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  Subjects -> WATER RESOURCES (Total: 160 journals)
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Aquatic Sciences
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ISSN (Print) 1015-1621 - ISSN (Online) 1420-9055
Published by Springer-Verlag Homepage  [2469 journals]
  • Corbicula incorporation to indicator parameters to assess the ecological
           status of northwestern Iberian estuaries

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      Abstract: Abstract Ecological status classification systems based on biological elements (e.g., macroinvertebrate communities) are dependent on their response to different pressures. However, there is a need to determine if invasive species should be incorporated to indicator parameters (i.e. metrics based on measurements of richness and diversity) or as a pressure affecting such parameters. Moreover, because ecosystem classification systems are lacking for northwestern Iberian estuaries, there is even the possibility to develop a new metric penalizing presence or abundance of invasive species. To increase our understanding on this topic, we analyze the taxonomic and functional responses of benthic macroinvertebrates to Corbicula invasion along the environmental gradient of 12 northwestern Iberian estuaries. Macroinvertebrate assemblages were described and compared between invaded and uninvaded sections. Additionally, to assess differences in community structure, macroinvertebrate assemblages’ similarity was examined between two distinct estuarine sections (freshwater and oligohaline vs transitional water and mesohaline) and among water body types, including and excluding Corbicula from the analysis. The salinity gradient was the main driver explaining changes in macroinvertebrate assemblages and in functional group distribution. Freshwater and transitional water sections clearly differed in macroinvertebrate assemblages and functional groups composition. In addition, differences among river types in macroinvertebrate composition were found. Corbicula inclusion or exclusion from multivariate community analysis significantly affected the results in functional feeding group composition in the Cantabric-Atlantic siliceous river axis type. Nevertheless, considering Corbicula as a pressure at the regional scale did not provide different results in diversity indices calculation. Hence, we argue that because Corbicula eradication is virtually impossible, it should be included as an additional metric evidencing its presence as a negative indication, or be included within other indicator metrics used in the assessment of the ecological status, for instance in invertebrate abundance metrics were its dominance should be indicative of invasion impairment.
      PubDate: 2022-06-25
       
  • Effects of inter- and intraspecific competition and food availability on
           shredder invertebrates from an Amazonian stream

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      Abstract: Abstract Shredders play an important role in leaf decomposition in headwater streams; however, their activities can be affected by irregular leaf availability, shredder density, and interactions between species. We performed two experiments to evaluate the effects of interspecific (InterComp) and intraspecific (IntraComp) competition and food availability on survival and leaf consumption of two shredder species, Triplectides egleri and Phylloicus elektoros, of an Amazonian stream. We hypothesized that: (i) shredder density (InterComp and IntraComp experiments) has a negative effect on shredder survival and leaf consumption due to increase in interactions between individuals (e.g. direct encounters) that will lead to competition; and (ii) low food availability (IntraComp experiment) will increase competition among individuals, decreasing shredder survival and leaf consumption. In both experiments, high densities of shredders caused direct encounters between individuals and led to a decrease in survival and leaf consumption. Moreover, In the IntraComp experiment, lower survival and leaf consumption were observed in treatments with low food availability, probably associated with competitive interactions for limited resources. Our results indicate that decreased food availability, increased shredder density, and inter-and intraspecific interactions lead to competition for food and space, resulting in direct encounters between shredders and the occurrence of events such as cannibalism, and/or can inhibit feeding activities (e.g., avoiding conspecifics), thereby decreasing survival and leaf consumption.
      PubDate: 2022-06-18
       
  • Unraveling the phytoplankton altitudinal dynamics in relation to
           environmental variables in a Himalayan River, Teesta, India

