Academic literature on the topic 'Macroinvertebrates, alpine river'

Hydromorphological alterations influence a wide range of environmental conditions as well as riparian vegetation and the structure of the macroinvertebrate community. We studied relationships between the structure and diversity of the macroinvertebrate community and hydromorphological and other environmental conditions in the river Gradaščica (central Slovenia). The Gradaščica river is a pre-Alpine torrential river that has been morphologically altered by humans. A selection of abiotic factors was measured, the ecomorphological status of the river was assessed, vegetation in the riparian zone was surveyed and benthic macroinvertebrates were sampled. Correlations between diversity and the structure of the macroinvertebrate community, environmental parameters and occurrence of invasive alien plant species in the riparian zone were identified. The significance of the influence of environmental parameters on the structure of the macroinvertebrate community was examined. We found that hydromorphological alterations in the river have had a significant influence on the diversity and composition of the macroinvertebrate community because of changes of flow velocity and the spread of invasive alien plant species that has followed those changes. Factors that also significantly influence the composition of macroinvertebrate community are distance from the source and conductivity. Our findings suggest minimization of further human hydromorphological changes of watercourses could prevent the loss of biodiversity of riverine ecosystems.

While macroinvertebrates are extensively investigated in many river ecosystems, meta-community ecology perspectives in alpine streams are very limited. We assessed the role of ecological factors and temporal dynamics in the macroinvertebrate meta-community assembly of an alpine stream situated in a dry-hot valley of Baima Snow Mountain, China. We found that spatial structuring and environmental filtering jointly drive the structure of macroinvertebrate meta-community, with relative contributions to the variance in community composition changing over time. RDA ordination and variation partitioning indicate that environmental variables are the most important predictors of community organization in most scenarios, whereas spatial determinants also play a significant role. Moreover, the explanatory power, identity, and the relative significance of ecological factors change over time. Particularly, in the years 2018 and 2019, stronger environmental filtering was found shaping community assembly, suggesting that deterministic mechanisms predominated in driving community dynamics. However, spatial factors had a stronger predictive power on meta-community structures in 2017, implying conspicuous dispersal mechanisms which may be owing to increased connectivity amongst sites. Thereby, we inferred that the alpine stream macroinvertebrate metacommunity composition can be regulated by the interaction of both spatial processes and environmental filtering, with relative contributions varying over time. Based on these findings, we suggest that community ecology studies in aquatic systems should be designed beyond single snapshot investigations.

Introduced fish can have detrimental effects on native biota inhabiting alpine freshwaters with the extent of their impact depending on variables such as habitat features. The present study aims to compare the recovery of macroinvertebrate communities following a fish eradication campaign in a mountain lake (Lake Dres, 2087 m a.s.l., Western Italian Alps) and its inflowing and outflowing streams. All fish were removed using mechanical methods, not producing side-effects for macroinvertebrates. During eradication, the lake community, which had previously been greatly affected, rapidly recovered to levels typical of never-stocked lakes. Stream communities, however, were apparently not impacted by fish populations and remained relatively stable, proving their greater capacity to withstand fish presence. The abundance of spatial refugia and invertebrate recruitment (via birth or immigration) can explain the observed stability in stream communities. Drifting macroinvertebrates are often called into question to explain the resistance of stream communities as they can partially offset predation via benthic recruitment, but our results show that stream resistance can be high even where drift is low, i.e., in the outflowing stream.

The Sub-Saharan alpine freshwater biodiversity is currently impacted by human settlements, climate change, agriculture, and mining activities. Because of the limited biodiversity studies in the region, a better understanding is needed of the important environmental variables affecting macroinvertebrate assemblages. In this paper, macroinvertebrate diversity responses to 18 environmental variables were studied at 30 sites along unique Rwenzori rivers at the equator in Uganda. We hypothesized that anthropogenic disturbance and local environmental variables affect macroinvertebrate diversity, irrespective of altitudinal gradients. Based on altitude and climate, the sites were subdivided into three altitude groups consisting of 10 sites each: upstream (US) 1400–1600 m.a.s.l.; midstream (MS) 1091–1399 m.a.s.l., and downstream (DS) 900–1090 m.a.s.l. A total of 44 macroinvertebrate families and 1623 individuals were identified. The macroinvertebrate diversity patterns were influenced by temperature, altitude, and latitude. Regression analysis revealed that temperature and nickel, were negative predictors of taxa richness. Nickel, which is released by mining activity, is detrimental to aquatic communities in Sub-Saharan alpine ecosystems. Significant longitudinal variation in macroinvertebrate diversity was observed between the sites, which were also affected by mineral and temperature gradients. Our study highlights the need for long-term monitoring in this region to detect and reduce the threats to river biodiversity from anthropogenic activity.

