1,720,972 research outputs found
The year after an extraordinary sedimentation event in a regulated Alpine river: The impact on benthic macroinvertebrate communities
No full textOn August 2017, a massive rock slope failure triggered an extreme sedimentation event in a regulated Alpine river. Consequently, high sediment load affected the river for about 1 month, with sediment concentration peaking up to several hundred g/L, and overall sediment yield of 0.4–0.8 Mm3. The availability of sound pre-event data concerning benthic macroinvertebrate assemblages gave us the opportunity to assess the impact of this unusually severe sediment disturbance through before/after comparison. Within 1 month from the event, all the monitored communities displayed low density, richness and diversity, with minimum values never recorded before, particularly at the most upstream investigated reach, and where riverbed aggradation was comparatively larger. Persisting riverbed alteration was also identified as a major determinant justifying the slow recovery observed during the year after the event. Overall, the high resilience of some taxa, suited to a baseline unnatural condition, allowed the fast recolonization of the investigated river reaches. However, the recovery of other taxa, more sensitive to sediment pressure, was slow or did not occur during the monitored year
Erosione localizzata al piede di ostacoli in alveo: studio sperimentale su un dispositivo di controllo
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Climate change and water exploitation as co-impact sources on river benthic macroinvertebrates
No full textClimate change can affect freshwater communities superimposing on other major stressors, such as water exploitation, with effects still poorly understood. The exacerbation of naturally-occurring periods of low flows has been reported as a major hydrological effect of water diversions, with severe impacts on river benthic macroinvertebrate communities. This study aimed at assessing long-term modifications of low-flow events in a large lowland Italian river possibly associated to climate change and the effects of these events, intensified by water withdrawals, on benthic macroin-vertebrates. A 77-year dataset on daily discharge was thus analyzed through Mann-Kendall test and Sen’s method to investigate modifications of the main hydrological parameters. Moreover, macroinvertebrates were collected during the low-flow periods that occurred from 2010 to 2015 at three sites downstream of water withdrawals, representing three different conditions of hydrological impairment. After assessing possible differences in taxonomical and functional composition between sites and impairment conditions, redundancy analysis and ordinary least squares regression were performed to link benthos metrics to environmental (hydrological and physico-chemical) characteris-tics. An increase in the duration of the low-flow periods and reduced summer flows were detected on the long term, and the magnitude of low flows was significantly altered by water withdrawals. These hydrological features shaped both structural and functional characteristics of benthic assemblages, highlighting the need for a more environmentally-sustainable water resource management in the current context of climate change
Response of benthic macroinvertebrates to different hydropower off-stream diversion schemes
No full textDespite significant advancement in environmental flow science, the release of minimum flows (MFs) still represents one of the main measures globally adopted to mitigate off-stream diversion in regulated rivers. In the Lake Como basin (Italy), we monitored water-depleted reaches below hydropower reservoirs and intakes and reaches unimpacted by water withdrawal. Our aim was to verify if the gradient in streamflow alterations resulted in detectable differences in the structure and functions of benthic assemblages, possibly identifying streamflow metrics explaining the observed differences. The macroinvertebrate assemblages sampled below reservoirs showed significant differences from those from unimpacted reaches, including the reduced relative richness of Ephemeroptera, Plecoptera and Trichoptera (mainly stoneflies) and the higher abundance and richness of dipterans. These differences were well explained by the corresponding streamflow pattern, characterized by a rather constant flow throughout the year, occasionally interrupted by sharp peaks related to spilling episodes. In contrast, the shift from unimpacted conditions was minor for benthic assemblages collected at reaches below intakes, where the seasonal streamflow variation was partly preserved. Our results suggest that an increase of the e-flow released by hydropower dams during the seasons characterized by larger run-offs could support improved benthic assemblages. Dewatered river sections below reservoirs could thus be prioritized for updating the current MF management, in the study area as well as in comparable contexts. At least to our knowledge, specific investigations are so far unavailable regarding the exploration of the different responses of benthic macroinvertebrates to intakes and reservoirs operations
Juvenile fish stranding induced by upstream gate operation: A risk assessment through eco-hydraulic modeling
