Comprehensive annual studies on the seasonal dynamics of heterotrophic protists in ice-covered hypereutrophic systems are scarce, despite their vital roles in aquatic microbial food webs. We examined the community composition and abundance of larger-bodied (>15 mu m) heterotrophic protists over 13 consecutive months in a northern temperate hypereutrophic lake that experiences four months of ice cover. The abundance of larger-bodied heterotrophic protists exhibited considerable seasonal variation, with an 852-fold annual fluctuation (from 100 to 85 200 individuals per liter), significantly surpassing the typical 10-50-fold variations observed in less extreme systems. Community functional composition underwent complete restructuring between the ice-covered and open-water periods: sessile Vorticella dominated under ice (17.7 times more abundant), while planktonic Strobilidium was 171 times more abundant during the open-water season. Testate amoebae (Difflugia) were absent under ice. Correlation analyses identified 17 significant associations between taxa and environmental parameters, with the strongest being Tintinnopsis sp.1 and redox potential (rho = 0.898). These findings highlight that ice cover prompts a fundamental restructuring of larger-bodied protist communities, with different functional groups prevailing under contrasting seasons. Climate-driven reductions in ice cover duration may alter the structure of protist communities in northern temperate lakes, potentially triggering cascading effects on microbial food webs.

Inland fisheries provide essential ecosystem services, yet they face growing threats from anthropogenic activities and climate change. To sustainably manage these fisheries under global change, understanding the main drivers of freshwater fish populations is key. Since the late 1980s, the Qu & eacute;bec government has conducted standardized gillnet surveys to monitor game fish species and their habitats. Here, we identified the main drivers influencing the abundance of walleye, brook trout, and lake trout. Through random forest models, we analyzed 662 lakes and 38 predictor variables, revealing that fish community composition shaped the abundance of the two salmonid species. The best model performance was for brook trout (R2 = 0.54), followed by lake trout (R2 = 0.46), and walleye (R2 = 0.44). Brook trout populations were larger in allopatric lakes, while lake trout abundances were smaller in association with large piscivores. On the other hand, climate was more important for walleye. The dominant explanatory variables varied across species, suggesting different ecological niches. Our findings deepen understanding of fish population drivers in Qu & eacute;bec lakes, highlighting the need for management plans to consider fish community context.

Processes underlying metacommunity structuring are important for understanding species tracking of environmental change at a landscape scale. Species' functional traits more closely reflect their ecological roles than taxonomy, therefore, adopting a functional approach allows us a better understanding of metacommunity structuring. Yet, uncertainties remain because prior studies have rarely considered how opposing species responses to environmental gradients may obscure signals of metacommunity structuring related with the environment. Joint species distribution models can help to overcome this challenge by evaluating responses to environmental gradients in a species-by-species approach while considering the role of both functional traits and phylogeny in shaping those responses. We applied joint species distribution models to three crustacean zooplankton metacommunities differing in landscape features from boreal Qu & eacute;bec (Canada) lakes. We integrated abiotic and non-zooplankton biotic environmental gradients, spatial structuring, functional traits (body size and feeding guild) and phylogeny. We found that abiotic conditions were the main driver of zooplankton metacommunity structure within each of the three study regions. In one region (C & ocirc;te-Nord), functional traits were most strongly linked to species responses to pH and conductivity, and not nutrient availability as expected. This region, a landscape showing less dispersal limitation, allowed species to be more efficiently sorted into environmentally appropriate patches than more dispersal limited regions. The integration of functional traits, as well as the species-by-species approach, provided an improved understanding of how environmental gradients and landscape features shape community composition. This is important considering the rapid pace of environmental change resulting from human activities, especially in mountainous and northern regions.

