Effects Of Dams Research Articles

Damming effects on hydrological abundance and eco-hydrological alteration in upstream wetlands of Eastern Himalaya

The effects of dams on hydrological conditions and ecological functioning of wetlands downstream are less well studied. Rivers and wetlands are vital environmental elements linked to natural and human ecosystems, so it is extremely important to study ecohydrological planning and human well-being. This study investigates the impact of the dam on the hydrological abundance and eco-hydrological alterations of Loktak Lake, which is located upstream of the Ithai barrage. For this purpose, the Indicator of Hydrological Alteration (IHA) was used to examine the ecohydrological threshold, failure rate, impact magnitude and ecohydrological deficit/surplus in a river section and the adjacent wetland in three temporal phases (I, 1996–2001; II, 2006–2011; and III, 2016–2021). The results show that the hydrological surplus has recently increased to 27.22% (phase III), while in phase I it was only 1.1%. Due to the decreasing failure rate of ecological optima, eco-hydrological surplus was recorded in both Loktak lakes, which is an obvious indication of a reduction in ecological distress that may lead to negative impacts on natural and human well-being. However, due to the constant high-water level in the lake, Phumdi is no longer able to reach the bottom of the lake during the dry season. Since it cannot absorb nutrients, the lake's vegetation declines and rotting sediments settle. Since the Ithai Dam closed the outlet that once connected the lake to the sea, fishermen can no longer dispose of the decomposing biomass. This study is important for dam management and planning to consider the impacts on wetlands downstream and to take measures to mitigate these impacts.

Considering dispersal costs to understand fish community dissimilarity in a high‐gradient basin of North America

AbstractFreshwater fish metacommunities are best understood when considering the dendritic structure of riverine networks. The dendritic structure imposes restrictions to dispersal associated with the connectivity. Many structures restrict the movement of fish even more, such as dams and the terrain slope (dispersal costs). We investigated the influence of environmental predictors and dispersal costs on the beta diversity of freshwater fishes from the Upper Tennessee River using Generalised Dissimilarity Modelling (GDM). In addition, we tested the effects of asymmetrical dispersal costs (high costs for upstream dispersal) on the nestedness of native and non‐native fishes. Environmental predictors were more important than dispersal costs for explaining the overall fish dissimilarity in the GDM models, with the turnover capturing most of the explanation compared to the species richness difference. Dam heights were the most important dispersal cost variable in the GDM, mainly for species turnover. Overall dissimilarity of the native fish subset was better explained by environmental and dispersal variables than non‐native fish (20.03% vs. 8.41%). Considering the native species assemblage subset, dispersal cost related to maximum channel slope between pairs of sites and watercourse distance increased the nestedness of adjacent upstream–downstream sites, whereas those attributed to dams reduced the nestedness. The results support that dams increase overall dissimilarity in the native fish metacommunity of the Upper Tennessee basin, but also reduce the nestedness of adjacent sites. Our findings improve the knowledge on how mechanisms and processes associated with dispersal costs in watersheds under the effects of dams create patterns of dissimilarity and nestedness.

Impacts of the High-Pressure Bratskoye Hydroelectric Power Station on the Zooplankton of the Bratskoye Reservoir

During the growing season of 2022, the studies were carried out in the water area of the Bratsk Reservoir (the Angara River) and in the near-dam site of the Bratsk high-level hydroelectric power station. The ecological effects of the hydroelectric dam on the zooplankton in the regulated section of the river were studied and the impact of the zooplankton downstream drift on the feeding conditions of the fish in the Bratsk Reservoir was assessed. It is established that the water column stratification is a significant factor in the ecological differentiation of plankton communities in the upper reaches of the hydroelectric power station. Unlike the warmed-up layer of the epilimnion, a specific, poor in species, low-abundant and low-productive plankton develops in the cold-water hypolimnion, which enters the dam intakes. A rigorous analysis does not reveal a transformation of the community composition, a statistically significant decrease in abundance and productivity, increased mortality of invertebrates during their passage through the dam, deterioration of the water ecological quality in the lower reaches of the hydroelectric power station. Both live and dead zooplankton drifting downstream from the reservoir makes up a significant proportion of the diet of fish, which during the feeding period come as close as possible to the hydroelectric power station and form aggregations exceeding those in the water area of the Bratsk Reservoir in density. The data obtained testify to the effective adaptation of lake-river planktocenosis to the specific natural and technogenic mode of operation of a large hydraulic structure. The local impact of the Bratsk hydroelectric power station has no ecologically significant negative effect on the plankton of the Bratsk Reservoir and the Angara River ecosystems and has a positive effect on the fish population in the lower reaches through the enrichment of its forage base.

