Pollutants in urban runoff: Scientific evidence on toxicity and impacts on freshwater ecosystems.

Urban runoff effluents transport multiple pollutants collected from urban surfaces. which ultimately reach freshwater ecosystems. We here collect the existing scientific evidence on the urban runoff impacts on aquatic organisms and ecosystem functions, assessed the potential toxicity of the most common pollutants present in urban runoff, and characterized the ecotoxicological risk for freshwaters.

Differential response of multiple stream ecosystem processes to basin- and reach-scale drivers.

Stream ecosystems are inherently dependent on their surroundings and, thus, highly vulnerable to anthropogenic impacts, which alter both their structure and functioning. Anchored in biologically-mediated processes, the response of stream ecosystem functioning to environmental conditions exhibits intricate patterns, reflecting both natural dynamics and human-induced changes. Our study aimed at determining the natural and anthropogenic drivers influencing multiple stream ecosystems processes (nutrient uptake, biomass accrual, decomposition, and ecosystem metabolism) at a regional scale.

Unravelling large-scale patterns and drivers of biodiversity in dry rivers.

More than half of the world's rivers dry up periodically, but our understanding of the biological communities in dry riverbeds remains limited. Specifically, the roles of dispersal, environmental filtering and biotic interactions in driving biodiversity in dry rivers are poorly understood. Here, we conduct a large-scale coordinated survey of patterns and drivers of biodiversity in dry riverbeds.

Using biological traits to assess diet selection: the case of the Pyrenean Desman.

Traditionally, researchers have assessed diet selection by comparing consumed versus available taxa. However, taxonomic assignment is probably irrelevant for predators, who likely base their selection on characteristics including prey size, habitat, or behavior. Here, we use an aquatic insectivore, the threatened Pyrenean Desman (), as a model species to assess whether biological traits help unravel the criteria driving food and habitat preferences.

Treated and highly diluted, but wastewater still impacts diversity and energy fluxes of freshwater food webs.

Wastewater treatment plants (WWTPs) have greatly improved water quality globally. However, treated effluents still contain a complex cocktail of pollutants whose environmental effects might go unnoticed, masked by additional stressors in the receiving waters or by spatiotemporal variability. We conducted a BACI (Before-After/Control-Impact) ecosystem manipulation experiment, where we diverted part of the effluent of a large tertiary WWTP into a small, unpolluted stream to assess the effects of a well-treated and highly diluted effluent on riverine diversity and food web dynamics.

Sea lamprey nests promote the diversity of benthic macroinvertebrate assemblages.

The habitat heterogeneity hypothesis states that increased habitat heterogeneity promotes species diversity through increased availability of ecological niches. We aimed at describing the local-scale (i.e.

Water diversion and pollution interactively shape freshwater food webs through bottom-up mechanisms.

Water diversion and pollution are two pervasive stressors in river ecosystems that often co-occur. Individual effects of both stressors on basal resources available to stream communities have been described, with diversion reducing detritus standing stocks and pollution increasing biomass of primary producers. However, interactive effects of both stressors on the structure and trophic basis of food webs remain unknown.

Latitude dictates plant diversity effects on instream decomposition.

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113° of latitude.

Interactive effects of discharge reduction and fine sediments on stream biofilm metabolism.

Discharge reduction, as caused by water diversion for hydropower, and fine sediments deposition, are prevalent stressors that may affect multiple ecosystem functions in streams. Periphytic biofilms play a key role in stream ecosystem functioning and are potentially affected by these stressors and their interaction. We experimentally assessed the interactive effects of discharge and fine sediments on biofilm metabolism in artificial indoor channels using a factorial split-plot design with two explanatory variables: water discharge (20, 39, 62, 141 and 174 cm3 s-1) and fine sediments (no sediment or 1100 mg L-1 of sediments).

Combined effects of urban pollution and hydrological stress on ecosystem functions of Mediterranean streams.

Urban pollution and hydrological stress are common stressors of stream ecosystems, but their combined effects on ecosystem functioning are still unclear. We measured a set of functional processes and accompanying environmental variables in locations upstream and downstream of urban sewage inputs in 13 streams covering a wide range of water pollution levels and hydrological variability. Sewage inputs seriously impaired stream chemical characteristics and led to complex effects on ecosystem functioning.

Framing biophysical and societal implications of multiple stressor effects on river networks.

Urbanization, agriculture, and the manipulation of the hydrological cycle are the main drivers of multiple stressors affecting river ecosystems across the world. Physical, chemical, and biological stressors follow characteristic patterns of occurrence, intensity, and frequency, linked to human pressure and socio-economic settings. The societal perception of stressor effects changes when moving from broad geographic regions to narrower basin or waterbody scales, as political and ecologically based perspectives change across scales.

Impact of wastewater effluent pollution on stream functioning: A whole-ecosystem manipulation experiment.

