Spring Water Temperature Research Articles

Interseismic Locking of the Xiaojiang Fault May Be Controlled by Pore Fluid Pressure

AbstractAlthough fault locking state has been widely acquired with space geodetic observations, the mechanisms controlling fault locking are poorly known. Here, we infer the locking state of the Xiaojiang fault with a viscoelastic deformation model and integrated GNSS data, based on which we probe the mechanism that may control the locking pattern of the fault. Our results reveal four highly locked asperities along the Xiaojiang fault, which are separated by weak locking zones. Relying on the inferred locking degree and spring water temperature along the fault, we construct a model to connect the fault hydraulic conductivity with the cooling process of upwelling water. Model results suggest that high spring water temperature correlates with high hydraulic conductivity. Further, we use an experimental law to infer that the obtained high hydraulic conductivity may associate with high pore fluid pressure, which in turn weakens the fault frictional strength and leads to weak locking.

Correlations Between Spatiotemporal Variations in Phytoplankton Community Structure and Physicochemical Parameters in the Seungchon and Juksan Weirs

The Yeongsan River is one of the four major rivers in South Korea. Since the construction of two weirs as part of the Four Major Rivers Project to secure water resources in 2011, issues with algal blooms have frequently arisen, prompting the Ministry of Environment of Korea to conduct continuous monitoring of water quality and algal outbreaks. This study, conducted between 2019 and 2023, examined the relationship between the phytoplankton community structure and physicochemical factors at the Seungchon and Juksan weirs. Phytoplankton were categorized into four groups (Bacillariophyceae, Chlorophyceae, Cyanophyceae, and other phytoplankton), and 20 dominant genera were selected for analysis. As microalgal species vary depending on environmental conditions, understanding the specific relationships among the microalgae observed in the study area can help explain their occurrence mechanisms and contribute to the development of effective management strategies. Therefore, we used principal component analysis (PCA) to analyze the seasonal variation patterns of the four microalgal groups and visualize key data features through dimensionality reduction. Additionally, PCA was employed to identify and visualize environmental factors related to seasonal variations in phytoplankton communities. PCA helped elucidate how different environmental factors influence phytoplankton fluctuations across seasons. We used canonical correspondence analysis (CCA) to investigate the relationships among the 20 dominant genera in each group and environmental factors. Additionally, CCA was used to analyze the relationship between the distribution of the top five dominant phytoplankton taxa in each group and various environmental factors. CCA allowed for a detailed examination of how these dominant taxa interact with environmental conditions. PCA revealed significant correlations between other phytoplankton and Chl-a in spring and Cyanophyceae and water temperature in summer. Bacillariophyceae was positively correlated with nitrogen-based nutrients but negatively with phosphate phosphorus (PO4-P). CCA revealed significant correlations between dominant genera and environmental factors. Stephanodiscus sp. was associated with nitrogen-based nutrients, whereas Microcystis sp. and Dolichospermum sp. were associated with water temperature and PO4-P. Stephanodiscus sp. affected water treatment through filtration and sedimentation issues, whereas Microcystis sp. and Dolichospermum sp. produced the toxin microcystin. These findings offer valuable insights for water quality management.

Interannual differences vs small-scale spatiotemporal variability of spring zooplankton in the Crimean marine hypersaline lake

