Review on environmental alterations propagating from aquatic to terrestrial ecosystems

Tightly intertwined: Waterscapes prompt urgent reconsideration of aquatic insects and their role in agricultural landscapes

In landscape ecology, the waterscape refers to permanent or temporary, running or stagnant surface waters within a terrestrial area. Across ecosystem boundaries, aquatic organisms and nutrients can reach terrestrial ecosystems, as formalised by the meta-ecosystem theory. Recent studies on aquatic insects emerging from temperate streams suggest that the extent of their biomass and fluxes across agricultural landscapes may have been neglected until now. Following a conceptual and empirical approach, we presently discuss how the temporal dynamics of floods coupled with the emergence and aerial fluxes of aquatic insects suggests that the waterscape can largely overlap the landscape. Depending on the season, various species and biomasses of aquatic insects could interact with the receiving terrestrial ecosystems and ultimately support vital ecosystem services and functions such as pollination, soil fertilisation, and control of crop pests or facilitation of their natural enemies. In the current context of a global collapse of terrestrial insect populations, we call for an urgent research effort to include the temporal dimension of waterscapes into landscape models to estimate the fluxes of insects emerging from all kinds of aquatic ecosystems and quantify their role in the functioning of terrestrial ecosystems in agricultural landscapes.

Impacts of seasonality on mercury concentrations, polyunsaturated fatty acids, and stable isotopes: implications for the use of tetragnathid spiders as sentinels

Riparian spiders are used in ecotoxicology as sentinels of bioavailable contaminants that are transferred from aquatic to terrestrial habitats via emergent aquatic insects. Spiders in the family Tetragnathidae are particularly of interest because a high proportion of their diet consists of emergent aquatic insects and their contaminant loads reflect the amount transferred through the food web to riparian predators. The transfer of contaminants can be determined through food web tracers such as stable isotopes and polyunsaturated fatty acids; however, it is unclear how contaminants and tracers vary over the course of a year. The objective of this study was to determine whether seasonality affected size, carbon and nitrogen stable isotopes, polyunsaturated fatty acid biomarkers, mercury, and other trace metal concentrations in tetragnathid spiders. Spiders were sampled fortnightly from a single site on the Stones River in Tennessee, USA, for an entire active season (April through October). Spider mass and length steadily increased from April to September to a maximum average value of 0.078 ± 0.03 g, then decreased in October. Seasonal trends were observed for carbon and nitrogen stable isotopes, with significantly decreased signatures occurring late in the active season. Overall, methyl mercury concentrations (range: 12.1-134.4 ng/g) and the methyl-total mercury ratio (range: 49%-98%) increased throughout the active season, with higher variability observed at the end of the active season. Collectively, our results indicate that seasonality affected several important endpoints and that spiders collected during the end of the active season may not be representative of spiders during the entire active season.

Global occurrence and environmental behavior of novel brominated flame retardants in soils: Current knowledge and future perspectives

Since polybrominated diphenyl ethers (PBDEs) are on the list of regulated chemicals, novel brominated flame retardants (NBFRs) have been produced as alternatives and extensively used since the end of the 19th century. A comprehensive assessment of the environmental burden of NBFRs, which are emerging contaminants with bio-toxic and carcinogenic properties, is urgently needed. Given that soil is a major sink for organic pollutants, this study systematically reviewed global data on NBFRs in soil for the period of 1990-2024 via a bibliometric analysis of 70 publications from the Web of Science Core Collection, reaching the following achievements. (1) NBFRs in soils have been reported in 17 countries or regions worldwide, ranging from not detected to 8.46 × 104 ng/g dw, showing an increasing trend over time, with severe contamination in Asia and Australia. (2) NBFR concentrations varied significantly across land use types: manufacturing land > electronic waste disposal areas > urban soil > farmland > forest > remote areas. (3) NBFRs with log KOA > 10 tend to settle from the air into the soil, where they may be absorbed by plant roots and bioaccumulate in the food chain. (4) Organism dietary habits and metabolism, along with the hydrophobicity and molecular weight of NBFRs, contribute to bioaccumulation differences. (5) Successive reductive debromination is the primary degradation pathway for NBFRs, and microorganisms such as the white-rot fungus P. ostreatus show potential for remediating NBFR-contaminated soil. This review clarifies the pollution status of soil NBFRs and provides a solid reference to develop management policies. Future research should focus on studying the transport mechanisms of NBFRs between soil and other media, and assessing the cumulative effects of high trophic level organisms on NBFRs.

Socioeconomic prerequisites determine national long-term biomonitoring efforts

In the current anthropogenic era characterised by human-induced environmental changes, long-term biomonitoring has become a crucial component for understanding ecological patterns and detecting shifts in biodiversity. However, spatiotemporal inconsistencies in biomonitoring efforts hinder transboundary progress in understanding and mitigating global environmental change effectively. The International Long-Term Ecosystem Research (ILTER) network is one of the largest standardised biomonitoring initiatives worldwide, encompassing 44 countries globally, including 26 European countries that are part of the European Long-Term Ecosystem Research network (eLTER). To better understand the establishment and development of such long-term biomonitoring efforts, we analysed spatial and temporal trends within the eLTER network. Additionally, we evaluated the environmental, social, and economic factors influencing engagement in biomonitoring activities within this European network. Our findings reveal a spatial imbalance, with biomonitoring efforts concentrated in Central and Western European countries, where monitoring initiatives have typically been established for a longer duration. Furthermore, our analyses underscore the complex interplay of economic, geographic, and cultural factors in the development of long-term ecological research infrastructures. Countries with greater geographic connectivity, slower economic growth, and higher research activity are more likely to be involved in the eLTER network. The intensity of biomonitoring significantly increased with greater research investments, economic growth, and elevated levels of tourism. In contrast, it decreased in countries that are more inward-facing and exhibit a belief in their ability to control environmental outcomes independently. Addressing spatial gaps in monitoring necessitates enhanced support and funding to ensure comprehensive ecological monitoring over extended time periods. This is essential for achieving transboundary sustainability and effective biodiversity conservation in the face of global change drivers.

A conceptual framework for landscape-based environmental risk assessment (ERA) of pesticides

While pesticide use is subject to strict regulatory oversight worldwide, it remains a main concern for environmental protection, including biodiversity conservation. This is partly due to the current regulatory approach that relies on separate assessments for each single pesticide, crop use, and non-target organism group at local scales. Such assessments tend to overlook the combined effects of overall pesticide usage at larger spatial scales. Integrative landscape-based approaches are emerging, enabling the consideration of agricultural management, the environmental characteristics, and the combined effects of pesticides applied in a same or in different crops within an area. These developments offer the opportunity to deliver informative risk predictions relevant for different decision contexts including their connection to larger spatial scales and to combine environmental risks of pesticides, with those from other environmental stressors. We discuss the needs, challenges, opportunities and available tools for implementing landscape-based approaches for prospective and retrospective pesticide Environmental Risk Assessments (ERA). A set of "building blocks" that emerged from the discussions have been integrated into a conceptual framework. The framework includes elements to facilitate its implementation, in particular: flexibility to address the needs of relevant users and stakeholders; means to address the inherent complexity of environmental systems; connections to make use of and integrate data derived from monitoring programs; and options for validation and approaches to facilitate future use in a regulatory context. The conceptual model can be applied to existing ERA methodologies, facilitating its comparability, and highlighting interoperability drivers at landscape level. The benefits of landscape-based pesticide ERA extend beyond regulation. Linking and validating risk predictions with relevant environmental impacts under a solid science-based approach will support the setting of protection goals and the formulation of sustainable agricultural strategies. Moreover, landscape ERA offers a communication tool on realistic pesticide impacts in a multistressors environment for stakeholders and citizens.