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      Abstract: Abstract An investigation was carried out to comprehend the altitudinal variation of phytoplankton and their distribution pattern in River Teesta. Phytoplankton were recorded at two different altitude levels of the river. A total of 35 genera of phytoplankton were recorded with dominated by diatoms. The altitudinal differences reflected comparatively high genus richness in the high-altitude region. Seasonal spectrum of phytoplankton was maximum during post-monsoon (7.67 ± 13.42 ul−1) and pre-monsoon (51.6 ± 24.52 ul−1) in the high-altitude and low-altitude region, respectively. On the whole, the major compositions of phytoplankton are represented as Bacillariophyceae > Cyanophyceae > Chlorophyceae across seasons. The k-dominance curve revealed that there was no remarkable difference in dominance pattern of phytoplankton among the sampling sites with 9 to 15 species accumulated 80% cumulative relative abundance across sites. Negative altitudinal gradient of diversity indices (Shannon and Simpson index) was recorded which implies lower diversity exists at higher altitude. Further, GAM model (R2 = 0.36) depicted statistically a nonlinear pattern of genus turnover against the altitudinal distance. The significant positive relationship was observed between phytoplankton genus turnover and altitudinal distance in the river. Canonical correspondence analysis reflected that water variables such as total alkalinity, total hardness, sp. conductivity, nitrate, total phosphate and silicate were the influential factors for the distribution of phytoplankton community in both the altitudes of the river Teesta.
      PubDate: 2022-06-06
       
  • Characteristics of N2O release from polluted creeks in the Taihu Lake
           Basin: sources and microbial populations

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      Abstract: Abstract Polluted rural creek systems are a potential primary source of nitrous oxide (N2O). However, to date, the N2O emission pathways of rural creek systems have yet to be investigated. In particular, the correlations between N2O emissions and ammonia-oxidizing archaea (AOA), ammoniating bacteria (AOB), and denitrifying communities remain poorly understood. In this paper, a sediment–water–environment simulation system was established to analyze the N2O emission pathways, and the correlations between N2O emissions and nitrogen-related functional genes for two creeks that have been polluted by domestic sewage and industrial wastewater have been studied. The results indicated that the N2O release rate of the creek polluted by domestic sewage was higher than that of the creek polluted by industrial wastewater, and the heterotrophic denitrification and nitrification were the main N2O emission pathways for the creek polluted by domestic sewage. On the contrary, nitrification and chemical denitrification were the primary N2O emission pathways for the creek polluted by industrial wastewater. The quantitative PCR (qPCR) results obtained for nitrogen-cycle functional genes in creek sediments indicated that the abundances of AOA genes (AOA amoA), AOB genes (AOB amoA), and denitrification genes (nosZ) were lower in the creek polluted by industrial wastewater than that in the creek polluted by domestic sewage. For the creek polluted by domestic sewage, the N2O emission rate exhibited a significant positive correlation with the abundances of AOA amoA and AOB amoA and a correlation with the abundances of the dominant nitrogen-cycling microorganisms (p < 0.05). However, no such correlations were found for the creek polluted by industrial wastewater. In the future, the patterns detected here will be useful as markers to distinguish whether water has been polluted by industry.
      PubDate: 2022-06-03
       
  • Hydrology influences carbon flux through metabolic pathways in the
           hypolimnion of a Mediterranean reservoir

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      Abstract: Abstract Global change is modifying meteorological and hydrological factors that influence the thermal regime of water bodies. These modifications can lead to longer stratification periods with enlarged hypolimnetic anoxic periods, which can promote heterotrophic anaerobic processes and alter reservoir carbon cycling. Here, we quantified aerobic and anaerobic heterotrophic processes (aerobic respiration, denitrification, iron and manganese reduction, sulfate reduction, and methanogenesis) on dissolved inorganic carbon (DIC) production in the hypolimnion of a Mediterranean reservoir (El Gergal, Spain) under two contrasting hydrological conditions: a wet year with heavy direct rainfall and frequent water inputs from upstream reservoirs, and a dry year with scarce rainfall and negligible water inputs. During the wet year, water inputs and rainfall induced low water column thermal stability and earlier turnover. By contrast, thermal stratification was longer and more stable during the dry year. During wet conditions, we observed lower DIC accumulation in the hypolimnion, mainly due to weaker sulfate reduction and methanogenesis. By contrast, longer stratification during the dry year promoted higher hypolimnetic DIC accumulation, resulting from enhanced methanogenesis and sulfate reduction, thus increasing methane emissions and impairing reservoir water quality. Aerobic respiration, denitrification and metal reduction produced a similar amount of DIC in the hypolimnion during the two studied years. All in all, biological and geochemical (calcite dissolution) processes explained most of hypolimnetic DIC accumulation during stratification regardless of the hydrological conditions, but there is still ~ 30% of hypolimnetic DIC production that cannot be explained by the processes contemplated in this study and the assumptions made.
      PubDate: 2022-05-16
       