Anthropogenic environmental changes impact freshwater biodiversity globally. While biodiversity assessments in freshwater environments have traditionally focused on individual groups of organisms or trophic levels, considering patterns of 'multitrophic biodiversity' across the food web provides a more comprehensive view of anthropogenic impacts and changes in communities along environmental gradients. Here we evaluate spatial biodiversity patterns in multitrophic communities of lake plankton (bacterioplankton-phytoplankton-zooplankton) across a lake-rich country: Canada. Capitalising on the first standardized survey at the country scale, we used random forest and structural equation models to identify natural and anthropogenic drivers of multitrophic alpha and beta diversity in 559 lakes from 11 ecozones. Our analyses revealed that multitrophic alpha diversity (assemblage richness) was positively related to water quality but negatively related to water clarity, while beta diversity (assemblage uniqueness) was negatively related to both water quality and water clarity. Agricultural land use in lake watersheds strongly affected water quality and clarity, thus indirectly shaping multitrophic alpha and beta diversity. Bacterio-, phyto- and zooplankton diversity were not well correlated and responded to distinct drivers, confirming the utility of multitrophic indices to provide an integrative view of diversity patterns. Finally, our analyses showed that facets of alpha and beta multitrophic diversity have contrasting responses to the indirect effect of a key human disturbance, watershed land use, thereby illustrating the value of considering multiple diversity facets in biodiversity assessments.

Light intensity directly affects phytoplankton and can alter the toxicity of phytotoxic pollutants present in natural water bodies. Light fluctuation in aquatic ecosystems often occurs as a function of water turbidity, water movement, cloud cover, and seasonality. Atrazine and simazine are commonly used herbicides that inhibit photosynthesis, posing significant risks to aquatic primary producers, and may be found simultaneously in aquatic ecosystems. The interactions between light and herbicide mixtures on phytoplankton growth and physiological state are poorly understood. Therefore, we addressed the toxicity of the herbicides, atrazine and simazine (individually and mixed), on the growth and photosynthetic activity of three freshwater phytoplankton under three light intensities. We found that the toxic effects of single and mixed herbicides are species-specific and significantly modulated by light intensity, with synergistic effects observed for herbicide mixtures under high light conditions. Atrazine and simazine (individually and mixed) toxicities on photosynthesis were greater for the three species grown under low light than under very low light. However, high-light adapted strains of M. aeruginosa were less sensitive to single and mixed herbicides than those adapted to low- and very low-light conditions. Under low- and high-light conditions, the photoprotective ability was extremely sensitive to the inhibitory effects of atrazine and simazine, individually and when mixed. Understanding these interactions is important because microalgae form the base of aquatic food webs and their impairment can have cascading effects on ecosystems. These findings underscore the importance of considering multiple environmental stressors in assessing the ecological risks of herbicides, highlighting potential impacts on aquatic primary productivity.

Increased human development since the Industrial Era has intensified toxic cyanobacterial blooms, which pose significant risks to public health and can cause detrimental effects on lake ecosystems. Mesotrophic lakes are particularly sensitive to nutrient shifts, making them critical systems for understanding bloom dynamics. Sedimentary DNA from paleolimnological archives provides valuable insights into community structure by situating contemporary data within the context of historical dynamics. We analyzed sediment cores from six mesotrophic lakes in Quebec and Ontario (Canada) that span a modern human land-use gradient. Cores were analyzed using sedimentary DNA techniques targeting specific cyanobacteria marker genes, including quantitative (q)PCR and 16S rRNA gene sequencing. Cladoceran assemblages from the same cores provided complementary food web data. We detected widespread increases in cyanobacteria abundance across all lakes, with a higher magnitude of increase in lakes located in high intensity land-use catchments. Bloom-forming orders (Nostocales, Chroococcales, Oscillatoriales) increased in relative abundance in some lakes, often replacing unicellular Synechococcales, which tended to dominate less-impacted systems. These cyanobacterial shifts often coincided with compositional changes in cladoceran assemblages, favoring small-bodied and ecologically flexible taxa such as Bosmina and Chydorus brevilabris. Overall, the analyses of paleogenetic records demonstrate that climate change, land-use intensity, and lake-specific traits have driven century-scale cyanobacterial increases and food-web shifts in mesotrophic lakes, with impacts on both bloom dynamics and cladoceran communities. Such long-term analyses are essential for revealing how interacting human and climatic pressures reshape aquatic ecosystems and guiding more effective management.