New insights about the toxicity of 2,4-D: Gene expression analysis reveals modulation on several subcellular responses in Chironomus riparius

Herbicides are the main class of pesticides applied in crops and are capable of polluting the surrounding freshwater system; thus, understanding their impact on non-target species, whose mechanism of action is not described, helps to elucidate the real risks of these pollutants to the environment. 2,4-dichlorophenoxyacetic acid (2,4-D) is frequently detected in water and, due to its persistence, poses a risk to wildlife. In this way, the present work aimed to describe the implication of exposure to concentrations of 2,4-D already reported in aquatic environments in several physiological mechanisms of C. riparius at molecular and biochemical levels. To achieve this, bioassays were conducted with fourth instar larvae exposed to three concentrations of 2,4-D (0.1, 1.0, and 7.5 μg L-1). Larvae were collected after 24 and 96 h of exposure, and the expression of 42 genes, related to six subcellular mechanisms, was assessed by Real-Time PCR (RT-PCR). Besides, the activity of the enzymes catalase (CAT), glutathione S-transferase (GST), and acetylcholinesterase (AChE) was determined. The main metabolic route altered after exposure to 2,4-D was the endocrine system (mainly related to 20-hydroxyecdysone and juvenile hormone), confirming its endocrine disruptor potential. Four of the eleven stress response genes studied were down-regulated, and later exposure modulated DNA-repair genes suggesting genotoxic capacity. Moreover, only one gene from each detoxification phase was modulated at short exposure to 1.0 μg L-1. The molecular responses were not dose-dependent, and some early responses were not preserved after 96 h, indicating a transient response to the herbicide. Exposure to 2,4-D did not alter the activity of CAT, GST, and AChE enzymes. The responses described in this study reveal new mechanistic pathways of toxicity for 2,4-D in non-target organisms and highlight potential ecological consequences for chironomids in aquatic systems at the edges of agricultural fields.

Phenotypic adaptation of Chironomus riparius to chronic Bti exposure: effects on emergence time and nutrient content

Insects with aquatic larval and terrestrial adult life stages are a key component of coupled aquatic-terrestrial ecosystems. Thus, stressors applied to water bodies adversely affecting those larvae have the potential to influence the riparian zone through altered emergence, with differences in prey availability, timing, or nutrition. In this study, the common model organism Chironomus riparius, a species of Chironomidae (Diptera), was used. This selection was further motivated by its wide distribution in European freshwaters and its importance as prey for terrestrial predators. A stressor of high importance in this context is the globally used mosquito control agent Bacillus thuringiensis var. israelensis (Bti) which has been shown to affect Chironomidae. Here, we investigated the ability of chironomid populations to adapt to a regularly applied stressor, leading to a reduced impact of Bti. Therefore, the initial sensitivity of laboratory populations of C. riparius was investigated under the influence of field-relevant Bti treatments (three doses × two application days) and different food sources (high-quality TetraMin vs. low-quality Spirulina). Following a chronic exposure to Bti over six months, the sensitivity of pre-exposed and naïve populations was re-evaluated. Food quality had a strong impact on emergence timing and nutrient content. In addition, alterations in emergence time as well as protein and lipid contents of chronically exposed populations indicated a selection for individuals of advantageous energetics, potentially leading to a more efficient development while combating Bti. Signs of adaptation could be confirmed in five out of 36 tested scenarios suggesting adaptation to Bti at the population level. Adaptive responses of one or several species could theoretically (via eco-evolutionary dynamics) result in a community shift, favouring the prevalence of Bti-tolerant species. (In)direct effects of Bti and the adaptive responses at both population and community levels could affect higher trophic levels and may determine the fate of meta-ecosystems.

Invasive species drive cross-ecosystem effects worldwide

Invasive species are pervasive around the world and have profound impacts on the ecosystem they invade. Invasive species, however, can also have impacts beyond the ecosystem they invade by altering the flow of non-living materials (for example, nutrients or chemicals) or movement of organisms across the boundaries of the invaded ecosystem. Cross-ecosystem interactions via spatial flows are ubiquitous in nature, for example, connecting forests and lakes, grasslands and rivers, and coral reefs and the deep ocean. Yet, we have a limited understanding of the cross-ecosystem impacts invasive species have relative to their local effects. By synthesizing emerging evidence, here we demonstrate the cross-ecosystem impacts of invasive species as a ubiquitous phenomenon that influences biodiversity and ecosystem functioning around the world. We identify three primary ways by which invasive species have cross-ecosystem effects: first, by altering the magnitude of spatial flows across ecosystem boundaries; second, by altering the quality of spatial flows; and third, by introducing novel spatial flows. Ultimately, the strong impacts invasive species can drive across ecosystem boundaries suggests the need for a paradigm shift in how we study and manage invasive species around the world, expanding from a local to a cross-ecosystem perspective.

PCB concentrations in riparian spiders (Tetragnathidae) consistently reflect concentrations in water and aquatic macroinvertebrates, but not sediment: Analysis of a seven-year field study

Tetragnathid spiders have been used as sentinels to study the biotransport of contaminants between aquatic and terrestrial environments because a significant proportion of their diet consists of adult aquatic insects. A key knowledge gap in assessing tetragnathid spiders as sentinels is understanding the consistency of the year-to-year relationship between contaminant concentrations in spiders and sediment, water, and macroinvertebrates. We collected five years of data over a seven-year investigation at a PCB contaminated-sediment site to investigate if concentrations in spiders were consistently correlated with concentrations in sediment, water, and aquatic macroinvertebrates. Despite significant year-to-year variability in spider PCB concentrations, they were not correlated with sediment concentrations (p = 0.186). However, spider PCB concentrations were significantly, positively correlated with PCB concentrations in water (p < 0.0001, annual r2 = 0.35-0.84) and macroinvertebrates (p < 0.0001; annual r2 = 0.59-0.71). Analysis of covariance (ANCOVA) showed that spider PCB concentrations varied consistently with water (β = 0.63) and macroinvertebrate PCB concentrations (β = 1.023) among years. Overall, this study filled a critical knowledge gap in the utilization of tetragnathid spiders as sentinels of aquatic pollution by showing that despite year-to-year changes in PCB concentrations across environmental compartments, consistent relationships existed between spiders and water and aquatic macroinvertebrates.

A synthesis of anthropogenic stress effects on emergence-mediated aquatic-terrestrial linkages and riparian food webs

Anthropogenic stress alters the linkage between aquatic and terrestrial ecosystems in various ways. Here, we review the contemporary literature on how alterations in aquatic systems through environmental pollution, invasive species and hydromorphological changes carry-over to terrestrial ecosystems and the food webs therein. We consider both the aquatic insect emergence and flooding as pathways through which stressors can propagate from the aquatic to the terrestrial system. We specifically synthesize and contextualize results on the roles of pollutants in the emergence pathway and their top-down consequences. Our review revealed that the emergence and flooding pathway are only considered in isolation and that the overall effects of invasive species or pollutants on food webs at the water-land interface require further attention. While very few recent studies looked at invasive species, a larger number of studies focused on metal transfer compared to pesticides, pharmaceuticals or PCBs, and multiple stress studies up to now left aquatic-terrestrial linkages unconsidered. Recent research on pollutants and emergence used aquatic-terrestrial mesocosms to elucidate the effects of aquatic stressors such as the mosquito control agent Bti, metals or pesticides to understand the effects on riparian spiders. Quality parameters, such as the structural and functional composition of emergent insect communities, the fatty acid profiles, yet also the composition of pollutants transferred to land prove to be important for the effects on riparian spiders. Process-based models including quality of emergence are useful to predict the resulting top-down directed food web effects in the terrestrial recipient ecosystem. In conclusion, we present and recommend a combination of empirical and modelling approaches in order to understand the complexity of aquatic-terrestrial stressor propagation and its spatial and temporal variation.