Ecosystems in the shallow marine hypersaline environment, such as marine lakes, are among the most changeable and have significantly lower species richness than freshwater and marine. It could be assumed that the intricate interconnections in hypersaline water ecosystems are easier to understand than in other aquatic ecosystems. Interannual differences vs small-scale spatiotemporal variabilities were studied in the spring zooplankton of hypersaline Lake Moynaki from 2019 to 2023. Salinity, water temperature, wind speed and direction were measured along with zooplankton sampling. The average spring wind speed and water temperature varied significantly from year to year, seemingly with a certain cyclicity. In total, 17 species were noted in zooplankton. The copepods Acanthocyclops vernalis and Arctodiaptomus salinus were not previously recorded in the lake. Bottom species were found in the plankton, among which the oligochaete Nais pseudobtusa, the gastropod Bittium reticulatum, and dragonfly larvae Gomphus sp. had not previously been found in the lake. Only four species, Gammarus aequicauda, Eucypris mareotica, Moina salina, and Cletocamptus retrogressus were regularly observed en masse. On average, the total zooplankton abundance near the windward shore was 2 times higher than that near the leeward shore and the abundance of individual species was from 2 to 5 times higher. If the values near only one coast were used, then the range of interannual differences would be underestimated or overestimated by approximately 2–4 times. Based on the zooplankton similarity in different years, all years except 2019, are grouped into a single cluster. Various changes are occurring in the lake, which are difficult to present as a complete picture of the cause-and-effect relationships that determine them.

Variations in the phenological patterns of a caddisfly inhabiting the same mountain massifs: Life‐history differences in different altitudinal zones

AbstractOrganisms inhabiting mountainous regions can experience large vertical environmental changes, and show different ecological characteristics between altitudes, thus facilitating allopatric fragmentation even in geographically close populations. This study compared the life‐history patterns of a species of limnephilid caddisfly, Asynarchus sachalinensis, in several genetically differentiated populations between alpine and sub‐alpine zones in a temperate mountainous region. We showed that in the sub‐alpine populations, larval development started earlier with increasing water temperature in spring, and adult emergence was also earlier. The occurrence of adults was extremely low in mid‐summer, probably due to summer diapause, followed by a larger number of ovary‐developed females in autumn. On the other hand, in the alpine zone, increasing water temperature was delayed compared to the sub‐alpine zone, and larval development occurred from early to mid‐summer. Adult emergence and ovary‐developed individuals were concentrated in mid‐summer. Hence, summer diapause was not observed. These results indicated life‐history differences between genetically differentiated populations at different altitudes. As the timing of adult occurrence and ovarian developmental patterns differ between populations at different altitudes, it is possible that reproductive isolation is facilitated or maintained between populations.

Hydrochemical Characterization, Geothermometry, and Origin of Ain Al-Harrah Hot Spring and Its Relationship to Al-Lith Geothermal System, Saudi Arabia.

The Al-Lith geothermal field in western Saudi Arabia is a characteristic medium-high enthalpy geothermal system, exhibiting features associated with tectonic activities linked to the Red Sea rifting. Ain Al-Harrah hot spring is located in the Al-Lith field, with discharge temperatures varying from 56 to 81 °C. The determination of water temperature and composition in a geothermal reservoir is critical to the design of utilization strategies, surface production facilities, and choice of materials. This research presents a comprehensive hydrochemical characterization of the Ain Al-Harrah hot spring and its relationship with the underlying geothermal system. This study was conducted in two main phases; first, the fieldwork involved the collection of water samples from the hot spring, measuring the temperature, pH, and electrical conductivity (EC) of the water. The second phase involved laboratory analyses of the collected samples, including major and trace element analyses, isotopic analysis, and geothermometry. The dominant hydrogeochemical processes in the region were determined by analyzing the hydrochemistry of the water samples. Thermal waters analyzed exhibited high concentrations of Na+ (410-463 mg/L), HCO3 - (64.48-90 mg/L), and Cl- (472.76-581.95 mg/L), intermediate levels of K+ (50.2-93.0 mg/L), and low levels of Mg2+ (1.27-2.04 mg/L). The total dissolved solids (TDS) concentration ranges between 1830 and 2055 mg/L. The hot spring is categorized as Na-HCO3 type facies that are moderately alkaline, with pH values ranging between 7.9 and 8.2. Analysis of trace element concentrations revealed that the hydrochemical processes were primarily governed by the abundance and solubility of trace elements in the rocks surrounding the hot spring, the pH, and the temperature of the hot spring water. The stable isotope data for δD (-12.36 to 15.21%) and δ18O (-2.84 to -3.38%) provided evidence that the thermal spring is of meteoric origin. Based on Na-K-Ca, K2/Mg, and quartz geothermometers, the temperature range of the reservoir was determined to be between 150 and 205 °C. The temperature range suggests a medium-to-high enthalpy geothermal system.

