored and shipped at -20°C until further processing. Environmental DNA extraction was performed using the DNeasy® PowerWater® Sterivex™ Kit following the Experienced User protocol for Vjosë samples and via a Phenol-Chloroform Isoamyl extraction for the Volga samples. A Taqman qPCR assay was developed using a newly designed primer and probe set. Standard curves obtained from an amplicon dilution series yielded a reaction efficiency of 88% and an R2-value of 0.995, with a calculated limit of quantification of 1801 copies/µL and a limit of detection of 59 copies/µL. Each eDNA sampling replicate was tested using five qPCR replicates, yielding ten qPCR reactions per sampling site in the Vjosë river and 40 qPCR reactions in the Volga river. With each batch of eDNA samples, four negative and two positive controls were analysed. At each site, we also collected benthic MHS samples with a 25x25 cm 500 µm net where 20 samples were taken to reflect microhabitat distribution and dominance. Benthos samples were subsampled in the lab and all zoobenthos hand-picked. Prosopistoma pennigerum occurrence was assessed as areal density (number of specimens per m2). While P. pennigerum occured in high frequencies and abundances in benthic samples along the Vjosë river main stem in all sampling seasons, qPCR of eDNA samples suggested slightly different occurrence patterns. Conversely, P. pennigerum was detected with high consistency at two sites in the Volga river (at Rzhev and a site 99 km downstream), where its frequency is much lower than in the Vjosë river. The success of detecting a benthic species in eDNA samples depends on a variety of factors that may have affected DNA quality and prevented better detection of P. pennigerum in the Vjosë river eDNA samples. We demonstrate the principal applicability of molecular methods to search for rare species in hot-spots of biodiversity in Central Europe. The remnant populations of P. pennigerum in the hydrodynamically minimally impaired Vjosë and the Volga highlight the conservation and protection needs in Eastern and Southern Europe. At the European scale, restoration efforts should be geared towards creating viable habitat conditions for large-river species such as P. pennigerum. Here, our qPCR assay can deliver crucial data for better management of Europe’s large rivers.

Influence of Hydraulic Connectivity on Carbon Burial Efficiency in Mackenzie Delta Lake Sediments

AbstractThe Arctic is undergoing accelerated changes in response to ongoing modifications to the climate system, and there is a need for local to regional scale records of past climate variability in order to put these changes into context. The Mackenzie Delta region in northern Canada is populated by numerous small shallow lakes. They are classified as no‐, low‐, and high‐closure (NC, LC, and HC, respectively) lakes, reflecting varying degrees of connection to the river main stem, and have different sedimentation characteristics. This study examines sedimentological (mineral surface area, grain size), carbon isotopic (bulk and molecular‐level) and inorganic isotopic (neodymium) characteristics of sediment cores from three lakes representing each class. We find that HC lake sediments exhibit strikingly different properties from the other lake sediments. Specifically, they are characterized by higher organic carbon loadings per unit mineral surface area and with relatively minor influence from allochthonous, petrogenic (rock‐derived) organic carbon. In contrast, LC and NC lakes have the potential to record basin‐scale climatic changes at a high resolution by virtue of enhanced detrital sedimentation. Overall the delta lakes have the capacity to bury about 2 MtC year−1, with little changes in the last 200 years. However, in the (near) future, an increased number of high closure lakes might change the carbon burial efficiency of the Mackenzie Delta as they seem to retain less carbon than NC and LC lakes.