Climate change is reshaping freshwater ecosystems worldwide, yet the extent to which its effects differ across trophic levels remains poorly understood. Despite growing evidence of community restructuring, few studies have jointly examined how multiple trophic levels respond to climate forcing within a functional and network-based framework. Herein, we assessed how fish and zooplankton communities respond to contemporary and projected end-of-century climate conditions using different shared socioeconomic pathways (SSP1-2.6, SSP3-7.0, and SSP5-8.5). By means of joint species distribution models and ecological network analyses, we examined fish-zooplankton co-responses to environmental gradients, quantified trait-environment relationships, and evaluated potential species interactions. We found that fish and zooplankton displayed distinct community and functional responses to current and projected climate gradients. Although both trophic levels were primarily influenced by climatic variables, fish exhibited stronger trait-climate relationships, including declining body size and increasing thermal tolerance with warming. Through ecological network analyses, we then demonstrated that freshwater communities tended to become more homogenized by 2100 under future climate change. Together, these results suggest contrasting climate sensitivities across trophic levels, potentially leading to trophic decoupling and functional reorganization of freshwater food webs at the regional scale. Our study highlights the value of combining trait-based and network approaches to better anticipate community-level responses to climate change.

Lakes are understudied during ice-covered periods; yet physical, hydrodynamical and biological processes continue under the ice. Ice cover reorganizes lake ecosystems by altering thermal stratification and solar radiation, creating conditions that support different organisms, food webs, and potential trophic cascades. We investigated seasonal shifts in biomass and vertical distribution of heterotrophic and autotrophic micro-organisms (heterotrophic bacteria, picoautotrophs, colorless and pigmented nanoflagellates) and zooplankton across winter in relation to limnological characteristics and hydrodynamics. Boreal Lake Simoncouche was sampled at five depths on six dates between autumn overturn (November 2020) and spring overturn (April 2021) for temperature, dissolved oxygen, chlorophyll-a, and plankton. Low chlorophyll-a and high heterotroph-to-autotroph biomass ratios indicated dominance of the heterotrophic energy pathway under ice. Heterotrophic micro-organisms also dominated during well-lit overturns, emphasizing the role of the microbial loop in all seasons. Zooplankton richness remained high under ice (18-22 taxa), with most species favoring deeper, warmer layers. Several species of rotifer and cladoceran sustained egg production through winter, ceasing only briefly in February. These findings highlight strong vertical and seasonal heterogeneity in winter-active plankton communities, shaped by stratification, light, and resources, and support the view that winter is biologically dynamic, with consequences for the subsequent open-water season.

Plankton, a diverse group of aquatic organisms, make Earth livable, regulate aquatic life, and provide benefits to human societies such as access to clean water, food security, and well-being. They also support economies and inspire biotechnological innovations. This article aims to raise awareness of the value of plankton to humanity and serves as an informative guide for aquatic professionals, policymakers, and anyone interested in plankton. We present the value of plankton across six themes of human interest: biogeochemistry; ecology; climate; the evolution of science; economy; and culture, recreation, and well-being. Guided by the 2022 Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services values assessment, we introduce the six themes under the Life Framework of Values to offer a comprehensive summary of the significance of plankton to humanity. In addition, we provide examples of plankton variables used in policy frameworks and recommendations for enhancing understanding of their value through long-term sustainable research and monitoring.

