1 INTRODUCTION The mineralisation of dissolved organic matter (DOM) by microbes is an important biogeochemical process in running waters, which strongly influences nutrient and carbon cycling at the landscape scale (Battin et al., 2008; Marx et al., 2017). Microbial DOM processing in streams and rivers controls the rates of fluvial carbon retention and carbon dioxide (CO2) outgassing, and alters the

CONFLICT OF INTEREST The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CONFLICT OF INTEREST The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CONFLICT OF INTEREST The authors declare no conflict of interest.

CONFLICT OF INTEREST No conflict of interest.

1 INTRODUCTION Gross primary production (GPP) by benthic microalgae growing on soft sediments (here benthic microalgae) may dominate whole-ecosystem GPP (Ask et al., 2009; Vadeboncoeur et al., 2001) and energy supply for higher trophic levels (Karlsson & Byström, 2005). As benthic microalgae have access to nutrients in the sediment (Bonilla et al., 2005; Daniels et al., 2015) they are regarded as primarily

1 INTRODUCTION In the era of rapid climate change, heatwaves, referred to as short-term extreme hot weather lasting from hours to days, could disproportionally shape species performance and distribution (Jentsch et al., 2007; Sandblom et al., 2016). Globally, freshwater ecosystems are among the most thermally threatened (Closs et al., 2016; Yousefi et al., 2020). Regionally, the intensity of heatwaves

1 INTRODUCTION Riverine floodplains are commonly considered among the most species-rich and productive ecosystems (Amoros & Bornette, 2002; Naiman et al., 1993; Tockner & Stanford, 2002; Ward et al., 1999). The complex interaction between topography, sediment transport and flow variations control the biodiversity in inter-connected and dynamic habitats of large river floodplains. Since the second half

1 INTRODUCTION Average global temperature has exponentially increased since the industrial revolution from 0.8 to 1.2°C, causing significant changes in the frequency, intensity, and predictability of weather events now and in the future (IPCC, 2018). For instance, premature spring snow melts, increased forest fires, and increases in aridity have been documented across the globe (Seager et al., 2007;

1 INTRODUCTION Biodiversity is currently decreasing at alarming rates, comparable to the rates reported for past mass extinctions (Barnosky et al., 2011; Ceballos et al., 2017). There is ample evidence that biodiversity loss can alter ecosystem functioning (Boyero et al., 2021; Hooper et al., 2012), but most experimental studies have simulated random species loss (Wardle, 2016). This often represents

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CONFLICT OF INTEREST The authors declare no conflict of interest.

CONFLICT OF INTEREST The authors declare no conflicts of interest.

1 INTRODUCTION Biological invasions continue to alter and, in some cases, detrimentally impact ecosystem function worldwide, resulting in a plethora of environmental, economic and social problems (Haubrock et al., 2021; Simberloff et al., 2013). Rates of biological invasion continue to increase, with intensifying trade and transport networks driving introductions from disparate biogeographical regions

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1 INTRODUCTION Parasites are the most commonly occurring type of consumers (Lafferty et al., 2006; Dobson et al., 2008), and as such have also been coined missing links in aquatic and terrestrial food-webs (Lafferty et al., 2008; Sommer et al., 2012). Even though parasites can represent substantial biomass in natural ecosystems and affect a wide range of ecosystem processes (Hatcher et al., 2012; Kuris

CONFLICT OF INTEREST The authors declare no financial or other conflict of interests.

1 INTRODUCTION Food webs in forested mountain streams usually rely on allochthonous inputs of nutrients (Vannote et al., 1980); however, these inputs are frequently seasonal. For example, in snow-pack fed streams, leaf litter and spawning salmon contributions peak in the autumn, wet atmospheric deposition peaks in winter, and soil runoff is highest during the spring melt. Determining the role of in

1 INTRODUCTION Global environmental changes, driven by changing climate, recovery from acidification, and changes in land-cover and land-use activities, have resulted in the depletion of essential nutrients such as nitrogen (N) and phosphorus (P) (Canham et al., 2012; Eimers et al., 2009; Huser et al., 2018; Isles et al., 2018) and the enrichment of terrestrial coloured dissolved organic carbon (DOC;

1 INTRODUCTION Climate change is increasing mean temperatures and the frequency of thermal extremes and heatwaves (Easterling et al., 2000; Meehl & Tebaldi, 2004). Therefore, the frequency and severity of summer heatwaves is also increasing in aquatic habitats (Frölicher et al., 2018; Woolway et al., 2021). Because species or populations have specific temperature preferences, increasing temperature

1 INTRODUCTION Biodiversity of freshwater ecosystems is declining at a far greater rate than terrestrial or marine biodiversity (Reid et al., 2019). This is in part due to biodiversity being concentrated in fresh waters, which harbour 10% of global animal biodiversity despite occupying only 2% of the Earth’s surface (Reid et al., 2019). Declines stem from anthropogenic pressure on freshwater ecosystems

