Climate warming and rising terrestrial dissolved organic carbon (tDOC) inputs are major stressors altering lake ecosystems. While their individual impacts on planktonic communities are well studied, their combined effects on heterotrophic microbes, key mediators of tDOC transfer to higher trophic levels, remain less understood. We conducted an in situ mesocosm experiment (METU Mesocosm System I, Türkiye) to assess the independent and combined effects of warming (+ 4 °C) and tDOC on bacterial and ciliate biomass and on ciliate community structure (taxonomic, functional, and size composition). Bacteria were enumerated using DAPI-stained epifluorescence microscopy, and ciliates analyzed with FlowCam imaging supported by Utermöhl microscopy for identification and counting. Synergistic effects were weak, with tDOC emerging as the dominant driver of nonlinear, temporally dynamic microbial responses. Bacterial biomass increased transiently under tDOC and combined treatments, whereas ciliate biomass rose only under tDOC. tDOC shifted ciliate feeding groups toward bacterivores, indicating bottom-up control, and functional size groups toward larger species, suggesting weakened top-down regulation. Overall, functional analyses revealed that brownification reshapes microbial food webs more strongly than moderate warming. Stronger warming or longer exposure may amplify temperature effects, while including nanoflagellates and grazing assays could further clarify microbial trophic dynamics under climate change.

Heatwaves are intensifying globally, reshaping the carbon and nitrogen cycles of shallow lakes. In arid regions, concurrent salinization driven by climate change and water abstraction further modifies greenhouse gas (GHG) emissions. We investigated how short-term heatwaves and warming influence GHG fluxes in shallow lakes differing in salinity and macrophyte coverage, using outdoor mesocosms in two contrasting climatic zones of Türkiye: Mersin (hot Mediterranean) and Ankara (cold semiarid). The 2022 heatwave 22 experiment (Aug.–Nov.) used 32 mesocosms (16 per site) at two salinities (4 and 40) exposed to a simulated 15-d heatwave targeting +5 °C, with twice-weekly GHG sampling. In 2023, a second 30-d warming experiment in Mersin site targeting +4.5-°C difference assessed longer-term effects with daily measurements. Seasonal temperature variation and salinity with associated ecosystem characteristics (like, macrophyte presence) emerged as the main drivers of GHG fluxes, while short-term heating had weak and context-dependent impacts. Methane (CH4) emissions were consistently higher at Mersin than Ankara but generally low and declined with seasonal cooling, showing no clear heatwave response. Nitrous oxide (N2O) emissions were near zero in the low salinity, macrophyte-dominated mesocosms and remained unaffected throughout the experiment. In contrast, the high salinity mesocosms showed greater variability, albeit with no clear heatwave response. Carbon dioxide (CO2) emissions show a weak heatwave response only after the 15-d heatwave period, suggesting a lagged response. During the longer warming experiment, however, high-salinity, macrophyte-free mesocosms shifted from net CO2 uptake to emission, after 30 d of warming. Overall, our findings show that salinity and macrophyte coverage, rather than short-term temperature extremes, may primarily regulate GHG emissions in shallow lakes, while prolonged warming may alter carbon cycling in high-salinity, macrophyte-free lake ecosystems.

Despite the crucial importance of pond landscapes for biodiversity conservation, they are less studied, especially in terms of their impacts on people and society. This paper presents the results of a survey carried out on the perceptions of inhabitants and stakeholders across 17 pond landscapes in six countries in Europe, as well as T & uuml;rkiye and Uruguay. We collected 117 and 590 answers from stakeholders and local inhabitants, respectively, through questionnaires, including questions about their perceptions and preferences. Our results show that pondscapes are widely valued for their benefit to the quality of life and biodiversity. Three Nature's Contributions to People are considered important by both groups: 'creation and maintenance of habitats', 'physical and psychological experiences' and 'maintenance of options' (i.e. potential opportunities offered by nature to ensure resilience). Similar perceived threats related to 'climate change' and 'pollution' have been identified by stakeholders and inhabitants in all countries and have a direct impact on the maintenance of the most important contributions. The perceptions of potential solutions to identify threats are quite similar for most pondscapes, with conservation and maintenance actions being the most important for enhancing ecosystems and societal resilience to climate change and other societal challenges.

Body size is a fundamental trait influencing ecological functions, trophic dynamics, and organismal fitness across ecosystems. However, the environmental drivers shaping body size patterns in pond ecosystems across broad spatial scales remain poorly defined. In this study, we assessed the main determinants of body size in cladocerans and copepods, key crustacean zooplankton groups, across 168 ponds including regions in Europe, Asia, and South America. We assess how temperature and latitudinal variation, food availability, and predation influence mean and maximum crustacean body sizes in zooplankton taxa. Using linear mixed models, we identified annual temperature and predation pressure as the strongest predictors of body sizes. Body size increased with lower temperature for both taxa, supporting the temperature-size rule. Fish presence was associated with smaller body sizes for both taxa, while copepod size metrics were additionally influenced by pond morphometry, showing a negative relationship with depth and a positive association with area. These findings suggest temperature and predation pressure act as major selective forces shaping crustacean body size in pond ecosystems. Understanding these patterns is essential for predicting how crustacean communities and processes they mediate may respond to ongoing climate warming, particularly in small-shallow freshwater ecosystems highly sensitive to environmental change.

