Agricultural land uses can impact stream ecosystems by reducing suitable habitat, altering flows, and increasing inputs of diffuse pollutants including fine inorganic sediment (<2 mm). These changes ...have been linked to altered community composition and declines in biodiversity. Determining the mechanisms driving stream biotic responses, particularly threshold impacts, has, however, proved elusive. To investigate a sediment threshold response by benthic invertebrates, an intensive survey of 30 agricultural streams was conducted along gradients of deposited sediment and dissolved nutrients. Partial redundancy analysis showed that invertebrate community composition changed significantly along the gradient of deposited fine sediment, whereas the effect of dissolved nitrate was weak. Pollution-sensitive invertebrates (%EPT, Ephemeroptera, Plecoptera, Trichoptera) demonstrated a strong nonlinear response to sediment, and change-point analysis indicated marked declines beyond a threshold of
∼
20% fine sediment covering the streambed. Structural equation modeling indicated that decreased habitat availability (i.e., coarse substrate and associated interstices) was the key driver affecting pollution-sensitive invertebrates, with degraded riparian condition controlling resources through direct (e.g., inputs) and indirect (e.g., flow-mediated) effects on deposited sediment. The identification of specific effects thresholds and the underlying mechanisms (e.g., loss of habitat) driving these changes will assist managers in setting sediment criteria and standards to better guide stream monitoring and rehabilitation.
In focus: Nash, L. N., Antiqueira, P. A. P., Romero, G. Q., de Omena, P. M., and Kratina, P. (2021). Warming of aquatic ecosystems disrupts aquatic‐terrestrial linkages in the tropics. Journal of ...Animal Ecology. Meta‐ecosystem ecology offers a holistic framework linking populations, communities and ecosystems in heterogeneous landscapes. This perspective is particularly relevant as anthropogenic drivers of environmental change proliferate, with the potential for impacts to propagate to spatially connected habitats. In aquatic ecosystems, reciprocal exchanges of energy, materials and organisms that form strong connections with adjacent terrestrial habitats can be disrupted by human impacts. Nash et al. (2021) demonstrate how a warming environment alters aquatic–terrestrial linkages by measuring rates of aquatic insect emergence and decomposition in a tropical context. While decomposition predictably increased with warming, insect emergence was greatly reduced. Using metabolic theory, I highlight how these results deviate from previous studies and help underscore the need for comparative research in different biomes. I conclude by exploring where progress can be made in quantifying, predicting and utilising the connectivity of ecosystems to fully realise the potential of a meta‐ecosystem perspective and help address the dual crises of biodiversity loss and climate change.
This In Focus article highlights Nash etal. (2021). The authors show how a warming environment may alter aquatic‐terrestrial linkages, potentially leading to adverse impacts onrecipient communities. More broadly,this suggests that because perturbations can propagate to spatially connectedhabitats, ecological connectivity is an attribute to quantify, predict, andmanage.
Global change assessments have typically ignored synthetic chemical pollution, despite the rapid increase of pharmaceuticals, pesticides, and industrial chemicals in the environment. The paucity of ...research on the ecological effects of these micropollutants undermines our efforts to address the freshwater biodiversity crisis. Understanding the responses of individual organisms to chemical pollution should help address this knowledge gap because individual‐level effects can cascade across populations, communities, and ecosystems with devastating consequences.
Inputs of treated municipal wastewater are a major source of micropollutants in receiving environments. Here, we assessed population and individual‐level influences of treated wastewater on freshwater gammarid amphipods (Gammarus spp.) in Swiss lowland streams in situ and tested effects of a micropollutant mixture on individual Gammarus fossarum using a common garden laboratory experiment. We hypothesised that population‐level effects of wastewater are mediated through asymmetric sensitivities of juvenile and adult gammarids to chemical pollutants. We expected that life‐stage specific sensitivities would reflect allometric theory relating body size to a wide range of organismal characteristics, including metabolism, growth, and mortality.
At the population level (i.e. field survey), we observed greatly reduced abundances of juvenile gammarids downstream of the wastewater discharge in three of the six sites surveyed, indicating the potential for demographic effects of pollution. At the individual level in a field transplant experiment, we found that the presence of wastewater led to a steeper positive relationship between gammarid body size and leaf consumption. In the laboratory experiment, we found that micropollutants had negative effects on consumption and growth rates, but a positive effect on survival. Differences in the relationship between gammarid body size and performance were subtle across treatments, although flatter slopes in growth appear to be a consistent response to chemical pollution. Faster growth rates appeared to be connected with reduced survival, placing individuals in control treatments and/or with smaller body size at greatest risk of mortality. Notably, juvenile gammarids had faster growth rates and lower survival than adults when exposed to micropollutants.