Effects of mosquito control using the microbial agent Bacillus thuringiensis israelensis (Bti) on aquatic and terrestrial ecosystems: a systematic review

BACKGROUND

The bacterium Bacillus thuringiensis serovar israelensis (Bti) is commercially produced in various formulations for use as a larvicide worldwide, targeting especially the aquatic larval stage of mosquitoes. However, there is a concern that repeated Bti treatments may have both direct and indirect impacts on non-target organisms (NTOs) and the ecosystems they inhabit. This review evaluates the evidence for such impacts.

METHODS

Literature was searched using six bibliographic databases, two search engines, and on specialist web sites. Eligibility screening was performed in two steps on (1) title/abstract, with consistency among reviewers assessed by double-screening 557 articles and (2) full text. Articles included after full text screening were critically appraised independently by two reviewers. Disagreements were reconciled through discussions. Key parameters of included studies are presented in narrative synthesis tables, including risk of bias assessments. Meta-analyses comparing treated with untreated ecosystems and using either the raw mean difference or log response ratio as effect size were performed.

REVIEW FINDINGS

Ninety-five articles covering 282 case studies were included in the review. From these, we identified 119 different response variables, which were divided into nine outcome categories. Most studies investigated NTO abundance or life history (reproduction related outcomes), but diversity and community composition are also well represented as outcome categories. The studies are highly variable in methodology, rigor, and spatio-temporal scale, spanning 1 day to 21 years and from < 1m2 to > 10,000 m2. Our metanalyses revealed a consistent negative effect of Bti treatment on abundances of Chironomidae and Crustacea, and also on chironomid emergence, although from a more restricted set of studies and regions. For most remaining response variables, we judged meta-analysis unfeasible, due to low study numbers or insufficient reporting of methods and results.

CONCLUSIONS

There is now a significant body of studies documenting effects of mosquito control using Bti on NTOs or other ecosystem properties, especially associated with negative effects on Chironomidae, as apparent from our meta-analyses. Accordingly, we suggest the potential for negative NTO or other ecosystem effects of Bti treatment should not be discounted a priori. Once a decision to proceed with Bti treatment has been taken, priority should be given to a well-designed program of ongoing monitoring and assessment. The paucity of rigorous studies conducted with low bias risk for most response variables undermines our capacity for evaluating how common many of the effects documented might be. Future research would benefit from a rigorous and well-replicated approach to studying Bti impacts in semi-field mesocosms or in the field, combined with a greater rigor in reporting key methodological details. A greater focus is needed on understanding the environmental factors which regulate the wider effects of mosquito control using Bti on NTOs and ecosystems, to enhance our capacity for predicting where and when Bti is most likely to have additional, negative and indirect ecological impacts.

Connecting distinct realms along multiple dimensions: A meta-ecosystem resilience perspective

Resilience research is central to confront the sustainability challenges to ecosystems and human societies in a rapidly changing world. Given that social-ecological problems span the entire Earth system, there is a critical need for resilience models that account for the connectivity across intricately linked ecosystems (i.e., freshwater, marine, terrestrial, atmosphere). We present a resilience perspective of meta-ecosystems that are connected through the flow of biota, matter and energy within and across aquatic and terrestrial realms, and the atmosphere. We demonstrate ecological resilience sensu Holling using aquatic-terrestrial linkages and riparian ecosystems more generally. A discussion of applications in riparian ecology and meta-ecosystem research (e.g., resilience quantification, panarchy, meta-ecosystem boundary delineations, spatial regime migration, including early warning indications) concludes the paper. Understanding meta-ecosystem resilience may have potential to support decision making for natural resource management (scenario planning, risk and vulnerability assessments).

Spadefoot Pelobates vespertinus (Amphibia, Pelobatidae) as a transmitter of fatty acids from water to land in a forest-steppe floodplain

The transfer of biomass and polyunsaturated fatty acids by the spadefoot P. vespertinus (previously subspecies of P. fuscus) from aquatic to terrestrial ecosystems was studied for five years in small floodplain water bodies of a forest-steppe zone. Average emergence of metamorphs from unit of water area, wet mass was 6.7 g m^-2 year^-1. A ratio of the emergence to biomass was calculated and represented as E/B coefficient (an analog of P/B production/biomass coefficient). The average E/B was found to be 0.038 year^-1. The introduced coefficient can be used for a coarse estimation of the emergence on the basis of tadpole biomass measurements. A considerable partitioning of tadpoles and metamorphs in the composition of fatty acids in their biomass was revealed. Tadpoles had significantly higher mean levels (percent of total fatty acids) of 16:0, 16:1n-9, 18:0, 20:5n-3 and 22:5n-3, while metamorphs had significantly higher levels of 14:0, 15:0, 17:0, 17:1n-8, 18:2n-6, 20:2n-6, 20:4n-6 and 22:5n-6, likely due to the shifting to terrestrial food. Metamorphs had significantly higher content of total fatty acids, mg g^-1 of wet weight, and, in spite of lower level, they had significantly higher content of eicosapentaenoic acid (20:5n-3, EPA) than tadpoles. Metamorphs also had significantly higher content of docosahexaenoic acid (22:6n-3, DHA) and sum of EPA + DHA than tadpoles. Average flux of EPA + DHA from unit of water area with metamorphs was 3.27 mg m^-2 year^-1. The metamorphs appeared to be qualitatively and quantitatively prominent prey for a number of terrestrial consumers.

Subsidy Quality Affects Common Riparian Web-Building Spiders: Consequences of Aquatic Contamination and Food Resource

Anthropogenic stressors can affect the emergence of aquatic insects. These insects link aquatic and adjacent terrestrial food webs, serving as high-quality subsidy to terrestrial consumers, such as spiders. While previous studies have demonstrated that changes in the emergence biomass and timing may propagate across ecosystem boundaries, the physiological consequences of altered subsidy quality for spiders are largely unknown. We used a model food chain to study the potential effects of subsidy quality: Tetragnatha spp. were exclusively fed with emergent Chironomus riparius cultured in the absence or presence of either copper (Cu), Bacillus thuringiensis var. israelensis (Bti), or a mixture of synthetic pesticides paired with two basal resources (Spirulina vs. TetraMin®) of differing quality in terms of fatty acid (FA) composition. Basal resources shaped the FA profile of chironomids, whereas their effect on the FA profile of spiders decreased, presumably due to the capacity of both chironomids and spiders to modify (dietary) FA. In contrast, aquatic contaminants had negligible effects on prey FA profiles but reduced the content of physiologically important polyunsaturated FAs, such as 20:4n-6 (arachidonic acid) and 20:5n-3 (eicosapentaenoic acid), in spiders by approximately 30% in Cu and Bti treatments. This may have contributed to the statistically significant decline (40%-50%) in spider growth. The observed effects in spiders are likely related to prey nutritional quality because biomass consumption by spiders was, because of our experimental design, constant. Analyses of additional parameters that describe the nutritional quality for consumers such as proteins, carbohydrates, and the retention of contaminants may shed further light on the underlying mechanisms. Our results highlight that aquatic contaminants can affect the physiology of riparian spiders, likely by altering subsidy quality, with potential implications for terrestrial food webs. Environ Toxicol Chem 2023;42:1346-1358. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Chronic Engineered Nanoparticle Additions Alter Insect Emergence and Result in Metal Flux from Aquatic Ecosystems into Riparian Food Webs

Freshwater ecosystems are exposed to engineered nanoparticles (NPs) through discharge from wastewater and agricultural runoff. We conducted a 9-month mesocosm experiment to examine the combined effects of chronic NP additions on insect emergence and insect-mediated contaminant flux to riparian spiders. Two NPs (copper, gold, plus controls) were crossed by two levels of nutrients in 18 outdoor mesocosms open to natural insect and spider colonization. We collected adult insects and two riparian spider genera, Tetragnatha and Dolomedes, for 1 week on a monthly basis. We estimated a significant decrease in cumulative insect emergence of 19% and 24% after exposure to copper and gold NPs, irrespective of nutrient level. NP treatments led to elevated copper and gold tissue concentrations in adult insects, which resulted in terrestrial fluxes of metals. These metal fluxes were associated with increased gold and copper tissue concentrations for both spider genera. We also observed about 25% fewer spiders in the NP mesocosms, likely due to reduced insect emergence and/or NP toxicity. These results demonstrate the transfer of NPs from aquatic to terrestrial ecosystems via emergence of aquatic insects and predation by riparian spiders, as well as significant reductions in insect and spider abundance in response to NP additions.

