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Aquatic Sciences
Journal Prestige (SJR): 1.109
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Number of Followers: 15  
 
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ISSN (Print) 1015-1621 - ISSN (Online) 1420-9055
Published by Springer-Verlag Homepage  [2469 journals]
  • Impacts of ozone oxidation and borohydride reduction on the optical
           properties of humic substance isolates

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      Abstract: Abstract The optical properties of dissolved organic matter (DOM) are of interest as they are used to monitor or optimize drinking and wastewater treatment and influence the fate of contaminants in surface waters. DOM optical properties are presented as resulting either from charge-transfer (CT) interactions or from a superposition model. Herein, we present investigations of the effects of reduction (sodium borohydride) and oxidation (ozone) on the absorbance and fluorescence of three humic substance isolates of different origins (soil, autochthonous and allochthonous aquatic isolates). Both ozone and borohydride treatments induce a strong decrease in light absorption properties of the three isolates. For fluorescence, the treatments induce a fluorescence increase for the soil isolate while for the aquatic isolates, they induce either an increase or decrease. The effect of reductive or oxidative treatments is discussed using both the CT and the superposition model. The variations in the isolate’s composition (phenolic, quinones, aromatics moieties) are used to discuss the observed differences in treatments effects between the three isolates. Overall, this study provides insight into the contributions of different compound classes to DOM optical properties as explained by the CT and superposition models.
      PubDate: 2022-10-01
       
  • Evaluation of Zayandehroud basin health in the Iranian plateau

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      Abstract: Abstract Expanding negative impacts of human activities on ecosystem integrity, often resulting in their destruction, are one of the key environmental issues facing mankind, highlighting the need to assess and control such destructive trends. To reduce these impacts, it is critical to monitor ecosystem health using quantitative and qualitative indicators to examine changes over time. This study aims to assess the health of Zayandehroud basin using the DPSIR Framework and the synthesis of Remote Sensing and GIS. Fourteen environmental and socio-economic indicators were selected to determine the ecosystem health of the basin, with their weights being calculated based on the Analytical Hierarchy Process. Furthermore, spatio-temporal changes of the ecosystem health over 27 years (1993–2020) were analyzed to measure ecosystem pressure, status and response. The results showed an increase in areas with moderate health classes during this period. Although the areas between the center and the east of the basin were fragile, the average ecosystem health status of the west section is better than other areas. In other words, the health of western Zayandehroud basin has improved over time, while it has deteriorated in the eastern and central basins. The results provide policymakers and managers with information on the main drivers of change, such as population growth, land-use change, and infringements on the riparian sections of the river. Opportunities are provided for responses which will reduce negative impacts on the health of the river basin and their communities. The linking of different ecological and environmental components in a logical hierarchical form provides significant knowledge on changes in ecosystem health over time.
      PubDate: 2022-09-29
       
  • Molecular level characterization of DOM along a freshwater-to-estuarine
           coastal gradient in the Florida Everglades

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      Abstract: Abstract Understanding dissolved organic matter (DOM) export to the ocean is needed to assess the impact of climate change on the global carbon cycle. The molecular-level characterization of DOM compositional variability and complexity in aquatic ecosystems has been analytically challenging. Advanced analytical studies based on ultra-high resolution mass spectrometry (FT ICR MS) have proven highly successful to better understand the dynamics of DOM in coastal ecosystems. In this work, the molecular signature of DOM along a freshwater-to-estuarine gradient in the Harney River, Florida Everglades was analyzed for the first time using a novel approach based on tandem high resolution ion mobility and ultra-high resolution mass spectrometry (ESI-TIMS-FT ICR MS). This method enhances traditional DOM molecular characterization by including the molecular isomeric complexity. An average of six and up to 12 isomers were observed per chemical formula and characteristic isomers to each section of the freshwater-to-estuarine gradient were successfully identified. We measured a decrease in the chemical complexity and diversity (both in the number of molecular formulas and number of isomers per chemical formula) with increasing salinity; this trend is representative of the biogeochemical transformations of DOM during transport and along source variations, showing both clear degradation products and formation of new components along the salinity transect. The inclusion of the isomeric content at the molecular formula allowed to differentiate isomeric species that are present along the transect (mainly lignin-type components) and responsible for the DOM refractory nature. DOM isomeric fingerprints characteristic of the molecular variability along the Everglades freshwater-to-estuarine gradient are also described.
      PubDate: 2022-09-23
       