  • Seasonal patterns of microhabitat selection in the Southern Iberian
           spined-loach Cobitis paludica

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      Abstract: Abstract The Southern Iberian spined-loach Cobitis paludica is an Iberian endemism threatened by human activities, including habitat destruction. For this reason, the development of conservation and the recovery plans for the species calls for a precise knowledge of its habitat requirements. Here, microhabitat use and selection patterns were investigated to determine the limiting factors for the species in different seasons, corresponding to a gradient in flow conditions. The microhabitat of the loach was analysed in the River Jarama (Tagus River basin, central Spain) in the period of maximum activity between March and September 2013. No significant differences in microhabitat use were found between males and females, and only very weak ontogenetic changes were detected. The microhabitat used by the loach varied significantly throughout the study period, generally adapting to the flow-mediated dynamics of available habitat. The most stable pattern throughout the year was the use of very low water velocities. Additionally, the loach made selective use of certain microhabitat features, with slight adjustments to the seasonally changing habitat conditions. The loach significantly selected positions with abundant silt substrate and aquatic vegetation, and avoided coarser substrates. The availability of fine substrates and abundant vegetation is therefore a critical habitat requirement for the loach, which needs instream structures that provide foraging substrate, refuge and safe positions for spawning. Selection of refuge elements (deep habitats, aquatic vegetation) was especially apparent under low-flow conditions. Human activities leading to the loss of these critical microhabitats may threaten the survival of already scarce loach populations.
      PubDate: 2022-05-12
       
  • Anthropogenic activities and habitat complexity influence fish functional
           diversity in a Neotropical reservoir

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      Abstract: Abstract Reservoir shorelines are usually colonized by submerged macrophytes, which may select fish species that are able to thrive in these environments, consequently influencing the functional diversity of fish assemblages. However, there are also intense anthropogenic activities in these environments (macrophyte removal), which may also affect the functional diversity of fish communities. Thus, this study aimed to evaluate the influence of anthropogenic activities and habitat complexity provided by submerged macrophytes on the functional diversity of the ichthyofauna of reservoirs. Fish sampling was carried out at three stations in marginal areas of the Itaipu reservoir, located in sites near and apart from artificial sand beaches and with and without submerged macrophytes. The functional traits used were morphometric measurements taken from sampled fish (intraspecific traits), which were used to calculate three functional diversity indices: functional richness, evenness, and divergence. In general, no patterns were found for the functional diversity indices concerning macrophyte removal (among sampling sites). In contrast, habitat complexity did influence the functional diversity of fish assemblages, with results differ depending on macrophyte density. While functional richness was higher with greater habitat complexity, the opposite was evidenced for functional evenness and divergence. These findings reinforce the importance of different habitats for the maintenance of fish functional diversity in marginal areas of reservoirs. They also contribute to the implementation of macrophyte management for the maintenance of fish biodiversity and the establishment of priority areas for conservation and tourism in these environments.
      PubDate: 2022-05-12
       
  • Air temperature effects on nitrogen and phosphorus concentration in Lake
           Chaohu and adjacent inflowing rivers