Microhabitat use by pre‐spawning Pacific lamprey Entosphenus tridentatus in a large, regulated river differs by year, river segment, and availability

Decreasing river flows and increasing water temperatures during the summer have been associated with holding behavior by pre-spawning Pacific lamprey Entosphenus tridentatus in the mainstem Willamette River (Oregon, USA). However, it is unclear if microhabitat use (≤ 2 m) by these lamprey is associated with particular habitat structure(s) or thermal refuge. We implanted radio tags into lamprey (n = 425) and conducted boat surveys to track individuals and document their microhabitat use in the mainstem Willamette River. 58 % of the lamprey were detected, representing 460 detections of 247 individuals across two years (2009 and 2010). Lamprey distributed significantly further upstream, and more were found in the main channel during a high flow year (2010) in comparison with a low flow year (2009). More lamprey held in the main channel across all river segments in 2010 than in 2009. Main channel habitats were significantly deeper than other microhabitats. Lamprey migrating into the upper river segment tended to use microhabitats other than the main channel. These other microhabitats included rock revetments and boulders/bedrock. Rock revetments were more prevalent in the middle – upper river segments, and a greater percentage of lamprey were associated with this microhabitat in these segments. The further upstream the lamprey migrated, the cooler, shallower, and faster water they encountered. One lamprey was associated with coolwater refuge (15.5 oC) in an alcove to the mainstem river (18.1 oC). We conclude that microhabitat use by pre-spawning Pacific lamprey differs by year (river flow), river segment, and availability in a large, regulated river.

Three-decadal erosion and deposition of channel bed in the Lower Atchafalaya River, the largest distributary of the Mississippi River

Many world's large rivers have experienced significant sediment reduction in the past century. However, channel aggradation near the mouth of these rivers may be still occurring or even accelerating, as evidenced by a recent study on the Lowermost Mississippi River. This study aims to investigate whether such a trend exists near the mouth of another large lowland alluvial river, the Atchafalaya River, which enters the Gulf of Mexico via two outlets — the natural mainstem and a man-made straight channel that is shorter and has a much greater slope. The overarching hypothesis is that, despite the reduction in riverine sediment delivery, lowland alluvial rivers such as the Lower Atchafalaya River in their backwater zone aggrade. We collected bathymetric survey records in 1977 and 2006 to analyze riverbed deformation. We utilized stage records at several gauging stations to determine the change in the hydraulic head over time. Geospatial techniques were used to develop channel bed Digital Elevation Models which were used to identify deformation of the 174-km channel bed of the Lower Atchafalaya River. We found a cumulative erosion of 6.34×107m3 and a cumulative deposition of 8.79×107m3, resulting in a net deposition of 2.45×107m3 during the study period. While much of the river including the man-made channel was in a degrading state, the last 35km of the river's natural mainstem experienced substantial aggradation. On average, riverbed elevation of the Lower Atchafalaya decreased by 1.47m in the upper 98km, but increased by 0.96m in the final 35km of the river's mainstem to the Gulf of Mexico. The channel erosion in the upstream reach will likely continue with the river discharge projected to increase, and the channel deposition in the downstream mainstem may accelerate because of sea-level rise.

Understanding the influence of multiple pollutant stressors on the decline of freshwater mussels in a biodiversity hotspot

The Clinch River watershed of the upper Tennessee River Basin of Virginia and Tennessee, USA supports one of North America's greatest concentrations of freshwater biodiversity, including 46 extant species of native freshwater mussels (Order Unionida), 20 of which are protected as federally endangered. Despite the global biological significance of the Clinch River, mussel populations are declining in some reaches, both in species richness and abundance. The aim of this study was to evaluate the exposure of adult resident mussels to a suite of inorganic and organic contaminant stressors in distinct sections of the Clinch River that encompassed a range of mussel abundance and health. To provide insight into the potential role of pollutants in the decline of mussels, including within a previously documented “zone of mussel decline”, the mainstem Clinch River (8 sites) and its tributaries (4 sites) were examined over two consecutive years. We quantified and related metals and organic contaminant concentrations in mussels to their associated habitat compartments (bed sediment, suspended particulate sediment, pore water, and surface water). We found that concentrations of organic contaminants in resident mussels, particularly the suite of 42 polycyclic aromatic hydrocarbons (PAHs) analyzed, were related to PAH concentrations in all four habitat (media) compartments. Further, PAH concentrations in mussel tissue (range 37.8–978.1 ng/g dry weight in 2012 and 194.3–1073.7 ng/g dry weight in 2013) were negatively related to the spatial pattern in mussel densities (rs = −0.64, p ≤ 0.05 in 2012 and rs = −0.83, p ≤ 0.05 in 2013) within the river, and were highest in the “zone of mussel decline”. In contrast, the suite of 22 metals analyzed in resident mussels were largely unrelated to the spatial pattern of variation of metals in the four habitat compartments except for Manganese (Mn; range 3630.5-23,749.2 μg/g dry weight in 2012 and 1540.4-12,605.8 μg/g dry weight in 2013) in surface water (rs = 0.58, p < 0.1) and pore water (rs = 0.76, p ≤ 0.05). This study revealed that PAHs and Mn are important pollutant stressors to mussels in the Clinch River and that they are largely being delivered through the Guest River tributary watershed. Accordingly, future conservation and management efforts would benefit by identifying, and ideally mitigating, the sources of PAHs, Mn, and other current or legacy mining-associated pollutants to the mainstem river and its tributaries.