  • Significant diurnal variation of CO2 flux from a shallow eutrophic lake:
           effects of submerged aquatic vegetation and algae bloom

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      Abstract: Abstract Shallow eutrophic lake with submerged aquatic vegetation (SAV) has high primary productivity, but its diurnal variation of CO2 flux remains unclear. Moreover, algae bloom has become a serious environmental problem; however, its effects are still unclear. Thus, monthly measurement in Lake Ulansuhai, a shallow eutrophic lake in China, was conducted throughout the ice-free period (April–October, 2019), to study monthly and diurnal variation of CO2 flux and the effects of algae bloom, SAV, and trophic state. Results show that the area with SAV (Site 1) acts as a CO2 sink during both daytime and nighttime in most months (spanning 5 months), and CO2 absorption during nighttime accounts for 25–45% of the total daily absorption. In contrast, the area with both SAV and algae (from May to September; Site 2) during whole ice-free period acts as a CO2 source during nighttime all the time, accounting for 30–100% (average of 80%) of the total daily emissions. Site 1 (without algae) during whole ice-free period acts as a net CO2 sink with CO2 flux of −7.3 ± 4.73 mmol m−2 d−1, whereas Site 2 (with algae) plays as CO2 source with CO2 flux of 5.54 ± 3.15 mmol m−2 d−1. Furthermore, monthly variation during 7 months suggests that total daily CO2 emission flux in April (after ice-melt period) at Site 1 (without algae) and Site 2 (with algae) reached 17.78 and 34.75 mmol m−2 d−1, respectively, indicating that the period plays an important role for CO2 emission budget during the whole ice-free period. Results show that the effects of algae bloom and SAV need to be paid more attention in further works.
      PubDate: 2022-09-21
       
  • Effects of relic low-head dams on stream denitrification potential:
           seasonality and biogeochemical controls

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      Abstract: Abstract The majority of dams in the contiguous United States are small, low-head dams that are no longer operational but can influence the water quality of contemporary stream ecosystems. Potential effects of low-head dams on stream nitrogen removal (denitrification) have been rarely quantified, and yet they can be an important part of the decision-making process of removing low-head dams. Here, we provide novel empirical data on potential denitrification rates and their biogeochemical controls above and below two mid-Atlantic low-head dams over a 2-year period. Our results show that low-head dams did not increase streambed potential denitrification in comparison to dam-free sections in the same rivers. In our study sites, potential denitrification above low-head dams was generally low (15.7 ± 3.5 µg N [kg sediment]−1 h−1) despite recurring events of water hypoxia (< 50% dissolved oxygen saturation) and high NO3− and DOC concentrations. Overall, we observed higher potential denitrification during winter samplings (9.2 and 50.1 µg N [kg sediment]−1 h−1 on average) and significant effects of sediment surface area and organic matter content on potential denitrification rates above the dams. Results from this study suggest limited effects of relic low-head dams on nitrogen removal and transport in stream ecosystems, and can contribute to the decision-making process of removing low-head dams.
      PubDate: 2022-09-20
       
  • Riparian and watershed land use alters food web structure and shifts basal
           energy in agricultural streams