Impact across ecosystem boundaries - Does Bti application change quality and composition of the diet of riparian spiders?

Emerging aquatic insects link aquatic and adjacent terrestrial food webs by subsidizing terrestrial predators with high-quality prey. One of the main constituents of aquatic subsidy, the non-biting midges (Chironomidae), showed altered emergence dynamics in response to the mosquito control agent Bacillus thuringiensis var. israelensis (Bti). As riparian spiders depend on aquatic subsidy, they may be affected by such changes in prey availability. Thus, we conducted a field study in twelve floodplain pond mesocosms (FPMs), six were treated with Bti (2.88 × 10⁹ ITU/ha, VectoBac WDG) three times, to investigate if the Bti-induced shift in chironomid emergence dynamics is reflected in their nutritional value and in the diet of riparian spiders. We measured the content of proteins, lipids, glycogen, and carbohydrates in emerged Chironomidae, and determined the stable isotope ratios of female Tetragnatha extensa, a web-building spider living in the riparian vegetation of the FPMs. We analysed the proportion of aquatic prey in spiders' diet, niche size, and trophic position. While the content of nutrients and thus the prey quality was not significantly altered by Bti, effects on the spiders' diet were observed. The trophic position of T. extensa from Bti-treated FPMs was lower compared to the control while the aquatic proportion was only minimally reduced. We assume that spiders fed more on terrestrial prey but also on other aquatic organisms such as Baetidae, whose emergence was unaffected by Bti. In contrast to the partly predaceous Chironomidae, consumption of aquatic and terrestrial primary consumers potentially explains the observed lower trophic position of spiders from Bti-treated FPMs. As prey organisms vary in their quality the suggested dietary shift could transfer previously observed effects of Bti to riparian spiders conceivably affecting their populations. Our results further support that anthropogenic stressors in aquatic ecosystems may translate to terrestrial predators through aquatic subsidy.

Aquatic-terrestrial transfer of neonicotinoid insecticides in riparian food webs

Current-use pesticides are ubiquitous in freshwaters globally, often at very low concentrations. Emerging aquatic insects can accumulate pesticides during their aquatic development, which can be retained through their metamorphosis into terrestrial adults. Emerging insects thus provide a potential, yet largely understudied linkage for exposure of terrestrial insectivores to waterborne pesticides. We measured 82 low to moderately lipophilic organic pesticides (logK_ow: -2.87 to 6.9) in the aquatic environment, emerging insects and web-building riparian spiders from stream sites impacted by agricultural land use. Insecticides, mainly neuro-active neonicotinoids were ubiquitous and had the highest concentrations in emerging insects and spiders (∑ insecticides: 0.1-33 and 1-240 ng/g, respectively), although their concentrations in water were low, even when compared to global levels. Furthermore, neonicotinoids, although not considered to be bioaccumulative, were biomagnified in riparian spiders. In contrast, concentrations of fungicides and most herbicides decreased from the aquatic environment to the spiders. Our results provide evidence for the transfer and accumulation of neonicotinoids across the aquatic-terrestrial ecosystem boundary. This could threaten food webs in ecologically sensitive riparian areas worldwide.

Copper Uptake and Its Effects on Two Riparian Plant Species, the Native Urtica dioica, and the Invasive Fallopia japonica

Copper accumulating in stream sediments can be transported to adjacent riparian habitats by flooding. Although being an essential element for plants, copper is toxic at high concentrations and restricts, among other things, plant growth. Besides copper, invasive plants, such as Fallopia japonica, which are known to be tolerant toward heavy metals, modify riparian habitats. If the tolerance of F. japonica is higher compared to native plants, this could accelerate invasion under high heavy metal stress. Therefore, we aimed to compare the effect of copper on two common riparian plants, the invasive F. japonica and the native Urtica dioica. We performed a pot experiment with a gradient from 0 to 2430 mg kg^-1 of soil copper. We hypothesized that (i) negative effects on plant growth increase with increasing soil copper concentrations with F. japonica being less affected and (ii) accumulating higher amounts of copper in plant tissues compared to U. dioica. In support of our first hypothesis, growth (height, leaf number) and biomass (above- and belowground) of F. japonica were impacted at the 810 mg kg^-1 treatment, while the growth of U. dioica was already impacted at 270 mg kg^-1. Due to 100% mortality of plants, the 2430 mg kg^-1 treatment was omitted from the analysis. In contrast, chlorophyll content slightly increased with increasing copper treatment for both species. While U. dioica accumulated more copper in total, the copper uptake by F. japonica increased more strongly after exposure compared to the control. In the 810 mg kg^-1 treatment, copper concentrations in F. japonica were up to 2238% higher than in the control but only up to 634% higher in U. dioica. Our results indicate that F. japonica might be able to more efficiently detoxify internal copper concentrations controlling heavy metal effects compared to the native species. This could give F. japonica a competitive advantage particularly in polluted areas, facilitating its invasion success.

A temporal perspective on aquatic subsidy: Bti affects emergence of Chironomidae

Emerging aquatic insects serve as one link between aquatic and adjacent riparian food webs via the flux of energy and nutrients. These insects provide high-quality subsidy to terrestrial predators. Thus, any disturbance of emergence processes may cascade to higher trophic levels and lead to effects across ecosystem boundaries. One stressor with potential impact on non-target aquatic insects, especially on non-biting midges (Diptera: Chironomidae), is the widely used mosquito control agent Bacillus thuringiensis var. israelensis (Bti). In a field experiment, we investigated emerging insect communities from Bti-treated (three applications, maximum field rate) and control floodplain pond mesocosms (FPMs) over 3.5 months for changes in their composition, diversity as well as the emergence dynamics and the individual weight of emerged aquatic insects over time. Bti treatments altered community compositions over the entire study duration - an effect mainly attributed to an earlier (∼10 days) and reduced (∼26%) peak in the emergence of Chironomidae, the dominant family (88% of collected individuals). The most reasonable explanation for this significant alteration is less resource competition caused by a decrease in chironomid larval density due to lethal effects of Bti. This is supported by the higher individual weight of Chironomidae emerging from treated FPMs (∼21%) during Bti application (April - May). A temporal shift in the emergence dynamics can cause changes in the availability of prey in linked terrestrial ecosystems. Consequently, terrestrial predators may be affected by a lack of appropriate prey leading to bottom-up and top-down effects in terrestrial food webs. This study indicates the importance of a responsible and elaborated use of Bti and additionally, highlights the need to include a temporal perspective in evaluations of stressors in aquatic-terrestrial meta-ecosystems.

Contaminant fluxes across ecosystems mediated by aquatic insects

Metals and organic contaminants in aquatic systems affect the coupling of aquatic and terrestrial ecosystems through two pathways: contaminant-induced effects on insect emergence and emergence-induced contaminant transfer. Consequently, the impact of aquatic contaminants on terrestrial ecosystems can be driven by modifications in the quantity and quality of adult aquatic insects serving as prey or contaminants entering terrestrial food webs as part of the diet of terrestrial predators. Here, we provide an overview of recent advances in the field, separating metals from organic contaminants due to their differential propensity to bioaccumulate and thus their potential contribution to either of the two pathways. Finally, this review highlights the knowledge gap in the relative impact of these pathways on terrestrial insectivores.