Our results demonstrate the potential for negative impacts of micropollutants in freshwater ecosystems. However, the results also show that organismal responses to chemical pollutants can be complex, whereby impacts at the individual level may act counter‐intuitively to population‐level dynamics. This highlights the need for more realistic experiments to better assess how organismal responses depend on life stage and body size, and how individual‐level effects propagate to higher levels of biological organisation. Our study shows how allometric theory can be used to examine the effects of stressors on underlying organismal biology, population demographics, and link with broader macroecological patterns.
Natural and anthropogenic disturbances commonly alter patterns of biodiversity and ecosystem functioning. However, how networks of interacting species respond to these changes remains poorly ...understood. We described aquatic food webs using invertebrate and fish community composition, functional traits and stable isotopes from twelve agricultural streams along a landscape disturbance gradient.
We predicted that excessive deposition of fine inorganic sediment (sedimentation) associated with agricultural activities would negatively influence aquatic trophic diversity (e.g. reduced vertical and horizontal trophic niche breadths). We hypothesized that multiple mechanisms might cause trophic niche ‘compression’, as indicated by changes in realized trophic roles.
Food‐web properties based on consumer stable isotope data (δ13C and δ15N) showed that increasing sediment disturbance was associated with reduced trophic diversity. In particular, the aquatic invertebrate community occupied a smaller area in isotopic niche space along the sedimentation gradient that was best explained by a narrowing of the invertebrate community δ13C range.
Decreased niche partitioning, driven by increasing habitat homogeneity, environmental filtering and resource scarcity all seemingly lead to greater trophic equivalency caused by the collapse of the autochthonous food‐web channel. Bayesian mixing‐model analyses supported this contention with invertebrate consumers increasingly reliant on detritus along the sedimentation gradient, and predatory invertebrates relying more on the prey using these basal resources.
The narrowing of the fish community δ13C range along the sedimentation gradient contributed to an apparent ‘trophic shift’ towards terrestrial carbon, further indicating the loss of the autochthonous food‐web channel. On the vertical trophic niche axis, fish became increasingly separated from aquatic invertebrates with an increase in their estimated trophic position. In combination, these responses were most likely mediated through reduced fish densities and a diminished reliance on aquatic prey.
Although species losses remain a major threat to ecosystem integrity, the functional roles of biota that persist dictate how food webs and ecosystem functioning respond to environmental change. Sedimentation was associated with nonlinear reductions in trophic diversity which could affect the functioning and stability of aquatic ecosystems. Our study helps explain how multiple mechanisms may radically reshape food‐web properties in response to this type of disturbance.
How ecological networks respond to perturbations remains poorly understood. The authors used stable isotopes to describe aquatic food webs along a landscape disturbance gradient. Increasing sedimentation was associated with reduced trophic diversity, seemingly driven by the collapse of the autochthonous food‐web channel. These changes may affect food‐web stability and ecosystem functioning.
Multiple anthropogenic drivers are changing ecosystems globally, with a disproportionate and intensifying impact on freshwater habitats. A major impact of urbanization are inputs from wastewater ...treatment plants (WWTPs). Initially designed to reduce eutrophication and improve water quality, WWTPs increasingly release a multitude of micropollutants (MPs; i.e., synthetic chemicals) and microbes (including antibiotic‐resistant bacteria) to receiving environments. This pollution may have pervasive impacts on biodiversity and ecosystem services. Viewed through multiple lenses of macroecological and ecotoxicological theory, we combined field, flume, and laboratory experiments to determine the effects of wastewater (WW) on microbial communities and organic‐matter processing using a standardized decomposition assay. First, we conducted a mensurative experiment sampling 60 locations above and below WWTP discharges in 20 Swiss streams. Microbial respiration and decomposition rates were positively influenced by WW inputs via warming and nutrient enrichment, but with a notable exception: WW decreased the activation energy of decomposition, indicating a “slowing” of this fundamental ecosystem process in response to temperature. Second, next‐generation sequencing indicated that microbial community structure below WWTPs was altered, with significant compositional turnover, reduced richness, and evidence of negative MP influences. Third, a series of flume experiments confirmed that although diluted WW generally has positive influences on microbial‐mediated processes, the negative effects of MPs are “masked” by nutrient enrichment. Finally, transplant experiments suggested that WW‐borne microbes enhance decomposition rates. Taken together, our results affirm the multiple stressor paradigm by showing that different aspects of WW (warming, nutrients, microbes, and MPs) jointly influence ecosystem functioning in complex ways. Increased respiration rates below WWTPs potentially generate ecosystem “disservices” via greater carbon evasion from streams and rivers. However, toxic MP effects may fundamentally alter ecological scaling relationships, indicating the need for a rapprochement between ecotoxicological and macroecological perspectives.
