Pond Communities Research Articles

Interactions Between Non-Native Western Mosquitofish and Native Bluegill Sunfish: Mesocosm Experiments.

Aquatic ecosystems are often negatively affected by invasive species. However, biotic resistance by native species, either by competition or predation, can reduce the impacts of invasions by non-native species. The Western Mosquitofish (Gambusia affinis) is one of the most impactful invasive species of freshwater fish and cause declines in native fish populations. Using two mesocosm experiments conducted in different years, we examined the ecological interactions between juveniles of the native fish, Bluegill Sunfish (Lepomis macrochirus), and adults of the invasive fish, G. affinis. We found evidence for interactions between L. macrochirus and G. affinis. However, interactions did not appear symmetric, with L. macrochirus generally more affected by intraspecific interactions than interspecific interactions whereas G. affinis was more affected by interspecific interactions than intraspecific interactions. The presence of either species of fish led to a decrease in the number of large zooplankton and a tendency for a decrease in the total number of zooplankton. Based on these results, native L. macrochirus appear to be able to reduce the ability of non-native G. affinis to establish or maintain populations through both competition and predation (i.e., acting as an intraguild predator). The consistency of our results across both experiments, with their different designs and their occurring in different years, gives weight to these conclusions. The reduction of or prevention of establishment of populations of invasive G. affinis would likely benefit the aquatic communities of ponds with fish, especially small-bodied native fish.

Effects of cyanotoxins on nitrogen transformation in aquaculture systems with microplastics coexposure: Adsorption behavior, bacterial communities and functional genes

Microcystin-LR (MC-LR) and microplastics (MPs) have attracted increasing attention as important new pollutants in freshwater fishery environments. However, there are few reports on the effects of long-term combined MC-LR and MPs pollution on nitrogen transformation and microbial communities in aquaculture ponds, and the resulting risks have yet to be determined. Therefore, in this study, traditional refractory MPs (polystyrene, PS), biodegradable MPs (polylactic acid, PLA) and MC-LR, which are common in freshwater fishery environments in China, were selected as pollutants to construct a microcosm that simulates freshwater aquaculture ponds. MC-LR coexposure to PS and PLA was tested to reveal the effects of these pollutants on nitrogen transformation and microbial communities in aquaculture ponds, as well as to elucidate the potential risks posed by traditional refractory MPs and biodegradable MPs to freshwater aquaculture ecosystems. The results revealed that the MPs had a relatively high adsorption rate for MC-LR and that PS presented a relatively high adsorption capacity, whereas PLA presented a relatively high desorption capacity. Single or combined MPs and MC-LR pollution disrupted the normal nitrogen cycle in the aquaculture system, causing an overall loss of nitrogen in the water, and denitrification and nitrogen fixation in the water were inhibited to a certain extent through the inhibition of nitrogen cycle-related functional genes, with the PS + MC-LR group having the greatest inhibitory effect. In addition, compared with single-pollutant exposure, combined exposure to MC-LR and MPs had a greater effect on the microbial community composition. Analysis of the integrated biomarker response (IBR) index revealed that the risk of combined exposure to MC-LR and PS was greater than that of single exposure, so this phenomenon merits further attention.

Umbrella index as a conservation tool across pondscapes: A case study using frogs, aquatic insects, and plants in South Africa

Biological surrogates are valuable for conservation when they are easy and cost-effective to sample, sensitive to anthropogenic change, and show similar assemblage patterns to other taxa. The umbrella index (UI) developed by Fleishman et al. (2000), aims to conserve most species in an ecosystem by focusing on a single or small group of co-occurring species to represent all species present. Here we focus on various lentic aquatic insects (‘aquatic insects’ henceforth refers to aquatic beetles, aquatic bugs, and dragonfly larvae), adult dragonflies, frogs, and aquatic plants as potential surrogates for pond communities in the Midlands, KwaZulu-Natal Province, South Africa. There were some cross-taxon correlations, but these were too weak to consider for surrogacy, largely due to dissimilar responses to the same environmental gradients. However, using UI we identified five dragonfly species, nine aquatic insect species, and three frog species as potential umbrella groups for their own taxa. The UI for same-group surrogates was flexible and covered most taxa, ranging from co-occurring habitat generalists to rare specialist species. Furthermore, all four endemic species sampled here were effective surrogate species for other local taxa, with two of them ranking top in their own taxonomic group. The lack of congruence among the different taxa means that one taxon cannot be used to stand in for another. However, the UI allowed efficient site prioritization, so long as a multi-taxon approach is used. We recommend the UI approach when selecting surrogates to represent aquatic fauna within a pondscape of the Midlands of South Africa.