Blue carbon ecosystems, particularly salt marshes, occur worldwide and provide key ecosystem services – such as carbon sequestrations and carbon storage, that play a prominent role in climate change mitigation. However, the contribution of salt marsh ecosystems to global carbon stocks remains poorly understood, hindering the development of policies and management strategies to protect these organic carbon stores. To date, no studies have assessed the sediment carbon stocks in salt marsh ecosystems along Türkiye’s coast. Here, we examine sedimentary carbon stocks along Türkiye’s coastlines, focusing on 15 coastal wetlands along the Aegean and Eastern Mediterranean coasts. To identify the factors controlling sediment carbon density (SCD), several sedimentary and vegetation variables, including sediment organic matter, clay fractions,

This study investigates how pondscapes, networks of ponds, and their surrounding environments contribute to supporting identities across diverse cultural contexts. Supporting identities is a non-material Nature’s Contribution to People referring to people’s sense of place, belonging and connection to nature. We draw on data on landscape features from 17 pondscapes across eight countries in Europe and South America, along with over 700 questionnaire responses. We assessed whether certain landscape features are associated with the perceived delivery of supporting identities and examined how personal characteristics, individual perspectives, and engagement in different activities shape people’s perceptions. Our findings indicate that the perceived delivery of supporting identities emerges from a combination of social and ecological factors rather than from landscape features alone. Although pondscape characteristics showed weak direct effects, pondscapes in warmer climates and with a higher proportion of natural land cover might be associated with a stronger sense of identity. In addition, a strong personal connection to nature and engagement in nature-based activities (wildlife watching, picnicking, hunting), were key pathways shaping perceptions, highlighting that identity-related benefits are context dependent and socially mediated. By integrating ecological and social dimensions, our study highlights the importance of incorporating non-material values into conservation and landscape management strategies.

The Central Anatolian region of Türkiye exhibits exceptionally high freshwater fish diversity and endemism and is increasingly exposed to the introduction of non-native taxa. We examined the diet composition, prey selectivity and interspecific dietary overlap among eight native and five non-native fish species across seven lakes in Central Anatolia. Fish were sampled using multimesh gill nets and fyke nets, and their stomach contents were identified. In addition, zooplankton and benthic macroinvertebrate communities were quantified to evaluate prey selectivity patterns. Aquatic insects were the main food sources (averaging 60%), followed by cladocerans (25%), for both native and non-native fish species. Horn's index indicated a high dietary overlap (>0.60) between several native and non-native species, suggesting substantial overlap in resource use and the potential for exploitative interactions. Native species generally exhibited more specialized diets, whereas non-native species tended to be generalists. Prey selectivity analysis revealed that both native and non-native species preferentially consumed aquatic insects over other available prey types, indicating shared reliance on benthic food resources. These findings suggest that non-native fishes may influence trophic structure and resource use patterns in freshwater ecosystems with high endemism. We emphasize the importance of region-specific monitoring and management strategies to mitigate the ecological impacts of non-native fishes and support the conservation of Türkiye's freshwater biodiversity.

Submerged macrophytes play a crucial role as primary producers and contribute essential ecosystem functions and services, but rising temperatures caused by climate change may alter their functional traits. We aimed to assess the effects of simulated climate warming (4.5 degrees C) on the functional trait responses of a submerged macrophyte, Stuckenia pectinata (L.) Borner, in a synchronized oligohaline (4 ppt salinity) mesocosm experiment conducted in two different climate regions in Turkey: cold semi-arid Ankara and hot, dry Mediterranean Mersin. The experiment was conducted using eight mesocosms at each site, with four replicates of each ambient temperature and warming treatment. Each mesocosm held 5000 L and was inoculated with natural sediment, plankton, macroinvertebrate and fish communities to represent natural oligohaline lake ecosystem. S. pectinata shoots collected from a single population from a coastal lake in Mersin were also inoculated in all mesocosms in similar abundances. Overall, we observed significant differences in macrophyte functional traits between the two sites with different climates, albeit with less pronounced effects of a 4.5 degrees C rise in temperature within each site. Specifically, higher macrophyte percent volume infested (PVI) and canopy height were observed in the warmer Mersin than in the colder Ankara, which we attributed to higher shading by phytoplankton (reflected by water column Chlorophyll a, Chl-a). The biomass ratio (%dry weight (DW)/wet weight (WW)) was notably higher in Ankara, suggesting that the macrophytes in Ankara acquired relatively more resources than those in Mersin. The pronounced differences between the two sites likely reflected not only temperature differences but also cascading ecosystem characteristics (e.g., water column Chl-a, water nutrients) due to climatic differences.

