There is a growing pressure of human activities on natural habitats, which leads to biodiversity losses. To mitigate the impact of human activities, environmental policies are developed and ...implemented, but their effects are commonly not well understood because of the lack of tools to predict the effects of conservation policies on habitat quality and/or diversity. We present a straightforward model for the simultaneous assessment of terrestrial and aquatic habitat quality in river basins as a function of land use and anthropogenic threats to habitat that could be applied under different management scenarios to help understand the trade-offs of conservation actions. We modify the InVEST model for the assessment of terrestrial habitat quality and extend it to freshwater habitats. We assess the reliability of the model in a severely impaired basin by comparing modeled results to observed terrestrial and aquatic biodiversity data. Estimated habitat quality is significantly correlated with observed terrestrial vascular plant richness (R2=0.76) and diversity of aquatic macroinvertebrates (R2=0.34), as well as with ecosystem functions such as in-stream phosphorus retention (R2=0.45). After that, we analyze different scenarios to assess the suitability of the model to inform changes in habitat quality under different conservation strategies. We believe that the developed model can be useful to assess potential levels of biodiversity, and to support conservation planning given its capacity to forecast the effects of management actions in river basins.
•We present a model for the simultaneous assessment of land & aquatic habitat quality.•We assess the reliability of the model as a proxy for biodiversity in river basins.•We demonstrate the suitability of the model for scenario analysis in river basins.•We recommend the model to assess biodiversity changes of conservation planning actions.
•EU Rivers’ capacity to dilute wastewater treatment plants discharges is assessed•Climate change will lead to a dilution factor decrease for 11% of the EU rivers•42% of the rivers will downgrade ...their ecological status due to climate change•More vulnerable sites are located in the Mediterranean countries
Impacts from urban wastewater treatment plants (WWTP) to receiving riverine surface water bodies (SWBs) depend on the load of contaminants discharged, as well as on their dilution capacity. Yet, climate change impacts on such dilution capacity and ultimately on the SWBs ecological status remain unclear. Here, we assess SWBs dilution capacity across the European continent to identify most vulnerable areas using information from centralized European databases. SWBs´ future dilution factor values are estimated based on representative concentration pathway scenarios impacts on rivers flow, and likely changes in European SWBs´ ecological status foretold. Results show that dilution factor in Europe increases by 5.4% in average. Yet, climate change effects are found to lead to a consistent dilution factor decrease for 11% of the 40074 European SWBs receiving WWTP discharge for the early century. This share reaches 17% for the midcentury period. We estimate that up to 42% of the SWBs receiving WWTP discharges and currently reaching a good ecological status show a 0.7 probability to have their ecological status downgraded due to climate change. Sites more vulnerable are located in the Mediterranean countries. Our findings highlight that climate change mitigation is essential for maintaining good ecological status in European SWBs.
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An increasing amount of carbon-based nanomaterials (CNM) (mostly fullerenes, carbon nanotubes and graphene) has been observed in aquatic systems over the last years. However, the potential toxicity ...of these CNM on aquatic ecosystems remains unclear. This paper reviews the existing literature on the toxic effects of CNM in aquatic organisms as well as the toxic effects of CNM through influencing the toxicity of other micro-pollutants, and outlines a series of research needs to reduce the uncertainty associated with CNMs toxic effects. The results show that environmental concentrations of CNM do not pose a threat on aquatic organisms on their own. The observed concentrations of CNM in aquatic environments are in the order of ngL−1 or even lower, much below than the lowest observed effect concentrations (LOEC) on different aquatic organisms (in the order of mgL−1). Toxic effects have been mainly observed in short-term experiments at high concentrations, and toxicity principally depends on the type of organisms, exposition time and CNM preparation methods. Moreover, we observed that CNM interact (establishing synergistic and/or antagonistic effects) with other micro-pollutants. Apparently, the resulting interaction is highly dependent on the chemical properties of each micro-pollutant, CNM acting either as carriers or as sorbents, thereby modifying the original toxicity of the contaminants. Results stress the need of studying the interactive effects of CNM with other micro-pollutants at environmental relevant concentrations, as well as their effects on biological communities in the long-term.
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•We review existing literature on the toxic effects of CNM in aquatic organisms.•CNM are not toxic for aquatic organisms at environmentally relevant concentrations.•Toxic effects of CNM are only observed at high concentrations.•Ecotoxicity depends on the type of organisms, exposition time and CNM preparation methods.•CNM modify the toxicity of other micro-pollutants.
