Adjacent Streams Research Articles

Integrative analyses of convergent adaptation in sympatric extremophile fishes

The evolution of independent lineages along replicated environmental transitions frequently results in convergent adaptation, yet the degree to which convergence is present across multiple levels of biological organization is often unclear. Additionally, inherent biases associated with shared ancestry and variation in selective regimes across geographic replicates often pose challenges for confidently identifying patterns of convergence. We investigated a system in which three species of poeciliid fishes sympatrically occur in a toxic spring rich in hydrogen sulfide (H2S) and an adjacent nonsulfidic stream to examine patterns of adaptive evolution across levels of biological organization. We found convergence in morphological and physiological traits and genome-wide patterns of gene expression among all three species. In addition, there were shared signatures of selection on genes encoding H2S toxicity targets in the mitochondrial genomes of each species. However, analyses of nuclear genomes revealed neither evidence for substantial genomic islands of divergence around genes involved in H2S toxicity and detoxification nor substantial congruence of strongly differentiated regions across population pairs. These non-convergent, heterogeneous patterns of genomic divergence may indicate that sulfide tolerance is highly polygenic, with shared allele frequency shifts present at many loci with small effects along the genome. Alternatively, H2S tolerance may involve substantial genetic redundancy, with non-convergent, lineage-specific variation at multiple loci along the genome underpinning similar changes in phenotypes and gene expression. Overall, we demonstrate variability in the extent of convergence across organizational levels and highlight the challenges of linking patterns of convergence across scales.

Agricultural Contribution of Chloride to a Saturated Riparian Buffer System: A Case Study in Central Illinois

ABSTRACT Increases in chloride concentrations in surface water and groundwater from anthropogenic sources is a growing concern throughout the world. In the midwestern United States, the agriculture contribution of chloride may elevate concentrations in surface and groundwater systems. A saturated riparian buffer (SRB), installed to reduce nutrient input into an adjacent stream, and the groundwater water upgradient were investigated to identify sources of chloride and to quantify the agricultural contribution. During a 7-year period, over 2,200 water samples collected from 35 wells, a diversion box, and a stream were analyzed for major anions. Additionally, the waters from four quarterly (seasonal) samplings (n = 155) during the seventh year were analyzed for cations. A cumulative probability curve identified three populations of chloride: (1) upgradient shallow groundwater; (2) diversion box (waters drained from an agricultural field), downgradient shallow groundwater (representing the SRB), diamicton groundwater (waters collected deeper from within the unweathered parent material); and (3) stream water. A background chloride concentration was established at 3.9 mg/L. Elevated concentrations above the background level coupled with principal component analysis suggest agricultural contribution from the diverted tile-drainage waters was a source of chloride. In winter and spring, chloride concentrations were highest in the diversion box, while up-gradient wells were the lowest. Waters downgradient of the diversion tiles had chloride concentrations lower than the tile but higher than the upgradient waters due to mixing of the diverted tile water and the upgradient groundwater. For the specific site, agriculture contributes chloride, but at concentrations below the chronic threshold of 230 mg/L.

Stream‐breeding salamander use of headwater stream networks in managed forests of western Washington, USA