Lakes face anthropogenic stressors such as climate change, salinization, and eutrophication, and microplastics (MPs) now emerge as a new concern since they act as vectors for pathogenic bacteria, giving rise to concern about environmental health. This study explores cultivable viable bacterial (CVB) biofilm communities on MPs along a salinity gradient (0.25 to 192.69‰) in 11 lakes in Türkiye. The MPs consisted mainly of fibers and 50-µm to 5-mm-sized fragments. The dominant cultivable bacterial phyla in both MP-associated biofilms and lake water were Proteobacteria and Firmicutes. On MPs, Pseudomonadaceae was the dominant family (94.7

Wetlands, despite their ecological value, have been extensively degraded worldwide. This study investigates the impact of 2 decades of wetland degradation, uncontrolled water use, and warming on the taxonomic and functional diversity of wetland bird communities in the Konya Closed Basin, T & uuml;rkiye. Using data from 2 breeding bird atlases (1998 and 2018) and historical satellite imagery, we assessed changes in wetland breeding bird diversity across various spatial scales and wetlands' seasonal shrinking patterns. We partitioned beta diversity into its turnover and nestedness components and calculated individual contributions of extinctions and colonizations to the overall changes in beta diversity. We utilized mixed-effect models and Wilcoxon tests to assess the significance of diversity changes. Our findings revealed widespread diversity losses at the local scale. We also found that the communities became more dissimilar, primarily because of local diversity losses. At the basin scale, functional diversity decline (66%) greatly exceeded taxonomic diversity decline (19%). Our satellite imagery analysis revealed an advancing wetland shrinking/drying over the study period. The diversity changes we found indicate that functional homogenization occurred at local and basin scales, and diversity losses at the local scale caused a subtractive heterogenization among the communities. We suggest that advancing wetland shrinking/drying dates due to climate change and human actions may be contributing to the decline of the late-breeding endangered diving ducks. Taken together, these findings suggest that a large-scale conservation plan, considering these seasonal and spatial changes, is needed to protect the remaining wetland bird diversity in the basin.

Amphibians are commonly occurring inhabitants of most lentic freshwater ecosystems, yet their global populations are in alarming decline. Ponds in particular play a crucial role in supporting amphibian biodiversity. In this study, we identified the main drivers influencing amphibian species richness by conducting a comprehensive ecological characterization in 201 ponds across seven European countries spanning a large latitudinal and longitudinal gradient. The amphibian species richness in each of these ponds was assessed using environmental DNA metabarcoding on water samples. The relative influence of climatic, local abiotic and biotic, and land use variables on variation in species richness across ponds was quantified using boosted regression trees. Our results suggest that local factors, particularly chlorophyll-a concentration, but also pond area and depth, are the main drivers of amphibian richness, together with climatic variables such as annual mean precipitation and temperature. The highest richness was observed in low-nutrient, fishless, intermediate-sized, shallow ponds, located in warmer regions with higher precipitation rates. These potential drivers of amphibian richness should be considered in the planning and implementation of amphibian conservation and management actions.

Ponds and pondscapes are crucial habitats for biodiversity and provide significant ecosystem services and socio-cultural benefits. However, effective management of these habitats requires an in-depth evaluation of how stakeholders perceive them and interact with them. This study aims to explore stakeholder relationships with their local ponds and pondscapes to better understand their interactions, expectations, concerns, and perspectives, ultimately informing more effective conservation and management strategies. Using stakeholder storylines and the Nature Futures Framework (NFF), we analyzed data gathered from participatory workshops in eight countries (United Kingdom, Belgium, Germany, Denmark, Spain, Switzerland, Turkey, and Uruguay). Thematic analysis was performed to identify key themes regarding stakeholders’ interactions, conservation expectations, climate change concerns, and management preferences related to local ponds and pondscapes across different countries. In addition, descriptive analysis was used to assess the different values that stakeholders assigned to ponds, including their ecological, cultural, and socio-economic significance. Our findings reveal a multifaceted relationship between stakeholders and pondscapes, deeply influenced by local socio-ecological contexts, including cultural heritage, biodiversity, recreation, and climate change concerns. Despite regional differences, stakeholders universally acknowledged the urgent need for sustainable conservation practices, envisioning future pondscapes that are resilient to climate change, rich in biodiversity, and capable of supporting diverse ecological and societal functions. Our study underscores the importance of integrating diverse stakeholder perspectives into pondscape management to foster more context-sensitive and sustainable conservation efforts that safeguard these vital habitats worldwide.