Exploitation of hydropower potential in alpine areas undermines the ecological integrity of rivers. Damming and water abstraction substantially alter the physical habitat template of rivers, with strong repercussions on aquatic communities and their resources. Tools are needed to predict and manage the consequences of these alterations on the structure and functioning of macroinvertebrate communities and resource availability in alpine streams. We developed habitat preference models for taxa, functional feeding guilds, and organic resources to quantify the effects of discharge alteration on macroinvertebrate communities in two alpine streams. Our physical habitat model related an indirect measure of bottom hydraulic forces (FST hemispheres) to the distribution of macroinvertebrate taxa and their resources. We observed that flow-dependent habitat availability for macroinvertebrate communities generally decreased with increasing water abstraction. We were able to relate these changes to near-bed hydraulic conditions. Our results suggest, however, the existence of upper discharge thresholds delimiting optimal habitat conditions for taxa. In contrast, we found weak effects of near-bed hydraulic conditions on resource distribution. Overall, our findings contribute towards predicting the impacts of water abstraction on macroinvertebrate communities in small alpine streams and the benefits of baseflow restoration.

Streams and rivers are becoming increasingly intermittent in Alpine regions due to the global climate change and related increases of local water abstractions, making it fundamental to investigate the occurrence of supraseasonal drying events and their correlated effects. We aimed to investigate leaf litter decomposition, the C:N ratio of the litter, and changes in associated macroinvertebrate communities in three reaches of the Po River: One upstream, consistently perennial, a perennial mid-reach with high hydrological variability, and an intermittent downstream reach. We placed leaf litter bags of two leaf types—chestnut and oak; both showed comparable decomposition rates, but the remaining litter mass was different and was attributed to the C:N ratio and palatability. Furthermore, (1) in perennial reaches, leaf litter decomposed faster than in the intermittent ones; (2) in intermittent reaches, the C:N ratio showed a decreasing trend in both leaf types, indicating that drying affected the nitrogen consumption, therefore the conditioning phase; (3) associated macroinvertebrate communities were richer and more stable in perennial reaches, where a higher richness and abundance of EPT taxa and shredders was observed. Our results suggest that the variations in the hydrology of mountain streams caused by global climate change could significantly impact on functional processes and biodiversity of benthic communities.

Abstract Rivers are heterogeneous and patchy-structured systems in which regional biodiversity of aquatic communities typically varies as a function of local habitat conditions and spatial gradients. Understanding which environmental and spatial constraints shape the diversity and composition of benthic communities is therefore a pivotal challenge for basic and applied research in river ecology. In this study, benthic invertebrates were collected from 27 sites across three hydro-ecoregions with the aim of investigating patterns in α- and β diversity. We first assessed the contribution to regional biodiversity of different and nested spatial scales, ranging from micro-habitat to hydro-ecoregion. Then, we tested differences in α diversity, taxonomic composition and ecological uniqueness among hydro-ecoregions. Variance partitioning analysis was used to evaluate the mechanistic effects of environmental and spatial variables on the composition of macroinvertebrate communities. Macroinvertebrate diversity was significantly affected by all the spatial scales, with a differential contribution according to the type of metric. Sampling site was the spatial scale that mostly contributed to the total richness, while the micro-habitat level explained the largest proportion of variance in Shannon–Wiener index. We found significant differences in the taxonomic composition, with 39 invertebrate families significantly associated with one or two hydro-ecoregions. However, effects of environmental and spatial controls were context dependent, indicating that the mechanisms that promote beta diversity probably differ among hydro-ecoregions. Evidence for species sorting, due to natural areas and stream order, was observed for macroinvertebrate communities in alpine streams, while spatial and land-use variables played a weak role in other geographical contexts.