Abstract Stream‐associated amphibians are sensitive bioindicators in headwater streams across the Pacific Northwest moist coniferous forests of North America. Much of this landscape is intensively managed for timber. Forest Practice (FP) rules determine harvest prescriptions on most private lands in Washington State and cover over 3.7 million hectares. Under these rules, non‐fish‐bearing headwater streams receive buffers on at least 50% of the stream length, including FP Sensitive Sites that receive 15–17 m radius no‐cut patch buffers. We evaluated how torrent (Rhyacotriton spp.) and giant (Dicamptodon spp.) salamander relative abundance is influenced by headwater stream network features that correspond to FP Sensitive Sites. In particular, we examined how salamander relative abundance in the two most common FP Sensitive Sites, tributary junctions (TJs) and perennial initiation points (PIPs), compared to densities in non‐Sensitive Site stream reaches, hereafter branches. We also evaluated salamander relative abundance and two hydrologic characteristics, dry channel and seeps. We analysed data collected in 2006 and 2007 from 17 amphibian‐occupied, non‐fish‐bearing basins in Western Washington with managed forest ages 30–80. We found no relationship between torrent salamander relative abundance and PIPs and TJs or between giant salamander relative abundance and TJs compared to branches. Consistent with expectations, giant salamander relative abundance was less in PIPs than in TJs and branches, and less in first‐order than second‐ and third‐order streams. Conversely, torrent salamander relative abundance lacked a clear relationship to stream order. Giant and torrent salamander relative abundance showed a negative relationship with the proportion of dry channels, but torrent salamanders were observed in short reaches of surface water located in predominantly dry channels. Importantly, reaches with seeps had 123% (CI: +103% to +146%) and 81% (CI: +49% to +121%) greater relative abundance of torrent and giant salamanders, respectively, than reaches without seeps. Practical implication: Current FP rules protect select side‐slope seeps as another category of Sensitive Sites but may too narrowly define the criteria of seeps to protect the full range of those being utilized by stream‐breeding salamanders. Studies focused on seeps and adjacent stream channel characteristics may better inform features important to stream‐breeding salamanders.

Water conductivity mediates differences in clitellate assemblages in spring fens and adjacent streams

Water conductivity mediates differences in clitellate assemblages in spring fens and adjacent streams

Special Particle Precipitation Signatures Over Giant Auroral Undulations During the 7 September 2015 Geomagnetic Storm

AbstractGiant undulations (GUs) have been well established to be the optical manifestation of the plasmapause surface wave (PSW) where the wave‐particle interactions provide particle sources to generate auroras. However, their detailed particles precipitation signatures in the ionosphere remain unclear. Here we analyze multi‐satellite conjugated observations in the ionosphere during a prominent GUs event, revealing the two‐zone precipitation pattern including energetic proton precipitations responsible for the main body of GUs and low‐energy electron precipitations for the edge of GUs. Interestingly, the occurrence of GUs is also accompanied with high‐energy particles precipitations of hundreds of keV and magnetic disturbances of three components. The sizes of sawtooth in the GUs correlate positively with the strength of adjacent subauroral polarization streams (SAPS). The two‐zone precipitation pattern and high‐energy particles precipitation over GUs are potentially related to the plasma sheet and very‐low frequency wave (VLF) modulation of the PSW, respectively.

Microbiomes on microplastics versus natural microcarriers: Stability and transformation during aquatic travel from aquaculture ponds to adjacent stream

Microplastics (MPs) with different physical-chemical properties are considered as vectors for the propagation of microbes in aquatic environments. It remains unclear how plastic types impact on the plastisphere and whether different MPs spread microbes more rapidly than natural materials in microbes across distinct water bodies as proposed previously. We used in-situ incubation to investigate the microbes attached on MPs of polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), versus that on two natural microcarriers (quartz sands and bamboo) during the travel from aquaculture ponds with impacted by fish farming to adjacent freshwater stream. The results showed that the microbial communities on the carriers were shaped not only by environmental conditions, which were primary determinants but also by carrier types. All the tested plastics did not carry more microbes than the natural carriers during the journey. The biofilm community composition on PVC is distinct from that on PE and PP MPs and natural carriers. The plastisphere of PE and PP kept microbial proportions as natural materials did but PVC retained less than nature materials. Bamboo carried more potential pathogens than plastic polymers and quartz. The results indicated that the communities of plastisphere is polymer-type dependent, and, compared with the natural materials, MPs did not show enhanced propagation of microbes, including pathogens, cross distinct environments.

Has climate change over the last ten years caused a banalisation of diatom communities in Cypriot streams?