Ponds are key freshwater habitats supporting biodiversity and ecosystem services, yet they remain understudied in the context of land use and climate change. We examined 240 ponds across eight countries (seven in Europe and Uruguay) to assess how internal pond characteristics, surrounding land cover and livestock intensity, seasonal climatic variation, and climate influence nutrient concentrations across spatial and temporal scales. Nutrient concentrations were strongly associated with internal features: shallow ponds and short hydroperiods had higher total nitrogen (TN) and total phosphorus (TP) concentrations, while thermal stratification, typically found in deeper ponds, was associated with higher TN, indicating enhanced internal nutrient recycling. Land use also played a significant role with agricultural intensity increasing nutrient concentration (both TN and TP), whereas forest cover reduced TP. Seasonal variation modulated these patterns, with higher TP concentrations observed in summer, and with dilution effects during wetter and cooler periods, particularly for TN in semi-permanent ponds. These findings underscore the combined influence of physical characteristics, landscape context, and climate variability on nutrient concentrations in ponds and highlight the need for integrated, multi-scale approaches to anticipate the impacts of global climate change effects on these ecologically valuable ecosystems.

While numerous studies have investigated the effects of climate-induced increase of allochthonous matter (AM), the differential impacts of multiple AM sources on plankton dynamics are poorly understood. Here, we investigated the effects of two different sources of AM on zooplankton biomass, composition, taxonomic and functional indices (richness and evenness) and functional stability in a six-week outdoor mesocosm experiment. The treatments included a single pulse of alder tree leaf leachate (L, the nutrient effect), HuminFeed® (HF, the brownification effect) and the two combined (HFL) relative to control (no AM addition). HF did not give enough brownification to change zooplankton biomass. L and HFL enhanced zooplankton and Daphnia biomass. The biomass increase was more pronounced in HFL than L. The taxonomic richness and functional evenness were higher in HFL, no significant change for HF and L. The zooplankton functional stability, measured as biomass, in HF was resistant to disturbance. The communities in L and HFL showed low resistance, and only HFL community recovered. Our results highlight the stronger effect of the higher quality of L (i.e. nutrient content) and suggest that its combination with HF may have had synergistic effects, emphasising the importance of considering AM source quality in studies on planktonic communities.

Rapid and drastic anthropogenic impacts are affecting global biogeochemical processes and driving biodiversity loss across Earth's ecosystems. In aquatic ecosystems, species distributions are shifting, abundances of many species have declined dramatically, and many are threatened with extinction. In addition to loss of diversity, the ecosystem functions, processes and services on which humans depend are also being heavily impacted. Addressing these challenges not only requires direct action to mitigate environmental impacts but also innovative approaches to identify, quantify and treat their effects in the environment. Mesocosms are valuable tools for achieving these goals as they provide controlled environments for evaluating effects of stressors and testing novel mitigation measures at multiple levels of biological organisation. Here, we summarise discussions from a survey of marine and freshwater researchers who use mesocosm systems to synthesise their opportunities and limitations for advancing solutions to grand ecological challenges in aquatic ecosystems. While most research utilising mesocosm systems in aquatic ecology has focused on quantifying the effects of environmental threats, there is a largely unexplored potential for using them to test solutions. To overcome spatio-temporal constraints, there are opportunities to scale up the size and time-scales of mesocosm studies, or alternatively, test the outcomes of habitat-scale restoration at a smaller scale. Enhancing connectivity in future studies can help to overcome the limitation of isolation and test an important aspect of ecological recovery. Conducting 'metacosm' studies: coordinated, distributed mesocosm experiments spanning wide climatic and environmental gradients and utilising more regression-based experimental designs can help to tackle the challenge of context dependent results. Finally, collaboration of theoretical, experimental and applied ecologists and biogeochemists with environmental engineers and technological developers will be necessary to develop and test the tools required to advance solutions to the impacts of human activities on Earth's vulnerable aquatic ecosystems.

Net ecosystem production (NEP) is an important indicator of lake ecosystem function and integrity. An earlier study, restricted to one geographical region, indicated that oxygen saturation levels (DO

This chapter focuses on shallow lakes and ponds, the most abundant freshwater ecosystems on Earth. We highlight that, although they are often neglected, their role in biodiversity, water provision, the carbon cycle, and recreation is disproportionate to their size and volume. The theory of alternative equilibria and regime shifts in shallow lakes is revisited considering recent empirical advances in drivers and feedback mechanisms, and the main structural and functional characteristics of the most typical regimes are described. We highlight the importance of a landscape perspective, as networks of ponds and shallow lakes represent hotspots of biodiversity, particularly in urban and agricultural settings, and in arid, semiarid, and polar areas. We describe restoration practices and some management guidelines considering the fragility of these ecosystems to many local and global changes including climate change, land-use change, and the biodiversity crisis.