AbstractAlpine and pre-alpine lotic ecosystems are often remote and not affected by humans, which makes them some of the world’s most pristine ecosystems. However, their status is often altered by the presence of reservoirs that are built to fulfill agricultural needs and hydroelectric demands. These reservoirs also disrupt stream continuity and alter the magnitude, timing, and frequency of natural flows. The present work assessed how high-altitude reservoirs affect the riverine ecosystems focusing on the following: (i) the macroinvertebrate communities, (ii) the breakdown of organic matter, and (iii) the thermal regime. Stretches altered by high-altitude reservoirs had the best conditions for most macroinvertebrate families due to a more stable flow conditions. The breakdown rate of coarse particulate organic matter was not affected by high-altitude reservoirs but its availability was higher in altered compared to pristine stretches. The presence of hydroelectric power plants modified the stream thermal regime. Reservoirs mitigate the atmospheric influence on stream water temperature while run of the river plants strengthen it in the diverted stretches. Where both these alterations were present, the thermal regime of the stream was more similar to the natural ones compared to stretches subjected to only one kind of alteration. This research showed how river impoundment alters the structure of macroinvertebrate communities and the function of the downstream lotic ecosystems and can provide the basis to correctly guide management strategies for lotic ecosystems affected by hydrological alterations.

Anthropic impacts adversely affect the productivity, integrity, connectivity, and resilience of riverine ecosystems, with widespread cumulative effects on the biota and biodiversity. The natural flow regime is a fundamental driver of physical and chemical processes, determining the morphological profile of the river systems and sustaining the complex network of ecological interactions and biological patterns. Therefore, in order to reach the environmental goals required by the binding legislation, and achieve a sustainable use of water resources, it is urgent to understand the mechanisms behind changes in the structure of biological communities along gradients of human disturbances which affect the flow regime. Indicators based on macroinvertebrates are widely used to assess the ecological status of water bodies, given their sensitivity/tolerance to pollution. However, in Alpine running waters, where chemical quality is less impacted than in lowland rivers, it is particularly important and valuable to detect the hydro-morphological alterations, and to discriminate them from chemical degradation, based on the responses of benthic macroinvertebrates to such multiple stressors. Therefore, this thesis aims at: i) examining the taxonomic and functional responses of macroinvertebrate communities to the different anthropogenic pressures acting on river systems; ii) evaluating the taxa/functional traits which mostly discriminate between hydrological and morphological alterations, and chemical degradation, to support effective bioindication methods. Focus of the research is to assess the macroinvertebrate community responses to the alterations caused by flow regulation and morphological alterations, which include water abstraction, diversion, stocking and the intermittent release of water from hydropower plants, banks artificialization and construction of weirs, dams, and other structures, each of these with environmental consequences of different scale and magnitude, such as the interruption of the longitudinal continuity, residual flow release and hydropeaking. The first part of this thesis is based on two empirical field studies, following respectively a manipulative and a mensurative approach, and focuses on changes in the taxonomic and functional composition due to river regulation and hydrological alterations. The first study, conducted in a set of seminatural streamside experimental flumes, simulates a residual flow stretch by reducing the discharge of the downstream sections (treatment) to 50% of the discharge of the upstream sections (control). Even within the short-term of our experiment (i.e., 3 weeks from the beginning of the simulation), we successfully simulated a small run-of-the river water abstraction and we recorded substantial changes in the EPT (Ephemeroptera, Plecoptera and Trichoptera) benthic assemblages. In fact, we observed shifts in functional (rather than taxonomic) EPT community composition over time, likely due to the active drift, from a typically rheophile to a more limnophile one as a response to the stress imposed by the flow reduction, related to decrease of flow. In the second study, we investigated the effectiveness of a hydropeaking mitigation measure on flow and biotic components, in a case study of hydropeaking reduction on a 10-km reach of the Noce Stream, a unique approach for Alpine streams to date. The hydrological analysis conducted applying two hydropeaking quantification indices (HP1 and HP2 of Carolli et al., 2015, and the COSH method by Sauterleute & Charmasson. 