Temporal dynamics of microbial communities in the water of polyculture pond system for Chinese swimming crab Portunus trituberculatus

Microorganisms as the vital component of aquaculture ecosystems, were involved in nutrient cycling, water quality regulation, and the health of cultured species. In this study, aquatic water samples were collected monthly to reveal microbial community compositions, functions, and interactions in different habitats (pond and waterway) during the culture stages of the Chinese swimming crab Portunus trituberculatus in Shandong Province. Due to the semi-closed conditions with limited water exchange, the α diversities were lower in the polyculture pond. The relative abundances of the dominant phyla varied dramatically, and most biomarkers were identified in the polyculture pond. The β diversity of the microbial communities significantly differed among culture stages and habitats. Furthermore, the heterogeneity of prokaryotic microorganisms was greater than that of eukaryotic microorganisms. In the polyculture pond, the microbial community was sensitive to nutrient cycling, with abundant functions related to “photoautotrophy”, “nitrogen_respiration” and “nitrate_respiration”, corresponding to P. trituberculatus culture activities. The co-occurrence network of the microbial community in the polyculture pond tended to be looser than that in the waterway, with a lower number of taxa and correlations. In addition, these networks had nonrandom patterns and formed “small world” topological structures. The low-abundance genera with a higher level of betweenness centrality scores were the hubs or connectors in the networks and might play an essential role in microbial community composition. Furthermore, potential pathogens (Vibrio, Acholeplasma, Photobacterium, and Flavobacterium) deserve more attention during P. trituberculatus culture. This study will be useful for understanding microbial communities in polyculture pond systems and will provide a reference for the health aquaculture of P. trituberculatus.

Principal determinants of aquatic macroinvertebrate communities in small shallow lakes and ponds

Principal determinants of aquatic macroinvertebrate communities in small shallow lakes and ponds

Community connectivity and local heterogeneity explain animal species co-occurrences within pond communities.

Metacommunity processes have the potential to determine most features of the community structure. However, species diversity has been the dominant focus of studies. Nestedness, modularity and checkerboard distribution of species occurrences are main components of biodiversity organisation. Within communities, these patterns emerge from the interaction between functional diversity, spatial heterogeneity and resource availability. Additionally, the connectivity determines the pool of species for community assembly and, eventually, the pattern of species co-occurrence within communities. Despite the recognised theoretical expectations, the change in occurrence patterns within communities along ecological gradients has seldom been considered. Here, we analyse the spatial occurrence of animal species along sampling units within 18 temporary ponds and its relationship with pond environments and geographic isolation. Isolated ponds presented a nested organisation of species with low spatial segregation-modularity and checkerboard-and the opposite was found for communities with high connectivity. A pattern putatively explained by high functional diversity in ponds with large connectivity and heterogeneity, which determines that species composition tracks changes in microhabitats. On the contrary, nestedness is promoted in dispersal-limited communities with low functional diversity, where microhabitat filters mainly affect richness without spatial replacement between functional groups. Vegetation biomass promotes nestedness, probably due to the observed increase in spatial variance in biomass with the mean biomass. Similarly, the richness of vegetation reduced the spatial segregation of animals within communities. This result may be due to the high plant diversity of the pond that is observed similarly along all sampling units, which promotes the spatial co-occurrence of species at this scale. In the study system, the spatial arrangement of species within communities is related to local drivers as heterogeneity and metacommunity processes by means of dispersal between communities. Patterns of species co-occurrence are interrelated with community biodiversity and species interactions, and consequently with most functional and structural properties of communities. These results indicate that understanding the interplay between metacommunity processes and co-occurrence patterns is probably more important than previously thought to understand biodiversity assembly and functioning.