Global change assessments have typically ignored synthetic chemical pollution, despite the rapid increase of pharmaceuticals, pesticides, and industrial chemicals in the environment. Inputs of treated municipal wastewater are a major source of synthetic chemicals in receiving aquatic ecosystems. We found that microbial activity and decomposition rates were positively influenced by the presence of treated effluent via warming and nutrient enrichment, despite negative effects of synthetic chemicals, leading to increased respiration and estimated carbon evasion in streams and rivers.
Micropollutants enter surface waters through various pathways, of which wastewater treatment plants (WWTPs) are a major source. The large diversity of micropollutants and their many modes of toxic ...action pose a challenge for assessing environmental risks. In this study, we investigated the potential impact of WWTPs on receiving ecosystems by describing concentration patterns of micropollutants, predicting acute risks for aquatic organisms and validating these results with macroinvertebrate biomonitoring data. Grab samples were taken upstream, downstream and at the effluent of 24 Swiss WWTPs during low flow conditions across independent catchments with different land uses. Using liquid chromatography high resolution tandem mass spectrometry, a comprehensive target screening of almost 400 organic substances, focusing mainly on pesticides and pharmaceuticals, was conducted at two time points, and complemented with the analysis of a priority mixture of 57 substances over eight time points. Acute toxic pressure was predicted using the risk assessment approach of the multi-substance potentially affected fraction, first applying concentration addition for substances with the same toxic mode of action and subsequently response addition for the calculation of the risk of the total mixture. This toxic pressure was compared to macroinvertebrate sensitivity to pesticides (SPEAR index) upstream and downstream of the WWTPs. The concentrations were, as expected, especially for pharmaceuticals and other household chemicals higher downstream than upstream, with the detection frequency of plant protection products upstream correlating with the fraction of arable land in the catchments. While the concentration sums downstream were clearly dominated by pharmaceuticals or other household chemicals, the acute toxic pressure was mainly driven by pesticides, often caused by the episodic occurrence of these compounds even during low flow conditions. In general, five single substances explained much of the total risk, with diclofenac, diazinon and clothianidin as the main drivers. Despite the low predicted acute risk of 0%–2.1% for affected species, a significant positive correlation with macroinvertebrate sensitivity to pesticides was observed. However, more effect data for pharmaceuticals and a better quantification of episodic pesticide pollution events are needed for a more comprehensive risk assessment.
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•∼400 compounds analyzed upstream, downstream and at the effluent of 24 WWTP.•Sum concentrations dominated by household chemicals.•Risk driven by lower concentrated pesticides also during low flow conditions.•Only a few substances drive the total risk but lack of pharmaceutical toxicity data.•Predicted risk is correlated to observed effects on invertebrates (SPEAR index).
Stream–riparian networks are subject to multiple human pressures that threaten key functions of aquatic and terrestrial ecosystems, drive habitat and diversity losses, affect riparian connectivity ...and cause stakeholder conflicts. Designing riparian landscapes in a way that they can simultaneously meet multiple competing demands requires a clear understanding of existing trade‐offs, and a landscape‐scale perspective on the planning of reforestation measures.
This study applied a landscape optimization algorithm for allocating riparian forest management measures in the intensively used agricultural catchment of the Zwalm River (Belgium). We optimized forest allocation to improve stream ecological quality (EPT index), functional diversity (diatoms) and riparian carbon processing (cotton‐strip assay), while minimizing losses in agricultural production potential. Regression models were developed to predict the target indicators for 489 segments of the Zwalm riparian corridor, using spatial variables on three different scales. For each riparian segment, we developed spatially explicit management measures, representing different intensities of riparian reforestation. The allocation and combination of these measures in the riparian corridor were optimized to identify (a) trade‐offs among the target indicators, (b) priority regions for reforestation actions and (c) the required reforestation intensity.
The results showed that all target indicators were affected by the area share of riparian forests and its landscape‐scale configuration. Reforestation of the Zwalm riparian corridor could significantly improve indicators for biodiversity and ecosystem functioning (e.g. up to +96% for EPT index), but would lead to a strong trade‐off with agricultural production. By optimizing the placement of management measures, we showed how these trade‐offs could be best balanced.
