Wetland restoration is widely promoted as a complementary nature-based climate solution, but its net carbon and GHG effects across wetland types and interventions remain poorly quantified at the global scale. We address this gap with a global meta-analysis spanning all major wetland types and restoration strategies. We conducted a global meta-analysis of 617 restored-altered pairs from 149 studies on five continents to assess how restoration influences major carbon stocks and greenhouse gas (GHG) fluxes relative to altered wetlands. Overall, across all wetland types studied, restoration significantly increased aboveground biomass, belowground biomass and soil carbon. Restored wetlands also exhibited significantly lower CO₂ fluxes, consistent with increased primary production and reduced aerobic decomposition following hydrological and vegetation recovery, but also higher CH₄ emissions particularly in peatlands where rewetting enhances anaerobic conditions. By contrast, neither N₂O flux (though close to) nor, particularly dissolved organic carbon concentration showed statistically significant overall changes. These global patterns were robust to sensitivity and leave-one-out analyses but varied strongly among wetland types and restoration approaches. Restored mangroves and peatlands more clearly exhibited significant biomass and soil carbon gains, whereas restored freshwater wetlands and peatlands significantly displayed strong belowground biomass and and decreases in both CO2 fluxes, though the later showed significant CH₄ flux increases. Other wetland types displayed more variable responses to restoration, if any. Hydrological restoration (mainly rewetting) produced the strongest improvements in aboveground biomass, soil carbon and N₂O flux reductions, though it significantly increased CH₄ flux. Vegetation recovery was significantly effective action increasing above- and belowground biomass, soil carbon, and decreasing CO2 fluxes. Data were dominated by studies from Asia, Europe and North America, by far made in the Northern hemisphere, highlighting major geographical gaps in Southern areas. Overall, our synthesis shows that wetland restoration reliably regenerates carbon stocks and reduces CO₂ emissions, supporting its inclusion in climate mitigation portfolios and nature-based solution frameworks. Short-term CH₄ emission increases and ecosystem-specific responses highlight the need for long-term monitoring, context-dependent restoration design and improved global coverage to optimise carbon benefits and inform on climate’s friendly restoration policies and actions.

Coastal wetlands deliver critical ecosystem services but remain highly degraded by anthropogenic and climatic pressures. This study presents an integrated structural, functional, and socio-economic assessment of Marjal dels Moros, a managed Mediterranean brackish marsh in eastern Spain, to evaluate restoration effectiveness and inform climate-based management. Six subsites representing well-preserved, altered, and restored conditions were analyzed for water and sediment properties, microbial community composition, and greenhouse gas (GHG) fluxes, alongside a multi-criteria socio-economic evaluation of restoration scenarios. Results revealed strong environmental heterogeneity mostly driven by the hydroperiod and salinity gradients, with restored sites exhibiting intermediate sediment characteristics and reduced proxies of pathogenic bacterial genera. Microbial ordination highlighted hydrological control of methane-cycling guilds, while GHG fluxes showed a clear functional gradient: as such, permanently inundated, nutrient-rich sites emitted high CO₂ and CH₄ fluxes whereas subsites with seasonal drying and higher salinity acted as near-neutral or CH₄-suppressing zones. These patterns confirm that hydroperiod and salinity management shape microbial guilds and carbon dynamics, directly influencing climate regulation services. Socio-economic analysis indicated stakeholder preference for measures enhancing natural hydrology, habitat diversity, and risk reduction, supporting restoration strategies. Findings underscore hydrology-first strategies, integrated monitoring of functional indicators, and inclusive governance as key to achieving ecological integrity, climate mitigation, and socio-economic co-benefits. The proposed framework offers transferable guidance for policy-relevant restoration of Mediterranean coastal wetlands under multi-use pressures.

