Hyporheic Research Articles

South America stygobiont crustaceans: a new species of Hyalellidae (Amphipoda) and new reports of Stygocarididae (Anaspidacea) and Protojaniridae (Isopoda) from Calingasta Valley, Pre-Andean region, San Juan, Argentina

We describe one new eyeless Hyalella species, H. cuyana n. sp., from the hyporheic zone of Calingasta River, San Juan Province, Argentina. Hyalella cuyana n. sp. differs morphologically from its stygobiont congeners by characters of antennae (both antennae subequal in size; aesthetascs elongated); coxal plate 4 (posteriorly without excavation); epimeral plates 1-3 (rounded posterodistally); male gnathopod 2 propodus (almond-shaped, ovate, palm slope strongly oblique); and pleopods (inner ramus reduced to 2-3 articles). We provide a detailed morphological comparison between stygobiont and stygophile Hyalella species. We comment on the sympatry and new report of stygobiont Malacostraca species Parastygocaris andina and Cuyojanira sp. Severe environmental changes and significant decline of habitat quality recorded along the Calingasta River increase the risk of extinction for this vulnerable and endemic fauna. We recommend that the new Hyalella species should be listed as Critically Endangered (CR) in the IUCN categorization according to criteria B1a as it is only known from the type locality; and criteria B1b iii (continuing decline, observed, inferred in the quality of habitat).

Analysis of the interaction between surface water and groundwater using gaseous tracers in a dynamic test at a riverbank filtration intake

AbstractWe discuss a study designed to elucidate the genesis and inflow conditions at riverbank filtration wells located on a mountain river. This article seeks to identify the most important drivers of spatio‐temporal dynamics of water flow in the hyporheic exchange zone, in natural conditions and conditions disturbed by the water abstraction. In our study we try to contribute to further understanding the dynamics of groundwater mixing with river water in the hyporheic exchange zone. We focus on understanding river/aquifer interactions at the scale of reach of an intake, especially the unidirectional water flows induced by water abstraction. To understand these issues, a two‐day field hydrogeological experiment was conducted based on a pumping test of increasing intensity. At each pumping stage, groundwater and river samples were collected to determine the concentration of noble gases, CFCs, SF6, stable isotope content, and the chemical composition of the water. The study results indicate a short pressure propagation time (of the order of several hours) between the intake and the river, which already results in the inflow of water from the river–aquifer mixing zone at low rates of water abstraction by the intake. As pumping rates increase, the conditions of mixing and inflow of water to individual wells stabilize or approach stabilized conditions in less than 1–2 days. The share of river water in the water flux flowing into the intake does not exceed 12%, whereas the ratio of river water to groundwater in the mixing zone is estimated at 1 to 7 or more. The range of the river‐aquifer mixing zone may reach up to 170 m from the river and this range can be identified with a good approximation as coinciding with the range of the zone of hyporheic exchange in the study area.

Real‐Time Monitoring and Postprocessing of Thermal Infrared Video Images for Sampling and Mapping Groundwater Discharge

AbstractGroundwater discharge along channels can affect stream discharge, chemistry, and ecological communities. Although the spatial distribution of groundwater springs along wide rivers can be investigated by areal thermal infrared (TIR) remote sensing, this technique is difficult to apply to mapping at a high spatial resolution and under riparian tree canopies. We present a real‐time monitoring and postprocessing method of ground‐based TIR video for determining groundwater discharge sampling points and mapping the surface water temperature. We applied this method to mapping two headwater streams in Hokkaido, Japan, in the summer. The first site was a 1.3‐km‐long reach underlain by Pleistocene andesite lava. Almost all of the springs were colder and had a different chemistry compared to that of the stream water, which supports the usefulness of TIR monitoring for determining groundwater discharge zones. Video postprocessing showed that cold groundwater springs were spaced every ∼100 m, and their distribution did not follow the topography. At the second site, cold and warm springs were underlain by Holocene volcanic ash. The cold springs mainly seeped from hyporheic and riparian zones downstream, while warm springs were at the footslope. Some cold springs had much higher solute concentrations than the stream and warm springs, which suggests that the water temperature is useful for inferring sources of groundwater discharge. At this site, the video postprocessing could map not only the locations of the cold springs but also the spatial heterogeneity of the stream temperature associated with groundwater inputs.