Genetic Connectivity of the West Indian Manatee in the Southern Range and Limited Evidence of Hybridization With Amazonian Manatees

The Antillean subspecies of the West Indian manatee is classified as endangered by the International Union for the Conservation of Nature (IUCN) Red List. In Brazil, the manatee population is listed as endangered with an estimated population size of 500–1,000. Historic hunting, recent habitat degradation, and fisheries bycatch have decreased the population size. The Amazonian manatee is listed as vulnerable by the IUCN with unknown population sizes within Brazil. The Antillean manatee occurs in sympatry with the Amazonian manatee in Brazil and hybridization has been previously indicated. To provide information on the genetic structure, diversity, and degree of hybridization in the sympatric zone near the Amazon River mouth, the mitochondrial DNA control region and 13 nuclear microsatellite markers were assessed on the two species. Samples were analyzed from the Antillean subspecies across its distribution in Brazil (n= 78) and from the Amazonian species (n= 17) at the Amazon River mouth and inland mainstem river. To assess the previously defined evolutionary significant units of Antillean manatees in the area, an additional 11 samples from Venezuela and Guyana were included. The Antillean manatee was found to be a single population in Brazil and had lower than average number of alleles (3.00), expected heterozygosity (0.34), and haplotype diversity (0.15) when compared to many other manatee populations. The low values may be influenced by the small population size and extended pressures from anthropogenic threats. Gene flow was identified with Venezuela/Guyana in admixed Antillean Brazil samples, although the two populations were found to be moderately divergent. The nuclear loci in Venezuela/Guyana Antillean manatee samples indicated high differentiation from the samples collected in the Amazon River (FST= 0.35 andRST= 0.18,p= 0.0001). No indication of nuclear hybridization was found except for a single sample, “Poque” that had been identified previously. The distribution of Antillean manatees in Brazil is extensive and the areas with unique habitat and threats would benefit from independent management and conservation actions. Gene flow, resulting in genetic diversity and long-term population stability, could be improved in the southern range through habitat restoration, and the establishments of travel corridors and protected areas, which are particularly important for successful parturition and neonatal calf survival.

Ecological effects and causal synthesis of oil sands activity impacts on river ecosystems: water synthesis review