To unveil possible changes in diatom communities in Cypriot streams over the last ten years or so, we selected samples from the years 2020, 2021, and 2022 for the “recent” dataset (N = 119) and samples from the years 2010 and 2011 for the “historical” dataset (N = 108). Biotic homogenization has become a truly global phenomenon. Here we show that, over the last ten years, in response to increased water temperature, conductivity, and discharge variability due to climate-change, Cypriot stream diatom communities include a higher number of trivial (= widespread, tolerant, and opportunistic), aerial, and thermophilic species, have reduced β-diversity and increased nestedness. Moreover, IndVal analysis shows that indicator species from the historical dataset were characteristic, often relatively rare species, while the indicators of the recent dataset were a group of typical trivial, eutraphentic, and thermophilic species. As is almost always the case, the diatom communities we studied were subjected to multiple stressors, often affecting them in opposite ways. Besides the increase in trivial species, the reduction in β-diversity, and the rise in nestedness mentioned above, the diatom assemblages we studied also showed an increase in α-diversity that could be due to a moderate reduction in nutrients in several sites. High-ecological-integrity ecosystems, such as springs, waterfalls, and dripping rock-walls, in particular springs that were shown to be excellent hydrologic refugia in climates heavily affected by climate change, and the stream sites close to them should be carefully protected, as they can be refugia for sensitive and characteristic species that can recolonize the adjacent streams after adverse climatic events.

Multi-scale network with attention mechanism for underwater image enhancement

Underwater images suffer from severe degradation due to the complicated environments. Though numerous approaches have been proposed, accurately correcting color bias meanwhile effectively enhancing contrast is still a difficult problem. In order to address this issue, a dedicated designed Multi-scale Network with Attention mechanism (MNA) is introduced in this work. Concretely, MNA contains four key characteristics: (a) setting more convolution layers in shallow flows, (b) letting connections from high-level to adjacent low-level stream progressively, (c) simplifying dual attention mechanism embedding it in conventional residual block, (d) exploiting channel attention module to fuse multi-scale information rather than conventional summation operation. Extensive experiments demonstrate that our MNA achieves better performance than some well-recognized technologies. Meanwhile, ablation study proves the effectiveness of each component in our MNA. In addition, extended applications demonstrate the improvement of our MNA in local feature points matching and image segmentation.

Riparian invader: A secondary metabolite of Impatiens glandulifera impairs the development of the freshwater invertebrate key species Chironomus riparius

Invasive species represent a significant threat to native biodiversity. The Himalayan Balsam Impatiens glandulifera is an annual plant, which is invasive in Europe and often inhabits the riparian zone. It produces several secondary metabolites causing, for example, growth inhibition of terrestrial plants and invertebrates. One of these metabolites is the quinone 2-methoxy-1,4-naphthoquinone (2-MNQ). The compound gets washed out from the above-ground parts of the plant during precipitation and may then leach into nearby waterbodies. Despite some evidence for the allelopathic effect of plant secondary metabolites on terrestrial invertebrates, little is known about how 2-MNQ affects the survival or development of aquatic dipteran larvae, despite the importance of this functional group in European freshwaters. Here, we investigated the effects of 2-MNQ on larvae of the river keystone species Chironomus riparius in acute and chronic scenarios. The toxicity of 2-MNQ towards the first and the fourth larval stage was determined in a 48-hour acute exposure assay. We show that 2-MNQ has a negative impact on the development, growth and survival of C. riparius. The LC50 of 2-MNQ was 3.19 mg/l for the first instar and 2.09 mg/l for the fourth instar. A ten-day chronic exposure experiment, where the water was spiked with 2-MNQ, revealed that 2-MNQ had a significantly negative impact on larval body size, head capsule size, body weight, development and survival. These results demonstrate the negative impact of the secondary metabolite 2-MNQ from the terrestrial plant I. glandulifera on a crucial macroinvertebrate inhabiting the adjacent stream ecosystem in riverine ecosystems. This may lead to a decline in population size, resulting in cascading effects on the food web.