Moving Bedforms Control CO2 Production and Distribution in Sandy River Sediments

AbstractStreams and rivers play an important role in the global carbon cycle. The origins of CO2 in streams are often poorly constrained or neglected, which is especially true for CO2 originating from heterotrophic metabolism in streambeds. We hypothesized that sediment movement will have a direct effect on stream metabolism, and thus, the aim of this study was to quantify the effect of moving bedforms on the production of CO2 in sandy streambeds. We conducted flume experiments where we used planar optodes to measure the distributions of O2 and CO2 under various streambed celerities. We combined these measurements with an assessment of bed morphodynamics and modeling to calculate O2 consumption and CO2 production rates. Our results indicate that sediment transport can strongly influence streambed metabolism and CO2 production. We found that bedform celerity controls the shape of the hyporheic zone and exchange flux, and is directly linked to the spatial and temporal distributions of O2 and CO2. It was also found that the most pronounced change in CO2 production occurred when the bed changed from stationary conditions to a slowly moving bed. A more gradual increase in O2 consumption and CO2 production rates was observed with further increase in celerity. Our study also points out that bedform movement causes hydraulic isolation between the moving and the non‐moving fraction of the streambed that can lead to a transient storage of CO2 in deeper sediments, which may be released in bursts during bed scour.

Clogging modulates the copper effects on microbial communities of streambed sediments

The hyporheic zone, i.e. the water-saturated sediment beneath and alongside the riverbed, is exposed to multiple stressors. Agricultural-watershed rivers are frequently exposed to two concomitant stressors: clogging and copper contamination. However, one stressor exposure can increase sensitivity to a second stressor. The aim of this study was to experimentally test the cumulative effects of these two stressors on copper distribution and structural and functional microbial communities responses in the hyporheic zone. A slow filtration column experiment was conducted to compare the effects of 3 treatments of increasing complexity: 'Reference', 'Copper-contaminated' (dissolved copper added at 191 µg L-1), and 'Clogging+Copper' (dissolved copper + addition of 2 cm of fine sediment). Microbial community structure and activities were studied at 4 column sediment depths. The results showed that clogging did not modify the distribution of copper, which remained fixed in the first few centimetres. In the first few centimetres, clogging had a stimulating effect on microbial activities whereas copper had limited effects mainly on leucine aminopeptidase activity and microbial community tolerance to copper. The subsurface zone thus hosts significant different microbial communities from the communities in the deeper zones that were protected from surface stressors. This experiment confirms the valuable filtering role played by the hyporheic zone and shows that microbial responses are strongly correlated to microhabitat-scale physicochemical conditions in sediment.

Logjam Characteristics as Drivers of Transient Storage in Headwater Streams

AbstractLogjams in a stream create backwater conditions and locally force water to flow through the streambed, creating zones of transient storage within the surface and subsurface of a stream. We investigate the relative importance of logjam distribution density, logjam permeability, and discharge on transient storage in a simplified experimental channel. We use physical flume experiments in which we inject a salt tracer, monitor fluid conductivity breakthrough curves in surface water, and determine breakthrough‐curve skewness to characterize transient storage. We then develop a companion numerical model in HydroGeoSphere to reveal flow paths through the subsurface (or hyporheic zone) that contribute to some of the longest transient‐storage timescales. In both the flume experiments and numerical simulations, we observe backwater formation and an increase in hyporheic exchange at logjams. Observed complexities in transient storage behavior depend largely on surface water flow in the backwater zone. As expected, multiple successive logjams provide more pervasive hyporheic exchange by distributing the head drop at each jam, leading to distributed but shallow flow paths. Decreasing the permeability of a logjam or increasing the discharge both facilitate greater surface water storage and volumetric rate of hyporheic exchange. Understanding how logjam characteristics affect solute transport through both the channel and hyporheic zone has important management implications for rivers in forested, or historically forested, environments.