Local variation in the timing and advancement of lake ice breakup and impacts on settling dynamics in a migratory waterbird

Timing of ice-out is important to fundamental hydrological and ecological processes in freshwater ecosystems at high northern latitudes. While earlier ice-out in lakes during the last century is a well-documented phenomenon across the Northern Hemisphere, local variation in the rate of advancement of ice-out has received little attention. Here, records of ice-out date in 1991-2020 from 37 small lakes in a boreal catchment area in southeastern Finland were used to study variation in the timing of ice-out and its advancement. In addition, data of settling phenology of migratory common goldeneyes (Bucephala clangula) at the study lakes were used to examine how between-year and within-season variation in the timing of ice-out affects lake settlement of the species. Overall, ice-out date (IOD, the timing of ice break-up in the spring) advanced 9.8 days during the 30-year study period, April temperature being more important than winter temperature (severity) in determining the IOD. Rate of the advancement of IOD in individual lakes varied from 1.5 to 16.1 days, having advanced more in relatively larger lakes. Lakes at higher elevations had later mean IOD than lakes at lower elevations. Within-season differences among the lakes in IOD increased from 1991 to 2020, this variation being mainly driven by temperature during the ice melting period. Lakes with late mean IOD were settled later in a season by breeding common goldeneyes than lakes with early IOD. The faster the ice melting progressed within a season, the faster common goldeneyes settled the breeding lakes. The results demonstrate how global warming differently affects IOD in boreal lakes even within the same catchment area. More research in the landscape context is needed to enhance our understanding of changes in IOD in boreal lakes and how differently advancing IOD affects local dynamics of species dependent on open water.

Antibiotics as a silent driver of climate change? A case study investigating methane production in freshwater sediments

Methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2) and is inter alia produced in natural freshwater ecosystems. Given the rise in CH4 emissions from natural sources, researchers are investigating environmental factors and climate change feedbacks to explain this increment. Despite being omnipresent in freshwaters, knowledge on the influence of chemical stressors of anthropogenic origin (e.g., antibiotics) on methanogenesis is lacking. To address this knowledge gap, we incubated freshwater sediment under anaerobic conditions with a mixture of five antibiotics at four levels (from 0 to 5000 µg/L) for 42 days. Weekly measurements of CH4 and CO2 in the headspace, as well as their compound-specific δ13C, showed that the CH4 production rate was increased by up to 94% at 5000 µg/L and up to 29% at field-relevant concentrations (i.e., 50 µg/L). Metabarcoding of the archaeal and eubacterial 16S rRNA gene showed that effects of antibiotics on bacterial community level (i.e., species composition) may partially explain the observed differences in CH4 production rates. Despite the complications of transferring experimental CH4 production rates to realistic field conditions, the study indicated that chemical stressors contribute to the emissions of greenhouse gases by affecting the methanogenesis in freshwaters.

Organic pollutants in protected plain areas: The occurrence of PAHs, musks, UV-filters, flame retardants and hydrocarbons in woodland soils

Protected woodlands are rare and small portions of the plain territory of northern Italy, where agricultural, industrial and urban activities strongly dominate the landscape. Such natural areas are frequently set on river floodplains and are therefore potentially conditioned by the contamination brought by the surface waters. We investigated the occurrence of multiple categories of organic pollutants, including Polycyclic Aromatic Hydrocarbons (PAHs), Musk fragrances, UV-filters, organophosphorus and novel brominated Flame Retardants (FRs) and Total Petroleum Hydrocarbons (TPH) in woodland soils of eight different protected areas. The samples collected in the floodplains of the Po, Adige and Fratta rivers resulted more contaminated, with levels of PAHs up to 633 ng g^-1. Moreover, these samples for the first time revealed the presence of personal care products, primarily 2-ethylhexyl-4-methoxycinnamate (EHMC) and tonalide (AHTN), in soils of protected woodlands, reaching respectively 3.4 ng g^-1 and 5.0 ng g^-1, together with the occurrence of both organophosphorus and brominated FRs, with total concentrations up to 15 ng g^-1. Higher concentrations of hydrocarbons, with TPH in the range 5-65 μg g^-1, were instead reflecting the inputs of long chain n-alkanes from epicuticular waxes more than petrogenic contamination.

Herbicide-Induced Shifts in the Periphyton Community Composition Indirectly Affect Feeding Activity and Physiology of the Gastropod Grazer Physella acuta

Herbicides are well known for unintended effects on freshwater periphyton communities. Large knowledge gaps, however, exist regarding indirect herbicide impacts on primary consumers through changes in the quality of periphyton as a food source (i.e., diet-related effects). To address this gap, the grazer Physella acuta (Gastropoda) was fed for 21 days with periphyton that grew for 15 days in the presence or absence of the herbicide diuron (8 μg/L) to quantify changes in the feeding rate, growth rate, and energy storage (neutral lipid fatty acids; NLFAs) of P. acuta. Periphyton biomass, cell viability, community structure, and FAs served as proxies for food quality that support a mechanistic interpretation of the grazers' responses. Diuron changed the algae periphyton community and fatty acid profiles, indicating alterations in the food quality, which could explain differences in the snails' feeding rate compared to the control. While the snails' growth rate was, despite an effect size of 55%, not statistically significantly changed, NLFA profiles of P. acuta were altered. These results indicate that herbicides can change the food quality of periphyton by shifts in the algae composition, which may affect the physiology of grazers.

Long-term changes in a small mammal community in a temperate zone meadow subject to seasonal floods and habitat transformation

We tested small mammal (SM) community response to the influence of seasonal floods and habitat transformation in a temporal zone meadow (west Lithuania). The habitat transitioned from a natural flooded meadow in 2008-2012 to a mowed and pastured area in 2020. SM were trapped in late summer to autumn using lines of 25 traps (145 in total), the number of trapping sessions being one or several per year. We tested the hypotheses that: (1) any reaction to the multiple disturbances is species-specific, that is, the relative abundance of SM species and their proportion in the community differs with respect to the flood magnitude and habitat transformation, and (2) at the guild level, disturbances favor habitat generalists, thereby changing the characteristics of SM community. The average relative density of SM was 20.25 individuals per 100 trap nights (range 7.56-40.67), with 4-year-long cyclical changes of density observed. In separate years, we recorded from 4 to 9 species; Shannon's diversity index varied from 0.46 to 2.19, with expressed change of the dominant species. Habitat generalist species were favored, while habitat specialists were disadvantaged. As the meadow transformation progressed, unfavored states in the SM community prevailed, with excessive numbers of granivore and herbivore species present. Our study suggests that multiple disturbances may lead to an increase in relative abundance, species richness, and diversity within the SM assemblages.

Bottom-up effects of fungicides on tadpoles of the European common frog (Rana temporaria)

Biodiversity is under pressure worldwide, with amphibians being particularly threatened. Stressors related to human activity, such as chemicals, are contributing to this decline. It remains, however, unclear whether chemicals exhibiting a fungicidal activity could indirectly affect tadpoles that depend on microbially conditioned leaf litter as food source. The indirect effect of fungicides (sum concentration of a fungicide mixture composed of azoxystrobin, carbendazim, cyprodinil, quinoxyfen, and tebuconazole: 100 µg/L) on tadpoles was assessed relative to leaf litter colonized by microbes in absence of fungicides (control) and a worst-case scenario, that is leached leaf litter without microbial colonization. The quality of leaf litter as food for tadpoles of the European common frog (Rana temporaria) was characterized through neutral lipid fatty acid profiles and microbial sum parameters and verified by sublethal responses in tadpoles (i.e., feeding rate, feces production, growth, and fatty acid composition). Fungicides changed the nutritious quality of leaf litter likely through alterations in leaves' neutral lipid fatty acid profiles (i.e., changes in some physiologically important highly unsaturated fatty acids reached more than 200%) in combination with a potential adsorption onto leaves during conditioning. These changes were reflected by differences in the development of tadpoles ultimately resulting in an earlier start of metamorphosis. Our data provide a first indication that fungicides potentially affect tadpole development indirectly through bottom-up effects. This pathway is so far not addressed in fungicide environmental risk assessment and merits further attention.