Effectiveness of an ecological flow regime to assure successful recruitment of anadromous Coregoninae populations in the Rupert River (northern Quebec, Canada)

AbstractObjectiveAs part of a large‐scale hydroelectric project, the mean annual flow of the Rupert River (northern Quebec, Canada) was reduced by 52% at its mouth in 2009. To protect fish habitat, an ecological flow regime that was modulated according to the biological seasons was implemented downstream from the diversion point. An 8‐year monitoring program, including 2 years before partial diversion, was carried out to verify the effectiveness of this mitigation measure on the total annual abundance of anadromous Coregoninae (Cisco Coregonus artedi and Lake Whitefish C. clupeaformis) larvae, which was used as biological indicator of recruitment success. The monitoring also aimed to determine the effects of flow modification on the timing of the larval drift and the spatial distribution of larvae in a river cross section.MethodsEach year, sampling consisted of installing drift nets during the entire downstream larval migration in a river cross section of the lower Rupert River. Drift nets were systematically placed to ensure representative sampling of the river section.ResultPrior to flow reduction, the estimated total number of larvae varied between 1.8 and 8.6 million. Over the following 6 years, the estimated larval population has remained steady at 3–4 million. Otherwise, larval drift characteristics have not changed since the flow reduction, as (1) the duration of the larval drift is the same as before, about 1 month in May and early June, with a peak period of about 8 days; (2) rise in water temperature in spring is a determining factor in the timing of larval drift; and (3) the larvae drift mainly near the surface of the water.ConclusionThe monitoring results indicate that the ecological flow regime implemented in the Rupert River was adequate to maintain anadromous coregonine populations.

Environmental DNA reveals patterns of biological invasion in an inland sea.

Non-native species have the potential to cause ecological and economic harm to coastal and estuarine ecosystems. Understanding which habitat types are most vulnerable to biological invasions, where invasions originate, and the vectors by which they arrive can help direct limited resources to prevent or mitigate ecological and socio-economic harm. Information about the occurrence of non-native species can help guide interventions at all stages of invasion, from first introduction, to naturalization and invasion. However, monitoring at relevant scales requires considerable investment of time, resources, and taxonomic expertise. Environmental DNA (eDNA) metabarcoding methods sample coastal ecosystems at broad spatial and temporal scales to augment established monitoring methods. We use COI mtDNA eDNA sampling to survey a diverse assemblage of species across distinct habitats in the Salish Sea in Washington State, USA, and classify each as non-native, native, or indeterminate in origin. The non-native species detected include both well-documented invaders and species not previously reported within the Salish Sea. We find a non-native assemblage dominated by shellfish and algae with native ranges in the temperate western Pacific, and find more-retentive estuarine habitats to be invaded at far higher levels than better-flushed rocky shores. Furthermore, we find an increase in invasion level with higher water temperatures in spring and summer across habitat types. This analysis contributes to a growing understanding of the biotic and abiotic factors that influence invasion level, and underscores the utility of eDNA surveys to monitor biological invasions and to better understand the factors that drive these invasions.

基于热传输与水混合的持续监测和数值模拟的泉水温度变异性解释: 以波兰南部Pieniny山脉Czarny Potok泉水为例

AbstractA numerical model of heat conduction and water mixing was developed, enabling a quantitative description of water temperature variability at a spring outflow. The study examined the Czarny Potok spring, located in the Pieniny Mountains of southern Poland, which was the subject of a 4-year series of water temperature observations. The presented model describes the soil and water environment in the immediate vicinity of the spring, assuming that the spring water temperature is shaped by the mixing of water flowing through the shallow zone that experiences seasonal fluctuation and the deeper neutral zone. It was also assumed that the conductive heat flow in the tested medium is conditioned by seasonal heating and cooling of the land surface. The thermal diffusivity of the bedrock was calculated on the basis of the phase shift and the attenuation of thermal amplitude at different depths, based on long-term monitoring of soil temperature. The heat conduction and water mixing models enabled calculation of the water temperature at the outflow. The obtained results are close to the empirical spring water temperatures. The estimated mean error was 0.075 °C and the mean absolute error was 0.188 °C. The results of the calculations suggest that the tested spring is recharged primarily by water flowing through the seasonal fluctuation zone (75%), while the remaining 25% captures a deeper circulation system associated with the neutral zone.