Research hotspots and trends of groundwater and ecology studies: Based on a bibliometric approach

Groundwater, as a critical component of the hydrological cycle, is essential for sustainable ecosystem development. To clarify the current status of domestic and overseas research, and to identify hotspots, frontier and future trends of groundwater and ecology research, this study utilizes bibliometric methods and CiteSpace software to examine relevant published articles in the Web of Science (WOS) and CNKI databases from 1978 to 2022. Specifically, this study analyzes (1) the annual number of published papers; (2) research institutions; (3) keywords; and (4) evolution of research hotspots. The findings reveal that the United States, China, and Germany are the top three countries in groundwater and ecology research. International research hotspots mainly focus on microbial ecology, climate change, groundwater-surface water interactions in the hyporheic zone, biodiversity, and submarine groundwater discharge, while domestic research hotspots mainly focus on ecological water conveyance, ecological flow, groundwater development and utilization, groundwater pollution, and groundwater and ecological protection. Both domestic and international research hotspots exhibit interdisciplinary features with diverse research objects and assessment methods. Future research in this area is expected to focus on topics such as contamination, groundwater quality, framework, mechanism, spatial distribution, and dissolved organic matter. Additionally, the study of ecological recharge, ecological flow, ecological protection, water intake and use will continue to be the hot topics domestically.

Solute transport characteristics in the streambed due to rigid non-submerged plants: Experiment and simulations

The presence of aquatic plants in natural and artificial rivers can cause substantial changes in the flow pattern. In this study, laboratory experiments and numerical simulations are conducted to explore the influences of rigid non-submerged plant densities on the transport of solutes in the hyporheic zone. The laboratory experiments and numerical modelling results show that solute enters into the streambed around plant, and solute in the overlying water experienced a sharp decrease at the beginning, followed by a gradual decline phase. The concentration in the shallow pore water increases rapidly, and increases at a decreasing rate with the increase of depth. The presence of a plant causes pressure gradients at the sediment–water interface before and after the plant. Specifically, the presence of plants induces the convection exchange of surface water and pore water, enables the solute to transport in the streambed through three circulation flows. Solute tends to transport to the root of the plant, or bypass the plant and return to the overlying water over time. The rate and quantity of solute transport in the streambed are related to the streamwise and spanwise distances of the plant. When the plant densities reach the distance that affect the flow structures near each other, smaller streamwise distances lead to the transport of fewer solutes into the streambed and prevent them from penetrating to the deeper part of the streambed, while larger spanwise distances have the same effect on solute transport in the streambed. The solute effective exchange depth for streamwise distance of 20 cm is 4.3 times that of 3 cm, while which for spanwise distance of 3 cm is 5.05 times that of 15 cm at time of 28 h. This study shows that the presence of aquatic plants leads to the circulation of solutes in the hyporheic zone, which promotes the transport of pollutants from overlying water to streambed through hyporheic exchange after the occurrence of a water pollution event. Further, plants densely in the streamwise direction and sparsely in the spanwise direction will reduce the range of pollutants transport in the streambed. This study is of great significance for water ecological restoration through rational arrangement density of aquatic plants.