It is well established that a global sanitation crisis threatens humans. By comparison, much less attention has been given to address the effects of this crisis on the health of ecosystems. We ...provide examples of how sewage can affect natural ecosystems and where hotspots in sewage contamination commonly overlap with these habitats. We highlight these issues for some of the major ecosystems spanning across terrestrial, aquatic, and coastal realms. Recent studies reveal that untreated and poorly treated sewage elevates concentrations of nutrients, pathogens, endocrine disruptors, heavy metals, and pharmaceuticals in natural ecosystems. We show many large areas (10,000's of km2) across the globe with high levels of sewage contamination and that these contamination hotspots overlap extensively in occurrence with coral reefs, salt marshes, and fish-rich river systems. Given the global extent of sewage pollution in and near natural habitats, conservation biologists and managers must address this threat. However, because of its size, conservationists cannot solve this problem alone. We therefore argue that conservation must combine forces with the human health sector to create cross-disciplinary synergisms in innovation and efficiency. New sewage management solutions are emerging, such as waste-free toilets and resource recovery to generate fuel and drinking water; but more innovation is needed - a demand that will most effectively be reached through cross-sector collaboration.
•Sewage pollution hotspots are common and occur globally.•Studies warn sewage pollution threatens biodiversity and ecosystem health.•A mapping exercise highlights global hotspots in sewage pollution commonly occur in terrestrial, aquatic, and marine systems.•Mitigating sewage pollution must be prioritized by both the conservation and public health sectors.
Summary
1. Mediterranean climate regions are characterised by long summer droughts that usually involve flow intermittency in low‐ to mid‐order streams. Flow intermittency implies flow cessation, ...drying and subsequent rewetting of the streambed, and affects both autotrophic and heterotrophic processes. The balance between these processes, as well as the balance in the use of carbon (C), nitrogen (N) and phosphorus (P) may change because of the ongoing increase in stream flow intermittency caused by global change in many regions. It is therefore crucial to understand better the consequences of this phenomenon.
2. Our two initial hypotheses were (i) that flow intermittency would impact more on autotrophic than on heterotrophic processes in stream biofilms owing to the higher water dependence of autotrophs, as well as differences in the water storage capacity of the stream biofilm compartments where autotrophic and heterotrophic processes mainly occur (surface cobbles versus hyporheic sediments) and (ii) that the C‐N‐P use by biofilms would change during the dry period (terrestrial phase) owing to the extreme water stress conditions. These hypotheses were tested by analysing the functional response of the main stream biofilms (epilithic, epipsammic and hyporheic) during flow cessation, desiccation and rewetting in a Mediterranean forested stream. The autotrophic response was characterised through changes in the photon yield, whereas the heterotrophic response was characterised by changes in the extracellular enzyme activities.
3. Streambed desiccation had clear effects on the functioning of stream biofilms. Autotrophic biomass decreased by 80% with streambed desiccation, but recovered rapidly after flow resumption. Heterotrophs were more resistant to water stress, especially in the epipsammic and hyporheic biofilms where bacterial cell density decreased only by 20%.
4. Extracellular enzyme activities remained relatively high, and the balance in the C‐N‐P use by biofilms changed during the dry period. The C and P breakdown capacities were maintained during dry conditions, especially in the epipsammic and hyporheic biofilms, but the degradation of N compounds sharply decreased. Elemental molar ratios (C:N and C:P) of the different biofilms also changed with streambed desiccation. C:P ratios increased from 80 to 300, while the C:N ratios increased from 10 to 16.
5. Given the contrasting responses of autotrophic and heterotrophic processes in the different biofilms, our results suggest that the current increase in flow intermittency extent is likely to increase the relative importance of heterotrophic processes in stream ecosystems, as well as the relative contribution of the hyporheic biofilm to C‐N‐P use. Our results further suggest that the longer streams remain dry, the more the biofilm stoichiometry will change.
Freshwater ecosystems are exposed to multiple stressors, but their individual and combined effects remain largely unexplored. Here, we investigated the response of stream biofilm bacterial ...communities to warming, hydrological stress and pesticide exposure. We used 24 artificial streams onto which epilithic (growing on coarse sediments) and epipsammic (growing on fine sediments) stream biofilms were maintained. Bacterial community composition and estimated function of biofilms exposed during 30 days to individual and combined stressors were assessed using 16S rRNA gene metabarcoding. Among the individual effects by stressors, hydrological stress (i.e. a simulated low-flow situation) was the most relevant, as it significantly altered 57% of the most abundant bacterial taxa (n = 28), followed by warming (21%) and pesticide exposure (11%). Regarding the combined effects, 16% of all stressor combinations resulted in significant interactions on bacterial community composition and estimated function. Antagonistic responses prevailed (57-89% of all significant interactions), followed by synergisms (11-43%), on specific bacterial taxa, indicating that multiple-stressor scenarios could lead to unexpected shifts in the community composition and associated functions of riverine bacterial communities.
Freshwater ecosystems such as rivers are of crucial importance for human well-being. However, human activities result in many stressors (e.g. toxic chemicals, increased water temperatures, and hydrological alterations) co-occurring in rivers and streams worldwide. Among the many organisms inhabiting rivers and streams, bacteria are ecologically crucial; they are placed at the base of virtually all food webs and they recycle the organic matter needed for bigger organisms. Most of these bacteria are in close contact with river substratum, where they form the biofilms. There is an urgent need to evaluate the effects of these stressors on river biofilms, so we can anticipate future environmental problems. In this study, we experimentally exposed river biofilms to a pesticide mixture, an increase in water temperature and a simulated low-flow condition, in order to evaluate the individual and joint effects of these stressors on the bacterial community composition and estimated function.