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      Abstract: Abstract We examined food web structure in headwater streams to determine whether riparian buffers can mitigate the effects of agricultural land use on stream ecosystem function. Study sites were located in the Midwestern US and divided into three land use groups (forested, buffered, agricultural) based on the amount of riparian forest and row crop agriculture in the watershed. Stable isotope analysis (δ13C and δ15 N) was performed on basal energy sources and consumers (6 invertebrate groups and 7 fish species) with isotopic metrics used to assess variation in food web structure related to land use, instream environmental parameters, and food resources. Land use differences were associated with community-wide isotopic shifts with all trophic diversity metrics greater in forested compared to agricultural streams, whereas buffered streams were generally intermediate. Agricultural streams had compressed food webs with high trophic redundancy indicative of a shared resource pool for all consumers. In contrast, forested and buffered stream food webs showed larger trophic niche area due to greater utilization of detrital energy and higher variability in trophic position among invertebrates and fish. Circular statistics revealed fish communities shifted to lower trophic positions and increased dependence on periphyton production in agricultural streams. The presence of riparian forests was associated with a broader range of resources used by consumers, expanded trophic diversity, and elevated fish trophic position in buffered streams. Results suggest that riparian forests can improve food web structure in streams impacted by croplands and provide further support for restoring buffer areas to moderate adverse effects of agriculture.
      PubDate: 2022-09-20
       
  • Site contributions to phytoplankton beta diversity along two subtropical
           reservoirs

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      Abstract: Abstract Information about species diversity, integration of local data, and the dynamics of regional diversity is essential for understanding the mechanisms that maintain diversity in biological communities, especially in aquatic environments, which have extensive connectivity. Here, we used phytoplankton community data from two subtropical reservoirs and evaluated the site contributions to phytoplankton beta diversity. We partitioned beta diversity into two mechanisms, replacement and differences in species richness and abundance, and we related to environmental heterogeneity. We tested whether there is a predominance of replacement or differences in richness and abundance in beta diversity, and whether environmental heterogeneity predicts beta diversity and its components. Our results indicated the temporal and spatial variation of the environmental conditions of the reservoirs. The species replacement was prevalent in lentic sites, while differences in richness and abundance contributed to lotic sites. Dissolved oxygen, total phosphorus, euphotic zone light availability, orthophosphate, water flow, and total dissolved solids were predictors of beta diversity and its components. Thus, studies that consider the local and regional variability of species in the function of environmental heterogeneity are essential in understanding ecological determinants and should be considered for the conservation of aquatic biodiversity and the maintenance of ecosystem services in reservoirs.
      PubDate: 2022-09-16
       
  • Taxonomic and functional aspects of diversity and composition of plankton
           communities in shallow lentic ecosystems along the human impact and
           environmental gradients

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      Abstract: Abstract Plankton communities constitute an important part of the biodiversity in shallow lentic ecosystems (SLEs). Understanding their diversity responses to increasing human pressure is required for the effective management of SLEs. Here we assessed the relationship between different properties of phytoplankton and zooplankton communities (abundance, taxonomic and functional diversity, and taxonomic and functional composition) and human impact (HII index), limnological features of SLEs (i.e., surface area and depth, trophic state, and hydrological connectivity), the biomass of submerged macrophytes, and the abundance of planktivorous fishes. For this, we sampled zooplankton from 28 sampling sites across nine SLEs (seven ponds, one channel, and one shallow lake). For 18 sampling sites across six of the ponds, we also sampled phytoplankton. We found that phytoplankton abundance was negatively associated with the higher HII, while zooplankton abundance and species richness increased with increasing HII. Hydrological connectivity was an important predictor of both phytoplankton and zooplankton diversity and composition. The functional diversity and composition of phytoplankton were more sensitive to environmental changes than their taxonomic diversity. Opposite patterns were recorded for zooplankton diversity metrics, presumably due to the dominance of non-predatory rotifers, which maintained constant functional diversity despite variations in taxonomic diversity along environmental gradients. Our results suggest that the taxonomic and functional diversity metrics of both phytoplankton and zooplankton should be considered simultaneously since they can show contrasting responses to human pressure and environmental changes in SLEs.
      PubDate: 2022-09-14
       