Geographic and hydromorphologic controls on interactions between hyporheic flow and discharging deep groundwater

Hyporheic exchange flow (HEF) at the streambed–water interface (SWI) has been shown to impact the pattern and rate of discharging groundwater flow (GWF) and the consequential transport of heat, solutes and contaminants from the subsurface into streams. However, the control of geographic and hydromorphological catchment characteristics on GWF–HEF interactions is still not fully understood. Here, the spatial variability in flow characteristics in discharge zones was investigated and averaged over three spatial scales in five geographically different catchments in Sweden. Specifically, the deep GWF discharge velocity at the SWI was estimated using steady-state numerical models, accounting for the real multiscale topography and heterogeneous geology, while an analytical model, based on power spectral analysis of the streambed topography and statistical assessments of the stream hydraulics, was used to estimate the HEF. The modeling resulted in large variability in deep GWF and HEF velocities, both within and between catchments, and a regression analysis was performed to explain this observed variability by using a set of independent variables representing catchment topography and geology as well as local stream hydromorphology. Moreover, the HEF velocity was approximately two orders of magnitude larger than the deep GWF velocity in most of the investigated stream reaches, indicating significant potential to accelerate the deep GWF velocity and reduce the discharge areas. The greatest impact occurred in catchments with low average slope and in reaches close to the catchment outlet, where the deep GWF discharge velocity was generally low.

Abiotic reduction of nitrate to ammonium by iron (oxy)(hydr)oxides and its stable isotope (δ15N, δ18O) dynamics

In this study, the kinetics and stable isotopic fractionation of nitrate (NO3−) reduction in Fe(II)/Fe(III) homogeneous/heterogeneous systems were investigated at circumneutral pH (i.e., pH 6.5 to 7.5) and ambient temperature (24 °C). Of the suite of iron (oxy)(hydr)oxides examined, NO3− reduction by Fe(II) was only significant in the presence of layered double hydroxide green rust (GR) minerals. Comparison of type 1 and type 2 GRs demonstrated that type 1 (GR(Cl−)) had the fastest NO3− reducing ability, with an Fe(II)-normalized pseudo first-order kinetic rate constant of kobs (NO3−) = 16.2 × 101 M−1 d−1. Anion concentrations (SO42− or Cl−) and the ratio of [Fe(II)] to [Fe(III)] also influenced reduction kinetics. Ammonium (NH4+) was the predominant reaction end-product (>50%) with the remaining reduced N species concluded to be comprised of N2(g) as other intermediates (nitrite (NO2−), nitric oxide (NO) and nitrous oxide (N2O) were not detected during NO3− reduction. Apparent nitrogen (δ15N-NO3−) isotopic fractionation (15ε) for GR(Cl−) and GR(SO42−) were were calculated to be 12.9 (CI: 8.2, 16)‰ and 37.9 (CI: 34, 41)‰, respectively. Similarly, oxygen (δ18O-NO3−) isotopic fractionation (18ε) differed between GR(Cl−) and GR(SO42−): 4.53 (CI: 2.5, 5.8)‰ and 14.4 (CI: 12, 16)‰. However, the ratio of 18ε:15ε for both minerals could be fitted to a linear regression of slope 0.369 (CI: 0.361, 0.377). These findings reaffirm the importance of GR minerals to NO3− reduction, especially in iron-rich systems hosting dynamic redox oscillations, including hyporheic zones, estuarine sediments and groundwater aquifers. These results also demonstrate that N and O stable isotope kinetic fractionation analyses as well as the ratio of 18ε:15ε can provide a means to distinguish between this abiotic anoxic reaction from anaerobic bacterial NO3− reduction processes.

Microbial community structural response to variations in physicochemical features of different aquifers.