The headwater regions of the Zwalm were identified as priority regions for reforestation actions. Facilitating connectivity among and further expansion of existing forest patches in the Zwalm headwaters showed to improve ecosystems with minimized trade‐offs.
Synthesis and applications. This study demonstrates, for the first time, the potential of landscape optimization algorithms to support the management and design of multifunctional stream–riparian networks. We identified riparian reforestation solutions that minimized trade‐offs between specific natural values and societal needs. Our spatially explicit approach allows for an integration into spatial planning and can inform policy design and implementation.
Samenvatting
Geïntegreerde waterloop‐oever‐netwerken zijn onderhevig aan veelvoudige menselijke drukken die de sleutelfuncties van aquatische en terrestrische ecosystemen bedreigen, habitat‐ en diversiteitsverliezen veroorzaken, de oeververbindingen aantasten, en daardoor vaak de conflicten tussen de belanghebbenden veroorzaken en aanwakkeren. Het ontwerpen van oeverlandschappen op een manier dat zij maximaal kunnen voldoen aan meervoudige doelstellingen vereist een duidelijk begrip van de bestaande afwegingen, en in het bijzonder een perspectief op landschapsschaal bij de planning van onder meer herbebossingsmaatregelen.
In deze studie werd een landschapsoptimalisatie‐algoritme toegepast voor de toewijzing van oeverbosbeheermaatregelen in het stroomgebied van de Zwalm (België), dat onderhevig is aan intensieve landbouwactiviteiten. Wij optimaliseerden de toewijzing van bosuitbreidingen om de ecologische kwaliteit van de beek, de functionele diversiteit en de oeverkoolstofverwerking te verbeteren, op danige wijze dat het verlies aan landbouwproductiepotentieel tot een minimum werd beperkt. Regressiemodellen werden ontwikkeld om de doelindicatoren te voorspellen voor 489 segmenten van de oeversystemen van de Zwalm, door gebruik te maken van ruimtelijke variabelen op drie verschillende schalen. Voor elk oeversegment ontwikkelden wij ruimtelijk‐expliciete beheersmaatregelen, die verschillende intensiteiten van oeverherbebossing vertegenwoordigen. De toewijzing en de combinatie van deze maatregelen in de oeversystemen werden geoptimaliseerd om (1) afwegingen tussen de doelindicatoren, (2) prioritaire regio's voor herbebossingsacties en (3) de vereiste herbebossingsintensiteit vast te stellen.
Uit de resultaten bleek dat alle doelindicatoren werden beïnvloed door het areaalaandeel van de oeverbossen en de configuratie daarvan op landschapsschaal. Herbebossing van de oevercorridor van de Zwalm zou de indicatoren voor biodiversiteit en werking van het ecosysteem aanzienlijk kunnen verbeteren, maar houdt een sterke wisselwerking met de landbouwproductie in. Door op een ruimtelijk‐expliciete manier de spreiding van beheersmaatregelen te optimaliseren, hebben wij aangetoond hoe deze verschillende noden en wensen het best in evenwicht kunnen worden gebracht.
De bovenloopgebieden van de Zwalm werden aangewezen als prioritaire gebieden voor herbebossingsacties. Het vergemakkelijken van de connectiviteit tussen en de verdere uitbreiding van de bestaande bosgebieden in de bovenloop van de Zwalm bleken de ecosystemen te verbeteren met zo weinig mogelijk nadelige compromissen.
Synthese en toepassingen. Deze studie toont voor het eerst het potentieel aan van landschapsoptimalisatie‐algoritmen om het beheer en het ontwerp van multifunctionele waterloop‐oever‐netwerken te ondersteunen. Wij hebben oeverbebossingsoplossingen geïdentificeerd die de afruil tussen specifieke natuurwaarden en maatschappelijke behoeften tot een minimum beperken. Onze ruimtelijk‐expliciete aanpak maakt een integratie in de ruimtelijke ordening mogelijk en kan hierdoor nuttige informatie verschaffen voor het ontwerpen en uitvoeren van geïntegreerd water‐ en landbeleid.
This study demonstrates, for the first time, the potential of landscape optimization algorithms to support the management and design of multifunctional stream–riparian networks. We identified riparian reforestation solutions that minimized trade‐offs between specific natural values and societal needs. Our spatially explicit approach allows for an integration into spatial planning and can inform policy design and implementation.
Multiple anthropogenic changes, such as climate change and chemical pollution, threaten the persistence of natural populations. Yet, their potential additive and interactive effects on organismal ...performance and fitness are poorly understood, thus limiting our ability to predict the effects of the global change.