Accurate quantification of greenhouse gas (GHG) fluxes from aquatic systems is essential for constraining regional and global carbon budgets. Closed floating chambers are widely used to measure carbon dioxide (CO₂) and methane (CH₄) fluxes at the water–air interface, yet large uncertainties persist due to subjective processing of chamber time series. In particular, the treatment of non-linear patterns and abrupt events such as ebullition often relies on expert judgement, which may strongly influence flux estimates. We present the first quantitative assessment of bias arising from expert subjectivity in the processing of floating chamber measurements. Seventeen researchers, all of whom participated in field sampling, independently evaluated a common dataset of 794 incubations from 36 European coastal wetlands. Each expert visually selected valid data segments and flagged abnormal time series prior to flux calculation. In total, 2,679 manual inspections were compared with fully automated flux estimates based on untrimmed time series. Experts showed substantial variability in handling non-linear or irregular concentration patterns. While flux variability was generally low for most CO₂ and CH₄ incubations, disagreements exceeded 100% for curved or abrupt time series. For CH₄, ebullition was a major source of divergence, but marked variability also occurred when ebullition contributed only marginally to total fluxes. This methodological experiment demonstrates that expert judgement introduces significant, previously unquantified uncertainty into aquatic GHG flux estimates. We advocate for transparent, standardised, and reproducible data-processing workflows, including automated tools for objective identification and treatment of non-linearities.

Coastal wetlands play a substantial role in regulating Earth’s climate through exchanges of greenhouse gases (GHGs). Current European policies promote widespread coastal wetland restoration to reverse historical losses and ongoing pressures. However, substantial uncertainty remains regarding how CO₂ and CH₄ fluxes respond to restoration across different coastal wetland types and whether these responses translate into net climate mitigation in terms of CO₂ equivalents (CO₂-eq). We measured simultaneous CO₂ and CH₄ fluxes using static chambers across four seasons at multiple locations spanning preserved, altered and restored sites within each of six European coastal wetlands of different ecological types. By comparing GHG exchanges and resulting CO₂-eq balances across wetlands, we identified the dominant biogeochemical drivers of CO₂ and CH₄ dynamics and assessed the climate mitigation potential of conservation and restoration actions. CO₂ fluxes were primarily controlled by landscape-scale vegetation cover and inundation, whereas CH₄ emissions responded to more subtle changes in water quality, salinity and wetland hydrodynamics. Comparisons of CO₂-eq balances between altered and restored sites revealed that seagrass replantation and eutrophication reversal generated significant mitigation benefits, driven by enhanced CO₂ uptake and reduced CH₄ emissions, respectively. In contrast, other restoration measures modified CO₂ and CH₄ fluxes in opposing directions, resulting in non-significant net climatic effects of CO2-eq balances. Overall, our results demonstrate that climate mitigation outcomes of coastal wetland restoration are both GHG-specific and wetland-type dependent, underscoring the need for tailored restoration strategies and robust, multi-GHG monitoring to detect and accurately quantify potential climatic benefits.

Coastal wetlands play a substantial role in regulating Earth's climate through exchanges of greenhouse gases (GHGs). Current European policies promote widespread coastal wetland restoration to reverse historical losses and ongoing pressures. However, substantial uncertainty remains regarding how carbon dioxide (CO2) and methane (CH4) fluxes respond to restoration across different coastal wetland types and whether these responses translate into net climate mitigation in terms of CO2 equivalents (CO2-eq). We measured simultaneous CO2 and CH4 fluxes using static chambers across four seasons at multiple locations spanning preserved, altered and restored sites within six European coastal wetlands of different ecological types. By comparing GHG exchanges and resulting CO2-eq balances across wetlands, we identified dominant biogeochemical drivers of CO2 and CH4 dynamics and assessed the climate mitigation potential of conservation and restoration actions. CO2 fluxes were primarily controlled by landscape-scale vegetation cover and inundation, whereas CH4 emissions responded to less evident changes in water quality, salinity and wetland hydrodynamics. Comparisons of CO2-eq balances between altered and restored sites showed that seagrass replantation was associated with significant mitigation potential under both 100-year and 20-year CH4 warming scenarios, while eutrophication reversal through improved water treatment was only significant under the 20-year scenario. In contrast, other restoration measures modified CO2 and CH4 fluxes in opposing directions, resulting in no significant net change in combined CO2-eq balances. Overall, our results demonstrate that climatic responses to coastal wetland restoration are both GHG-specific and wetland-type dependent, underscoring the need for tailored restoration strategies and robust, multi-GHG monitoring to detect and accurately quantify potential climatic benefits.