Dynamics of Phytoplankton Communities and Environmental Drivers in Chinese Mitten Crab Aquaculture Ponds: Highlighting the Need for Cyanobacteria Control

Pond culture is the primary method for cultivating Chinese mitten crab (Eriocheir sinensis), with phytoplankton significantly influencing their growth. Green algae benefit crab growth by serving as supplementary food, while cyanobacteria, particularly during blooms, hinder it and pose health risks. Environmental changes in nutrient levels, temperature, and light significantly affect phytoplankton communities in ponds, impacting both ecosystem stability and crab growth. However, there is a limited understanding regarding the patterns of phytoplankton changes within adult Chinese mitten crab culture ponds. This study conducted monthly collection and analysis of phytoplankton throughout the culture cycle in typical adult Chinese mitten crab culture ponds, concurrently measuring physical and chemical water parameters to explore the correlation between phytoplankton changes and environmental factors. The results revealed distinct seasonal variations in phytoplankton composition. Chlorophyta and Bacillariophyta, such as Chlorella, Pediastrum, and Cocconeis, predominated in spring, while Chlorophyta and cyanobacteria, such as Volvox, Anabaena, and Microcystis, dominated in summer, and cyanobacteria and Bacillariophyta, such as Microcystis, Dolichospermum, and Cocconeis, prevailed in autumn. Total phytoplankton density consistently increased throughout the culture period. Microcystis constituted the majority of cyanobacteria biomass throughout most months. Although the total phytoplankton biomass fluctuated, cyanobacteria biomass consistently rose each month, reaching a peak of 61.7 mg/L in October. Water temperature and pH emerged as the primary environmental drivers influencing changes in phytoplankton community structure. Cyanobacteria density reached its peak between 18 and 26 °C and at a pH range of 7.5–8.5. These findings highlight the need for environmental regulation and cyanobacteria control in Chinese mitten crab culture ponds, thus promoting the health and sustainability of the Chinese mitten crab culture.

Multidimensional trait space outlines the effects of changes in abiotic filtering on aquatic plant community from sub-Antarctic ponds

In the current context of climate changes, which causes strong habitat variation, an understanding of the mechanisms underlying plant community dynamics is crucial to predict species fates. The taking of inter- and intraspecific trait variability into account would aid the identification of these mechanisms. Recently, a method involving the calculation of hypervolumes (n-dimensional spaces of trait values) was developed for the study of plant responses to their environments. Through hypervolume comparison, we examined the effects of interannual variations in abiotic conditions on aquatic plant communities in ponds of the sub-Antarctic Iles Kerguelen. This model system is particularly relevant for the examination of the consequences of climate changes–related habitat variation, as aquatic plant communities are adapted to cold and overall stable habitat conditions and the sub-Antarctic climate is changing rapidly. We conducted field sampling over four years at three sites. For all aquatic species, we measured five foliar, shoot, and clonal traits characterizing individual growth strategies that are likely to respond to variations in abiotic conditions on 1565 ramets over the four years. We measured 10 abiotic variables to characterize the plants’ habitats every three months during the survey period. Hypervolumes were calculated for each site and year to assess variation in aquatic plant strategies at the community level. We demonstrated (i) the importance of spatiotemporal gradients of trophic status, temperature, and pH and dissolved oxygen concentration for the functional structure of aquatic plant communities; (ii) that the shape of the mean response was trait dependent, with traits related to plant metabolism (specific leaf area and specific internode mass) and three-dimensional space exploration (height and internode length) responding to the three spatiotemporal abiotic gradients; (iii) that selection pressures were especially high on aerial traits relative to clonal traits; and (iv) that given the community response to interannual variations of abiotic conditions, environmental changes should impact macrophyte community productivity. Synthesis. We conclude that the examination of interannual abiotic variation over four years is sufficient to detect rapid responses of macrophyte communities, with likely reliance on phenotypic plasticity. Our findings may inform the characterization of future functional changes in aquatic plant communities of the sub-Antarctic region, where similar species are found.

