Hydrobiologia

Inland waters in the Northern Hemisphere are experiencing increased annual runoff due to higher overall precipitation as well as intensified short-term events such as heavy rainfall, floods and storms. These events affect the total loading and variability of inputs of allochthonous, coloured dissolved organic matter (cDOM) and inorganic nutrients into lakes. Previous studies have shown that increased total cDOM and inorganic nutrient loads affect phytoplankton biomass and metabolic rates, but it is unknown how the effects of different cDOM and nutrient pulse scenarios are modified by spatial and seasonal differences in lake characteristics. Here, we conducted a coordinated, standardized mesocosm experiment across three lakes with different ambient cDOM and nutrient concentrations. In two of these lakes, the experiment was implemented in two seasons. The same total amounts of cDOM, nitrate and phosphate were added to all mesocosms, but in pulses that differed in intensity and frequency. We found that pulse intensity and frequency affected chlorophyll a and phycocyanin concentrations and metabolic rates, i.e. gross primary production and respiration, differently. Specifically, more pronounced effects were found in response to the extreme pulse scenario compared to those with more frequent, smaller pulse additions. Furthermore, the effects were mainly temporary and varied more among lakes than between seasons. The clearest differences between the extreme and more gradual runoff scenarios were found in the lake with the lowest background cDOM and nitrate concentrations, likely because lower light limitation and possibly stronger initial N-limitation caused a faster response to the nutrient addition. Our results highlight that both antecedent lake conditions and characteristics of runoff events can affect phytoplankton biomass and metabolic rates and that comparative experimental approaches are needed to reveal the complexity of the responses.

Freshwater salinization is of increasing concern for integrity and functioning of freshwater habitats worldwide. Experiments so far often have studied drastic salt additions, while gradient designs have been performed less commonly. We tested the effect of freshwater salinization in a mesocosm exposing the plankton community of the oligotrophic Lake Lunz, Austria, to a four-fold salinization gradient (control, 0.2, 1, a 5 ppt salt). Salinity was manipulated in a factorial design with enrichment, with 10 g L-1 and 30 g L-1 phosphorus, resulting in 8 treatments with 3 replicates each. We followed the effects of salinization on diversity, community composition and resource use over 36 days. Community composition was assessed by amplicon sequencing, Diversity loss and community turnover followed upon salt addition. All levels of salinization caused pronounced changes in community composition, with 5 ppt causing the most drastic changes. Salinization caused trophic downgrading by kicking out especially protistan consumers and rotifers, while some green algae and chrysophytes were especially tolerant, resulting in reduced phylogenetic and functional diversity with increasing salinization. In line with reduced top down control, salinization affected temporal variability in chlorophyll-a (chl-a) and resource use (RUE), with higher salinity causing more extreme fluctuations in chl-a and RUE. Enrichment overall aggravated salinization, enhancing temporal turnover and temporal fluctuations in resource use.

Quagga mussels (Dreissena rostriformis bugensis) are ecosystem engineers that can alter nutrient cycling, benthic-pelagic coupling, and food-web structure in deep lakes. Although their invasion trajectories are well documented in the Laurentian Great Lakes in North America, depth-specific population dynamics remain poorly resolved in recently invaded European perialpine lakes. We analyzed five annual lake-wide surveys (2021-2025) from 54 stations spanning 2.4-253 m depth in Lake Constance to quantify changes in quagga mussel density, biomass, and shell-length distribution. Contrary to expectations of lake-wide exponential growth, shallow-water populations (< 20 m) showed no significant increase during the study period and appear to have reached carrying capacity before monitoring began. In contrast, densities increased monotonically at intermediate depths (40-125 m), indicating ongoing expansion into deeper strata. Mean shell length declined with depth, and size distributions in shallow waters shifted toward larger individuals, consistent with a transition from active recruitment to somatic growth of established mussels. Compared with the Laurentian Great Lakes, Lake Constance already has substantially higher shallow-water biomass, whereas deeper invasion trajectories are broadly similar. These results show that quagga mussel invasion in deep European lakes can combine rapid littoral saturation with slower profundal expansion, complicating direct transfer of predictions from the Great Lakes. Continued depth-stratified monitoring will be essential for anticipating future ecosystem effects in perialpine lakes.