No full textRapidly changing flows in regulated rivers can significantly impair freshwater biotas. At present, this issue is mostly addressed by hydropeaking research. In contrast, only limited information is available concerning the environmental effects of sharp streamflow variations determined by manmade manipulation other than hydroelectricity generation.In this paper, we assessed the stranding risk of juvenile marble trout (Salmo marmoratus), an endemic species of particular interest in the study area, during rapid streamflow decrease controlled by upstream gate operation. Our investigation focused on the falling limb of a regulated flood hydrograph in a residual-flow reach of the Ticino River, located few kilometers below its outlet from Lake Maggiore (Northern Italy).The stranding risk assessment was carried out by coupling two-dimensional unsteady flow simulation and standard habitat suitability modeling. Specifically, we adopted univariate habitat suitability curves, and a threshold for the critical rate of decrease of the water surface elevation (downramping rate), commonly used in hydropeaking assessments. Our results evidenced potential stranding occurrence of the target fish species, and possible mitigation by reducing the rate of streamflow decrease before restoring the minimum flow after flood spilling. However, more reliable estimates, including partitioning the stranding risk into classes, are challenged in our opinion by difficulties arising from extensive field validation and related selection of model parameters.In a global context characterized by the urgent need of mitigating the hydro-morphological alteration of regulated rivers, we are confident that the presented approach could support an improved streamflow management in river reaches below reservoirs and regulated lakes, therefore arousing attention and research advancement by the scientific community
Impacts of fine sediment input on river macroinvertebrates: the role of the abiotic characteristics at mesohabitat scale
No full textInstream hydraulics and riverbed substrate allow for the identification of mesohabitats, and contribute in shaping benthic macroinvertebrate assemblages. However, the role of different depositional conditions between mesohabitats in determining macroinvertebrate response to large sediment input still needs investigation. We studied the evolution of sediment deposits and benthic assemblages in two mesohabitats (a riffle and a glide) of an Alpine river affected by an extreme sediment input. Substrate and hydraulic characteristics were measured in each mesohabitat for 18 months after the sedimentation event. Benthic macroinvertebrates were sampled concurrently, and available pre-event data allowed for before/after comparison. We found evidence of a different response of benthic communities to siltation, associated to the physical structure of the mesohabitat they inhabit. Both substrate and macroinvertebrates were less impacted and recovered faster in the riffle than in the glide. Assemblages in the glide adjusted to the modified habitat through strong proliferation of sand tolerant and preferring families, resulting in higher density and lower diversity compared to the riffle. Our results could support the improvement of the impact assessment of sediment input events. This is particularly relevant given the current global warming, inducing the increase in frequency and intensity of severe rainfall events, and subsequent landslides
Assessing the impacts of hydropeaking on river benthic macroinvertebrates: A state-of-the-art methodological overview
Full text linkAs the global demand for renewable electricity grows, hydropower development of river basins increases across the world. Hydropeaking, i.e., streamflow alteration consisting of daily or subdaily rapid and marked discharge fluctuations, can affect river reaches below hydropower units. Environmental effects of hydropeaking include geomorphological alterations and possible modifications of the freshwater biota. Among affected instream communities, benthic macroinvertebrates are receiving increasing attention and the related scientific research has experienced significant progress in the last decade. In this context, this paper aims to summarize state-of-the-art methods for the assessment of hydropeaking impacts on benthic macroinvertebrate communities. The present review could support the proper design of monitoring plans aimed at assessing the ecological impacts of hydropeaking and the effects of possible mitigation strategies
Considering mesohabitat scale in ecological impact assessment of sediment flushing
Full text linkBenthic macroinvertebrates respond to several factors characterizing the physical habitats, as water depth, current and streambed substrate. Thus, anthropogenic disturbances altering these factors may have different effects on benthos, also depending on mesohabitats. These disturbances include sediment flushing operations, commonly carried out to recover reservoir capacity, and investigating their effects at mesohabitat scale could be relevant for an adequate ecological impact assessment of these operations. Here, we compared benthic macroinvertebrate communities sampled before and after a controlled sediment flushing operation in three different mesohabitats (a pool, a riffle and a step-pool) of an Alpine stream. Contrary from expectations, the composition of macroinvertebrate assemblages was not significantly different among mesohabitats. Moreover, the impact of sediment flushing was more significant in terms of density rather than in richness. Two stressor-specific indices were tested, but only one (the Siltation Index for LoTic EcoSystems - SILTES) clearly detected the impact of sediment flushing on the macroinvertebrate community structure. Finally, some differences in the temporal trajectories and recovery times to pre-flushing conditions were observed among mesohabitats, both if the three mesohabitats were considered separately and if all their possible combinations were accounted for. Particularly, riffle was the most sensitive mesohabitat, not fully recovering one year after the sediment disturbance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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