Aquatic Insects Transfer Pharmaceuticals and Endocrine Disruptors from Aquatic to Terrestrial Ecosystems

A wide range of pharmaceuticals and endocrine disrupting compounds enter freshwaters globally. As these contaminants are transported through aquatic food webs, understanding their impacts on both aquatic and terrestrial ecosystems remains a major challenge. Here, we provide the first direct evidence of the transfer of pharmaceuticals and endocrine disruptors through the aquatic-terrestrial habitat linkage by emerging aquatic insects. We also show that the type of insect metamorphosis and feeding behavior determine the bioaccumulation patterns of these contaminants. Adult Trichoptera, an important food source for riparian predators, showed an increased body burden of pharmaceuticals and endocrine disruptors. This implies that terrestrial predators, such as spiders, birds, and bats, are exposed to mixtures of pharmaceuticals and endocrine disruptors of aquatic origin, which may impact their physiology and population dynamics. Overall, our study provides valuable insights into the bioaccumulation patterns and trophic cross-ecosystem transfer of these contaminants, from aquatic primary producers to terrestrial predators.

Sampling rates for passive samplers exposed to a field-relevant peak of 42 organic pesticides

Pesticide concentrations in agricultural streams are often characterised by a low level of baseline exposure and episodic peak concentrations associated with heavy rainfall events. Traditional sampling methods such as grab sampling, which are still largely used in governmental monitoring, typically miss peak concentrations. Passive sampling represents a cost-efficient alternative but requires the additional determination of sampling rates to calculate time-weighted average (TWA) water concentrations from the accumulated pesticide mass in the sampler. To date, sampling rates have largely been determined in experiments with constant exposure, which does not necessarily reflect field situations. Using Empore styrene-divinylbenzene (SDB) passive sampler disks mounted in metal holders, we determined sampling rates for 42 organic pesticides, of which 27 sampling rates were lacking before. The SDB disks were in an artificial channel system exposed to a field-relevant pesticide peak. We used an open-source algorithm to estimate coefficients of equations for the accumulated pesticide mass in disks and to determine exposure time-dependent sampling rates. These sampling rates ranged from 0.02 to 0.98 L d^-1 and corresponded to those from previous studies determined with constant exposure. The prediction of sampling rates using compound properties was unreliable. Hence, experiments are required to determine reliable sampling rates. We discuss the use of passive sampling to estimate peak concentrations. Overall, our study provides sampling rates and computer code to determine these under peak exposure designs and suggests that passive sampling is suitable to estimate peak pesticide concentrations in field studies.

Environmental and socioeconomic effects of mosquito control in Europe using the biocide Bacillus thuringiensis subsp. israelensis (Bti)

Bacillus thuringiensis subsp. israelensis (Bti) has been used in mosquito control programs to reduce nuisance in Europe for decades and is generally considered an environmentally-safe, effective and target-specific biocide. However, the use of Bti is not uncontroversial. Target mosquitoes and affected midges represent an important food source for many aquatic and terrestrial predators and reduction of their populations is likely to result in food-web effects at higher trophic levels. In the context of global biodiversity loss, this appears particularly critical since treated wetlands are often representing conservation areas. In this review, we address the current large-scale use of Bti for mosquito nuisance control in Europe, provide a description of its regulation followed by an overview of the available evidence on the parameters that are essential to evaluate Bti use in mosquito control. Bti accumulation and toxin persistence could result in a chronic expose of mosquito populations ultimately affecting their susceptibility, although observed increase in resistance to Bti in mosquito populations is low due to the four toxins involved. A careful independent monitoring of mosquito susceptibility, using sensitive bioassays, is mandatory to detect resistance development timely. Direct Bti effects were documented for non-target chironomids and other invertebrate groups and are discussed for amphibians. Field studies revealed contrasting results on possible impacts on chironomid abundances. Indirect, food-web effects were rarely studied in the environment. Depending on study design and duration, Bti effects on higher trophic levels were demonstrated or not. Further long-term field studies are needed, especially with observations of bird declines in Bti-treated wetland areas. Socio-economic relevance of mosquito control requires considering nuisance, vector-borne diseases and environmental effects jointly. Existing studies indicate that a majority of the population is concerned regarding potential environmental effects of Bti mosquito control and that they are willing to pay for alternative, more environment-friendly techniques.

The acute toxic effects of hexavalent chromium on the liver of marine medaka (Oryzias melastigma)

Chromium is toxic to marine animals and can cause damage to many of their organs, including the liver. To test the toxicity of chromium on marine organisms, we exposed the liver of the marine medaka (Oryzias melastigma) with hexavalent chromium [Cr(VI)]. Our results show that Cr enrichment in the liver demonstrates a positive correlation to the exposure concentration. With the increase of Cr(VI) concentration, pathological changes including nuclear migration, cell vacuolization, blurred intercellular gap, nuclear condensation, become noticeable. To further study changes in gene expression in the liver after Cr(VI) exposure, we used RNA-seq to compare expression profiles before and after Cr(VI) exposure. After acute Cr(VI) exposure (2.61 mg/l) for 96 h, 5862 transcripts significantly changed. It is the first time that the PPAR pathway was found to respond sensitively to Cr(VI) exposure in fish. Finally, combined with other published study, we found that there may be some difference between Cr(VI) toxicity in seawater fish and freshwater fish, due to degree of oxidative stress, distribution patterns and detailed Cr(VI) toxicological mechanisms. Not only does our study explore the mechanisms of Cr(VI) toxicity on the livers of marine medaka, it also points out different Cr(VI) toxicity levels and potential mechanisms between seawater fish and freshwater fish.

Effect of Bt toxin Cry1Ab on two freshwater caddisfly shredders - an attempt to establish dose-effect relationships through food-spiking

Genetically modified organisms (GMOs), which produce Bacillus thuringiensis (Bt) toxins, are widely used in agriculture in some parts of the world. Despite this, ecotoxicological methods, tailored to GMOs, are lacking to assess effects on aquatic environments. With the objective to investigate a food-related exposure pathway for aquatic shredders, we used a new food-spiking method while caddisfly larvae (Chaetopteryx spec., Sericostoma spec.) served as test species. Pure Cry1Ab toxins were spiked on black alder leaf discs and subsequently used in a feeding experiment. The toxin did not influence larval mortality compared to the control. The results, however, showed significant effects on larval lipid content (Chaetopteryx spec.) and development (Sericostoma spec.) at concentrations of 17.2 and 132.4 ng Cry1Ab/mg leaf, respectively. These changes are indicative for impacts on the fitness of the specimen and thus relevant in a risk assessment context. Ultimately, the food-spiking method allowed applying different Bt toxin concentrations leading to the establishment of dose-response relationships for various response variables. The use of long test durations and sublethal endpoints (consumption, lipid content, growth, larval instars) is, moreover, advisable when testing GMO effects.

Nanoparticles transported from aquatic to terrestrial ecosystems via emerging aquatic insects compromise subsidy quality

Nanoparticle contaminants enter aquatic ecosystems and are transported along the stream network. Here, we demonstrate a novel pathway for the return of nanoparticles from aquatic to terrestrial ecosystems via cross-boundary subsidies. During their emergence, trichopteran caddisflies carried titanium dioxide and gold nanoparticles into their terrestrial life stages. Moreover, their emergence was delayed by ≤30 days, and their energy reserves were depleted by ≤25%. Based on worst case estimates, it is suggested that terrestrial predators, such as bats feeding on aquatic prey, may ingest up to three orders of magnitude higher gold levels than anticipated for humans. Additionally, terrestrial predator species may suffer from alterations in the temporal availability and nutritional quality of their prey. Considering the substantial transfer of insect biomass to terrestrial ecosystems, nanoparticles may decouple aquatic and terrestrial food webs with important (meta-)ecosystem level consequences.