  • A bibliometric study on the use of diatoms in water quality monitoring and
           bioassessment in Africa across 10-year (2012–2022) period

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      Abstract: Living organisms are used in water quality evaluation, thus reflecting the constantly changing physical and chemical characteristics of aquatic ecosystems. Diatoms are among the aquatic organisms used in water quality monitoring of both lentic and lotic ecosystems. The objectives of our present study were to summarize the topics in diatoms for water quality evaluation, and identify the past trends as well as the future directions through the analyses of trends in diatoms bioassessment topics in Africa. We retrieved diatoms distribution data from Web of Science (WoS) database using the following keywords “Diatoms for water quality monitoring in Africa”, and “Diatoms for bioassessment in Africa”. We used VOS viewer software (version 1.16.15) in the construction of knowledge map of application diatoms in monitoring and bioassessment. A total of 481 documents on diatom in water quality monitoring and bioassessment were found. A subsequent thresholding of keywords centered on 15 times occurrence yielded 37 keywords. Diatom indicators were related to diversity, benthic diatoms, communities, community structure, assemblages, land-use, and water quality as clustered by VOS viewer software. Regionally, South Africa is one of the top most developed country in Africa, and this has been attributted to greater infrastructural, human resource, and financial capacity to carry out research that led to substantial collaborations both locally and globally. Institutionally, the connection between University of Cape Town and Bayworld Centre for Research and Education in South Africa was strongest probably due to their better infrastructural capacity in diatoms research. Therefore, the study provided insights that are likely to contribute to the future development of water quality monitoring framework using diatoms in Africa, thereby enhancing global environmental sustainability. Graphical abstract
      PubDate: 2022-09-14
       
  • Phosphorus sorption characteristics and interactions with leaf
           litter-derived dissolved organic matter leachate in iron-rich sediments of
           a sub-tropical ephemeral stream

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      Abstract: Abstract This study investigated the influence of dissolved organic matter (DOM) additions on phosphate sorption kinetics of iron-rich sediments (39–50% hematite and goethite) from an ephemeral stream in the arid Pilbara region of sub-tropical northwest Australia. While phosphate sorption in stream sediments is known to be strongly influenced by sediment mineralogy as well as interactions with DOM, the mechanisms and significance of DOM on P-release from sediments with high sorption capacities, are largely undescribed. We assessed phosphorus (P) sorption behaviours by adding a range of solutions of known inorganic P concentrations that were amended with variable loadings of DOM derived from leachates of leaf litter to sediments from stream pools during the non-flowing phase. We compared the sorption capacity of the sediments and concurrent changes in DOM composition measured using fluorescence spectroscopy. We show that the low-dose DOM addition (~ 4 mg L−1 DOC) had the effect of reducing sediment P adsorption capacity, while for the high-dose DOM addition (~ 45 mg L−1 DOC), it was increased. The high-dose DOM was similar to pore water DOC and likely saturated sediment surface adsorption sites and produced P–OM–Fe complexes. This resulted in increased removal of P from solution. Sediment P sorption characteristics were well fitted to both Freundlich and Langmuir isotherm models regardless of DOC concentration. Langmuir P sorption maxima ranged from 0.106 to 0.152 mg g−1. General P sorption characteristics of these iron-rich sediments did not differ among pools of contrasting hydrological connectivity. Our results show how humic-rich DOM can modulate the sediment P availability in dryland streams. Unravelling the complexities of P availability is of particular significance to further our understanding of biogeochemical processes in aquatic ecosystems where P often acts as a limiting nutrient.
      PubDate: 2022-09-12
       
  • Riparian cover buffers the effects of abiotic and biotic predictors of
           leaf decomposition in subtropical streams