Water availability and proximity to natural areas influence plant and terrestrial invertebrate communities in urban stormwater basins and ponds

Water availability and proximity to natural areas influence plant and terrestrial invertebrate communities in urban stormwater basins and ponds

Profiling sediment bacterial communities and the response to pattern-driven variations of total nitrogen and phosphorus in long-term polyculture ponds

Sediment bacterial communities are decisive drivers of nutrient cycling processes in aquaculture ecosystems and are readily affected by surrounding environmental factors. However, the knowledge of sediment nutrient accumulations and bacterial community structure is limited in the emerging polyculture systems. Herein, we investigated the profiles of sediment properties and bacterial communities in six typical polyculture ponds and primarily explored the influence of total nitrogen and phosphorus on the bacterial species and diversity. In almost all sediment samples, Proteobacteria, Chloroflexi, and Bacteroides were the dominant species at the phylum level, and the five most abundant bacterial genera were Sulfurovum, Woeseia, Ilumatobacter, Robiginitalea, and Cyanobium_PCC-6307. A clear different bacterial community was observed with the most dominant bacterial phylum Firmicutes and the lowest bacterial diversity in TZ1 pond sediment; meanwhile, the TZ1 pond also showed the highest TN and TP concentrations. Notably, sediments from WZ1 and WZ2 ponds in low-latitude regions exhibited higher bacterial richness and diversity. Based on Pearson’s correlation analysis, bacterial α-diversity indices showed significant negative correlation with sediment TP content, and TN content contributed the most to the abundance of sediment dominant bacterial genus, indicating that the bacterial community is highly associated with sediment nutrient concentrations. Moreover, co-occurrence network analysis further revealed some keystone taxa that exhibited high correlations with other bacterial species, especially the high-abundance genus Robiginitalea bridging a large number of connections. Compared to traditional mono-mariculture pattern, our study provided direct evidence of lower nutrient loadings and different bacterial communities in the polyculture ponds. This could assist polyculture practitioners in developing effective strategies for detailed nutritional management.

Diversity and distribution of chironomids in Central European ponds.

Ponds are common freshwater habitats in the European landscape that substantially contribute to local and regional biodiversity. Chironomids often dominate invertebrate communities in ponds but are usually disregarded in ecological studies due to relatively complicated taxonomy and identification issues. We present a comprehensive overview of the chironomid diversity in 246 ponds spanning a wide range of conditions extending from the Pannonian Plain to the Carpathians. Altogether, we recorded 225 taxa including 192 species from six subfamilies (Podonominae, Tanypodinae, Diamesinae, Prodiamesinae, Orthocladiinae and Chironominae). However, the chironomid taxa inventory is far from complete and about 16% of the total diversity of pond-dwelling chironomids remains undetected. Chironomid alpha diversity showed a significant unimodal pattern along the elevation gradient with the highest number of taxa per pond expected around 790 m a.s.l. Gamma diversity also peaked in mid-elevations (600-800 m), and the common chironomid taxa partitioned the 2100-m long altitudinal gradient relatively evenly. The heterogeneity of chironomid communities among ponds measured as beta diversity was significantly higher in elevations below 800 m. Temperature and the proportion of surrounding forests significantly influenced alpha diversity of chironomid communities, while urban land cover and pond size had no significant effect. Ponds with a mean annual air temperature of approximately 4.8°C and a low proportion of surrounding forests are expected to harbour the most diverse chironomid communities. Our study showed that chironomids represent a very diverse and often exceptionally rich group of pond-dwelling macroinvertebrates. Given the high diversity and broad range of occupied niches, chironomids should not be overlooked in pond ecology studies. On the contrary, they should be considered a potential model group.