Revisiting the Impact of Dams on Malaria and Agriculture

We estimate the effect of large dams on malaria incidence in India between 1975 and 1995. We combine instrumental variables approach with a panel model with unobserved common factors allowing us to fully capture the endogeneity of dam location and unobserved time-varying heterogeneity. Dams result in increased malaria incidence in districts where dams are located and in downstream areas. We find that the construction of a large dam increases a district’s annual malaria incidence by about 0.9 to 1.4 percent, and by about 1 to 1.5 percent in downstream districts. We also find that this malaria-increasing effect of dams persists over time. Our results imply that the construction of dams in malaria-sensitive areas should be coupled with direct interventions, such as the wide deployment of insecticide-treated nets or the roll-out of future vaccines. Furthermore, we examine the contribution of agricultural development to this malaria-increasing effect of dams. We find that dam construction benefits agriculture in the vicinity of dams, as well as in downstream areas. These positive effects are driven by increased irrigation and cultivation in the vicinity of dams, while they are driven by changes in cropping patterns in downstream areas, where the cultivation of high-yielding variety crops increases. Finally, a back-of-the-envelope calculation suggests that the agricultural production gains from dam construction dominate the economic losses resulting from increased malaria.

Cumulative effects of dams on migratory fishes across the conterminous United States: Regional patterns in fish responses to river network fragmentation

AbstractGlobally, dams fragment river networks, threatening migratory fishes which require access to distinct habitats to complete their life cycles. Efforts to understand how cumulative effects of multiple dams affect migratory fishes across large regions, such as a country or continent, could help to identify locations for connectivity‐enhancing actions to conserve migratory fishes. To address this, we evaluated cumulative effects of dams on migratory fishes in rivers across nine ecoregions of the conterminous USA. First, using fish data from thousands of sites (N = 45,989), we summarized ecoregional patterns in assemblages, quantifying the number of migratory species comprising assemblages, showing the prominence of potamodromous species across the large region as well as differences in migratory life history traits among ecoregions. Next, we compared the importance of a set of river network fragmentation metrics that captured influences of multiple dams in networks versus other anthropogenic landscape stressors and natural landscape factors that impact migratory fishes by ecoregion. We found that migratory fishes were more sensitive to cumulative dam effects than other stressors including urbanization and agriculture in the eastern USA. To further identify specific effects of environmental variables on potamodromous fishes, we conducted Boosted Regression Trees analysis in the eastern ecoregions. Our results suggested that the key natural influences on river fishes included catchment area as well as river baseflow and air temperature, suggesting that migratory fishes may be affected by changing climate. Additionally, we found that downstream dams were more influential than other human stressors to potamodromous fishes, underscoring the importance of enhancing connectivity within river networks to conserve migratory fishes. Collectively, our results provide new insights in identifying threats to migratory fish species across the USA, providing information that can aid in conserving this vulnerable but ecologically and socioeconomically important group of fishes.

Three Gorges Dam Operations Affect the Carbon Dioxide Budget of a Large Downstream Connected Lake

AbstractThe effects of dams on carbon dioxide (CO2) fluxes in downstream lakes remain elusive. Here we combined eddy covariance observations and random forest models to examine multi‐decadal variations in CO2 fluxes in the Poyang Lake, the largest freshwater lake in China, and quantified the contribution of the Three Gorges Dam (TGD), the world's largest hydraulic project. We found the lake fluctuated between CO2 source and sink in 1961–2016, and tended to be CO2 sink in the post‐TGD period (2003–2016) when vegetation expanded early and spatially due to declining water level. TGD can explain approximately 6% of the total differences in annual CO2 fluxes, with major contributions in the impoundment period (up to 22% in middle September to October). The results show a positive side of operational major hydraulic projects on lake carbon sink, and probably caution the negative side of carbon release after dam removal.