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      Abstract: Abstract Stream functioning is energetically dependent on terrestrial vegetation due to the input of leaves. The decomposition process of this allochthonous resource may be controlled by leaf identity and abiotic and biological predictors that are also influenced by the presence of riparian cover. In subtropical Uruguayan streams, most of the riparian zones have been reduced, and the response of the decomposition process to the predictors may depend on the presence of riparian cover. We analyzed the importance of leaf identity and riparian cover on the abiotic and biotic predictors of leaf decomposition in rangeland streams, comparing two stream types (open canopy stream, OCS, and riparian forest stream, RFS). Decomposition experiments of native species (Eryngium pandanifolium and Schoenoplectus californicus) and the exotic Eucalyptus globulus were carried out. There were no significant differences in decomposition rate between the stream types; however, some predictors had significant, albeit differential, effects on the decomposition process depending on the presence of riparian forest. In OCS, the decomposition rates were positively influenced by NH4-N and streamflow but negatively by PO4-P, conductivity, and proportions of scrapers. Most of these variables had nonsignificant effects on decomposition rates in RFS. Experimentation procedures are needed to establish the mechanisms by which the presence of riparian cover modulates the response of the leaf decomposition to the effects of abiotic and biotic variables in subtropical streams. Leaf decomposition is much more affected by changes in leaf identity, suggesting that riparian changes that are accompanied by changes in leaf inputs may strongly affect this ecosystem function.
      PubDate: 2022-09-11
       
  • Ecosystem metabolism in sub-Antarctic streams and rivers impacted by
           non-native beaver

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      Abstract: Abstract Beavers can modify the hydrology, morphology, chemistry, and biology of ecosystems, though we have limited understanding of how beaver activity alters whole-ecosystem functions. We analyzed the effect of beaver activity and beaver dams on ecosystem metabolism in sub-Antarctic streams and rivers, where beavers are a non-native species. We characterized ecosystem metabolism (gross primary production and ecosystem respiration, GPP and ER) during 1–4 days in six streams and rivers with current beaver activity and dams (active) and three streams with no dams and no beavers (abandoned) as follows: Current beaver activity enhanced metabolism; GPP and ER were higher in sites with beaver activity than in more heterotrophic, abandoned sites. Beavers affect whole-ecosystem metabolism despite no detectable effects on physical and chemical variables in sub-Antarctic streams and rivers.
      PubDate: 2022-09-07
       
  • Denitrification in intertidal sediments of a tropical estuary subject to
           increasing development pressures

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      Abstract: Abstract Darwin Harbour is a working port and the most populated city in the Northern Territory of Australia. This macrotidal estuary is located in the wet–dry tropics of Northern Australia and notwithstanding mounting development pressures in the region, is largely unmodified. The prevailing oligotrophic condition of estuarine waters suggest that biogeochemical cycling in sediments remain active, buffering the influence of anthropogenic inputs. We tested the hypothesis that nutrient hotspots exist in depositional low-velocity zones, with a gradient of high to low nitrogen processing from the upper to outer reaches of the estuary. A number of factors were examined for their influence on the effectiveness of denitrification in these depositional zones, a putative key process driving nitrogen removal, with particular emphasis on carbon-loading extremes in tidal creeks, spatial gradients along the estuary and the influence of seasonality. There were significant differences in process rates between hypereutrophic/eutrophic tidal creeks that receive the largest proportion of treated sewage loads in the region and the mesotrophic/oligotrophic tidal creeks that were comparatively undisturbed. Net benthic nutrient fluxes and dinitrogen efflux rates were more than an order of magnitude higher and lower, respectively, in degraded (hypereutrophic/eutrophic) tidal creek systems where denitrification efficiency (DE%) was < 40%. Denitrification (Dinitrogen efflux) rates in tidal creeks (mesotrophic/oligotrophic) and broader estuarine sites were high (~ 8 mmol N m−2 day−1) and denitrification efficiency remained > 65%, particularly during the wet season. On a whole-of-estuary basis, denitrification in conjunction with mechanisms such as burial could feasibly make a substantial impact, abating the influence of anthropogenic inputs. Although considerable variability was encountered, particularly across seasons, the hypothesis of elevated denitrification rates as nutrient hotspots in depositional zones along the estuary was not convincing. More influential are tidal creeks as potential ‘reactors’ for N cycling and removal, but their capacity can be degraded by overloading with nutrients.
      PubDate: 2022-09-04
       