Nutrient availability, ecosystem productivity, and consumer assemblages are intricately linked through complex interactions and feedbacks. Nutrients influence the diversity and functional roles of consumers via shifts in resource quality and quantity, and consumers can alter ecosystem production and nutrient availability. However, our understanding of how characteristics of consumers respond to and influence concomitant shifts in nutrient availability and production is limited. We quantified the response of well-studied consumer assemblages (benthic invertebrates and zooplankton) to realistic nutrient loads that altered gross primary production (GPP) and ecosystem respiration (ER). We fertilized 14 outdoor experimental ponds for 2 months and monitored total water column carbon (TC), nitrogen (TN), and phosphorus (TP), GPP, ER, and net ecosystem production (NEP) weekly. Then, we evaluated how fertilization and the variation in nutrients and metabolism caused by fertilization were related to shifts in consumer assemblages. Fertilization increased water column TN and TP and reduced TC:TP ratios, TN:TP ratios, and rates of GPP and ER. However, consumer assemblages were more tightly linked to variation in nutrient availability and production across ponds than to fertilization. Greater declines in benthic diversity occurred in ponds with higher average TN:TP ratios during the experiment. Consistent with predicted effects of cladocerans on nutrient availability, shifts in cladoceran abundances were positively associated with average water column TN:TP ratios during the experiment. Finally, elevated GPP and ER were associated with greater increases in the abundance of benthic invertebrate predators, suggesting the possibility of top-down control. Our study highlights the critical role of consumer-mediated processes in the interaction between nutrient availability and production. Manuscript HighlightsO_LIFertilization reduced pond gross primary production and ecosystem respiration rates. C_LIO_LIInvertebrate predator abundance was inversely related to gross primary production. C_LIO_LIShifts in consumer assemblages were tightly linked to nutrients and production. C_LI

Downstream migration and sea entry are periods of high mortality for sea trout smolts and migration timing is a critical aspect of survival. We aimed to investigate migration timing of PIT-tagged sea trout smolts across a latitudinal gradient in five freshwater systems across Europe: Norway, Sweden, Denmark, France and Portugal. In two systems, smolt migration was further examined to assess a) differences in sex, body size and condition between autumn and spring migrants; b) the influence of spatial origin within the stream; and c) relationships between individual body size and migration date. Tagged smolts were not detected migrating in the Portuguese watershed. Spring migration timing differed significantly between watersheds in Norway, Sweden, Denmark and France. Generally, there was a trend of earlier migration at lower latitudes. Autumn vs spring migration was examined in Gudso-Denmark. Autumn migrants were larger in both length and mass, with no differences in sex ratios or body condition. Fish originating from an upstream site were more likely to migrate in the autumn compared to the spring and vice versa. Size dependent migration was found in the Swedish system, Haga [a]-Sweden, with larger individuals migrating earlier in the spring than smaller individuals. Outward-migrating smolts were also more likely to originate from a downstream site than an upstream site. Overall, these results show both large-scale geographic and fine-scale individual influences on migration timing. Given that climate change may have large impacts on migration patterns in sea trout, understanding variability in migratory patterns across a latitudinal gradient is an important tool for predicting responses to environmental changes.