Human activities change suspended sediment concentration along rivers

Humans have drastically disrupted the global sediment cycle. Suspended sediment flux and concentration are key controls over both river morphology and river ecosystems. Our ability to understand sediment dynamics within river corridors is limited by observations. Here, we present RivSed, a database of satellite observations of suspended sediment concentration (SSC) from 1984 to 2018 across 460 large (>60 m wide) US rivers that provides a new, spatially explicit view of river sediment. We found that 32% of US rivers have a declining temporal trend in sediment concentration, with a mean reduction of 40% since 1984, whereas only 2% have an increasing trend. Most rivers (52%) show decreasing sediment concentration longitudinally moving downstream, typically due to a few large dams rather than the accumulated effect of many small dams. Comparing our observations with modeled ‘pre-dam’ longitudinal SSC, most rivers (53%) show different patterns. However, contemporary longitudinal patterns in concentration are remarkably stable from year to year since 1984, with more stability in large, highly managed rivers with less cropland. RivSed has broad applications for river geomorphology and ecology and highlights anthropogenic effects on river corridors across the US.

Ecological effect of a small dam on the macroinvertebrate assemblage and water quality of Koga River, Northwest Ethiopia

There has been an increasing effort to construct dams across rivers to control the flow of the streams and secure water storage, and river damming has become one of the most prominent human impacts on the freshwater ecosystem. Nonetheless, the effect of river damming on the river ecosystem is only partially understood in Ethiopia. This study is aimed to assess the ecological effect of small dams on macroinvertebrate assemblages and the water quality of the Koga River ecosystem. A total of 15 sites; five from upstream, five from the dam, and five from downstream of the Koga River was sampled for macroinvertebrates and water quality parameters. The sampling was done from September to November 2016. A total of 40 families of macroinvertebrates were recorded, among which Coenagrionidae, Belostomatidae, Naucoridae, and Physidae were the most abundant. The biodiversity of macroinvertebrates was significantly higher in the downstream location of Koga Dam, where there was an attenuated sediment load to the river. Among the functional feeding groups, the percentage of filterer-collectors was higher in the upstream locations, whereas scraper families were higher in the downstream locations of the dam. Vegetation cover, turbidity, and pH were identified as the most important water quality factors delineating the pattern of macroinvertebrate community structure in the river system. Turbidity and orthophosphate concentrations were higher in the upstream sampling locations. The average sediment layer thickness was higher on the upstream side of the dam. The results suggest that sediment adversely affects the macroinvertebrate assemblage. Higher concentrations of sediment and phosphate were noted in the upstream location of the dam. The water quality (turbidity and nutrient concentrations) of the stream was affected by River Damming by influencing the sediment and nutrient dynamics of the river. Therefore, planning and implementation of an integrated watershed and dam management system are suggested to prolong the useful lifespan of the dam and sustain its ecological integrity.

Cover Image

The cover image is based on the Original Article Effects of small hydropower dams on macroinvertebrate and fish assemblages in southern Brazil, by Thiago B. A. Couto et al., https://doi.org/10.1111/fwb.14078.

Effects of dam building on N2O-producing and N2O-reducing community structures in river sediments and the associated N2O emission potential