We conducted a laboratory experiment to study the singular and combined effects of experimental heat waves and micropollutants (i.e. low‐concentration toxicants; henceforth micropollutants MPs) on the freshwater snail, Lymnaea stagnalis. To comprehensively understand physiological and ecological consequences of stress, we studied a broad range of traits from respiration rate to feeding performance and growth. We also determined traits contributing to fitness and immune responses, as these are key traits in determining both organismal fitness and interspecific (e.g. host–parasite) interactions. We tested whether a constant exposure to MPs affects the ability of snails to tolerate heat waves (8 days of 23.5°C), and subsequently to recover from them, and whether the effects are immediate or delayed.
We found strong immediate additive effects of both stressors on reproduction, while they synergistically increased respiration and antagonistically decreased food consumption. Moreover, these effects were transient. Although the heat wave increased metabolic rates, individuals did not increase their resource uptake. This caused an apparent imbalance in resource levels—a probable cause for the observed trade‐off between immune function and reproductive traits (i.e. phenoloxidase‐like activity decreased, while reproductive output increased). In addition, exposure to MPs led to a temporarily reduced reproductive output.
Our results indicate that even short‐term heat waves and low concentrations of chemical pollution can have large, mainly additive impacts on organismal fitness (e.g. altering susceptibility to infections and reproductive output). This suggests that long‐term effects of existing stressors and heat waves need to be considered when assessing the resilience of natural populations.
Ecosystems face multiple anthropogenic threats globally, and the effects of these environmental stressors range from individual‐level organismal responses to altered system functioning. Understanding ...the combined effects of stressors on process rates mediated by individuals in ecosystems would greatly improve our ability to predict organismal multifunctionality (e.g. multiple consumer‐mediated functions). We conducted a laboratory experiment to test direct and indirect, as well as immediate and delayed effects of a heat wave (pulsed stress) and micropollutants (MPs) (prolonged stress) on individual consumers (the great pond snail Lymnaea stagnalis) and their multifunctionality (i.e. consumption of basal resources, growth, reproduction, nutrient excretion and organic‐matter cycling). We found that stressful conditions increased the process rates of multiple functions mediated by individual consumers. Specifically, the artificial heat wave increased process rates in the majority of the quantified functions (either directly or indirectly), whereas exposure to MPs increased consumption of basal resources which led to increases in the release of nutrients and fine particulate organic matter. Moreover, snails exposed to a heat wave showed decreased reproduction and nutrient excretion after the heat‐wave, indicating the potential for ecologically relevant delayed effects. Our study indicates that the immediate and delayed effects of stressors on individual organisms may directly and indirectly impact multiple ecosystem functions. In particular, delayed effects of environmental stress on individual consumers may cumulatively impede recovery due to decreased functioning following a perturbation. Reconciling these results with studies incorporating responses at higher levels of biological complexity will enhance our ability to forecast how individual responses upscale to ecosystem multifunctionality.
The growing threat of global climate change has led to a profusion of studies examining the effects of warming on biota. Despite the potential importance of natural variability such as diurnal ...temperature fluctuations, most experimental studies on warming are conducted under stable temperatures. Here, we investigated whether the responses of an aquatic invertebrate grazer (Lymnaea stagnalis) to an increased average temperature differ when the thermal regime is either constant or fluctuates diurnally. Using thermal response curves for several life‐history and immune defense traits, we first identified the optimum and near‐critically high temperatures that Lymnaea potentially experience during summer heat waves. We then exposed individuals that originated from three different populations to these two temperatures under constant or fluctuating thermal conditions. After 7 days, we assessed growth, reproduction, and two immune parameters (phenoloxidase‐like activity and antibacterial activity of hemolymph) from each individual. Exposure to the near‐critically high temperature led to increased growth rates and decreased antibacterial activity of hemolymph compared to the optimum temperature, whilst temperature fluctuations had no effect on these traits. The results indicate that the temperature level per se, rather than the variability in temperature was the main driver altering trait responses in our study species. Forecasting responses in temperature‐related responses remains challenging, due to system‐specific properties that can include intraspecific variation. However, our study indicates that experiments examining the effects of warming using constant temperatures can give similar predictions as studies with fluctuating thermal dynamics, and may thus be useful indicators of responses in nature.
We investigated whether the responses of an aquatic invertebrate grazer to optimal and high average temperatures differ when the thermal regime is either constant or fluctuates diurnally. The results indicate that the temperature level per se, rather than the variability in temperature was the main driver altering trait responses. Our study indicates that experiments examining the effects of warming using constant temperatures can give similar predictions as studies with fluctuating thermal dynamics, and may thus be useful indicators of responses in nature.
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