Oil sands development in the lower Athabasca River watershed has raised considerable public and scientific concerns regarding perceived effects on environmental health. To address this issue for tributaries and the mainstem of the Athabasca River in the Athabasca Oil Sands Region, the Water Component of the Joint Oil Sands Monitoring (JOSM) plan produced monitoring assessments for seven integrated themes: atmospheric deposition, tributary water quality, river mainstem water quality, groundwater quality and quantity, water quality and quantity modelling, benthic invertebrate condition, and fish health. Our review integrates and synthesizes the large and diverse datasets assembled in the seven JOSM theme assessments to (i) evaluate possible environmental effects based on known sources and candidate proximal causes and (ii) determine the importance of cause-and-effect pathways related to contaminant, sediment, and nutrient inputs. Although JOSM research identified ecological effects that appear to be associated with contaminant exposure, the source of this exposure is confounded by co-location of, and inability to differentiate between, oil sands operations (principally released by atmospheric emission) and inputs from the natural bitumen outcrops (e.g., erosional material transported by surface and groundwater flows). Nutrient enrichment from treated municipal sewage effluent was the dominant ecological effect observed for the mainstem Athabasca River, associated with increased fish size and changes in invertebrate assemblages, likely because this pollution source is discharged directly into the river. If the direct release of treated oil sands process water occurs in the future, then the potential ecological impact of these direct industry releases will need to be evaluated carefully. The ecological causal assessment method proved to be a useful tool for better understanding how stressor sources relate to ecological effects through candidate proximate causes. Factors that confound our ability to assess the ecological effects of oil sands development focus on our inability to adequately differentiate between contaminants supplied from natural and anthropogenic contaminant sources. Our causal synthesis identifies options for changes in future monitoring to better anticipate and detect degradation in the ecosystem health of the lower Athabasca River and its tributaries.

Spatiotemporal change analysis of permanganate index in the middle and lower mainstem of the Yangtze River since 2004

高锰酸盐指数是我国水环境质量评价和污染控制考核的重要指标，其浓度高低能反映水体受到有机物污染的严重程度.2003年三峡水库投入运行后，长江中下游干流水文情势发生了重大变化.为此，研究了长江中下游干流耗氧有机污染物的典型参数——高锰酸盐指数的时空变化特征.结果表明，长江中下游干流水体：2004年以来，高锰酸盐指数总体趋降，且目前已处于较低水平并趋于稳定；不同江段和水期高锰酸盐指数变化趋势不一致；耗氧有机污染物以溶解态为主，且溶解态所占比例沿程趋于降低，南津关、汉口、吴淞口下23 km断面溶解态占比中位值分别为0.862、0.734和0.598；可沉降颗粒物对水体中高锰酸盐指数浓度影响较低，尤其在研究河段上游段，悬浮颗粒中所含耗氧物质占总量比例中位值分别为0.138、0.266和0.402；上游江段水体同一监测断面不同测线和测点间高锰酸盐指数测定值差异不显著；河口段则存在显著差异，尤其是表层和底层之间；沿江城市江段近岸水域水体中耗氧物质污染程度较低，其澄清样中高锰酸盐指数均值在1.91～3.45 mg/L之间，仅局部城市江段和水期出现值高于6.0 mg/L的现象.;Permanganate index (COD_Mn) is an important parameter for water quality assessment and pollution control supervision in China. Its concentration reflects the severity of organic pollution. Since the Three Gorges Reservoir was put into operation in 2003, the hydrological condition of in the middle and lower Yangtze River mainstem has been changed significantly. Therefore, the characteristics of spatiotemporal distributions of organic substances(OS) corresponding to permanganate index in the middle and lower mainstem of the Yangtze River under new hydrological condition were studied. The results show that in the middle and lower reaches of the Yangtze River: Since 2004, COD_Mn has been decreasing generally, and it is currently at a low level and tends to stabilize. The trend of COD_Mn in the different river sections and the water period is inconsistent. OS(COD_Mn) in the water column are mainly in the dissolved state, and the proportion of the dissolved state tends to decrease along the direction from upstream to downstream. The median values of C_clarified/C_original ratio in Nanjinguan, Hankou and 23 km below Wusongkou, are 0.862, 0.734 and 0.598 respectively. The effect of the precipitable particles on the COD_Mn concentration in the water is low, especially in the upstream section. The median values of (1-C_filtered/C_original) ratios in Nanjinguan, Hankou and 23 km below Wusongkou were 0.138, 0.266 and 0.402, respectively. There is no significant difference between the different lines and measuring points in the transverse profile in the section on upstream end of studied reach, but significant difference in the estuary section, especially between the surface layer and the bottom layer in the vertical direction. Oxygen-consumed organic pollution is not serious in the coastal waters of urban reaches, and the average concentration of COD_Mn of the clarified samples is between 1.91 and 3.45 mg/L, and the concentration value is seldom higher than 6.0 mg/L.