  • Toxic metal pollution of aquatic ecosystems of European Union nature
           protection areas in a region of intensive agriculture (Lake Gopło,
           Poland)

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      Abstract: Abstract The paper presents the results of research into toxic metal concentrations in the surface layer of bottom sediments in Lake Gopło. The research objectives were to identify the levels and spatial variability of Cu, Pb, Cd, Zn, Ni, Cr, As and Hg concentrations, their potential sources and the determinants of pollution levels. Metal contamination of the sediments was assessed using the geoaccumulation index (Igeo), pollution load index (PLI) and ecological risk index (RI). Chemometric methods (Pearson correlation, principal component analysis (PCA) and cluster analysis (CA) were used to determine the relationship between sampling sites and concentrations of toxic metals, thereby identifying the sources of contamination. The research found that grain-size composition, carbonate content and organic matter content in the bottom surface sediments of Lake Gopło are all characterised by low diversity. Therefore, the lithological features of the sediments are not a major factor in the concentrations and spatial variability of the metals. It was found that the metal concentrations in the great majority of samples were above regional geochemical background levels. The geochemical indices (Igeo, PLI, RI) indicate that the degree of toxic metal pollution in the sediments is slight in the central and southern parts of the lake and high in the northern part. The chemical analysis results showed that the samples in the central and southern parts of the lake differ little in their shares and concentrations of individual metals. This provides evidence that, as well as geogenic sources, their presence in sediments can be associated with non-point sources related to agricultural activities and with atmospheric sources (mainly the products of fossil fuel combustion). The higher concentrations of metals (especially Ni, Cd, Cr and Hg) in the northern part of the lake are influenced by the supply of industrial and communal pollutants from the lakeside town of Kruszwica. A factor limiting the migration of pollutants from the northern part of the lake towards the south is the lake’s morphology of the lake, which hinders water exchange between the northern part and the rest of the lake.
      PubDate: 2022-08-29
       
  • Ensemble of models shows coherent response of a reservoir’s
           stratification and ice cover to climate warming

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      Abstract: Abstract Water temperature, ice cover, and lake stratification are important physical properties of lakes and reservoirs that control mixing as well as bio-geo-chemical processes and thus influence the water quality. We used an ensemble of vertical one-dimensional hydrodynamic lake models driven with regional climate projections to calculate water temperature, stratification, and ice cover under the A1B emission scenario for the German drinking water reservoir Lichtenberg. We used an analysis of variance method to estimate the contributions of the considered sources of uncertainty on the ensemble output. For all simulated variables, epistemic uncertainty, which is related to the model structure, is the dominant source throughout the simulation period. Nonetheless, the calculated trends are coherent among the five models and in line with historical observations. The ensemble predicts an increase in surface water temperature of 0.34 K per decade, a lengthening of the summer stratification of 3.2 days per decade, as well as decreased probabilities of the occurrence of ice cover and winter inverse stratification by 2100. These expected changes are likely to influence the water quality of the reservoir. Similar trends are to be expected in other reservoirs and lakes in comparable regions.
      PubDate: 2022-08-24
       
  • Characterizing spatial and temporal variation in stable hydrogen isotopes
           (δ2H) between two distinct lentic freshwater food webs