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      Abstract: Abstract The relationship between nitrogen and phosphorus concentrations in rivers and lakes and their influencing factors have been global concerns. However, how air temperature changes affect the nitrogen and phosphorus concentrations in rivers and lakes remains unknown. In this study, we conducted analyses linking the characteristics of air temperature to monthly nitrogen and phosphorus monitoring datasets of the lake and adjacent inflowing rivers in the Lake Chaohu basin from 2014 to 2018. We found that the variations in the mean air temperature of the antecedent 7 days significantly affected the nitrogen and phosphorus concentrations in shallow eutrophic lakes, and the air temperature threshold ranged from 3 to 27 °C. As the air temperature increased, the nitrogen concentrations in Lake Chaohu decreased, but the phosphorus concentrations showed an upwards trend. The lake had a “buffer” function, as indicated by the more pronounced response of nitrogen and phosphorus to increasing air temperature in western Lake Chaohu (TN = − 0.085 mg L−1 °C−1, TP = + 0.004 mg L−1 °C−1) than eastern Lake Chaohu (TN = − 0.034 mg L−1 °C−1, TP = + 0.003 mg L−1 °C−1). The decreasing trend of nitrogen concentrations (average declining rate: 0.090 mg L−1 °C−1) in inflowing rivers with increasing air temperature was even more pronounced than that in Lake Chaohu. However, no significant statistical relationship was found between the phosphorus concentrations and air temperature in most inflowing rivers. Therefore, this study emphasizes the need to further unravel the coupling mechanism between internal nutrient loads and climate factors while reducing external nutrient loads.
      PubDate: 2022-05-11
       
  • Fish body geometry reduces the upstream velocity profile in subcritical
           flowing waters

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      Abstract: Abstract Fish body geometry is highly variable across species, affecting the fluid-body interactions fish rely on for habitat choice, feeding, predator avoidance and spawning. We hypothesize that fish body geometry may substantially influence the velocity experienced by fish swimming. To test this hypothesis, we built nine full-scale physical prototypes of common freshwater fish species. The prototypes were placed in a large laboratory flume and upstream time-averaged velocity profiles were measured with increasing distance from the anterior-most location of each body. The measurements revealed that the body geometry can have a significant influence on the velocity profile, reducing the flow field at a distance of one body length upstream of the fish. Furthermore, it was found that the upstream velocity profiles from the nine fish species investigated in this study can be normalized to a single fit curve based on the freestream velocity and fish body length under subcritical flow conditions. These findings are significant, because they show that conventional point velocity measurements overlook the reducing effect of the fish body on the upstream flow field, creating a systematically biased representation of the velocity experienced by fish in subcritical flowing waters. This bias is illustrated by velocity field maps created with and without the presence of the physical models for three different fish species. Finally, we provide an example of how point velocity measurements can be recalculated to provide upstream velocity field maps closer to “the fish’s perspective”.
      PubDate: 2022-05-03
       
  • Dynamics of the stream–lake transitional zone affect littoral lake
           metabolism

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      Abstract: Abstract Lake ecosystems, as integrators of watershed and climate stressors, are sentinels of change. However, there is an inherent time-lag between stressors and whole-lake response. Aquatic metabolism, including gross primary production (GPP) and respiration (R), of stream–lake transitional zones may bridge the time-lag of lake response to allochthonous inputs. In this study, we used high-frequency dissolved oxygen data and inverse modeling to estimate daily rates of summer epilimnetic GPP and R in a nutrient-limited oligotrophic lake at two littoral sites located near different major inflows and at a pelagic site. We examined the relative importance of stream variables in comparison to meteorological and in-lake predictors of GPP and R. One of the inflow streams was substantially warmer than the other and primarily entered the lake’s epilimnion, whereas the colder stream primarily mixed into the metalimnion or hypolimnion. Maximum GPP and R rates were 0.2–2.5 mg O2 L−1 day−1 (9–670%) higher at littoral sites than the pelagic site. Ensemble machine learning analyses revealed that > 30% of variability in daily littoral zone GPP and R was attributable to stream depth and stream–lake transitional zone mixing metrics. The warm-stream inflow likely stimulated littoral GPP and R, while the cold-stream inflow only stimulated littoral zone GPP and R when mixing with the epilimnion. The higher GPP and R observed near inflows in our study may provide a sentinel-of-the-sentinel signal, bridging the time-lag between stream inputs and in-lake processing, enabling an earlier indication of whole-lake response to upstream stressors.
      PubDate: 2022-04-27
       