The community structure of groundwater microorganisms has a significant impact on groundwater quality. However, the relationships between the microbial communities and environmental variables in groundwater of different recharge and disturbance types are not fully understood. In this study, measurements of groundwater physicochemical parameters and 16S rDNA high-throughput sequencing technology were used to assess the interactions between hydrogeochemical conditions and microbial diversity in Longkou coastal aquifer (LK), Cele arid zone aquifer (CL), and Wuhan riverside hyporheic zone aquifer (WH). Redundancy analysis indicated that the primary chemical parameters affecting the microbial community composition were NO3 -, Cl-, and HCO3 -. The species and quantity of microorganisms in the river-groundwater interaction area were considerably higher than those in areas with high salinity [Shannon: WH (6.28) > LK (4.11) > CL (3.96); Chao1: WH (4,868) > CL (1510) > LK (1,222)]. Molecular ecological network analysis demonstrated that the change in microbial interactions caused by evaporation was less than that caused by seawater invasion under high-salinity conditions [(nodes, links): LK (71,192) > CL (51,198)], whereas the scale and nodes of the microbial network were greatly expanded under low-salinity conditions [(nodes, links): WH (279,694)]. Microbial community analysis revealed that distinct differences existed in the classification levels of the different dominant microorganism species in the three aquifers. Environmental physical and chemical conditions selected the dominant species according to microbial functions. Gallionellaceae, which is associated with iron oxidation, dominated in the arid zones, while Rhodocyclaceae, which is related to denitrification, led in the coastal zones, and Desulfurivibrio, which is related to sulfur conversion, prevailed in the hyporheic zones. Therefore, dominant local bacterial communities can be used as indicators of local environmental conditions.

Composition and distribution of hyporheic and macrobenthic fauna in a Neotropical mountain river, Colombia

This study examined the composition and diversity of the invertebrate communities that inhabit the hyporheic zone (HZ) in the upper and lower basins of the Dagua River, a tropical mountain stream, and their relationship with the macrobenthic fauna. In the HZ, different taxa were collected, many of which have been reported in several regions worldwide, suggesting that the biodiversity of the hyporheic community in Colombian rivers may be high. Although the hyporheic and macrobenthic fauna shared a moderate percentage (> 50 %) of taxa, their ecological structures were different. The analysis of hyporheic filtrate water showed the presence of microplastic (MP) fibers as well as fauna, a condition that, based on the literature review, could represent a risk for the normal functioning of this river ecosystem.

Effects of plastisphere on phosphorus availability in freshwater system: Critical roles of polymer type and colonizing habitat

Biofilm covered microplastics (BMPs) can act as vectors for the transport of exogenous microbial groups to aquatic ecosystem. However, a consensus regarding the formation and development of BMPs and their effect on phosphorus (P) availability has not been reached. Herein, plastic particles made of fuel-based (PET) and biobased polymers (PLA) were deployed in water and hyporheic zones of an urban river for biofilm colonization. Then, BMPs were transferred to lab incubation to study their effects on the P availability. The results showed that different microplastic biofilms had various bacteria and phytoplankton compositions. Additionally, BMPs induced a shift in the microbial co-occurrence patterns co-differentiated by polymer type and colonizing habitats. Network analyses revealed that the structure of PLA BMPs was more robust, while PET colonized in the hyporheic zone reduced network complexity with looser connections between species, and stronger negatively correlated interactions. However, PET formed denser biofilms by the excretion of extracellular polymeric substances from microalgae, which contributed to the better capacity of P utilization. PET colonized in the water/hyporheic zone significantly decreased soluble reactive phosphate by 42.5 % and 30.8 %, respectively. The abovementioned results indicated that BMPs have the potential to disrupt nutrient availability. This study broadens our perspectives for the ecological effects of BMPs in the aquatic environment.