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      Abstract: Abstract We investigated variability in δ2H values for two aquatic food webs involving avian consumers (lesser scaup, Aythya affinis Eyton and tree swallow, Tachycineta bicolor Vieillot) foraging from boreal lakes in the Yukon Flats (Alaska, United States) and wetlands in the Prairie Pothole Region (Saskatchewan, Canada), respectively. Generalized linear mixed-effects models were used to decompose sources of variation in water and tissue δ2H. We found inter-annual variation in boreal lakes δ2HW influenced by surface water connectivity (e.g., open vs. closed basins) and distance to the nearest river. Prairie pothole wetland δ2HW displayed intra-annual variability dictated by wetland type (e.g., semipermanent and seasonal) with a range greater than 60‰, which incrementally increased over the summer months. Variance in invertebrate δ2HI was explained by taxonomic category, but factors such as the relative distance to the nearest river (boreal model) and wetland type (prairie model) should be explored in future studies. Lesser scaup duckling feather δ2HF displayed inter-annual and spatial variability with the top model explaining 86% of the overall variation, including the following fixed effects: basin type (open/closed), year, and calendar date of sampling. Similar spatial patterns with known lesser scaup prey items, such as relative site distance to the nearest river, most closely aligned with Amphipoda δ2HI. Variation in tree swallow nestling δ2HF was attributed to sampling date with the top model explaining 38% of overall variation, while sampled prey items (e.g., Chironomidae) did not closely follow this pattern. Our findings quantify the extreme temporal and spatial δ2H variability in food webs fundamentally linked to seasonal evaporative effects in shallow lentic aquatic ecosystems.
      PubDate: 2022-08-24
       
  • High temperature, predation, nutrient, and food quality drive dominance of
           small-sized zooplankton in Neotropical lakes

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      Abstract: Abstract Body size plays a key role in the functioning of communities and ecosystems. However, this ecological trait is commonly under strong selection pressure by environmental drivers, such as temperature, nutrients, predation, and food quality. Understanding how environmental factors interact to shape the body size structure of communities is, therefore, of fundamental and applied interest. Using a unique database from 12 Neotropical lakes, we quantified the community-weighted mean trait (CWM) of zooplankton body size. We investigated how temperature, total phosphorus, abundance of predators (planktivorous fish) and food availability (abundance of edible and inedible algae) affect CWM of zooplankton body size. We also analyzed the interactions among these environmental predictors, and their cascading effects on zooplankton body size. We found that planktivorous fish, inedible algae, and edible algae had strong direct impacts on CWM of zooplankton body size. In particular, planktivorous fish and inedible algae decreased the CWM of body size, whereas edible algae increased it. Temperature and total phosphorus indirectly affected CWM of body size by increasing the abundance of planktivorous fish and inedible algae, and decreasing the abundance of edible algae. Our findings illustrate that environmental factors act in combination and affect zooplankton body size through multiple pathways. Therefore, focusing on the interaction between environmental predictors rather than just their isolated effects may provide a more mechanistic understanding of how environmental changes drive the body size structure of biotic communities.
      PubDate: 2022-08-09
       
  • Cold-tolerant traits that favour northwards movement and establishment of
           Mediterranean and Ponto-Caspian alien aquatic invertebrates

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      Abstract: Abstract Over recent decades, many Mediterranean and Ponto-Caspian aquatic invertebrate species have dispersed northwards and established as non-native species in colder regions. We hypothesized that these species have cold-tolerant traits, which facilitate dispersal into colder climates. Thanks to these traits, Southern European aquatic species are able to cross biogeographic boundaries. We downloaded the list of all alien invertebrate species that were fully aquatic (i.e. lacking terrestrial adults) from the GRIIS database and picked out those Mediterranean and Ponto-Caspian species that have undergone northwards range expansion. We identified traits that may facilitate dispersal to colder climates including the following: small size; capacity for behavioural thermoregulation; feeding habit (omnivorous, filter-feeders, food generalists); quiescence and dormancy (or diapause); freezing avoidance (presence of cryoprotectants); tolerance to low temperatures or eurythermicity; active dispersal; and enhanced reproduction. We statistically tested the null hypotheses that Mediterranean and Ponto-Caspian alien aquatic invertebrate species that dispersed into the north have all of these traits. We used contingency tables populated with raw frequency data with χ2—tests and assessed statistical significance at α of 0.05. We identified 95 Mediterranean and Ponto-Caspian alien aquatic invertebrate species that have shown northwards range extension, 10 (10%) of which were of Mediterranean origin and 85 (90%) of Ponto-Caspian origin. We found that this northwards dispersal from Southern Europe is mainly limited to a few following groups of aquatic invertebrates: small crustaceans, molluscs, cnidarians and annelids. Ability to go to diapause, hibernation or resting period, temperature tolerance and small size were the traits most commonly shared by these organisms. We conclude that Mediterranean and Ponto-Caspian aquatic invertebrate species showing northwards range expansion have cold-tolerant strategies. The traits analysed can favour the establishment of the species.
      PubDate: 2022-07-26
      DOI: 10.1007/s00027-022-00879-y
       