  • Community stability and seasonal biotic homogenisation emphasize the
           effect of the invasive tropical tanner grass on macrophytes from a highly
           dynamic neotropical tidal river

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      Abstract: Abstract We described the spatial and temporal dynamics of aquatic macrophytes in a Neotropical coastal estuarine river, and identified the negative effects associated to the presence and dominance of the invasive tanner grass. We compared macrophyte beds along the Guaraguaçu River (South Brazil) over four years, using taxonomic and functional dimensions. Biodiversity descriptors were higher in the driest periods compared to the rainiest, although this difference seems to be decreasing over the studied years. Moreover, the spatial organization of biodiversity and community structure slightly changed over time. Such spatial community stability was highlighted by the dominance of the highly invasive tanner grass. In beds dominated by the invasive species, the biodiversity was reduced. As aquatic macrophytes represent an important group in water bodies, the long-term loss of seasonal differences in community structuring is of concern, mainly regarding its potential to impact other groups and ecosystem functioning. By analysing data from standardized monitoring, we were able to identify a poorly discussed facet of biotic homogenisation—the seasonal homogenisation. We also discussed the impact of massive development of invasive species and its consequences for biodiversity in a Neotropical river of outmost importance for biological conservation.
      PubDate: 2022-04-05
      DOI: 10.1007/s00027-022-00858-3
       
  • Climatic and geographic variation as a driver of phenotypic divergence in
           reproductive characters and body sizes of invasive Gambusia holbrooki

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      Abstract: Abstract Understanding the invasion success of alien species includes developing knowledge on how the biological traits of their populations respond to spatial differences in environmental conditions. For invasive fishes, while the influence of latitudinal and climatic gradients on their biological traits over large spatial scales is well established, there is less certainty in how these vary over smaller scales. Here, we tested the influence of a climatic and geographic gradient on the reproductive traits and body sizes of the invasive mosquitofish Gambusia holbrooki across five climatic regions in Turkey. The results revealed that the environmental conditions across eight sites provided two gradients: a latitudinal gradient (where northern sites were cooler with less rainfall) and a coastal–inland gradient (where changes were apparent from coastal areas and into inland areas). These gradients had marked effects on the traits of both sexes. In sites in coastal and southern areas, males had significantly larger gonopodia and females had greater fecundity than in inland and warmer areas, and with both sexes having body sizes that were smaller. The spatial differences in the male traits were suggested as being driven by differences in selection pressures at the sites that related to differences in their population abundances. The results revealed that environmental conditions across a relatively small spatial scale had some strong influences on the expression of specific biological traits of these mosquitofish populations, but with further work needed to test how these influences affect their invasion success.
      PubDate: 2022-04-02
      DOI: 10.1007/s00027-022-00862-7
       
  • Range expansion of Kellicottia bostoniensis (Rousselet, 1908) (Rotifera)
           throughout a biogeographic boundary between the Brazilian savanna and the
           Amazon

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      Abstract: Abstract The freshwater rotifer Kellicottia bostoniensis (Rousselet, 1908), native from North America, has been considered invasive in European, Russian and South American waterbodies. More than reporting its presence, for the first time, in Araguaia River, which plays critical role in a set of floodplain systems in the Brazilian savanna, we aim to understand how this invader react to new physical, chemical and hydrodynamics conditions, which can be helpful for predicting its invasiveness and colonization success in other similar non-native ranges. We use population data of K. bostoniensis and environmental variables surveyed across the meandering middle-stretch of the Araguaia River. The highest frequencies of K. bostoniensis were registered in sites of lower mean temperatures, higher pH and dissolved oxygen at sites with higher hydrodynamics. However, the highest abundance was found in a backwater site, a more lentic habitat in which total body size was slightly higher than those with lotic conditions. Both the abundance values and body length were the lowest registered in non-native areas, suggesting the initial phase of the invasion process. Also, the trade-off between abundance and body size may allow population to persist in flowing water conditions, thus playing fundamental role in population recruitment and dispersal, favoring the propagation of this organism in the river curse and adjacent environments. Specifically, stepping stones created by the river meanders would increase population growth and the rapid spread of K. bostoniensis through Araguaia River. Due to its wide environmental tolerance, morphological plasticity and high dispersal ability, we further anticipate continued dispersion of K. bostoniensis to other Brazilian basins highlighting the need for persistent monitoring upstream and downstream of this freshwater ecotone.
      PubDate: 2022-03-31
      DOI: 10.1007/s00027-022-00861-8
       