Hyporheic exchange law driven by spur dikes: Numerical modeling

The study of hyporheic exchange and the temperature response law driven by spur dikes is helpful to promote the protection of ecological river environments. Taking the river channel course with a spur dike as the research object, the numerical simulation method was used to study the influence of the river width narrowing rate (L/B), spur dike angle (θ), surface water velocity (U), and hydraulic conductivity (K) on the hyporheic exchange characteristics and the temperature response of the hyporheic zone. Research shows that the degree of hyporheic exchange and the spatial range of the temperature response of the hyporheic zone are positively correlated with the river width narrowing rate, surface water velocity and hydraulic conductivity and negatively correlated with the spur dike angle. The temperature response law of the hyporheic zone is affected by spur dikes in different spatial locations in the following ways, from the cross-section, the upstream response area of the spur dike deepens near the dam bank, while the downstream response area deepens on the other side of the spur dikes, and the downstream response area affected by spur dikes is significantly larger than the upstream response area in the vertical range. From the side section, the response area of the curved boundary appears around the spur dike in the central section of the river, and the curvature radius of the response area of the curved boundary around the spur dike in the side section near the dam is smaller. From the longitudinal section, the sensitivity of the temperature response of the shallow section is significantly stronger than that of the deep section. Consequently, we found that the hyporheic exchange law driven by spur dikes. We offer recommendations for future studies seeking to choose the reasonable structure of the spur dam in practical engineering, and optimize the design of the spur dam.

The family Hydroptilidae Curtis (Trichoptera) in the Ogasawara Islands, northwestern Pacific, with particular reference to adaptive radiation in the oceanic islands

The caddisfly family Hydroptilidae Curtis was revised for the oceanic Ogasawara (Bonin) Islands, northwestern Pacific. Six endemic species of the genus Hydroptila Dalman 1819 (H. demersa Ito & Sasaki sp. nov., H. ishiura Ito & Sasaki sp. nov., H. tokoyo Ito & Sasaki sp. nov., H. hahajima Ito & Sasaki sp. nov., H. nagahama Ito & Sasaki sp. nov. and H. ogasawaraensis Ito 2011, in Ito et al. 2011) are recognized based on larval and adult morphology and molecular analysis. Each of six species was not distributed widely but limited to a narrow area: H. ogasawaraensis on Chichi-jima, H. tokoyo on southern Chichi-jima, H. demersa and H. ishiura on Ani-jima and northern Chichi-jima, H. hahajima on southern Haha-jima, and H. nagahama on central Haha-jima. This speciation pattern in the small area might be an example of adaptive radiation in these oceanic islands. The larva of H. demersa has an elongate and depressed head capsule and makes a slightly compressed case with rough surface, suggesting that it inhabits the hyporheic zone, where aquatic organisms are scarce in the oceanic islands. The other five species, H. ishiura, H. tokoyo, H. hahajima, H. nagahama, and H. ogasawaraensis, were often found in hygropetric habitats and small waterfalls, where other species of microcaddisflies are absent. Small dorsal sclerites of abdominal segments I-III of larvae in the five species may be another adaptation to this microhabitat with rapid water flow.

Temporal moments of one-dimensional advective-dispersive transport with exchange represented via memory function models: Application to river corridor transport

Practical simulation of solute transport in river corridors often relies on one-dimensional transport models with solute flux between river and hyporheic zone governed by a mass exchange term, perhaps most generally expressed using the ‘memory function’ formalism. While expressions for temporal moments of solute breakthrough curves (BTCs) are available for a number of such models, those for memory function forms are not, to our knowledge. Here we report closed-form BTC temporal moment expressions for memory function forms, found by exploiting the connection to phase exposure-dependent exchange (PhEDEx) formulations. We use these results to investigate the general capability of the memory function form to accommodate specific scaling of river tracer temporal moments reported in the literature, and we apply the method to identification of parameters in application to two recent tracer tests. The applications involve a simple numerical solution to the memory function river corridor transport model calibrated using measured temporal moments of the tracer test BTCs. The numerical model is validated only for the classical case of the transient storage model without lateral inflow, the analytical solution for which we adapt from the Lassey solution for mobile-immobile exchange in porous media. It should be noted that the temporal moments results obtained here in the context of river corridor transport also apply to one-dimensional transport in two-domain (mobile-immobile) porous media, when governed by a two-domain memory function model.