2014) confirmed a partial mitigation of the hydropeaking in the stretch. As a consequence of the change in hydrological regime, we observed a different taxonomic and functional recovery in the benthic and hyporheic communities. In fact, macrobenthos was negatively affected by the reduced dilution of point and diffuse pollution; conversely, the hyporheic communities showed an increase in diversity and abundance of interstitial taxa, especially those exclusive to the hyporheic zone, likely due to changes in the interstitial space availability, brought by a reduction of clogging caused by fine sediments which were previously released with each hydropeaking wave. The second part of the thesis is based on large dataset analysis where expert knowledge has been integrated with machine learning and data-based approaches: the focus of thesis shifts towards a holistic approach, extending the investigation to the entire watershed of the Trentino Province by including macroinvertebrate field data collected between 2009 and 2019 from 160 sampling sites, distributed over 90 rivers and streams. Based on the expertise of field operators from the local Environment Agency (APPA), and the quality indices currently used according to the Water Framework Directive (WFD), all the APPA stream sites were classified according to the presence of known hydrological, morphological, and chemical alterations, including the co-occurrence of two or more alteration types; sites in pristine conditions were also identified. Seasonality, stream order and type, and other stream characteristics associated with the elevation gradient are important in flow-ecology investigation, and for this reason were included in the analysis. Moreover, these features are proxies for other variables which are closely related with the structure of the benthic community, such as current velocity, organic matter availability and substrate composition, and can also be related to the probability of expecting the presences of small hydropower plants and/or a diffuse or localized pollution sources. This second section of the thesis is divided into two parts: the first part describes the initial overall qualitative and quantitative analysis, which was conducted to determine to which extent a functional diversity-based approach better recognizes patterns in the benthic community compared to the WFD diversity indices. The second part describes the machine learning approach which we used to examine the degree to which a-priori expert classification matched data-driven classification based on the taxonomic and functional composition of benthic macroinvertebrates across different binary classification disturbances. A Random Forest analysis was performed independently on benthic-macroinvertebrate abundance (expressed as number of individuals per m2) and their functional compositions. The majority of stream sites were a-priori classified as impacted by either one or a combination of anthropogenic alterations (80%), with only 16% of sites in reference or pristine conditions. We observed high variability in benthic community assemblages, likely due to complex environmental interactions and caused by the cumulative/synergic effect of different alterations that negatively affect the discrimination between stressor-specific responses. The overall results of these large-dataset based analyses showed relevant outcomes, the main one being the good discrimination of unaltered sites from the altered ones, but a low discriminating power for the types of alteration (hydrological, morphological, pollution pf combination of two or three of them) based on taxonomic and functional composition of the benthic communities. The functional parameters directly related to the stream longitudinal preference, microhabitat preferences, flow velocity, hydrological and thermal regime, and food availability in the river network, well the most suitable to identify any type of river degradation. A further step in the detection of significant indicator taxa/traits was achieved with the machine learning approach, which resulted in robust and dependable predictive models, that identified the specific taxa and traits related to different stressors, thus representing a promising tool to support environmental assessment and water management. Overall, this thesis contributes to the identification of appropriate indicators based on macroinvertebrates taxonomic and functional sensitivity to different specific stressors, to use in the assessment of the Ecological Status of streams in mountain areas, with relevant outcomes for the water management of Alpine running waters, with particular regard to the definition of environmental flows, and to the mitigation of hydropeaking.