Population status and conservation outlooks of Yangtze finless porpoise in the Lake Poyang

长江江豚（Neophocaena asiaeorientalis asiaeorientalis）是一种小型齿鲸，仅分布在长江中下游干流和洞庭湖及鄱阳湖中，其种群数量仅约1000头，极度濒危.鄱阳湖是长江江豚最重要的栖息地之一，估算种群数量约450头，是长江江豚最后的避难所.本文系统地总结了鄱阳湖长江江豚种群生态学、保护遗传学和保护生物学的研究进展，着重探讨了各种人类活动对其种群迁移活动的影响，并对鄱阳湖长江江豚种群面临的威胁、保护对策和未来研究方向等进行了总结和展望，以期为今后的保护工作提供借鉴.;Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is now likely the sole cetacean in the Yangtze River, which is only distributed in the middle and lower reaches of the Yangtze River mainstem, Lake Dongting and Lake Poyang. The population size is only about 1000 and critically endangered. As the most critical habitat of Yangtze finless porpoise, Lake Poyang is the last refuge of Yangtze finless porpoise with an estimated population size of about 450. This paper is a systematic summary of the research progress on the population ecology, conservation genetic and conservation biology of the Yangtze finless porpoise population in the Lake Poyang, with emphasis on the influence of various human activities on its population migration activities, and concluding remarks and outlook on the threats to Yangtze finless porpoise population in Lake Poyang, conservation measures and future research directions, aiming to provide a reference for the related conservation.

渭河干流和秦岭北麓典型支流浮游植物功能群特征及水质评价

渭河干流和秦岭北麓典型支流浮游植物功能群特征及水质评价

Identification of Priority Conservation Areas for Protected Rivers Based on Ecosystem Integrity and Authenticity: A Case Study of the Qingzhu River, Southwest China

The establishment of protected areas for a river (PARs) is an efficient approach for the conservation of its ecosystem and biodiversity. This study selected the free-flowing Qingzhu River, located in the mountains of southwest China and one of 34 global biodiversity hotspots, as a case study. This study applied the ecosystem approach to develop a model for identifying priority conservation areas for a river (PCARs) based on integrity and authenticity. Three model elements were selected, namely streams, forest and human activity, characterized by three indicators: irreplaceability, tree cover and human activity, respectively. The spatial distributions of these indicators were overlaid according to different weights to generate a map (SCPV) of comprehensive protected value (CPV), which was used to indicate ecosystem integrity and authenticity in the study catchment. Lastly, PCARs were identified by comparing existing protected areas with the calculated SCPV. The application of the model to the Qingzhu River indicated the area of PCARs to be ~71.88 km2, accounting for 15.13% of the total PAR area. Priority reaches for protection were then identified, with many falling within the mainstem of the river in the middle and lower reaches. The total length of priority protected reaches was ~75.97 km, accounting for 49.33% of the total length of the river mainstem within Qingchuan County. This study validated the model at both the theoretical and practical level, confirming that the model is useful for facilitating the precise protection and smart management of rivers.

Textural and mineralogical maturities and provenance of sands from the Budhi Gandaki-Narayani Nadi, central Nepal