Micro‐computed tomography scanning approaches to quantify, parameterize and visualize bioturbation activity in clogged streambeds: A proof of concept

AbstractFine particle clogging and faunal bioturbation are two key processes co‐occurring in the hyporheic zone that potentially affect hyporheic exchange through modifications in the sediment structure of streambeds. Clogging results from excessive fine sediment infiltration and deposition in rivers, and it is known to decrease matrix porosity and potentially reduce permeability. Faunal bioturbation activity may compensate for the negative effect of clogging by reworking the sediment, increasing porosity, and preventing further infiltration of fines. Although both processes of clogging and bioturbation have received significant attention in the literature separately, their combined effects on streambed sediment structure are not well understood, mostly due to the lack of a standard methodology for their assessment. Here, we illustrate a novel methodology using X‐ray computed tomography (CT), as proof of concept, to investigate how, together, clogging and bioturbation affect streambed porosity in a controlled flow‐through flume. By visualising gallery formations of an upward conveyor macroinvertebrate; Lumbriculus variegatus as a model species, we quantified bioturbation activity in a clogged streambed, focusing on orientation, depth, and volume at downwelling and upwelling areas of the flume. Gallery creation increased the porosity of the streambed sediment, suggesting a potential improvement in permeability and a possible offset of clogging effects. We illustrate the promising use of X‐ray CT as a tool to assess bioturbation in clogged streambeds, and the potential role of bioturbation activity supporting hyporheic exchange processes in streambeds, warranting further studies to understand the extent of bioturbation impacts in natural systems.

Metal bioaccumulation in stygophilous amphipod Synurella ambulans in the hyporheic zone: The influence of environmental factors

Given the increasing need to protect vulnerable freshwater ecosystems and make them more resilient to human use and climate change, biomonitoring of the hyporheic zone (HZ), which plays a critical role in pollution attenuation, is essential. The aim of the present study was to assess the potential of the amphipod species Synurella ambulans as a bioindicator of metal contamination in the HZ of the Sava River (Croatia). Amphipods were collected during the four seasons at two sampling sites (average sampling depth 55 cm) differing in type (agricultural and urban) and intensity (diffuse and point source contamination) of anthropogenic influence, one located upstream (Medsave), and the other downstream (Jarun) of the wastewater treatment plant discharge. Concentrations of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Rb, Sn, Zn, Ca, K, Mg and Na were measured in the interstitial water, sediments and specimens of S. ambulans by HR ICP-MS. Physicochemical parameters (temperature, DO, O2 saturation, pH, conductivity, alkalinity, total water hardness, CODKMnO4, nutrients) were measured in the interstitial water, while organic carbon was measured in the interstitial water and sediments. Metal concentrations in interstitial water and sediments were below thresholds set by environmental quality standards. Metal concentrations in S. ambulans were classified as follows: higher at the Jarun site (Al, Cr, Fe, Ni, Pb, Sn), higher at the Medsave site (Cd, Cu, Rb) and mostly comparable at both sites (Co, Mn, Zn). Bioaccumulation factors were generally higher at Jarun, with average values ranging from 322 to 143,278 L kg−1. Bioaccumulation of metals in S. ambulans depended on various environmental factors, with metal exposure level and dissolved macro elements showing the strongest association with metals accumulated in S. ambulans. The findings provided the first evidence on the suitability of S. ambulans as a good bioindicator of chronic metal contamination in the HZ.

Temporal dynamic of antibiotic resistance genes in the Zaohe-Weihe hyporheic zone: driven by oxygen and bacterial community