A vertical separation in light and nutrient availability is observed in many terrestrial and aquatic ecosystems. In lakes and oceans, the opposing vertical gradients of light and nutrients typically observed are believed to promote phagomixotrophy, a generalist strategy that combines resource acquisition through photoautotrophic and phagoheterotrophic pathways. While phagomixotrophy is widespread, it is not well understood how this strategy performs against pure specialist strategies in a resource competition context. We simulate the dynamics of three competitors (pure photoautotroph, phagomixotroph, pure phagoheterotroph) and bacterial prey over the vertical dimension of a water column to investigate what conditions of resource availability favor mixotrophy and how the presence of the phagomixotroph alters community dynamics. Since mixotrophs can be more or less photoautotrophic, we incorporated this variability into our model. Under weak vertical mixing, mixotrophs persist under most light and nutrient conditions and negatively affect specialists. Mixotrophs can even be dominant competitors when they display an optimal degree of phototrophy, which is positively related to water transparency and negatively related to nutrient supply. The model indicates that the spatial organization of nanophytoplankton communities in water columns could arise through vertical niche partitioning of multiple resource acquisition strategies and that phagomixotrophy can promote overall community production. Une s & eacute;paration verticale de la disponibilit & eacute; de la lumi & egrave;re et des nutriments peut & ecirc;tre observ & eacute;e dans de nombreux & eacute;cosyst & egrave;mes terrestres et aquatiques. Dans les lacs et les oc & eacute;ans, on observe des gradients verticaux oppos & eacute;s de lumi & egrave;re et de nutriments qui sont consid & eacute;r & eacute;s comme des facteurs favorisant la phago-mixotrophie, une strat & eacute;gie de nutrition g & eacute;n & eacute;raliste qui combine la photo-autotrophie et la phago-h & eacute;t & eacute;rotrophie pour l'acquisition des ressources. Bien que la phago-mixotrophie soit r & eacute;pandue, les performances de cette strat & eacute;gie dans le cadre de la comp & eacute;tition pour les ressources contre des strat & eacute;gies sp & eacute;cialis & eacute;es sont mal comprises. Nous avons simul & eacute; la dynamique de trois comp & eacute;titeurs (photo-autotrophe pur, phago-mixotrophe, phago-h & eacute;t & eacute;rotrophe pur) et de bact & eacute;ries sur la dimension verticale d'une colonne d'eau pour & eacute;tudier quelles conditions de disponibilit & eacute; des ressources favorisent la mixotrophie et comment la pr & eacute;sence d'un phago-mixotrophe modifie la dynamique de la communaut & eacute;. Les mixotrophes pouvant & ecirc;tre plus ou moins photo-autotrophes, nous avons int & eacute;gr & eacute; cette variabilit & eacute; fonctionnelle dans notre mod & egrave;le. Quand la colonne d'eau est peu m & eacute;lang & eacute;e, les mixotrophes subsistent dans la plupart des conditions de lumi & egrave;re et de nutriments et affectent n & eacute;gativement les sp & eacute;cialistes. Les mixotrophes peuvent m & ecirc;me dominer la communaut & eacute; lorsque leur degr & eacute; de phototrophie, qui est positivement li & eacute; & agrave; la transparence de l'eau et n & eacute;gativement & agrave; l'apport de nutriments, est optimal. Le mod & egrave;le montre que l'organisation spatiale des communaut & eacute;s nanophytoplanctoniques dans les colonnes d'eau pourrait r & eacute;sulter de la partition verticale des niches de comp & eacute;titeurs pr & eacute;sentant des strat & eacute;gies d'acquisition de ressources contrast & eacute;es, et que la phago-mixotrophie peut favoriser la production globale de la communaut & eacute;.

The browning of freshwater ecosystems is increasingly evident in temperate and northern regions, with widespread ramifications for lake physics, chemistry, and biology. Contrasting results on how freshwater browning may impact fish have been reported, but there has been no comprehensive examination of how browning may cause cascading effects on individual- to population- to community-level traits of freshwater fishes. We addressed this knowledge gap by summarizing the existing literature and conducting a series of original analyses to: (i) explore the effects of a brown water gradient on populations of eight economically important species of fish across 871 lakes; and (ii) examine how a brown water gradient may influence community trait compositions across 303 lakes. From our literature synthesis, we found that fish growth is often negatively associated with browner waters, despite browning generally showing no effect on fish foraging. We also demonstrated that browner waters had greater abundances of northern pike (Esox lucius) and walleye (Sander vitreus), but lower numbers of lake trout (Salvelinus namaycush), yellow perch (Perca flavescens), largemouth bass (Micropterus salmoides), smallmouth bass (M. dolomieu), and lake whitefish (Coregonus clupeaformis). Moreover, we showed that fish communities were significantly more likely to contain species with larger eyes in browner lakes. Lastly, we examined relationships between various metrics of browning (i.e. dissolved organic carbon, Secchi transparency, water colour) and present a framework for how the effects of freshwater browning on fish may scale from individuals to populations to communities.

Environmental stress caused by anthropogenic impacts is increasing worldwide. Understanding the ecological and evolutionary consequences for biodiversity will be crucial for our ability to respond effectively. Historical exposure to environmental stress is expected to select for resistant species, shifting community composition toward more stress-tolerant taxa. Concurrent with this species sorting process, genotypes within resistant taxa that have the highest relative fitness under severe stress are expected to increase in frequency, leading to evolutionary adaptation. However, empirical demonstrations of these dual ecological and evolutionary processes in natural communities are rare. Here, we provide evidence for simultaneous species sorting and evolutionary adaptation across multiple species within a natural freshwater bacterial community. Using a two-phase stressor experimental design (acidification pre-exposure followed by severe acidification) in aquatic mesocosms, we show that pre-exposed communities were more resistant than naive communities to taxonomic loss when faced with severe acid stress. However, after sustained severe acidification, taxonomic richness of both pre-exposed and naive communities eventually converged. All communities experiencing severe acidification became dominated by an acidophilic bacterium, Acidiphilium rubrum, but this species retained greater genetic diversity and followed distinct evolutionary trajectories in pre-exposed relative to naive communities. These patterns were shared across other acidophilic species, providing repeated evidence for the impact of pre-exposure on evolutionary outcomes despite the convergence of community profiles. Our results underscore the need to consider both ecological and evolutionary processes to accurately predict the responses of natural communities to environmental change.