Application timing as a mitigation tool for pesticide leaching to drains in northwest Europe

Study regionArtificially drained agricultural land in northwest Europe. Study focusThe use of application timing as a mitigation tool for pesticide leaching to drains was investigated by simulating pesticide fate after application every day in a pesticide-specific application window, using the agro-hydrological model DAISY. The simulations were carried out for six combinations of pesticide-crop-seasons using three synthetically generated climate series and 800 soil profiles. The simulated drain concentrations were transformed to normalized pesticide concentrations in a hypothetical adjacent stream. Each application day was then characterized by the maximum normalized hourly pesticide concentration in the stream, expressed as the maximum hourly toxic unit (mTU), occurring within 300 days after application. New hydrological insights for the regionThe result showed that if the pesticide was applied consistently every year at the best application day, pesticide leaching, in terms of the 90th percentile of mTU, could be reduced by up to 62% compared to a random application. If the pesticide application day was restricted to vary in a five-day period, the 90th percentile of mTU could be reduced by up to 21%. Thus, our study shows that there is a significant mitigation potential for reducing pesticide leaching to drains by tailoring the timing of pesticide application to weather conditions.

Large Wood Transport and Accumulation Near the Separation Zone of a Channel Confluence

AbstractFallen trees enter the adjacent stream and are carried away downstream by the current. As the stream joins another one, the complex hydrodynamics near their confluence make the movement of wood hard to predict. These woods may accumulate near the confluence resulting in backwater and subsequent potential flooding. A laboratory study was conducted to investigate the movement and accumulation behavior of individual pieces of wood near the confluence. The characteristics of wood (i.e., the length, diameter, and density) and the hydraulic conditions (i.e., the discharge ratio and the release distance) were varied in this investigation. It was found that the wooden pieces released from the tributary got occasionally trapped in the flow separation zone of the confluence, whereupon they were mainly trapped by a clockwise vortex and continued to stay driven by a reverse cluster of currents within this zone. The accumulation probability of wood was mainly related to its length, the discharge ratio and the release distance. The effect of wood diameter and density within the tested parameters was negligible. The probability increased with an increase in the discharge ratio as well as a decrease in the release distance. The longer pieces had a higher probability of being trapped, whereas for those exceeding some critical value, the probability was nearly the same, or dropped sharply. A generalized model for wood accumulation near the confluence was developed for practical application. These findings carry significant implications for river management, particularly in preventing the risk of flooding caused by wood blockage.

Seasonal variation in the Chironomidae (Diptera) communities of two Faroese streams

Seasonal variation of freshwater invertebrate communities is strongly influenced by abiotic factors including temperature and precipitation which, in turn, are predicted to be affected by climate change. It is important to study these effects, not least since they may affect higher trophic levels and ecosystem dynamics. Our aim with this study was to compare the seasonal variation of the community composition of Chironomidae (Diptera) in two streams in the Faroe Islands and to see how this related to abiotic factors. Additionally, we studied the life cycle of Tvetenia calvescens (Edwards 1929), the dominant species in the streams. For this purpose, Chironomidae larvae were collected from two adjacent streams of different sizes in the Faroe Islands at regular intervals over the course of 15 months. We found that Tvetenia calvescens was the most abundant species in the streams, followed by Eukiefferiella minor (Edwards 1929). The community composition varied in different months and between the two streams and was shaped by water temperature and flow velocity. Larval densities were generally higher in the smaller stream than in the larger stream, but densities were not correlated with water temperature, monthly temperature amplitude or flow velocity. We found that in both streams Tvetenia calvescens was bivoltine with adult emergence in May/June and September/October.

A Gulf Stream frontal eddy harbors a distinct microbiome compared to adjacent waters.

Mesoscale oceanographic features, including eddies, have the potential to alter productivity and other biogeochemical rates in the ocean. Here, we examine the microbiome of a cyclonic, Gulf Stream frontal eddy, with a distinct origin and environmental parameters compared to surrounding waters, in order to better understand the processes dominating microbial community assembly in the dynamic coastal ocean. Our microbiome-based approach identified the eddy as distinct from the surround Gulf Stream waters. The eddy-associated microbial community occupied a larger area than identified by temperature and salinity alone, increasing the predicted extent of eddy-associated biogeochemical processes. While the eddy formed on the continental shelf, after two weeks both environmental parameters and microbiome composition of the eddy were most similar to the Gulf Stream, suggesting the effect of environmental filtering on community assembly or physical mixing with adjacent Gulf Stream waters. In spite of the potential for eddy-driven upwelling to introduce nutrients and stimulate primary production, eddy surface waters exhibit lower chlorophyll a along with a distinct and less even microbial community, compared to the Gulf Stream. At the population level, the eddy microbiome exhibited differences among the cyanobacteria (e.g. lower Trichodesmium and higher Prochlorococcus) and in the heterotrophic alpha Proteobacteria (e.g. lower relative abundances of specific SAR11 phylotypes) versus the Gulf Stream. However, better delineation of the relative roles of processes driving eddy community assembly will likely require following the eddy and surrounding waters since inception. Additionally, sampling throughout the water column could better clarify the contribution of these mesoscale features to primary production and carbon export in the oceans.