  • Phytoplankton taxonomic and functional diversity in two shallow alluvial
           lakes with contrasting river connectivity

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      Abstract: Abstract The mechanisms behind phytoplankton diversity patterns in natural ecosystems still remain elusive. In two shallow lakes with contrasting river connectivity, we first explored how diversity within each sampling (alfa diversity, α), among samplings (beta diversity, β1), and among hydrological seasons (β2) contributed to the diversity registered throughout the whole year (gamma diversity, γ). Then we estimated the importance of several environmental and temporal factors as structuring factors of these diversity patterns. To do this, we sampled the two lakes—one laterally isolated and other laterally connected lake with the Paraná River System—during a complete hydrological year. For the analyses, we considered both the species and the functional group level. At the species level, temporal variation (β1 + β2) made the main contribution for gamma diversity at the connected lake, possibly related to the constant species input from the river system. For the isolated lake, however, α was the main contributor. Regarding functional groups, α was the most important for both lakes, although no element of gamma diversity was different from the null model. Environmental factors like conductivity, turbidity, nutrient availability, and flood phases appeared as more relevant for the connected lake. Temporal processes (e.g., succession, ecological drift) were critical for the observed diversity patterns in both lakes. These results were consistent particularly considering the taxonomical approach. Our main findings are that the environment influences phytoplankton diversity patterns; however, other dynamics occurring on temporal scales may be more relevant for the phytoplankton community.
      PubDate: 2022-03-31
      DOI: 10.1007/s00027-022-00857-4
       
  • Drivers of fish trophic guild composition in lakes of the Upper
           Paraná River floodplain

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      Abstract: Abstract In freshwater ecosystems, flood pulses, the degree of connectivity between environments, and the vegetation mosaic are among the main variables affecting environmental structure at the landscape scale. At a finer scale, local limnological conditions seem to be more important for structuring river fish assemblages. However, rather than exerting isolated effects, these limnological characteristics can have combined impacts on the environment. We evaluated the main drivers of the spatial structuring of fish trophic guilds in the littoral zone of lakes in the Upper Paraná River floodplain (UPRF) and determined the relative importance of limnological conditions, spatial distance, and riparian vegetation. We sampled fish and limnological variables in June, September, and December of 2011, and classified the fish species into trophic guilds. We used variation partitioning analysis to assess the influence of the three sets of predictors and distance-based redundancy analysis to visualize the position of samples, as described by the composition of trophic guilds in multivariate space. The distribution of trophic guilds was mainly influenced by limnological variables, i.e., conductivity, chlorophyll a, and pH, in periods of low water. Spatial and riparian vegetation predictors, despite being low, also influenced the distribution because limnological variables and riparian vegetation of the UPRF have a well-defined spatial structure due to differences between rivers. The lakes with Class III riparian vegetation (dominated by tree species) supported most of the trophic guilds, including insectivores. This indicates that allochthonous materials, even when they occur in smaller proportions, contribute to the structuring of fish communities in periods of low water.
      PubDate: 2022-03-31
      DOI: 10.1007/s00027-022-00860-9
       
  • Different mechanisms drive beta diversity of freshwater fishes across
           similar ecoregions in India