Predicting and explaining karst spring dissolved oxygen using interpretable deep learning approach

AbstractDissolved oxygen (DO) is one of the most important indicators of water quality and an essential measure for the aquatic organisms and the local ecosystem. DO concentrations in karst spring flow involves complex hydrological processes because of the heterogeneous nature of the karst system. In this study, an interpretable and explainable model that integrates the shapley additive explanations (SHAP) algorithm with the long short‐term memory network model (LSTM) is proposed to evaluate the contributions of karst spring discharge, precipitation, water temperature, and specific conductance to DO concentrations in karst spring flow. The hybrid model can predict the temporal fluctuations of DO levels and provide a robust characterization of DO behaviours. To demonstrate the applicability of the proposed model, we adopted the hydrological and meteorological data from Barton Springs, situated within a highly karstified segment of the Edwards aquifer characterized by extensive fractures and openings. The optimal prediction performance is achieved with a 14‐day time step, which is considered as the effective response time between various hydrological processes and DO concentrations at Barton Springs. It reveals that the influence of karst spring discharge, precipitation, water temperature, and specific conductance in previous 14 days collectively contribute to the current DO concentration in karst spring flow. The SHAP values of input features provide both local and global explanations, demonstrating the magnitude and the direction of each feature's impact on DO levels in karst spring flow. In descending order, the contributions of various hydrological processes to DO are ranked as follows: precipitation, karst spring discharge, temperature, and specific conductance. Precipitation and discharge exhibit positive SHAP values, indicating that increases in these hydrological processes contribute to higher DO levels in the karst flow. Water temperature and specific conductance have negative SHAP values, suggesting that higher water temperature and specific conductance will lead to decreased DO levels in the karst flow.

Climate change effects on hatching success and embryonic development of fish: Assessing multiple stressor responses in a large-scale mesocosm study

Climate change threatens freshwater fish species due to predicted changes in thermal, sedimentary and hydrological properties of stream ecosystems. Gravel-spawning fish are particularly sensitive to such alterations as warming, higher inputs of fine sediment and low-flow all have potentially negative effects on the functionality of their reproductive habitat, the hyporheic zone. Multiple stressors can interact in synergistic and antagonistic manners, causing surprise-effects that cannot be predicted from the additive consideration of individual stressors. For obtaining reliable, yet realistic data on the climate change stressor effects warming (+3–4 °C), fine sediment (increase in <0.85 mm by 22 %) and low-flow (eightfold discharge-reduction), we constructed a unique large-scale outdoor-mesocosm facility consisting of 24 flumes to study individual and combined stressor responses in a fully-crossed, 3-way-replicated design. To acquire representative results reflecting individual susceptibilities of gravel-spawning fish species due to taxonomic affiliation or spawning seasonality, we studied hatching success and embryonic development in the three fish species brown trout (Salmo trutta L.), common nase (Chondrostoma nasus L.) and Danube salmon (Hucho hucho L.). Fine sediment had the most significant single negative effect on both hatching rates and embryonic development (−80 % in brown trout, −50 % in nase, −60 % in Danube salmon). When fine sediment was combined with one or both of the other stressors, we observed strongly synergistic stressor responses, being distinctly stronger in the two salmonid species than in the cyprinid nase. Danube salmon was most susceptible to synergistic effects due to warmer spring water temperatures exacerbating the fine sediment-induced hypoxia, hence leading to complete mortality of fish eggs. This study highlights that individual and multiple-stressor effects depend strongly on life-history traits of respective species and that climate change stressors have to be assessed in combination to obtain representative results due to the high level of synergisms and antagonisms detected in this study.