Coastal wetlands of the Laurentian Great Lakes support abundant populations of fish, invertebrates, and vegetation, though the trophic linkages connecting primary production and lower consumers is not well understood in these systems. We implemented a multiple-tracer approach to evaluate trophic pathways, pairing traditional food web isotope tracers like carbon ({delta}13C) and nitrogen ({delta}15N) with total mercury concentrations (THg). We predicted that filamentous algae would be the dominant energy resource in the diet of lower trophic-level invertebrates in the Grand River Estuary, a network of riverine coastal wetlands adjacent to Lake Michigan. In addition, we predicted that adding THg as a tracer would improve the resolution of our food web models by clarifying trophic levels and relationships between wetland species. Four basal energy sources were sampled, including filamentous algae, emergent macrophytes, submersed macrophytes, and phytoplankton, along with organic detritus. Aquatic invertebrates were sampled across multiple functional guilds to represent primary and secondary consumers and included amphipods and odonates. Our findings suggest that organic detritus is the dominant resource responsible for energetically supporting these lower trophic levels in the Grand River estuary, although submersed macrophytes were important alternative energy sources for secondary consumers. THg concentrations enhanced the resolution of dietary contribution estimates in MixSIAR models applied to consumer and source data. Isotope biplots revealed that THg concentrations were a more reliable predictor of trophic position than {delta}15N in Grand River Estuary (GRE) sites. This methodology has important implications for future food web studies in complex ecosystems such as coastal wetlands and demonstrates the novel use of mercury as an ecological tracer in a Bayesian mixing model approach.

The prevalence of nitrogen limitation and nitrogen-phosphorus co-limitation (henceforth referred to as nitrogen-related limitation) in Norwegian lakes and their relationships with atmospheric nitrogen deposition, climate, dissolved organic matter (DOM), and catchment characteristics were assessed across space and time. Routine monitoring data from 1,529 lakes in the national Vannmiljo database were analyzed for two multi-year periods (1995-2009 and 2010-2025). Limitation was inferred using the molar NO--N/TP ratio as an indicator of dissolved inorganic nitrogen availability. Nitrogen-related limitation was widespread in both periods and exhibited strong regional structure, with highest prevalence in northern regions and lowest prevalence in southwestern Norway. Overall prevalence increased from 31% to 38% between periods, with significant increases in western regions. Regional-scale models identified climate, forest cover, DOM, agriculture, and atmospheric nitrogen deposition as predictors of limitation probability, whereas study period per se and bog/peatland cover were not significant. At the local scale, atmospheric nitrogen deposition and DOM were the only consistent predictors, with substantially lower explanatory power than at the regional scale. These results indicate that large-scale environmental gradients play a major role in shaping nutrient stoichiometry in Norwegian lakes. Because the monitoring dataset primarily represents lakes affected by human activities, the findings are particularly relevant for water management. The widespread occurrence of nitrogen-related limitation suggests that nitrogen availability may influence phytoplankton growth in many systems and that dual-nutrient management strategies addressing both nitrogen and phosphorus may be required in many regions.

Fall-run Atlantic Sturgeon occupy riverine habitat for extensive periods of up to several months during periods of spawning. It is generally not feasible to eliminate potential anthropogenic stressors during the entire time Atlantic Sturgeon are on spawning habitat. If data were available to accurately predict when eggs and larvae are in the water column, potential impacts could be minimized for this relatively short timeframe, compared to the entire season of freshwater residency by adults. This research used acoustic telemetry data for adult female sturgeon, along with water temperature and discharge, to predict when females were likely releasing eggs versus merely staging in spawning habitat waiting to spawn. The descriptive and Bayesian model results predict that egg release is associated with water temperatures ranging from 20-26{degrees}C and pulses in river discharge, often confining egg release to a few days or weeks. By using weather data that predict relatively short periods of when egg release occurs versus longer periods that includes staging, resource managers can more feasibly collaborate with water usage groups to ameliorate egg/larvae survival.

The Zvitan (Zavitan) Stream is one of the major basaltic drainage systems of the Levant Region in Israel. The present short communication focuses specifically on the sector adjacent to Katzrin, integrating geomorphological, hydrological, ecological, and amphibian distribution data within the broader watershed context. The stream originates in the central Golan plateau and flows westward into the Yehudiya Reserve before joining the Meshushim Stream and ultimately draining into Lake Kinneret. In the Katzrin sector, the stream is characterized by deeply incised basalt canyons, winter spring discharge and semi-permanent pools sustained by springs and seepage. Seasonal hydrological fluctuations strongly influence aquatic habitats and amphibian breeding success. Amphibian species documented in the Golan Heights include Salamandra salamandra infraimmaculata, Triturus vittatus (currently Ommatotriton vittatus), Hyla savignyi, Bufotes viridis, Pelophylax bedriagae (formerly Rana ridibunda), and Pelobates syriacus. Their distribution is closely associated with water availability, elevation, temperature, and hydroperiod, as demonstrated in northern Israel habitats. The Katzrin sector of Zvitan represents an intermediate ecological zone where Mediterranean and steppe elements converge, creating heterogeneous amphibian assemblages. This observation, carried out at a specific site in the Zavitan Stream, aimed to examine the ecological conditions and identify which amphibian species inhabit this pool, where environmental conditions may differ from those in the main stream channel.