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      Abstract: Abstract As an important component of overall diversity, β-diversity is driven by spatial and temporal variability of several ecological factors. While changes to β-diversity can be the result of a combination of these factors, it is still unclear whether the same driving factors govern regions with similar β-diversity. We studied lower–middle-order streams in two river basins (three of them located in the state of Madhya Pradesh ‘MP’ and four located in West Bengal ‘WB’) in India, approximately 1600 km apart. Fish abundance and environmental data were collected from 2015 to 2017. While spatial variables constructed from geographic or fluvial distances are often used in evaluating dispersal effects, studies using terrain properties are relatively fewer. In tropical stream systems, which can undergo drastic seasonal transformations, terrain properties along with distances are likely to influence dispersal. Heterogeneity indices for both environment (Environmental heterogeneity, EH) and topography (Topographic heterogeneity, TH) were calculated. Influence of environmental and spatial variables (fluvial distance and TH) on β-diversity was modeled using dbRDA (distance-based redundancy analysis). β-diversity did not vary across seasons (i.e., temporally) in either regions, but did vary across streams (i.e., spatially). MP had a higher TH while WB displayed greater EH. Both regions showed a positive beta diversity–environmental heterogeneity relationship and EH–TH relationship across streams. Although both basins rest in the tropics, different mechanisms seem to explain community assembly. Variation partitioning showed a stronger influence of environmental filtering on fish communities in WB, and dispersal limitation reflected by spatial factors in MP. Our findings highlight that different mechanisms can drive β-diversity within the same tropical realm and the need to consider the role of topography, along with traditionally acknowledged spatial descriptors, in studies exploring the mechanisms driving β-diversity of fishes in riverine ecosystems.
      PubDate: 2022-03-26
      DOI: 10.1007/s00027-022-00859-2
       
  • Patterns and controls of carbon dioxide concentration and fluxes at the
           air–water interface in South American lowland streams

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      Abstract: Abstract Carbon dioxide (CO2) emission from fluvial systems represents a substantial flux in the global carbon cycle. However, variation in fluvial CO2 fluxes at the air–water interface as well as its drivers are poorly understood, especially in non-forested headwaters. Here, we measured CO2 concentration and fluxes in 14 lowland open-canopy streams (Pampean region, Argentina) that cover a wide range of land use and water quality. We also analyzed drivers of CO2 concentration and fluxes, including factors related to metabolism, gas solubility, alkalinity, and gas transfer. Metabolic rates varied considerably among the study sites, but most streams (i.e., 8 out of the 11 where we were able to estimate ecosystem metabolism) were net heterotrophic. Metabolic differences among sites were mostly driven by the aromatic carbon content and the percent of the stream reach covered by primary producers. All streams, even those that were not net heterotrophic were CO2 supersaturated. Alkalinity combined with in-stream primary production explained 52.3% of the variance in the partial pressure of CO2 (pCO2), but our observations suggest that pCO2 might be controlled by external groundwater inputs of dissolved inorganic carbon rather than by internal metabolism. All streams were net emitters of CO2 to the atmosphere. Significantly more variance in CO2 flux was explained by gas transfer velocity (63.7%) than by pCO2 (21.9%). We also observed high spatial heterogeneity in CO2 fluxes within each stream, which was associated with flow variation and the presence of different macrophyte and algae patches. Overall, our results indicate that CO2 emission in these extremely low turbulence streams is controlled by a combination of external and internal biogeochemical processes and limited atmospheric exchange.
      PubDate: 2022-03-25
      DOI: 10.1007/s00027-022-00852-9
       