The impact of Atlantic Multidecadal Variability on Baltic Sea temperatures limited to winter

We analyze multidecadal temperature fluctuations of the Atlantic Ocean and their influence on Northern Europe, focusing on the Baltic Sea, without a priori assuming a linear relationship of this teleconnection. Instead, we use the method of low-frequency component analysis to identify modes of multidecadal variability in the Baltic Sea temperature signal and relate this signal to the Atlantic climate variability. Disentangling the seasonal impact reveals that a large fraction of the variability in Baltic Sea winter temperatures is related to multidecadal temperature fluctuations in the North Atlantic, known as Atlantic Multidecadal Variability (AMV). The strong winter response can be linked to the interaction between the North Atlantic Oscillation and the AMV and is maintained by oceanic inertia. In contrast, the AMV does not influence the Baltic Sea’s summer and spring water temperatures.

Thermo-hydrological modeling of temperature variations in the spring waters of a headwater catchment (Strengbach critical zone Observatory–France)

This study is geared towards evaluating the hydrological information that can be extracted from spring water temperature variations in shallow and thin aquifers of headwater catchments. A series of temperature variations (from 2013 to 2017) in four spring water sources at the Strengbach Critical Zone Observatory (CZO) was analyzed and interpreted by relying upon a coupled two-dimensional unsaturated–saturated flow and heat transfer model specifically designed for the study. Temperature variations of spring waters at the Strengbach catchment obey a seasonal non-phased and attenuated cyclicity compared with temperature inputs from the air or very shallow waters in soils. Simulation results show that, within the shallow subsurface horizons, heat transfer is mainly controlled by thermal conduction and not by fluid flow. The results also emphasize that the depth and temperature value of the thermal invariance zone are key parameters to surface temperature attenuation patterns in the first meters beneath the surface. The average maximum porosity (or saturated water content) is another important parameter impacting heat transfers in the shallow subsurface. Stronger attenuations and delays of the thermal signal occur as the porosity increases. These different results indicate that temperature variations in the spring waters, especially the attenuation and phase shift of the signals compared with incoming air-surface water temperatures, do not bring information on hydrological transfers. In very shallow systems, characteristics, such as flow velocities and water residence times, cannot be inferred from temperature variations. Nevertheless, this study suggests that spring water temperature variations could become a way of identifying the usually poorly known saturated water content and its spatial variability at the catchment scale.

Interdisciplinary approach to solve unusual mortalities in the European common frog (Rana temporaria) in two high-mountain ponds affected by climate change

The global decline in amphibian populations is a major environmental issue. Chytridiomycosis, Ranaviruses and the red-leg syndrome have been identified in unusual mortality events. However, these infections do not account for all causes of declining amphibian populations. Moreover, several cases of amphibian mortality are difficult to solve without resorting to an interdisciplinary approach. Two cases of unusual mortality in Rana temporaria occurred at two high-mountain ponds (northwest Italy) in April and May 2021. Water and frog samples were analysed to understand the possible causes responsible for the unusual mortalities. Results of the main physicochemical (pH, conductivity, dissolved oxygen, chemical and biochemical oxygen demand) and nutrient (ammonia/ammonium, nitrite, nitrate, total phosphorus) parameters revealed a good condition of the water quality, with the absence of the main cyanotoxins (microcystins/nodularins). However, unseasonably high spring water temperatures were recorded in both ponds (12.73 °C and 14.21 °C for Frog Pond and Selleries Pond, respectively). Frogs (n = 50; snout–vent length: 7.0–9.8 cm; body mass: 85–123 g) collected from Frog Pond mainly presented bumps on the ventral cavity and dermal ulceration associated with the isolation of Carnobacterium maltaromaticum. On the other hand, frogs (n = 5; snout–vent length: 8.0–9.1 cm; body mass: 87–92 g) from Selleries Pond presented petechiae and dermal ulcerations on the rear limbs associated with the isolation of Aeromonas salmonicida and A. sobria. In both mortality events, the interdisciplinary approach revealed an association between frog mortalities and the isolation of bacteria. Isolated bacteria are considered opportunistic pathogens, and the high values of the water temperature has certainly led a stress on the frogs, favouring the spread of bacteria and the death of the frogs. Further studies are needed to assess the pathophysiological effects of the opportunistic bacteria here isolated, clarifying the interactions between emerging pathogens and climate change.