Coastal wetland restoration is widely promoted as a tool for climate change mitigation, but its effect on the carbon cycle is not well constrained. We conducted a systematic review and meta-analysis of peer-reviewed field studies that directly contrasted restored with altered sites, covering carbon stocks and greenhouse gas fluxes across mangroves, saltmarshes, seagrass meadows, brackish systems, and coastal freshwater wetlands. Literature searches yielded 66 studies and 257 pairwise restored versus altered site comparisons. Multilevel random-effects models with nested study effects showed significant increases after restoration in soil carbon, aboveground biomass, and belowground biomass. Mean greenhouse gas flux changes after restoration were non-significant for CO₂, CH₄, and N₂O. Meta-regressions detected no significant differences among wetland types, though this result is constrained by unbalanced evidence across systems and studied parameters. The available data are geographically biased toward tropical and subtropical Asia, with minimal coverage in Africa and limited data from temperate and cold coastal regions. Among the covered variables dissolved organic carbon is critically underrepresented, constraining whole-system impact estimates. Overall, the data examined in this study show that restoration consistently rebuilds biomass and soil carbon without a detectable systematic “cost” from methane or nitrous oxide, indicating positive outcomes for greenhouse gas fluxes. To translate these findings into policy-ready estimates, monitoring of greenhouse gases and dissolved organic carbon should be expanded, altered versus restored designs should be prioritized, and underrepresented regions and wetland types should be targeted.

Macrophytes play a fundamental role in structuring freshwater ecosystems, including the provision of habitat and refuge for other organisms such as zooplankton. Yet, the role of invasive macrophytes in shaping biological communities remains unclear. This study examines how three invasive macrophytes with different growth forms, namely, Egeria densa (submerged), Ludwigia spp. (emergent), and Pistia stratiotes (free-floating) affect zooplankton density and diversity using a mesocosm experiment. Each of the ten mesocosms was divided into three sections with plants and one with open water as control, while fish predators were added to half of the mesocosms. We sampled over four weeks, both during day and night time. Zooplankton assemblages differed considerably among the sections, with macrophyte sections all showing higher abundance and richness when compared to that of open water. The greatest density occurred in between the roots of the floating plant P. stratiotes. During the night, zooplankton migrated outside the macrophytes, and differences were smaller between the sections. The presence of fish had negligible effects on the community. These findings highlight the role of invasive macrophytes in shaping freshwater systems and give important insights into biodiversity management and conservation in invaded habitats.

Permanent ponds are key landscape units that supply various ecosystem services. Notably, the export of aquatic subsidies to land via emerging insects may significantly influence terrestrial food webs. Polyunsaturated fatty acids (PUFA), which enhance consumer fitness, are among the essential exported components. The patterns and drivers of dietary exports from ponds via insects remain poorly known, particularly at continental scales. We analyzed the exports of biomass, lipid, and fatty acid contents from emerging insects, sampled in 36 ponds across 11 European countries, from 36°N to 59°N and from 26°W to 19°E, over four seasons. We found that biomass and fatty acid exports decreased with increasing latitude and were higher in spring and summer. Seasonal effects also increased with higher latitudes. Temperature was the most important predictor of insect biomass, explaining 27.6% of the total variation and showing an unimodal response. Thus, increasing temperature may promote exports in colder regions and seasons but may negatively influence biomass exports in already warm regions. The exports of total lipids, PUFA, and eicosapentaenoic acid were correlated to exported biomass, while those of docosahexaenoic acid were linked to the emergence of Chaoboridae. Our findings indicated that PUFA contents were affected by taxonomic insect community composition and pond trophic state (indicated by chlorophyll a ). Two of the correlates identified here (temperature and trophic state) are influenced by anthropogenic activity via climate and land use change, respectively. Thus, human activity impacts the food webs in and around ponds by influencing the quantity and quality of nutritional exports.