  • The direct influence of climate change on marginal populations: a review

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      Abstract: Abstract Climatic changes and their impact on animals and plants at the margins of their distributions are evident in terrestrial, limnic, and marine environments. I review and summarise the literature related to the direct physiological effects of climate change on marginal populations in all realms and categories. I summarise literature showing physiological and ecological emphasis but do not include studies on modelling, genetic or range shift. I found a great discrepancy in representation of each category, with the majority of studies and the greatest variety of species represented in the marine environment and the least research conducted in limnic environments. The least represented in all environments and marginalities was the plant kingdom, including algae. I identified an uneven distribution of studies around the globe with a major focus on Europe and North America. Literature results show an overarching negative impact on organismal physiology independent of a realm and/or geographic location, potentially leading to species and hence biodiversity loss, and tightly coupled with this, a loss of ecosystem functions at the respective sites. All these points may lead to unstable ecosystems and socio-economic implications at the respective sites.
      PubDate: 2022-03-25
      DOI: 10.1007/s00027-022-00856-5
       
  • Patterns of microbial abundance and heterotrophic activity along nitrogen
           and salinity gradients in coastal wetlands

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      Abstract: Abstract Coastal wetlands are valuable aquatic ecosystems with high biological productivity, which provide services such as a reduction in nitrogen loading into coastal waters and storage of organic carbon acting as carbon dioxide sinks. The predicted rise of sea level or freshwater extractions, particularly in the arid Mediterranean biome, will salinize many coastal wetlands. However, there is considerable uncertainty about how salinization will affect microbial communities and biogeochemical processes. We determined the abundance of total prokaryotes, cyanobacteria, and viruses and quantified the heterotrophic production of prokaryotes sensitive- (predominantly Bacteria) and resistant- (predominantly Archaea) to erythromycin in 112 ponds from nine coastal wetlands. We explored the main drivers of prokaryotic abundance and heterotrophic production using generalized linear models (GLMs). The best GLM, including all the wetlands, indicated that the concentration of total dissolved nitrogen (TDN) positively affected the total abundance of prokaryotes and the heterotrophic erythromycin-resistant (ery-R) production. In contrast, heterotrophic erythromycin-sensitive (ery-S) production was negatively related to TDN. This negative relationship appeared to be mediated by salinity and virus abundance. Heterotrophic ery-S production declined as salinity and virus abundance increased. Consequently, we observed a switch from heterotrophic ery-S production towards ery-R production as salinity and virus abundance increased. Our results imply that microbial activity will change from heterotrophic bacterial-dominated processes to archaeal-dominated processes with anthropogenic nitrogen and salinization increases. However, more studies are required to link the mineralization rates of dissolved nitrogen and organic carbon with specific archaeal taxa to enable more accurate predictions on future scenarios in coastal wetlands.
      PubDate: 2022-03-17
      DOI: 10.1007/s00027-022-00855-6
       
  • Impact of zebra mussels on physiological conditions of unionid mussels in
           Texas

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      Abstract: Abstract Zebra mussels (Dreissena polymorpha) are an invasive species known to detrimentally affect native unionid mussels, a highly imperiled group of organisms. Yet, no study has compared the impact of infestation (direct attachment to unionid mussel shells) and presence of zebra mussels on glycogen storage under controlled conditions, nor examined the impact of zebra mussels at the southern edge of their North American distribution. Hence, the objectives of this study were to (1) examine the impact of infestation versus presence of zebra mussels with experiments in the laboratory and (2) collect data on glycogen concentrations of unionid mussels at field sites with and without zebra mussels. In the experiment, tissue samples were collected after 30 days from treatment tanks where (1) Threeridge (Amblema plicata) were artificially infested with zebra mussels, (2) zebra mussels were present with similar biomass, but shells of A. plicata were not infested, and (3) control tanks where zebra mussels were absent. Results from the experiments showed zebra mussel presence and infestation reduced glycogen by 38% and 66%, respectively. Results from the field were consistent with these findings. Variation in glycogen concentrations of mussels collected in the field was best explained by chlorophyll-a concentrations (coarse measure of food resource) and zebra mussel densities. Zebra mussels showed similar detrimental effects as in other studies despite their lower densities, which could be due to the additional metabolic costs associated with higher water temperatures. Our study suggests that the combined impact of invasive species and rising temperatures due to global warming needs to be considered for conservation and management plans.
      PubDate: 2022-03-15
      DOI: 10.1007/s00027-022-00853-8
       
 
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