Hydrogeochemistry of Fault-Related Hot Springs in the Qaidam Basin, China

Hydrogeochemical characterization studies are regarded as an important method for determining the origin of hot springs. The major elements, trace elements, and stable isotopes of four groups of hot spring water samples and two groups of gas samples collected from the intersection of the Altyn Tagh fault zone and the East Kunlun fault belt were investigated in this study. The hot spring water temperature ranged between 6 °C and 14 °C. The water chemistry types of the hot springs were Na·Mg-Cl, Mg·Na-Cl·HCO3, Na-Cl·SO4, and Na-Cl·HCO3. The δD values ranged from −50.00% to −68.60%, while the δ18O values ranged from −6.90% to −8.60%. The hot spring water was recharged mainly by infiltrating precipitation, with a recharge elevation of 3390~3676 m. The heat storage temperature ranged from 66.7 to 164.9 °C. The circulation depth was estimated to range between 1043 and 2679 m. The strontium isotopic composition of the water samples in response to the main weathering sources comprised carbonate and sulfate. CO2 was the main component in the hot spring gas in the study region, and its content was over 95%. The 3He/4He-R/Ra relationship diagram revealed that the mantle-sourced helium from the Yitunbulake spring was 3.06%. In comparison, that from the Aiken spring was 7.38%, which indicated an intrusion of mantle-source material mixed into the hot springs in the study region. The crustal marine limestone contributed significantly to the carbon inventory of the hot spring gas samples (&gt;75%). The dissolution of the marl aquifer resulted in the release of CO2. Carbon was primarily obtained through metamorphism and hydrothermal reactions in the basement lithologies. The Yitunbulake and Aiken hot springs are found near the intersection of the Arjin and East Kunlun fractures, where the water–rock response is relatively strong and the depth of circulation and thermal storage temperature are both high. This causes relatively high ambient pressure to be released from the deep fluid, resulting in microseismic activity in this region. The continuous observation of Aiken spring water chemistry allows for the monitoring of fracture activity in the region. The results of the study could serve as a foundation for further exploration of the relationship between geothermal water and deep faults, shallow geological formations, hydrogeological conditions, and geothermal resource development in the region.

Hydrogeochemical characteristics and genesis of Hongshuilantang Hot Spring and its water temperature anomalies during the Rushan earthquake swarm in Eastern China

Water temperatures of hot springs close to tectonic fault zones often show some variations before earthquakes, and analyses of earthquake precursors in hot springs have significant referential meaning for earthquake monitoring and forecasting. This study measured the concentration of major ions in water from the Hongshuilantang Hot Spring in 2017 and 2020. The ion composition was classified by hydrochemistry into the HCO3·SO4-Na chemical type. The composition of hydrogen and oxygen isotopes in the Hongshuilantang Hot Spring were located near the global meteoric water line (GMWL), indicating that the recharge source of the hot spring was meteoric water. The δD and δ18O values were not plotted on the Glogal Meteroric Water Line (GMWL), and there were some deviations, which suggested that hot spring water underwent water–rock interactions. Deep circulation water played an important role during the evolution process of thermal water. Water temperature showed a decreasing trend from October 2013 to June 2015 during the Rushan earthquake swarm in eastern China. Because of the occurrence of the earthquake swarm, we inferred that regional stress in this area began to be released, allowing continuous rebalancing. Free surface water appeared in some aquifers, and the seepage of low-temperature underground water into the upper aquifer led to a drop in water temperature in the hot spring. The Hongshuilantang Hot Spring and the epicenter of the Rushan earthquake swarm were located on the Muping–Jimo seismological fault zone, with the same seismotectonic system and some genesis relationships.

