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Abandoned mines cause serious environmental damage to their surroundings with considerable impacts on freshwater ecosystems. These impacts occur mainly due to the uncontrolled discharge of polluted effluents, which may contain high concentrations of heavy metals. Currently, no real solution exists for this important environmental problem, leaving a legacy of global pollution. This study aimed to assess the impact of a metal mining effluent from an abandoned mine on freshwater ecosystems, using aquatic biofilms as an ecological indicator. At the same time, the efficiency of different innovative treatment technologies in reducing the ecological impacts caused by mining effluents was evaluated, consisting of nanofiltration and nanofiltration combined with electrocoagulation. To do that, aquatic biofilms obtained from a pristine stream, were exposed, under microcosms conditions, to a metal mining effluent, untreated or treated by the innovative treatment technologies and responses were compared with unexposed biofilm which served as control. The structural and functional responses of the biofilm were measured with throughout time. Biofilms that were exposed to the untreated mining effluent showed significant differences respect to the rest of treatments and the control, particularly exhibiting inhibitory effects on photosynthetic efficiency just after 24 h of exposure and a progressive shift of the photosynthetic community composition throughout the exposure period. The treatment technologies significantly reduced the ecological impact caused by the metal mining effluent. However, metal bioaccumulation in biofilm revealed a potential long-term impact. These observations evidenced the biofilm as a useful ecological indicator to assess the ecological impact caused by metal mining effluents on freshwaters and the efficiency of different treatment technologies to reduce it. This work was supported by the European Commission LIFE program throughout the LIFE DEMINE project (LIFE16 ENV/ES/000218).

Interactions between emerging contaminants and other drivers of community structure and function are poorly known. We used laboratory microcosms to investigate the single and combined effects of grazing and triclosan toxicity on the structure and function of stream periphyton. Grazing alone strongly reduced algal biomass, but also reduced oxidative stress and increased periphyton productivity and phosphorus (P) uptake capacity. This suggests that grazed algal communities can compensate for reduced biomass by enhanced growth after being released from grazing. Triclosan exposure (11.6 ± 1.1 μg L−1) reduced the detoxification capacity and P-uptake capacity of periphyton and altered diatom taxonomic composition. This indicates that triclosan at environmentally relevant concentrations affects the capacity of periphyton to remove dissolved nutrients and to cope with toxicant mixtures commonly occurring in streams. Triclosan exposure and grazing pressure had negative synergistic effects on algal size-class distribution and diatom mortality, since the effects of triclosan were higher than expected when periphyton was subject to grazing. Periphyton exposed to toxic substances such as triclosan had a lower capacity to cope with grazing than unexposed communities, because toxicity can limit algal regrowth after release from grazing and promote the loss of less abundant species. This synergism may have important implications because grazing pressure will magnify the negative effects of toxicants on community structure and ecosystem functions such as primary production and nutrient cycling This study was supported by the European Commission through the project Modelkey (Project 511237-2 GOCE). Additional funds were provided by the European Keybioeffects Project (MRTN-CT-2006-035695), VIECO (009/RN08/011), SCARCE (Consolider-Ingenio 2010, CSD2009- 00065) and Fluvialmultistress (CTM2009-14111-CO2-01) and MPCUdG2016/120

We examined the presence of pesticides in the Llobregat river basin (Barcelona, Spain) and their effects on benthic biological communities (invertebrates and diatoms). The Llobregat river is one of Barcelona’s major drinking water resources. It has been highly polluted by industrial, agricultural, and urban wastewaters, and—as a typical Mediterranean river—is regularly subjected to periodic floods and droughts. Water scarcity periods result in reduced water flow and dilution capacity, increasing the potential environmental risk of pollutants. Seven sites were selected, where we analysed the occurrence of 22 pesticides (belonging to the classes of triazines, organophosphates, phenylureas, anilides, chloroacetanilides, acidic herbicides and thiocarbamates) in the water and sediment, and the benthic community structure. Biofilm samples were taken to measure several metrics related to both the algal and bacterial components of fluvial biofilms. Multivariate analyses revealed a potential relationship between triazine-type herbicides and the distribution of the diatom community, although no evidence of disruption in the invertebrate community distribution was found. Biofilm metrics were used as response variables rather than abundances of individual species to identify possible cause-effect relationships between pesticide pollution and biotic responses. Certain effects of organophosphates and phenylureas in both structural and functional aspects of the biofilm community were suggested, but the sensitivity of each metric to particular stressors must be assessed before we can confidently assign causality. Complemented with laboratory experiments, which are needed to confirm causality, this approach could be successfully incorporated into environmental risk assessments to better summarise biotic integrity and improve the ecological management., This study was supported by the European Commission project MODELKEY (Project 511237-2 GOCE). Additional funds were provided by the European Project Keybioeffects (MRTN-CT-2006-035695), by the Spanish Ministry of Science and Technology (Project GCL2006-12785/HID), and by the programme VIECO (009/RN08/011) of the Ministry of the Environment and Rural and Marine Affairs.