Anthropic impacts adversely affect the productivity, integrity, connectivity, and resilience of riverine ecosystems, with widespread cumulative effects on the biota and biodiversity. The natural flow regime is a fundamental driver of physical and chemical processes, determining the morphological profile of the river systems and sustaining the complex network of ecological interactions and biological patterns. Therefore, in order to reach the environmental goals required by the binding legislation, and achieve a sustainable use of water resources, it is urgent to understand the mechanisms behind changes in the structure of biological communities along gradients of human disturbances which affect the flow regime. Indicators based on macroinvertebrates are widely used to assess the ecological status of water bodies, given their sensitivity/tolerance to pollution. However, in Alpine running waters, where chemical quality is less impacted than in lowland rivers, it is particularly important and valuable to detect the hydromorphological alterations, and to discriminate them from chemical degradation, based on the responses of benthic macroinvertebrates to such multiple stressors. Therefore, this thesis aims at: i) examining the taxonomic and functional responses of macroinvertebrate communities to the different anthropogenic pressures acting on river systems; ii) evaluating the taxa/functional traits which mostly discriminate between hydrological and morphological alterations, and chemical degradation, to support effective bioindication methods. Focus of the research is to assess the macroinvertebrate community responses to the alterations caused by flow regulation and morphological alterations, which include water abstraction, diversion, stocking and the intermittent release of water from hydropower plants, banks artificialization and construction of weirs, dams, and other structures, each of these with environmental consequences of different scale and magnitude, such as the interruption of the longitudinal continuity, residual flow release and hydropeaking. The first part of this thesis is based on two empirical field studies, following respectively a manipulative and a mensurative approach, and focuses on changes in the taxonomic and functional composition due to river regulation and hydrological alterations. The first study, conducted in a set of seminatural streamside experimental flumes, simulates a residual flow stretch by reducing the discharge of the downstream sections (treatment) to 50% of the discharge of the upstream sections (control). Even within the short-term of our experiment (i.e., 3 weeks from the beginning of the simulation), we successfully simulated a small run-of-the river water abstraction and we recorded substantial changes in the EPT (Ephemeroptera, Plecoptera and Trichoptera) benthic assemblages. In fact, we observed shifts in functional (rather than taxonomic) EPT community composition over time, likely due to the active drift, from a typically rheophile to a more limnophile one as a response to the stress imposed by the flow reduction, related to decrease of flow. In the second study, we investigated the effectiveness of a hydropeaking mitigation measure on flow and biotic components, in a case study of hydropeaking reduction on a 10-km reach of the Noce Stream, a unique approach for Alpine streams to date. The hydrological analysis conducted applying two hydropeaking quantification indices (HP1 and HP2 of Carolli et al., 2015, and the COSH method by Sauterleute & Charmasson. 2014) confirmed a partial mitigation of the hydropeaking in the stretch. As a consequence of the change in hydrological regime, we observed a different taxonomic and functional recovery in the benthic and hyporheic communities. In fact, macrobenthos was negatively affected by the reduced dilution of point and diffuse pollution; conversely, the hyporheic communities showed an increase in diversity and abundance of interstitial taxa, especially those exclusive to the hyporheic zone, likely due to changes in the interstitial space availability, brought by a reduction of clogging caused by fine sediments which were previously released with each hydropeaking wave. The second part of the thesis is based on large dataset analysis where expert knowledge has been integrated with machine learning and data-based approaches: the focus of thesis shifts towards a holistic approach, extending the investigation to the entire watershed of the Trentino Province by including macroinvertebrate field data collected between 2009 and 2019 from 160 sampling sites, distributed over 90 rivers and streams. Based on the expertise of field operators from the local Environment Agency (APPA), and the quality indices currently used according to the Water Framework Directive (WFD), all the APPA stream sites were classified according to the presence of known hydrological, morphological, and chemical alterations, including the cooccurrence of two or more alteration types; sites in pristine conditions were also identified. Seasonality, stream order and type, and other stream characteristics associated with the elevation gradient are important in flow-ecology investigation, and for this reason were included in the analysis. Moreover, these features are proxies for other variables which are closely related with the structure of the benthic community, such as current velocity, organic matter availability and substrate composition, and can also be related to the probability of expecting the presences of small hydropower plants and/or a diffuse or localized pollution sources. This second section of the thesis is divided into two parts: the first part describes the initial overall qualitative and quantitative analysis, which was conducted to determine to which extent a functional diversitybased approach better recognizes patterns in the benthic community compared to the WFD diversity indices. The second part describes the machine learning approach which we used to examine the degree to which a-priori expert classification matched data-driven classification based on the taxonomic and functional composition of benthic macroinvertebrates across different binary classification disturbances. A Random Forest analysis was performed independently on benthicmacroinvertebrate abundance (expressed as number of individuals per m2) and their functional compositions. The majority of stream sites were a-priori classified as impacted by either one or a combination of anthropogenic alterations (80%), with only 16% of sites in reference or pristine conditions. We observed high variability in benthic community assemblages, likely due to complex environmental interactions and caused by the cumulative/synergic effect of different alterations that negatively affect the discrimination between stressor-specific responses. The overall results of these large-dataset based analyses showed relevant outcomes, the main one being the good discrimination of unaltered sites from the altered ones, but a low discriminating power for the types of alteration (hydrological, morphological, pollution pf combination of two or three of them) based on taxonomic and functional composition of the benthic communities. The functional parameters directly related to the stream longitudinal preference, microhabitat preferences, flow velocity, hydrological and thermal regime, and food availability in the river network, well the most suitable to identify any type of river degradation. A further step in the detection of significant indicator taxa/traits was achieved with the machine learning approach, which resulted in robust and dependable predictive models, that identified the specific taxa and traits related to different stressors, thus representing a promising tool to support environmental assessment and water management. Overall, this thesis contributes to the identification of appropriate indicators based on macroinvertebrates taxonomic and functional sensitivity to different specific stressors, to use in the assessment of the Ecological Status of streams in mountain areas, with relevant outcomes for the water management of Alpine running waters, with particular regard to the definition of environmental flows, and to the mitigation of hydropeaking.