Influence of hydrothermal conditions on algae of the Shurinda thermal spring (Bauntovsky district, Republic of Buryatia)

Studies of the water temperature in the Shurinda thermal spring in the winter of 2009 and 2021 showed lower values in 2021. The number of habitats with different temperatures increased in the space of the thermal field. In 2021, 10 previously unrecorded species were identified in the flora of macroalgae and cyanobacterial mats, including aggregations of Spirogyra sp. The greatest diversity of cyanobacterial mats was found in the temperature range of 50-25°С; in the range of 20-10°С, accumulations of Spirogyra sp. occupied the entire water column. Cyanobacteria again prevailed in the area with a temperature of 4.0ºС. The higher species diversity of algae in March 2021 is due to the lower temperatures of the therms and their lower flow, which led to a greater diversity of temperature within the thermal spring.

Body size dictates physiological and behavioural responses to hypoxia and elevated water temperatures in Murray cod (Maccullochella peelii).

Increasing drought frequency and duration pose a significant threat to fish species in dryland river systems. As ectotherms, fish thermal and hypoxia tolerances directly determine the capacity of species to persist in these environments during low flow periods when water temperatures are high and waterbodies become highly stratified. Chronic thermal stress can compound the impacts of acute hypoxic events on fish resulting in significant fish mortality; however, it is not known if all size classes are equally susceptible, or if the allometric scaling of physiological processes means some size classes are disproportionately affected. We investigated the physiological responses of Murray cod (Maccullochella peelii) over a four-fold body size range (0.2-3000g) to acute changes in water temperature and oxygen concentration following 4 weeks of acclimation to representative spring (20°C) and summer (28°C) water temperatures. We recorded maximum thermal tolerance (CT max), oxygen limited thermal tolerance (PCTmax ), lowest tolerable oxygen level (as the oxygen level at which lose equilibrium; O2,LOE), gill ventilation rates and aerial surface respiration threshold, blood oxygen transport capacity and lactate accumulation. Acclimation to elevated water temperatures improved thermal and hypoxia tolerance metrics across all size classes. However, body size significantly affected thermal and hypoxia responses. Small M. peelii were significantly less hypoxia tolerant than larger individuals, while larger fish were significantly less thermal tolerant than smaller fish. Hypoxia constrained thermal tolerance in M. peelii, with both small and large fish disproportionally compromised relative to mid-sized fish. Our findings indicate that both very small/young (larvae, fry, fingerlings) and very large/older M. peelii in dryland rivers are at significant risk from the combined impacts of a warming and drying climate and water extraction. These data will inform policy decisions that serve to balance competing demands on precious freshwater resources.

Statistical analysis of karst springs in Lower Austria

Abstract Karst springs play a central role in Austria’s water supply. This paper aims to provide an overview of the karst springs of Lower Austria, analysing statistical correlations of spatial distribution, discharge, electrical conductivity (EC), and temperature. As part of a project with the provincial government of Lower Austria, older data from numerous studies have been combined with the self-generated data in a GIS database. This database contains data on 2056 karst springs. Most of the recorded springs are located in the Northern Calcareous Alps, although karst springs also occur in the Central Alpine Permomesozoic, the Waschberg zone and the Bohemian Massif, some of which are also of regional importance for drinking water supply. Chemical analyses show that limestone, dolomite and mixed springs are widespread in Lower Austria and occur with similar frequency. Gypsum springs, which are characterised by a significantly higher total mineral-isation, are also of regional importance. The statistical analysis shows that spring water temperatures correlate well with the mean annual air temperature at the mean catchment elevation. The temperature decrease with increasing elevation corresponds to the air temperature gradient in the Eastern Alps (0.47 °C/100 m). In addition, the springs show a negative correlation of the EC with the mean catchment elevation, which can be explained by a decrease in soil cover and thus reduced CO2 uptake of the water, as well as dilution by rainwater. This leads to less carbonate dissolution, which is also reflected in less HCO3 − contents. Corrected for the elevation effect, the investigated dolomite springs, have on average a 2.7% higher EC than limestone springs. A difference was also found between the Hauptdolomit and the Wettersteindolomit rock types, which are widespread in Lower Austria, with the latter displaying higher values on average by 2.2%. This indicates longer residence times of the spring water due to less karstification of the Wettersteindolomit.