Loss of amphibian species alters periphyton communities in montane ponds

Amphibian larvae can affect the structure and functioning of freshwater ecosystems, but their effects have been little explored although amphibian biodiversity is rapidly declining. Given that larvae of different amphibian species belong to different trophic levels, their effects on freshwater communities and processes can be expected to differ, with herbivores likely having direct effects on algae and predators having indirect effects through trophic cascades. We explored this question through a mesocosm experiment conducted in montane ponds, using an anuran and a urodele species affected by emergent diseases. We used different scenarios of reduction and loss of one or both species, and compared them to a control scenario representing a typical amphibian community in the study area composed of four species, with total larval density held constant. Loss of the anuran resulted in lower chlorophyll concentration and algal density, likely due to replacement by more efficient grazers. Loss of the urodele produced similar trends but weaker, possibly due to an increase of invertebrate grazing activity in the absence of this predator. Our study shows how the loss of amphibian species can alter the structure of montane ponds, but also how the mechanisms involved and the intensity of effects differ for different species.

Diversity of Macrophytes and Macroinvertebrates in Different Types of Standing Waters in the Drava Field

The diversity of macrophytes and macroinvertebrates in small standing waters of different origins and characteristics was investigated. This survey covered 19 ponds in the Drava field in northeastern Slovenia. The influence of the macrophytes on the macroinvertebrates was investigated and the main environmental factors that had the most significant influence on the composition of the two communities were identified. Sixty-seven taxa of macrophytes and seventy-three families of macroinvertebrates were identified. We found that a diverse macrophyte community has a positive effect on the macroinvertebrate community. In contrast, the dominance of a single macrophyte species has a strong negative influence on the richness of the macroinvertebrate community. The taxonomic richness and abundance of the macroinvertebrate community in the natural ponds was statistically significantly higher than that in artificial ponds. The significant differences in the environmental characteristics between the natural and artificial ponds, such as the macrophyte cover, conductivity, and riparian zone width, may account for these differences. Our study suggests that a greater diversity of macrophyte and macroinvertebrate communities in natural ponds is enabled by abundant but diverse macrophyte cover, low phosphorus content, and wide riparian zones, which require appropriate management of ponds and their catchments.

Exploitation and survival of Yellow Perch introduced into community ponds

Increased urbanization paired with stagnant or decreasing fishing license sales has bolstered the importance of community fishing programs. Community fisheries require fish introductions, have highly variable chemical and physical characteristics, and are situated in urban settings with non-traditional fishers that can prefer unique species. Community ponds also often receive high angling pressure and exploitation that can hinder the establishment of sustainable populations. We evaluated angler exploitation and its effects as well as biotic (i.e., stocking density, predator relative abundance) and abiotic (i.e., water temperature, pond size, pond depth) factors affecting survival of stocked adult Yellow Perch Perca flavescens in community ponds. We tagged 580 adult Yellow Perch (≥150 mm) and stocked them into four community ponds at 74 or 148 fish/ha in September 2018. We collected two years of fishery dependent (angler tag reporting) and independent recapture data to estimate angler exploitation and survival of Yellow Perch using a joint live-recapture and dead-recovery model. We estimated anglers harvested 44% (95% CI ± 6%) of stocked Yellow Perch across the four ponds in two years, with the majority (81%) coming from one pond. Additionally, anglers harvested 66% of captured Yellow Perch and harvest probability increased with fish size. Seasonal exploitation ranged from 0% to 37% and was more prevalent in cold water seasons. Yellow Perch survival was negatively related to harvest (β = −0.14; 95% CI = −0.17 to −0.10) and a quadratic effect of water temperature (temperature: β = 0.28; 95% CI = 0.02–0.53; temperature2: β = 0.01; 95% CI = −0.01–0.01). Yellow Perch survival was not related to stocking density or pond characteristics. After two years, cumulative survival in three ponds ranged from 0.83 to 0.87 whereas survival in one pond with high exploitation was 0.22. Our results suggest Yellow Perch can be successfully introduced in community fisheries, but populations may not be sustainable when harvest is high. Thus, management strategies to mitigate excessive harvest or multiple put-and-take stockings may be necessary to maintain Yellow Perch populations in community fishing programs.

Partial genomic characterization of Chromobacterium piscinae from India reveals multi drug resistance.