While previous studies have investigated environmental and biotic variables influencing plankton community composition, comprehensive analyses across multiple trophic levels and broad spatial scales remain limited. Using a Joint Species Distribution Modelling framework, we identified key abiotic and biotic variables, including body size and fish presence that shape variation in plankton food webs across Canadian lakes. We analyzed the joint responses of plankton biomass to lake morphometry, water physico-chemistry, and fish species presence, using data collected from 301 lakes spanning the four main national continental catchments. We also examined how the body size trait modulated plankton food web associations with these variables. Results showed that lake nutrient and ion status were the most important factors explaining variation in plankton community composition, particularly in the Arctic and Hudson continental basins, which exhibited large environmental gradients. Lake morphometry also played an important role, especially in shaping communities in large, shallow lakes. Plankton body sizes modulated some niche responses, but these effects varied across continental basins and plankton trophic levels. Little residual variation in the models indicated limited roles of plankton species interactions or unmeasured environmental variables. While fish presence only explained small amounts of variation, further studies should instead assess and incorporate fish biomass data. Our findings suggest that future national strategies for the study of Canadian freshwaters should combine a continental-scale perspective (e.g., gradients across ecozones, climate regions, biogeographic zones) with regionally focused monitoring programs to better capture critical factors influencing different lake ecosystems.

Models are needed to predict changes in game fish abundances with respect to climatic factors undergoing change, but such models are often limited by data availability and the capacity of statistical methods to fit challenging ecological datasets. We use current methods in machine learning to describe the responses of 10 fish species to climatic factors across Québec. We assembled a new province-wide, synthetic dataset of fish catches spanning almost 50 years and 6000 sites. Extreme Gradient Boosting (XGBoost) models revealed that climatic factors are more important predictors of trends in game fish catches than nuisance factors (sampling gear, time), lending support to collating other heterogeneous datasets for analyses. Mean annual temperature and precipitation were the most important drivers of species catches. Fish thermal preference guilds predicted primarily species responses to temperature, suggesting that warmer and wetter climates may not favour the same species. Despite the challenging nature of these datasets, XGBoost models provided excellent fit, predictive capacity, and interpretability, thereby illustrating that large, heterogeneous datasets can be used to inform freshwater fisheries management in a changing climate.

Ecological networks offer a comprehensive view of communities by capturing potential species interactions. While valuable for studying ecological change in the Anthropocene, many studies lack data across expansive temporal and spatial gradients. We addressed this gap by applying network approaches to paleolimnological records capturing strong land-use changes. We analyzed cladoceran assemblages, key aquatic organisms with identifiable subfossils, using two paleolimnological methods: (i) top-bottom comparisons of sediment records from 101 Canadian lakes with varying land-use intensity, and (ii) high-resolution core records from two impacted lakes in eastern Canada. We used correlation matrices of taxon relative abundances to calculate network metrics across land-use types and time periods. We found that lake communities currently experiencing high human impact changed through time, showing a decrease in connectance (proportion of realized to potential links) and an increase in modularity (measure of network subcommunities); these patterns were also observed in our full core analyses as well as in our randomized simulation exercise. Overall, this first pan-Canadian study of zooplankton paleo-networks provides new insights into how lake food webs have changed over a period of accelerated anthropogenic change.