Dam construction is regarded as the greatest anthropogenic disturbance in aquatic ecosystems, and it promotes denitrification, through which large N2O emissions occur. However, the effect of dams on N2O producers and other N2O-reducing microorganisms (especially for nosZ II), and the associated denitrification rates remain poorly understood. This study systematically investigated the spatial variation of potential denitrification rates in dammed river sediments in winter and summer and the microbial processes driving N2O production and reduction. Sediments in the transition zone of dammed rivers were found to be critical for N2O emission potential, with lower potential denitrification rate and N2O production rate in winter than in summer. In dammed river sediments, the dominant N2O-producing microorganisms and N2O-reducers were nirS-harboring bacteria and nosZ I-harboring bacteria, respectively. Diversity analysis showed that diversity of N2O-producing did not differ significantly between upstream and downstream sediments, whereas the population size and diversity of N2O-reducing microbial communities in upstream sediments significantly decreased, leading to biological homogenization. Further ecological network analysis revealed that the ecological network of nosZ II microbes was more complex than that of nosZ I microbes, and both exhibited more cooperation in the downstream sediments than in the upstream sediments. Mantel analysis showed that the potential N2O production rate was mainly influenced by electrical conductivity (EC), NH4+, and TC content, and that higher nosZ II/nosZ I ratios contributed to improved N2O sinks in dammed river sediments. Moreover, the Haliscomenobacter genus from the nosZ II-type community in the downstream sediments contributed significantly to N2O reduction. Collectively, this study elucidates the diversity and community distribution of nosZ-type denitrifying microorganisms influenced by dams, and also highlights the non-negligible role played by nosZ II-containing microbial groups in mitigating N2O emissions from dammed river sediments.

Crayfish assemblages correlate with dam‐induced effects on abiotic factors and predatory fish assemblages in Alabama streams

AbstractStream faunal assemblage structure is tied closely to hydrology and associated physiochemical properties. By altering natural flows, dams and their impoundments impact faunal assemblages over long distances. Although numerous studies have assessed the effect of dams on stream fauna, information is lacking for crayfishes. In this study, we characterized the effects of relatively large storage dams on crayfish assemblage structures. Over 2 years, we sampled three impounded and two unimpounded streams across two drainages in Alabama, United States, to identify biotic and abiotic factors correlated with crayfish assemblage metrics. Compared to impounded streams, unimpounded streams had greater habitat complexity (e.g., aquatic vegetation and woody debris), fewer predator fishes, lower minimum temperatures, and more variable discharges. These characteristics correlated with a higher density and diversity of crayfishes and smaller adults in impounded compared to unimpounded streams. Crayfish species assemblages differed between drainages, as did the biotic and abiotic factors affecting crayfish assemblages in each drainage, suggesting that these factors were species‐specific in their effects. Additionally, analysis of land uses suggested that factors other than dams may have also contributed to the observed differences in assemblage structures between impounded and unimpounded streams. For instance, in the more urbanized drainage, crayfish assemblages were more similar between up and downstream sections in all streams, regardless of impoundment. Our results indicate that large dams alter stream crayfish assemblage structure, with potentially cascading effects in trophic and organic matter dynamics both up and downstream.

Field survey and analysis of water flux and salinity gradients considering the effects of sea ice coverage and rubber dam: a case study of the Liao River Estuary, China

Predicting net river fluxes is important to promote good water quality, maritime transport, and water exchange in estuaries. However, few studies have observed and evaluated net water fluxes to estuaries under complex conditions. This study used advanced survey techniques to obtain high-frequency monitoring data of cross-sectional current velocity, water level, and salinity in the Liao River Estuary (LRE) from 2017 to 2020. The net water flux into the sea was computed based on field data and the impacts of the rubber dam and sea ice cover on water flux and salinity processes were analyzed in the study region. In the Liao River Station (LRS), the fluctuations of water level and discharge were not obvious in winter due to the sea ice cover. There were significant seasonal and inter-annual changes in water fluxes due to variability in river discharge and tidal oscillations. The results also showed that the net water flux into the sea from the LRS was positive in wet season, and greater during ebb tides than flood tides. The net water fluxes in the normal and dry seasons were mostly negative due to the influence of tides, indicating that the annual runoff from the Liao River fluctuated greatly throughout the year. The water flux in the LRS was more suitable for representing water flux into the sea than the Liujianfang Hydrometric Station (LHS) in the LRE. The impacts of the rubber dam and Panshan Sluice on water fluxes to the sea were both significant. Lower salinity in the study area coincided mostly with height water fluxes to the sea and periods when the rubber dam was raised. This study results provide us new insights to measure the water flux into sea under the condition of ice cover in the tidal reach of estuary and the method can be used for water flux observation for other estuaries.

Dam Safety Evaluation Method after Extreme Load Condition Based on Health Monitoring and Deep Learning.