Capelin (Mallotus villosus), a key forage fish in the Northwest Atlantic, links zooplankton to predators including commercial fishes, seabirds, and marine mammals, yet its life-cycle movements in the Gulf of St. Lawrence (GSL) remain poorly understood. Between 2022 and 2024, otoliths from 927 individuals collected during and after spawning were analysed by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Building on previous work on regional structuring, seven trace elements (Li, B, Mg, K, Zn, Sr, Ba) were used to discriminate three regions. Early-life regional signatures were inferred through an edge-to-core approach, assigning otolith core chemistry to one of these regions using quadratic discriminant analysis. The core was treated as an integrated early-life signal (late-larval to early juvenile period) rather than a strictly natal signature. Spatial variation in core chemistry was consistent across cohorts, mirroring the stability documented on the otolith edge. Results revealed widespread dispersal alongside partial regional residency: individuals with northeastern early-life signatures showed the strongest correspondence between early-life and capture regions, whereas other regions were more connected. Fish sampled during spawning were more often reassigned to their inferred early-life region than post-spawning fish, a regional-scale homing-like pattern consistent with regional spawning fidelity. This coexistence of dispersive and resident strategies likely generates a portfolio effect buffering the population against environmental variability and localised reproductive failures.

Thiamine Deficiency Complex (TDC) is a reproductive disorder that affects recruitment of diverse salmonine populations globally. Typical symptoms include behavioral and neurological abnormalities and high offspring mortality. TDC is common in hatcheries that rear salmonines obtained from wild populations, and symptoms are mitigated by thiamine treatment. However, no studies have quantified thiamine concentrations in wild embryos. Here, we evaluated whether fertilized eggs and/or embryos may acquire thiamine from natural sources (e.g., biotic breakdown products and diet) during development. Lake trout (Salvelinus namaycush) gametes were obtained from feral adults in Lake Champlain and fertilized eggs were grouped by family with paired rearing under natural (Lake Champlain) and artificial (controlled laboratory) conditions. Average thiamine concentrations were similar between lake-reared and laboratory-reared fish prior to hatch; however, lake-reared fish experienced significant increases in thiamine concentrations at and after hatching compared to previous stages and compared to laboratory-reared fish; laboratory-reared fish experienced no increases in thiamine concentrations. Water samples revealed an abundance of thiamine precursors and byproducts in the natural environment, which may serve as sources of thiamine for developing embryos. These results demonstrate that salmonine embryos can acquire thiamine from natural sources during development, which may mitigate effects of TDC.

Philippine freshwater ecosystems are considered one of the most diverse ecosystems harboring numerous fish species. However, in the Philippines, these ecosystems are threatened by invasive species that potentially disrupt ecological balance. In this study, we focused on the vermiculated sailfin catfish Pterygoplichthys disjunctivus, an invasive aquarium species reported in several Philippine aquatic ecosystems. Despite its documented spread, its potential range under a rapidly changing climate remains poorly understood for the country. Hence, in this study, we utilized the MaxEnt model to predict its near-current and future habitat suitability in the Philippines. Using 11 reported occurrences, our model showed high predictive accuracy (AUC = 0.882{+/-} .034, TSS = 0.7394 {+/-} 0.154, SEDI = 0.971 {+/-} 0.019). Across the current and future scenarios, slope was the primary contributor (78.7% - 81.3%), followed by BIO 10 or the mean temperature of the warmest quarter(18% - 27.8%), and flow accumulation (0% - 5.2%). However, for the SSP126 scenario, BIO10 is projected to triple by 2050 (18 - 48%). Current projections identify high-risk regions, particularly central Luzon (Laguna de Bay and Lake Taal), the Cagayan River Valley, and portions of eastern Mindanao (Agusan Marsh and Lake Mainit). Sankey transition analysis confirms a high habitat stability rate (>73%) for high-suitability pixels in both SSPs, indicating persistent invasion risk. Overall, our study provides a framework for invasive species management and contributes to the conservation of Philippine aquatic ecosystems.