ABSTRACTThe biodiversity of freshwater ecosystems globally is facing severe threats due to various anthropogenic stressors, such as habitat degradation, introduction of invasive species, and pollution. Assessing the effects of human‐induced environmental stressors on population and community persistence requires accurate biodiversity estimates. While environmental DNA (eDNA) metabarcoding has emerged as a promising tool, its effectiveness in capturing rapid biodiversity responses to acute stressors across levels of biological organization (community, population, and intra‐specific levels) remains to be investigated. In this study, we tested the efficacy of eDNA metabarcoding in assessing rapid changes in aquatic zooplankton and insect communities by conducting a two‐month mesocosm experiment with pulses of glyphosate‐based herbicide under contrasting nutrient levels (mesotrophic and eutrophic). We examined the effects of treatments on community assemblages, family richness, and intraspecific diversity, and compared our findings with those obtained through a microscopy approach. Metabarcoding revealed partially congruent ecological findings with microscopy, indicating its potential in assessing rapid community changes. The herbicide induced shifts in community composition and differentially impacted zooplankton and insect family richness (increase in insects, and decrease in crustaceans and rotifers), suggesting a gradient of tolerance to the herbicide among taxa and potential top‐down regulation by insect larvae that may counteract the advantage gained by herbicide‐tolerant zooplankton. Finally, we showed that nutrient enrichment exacerbated the negative effects of the herbicide on intraspecific diversity, highlighting concerns about genetic erosion. Our findings underscore the complexity of responses to herbicide and nutrient enrichment in freshwater ecosystems. We conclude that eDNA metabarcoding can not only be used to estimate rapid changes in invertebrate communities but also provides additional value by offering a broader perspective on diversity dynamics and potential cascading effects at different scales of biological organization.

Cell size is a critical regulator of many metabolic processes in protists. We explored whether body size and abundances vary consistently in phytoplankton capable of both autotrophy and heterotrophy (mixoplankton) by manipulating environmental stoichiometric conditions in a mesocosm experiment. We applied two allochthonous subsidy treatments: high C: nutrient ratios (leaves) should favour bacterivory through phagotrophy, while low ratios (insects) should favour autotrophy. We identified three focal mixoplankton taxa, common in our study system and that represented facultative (Cryptomonas sp. and Plagioselmis sp) and more obligate phagotrophs (Ochromonas sp.). Ochromonas was largest in the leaf treatment, which were also associated with larger sizes in Cryptomonas (but not the other cryptophyte). The obligately mixotrophic Ochromonas responded more significantly to conditions favouring phagotrophy than did the facultative phagotrophic cryptophytes. All mixoplankton taxa densities declined with insect subsidies that favour autotrophy. Future research should examine a wider range of mixoplankton under varying ecological conditions.

Recreational inland fisheries play a vital role in the economy and culture of Canada. However, human activities and climate change are significant threats to lakes that sustain such fisheries, bolstering the need to maintain ecosystem quality while sustaining fisheries through approaches such as ecosystem-based management. Despite the importance of zooplankton communities for fish diet, very few freshwater management plans have integrated information from this lower trophic level. Here, we used a dataset including game fish abundance, crustacean zooplankton community composition and associated habitat variables in 94 north temperate lakes across the province of Quebec, Canada. Our study aimed to uncover whether zooplankton taxonomic and functional community properties were related to walleye, brook trout, and lake trout occurrence and abundance. Our analyses revealed that both taxonomic and functional zooplankton composition were significant predictors of focal fish species occurrence, albeit less so than environmental or fish community composition variables. When examining the importance of 30 different zooplankton community indices for target fish species abundance, structural equation modeling revealed that zooplankton was more important for walleye than for the two other fish species. Overall, this research improves our understanding of zooplankton-fish interactions and how these shape north temperate lake communities, with a perspective of improving fisheries conservation and management.

Human activities such as agriculture and urban development are linked to water quality degradation. Canada represents a large and heterogeneous landscape of freshwater lakes, where variations in climate, geography and geology interact with land cover alteration to influence water quality differently across regions. In this study, we investigated the influence of water quality and land use on bacterial communities across 12 ecozones. At the pan-Canadian scale, total phosphorus (TP) was the most significant water quality variable influencing community structure, and the most pronounced shift was observed at 110 μg/L of TP, corresponding to the transition from eutrophic to hypereutrophic conditions. At the regional scale, water quality significantly explained bacterial community structure in all ecozones. In terms of land use effect, at the pan-Canadian scale, agriculture and, to a lesser extent, urbanisation were significant land use variables influencing community structure. Regionally, in ecozones characterised by extensive agriculture, this land cover variable was consistently significant in explaining community structure. Likewise, in extensively urbanised ecozones, urbanisation was consistently significant in explaining community structure. Overall, these results demonstrate that bacterial richness and community structure are influenced by water quality and shaped by agriculture and urban development in different ways.