We present an overview of possible links between chemical contamination and the diversity of fluvial communities, in order to assess how conventional and more recently developed methodologies used to estimate the diversity of rivers and streams could be used to explore this relationship. We analyze different trophic levels (bacteria, autotrophic biofilm, benthic macroinvertebrates and fish) and discuss their usefulness in diversity-related studies. We present some practical examples of their application. We strongly recommend that future research should involve a multi-index approach and multidisciplinary studies that integrate chemical and biological analyses to assess effectively the relationship between biological diversity and chemical contamination.

The Water Framework Directive of the European Union requires achievement of good chemical and ecological status in river systems. Risk assessment for toxicants is mostly based on individual single-species tests, though extrapolation of such results to ecosystem evaluation is often afflicted with uncertainties. Advances include higher-tier testing, which comprises use of multi-faceted ecotoxicity tests, and community (multi-species) tests. Including several trophic levels in pollutant testing shows that both direct and indirect effects occur in biological communities. Direct effects are expressed as changes in community composition, growth rates, metabolism and death rate. Indirect effects at other trophic levels (primary producers, consumers, predators) are exerted through trophic links. Biofilm-grazers comprise a simple food chain, where potential and negative effects affecting one of them could be magnified through the food web (bottom-up versus top-down effects), thus reinforcing or decreasing the ability of biofilms to be indicators of the effects of toxicants in aquatic ecosystems.

This chapter summarizes field and laboratory investigations dealing with metals and pesticides (90) and emerging compounds’ (10) effects on fluvial communities. The Arkansas River case study is a good example showing how field observations, together with long-term natural experiments and microcosm experiments, provide consistent evidence of metals effects on macroinvertebrate communities. In the case of biofilms, microcosm and mesocosm experiments confirm that metals and pesticides are responsible for the loss of sensitive species in the community, and that this influence is modulated by several biological and environmental factors. Information about the effects of emerging pollutants is very scarce, highlighting the existence of a missing gap requiring future investigations. The examples provided and the recommendations given are proposed as a general guide for studies aiming to link chemical pollution with ecological alterations.

A wide range of human pharmaceuticals are present at low concentrations in freshwater systems, particularly in sections of polluted river. These compounds show high biological activity, often associated with a high stability. These characteristics imply a potential impact of these substances on aquatic biota even when present at low environmental concentrations. Low flow conditions in Mediterranean rivers, most of which flow through densely populated areas and are subjected to intensive water use, increase the environmental risk of these emergent compounds. Here, we studied whether pharmaceuticals in river water affect the local benthic community structure (diatoms and invertebrates). For this purpose, we analyzed the occurrence of pharmaceuticals along the Llobregat River and examined the benthic community structure (diatoms and invertebrates) of this system. Some pharmaceutical products in the Llobregat River registered concentrations greater than those cited in the literature. Multivariate analyses revealed a potential causal association between the concentrations of some anti-inflammatories and beta-blockers and the abundance and biomass of several benthic invertebrates (Chironomus spp. and Tubifex tubifex). Further interpretation in terms of cause-and-effect relationships is discussed; however, it must be always taken with caution because other pollutants also may have significant contributions. Combined with further community experiments in the laboratory, our approach could be a desirable way to proceed in future risk management decisions.