Intraspecific morphological variability presents a complex challenge for biological systematics and biomonitoring, particularly for organisms with high phenotypic plasticity, such as zooplankton. Morphological differences between individuals of the water flea species Bosmina longirostris (Crustacea: Cladocera) are difficult to distinguish visually, parthenogenetic females look morphologically uniform within the species; nevertheless, they demonstrate differences attributable to their geographic origin and developmental stage. A reference dataset of microscopic images was created for the study, including populations from two geographically separated regions (seven ones from European Russia and seven ones from Sakhalin Island in the Pacific Ocean (Far East of Russia) and two age groups, demonstrating the ability of a neural network classify to successfully the intraspecific morphological variation. This study demonstrates that deep learning methods are prospective for the detection and understanding of fine morphological intraspecific differences in the cladocerans.

Algae require specific acclimation strategies to cope with spectral variability in shallow marine habitats. We investigated how the siphonous green alga Derbesia alters its photosynthetic and metabolic processes under white (WL), blue (BL), green (GL), red (RL), and far-red light (FL) by conducting photobiological and transcriptomic sampling over a 10-day period. Our results show two contrasting photoacclimation strategies: BL and GL promoted metabolic activity associated with growth, whereas FL and RL induced a low-light-like survival strategy characterized by reduced growth and suppression of the core metabolism. Photosynthetic acclimation across all conditions primarily occurs within the light dependent reactions. BL and GL promoted early acclimation marked by the immediate activation of light-harvesting complexes (LHCs) and a key transcriptional regulator MYB, and showed better acclimation marked by the sustained activation of ATPases, ATP transporters, and hormone-signaling components. BL induced a distinct transcriptional shift during the transition to prolonged exposure, including enhanced cyclic electron transport, and key regulators of protein synthesis, DNA replication, and transcriptional regulation. In contrast, FL, and to a lesser extent RL, triggered responses resembling low light acclimation with constrained growth, characterized by inefficient energy utilization, enlarged antenna systems, chloroplast proliferation with aggregations, and reduced growth rates. This study suggests high accumulation of core photopigments and reduction in chlorophyll a/b is an acclimatory response to FL, and consistently higher activation of core metabolic processes under WL likely indicates the evolutionary adaptation of Derbesia to shallow coastal environments where broad-spectrum light predominates. Additionally, our newly sequenced draft genome of the Derbesia strain for this study could serve as a genomic resource for future molecular photobiology research in Bryopsidales algae.

Seaweed cultivation has recently gained increased attention in North-West Europe as a sustainable source of biomass for biobased products. However, yields need to increase to make the seaweed sector economically viable. To achieve this, higher yielding varieties can be bred but this requires variation for yield and yield-related traits among genotypes. To reliably select high-yielding genotypes, an understanding is required of how both within-farm and between-farm environmental differences affect phenotypes and how to identify simple and reliable proxies for yield. In this study we evaluated growth of nine Saccharina latissima genotypes on two farms, 12 km apart, within the same season. We observed a threefold difference in yield among genotypes, demonstrating the potential for improvement through selection and breeding. Blade thickness and blade size-related traits were strongly correlated with yield, highlighting their potential to serve as rapid and non-destructive proxies for yield, thereby accelerating selection. Furthermore, we demonstrated the importance of adequate replication in farm trials to improve genotype performance estimation by correcting for within-farm spatial variation. Moreover, phenotypic variation was most explained by the genotype and environment, highlighting the importance of both genotype and site selection. Although genotype by environment interactions (GxE) were significant, its contributions were small, indicating stable genotype ranking across farms. Overall, these results are promising for breeding improved S. latissima as it indicates that genotype performance is consistent across close by locations and that local S. latissima populations harbour substantial phenotypic variation that can be used to breed for increased yield. Highlights- Local genetic resources harbour substantial variation in yield and morphology for breeding. - Minor GxE allows for breeding across farms. - Blade thickness and blade size related traits are good predictors of yield. - Correction for on-farm spatial variation improves genotype performance estimation.