The widespread spread of antibiotic resistance genes (ARGs) in hyporheic zone (HZ) has become an emerging environmental problem due to their potentially harmful nature. In this research, three different oxygen treatment systems were set up to study the effects of oxygen changes on the abundance of ARGs in the HZ. In addition, the effects of temperature and salinity on ARGs were investigated under aerobic and anaerobic systems, respectively. The bacterial community composition of sediment samples and the relationship with ARGs were analyzed. The explanation ratio and causality of the driving factors affecting ARGs were analyzed using variation partitioning analysis (VPA) and structural equation model (SEM). The relative abundance of ARGs and mobile genetic elements (MGEs) in the anaerobic system increased significantly, which was higher than that in the aerobic system and the aerobic-anaerobic interaction system. The experiment of salinity and temperature also further proved this result. There were many bacterial communities that affected tetracycline and sulfonamide ARGs in sediments, and these host bacteria are mainly concentrated in Proteobacteria, Firmicutes and Bacteroidetes. VPA and SEM further revealed that the abundance of ARGs was mainly influenced by changes in bacterial communities and oxygen conditions, and horizontal gene transfer (HGT) of MGEs also had a positive effect on the spread of ARGs. Those findings suggest that complex oxygen conditions in the HZ alter bacterial communities and promote MGEs-mediated horizontal transfer, which together lead to the spread of ARGs. This study has value as a reference for formulating effective strategies to minimize the propagation of ARGs in underground environment.

Underflows: Queer Trans Ecologies and River Justice. By Cleo Wölfle Hazard

“Rivers matter for queer trans life,” begins Underflows: Queer Trans Ecologies and River Justice, by Cleo Wölfle Hazard (3). The concluding sentence of the introduction responds: “Queer trans lives matter for rivers” (35). The interplay between these two ideas structures the book, which brings together feminist science studies, Indigenous science, queer theory, and river ecology to advance both a method and an overlooked research subject: the hidden yet vibrant movements—both material and political—that percolate beneath surfaces. For Wölfle Hazard, these underflows encompass both the unseen hyporheic zone beneath a river’s bed and “latent discourses that lie hidden or disregarded,” from queer and trans sciences, to the Indigenous protocols ignored by settler-colonial governance regimes (8). The concept of underflows unites these various concerns and guides Wölfle Hazard’s assertion of queer trans thought as a vital strategy for “transfiguring settler-colonial riverine science into a tool for justice” (8). Embodying a dynamic approach to the “promiscuous ecological productivity of amphibious landscapes,” Wölfle Hazard’s methodology is itself wonderfully promiscuous as it embraces the interplay between metaphor and materiality (xvii). For example, they figure their methodology as the “raindrop nucleus” of Indigenous and co-generated research methods surrounded by the “condensate” of “kitchen table ethnography”—a playful, queer, and feminist response to traditional field ethnography—along with queer trans critical physical geography and ecopoetics (28). This dynamic methodology yields an exciting study that traverses five sites of water conflict and river restoration along the US West Coast. Through an ethics of collaboration with human and more-than-human communities, Wölfle Hazard explores how rivers—through their simultaneous sense of direction and unruliness—embody “resistance to Manifest Destiny projects” (8). Chapter 1 engages “hyporheic imaginaries” and multispecies commons while thinking alongside salmon and beavers about riverine ecology in California’s Scott River. The second chapter imagines a field praxis informed by queer-trans subjectivities spanning “fishy feelings from the field to sites of scientific performance” such as conferences, journal articles, and policy debates (82). In Chapter 3, Wölfle Hazard traces the contours of queer trans collaboration with beavers, noting how beavers “flout boundaries” and inspire their human collaborators to do the same, suggesting a “beavery trans ethics” that rejects settler management regimes (123). Chapter 4 thinks alongside queer performances of grief and mourning as a way for ecologists to affectively attune to species extinction. In the subsequent chapter, subtitled “Cruising a Waterfront with José Esteban Muñoz,” Wölfle Hazard engages queer ecopoetics to theorize queer ecologies in urban river waterfront spaces. He reflects here on “cruising the Duwamish in search of its specific histories and futurities of resistance to enclosure,” while thinking alongside Indigenous and environmental justice politics (191). The epilogue introduces a new collaboration with Karuk practitioners along the Klamath River to develop a river model of justice. Even as the book is organized into discrete chapters, six prefatory sections titled “Underflow” invite ways of thinking under, through, and beyond the chapters.