Water Typology in the Amazon: Close Correlation with the Hydrogeochemistry of River Basins

A study on the typology of Amazonian waters was developed in the North Geographic Region of Brazil, considering a set of historical data from 1995 to 2022. The objective was to discuss and point out which environmental parameters are considered preponderant within the classification criteria of Amazonian waters. Historical data on temperature, density, pH, conductivity, oxygen, transparency, light attenuation, turbidity, color, total and dissolved solids, hardness, alkalinity, CaCO3, BOD, COD, main cations and anions, iron, C, N and P fractions, silicate, trace elements (Al, Cu, Zn and Mn) and chlorophyll a were analyzed. The analysis comprised water samples from the National Hydrometeorological Network (Sub-Basins 10 to 19), with a total of 36 basins, including tributaries, lakes and adjacent streams. The historical series was statistically analyzed through the techniques of Cluster, Principal component analysis (PCA), Piper Diagram and image interpolation by the ordinary kriging method. The results indicated a strong seasonal trend, with an evident distinction between the flood and ebb periods. The typology of white, black and clear waters was also evidenced, this last group being an intermediate class to the others, due to the physical-chemical standards. The PCA highlighted the parameters conductivity, pH, calcium, bicarbonate and Dissolved inorganic carbon (DIC) (Factor 1), and turbidity and alkalinity (Factor 2) as preponderant in the water classification. The ionic balance demonstrated that the white waters stood out for the highest concentrations of calcium and magnesium. The results suggest a pattern of calcic waters oscillating towards sodic and carbonated waters, with a subgroup in the northern eastern region of seasonally sodic-chlorinated waters, due to the influence of ocean tides. Image interpolation suggested a predominance of white waters in the western southern zone (Western Amazon) and white waters transitioning to clear waters in the eastern zone (Eastern Amazon). The analysis also showed a predominant strip of black and clear waters in the northern zone, and a strip of white waters in the central Amazon.

Applicability of central composite design and response surface methodology for optimizing treatment of landfill leachate using coagulation-flocculation

Without proper treatment, leachate can contaminate adjacent groundwater, soils, and streams, resulting in potential risks to public health, the environment, and surrounding biodiversity. This work aims to treat landfill leachate by coagulation-flocculation and optimize the results using the central composite design in combination with the response surface methodology in the Mohammedia-Benslimane landfill in Morocco. The optimization of the process allowed us to find optimal removal efficiencies of color, polyphenols, and nitrates, which reached 68.8%, 77.5%, and 81.0%, respectively. The optimum conditions in this study were pH 7.66, 9.5 g/L of coagulant dose, 9.1 ml/L of flocculant dose, and 10 min of agitation time. The models obtained for the 3 responses are reliable, reproducible, and well-fitted. By optimizing the leachate treatment at the Mohammedia-Benslimane landfill using coagulation-flocculation and the response surface methodology, our study offers an efficient and reliable approach to address the challenges of landfill leachate treatment. The results obtained from this research have significant implications for liquid waste management, particularly in the context of landfill leachate treatment.