The global study of freshwater clams in the genus Corbicula is frequently confounded by invasive androgenetic lineages that experience mitochondrial DNA capture and clonal propagation. In contrast, the endemic Corbicula of Sulawesi's ancient lakes reproduce sexually, offering a uniquely reliable system for mitochondrial population genetics. This study provides the first population-genetic framework for two endemic species, Corbicula possoensis (Lake Poso) and C. linduensis (Lake Lindu), using the cytochrome c oxidase subunit I (COI) marker. We analysed 90 newly generated COI sequences from C. possoensis (six stations) and C. linduensis (three stations), integrated with reference sequences from GenBank, to assess genetic diversity, population structure, and phylogeographic patterns. Hierarchical AMOVA revealed deep divergence between the two lakes ({Phi}_CT = 0.607), consistent with prolonged independent isolation rather than a single shared vicariance event, as the two species do not form a sister pair in the phylogeny. Within Lake Poso, C. possoensis exhibited exceptionally high genetic diversity (24 haplotypes; h = 0.876; {pi} = 0.016) and pronounced micro-geographic structuring into three phylogeographic zones (North: Tentena and Siuri; East: Tando Nceppo and Busogo Beach; Southwest: Bancea and Pendolo), each characterised by distinct haplogroups. Remarkably, the maximum divergence between zones (K2P = 2.33%) approached the interspecific distance between C. possoensis and C. linduensis (K2P = 2.42%), indicating that within-lake mitochondrial divergence has reached near-interspecific levels. Conversely, C. linduensis displayed near-panmixia and extreme genetic depauperation (3 haplotypes; h = 0.246; {pi} = 0.0004), indicating long-term demographic stasis within a restricted habitat. The deep phylogeographic zonation in C. possoensis suggests that its discrete populations should be treated as separate Management Units (MUs) in conservation planning to preserve locally adapted gene complexes, whereas the severely depauperate gene pool of C. linduensis renders it critically vulnerable to environmental disturbance and invasive species, warranting urgent IUCN Red List assessment. To validate these mitochondrial boundaries and inform future conservation strategies, multi-marker and genome-wide reassessments are strongly recommended.

Fistulobalanus albicostatus Pilsbry, 1916 (Thoracica: Balanidae) is a tropical to temperate species distributed in the NW Pacific. The previously known northernmost record of this species in Japan was from Aomori Prefecture, at the northern end of Honshu Island, Japan. However, field surveys conducted in 2023 and 2026 confirmed the occurrence of F. albicostatus in Hakodate Bay, the southern end of Hokkaido, Japan, across the Tsugaru Strait, thereby extending the northern limit of its known distribution. A line transect survey conducted in May 2026 recorded seven living individuals within an area of 128 m. F. albicostatus was rare on the mid-high shores, accounting for only 2% of all barnacle individuals in a quadrat survey. The basal diameter of the living individuals ranged from 0.76 to 1.23 cm, and all individuals possessed ovaries. Based on characteristics of both morphological and COI gene, the specimens were identified as F. albicostatus, and belonged to the same haplotype of populations that are present in Honshu Island. The establishment of F. albicostatus in Hokkaido suggests an ongoing northward range shift of this warm-water species, with the potential for further expansion under continued ocean warming.