Effects of a Systemic Pesticide Along an Aquatic Tri-Trophic Food Chain

Systemic pesticides, such as the neonicotinoid imidacloprid, can be introduced into aquatic ecosystems through contaminated plant material, which is the basis for detrital (brown) aquatic food-webs. With the aim of exemplarily assessing for indirect effects on the level of predators, we first offered imidacloprid contaminated and uncontaminated alder leaves to the stonefly shredder Protonemura sp. for 72 h. Shredder survival, leaf decomposition, body length and biomass were all between 20% and 50% lower under imidacloprid exposure compared to uncontaminated conditions, indicating physiological implications. Subsequently, these shredders were provided as prey to stonefly predators (Isoperla sp.) kept in cages in a stream. Predator biomass and length decreased by up to 11% and 4.3%, respectively, when feeding on imidacloprid exposed prey. Our study hence suggests that plant material contaminated with systemic pesticides can exert adverse effects in aquatic predators when preying on shredders consuming such leaves, which warrants a further consideration of this pathway.

Toxicity of the insecticides spinosad and indoxacarb to the non-target aquatic midge Chironomus riparius

Spinosad and indoxacarb are two relatively new insecticides mainly used in agriculture to control insect pests. However, at their current application rates, non-target aquatic insect species may also be impacted. In this study, larvae of the non-biting midge Chironomus riparius were exposed in the laboratory to both insecticides and their effects evaluated at the organismal level, using standard ecotoxicological tests, and at the biochemical level, by monitoring specific oxidative stress, neuronal, and energy metabolism biomarkers. Chronic exposure to both insecticides compromised growth and emergence of C. riparius. Short-term exposures revealed alterations at biochemical level that might be related to the toxicological targets of both insecticides. Growth and development time were the most sensitive endpoints at individual level for both pesticides, while at the biochemical level, the electron transport system activity was the most sensitive biomarker for spinosad exposure, suggesting an increase in energy demands associated with the activation of defense mechanisms. Glutathione-S-transferase was the most sensitive biomarker for indoxacarb exposure, underlining the role of this enzyme in the detoxification of indoxacarb. Additionally, changes in lactate dehydrogenase and glutathione peroxidase activities were observed for both insecticides, and evidences of oxidative damage were found for spinosad. This study contributes to the growing knowledge on sublethal effects of novel insecticides on non-target aquatic invertebrates and strengthens the usefulness of biochemical biomarkers to support the interpretation of their potentially deleterious effects on aquatic insects near agricultural fields.

Alternative transient states and slow plant community responses after changed flooding regimes

Climate change will have large consequences for flooding frequencies in freshwater systems. In interaction with anthropogenic activities (flow regulation, channel restoration and catchment land-use) this will both increase flooding and drought across the world. Like in many other ecosystems facing changed environmental conditions, it remains difficult to predict the rate and trajectory of vegetation responses to changed conditions. Given that critical ecosystem services (e.g. bank stabilization, carbon subsidies to aquatic communities or water purification) depend on riparian vegetation composition, it is important to understand how and how fast riparian vegetation responds to changing flooding regimes. We studied vegetation changes over 19 growing seasons in turfs that were transplanted in a full-factorial design between three riparian elevations with different flooding frequencies. We found that (a) some transplanted communities may have developed into an alternative stable state and were still different from the target community, and (b) pathways of vegetation change were highly directional but alternative trajectories did occur, (c) changes were rather linear but faster when flooding frequencies increased than when they decreased, and (d) we observed fastest changes in turfs when proxies for mortality and colonization were highest. These results provide rare examples of alternative transient trajectories and stable states under field conditions, which is an important step towards understanding their drivers and their frequency in a changing world.

Diverging response patterns of terrestrial and aquatic species to hydromorphological restoration

Although experiences with ecological restoration continue to accumulate, the effectiveness of restoration for biota remains debated. We complemented a traditional taxonomic analysis approach with information on 56 species traits to uncover the responses of 3 aquatic (fish, macroinvertebrates, macrophytes) and 2 terrestrial (carabid beetles, floodplain vegetation) biotic groups to 43 hydromorphological river restoration projects in Germany. All taxonomic groups responded positively to restoration, as shown by increased taxonomic richness (10-164%) and trait diversity (habitat, dispersal and mobility, size, form, life history, and feeding groups) (15-120%). Responses, however, were stronger for terrestrial than aquatic biota, and, contrary to our expectation, taxonomic responses were stronger than those of traits. Nevertheless, trait analysis provided mechanistic insights into the drivers of community change following restoration. Trait analysis for terrestrial biota indicated restoration success was likely enhanced by lateral connectivity and reestablishment of dynamic processes in the floodplain. The weaker response of aquatic biota suggests recovery was hindered by the persistence of stressors in the aquatic environment, such as degraded water quality, dispersal constraints, and insufficient hydromorphological change. Therefore, river restoration requires combined local- and regional-scale approaches to maximize the response of both aquatic and terrestrial organisms. Due to the contrasting responses of aquatic and terrestrial biota, the planning and assessment of river restoration outcomes should consider effects on both components of riverine landscapes.

Phytoremediation: green technology for the removal of mixed contaminants of a water supply reservoir

The Iraí Reservoir, a water supply in Brazil, is constantly impacted by anthropogenic activities such as waste inputs from agriculture, hospitals and urbanization, resulting toxic cyanobacterial blooms causing economic, social and environmental problems. This study assessed the concentration of some common contaminants of the Iraí Reservoir, namely paracetamol, diclofenac and microcystin-LR and tested whether a laboratory scale Green Liver System^® would serve as a suitable technology to remove these contaminants. Further, the study investigated whether the pollutants caused adverse effects to the macrophytes using catalase as a biomarker for oxidative stress and investigated whether biotransformation (glutathione S-transferase) was a main route for detoxification. Egeria densa, Ceratophyllum demersum and Myriophyllum aquaticum were exposed to a mixture of the three contaminants for 14 days in a concentration range similar to those detected in the reservoir. The plants removed 93% of diclofenac and 100% of MC-LR after 14 days. Paracetamol could not be detected. Catalase and glutathione S-transferase enzyme activities remained unaltered after the 14-day exposure, indicating that the mixture did not cause oxidative stress. The study showed that the aquatic macrophytes used are suitable tools to apply in a Green Liver System^® for the remediation of mixed pollutants.

Waterborne and diet-related effects of inorganic and organic fungicides on the insect leaf shredder Chaetopteryx villosa (Trichoptera)