Measuring reliable greenhouse gases (GHGs) fluxes at the interface between water bodies and the atmosphere in inland waters is crucial in the context of climate change but remains highly challenging. GHG fluxes can be measured directly in-situ with chambers placed at the water-atmosphere interface and connected to portable gas analysers providing high-frequency timeseries of GHGs partial pressures inside the chamber. Fluxes are usually assumed constant over the time of incubation, but varying GHG sources and changing environmental conditions and/or ebullition from the sediment produce non-linear patterns and breakpoints in the timeseries, not mentioning the possibility for poor manipulation of the device, disturbance of the sampling site by the operator, or malfunctioning sensors. Accordingly, it is common procedure to visualize and select part of the measurements manually for each incubation before proceeding with fluxes computation. In the ongoing Horizon Europe project RESTORE4Cs, we have performed CO2 and CH4 chamber measurements in 36 different sites located in 6 major coastal wetlands across Europe, including intertidal saltmarshes and seagrass beds, freshwater and brackish ponds and marshes, and coastal lagoons. Between October 2023 and August 2024, we have gathered a database of 822 floating chamber incubations, collected by multiple operators and with 3 different gas analysers. Here we focus on the data processing part and assess to what extent we need expert evaluation of the time series to produce reliable flux estimates. We have developed an automated data processing script able to compute fluxes estimates for all incubations. Timeseries are fitted with both a linear and non-linear models. The script identifies potential bubbling in CH4 measurements and estimates the diffusive versus ebullitive components based on the statistical characteristics of the first derivative of pCH4. All incubations were manually inspected by 16 members of our team, all experts in GHG chamber measurements with various levels of experience. About half of these timeseries were inspected independently by at least 3 experts, enabling to compare if and why experts disagree. For both CO2 and CH4, non-linear fitting performed better than linear models for 69% incubations, indicating a substantial number of non-linear patterns in the dataset; however, the difference between the two models was less than 10% for 86% of the incubations. The ebullition pathway was the dominant CH4 flux in less than 10% of the incubations. Experts disagreed substantially on the data selection in 34% of the incubations, which produced uncertainties in flux estimates larger than 10% of the inter-expert flux average. The highest discrepancies were related to suspicious or non-linear features in the time series. To avoid subjectivity and ensure robustness and repeatability of flux estimates, we present guidelines on how CO2 and CH4 incubation time series should be processed, regardless of whether they are processed automatically or after an expert manual inspection.

Coastal wetlands are crucial for biodiversity and act as critical buffers for carbon sequestration and atmospheric greenhouse gases (GHG) concentrations, yet their degradation often turns them into GHG sources. Restoration is widely implemented to recover these services, but it remains unclear whether interventions successfully re-establish the microbial functional diversity underpinning biogeochemical cycles. We tested the hypothesis that restoration aligns prokaryotic community structure with natural references, analyzing, a European gradient of coastal wetlands, comparing well-preserved, altered, and restored sites in water and sediment. Using 16SrRNA-metabarcoding and IndVal-Analysis, we characterized community assembly identifying diagnostic functional consortia. Results revealed a marked difference in water and sediment recovery after restoration. Bacterioplankton communities rapidly converge to natural references, while sediment microbiome displayed significant "ecological memory". Restored wetlands show sediment communities structurally distinct from well-preserved, retaining alteration-associated guilds decades. Results support the initial hypothesis: restoration processes in coastal wetlands can re-establish communities and metabolisms resembling well-preserved conditions in the water in the short term, while sediments retain microbial communities and metabolisms inherited from altered conditions for a long time. Future strategies must integrate active sediment interventions using molecular bioindicators to validate not only the landscape appearance, but the effective reactivation of ecosystem processes and microbiota-related services. ### Competing Interest Statement The authors have declared no competing interest. project RESTORE4Cs - Modelling RESTORation of wEtlands for Carbon pathways, Climate Change mitigation and adaptation, ecosystem services, and biodiversity, Co-benefits (DOI: 10.3030/101056782), co-funded by the European Union under the Horizon Europe research and innovation programme, 101056782 CLIMAWET-CONS (PID2019-104742RB-I00), funded by the Agencia Estatal de Investigation of the Spanish Government project ECCAEL (PROMETEO CIPROM-2023-031), funded by the Generalitat Valenciana