Microplastics (MP) are widespread in aquatic ecosystems and pose a threat to freshwater biodiversity. While numerous studies examine physiological effects on aquatic organisms, less is known about how MP alter chemically mediated interactions that regulate predator-prey dynamics. Predator-induced defenses in Daphnia depend on detecting kairomones and represent an important form of adaptive phenotypic plasticity. Whether MP interfere with these responses, and through which mechanisms, remains unclear. Here, we show that polystyrene MP impair predator-induced defenses across Daphnia species by disrupting predator-cue-mediated plasticity at the behavioral, morphological, and molecular levels. In D. longicephala, chronic exposure to PS fragments weakened Notonecta-induced morphological defenses, whereas additive-containing PS fragments nearly suppressed defense formation and reduced body size. Consistent with these phenotypic effects, proteomic analyses revealed alterations in pathways related to molting and chitin metabolism, linking MP exposure to impaired defense formation. In D. magna, PS particles attenuated fish kairomone-induced diel vertical migration, with stronger effects for larger particles, consistent with reduced effective availability or perception of predator cues. Natural limestone particles caused only minor effects, indicating particle-specific rather than general particle-driven responses. Our findings demonstrate that MP can disrupt adaptive predator-prey interactions with potential cascading consequences for freshwater food webs.

Subalpine forests in the Alps are fragile ecosystems that play a crucial role in regional water resources and the local climate. These ecosystems are ecologically significant due to their unique biodiversity and vulnerability to climate change. While several components of the hydrological balance have been studied, the interplay between catchment-scale processes and plot-scale drivers such as fog presence and forest age remains insufficiently understood. To address this, we investigated the hydrological balance of a subalpine coniferous forest catchment at the Renon site in the Italian Alps, integrating observations across spatial scales. The study area includes a mosaic of mature and younger regrowth forest, where both interannual and seasonal variability in precipitation and fog presence are pronounced. At the catchment scale, we quantified above-canopy precipitation, evapotranspiration (ET, measured via eddy covariance at the ICOS tower), stream discharge, and soil moisture dynamics. Within the catchment, we characterised water partitioning using sap flow sensors for tree transpiration, throughfall and stemflow collectors with rain gauges above and below the canopy and epiphyte sampling. Mixed fog-rain events frequently coincided with higher throughfall. However, these changes had a minor effect on soil water storage and catchment discharge in the annual water balance, which was nearly closed. At the plot scale, our results show that tree transpiration was higher in the younger forest structure, while canopy interception is a dominant process in water partitioning in the older forest structure, where lichen abundance likely enhances interception. This study highlights the importance of multi-scale monitoring in temperate mountain forests, where forest age influences water partitioning, and fog presence, though not directly quantified, can still contribute to reducing evaporative processes. Such contributions may gain importance under changing climate conditions, albeit less prominently than in tropical or subtropical cloud forests.

Lake Constance is a pre-Alpine, monomictic, oligotrophic lake situated at the southern end of Germany composed of two main water bodies: deep, oligotrophic Upper Lake Constance (ULC) and the shallow, more mesotrophic Lower Lake Constance (LLC). To date, no sequencing-based study exists of the seasonal succession of the microbial plankton in Lake Constance. Over one-year, microbial plankton communities were sampled biweekly from the top 20 m of the water column in both sites and separated into nanoplankton (NP) and picoplankton (PP). Communities were analysed using rDNA amplicon sequencing: NP samples were analysed by 18S rDNA, and PP samples by 18S and 16S rDNA sequencing. Temporal community diversity was compared between sites and the effect of two major environmental perturbations, winter vertical mixing in ULC and oxygen depletion of the bottom-water layer in LLC, on the community was examined. Despite strong environmental contrasts, microbial plankton communities exhibited conserved seasonal temporal dynamics across basins. In contrast, pronounced compositional shifts occurred during mixing and oxygen depletion events. Approximately 20% of detected taxa were positively associated with these events, with log fold changes reaching 9.82, reflecting rare or undetectable taxa outside these periods. Taxa favoured by these perturbations commonly exhibited high metabolic flexibility, including mixotrophy, fermentation, or anaerobic respiration, or possessed functional traits conferring tolerance to altered redox and mixing regimes. Our results suggest that the temporal dynamics of freshwater microbial plankton communities are driven by deterministic processes and highlight the profound impact of large, and less known, environmental changes on these communities.