Species of genus Chromobacterium have been isolated from diverse geographical settings, which exhibits significant metabolic flexibility as well as biotechnological and pathogenic properties. This study describes the isolation, characterization, draft assembly, and detailed sequence analysis of Chromobacterium piscinae strain W1B-CG-NIBSM isolated from water samples from multi use community pond. The organism was characterized by biochemical tests, Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI TOF-MS) and partial genome sequencing. The partial genomic data ofChromobacterium pisciane isolate W1B NIBSM strainwas submitted to GenBank with Bio project number PRJNA803347 and accession no CP092474. An integrated genome analysis of Chromobacterium piscinae has been accomplished with PATRIC which indicates good quality genome. DNA sequencing using the illumina HiSeq 4000 system generated total length of 4,155,481bp with 63 contig with G + C content is 62.69%. This partial genome contains 4,126 protein-coding sequences (CDS), 27 repeats region and 78 transfer RNA (tRNA) genes as well as 3 ribosomal RNA (rRNA) genes. The genomic annotation of Chromobacterium W1B depicts 2,925 proteins with functional assignments and 1201 hypothetical proteins. A repertoire of specialty genes implicated in antibiotic resistance (45 genes), drug target (6 genes), Transporter (3 genes) and virulence factor (10 genes). The genomic analysis reveals the adaptability, displays metabolic varied pathways and shows specific structural complex and various virulence factors which makes this strain multi drug resistant. The isolate was found to be highly resistant to β-lactam antibiotics whereas it showed sensitivity towards aminoglycosides and fluoroquinolone antibiotics. Hence, the recovery of Chromobacterium piscinae from community pond evidenced for uncertain hidden source of public health hazard. To the best of authors knowledge this is first report of isolation and genomic description of C. piscinae from India.

Uncovering Anaerobic Hydrocarbon Biodegradation Pathways in Oil Sands Tailings from Two Different Tailings Ponds via Metabolite and Functional Gene Analyses.

Oil sands tailings, a slurry of alkaline water, silt, clay, unrecovered bitumen, and residual hydrocarbons generated during bitumen extraction, are contained in ponds. Indigenous microbes metabolize hydrocarbons and emit greenhouse gases from the tailings. Metabolism of hydrocarbons in tailings ponds of two operators, namely, Canadian Natural Upgrading Limited (CNUL) and Canadian Natural Resources Limited (CNRL), has not been comprehensively investigated. Previous reports have revealed sequential and preferential hydrocarbon degradation of alkanes in primary cultures established from CNUL and CNRL tailings amended separately with mixtures of hydrocarbons (n-alkanes, iso-alkanes, paraffinic solvent, or naphtha). In this study, activation pathway of hydrocarbon biodegradation in these primary cultures was investigated. The functional gene analysis revealed that fumarate addition was potentially the primary activation pathway of alkanes in all cultures. However, the metabolite analysis only detected transient succinylated 2-methylpentane and 2-methylbutane metabolites during initial methanogenic biodegradation of iso-alkanes and paraffinic solvent in all CNUL and CNRL cultures amended with iso-alkanes and paraffinic solvent. Under sulfidogenic conditions (prepared only with CNUL tailings amended with iso-alkanes), succinylated 2-methylpentane persisted throughout incubation period of ~ 1100days, implying dead-end nature of the metabolite. Though no metabolite was detected in n-alkanes- and naphtha-amended cultures during incubation, assA/masD genes related to Peptococcaceae were amplified in all CNUL and CNRL primary cultures. The findings of this present study suggest that microbial communities in different tailings ponds can biodegrade hydrocarbons through fumarate addition as activation pathway under methanogenic and sulfidogenic conditions.

Algal communities in urban freshwater ponds: prospects for biodiesel production

Algal communities in urban freshwater ponds: prospects for biodiesel production

Disentangling drivers of temporal changes in urban pond macroinvertebrate diversity