Dense beds of aquatic plants are often perceived as nuisance and therefore mechanically removed, often at substantial cost. Such removal, however, may affect a range of ecosystem functions and consequently also the ecosystem services that benefit society. We studied five cases: River Otra (Norway), River Spree (Germany), Lake Kemnade (Germany), Lake Grand‐Lieu (France) and Hartbeespoort Dam (South Africa). In all, nuisance aquatic plant growth is managed, but dominant species, geographic setting and major societal uses are different. We quantified 12 final ecosystem services as flows per area and year in biophysical and monetary terms. Quantified services were food and fodder production, commercial fisheries, hunting and gathering wild products, hydropower production, drinking and irrigation water production, flood prevention, carbon sequestration, active and passive recreation and biodiversity conservation (nonuse). These services were related to aquatic plant cover via a range of ecosystem functions, and the effects were estimated of three plant removal regimes on the relative importance of the quantified ecosystem services and on the total sum of the monetary estimates (total economic value, TEV). The three removal regimes were ‘maximum removal’, ‘current practice’ and ‘do nothing’. In all five cases, TEV was dominated by different forms of recreation. TEV was highest for Lake Kemnade, where visitor densities were highest. TEV was most sensitive to the different management regimes in Lake Kemnade, because a threshold in aesthetic appreciation was passed in the ‘do‐nothing’ regime, and in Hartbeespoort Dam, because of the effect on boating and angling. In the other cases, the different removal regimes had little effect on the estimated TEV. Synthesis and applications . Since recreation dominated the estimated societal benefits in the studied ecosystems, also where provision of hydropower, drinking water or irrigation water were relevant, effects on recreation should be a core consideration in the management of nuisance aquatic plants. Furthermore, aquatic plant management strategies will benefit from taking into account the differences in perceived nuisance among different categories of recreative users before engaging in costly removal.

Aquatic plants (macrophytes) are important for ecosystem structure and function. Macrophyte mass developments are, however, often perceived as a nuisance and are commonly managed by mechanical removal. This is costly and often ineffective due to macrophyte regrowth. There is insufficient understanding about what causes macrophyte mass development, what people who use water bodies consider to be a nuisance, or the potential negative effects of macrophyte removal on the structure and function of ecosystems. To address these gaps, we performed a standardized set of in situ experiments and questionnaires at six sites (lakes, reservoirs, and rivers) on three continents where macrophyte mass developments occur. We then derived monetary values of ecosystem services for different scenarios of macrophyte management (“do nothing”, “current practice”, “maximum removal”), and developed a decision support system for the management of water courses experiencing macrophyte mass developments.We found that (a) macrophyte mass developments often occur in ecosystems which (unintentionally) became perfect habitats for aquatic plants, that (b) reduced ecosystem disturbance can cause macrophyte mass developments even if nutrient concentrations are low, that (c) macrophyte mass developments are indeed perceived negatively, but visitors tend to regard them as less of a nuisance than residents do, that (d) macrophyte removal lowers the water level of streams and adjacent groundwater, but this may have positive or negative overall societal effects, and that (e) the effects of macrophyte removal on water quality, greenhouse gas emissions, and biodiversity vary, and likely depend on ecosystem characteristics and macrophyte life form. Overall, we found that aquatic plant management often does not greatly affect the overall societal value of the ecosystem, and we suggest that the “do nothing” option should not be easily discarded in the management of perceived nuisance mass developments of aquatic plants.

Dense beds of water plants can be perceived as nuisance, but this perception, however, may not be similar for different user categories, and this may affect their willingness-to-pay (WTP) for plant removal. A questionnaire survey was used to test this for residents and visitors and find underlying socio-cultural or economic drivers. We studied five cases where nuisance water plant growth is managed: the rivers Otra (Norway) and Spree (Germany), and the lakes Kemnade (Germany), Grand-Lieu (France), and Hartbeespoort Dam (South Africa). We used a different payment vehicle for residents (annual household tax) and visitors (tourist tax). The survey included questions on days spent on specific types of activity per year, the importance attached to different functions and activities, overall environmental attitude, perception of the plants, socio-demographic respondent characteristics and WTP for increased plant removal. We observed no increase in WTP for increased removal in most sites. The two most important drivers of variation in current WTP were income, and whether respondents were engaged in boating and angling and thus perceived the plants negatively. Variation in WTP among sites was considerable, and mainly related to the mixture of activities among respondents. Differences between residents and visitors were less important than those among sites. Our observations bear importance for water management: information on differences in experienced nuisance among user categories and the frequency of use by these categories is useful as guidance for the design and implementation of any plant removal plan.