The ecological effects of wastewater treatment plant (WWTP) effluents on stream ecosystems cause growing concern. However, it is difficult to assess these effects as most streams receiving WWTP effluents are also affected by other stressors. We performed a whole-ecosystem manipulation experiment following a BACI design (Before-After/Control-Impact) in order to exclude the influence of other potentially confounding factors.

Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter.

Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale.

Immediate and legacy effects of urban pollution on river ecosystem functioning: A mesocosm experiment.

Effluents from urban wastewater treatment plants (WWTP) consist of complex mixtures of substances that can affect processes in the receiving ecosystems. Some of these substances (toxic contaminants) stress biological activity at all concentrations, while others (e.g.

Determining diet from faeces: Selection of metabarcoding primers for the insectivore Pyrenean desman (Galemys pyrenaicus).

Molecular techniques allow non-invasive dietary studies from faeces, providing an invaluable tool to unveil ecological requirements of endangered or elusive species. They contribute to progress on important issues such as genomics, population genetics, dietary studies or reproductive analyses, essential knowledge for conservation biology. Nevertheless, these techniques require general methods to be tailored to the specific research objectives, as well as to substrate- and species-specific constraints.

Priming of leaf litter decomposition by algae seems of minor importance in natural streams during autumn.

Allochthonous detritus of terrestrial origin is one of the main energy sources in forested headwater streams, but its poor nutritional quality makes it difficult to use by heterotrophs. It has been suggested that algae growing on this detritus can enhance its nutritional quality and promote decomposition. So far, most evidence of this "priming effect" is derived from laboratory or mesocosm experiments, and its importance under natural conditions is unclear.

Multiple stressor effects on biodiversity and ecosystem functioning in a Mediterranean temporary river.

The hydrological and biological complexity of temporary rivers as well as their importance in providing goods and services is increasingly recognized, as much as it is the vulnerability of the biotic communities in view of climate change and increased anthropogenic pressures. However, the effects of flow intermittency (resulting from both seasonal variations and rising hydrological pressure) and pollution on biodiversity and ecosystem functioning have been overlooked in these ecosystems. We explore the way multiple stressors affect biodiversity and ecosystem functioning, as well as the biodiversity-ecosystem functioning (B-EF) relationship in a Mediterranean temporary river.

Testing wastewater treatment plant effluent effects on microbial and detritivore performance: A combined field and laboratory experiment.

The amount of pollutants and nutrients entering rivers via point sources is increasing along with human population and activity. Although wastewater treatment plants (WWTPs) greatly reduce pollutant loads into the environment, excess nutrient loading is a problem in many streams. Using a Community and Ecosystem Function (CEF) approach, we quantified the effects of WWTP effluent on the performance of microbes and detritivores associated to organic matter decomposition, a key ecosystem process.

Effects of human-driven water stress on river ecosystems: a meta-analysis.

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).

River ecosystem processes: A synthesis of approaches, criteria of use and sensitivity to environmental stressors.

River ecosystems are subject to multiple stressors that affect their structure and functioning. Ecosystem structure refers to characteristics such as channel form, water quality or the composition of biological communities, whereas ecosystem functioning refers to processes such as metabolism, organic matter decomposition or secondary production. Structure and functioning respond in contrasting and complementary ways to environmental stressors.

River doctors: Learning from medicine to improve ecosystem management.

Effective ecosystem management requires a robust methodology to analyse, remedy and avoid ecosystem damage. Here we propose that the overall conceptual framework and approaches developed over millennia in medical science and practice to diagnose, cure and prevent disease can provide an excellent template. Key principles to adopt include combining well-established assessment methods with new analytical techniques and restricting both diagnosis and treatment to qualified personnel at various levels of specialization, in addition to striving for a better mechanistic understanding of ecosystem structure and functioning, as well as identifying the proximate and ultimate causes of ecosystem impairment.

Habitat Complexity in Aquatic Microcosms Affects Processes Driven by Detritivores.

Habitat complexity can influence predation rates (e.g. by providing refuge) but other ecosystem processes and species interactions might also be modulated by the properties of habitat structure.

Drought and detritivores determine leaf litter decomposition in calcareous streams of the Ebro catchment (Spain).

Drought, an important environmental factor affecting the functioning of stream ecosystems, is likely to become more prevalent in the Mediterranean region as a consequence of climate change and enhanced water demand. Drought can have profound impacts on leaf litter decomposition, a key ecosystem process in headwater streams, but there is still limited information on its effects at the regional scale. We measured leaf litter decomposition across a gradient of aridity in the Ebro River basin.

Differences in the sensitivity of fungi and bacteria to season and invertebrates affect leaf litter decomposition in a Mediterranean stream.

Microorganisms are key drivers of leaf litter decomposition; however, the mechanisms underlying the dynamics of different microbial groups are poorly understood. We investigated the effects of seasonal variation and invertebrates on fungal and bacterial dynamics, and on leaf litter decomposition. We followed the decomposition of Populus nigra litter in a Mediterranean stream through an annual cycle, using fine and coarse mesh bags.