It is well-documented that fungicides can affect crustacean leaf shredders via two effect pathways, namely waterborne exposure and their diet (i.e., via dietary uptake of fungicides adsorbed to leaf material and an altered microorganism-mediated food quality). As a consequence of different life history strategies, the relevance of these effect pathways for aquatic shredders belonging to other taxonomic classes, for instance insects, remains unclear. Therefore, we investigated waterborne and diet-related effects in larvae of the caddisfly leaf shredder Chaetopteryx villosa (Insecta: Trichoptera) and compared our observations to previous reports on effects in adults of the crustacean leaf shredder Gammarus fossarum (Malacostraca: Amphipoda). We assessed acute waterborne effects of an organic fungicide mixture (OFM) and the inorganic fungicide copper (Cu) on the leaf consumption (n = 30) of the fourth-/fifth-instar larvae of C. villosa and their food choice (n = 49) when offered leaf material, which was either conditioned in presence or in absence of the respective fungicide(s). Moreover, the larval leaf consumption (n = 50) and physiological fitness (i.e., growth as well as lipid and protein content) were examined after subjecting C. villosa for 24 days towards the combination of both effect pathways at environmentally relevant concentrations. G. fossarum and C. villosa exhibited similar sensitivities and the same effect direction when exposed to the OFM (either waterborne or dietary pathways). Both shredders also showed the same effect direction when exposed to dietary Cu, while with regards to mortality and leaf consumption C. villosa was less sensitive to waterborne Cu than G. fossarum. Finally, as observed for G. fossarum, the combined exposure to OFM over 24 days negatively affected leaf consumption and the physiology (i.e., growth and lipid reserves) of C. villosa. While no combined Cu effects were observed for larval leaf consumption, contrasting to the observations for G. fossarum, the physiology of both shredders was negatively affected, despite partly differing effect sizes and directions. Our results suggest that C. villosa and G. fossarum are of comparable sensitivity towards waterborne and diet-related organic fungicide exposure, whereas the trichopteran is less sensitive to Cu-based waterborne fungicide exposure. However, when both pathways act jointly, organic and inorganic fungicides can affect the physiology of shredder species with completely different life history strategies. As caddisflies represent a subsidy for terrestrial consumers, these observations indicate that fungicide exposure might not only affect aquatic ecosystem functioning but also the flux of energy across ecosystem boundaries.

Salt in freshwaters: causes, effects and prospects - introduction to the theme issue

Humans are globally increasing the salt concentration of freshwaters (i.e. freshwater salinization), leading to significant effects at the population, community and ecosystem level. The present theme issue focuses on priority research questions and delivers results that contribute to shaping the future research agenda on freshwater salinization as well as fostering our capacity to manage salinization. The issue is structured along five topics: (i) the estimation of future salinity and evaluation of the relative contribution of the different drivers; (ii) the physiological responses of organisms to alterations in ion concentrations with a specific focus on the osmophysiology of freshwater insects and the responses of different organisims to seawater intrusion; (iii) the impact of salinization on ecosystem functioning, also considering the connections between riparian and stream ecosystems; (iv) the role of context in moderating the response to salinization. The contributions scrutinise the role of additional stressors, biotic interactions, the identify of the ions and their ratios, as well as of the biogeographic and evolutionary context; and (v) the public discourse on salinization and recommendations for management and regulation. In this paper we introduce the general background of salinization, outline research gaps and report key findings from the contributions to this theme issue.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Salinity impacts on river ecosystem processes: a critical mini-review

In many dry parts of the world, salinization of water resources threatens freshwater biodiversity and the livelihood of people. However, ecological impact studies remain scarce. Here, we review field-observations of salinity impacts on ecosystem processes such as leaf decomposition, metabolism, biomass production and nutrient cycling, with a special emphasis on dryland ecosystems. In addition, we discuss the potential linkages of these processes to ecosystem service delivery-the benefits that humans derive from ecosystems-as additional nature conservation arguments and the challenges associated with this endeavour.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Conserving connectivity: Human influence on subsidy transfer and relevant restoration efforts

Conservation efforts tend to focus on the direct impacts humans have on their surrounding environment; however there are also many ways in which people indirectly affect ecosystems. Recent research on ecological subsidies-the transfer of energy and nutrients from one ecosystem to another-has highlighted the importance of nutrient exchange for maintaining productivity and diversity at a landscape scale, while also pointing toward the fragility of ecotones and vulnerability of subsidies to human activities. We review the recent literature on landscape connectivity and ecosystem subsidies from aquatic systems to terrestrial systems. Based on this review, we propose a conceptual model of how human activities may alter or eliminate the flow of energy and nutrients between ecosystems by influencing the delivery of subsidies along the pathway of transfer. To demonstrate the utility of this conceptual model, we discuss it in the context of case studies of subsidies derived from salmon, marine mammals, sea turtles, sea birds, and shoreline debris. Subsidy restoration may require a different set of actions from simply reversing the pathway of degradation. We suggest that effective restoration and conservation efforts will require a multifaceted approach, targeting many steps along the subsidy transfer pathway, to address these issues.

Aquatic community response to volcanic eruptions on the Ecuadorian Andean flank: evidence from the palaeoecological record

Aquatic ecosystems in the tropical Andes are under increasing pressure from human modification of the landscape (deforestation and dams) and climatic change (increase of extreme events and 1.5 °C on average temperatures are projected for AD 2100). However, the resilience of these ecosystems to perturbations is poorly understood. Here we use a multi-proxy palaeoecological approach to assess the response of aquatic ecosystems to a major mechanism for natural disturbance, volcanic ash deposition. Specifically, we present data from two Neotropical lakes located on the eastern Andean flank of Ecuador. Laguna Pindo (1°27.132'S-78°04.847'W) is a tectonically formed closed basin surrounded by a dense mid-elevation forest, whereas Laguna Baños (0°19.328'S-78°09.175'W) is a glacially formed lake with an inflow and outflow in high Andean Páramo grasslands. In each lake we examined the dynamics of chironomids and other aquatic and semi-aquatic organisms to explore the effect of thick (> 5 cm) volcanic deposits on the aquatic communities in these two systems with different catchment features. In both lakes past volcanic ash deposition was evident from four large tephras dated to c.850 cal year BP (Pindo), and 4600, 3600 and 1500 cal year BP (Baños). Examination of the chironomid and aquatic assemblages before and after the ash depositions revealed no shift in composition at Pindo, but a major change at Baños occurred after the last event around 1500 cal year BP. Chironomids at Baños changed from an assemblage dominated by Pseudochironomus and Polypedilum nubifer-type to Cricotopus/Paratrichocladius type-II, and such a dominance lasted for approximately 380 years. We suggest that, despite potential changes in the water chemistry, the major effect on the chironomid community resulted from the thickness of the tephra being deposited, which acted to shallow the water body beyond a depth threshold. Changes in the aquatic flora and fauna at the base of the trophic chain can promote cascade effects that may deteriorate the ecosystem, especially when already influenced by human activities, such as deforestation and dams, which is frequent in the high Andes.

Repeated pulse exposures to lambda-cyhalothrin affect the behavior, physiology, and survival of the damselfly larvae Ischnura graellsii (Insecta; Odonata)

Damselflies form an essential part of the aquatic and terrestrial food web. Pesticides may, however, negatively affect their behavior, physiology, and survival. To assess this, a 42-day-lasting bioassay was conducted, during which damselfly larvae (Ischnura graellsii; n = 20) were repeatedly exposed to lambda-cyhalothrin (3 days at; 0, 10, 50, 250, 1250, and 6250ng LCH L^-1), followed by recovery phases (4 days) in pesticide-free medium for six weeks. This exposure design was used to simulate frequent runoff events in the field. Variables related to the behavior (strikes against prey and capture success), growth, physiology (lipid content and fatty acid composition), as well as mortality were assessed throughout the experiment. The two highest LCH concentrations induced 100% mortality within the first 48h, whereas 85% of the test organisms survived 28 days under control conditions. The number of strikes against prey was not affected by LCH. In contrast, prey capture success decreased significantly (up to ~50% at 250ng LCH L^-1, for instance, after the third pulse exposure) following LCH-exposures compared to the control. This difference was not observed after recovery phases, however, which did not counteract the enhanced energy demand for detoxification and defense mechanisms indicated by a lower growth rate (up to ~20%) and lipid content (up to ~30%) of damselflies at 50 and 250ng LCH L^-1. In addition, two essential fatty acids (eicosapentaenoic acid and arachidonic acid) and two precursors (linolenic acid and α-linolenic acid) decreased in their concentrations upon exposure towards 250ng LCH L^-1. Thus the results of this study indicate that long-term exposure towards LCH pulses can affect damselfly behavior, physiology and survival. Given the essential role of damselflies in food web dynamics, these effects may potentially translate into local population impairments with subsequent bottom-up directed effects within and across ecosystem boundaries.