Use of legacy nitrogen as a resource: Unfertilized lotus fields contribute to water quality improvement and biodiversity conservation

Managing legacy nitrogen (N) that has accumulated over decades of intensive agriculture is necessary to balance agricultural production and environmental conservation. Using legacy N as a resource can reduce extant legacy N. The uplands of Japan's Lake Inba watershed are dominated by agroecosystems, and spring waters in the lowlands contain high NO3-N concentrations. We focused on an unfertilized, commercial lotus (Nelumbo nucifera) farm where paddy fields are irrigated with spring waters. We hypothesized that the lotus field could reduce the export of legacy N and provide habitat for fish (co-benefit). Dating of spring waters using sulfur hexafluoride revealed that the residence time of water at the study site was 12.5 years and suggested that the spring waters contained legacy N. We found large reductions of NO3-N and total nitrogen (TN) concentrations in water that passed through the lotus fields. A meta-analysis revealed that the reductions of NO3-N concentrations were highest in unfertilized lotus fields, and reductions of TN concentrations were higher in unfertilized paddy and lotus fields than in fertilized fields. The N removal by harvesting lotus roots 38.7 kg N/ha/year was smaller than the literature-based rate of N removal by denitrification. We used environmental DNA metabarcoding to identify the fish fauna in the lotus fields and an adjacent stream. The native fish richness was a little lower in the lotus fields than in the stream, but the presence of two endangered fish species in the lotus field suggested a moderate biodiversity conservation function. Our case study could be a good example of a nature-based solution to harness ecosystem functions to reduce legacy N.

Adjacent and downstream effects of forest harvest on the distribution and abundance of larval headwater stream amphibians in the Oregon Coast Range

Forest harvest is a primary landscape-scale management action affecting riparian forests. Although concerns about impacts of forest harvest on stream amphibians is generally limited to areas adjacent to harvest, there is a paucity of information regarding potential downstream effects of forest harvest on these species. We designed a before-after, control-impact (BACI) experiment to quantify potential impacts of clearcut logging that included 12-m buffers or smaller variable-width buffers on the distribution and abundance of headwater stream amphibians in adjacent and downstream areas. We sampled larval coastal tailed frogs (Ascaphus truei), coastal giant salamanders (Dicamptodon tenebrosus), and Columbia torrent salamanders (Rhyacotriton kezeri) across 3,915 sampling occasions that spanned 13 study reaches in 2008–2011 (pre-harvest) and 2013–2016 (post-harvest) as part of the Trask River Watershed Study in the Oregon Coast Range, U.S.A. We analyzed these data using occupancy models to estimate occupancy and (when possible) relative abundance, while accounting for various sources of imperfect detection. All species exhibited reduced occupancy adjacent to clearcuts with variable-width buffers (odds ratios [ORs] ranged = 0.24–0.48), and these negative impacts were not always diminished when increasing the buffer size to 12 m (ORs ranged = 0.20–3.56). Dicamptodon tenebrosus was the only species to have occupancy impacted in downstream areas, and this negative impact was related to clearcut logging with uniform 12-m buffers (OR = 0.60). This species was also the only species to have abundance negatively impacted by forest harvest in downstream areas (OR = 0.41 with uniform 12-m buffers, OR = 0.38 with variable-width buffers), albeit impacts to abundance were not evaluated for R. kezeri. Ascaphus truei abundance increased in areas downstream of clearcut logging with uniform 12-m buffers (OR = 2.92). Although we found the direction and magnitude of responses varied by species, our study confirms that clearcut logging can have negative impacts on amphibians that inhabit the adjacent stream areas. Perhaps more importantly, we also found that forest harvest can have negative effects on stream amphibians downstream of the harvested area and that increasing the buffer size to 12 m did not necessarily diminish these impacts in adjacent and downstream areas. Altogether, our study provides a nuanced picture of adjacent and downstream effects of forest harvest on three endemic headwater stream amphibians, and our findings demonstrate that forest management practices should consider downstream effects on aquatic taxa when assessing the impact of harvesting trees near headwater streams.

Environmental risk assessment for fecal contamination sources in urban and peri-urban estuaries, in Escambia and Santa Rosa counties, FL, USA.