Phytoplankton is an essential resource in aquatic ecosystems, situated at the base of aquatic food webs. Plastic pollution can impact these organisms, potentially affecting the functioning of aquatic ecosystems. The interaction between plastics and phytoplankton is multifaceted: while microplastics can exert toxic effects on phytoplankton, plastics can also act as a substrate for colonisation. By reviewing the existing literature, this study aims to address pivotal questions concerning the intricate interplay among plastics and phytoplankton/phytobenthos and analyse impacts on fundamental ecosystem processes (e.g. primary production, nutrient cycling). This investigation spans both marine and freshwater ecosystems, examining diverse organisational levels from subcellular processes to entire ecosystems. The diverse chemical composition of plastics, along with their variable properties and role in forming the "plastisphere", underscores the complexity of their influences on aquatic environments. Morphological changes, alterations in metabolic processes, defence and stress responses, including homoaggregation and extracellular polysaccharide biosynthesis, represent adaptive strategies employed by phytoplankton to cope with plastic-induced stress. Plastics also serve as potential habitats for harmful algae and invasive species, thereby influencing biodiversity and environmental conditions. Processes affected by phytoplankton-plastic interaction can have cascading effects throughout the aquatic food web via altered bottom-up and top-down processes. This review emphasises that our understanding of how these multiple interactions compare in impact on natural processes is far from complete, and uncertainty persists regarding whether they drive significant alterations in ecological variables. A lack of comprehensive investigation poses a risk of overlooking fundamental aspects in addressing the environmental challenges associated with widespread plastic pollution.

Mass development of macrophytes is an increasing problem in many aquatic systems worldwide. Dense mats of macrophytes can negatively affect activities like boating, fishing or hydropower production and one of the management measures often applied is mechanical removal. In this study, we analyzed the effect of mechanical macrophyte removal on phytoplankton, zooplankton, and macroinvertebrate (pelagic and benthic samples) assemblages. Our study covered five sites in four countries in Europe and Africa with highly variable characteristics. In all sites, dense mats of different macrophyte species (Juncus bulbosus in a river in Norway; a mix of native macrophytes in a German river, Elodea nuttallii in a lake in Germany, Ludwigia spp. In a French lake and Pontederia crassipes in a South African lake) are problematic and mechanical removal was applied. In every country, we repeated the same BACI (Before-After-Control-Impact) design, including "before", "one week after", and "six weeks after" sampling in a control and an impact section. Repeating the same experimental design at all sites allowed us to disentangle common effects across all sites from site-specific effects. For each taxonomic group, we analyzed three structural and three functional parameters, which we combined in a scoring system. Overall, the removal of macrophytes negatively affected biodiversity, in particular of zooplankton and macroinvertebrate assemblages. In contrast, plant removal had positive effects on the phytoplankton assemblages. Effects were more pronounced one week after removal than six weeks after. Consequently, we suggest a stronger consideration of the effect of plant removal on biodiversity to arrive at more sustainable management practices in the future.

Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ESs), including water quality improvement and supply, food provisioning, and biodiversity support, despite significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However, ponds are largely overlooked in management plans and legislation, and ecological research has focused on large freshwater ecosystems, such as rivers or lakes. Protection of ponds is often insufficient or indirectly provided via associated habitats such as wetlands. This situation is likely exacerbated by the lack of a full-scale understanding of the importance of ponds. In this review, we provide a detailed overview of permanent ponds across Europe, including their usages and the biodiversity they support. By discussing the concepts of pondscape and metacommunity theory, we highlight the importance of connectivity among and between ponds and identified fluxes of emerging insects as another ES of ponds. Those insects are rich in essential nutrients such as polyunsaturated fatty acids (PUFAs), delivered through them to the terrestrial environment; however, the extent and impact of this ES remains largely unexplored. Several potential stressors, especially related to ongoing global change, that influence pond diversity and integrity are discussed. We provide our insights on future pond management. Adaptive measures, taking into account the pond system per se within the pondscape, are the most promising to mitigate the loss of natural ponds and restore and conserve natural small waterbodies as refuges and diversity hotspots in increasingly urbanized landscapes.