The Budhi Gandaki-Narayani Nadi in the Central Nepal flows across fold-thrust belts of the Tethys Himalaya, Higher Himalaya, Lesser Himalaya, and the Sub-Himalaya, and is located in sub-tropical to humid sub-tropical climatic zone. Within the Higher Himalayas and the Lesser Himalayas, a high mountain and hilly region give way the long high-gradient, the Budhi Gandaki Nadi in the northern region. At the southern region within the Sub-Himalayas, having a wide Dun Valley, gives way the long low-gradient Narayani Nadi. Sands from Budhi Gandaki-Narayani Nadi were obtained and analysed for textural maturity and compositional maturity. The textural analyses consisted of determining roundness and sphere city of quartz grains for shape, and determining size of sand for matrix percent and various statistical measures including sorting. The analysis indicates that the textural maturity of the majority of sands lies in sub mature category though few textural inversions are also remarkable. Sands from upstream to downstream stretches of the main stem river show depositional processes by graded suspension in highly turbulent (saltation) current to fluvial tractive current, as confirmed from the C-M patterns.&#x0D; The compositional variation includes quartz, feldspar, rock fragments, mica, etc. The quartz grain percent slightly increases from the mountains to the lower relief areas. The percent feldspar decreases rapidly whereas the percent rock fragment decreases gradually along the downstream transport of sediment. The Budhi Gandaki-Narayani Nadi sands range from sublitharenite to lithic arenite composition in QFL diagram, and are remarkably poorer in feldspar compared to rock fragment. Among the rock fragments, the high-grade metamorphic rock fragmentsare dominant in the upstream stretch of the main stem Narayani Nadi stretch while the sedimentary lithics are remarkable in the downstream stretch. The QFL plots also show that the studied sands belong to recycled orogeny provenance and agree with the current tectonic setting of the Himalayas. Mineralogically, the sands (MMI=100%–203%) are not as matured as the normal sands. MMI fluctuates along downstream distance due to mixing of sediments from the major tributaries at various places along the main stem river.

Temporal and Spatial Characteristics of Total Phosphorus in the Middle and Lower Yangtze River Mainstem Under New Water and Sediment Conditions

After the completion of the Three Gorges Reservoir and the upstream reservoir group of the Yangtze River, new water and sediment conditions appeared in the middle and lower reaches of the Yangtze River, and its influence on the phosphorus concentrations in water has attracted much attention. Therefore, the spatial and temporal distributions of total phosphorus (TP) concentrations in the middle and lower reaches of the mainstem under the new water and sediment conditions were studied. The results show that:① after the construction of the Three Gorges Reservoir, the concentrations of TCP (samples were allowed to settle for 30 min) in the middle and lower reaches of the Yangtze River fluctuates between 0.10 and 0.15 mg·L-1, and generally increased during 2004-2010 and then decreased during 2014-2019, and increases along the flow direction. The concentrations of dissolved total phosphorus (TDP) have slowly increased with time. ② The settleable solids influence the phosphorus content to varying degrees. The median values of TCP/TP ratio in Nanjinguan, Hankou, and 23 km below Wusongkou, are 0.900, 0.720, and 0.609, respectively, which decreases successively from upstream to downstream. The proportion of TPP (total particulate phosphorus)/TP shows an increasing trend along the flow direction. The median values of TPP/TP ratios in Nanjinguan, Hankou, and 23 km below Wusongkou were 0.439, 0.567, and 0.738, respectively. ③ According to the "Environmental quality standard for surface water GB 3838-2002", the water quality was assessed using TCP concentrations, and the assessment results showed that the water quality of the middle and lower reaches of the Yangtze River was generally good. However, considering the influence of settleable solids, the water quality categories assessed based on TP concentrations would be worse, especially near estuaries. ④ In the middle and lower reaches of Yangtze River, there is little difference in the phosphorus concentration of different monitoring sites in the upper section of main stream; however, the difference is obvious near the estuary. ⑤ The concentration of TCP in the coastal waters of the urban river section of the middle and lower reaches of the Yangtze River is significantly higher than that of the main channel, and there are obvious coastal pollution zones in the coastal waters of the urban river section.