Spatiotemporal Variation of Riverine Dissolved Organic Matter Degradation Based on EEMs-PARAFAC: A Case Study of Shili River in Jiujiang, Jiangxi Province, China, as a Typical Demonstration City of the Yangtze River protection Strategy

This study investigated the spatio-temporal distribution of dissolved organic matter (DOM) composition and its sources before and after degradation in the Shili River watershed in Jiujiang (China). Spatio-temporal variation of riverine DOM water samples before and after five days of degradation in a simulated channel was characterized by spectral feature analysis using three-dimensional excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis. Across all water samples (#1,#2 and #3) before and after degradation, a total of four fluorescent components in DOM were identified: C1, C2, C3, and C4. The aromaticity index (SUVA254) was negatively correlated with the C2 and C3 components and biological index (BIX) and freshness index (β:α), but it had little correlation with the humification index (HIX). The greater the aromaticity of DOM in water, the lower the proportion of recently produced DOM and its biological activity. The C3 component had a strong positive correlation with BIX, β:α, and C2. The results suggested that C2 and C3 were derived from the same substances. According to the fluorescence parameters, DOM was dominated by autochthonous contributions. The fluorescence intensity of DOM increased gradually along the direction of water flow. The increase of water temperature in spring and autumn enhanced the endogenous level of DOM. The levels and fluctuations of BIX and β:α in different seasons and different sampling points were basically consistent. DOC concentration does not fully represent the localized nature of the DOM. The analysis of some fluorescence parameters and light absorption parameters showed that the DOM source was more internal than terrestrial. This study reveals the composition, source and temporal and spatial characteristics of DOM in the Shili River Basin, which has theoretical guiding significance for water environment management.

Temporal-spatial distribution and ecological evaluation of macroinvertebrate functional feeding groups in Yongding River Basin

We investigated community structure of macroinvertebrate, water environment factors, hydrological factors at 23 sampling sites of the Yongding River basin from spring 2017 (April) to autumn 2017 (November). We analyzed the composition, spatial and temporal distribution of the macroinvertebrate functional feeding groups, as well as their responses to changes in riverine habitat. A total of 78 macroinvertebrate species were identified, with 52, 50 and 53 macroinvertebrate species in spring, summer and autumn respectively. The dominant functional feeding groups were gather-collectors, followed by predators, while the proportion of scrapers, filter-collectors and shredders were extremely low. Dominant species in the three seasons were all gather-collectors, including Orthocladius, Rheotanytarsus, Cricotopus in spring, Glyptotendipes in summer, and Polypedilum, Chironomus, Orthocladius in autumn. Results of redundancy analysis showed that the functional feeding groups of macroinvertebrate community structure were mainly influenced by water temperature, flow velocity, salinity, and total phosphorus in spring, by total phosphorus, dissolved oxygen, conductivity and flow capacity in summer, and by total phosphorus and dissolved oxygen in autumn. Total phosphorus had positive correlation with gather-collectors in all three seasons, indicating that the functional feeding groups of macroinvertebrates were affected by water pollution. The evaluation based on the metrics of functional feeding groups showed that: 1) in terms of material cycle, primary productivity of Guishui River were significantly higher than other regions, and that in autumn were significantly higher than other seasons. The secondary productivity and decomposition capacity of Yanghe River were significantly higher than other regions, and those in spring were significantly higher than other seasons. The autotrophy/heterotrophy of Yanghe River was significantly lower than other regions, and that in spring were significantly higher than other seasons. 2) The longitudinal transport capacity of Sanggan River was significantly higher than other regions, and that in autumn was significantly higher than other seasons. 3) The lateral input capacity of Guishui River was significantly higher than other regions, and that in summer was significantly higher than other seasons.