1 INTRODUCTION Zooplankton such as copepods occupy an intermediate trophic position in the aquatic food web of most lake ecosystems (Lampert & Sommer, 2007). They inhabit lakes with a broad range of physicochemical and optical properties and are thus exposed to a variety of environmental threats and stressors that require specific responses. To survive and succeed under highly variable conditions,

1 INTRODUCTION Streams are open windows for carbon dioxide (CO2) emissions to the atmosphere due to the commonly observed 5–15 times greater CO2 supersaturation in the water than in air (Cole et al., 2007; Rebsdorf et al., 1991). Extensive research has shown the significance of stream emissions in stream networks and in regional and global carbon budgets (Lauerwald et al., 2015; Sand-Jensen & Staehr

1 INTRODUCTION Globally, freshwater biodiversity is at risk from anthropogenic forces (e.g., climate change, water pollution, flow modification, habitat degradation; Dudgeon et al., 2006; Reid et al., 2019), with non-indigenous species being a leading cause of these declines (Dudgeon et al., 2006; Parker et al., 1999; Reid et al., 2019). Parasites are integral ecosystem members and, like hosts, can

1 INTRODUCTION The productive potential of secondary consumers in freshwater ecosystems ultimately is dependent upon the availability of resources at the base of the food web and the efficiency with which they are mobilised to higher trophic levels. In-lake primary production often is considered the main driver of secondary productivity, but there is evidence that terrestrial organic matter also may

1 INTRODUCTION Several factors, from host genetic background and sex to environmental conditions, contribute to host susceptibility to parasite infections (Carius et al., 2001; Debes et al., 2017; Nunn et al., 2009; Wilson et al., 2002). Many of these effects are at least partly mediated by differences in host immune function, which is the primary physiological defence against parasites (reviewed in

1 INTRODUCTION River regulation threatens a wide range of river-dependent biota, including riparian plants (Poff et al., 1997). This is because riverine biota are adapted to natural flow regimes (Bunn & Arthington, 2002) and regulation alters flow, resource, and disturbance regimes (Nilsson & Svedmark, 2002) resulting in changes to physical, chemical, and biological processes (Poff & Zimmerman, 2010)

1 INTRODUCTION Biodiversity is facing the strongest crisis since the last mass extinction, with extinction rates estimated to be 100 times higher than background rates (Ceballos et al., 2015). The current biodiversity crisis is caused by multiple processes such as habitat modifications, climate change, overexploitation, spread of diseases, anthropogenic nitrogen deposition, and introduction of invasive

1 INTRODUCTION It is well known that coping with increasing aridity is a physiological challenge for all organisms (Chown et al., 2011). Aridity influences biodiversity at multiple levels, shaping species distributions at fine and large geographical scales (Craine et al., 2013; Rajpurohit et al., 2013; Watling & Braga, 2015), driving lineages diversification (Catullo & Keogh, 2014; Dorn et al., 2014;

1 INTRODUCTION While efforts to control eutrophication have been successful in several lakes (Jenny et al., 2020; Jochimsen et al., 2013; Sas, 1989), eutrophication remains a leading global water quality issue (Downing, 2014; Jenny et al., 2020; UNEP-IETC/ILEC, 2001). Wang et al. (2017) estimated that 63% of the 2,000 lakes they studied globally are presently eutrophic. Large lakes are particularly

1 INTRODUCTION Ecological processes in shallow aquatic ecosystems can be strongly impacted by wind (Janatian et al., 2020; Stockwell et al., 2020). Wind can directly affect the base of the aquatic food web: the primary producers including macrophytes, benthic algae and phytoplankton. For example, macrophyte establishment may be inhibited directly because of stem breakage, uprooting, or limitations

1 INTRODUCTION Organisms commonly encounter environments that negatively impact their fitness, and many environmental stressors recur on a seasonal basis. Representative examples are temperate eutrophic lakes and ponds that experience seasonal algal blooms dominated by toxic cyanobacteria (O'Neil et al., 2012; Paerl & Huisman, 2008). Zooplankton that feed on phytoplankton, such as the non-selective

1 INTRODUCTION Headwater streams are tightly coupled to adjacent riparian zones via the input of organic matter from land to water (Fisher & Likens, 1973; Tank et al., 2010). Leaf litter is an important fraction of this input, and its decomposition fuels a range of stream biogeochemical processes (Tank et al., 2010,2018; Webster et al., 2009) as well as headwater food webs (Wallace et al., 1997). Decomposition

1 INTRODUCTION Modification of natural flow dynamics in rivers can transform riverine food webs, changing the basal resources and trophic pathways driving consumer production (Kopf et al., 2019; Rees et al., 2020). There is a need to better understand how flow regimes transform food-web structure, but hindering that understanding is the challenge of resolving consumer–resource linkages. Characterising

1 INTRODUCTION Understanding the main drivers of species distribution patterns and the mechanisms of coexistence is the central goal of ecology. Competition for resources and other ecological interactions often lead to the divergence of clades into multiple niches and the appearance of novel traits (Gilbert et al., 2018; Rüber et al., 1999). Over the course of evolution, some taxonomic groups accumulate