Fecal pollution of estuaries and adjacent creeks and streams is of significant concern along the Gulf of Mexico. The prospective threat to human life and water quality impairment via fecal pollution is a substantial danger to the strength and resistance of coastline areas. Pensacola, FL, has a prosperous coastal tourism industry that is utilized for numerous other uses, such as recreational watersports and boating, seafood, and shellfish harvesting. However, the frequency and severity of fecal contamination present possible socio-economic issues, specifically financial hardships. Therefore, understanding the source, abundance, and fate of fecal microbial pollutants in aquatic systems signifies an imperative initial stage for detecting the host sources and techniques to lessen their transport from the landscape. This research aimed to quantify the fecal indicator bacteria (FIB), Escherichia coli, and perform microbiological fecal source tracking to verify if the fecal inputs are of either animal or human host origin. Surface water samples were taken from urban and peri-urban creeks for two sampling periods (February 2021 and January 2022), and IDEXX Colilert-18 (USEPA Standard Method 9223) was used for E. coli enumeration. DNA extractions were obtained from each sample, and quantitative PCR was utilized for fecal microbial source tracking (MST) to detect human, dog, ruminant, and bird host-specific Bacteroides DNA. The result indicates elevated quantities of FIB, E. coli, that surpass the threshold considered safe regarding human health. E. coli at six sites over the two sampling periods exceeded the impairment threshold, reaching as high as 866.4 MPN/100ml. Fecal source tracking identified human host fecal contamination at four of nine sites, dogs at three of nine, and birds at one site. However, those sites with sources identified via MST all had E. coli levels below impairment thresholds. No sites were determined to be positive for ruminant as a source or for the pathogen Helicobacter pylori. No canine host fecal inputs were found in January 2022, and only one site with human sewage. Our results highlight the utility of MST in assessing bacterial inputs to water bodies and the challenges.

Helios 2 observations of solar wind turbulence decay in the inner heliosphere

Aims. A linear scaling of the mixed third-order moment of the magnetohydrodynamic (MHD) fluctuations is used to estimate the energy transfer rate of the turbulent cascade in the expanding solar wind. Methods. In 1976, the Helios 2 spacecraft measured three samples of fast solar wind originating from the same coronal hole, at different distances from the Sun. Along with the adjacent slow solar wind streams, these intervals represent a unique database for studying the radial evolution of turbulence in samples of undisturbed solar wind. A set of direct numerical simulations of the MHD equations performed with the Lattice-Boltzmann code FLAME was also used for interpretation. Results. We show that the turbulence energy transfer rate decays approximately as a power law of the distance and that both the amplitude and decay law correspond to the observed radial temperature profile in the fast wind case. Results from MHD numerical simulations of decaying MHD turbulence show a similar trend for the total dissipation, suggesting an interpretation of the observed dynamics in terms of decaying turbulence and that multi-spacecraft studies of the solar wind radial evolution may help clarify the nature of the evolution of the turbulent fluctuations in the ecliptic solar wind.

Water temperature dynamics in a headwater forest stream: Contrasting climatic, anthropic and geological conditions create thermal mosaic of aquatic habitats.

The thermal regime of streams is a relevant driver of their ecological functioning. As this regime is presently submitted to numerous alterations (among others, impoundments, and climate change), it seems important to study both their effects and potential recovery from the latter. Thus, we investigated the surface and hyporheic water temperature along a small headwater stream with contrasting environmental contexts: forest landscape, open grassland landscape without riparian vegetation, several artificial run-of-the-river impoundments and one discharge point of a by-pass impoundment. The main objectives were to study the influence of these contrasting contexts on surface and subsurface water temperature at a local scale. Contrasting contexts were supposed to create effects on both surface and hyporheic thermal regimes at a local scale. Differences of thermal regimes between surface and hyporheos were expected, as well as between geological contexts. Sensors located at multiple stations allowed monitoring of stream and hyporheos temperature along the stream, while comparison with adjacent reference stream allowed for surface water thermal regime benchmark. Impoundments and landscapes significantly influenced stream thermal regime at a local scale (impoundments created up to +3.7°C temperature increase in average). Their effect on hyporheos thermal regime was less marked than the ones generated by solar radiation or geological features. Hyporheos thermal regime varies from stream one by temperature dynamics delay (up to 18h) and decrease (up to -7°C between surface and hyporheos temperature in average). These coupled effects create a mosaic of thermal habitats, which could be used for river biodiversity preservation and restoration.