Changing weather patterns and receding glaciers are predicted to increase flow intermittency in alpine streams. If aquatic macroinvertebrate communities largely comprise taxa adapted to perennial flows, an increase in flow intermittency substantially reduces biodiversity and affects functional processes. We conducted a before-after-control-impact field experiment to examine how macroinvertebrate communities in an alpine headwater stream responded to and recovered from a repeated experimental increase in flow intermittency. Flow in one channel was manipulated to simulate increased summer intermittency (June–September) over two consecutive years, whilst an adjacent channel served as a control. We monitored the density of benthic macroinvertebrates, periphyton and organic matter at approximately monthly intervals over three years during the snow-free period. Before manipulation, both channels had similar ecological properties. The flow manipulation reduced the overall macroinvertebrate density, and especially the proportional rheophile density, across both years. Recovery of the macroinvertebrate community following experimental flow intermittency took more than a year, and longer than our study period. This could be due to long aquatic life stages, dispersal limitation and biotic interactions. We conclude that climate-induced changes in alpine stream flow regimes can lead to a fundamental shift in macroinvertebrate assemblages through local extinctions, mostly of rheophilic species.

Mass development of macrophytes in freshwater ecosystems is today considered a worldwide problem and substantial resources are spent on macrophyte removal each year. By removing the dominant primary producer, however, this management practice radically changes the ecosystem overnight. Here, we studied short-term effects of the removal of a mass development of free-floating (Pontederia crassipes), submerged (Elodea nuttallii) and emergent (mix of Ludwigia grandiflora and L. peploides) macrophytes on fluxes of CH4 and CO2 in three lakes. In our field experiment, we assigned an impact site where macrophytes were removed, and a control site where vegetation remained. Before and after removal, diffusive fluxes of CO2 and CH4 were determined in lakes dominated by P. crassipes and E. nuttallii, whereas total emission of CH4 was determined in all three case study lakes. Additionally, plant biomass, and physical and chemical parameters were measured before and after removal. While removal of emergent Ludwigia spp. showed no clear effect on total CH4 emission, removal of submerged E. nuttallii reduced both CO2 fixation and total CH4 emission. Removal of free-floating P. crassipes, on the other hand, increased CH4 fluxes and stimulated phytoplankton blooms. The lack of a universal response across our case study lakes suggests that both macrophyte life forms and environmental parameters can be important factors determining effects of removal. Additionally, indirect effects of macrophyte removal on temperature and dissolved oxygen can help to explain carbon emissions. Long-term effects should be studied to allow development of sustainable management practices.

Macrophytes play an important role in the functioning and structuring of aquatic environments but rapid mass development of invasive macrophytes is causing global concerns. Macroinvertebrate richness and abundance are strongly influenced by macrophytes as macrophytes offer habitats and food resources, increase structural heterogeneity, and provide refuges. Meanwhile, the presence of macrophytes affects the efficiency of standard sampling methods for macroinvertebrates. These effects are not well studied but are leading to biased management decisions. To fill in this knowledge gap, we analysed macroinvertebrate communities from four lakes in four countries in Europe and Africa with mass development of invasive macrophytes. We compared macroinvertebrate communities in sediment samples from a plant-free part of the lake with those in sediment and sweep samples taken within macrophyte stands. We showed that taxa richness and density were higher in sediment samples beneath invasive macrophyte stands compared to plant-free habitats. Unique taxa were found in each sample type. Sampling efficiency of each sampling method varies greatly across lakes especially when replication is low. The taxonomic richness of macroinvertebrates within invasive macrophyte stands is often underestimated compared to open water sections with the same number of samples. To reach a high sampling coverage, a higher number of samples is necessary for sampling within invasive macrophytes. Our findings call for the development of a method that allows for comparable sampling within and outside of macrophyte stands. Such method will be the foundation for future research and management of aquatic systems.