  • Patterns of genetic diversity of brown trout in a northern Spanish
           catchment linked to structural connectivity

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      Abstract: Abstract The alteration of structural connectivity in fluvial networks is important for the genetic dynamics of aquatic species. Exploring the effects of network fragmentation through genetic analysis is crucial to assess the conservation status of riverine species. In this study, we investigated the genetic consequences of the altered connectivity of brown trout in the Deva–Cares catchment (northern Spain). We investigated (1) genetic diversity, (2) genetic differentiation and genetic structure, (3) migration rates and effective population size and (4) genetic differentiation and riverscape characteristics. Analysis of the genetic variation among 197 individuals from the 13 study sites revealed a high degree of genetic differentiation (FST = 0.181). Below-barrier study sites had higher genetic diversity and lower FST values, while headwater and above-barrier study sites had lower genetic diversity and higher FST values. Most of the genetic groups identified were separated by one or more impermeable barriers. We reported an abrupt decrease in genetic diversity and effective population size in upper course tributaries and isolated reaches. Likewise, a downstream-biased gene flow was found, and it was most likely related to the fragmentation caused by barriers, since the results from migration indicated that gene flow between groups without impermeable barriers was higher bidirectionally. Isolation by impermeable barriers played a more important role than hydrological distance in determining the genetic structure. Most of the genetic groups showed small effective population sizes. Genetic analysis at the river network scale provides evidence for the role of barriers in determining genetic diversity patterns, highlighting the importance of maintaining and restoring river longitudinal connectivity.
      PubDate: 2022-07-26
      DOI: 10.1007/s00027-022-00877-0
       
  • Aquatic organic matter decomposition in the terrestrial environments of an
           intermittent headwater stream

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      Abstract: Abstract Rivers and their riparian zones are linked by reciprocal subsidies such as leaf fall or the emergence of biphasic aquatic organisms. Transfers of subsidies from freshwater to terrestrial ecosystems have been broadly studied, yet few studies have explored the transfer of aquatic organic matter (AOM) to surrounding terrestrial ecosystems as a response of hydrological variability. When rivers dry or flood, AOM can be transferred to terrestrial ecosystems and decomposed by terrestrial organisms; however, this process remains poorly investigated. In this study, we monitored the decomposition rate of several types of AOM (algae, macroinvertebrate and fish) exposed to different drying intensity, on the gravel bars and in the riparian zone of an intermittent headwater stream. The contribution of different terrestrial organisms to this decomposition rate was also explored. We showed that decomposition rates did not differ between the gravel bars and riparian zone although the invertebrate assemblages, which colonized the AOM, did. The decomposition rates depended mainly on the type of organic matter, with AOM of animal origin being decomposed more rapidly than that of vegetal origin. Microorganisms and vertebrates contributed most to the decomposition. Our results suggest that stranded AOM is consumed by terrestrial organisms; however, environmental conditions such as temperature and humidity can affect its decomposition. As extreme hydrological events are becoming more frequent, we need further research to explore how stranded AOM decomposition changes across seasons, river types and climates to improve our understanding of this process and its importance for terrestrial food webs.
      PubDate: 2022-07-11
      DOI: 10.1007/s00027-022-00878-z
       
 
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