Human appropriation of water resources may induce water stress in freshwater ecosystems when ecosystem needs are not met. Intensive abstraction and regulation cause river ecosystems to shift towards ...non-natural flow regimes, which might have implications for their water quality, biological structure and functioning. We performed a meta-analysis of published studies to assess the potential effects of water stress on nutrients, microcontaminants, biological communities (bacteria, algae, invertebrates and fish), and ecosystem functions (organic matter breakdown, gross primary production and respiration). Despite the different nature of the flow regime changes, our meta-analysis showed significant effects of human-driven water stress, such as significant increases in algal biomass and metabolism and reduced invertebrate richness, abundance and density and organic matter decomposition. Water stress also significantly decreased phosphate concentration and increased the concentration of pharmaceutical compounds. The magnitude of significant effects was dependent on climate, rainfall regime, period of the year, river size and type of water stress. Among the different causes of water stress, flow regulation by dams produced the strongest effects, followed by water abstraction and channelization.
A multitude of pharmaceuticals enter surface waters via discharges of wastewater treatment plants (WWTPs), and many raise environmental and health concerns. Chemical fate models predict their ...concentrations using estimates of mass loading, dilution and in-stream attenuation. However, current comprehension of the attenuation rates remains a limiting factor for predictive models. We assessed in-stream attenuation of 75 pharmaceuticals in 4 river segments, aiming to characterize in-stream attenuation variability among different pharmaceutical compounds, as well as among river segments differing in environmental conditions. Our study revealed that in-stream attenuation was highly variable among pharmaceuticals and river segments and that none of the considered pharmaceutical physicochemical and molecular properties proved to be relevant in determining the mean attenuation rates. Instead, the octanol–water partition coefficient (Kow) influenced the variability of rates among river segments, likely due to its effect on sorption to sediments and suspended particles, and therefore influencing the balance between the different attenuation mechanisms (biotransformation, photolysis, sorption, and volatilization). The magnitude of the measured attenuation rates urges scientists to consider them as important as dilution when aiming to predict concentrations in freshwater ecosystems.
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•In-stream attenuation was highly variable among pharmaceuticals and river segments.•Kow influenced attenuation through effect on sorption to sediments.•Likely coupling between pharmaceuticals and phosphorus attenuation.•In-stream attenuation as important as dilution to explain concentrations.
Rivers are heterogeneous at various scales. River metabolism estimators based on oxygen time series provide average estimates of net oxygen production at the scale of a river reach. These estimators ...are derived for homogeneous river reaches. For this reason, they cannot be used to analyze how exactly they average over longitudinal variations in net production, reaeration, oxygen saturation concentration and flow velocity. We try to fill this gap by using a general analytical solution of the transport‐reaction equation to (1) demonstrate how downstream oxygen concentration is affected by upstream concentration and (possible) longitudinally varying values of net production, reaeration, oxygen saturation concentration and flow velocity within a reach, and (2) derive how the net production estimate depends on varying upstream river parameters. In addition, we derive a new net production estimator that extends previously suggested estimators. The equations derived in this paper provide a general framework for understanding the assumptions underlying net production estimators. They are used to derive recommendations on the use of single station or two stations measurement layouts to get accurate river metabolism estimates. The estimator is implemented in the freely available statistics and graphics software package R (www.r‐project.org). This makes it easily applicable to observed oxygen time series. Empirical evidence of the significance of heterogeneity in rivers is demonstrated by applying the estimator to four subsequent reaches of a river using oxygen measurements from the ends of all reaches.
Freshwater ecosystems are confronted with multiple chemical, biological and physical stressors. Co-occurring stressors commonly result in additive responses, but non-additive interactions may also ...occur, hindering our predicting capacity. Despite growing interest in multiple stressor research, the response of freshwater communities to co-occurring chemical and climate change-related physical stressors remains largely unexplored. Here, we used a microcosm approach to evaluate the effect of the combined action of chemical and physical stressors on river biofilms. Results showed that additive responses dominated, whereas 14.5% of all responses were non-additive (75% antagonisms and 25% synergisms). Among these non-additive interactions, physical stressors dominated over chemicals and drove the overall responses. Overall, the occurrence of these non-additive interactions, together with the dominance of the climate-change related physical stressors, might lead to unexpected responses as a result of climate change.
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•River ecosystems are often affected by a combination of chemical and physical stressors.•A full factorial design revealed the short-term effects of four stressors on river biofilms.•Responses to stressors combination were 85.5% additive and 14.5% non-additive.•Non-additive responses were classified as antagonisms (75%) and synergisms (25%).
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