Determinants of bacterioplankton structures in the typically turbid Weihe River and its clear tributaries from the northern foot of the Qinling Mountains

The Weihe River is the largest tributary of the typically sediment-laden Yellow River in China. Assuming that high sediment concentrations may increase the turbidity of water bodies, and therefore affect riverine ecosystem, in which the bacterioplankton are crucial components and serve as important indicators of environmental and ecological status through their structure and response to the environment change, it is essential to deep understanding the bacterioplankton structure and influencing factors in turbid and clear river ecosystems. Here, high-throughput sequencing was used to analyze the differences in bacterioplankton structure and major determinants in the typically turbid Weihe River and its clear tributaries from the northern foot of the Qinling Mountains from October to November 2017 and April to May 2018. The results demonstrated that bacterioplankton communities shared similar dominant subcommunities in the Weihe River mainstem and its tributaries, mainly consisting of Proteobacteria and Bacteroidetes phyla and Flavobacterium and Acinetobacter genera. The Faith phylogenetic diversity (PD) index was significantly higher in the turbid mainstem than in the tributaries and was related to turbidity (Turb). Variation partitioning analysis (VPA) showed that geographical distance exhibited notable influences on the community composition in the mainstem; however, the communities in the tributaries had a much stronger response to local environmental factors. Bacteria exhibited a significant distance-decay relationship in the mainstem, whereas geographical distance was not correlated with community dissimilarities in the tributaries. Chlorophyll a emerged as the major determinant of the bacterioplankton structure in the turbid Weihe River, indicating the importance of phytoplankton-bacterioplankton relationships in the turbid river system. These results provide important insights into future research on microbial ecology, environmental monitoring and classified management in diverse river systems.

Lock operations influence upstream passages of invasive and native fishes at a Mississippi River high-head dam

Asian carps continue to expand their range in North America, necessitating efforts to limit the spread and establishment of reproducing populations. Mississippi River Lock and Dam 19 is a high-head dam that represents a population ‘pinch-point’ as passage through the lock chamber is the only means by which fishes can complete upstream movement. As such, this location could be a pivotal control point for minimizing the spread of invasive fishes in the Upper Mississippi River and a possible candidate site for installation of deterrent measures. Our objectives were (1) to study the timing (i.e., weekly and diel) and behavior of fishes in the downstream lock approach, (2) evaluate the relation of presence in the downstream lock approach with environmental factors and lock operation, and (3) identify any upstream or downstream passage events through the lock chamber and the relation between these events and the operation of the lock. Acoustic transmitters were surgically implanted into 262 Asian carps and 216 native fishes to monitor fish activity on a telemetry receiver array deployed around and within the lock for 622 days during 2017–2018. One hundred eighty-six telemetered fish were detected in the downstream lock approach. We documented 14 upstream Asian carp passages and 10 upstream native fish passages; these passages coincided with a specific sequence of large vessel lockages. The results of this study advance our understanding of fish presence and behavior at a Mississippi River mainstem lock and dam and inform the development and testing of deterrent systems at this location or at similar pinch-point lock and dams.

Environmental influences on migration patterns and pathways of a threatened potamodromous fish in a regulated lowland river network

AbstractIn riverine ecosystems, movements of biota among different parts of the river network are fundamental to the functioning and sustainability of populations, especially for fish. Globally, human activities (e.g., dam construction and altered flow regimes) have impaired riverine fish movements through reduced river connectivity, leading to well‐documented population declines. This study examined the timing and extent of movement of a nationally threatened potamodromous fish, silver perch (Bidyanus bidyanus), among different parts of the mid‐Murray River network in south‐eastern Australia using acoustic telemetry to identify the relative importance of different environmental variables (including river discharge) influencing timing and extent of movements. A total of 203 silver perch (fork length range 120–415 mm) was tagged in the Murray River. Silver perch occupied extended reaches of river (hundreds of kilometres) and multiple habitats throughout the river network, ranging from a large mainstem river to inflowing tributaries, anabranches and floodplain habitats. Movements were associated with aspects of the flow regime, such as small to moderate mainstem discharge rises and elevated tributary discharge. These results emphasise the importance of managing silver perch populations within an integrated riverscape context rather than solely focusing on reach/river scales. The inter‐relationship between silver perch movement and river discharge highlights the susceptibility of the species to river regulation, which has previously been implicated in its decline. The information on migratory behaviours in this study provides empirical evidence to support refinement and implementation of targeted restoration strategies, such as environmental flows, to assist the management and conservation of an imperilled species.