Ponds are key elements for ecosystem functions in urban areas. However, little is known about pond biodiversity changes over time and the drivers underlying such changes. Here, we tested whether past species assemblages, land cover and pond environmental change influence pond macroinvertebrate species richness and temporal beta diversity. We also compared spatial and temporal beta diversity, and investigated species-specific colonization and extinction rates over time. We sampled for presence of Odonata and Trichoptera (larvae), and Coleoptera and Hemiptera (larvae and adults) species in 30 ponds in Stockholm, Sweden, in 2014 and 2019. Past species richness was the best predictor of current species richness, whereas temporal changes in land cover and pond environment were not significantly related to current species richness. No correlations between temporal beta diversity and land cover or pond environmental changes were detected. However, ponds showed large changes in their temporal beta diversity, with equal contributions from species gains and losses. The probability of species colonizing and going extinct from ponds revealed that more common species were more likely to colonize a pond, while uncommon species were more likely to go extinct in a pond. Within our 5-year study, we found (i) highly similar spatial and temporal beta diversity, (ii) that past species richness is a good predictor of current species richness; however, the same does not hold true for species composition. The high dynamics of urban pond communities suggest that a large number of ponds are required to maintain high species richness at a landscape level.

Combined effects of climate warming and pharmaceuticals on a tri-trophic freshwater food web

Multiple anthropogenic stressors influence the functioning of lakes and ponds, but their combined effects are often little understood. We conducted two mesocosm experiments to evaluate the effects of warming (+4 °C above ambient temperature) and environmentally relevant concentrations of a mixture of commonly used pharmaceuticals (cardiovascular, psychoactive, antihistamines, antibiotics) on tri-trophic food webs representative of communities in ponds and other small standing waters. Communities were constituted of phyto- and zooplankton and macroinvertebrates (molluscs and insects) including benthic detritivores, grazers, omnivorous scrapers, omnivorous piercers, water column predators, benthic predators, and phytophilous predators. We quantified the main and interactive effects of warming and pharmaceuticals on each trophic level in the pelagic community and attributed them to the direct effects of both stressors and the indirect effects arising through biotic interactions. Warming and pharmaceuticals had stronger effects in the summer experiment, altering zooplankton community composition and causing delayed or accelerated emergence of top insect predators (odonates). In the summer experiment, both stressors and top predators reduced the biomass of filter-feeding zooplankton (cladocerans), while warming and pharmaceuticals had opposite effects on phytoplankton. In the winter experiment, the effects were much weaker and were limited to a positive effect of warming on phytoplankton biomass. Overall, we show that pharmaceuticals can exacerbate the effects of climate warming in freshwater ecosystems, especially during the warm season. Our results demonstrate the utility of community-level studies across seasons for risk assessment of multiple emerging stressors in freshwater ecosystems.

Salinity-controlled distribution of prokaryotic communities in the Arctic sea-ice melt ponds.

The thawing of snow and sea ice produces distinctive melt ponds on the surface of the Arctic sea ice, which covers a significant portion of the surface sea ice during summer. Melt-pond salinity impacts heat transfer to the ice below and the melting rate. It is widely known that melt ponds play a significant role in heat fluxes, ice-albedo feedback, and sea-ice energy balance. However, not much attention has been given to the fact that melt ponds also serve as a unique microbial ecosystem where microbial production begins as soon as they are formed. Here, we investigated the role of melt pond salinity in controlling the diversity and distribution of prokaryotic communities using culture-dependent and -independent approaches. The 16S rRNA gene amplicon based next generation sequencing analysis retrieved a total of 14 bacterial phyla, consisting of 146 genera, in addition to two archaeal phyla. Further, the culture-dependent approaches of the study allowed for the isolation and identification of twenty-four bacterial genera in pure culture. Flavobacterium, Candidatus_Aquiluna, SAR11 clade, Polaribacter, Glaciecola, and Nonlabens were the dominant genera observed in the amplicon analysis. Whereas Actimicrobium, Rhodoglobus, Flavobacterium, and Pseudomonas were dominated in the culturable fraction. Our results also demonstrated that salinity, chlorophyll a, and dissolved organic carbon were the significant environmental variables controlling the prokaryotic community distribution in melt ponds. A significant community shift was observed in melt ponds when the salinity changed with the progression of melting and deepening of ponds. Different communities were found to be dominant in melt ponds with different salinity ranges. It was also observed that melt pond prokaryotic communities significantly differed from the surface ocean microbial community. Our observations suggest that complex prokaryotic communities develop in melt ponds immediately after its formation using dissolved organic carbon generated through primary production in the oligotrophic water.