The safety operation of dams after extreme load is an important frontier research topic in the field of dam engineering. The dam health monitoring provides a reliable data basis for a safety evaluation after extreme loads. This study proposes a novel data-driven fusion model for a dam safety evaluation after extreme load based on monitoring data derived by sensors. First, the relationship between dam environmental quantity and effect quantity is deeply excavated based on bidirectional long short-term memory (BiLSTM) network, which is a deeply improved LSTM model. Aiming at the parameter optimization problem of BiLSTM model, sparrow search algorithm (SSA), which is an advanced optimization algorithm, is integrated. Second, conducting the constructed SSA-BiLSTM model to estimate the change law of dam effect quantity after the extreme load. Finally, the Mann-Whitney U-test theory is introduced to establish the evaluation criterion of the dam safety state. Project case shows that the multiple quantitative prediction accuracy evaluation indicators of the proposed method are significantly superior to the comparison method, with mean absolute percentage error (MAPE) and mean absolute error (MAE) values decreasing by 30.5% and 27.8%, respectively, on average. The proposed model can accurately diagnose the dam safety state after the extreme load compared with on-site inspection results of the engineering department, which provides a new method for dam safety evaluation.

Socio-ecological challenges of hydroelectric dams among ethnic minorities in northern Laos

Globally, hydroelectric dams are increasingly considered to be a sustainable source of renewable energy. Many countries have invested in hydroelectric projects to boost the local and national economies. The findings of recent hydroelectric projects are mixed. Even though the construction of these dams has provided immediate benefits to surrounding communities, long-term negative implications of hydroelectric development have called into question the true sustainability of hydroelectric projects. These negative impacts of hydroelectric dams include the resettlement of marginalized communities, in addition to significant alterations to the local environment and economy. Taking both the positive and negative impacts of hydroelectric development into consideration, this paper examines how such hydroelectric dam development projects have led to the extreme marginalization of already vulnerable ethnic groups in Laos. Particularly, it focuses on the effects of hydroelectric dams on one of the largest ethnic groups in northern Laos, the Khmou. The findings suggest that the construction of hydroelectric dams act as a double-edged sword for the local environment, people, and economy. This study is an attempt to synthesize the existing knowledge to shed light on the negative implications that hydroelectric developments have had on ethnic minorities, particularly Khmou in northern Laos. Even though this paper has a geographical focus on northern Laos, the findings are relevant for understanding the impacts of hydroelectric dams on various historically marginalized populations in other parts of the Global South.

Effects of small hydropower dams on macroinvertebrate and fish assemblages in southern Brazil

Abstract Hydropower dams affect freshwater biodiversity by virtue of modifying flow regimes and degrading habitat conditions both above and below the water impoundment and diversion structure. In recent decades, there has been a global proliferation of Small Hydropower Plants (SHPs) propelled by incentive policies and a general perception that small dams are less harmful to the environment. However, limited science is available on the effects of SHPs on freshwater biodiversity, which is concerning considering their sheer numbers and the high variability in the size and operation of dams classified as SHPs. We investigated the ecological effects of 12 SHPs on macroinvertebrate and fish assemblages of the Chapecó River Basin, Brazil. Our study included sites located upstream of the SHPs and sites directly affected by their operations (i.e., reservoir, dewatering section and downstream of the powerhouse). This design allowed us to quantify shifts in taxonomic composition and examine the relative role of different SHP attributes (e.g., dam height, reservoir area, age) in explaining these changes. Our results reveal that SHPs modify the composition of both macroinvertebrate and fish assemblages, but the magnitude of such changes vary widely among dams. Both assemblages exhibited directionality in taxonomic shifts, resulting in a gradual replacement of taxa associated with fast‐flowing habitats by other groups more commonly associated with standing waters. We also found that changes in assemblage structureare related to structural (dam height, reservoir area) and spatial attributes (distance from headwaters) of SHPs, although the predictive power of these attributes varied taxonomically and among reservoir, dewatering and downstream sites. Overall, our results demonstrate that SHPs have important and heterogeneous effects on freshwater assemblages, which may manifest individually or cumulatively across the riverscape. This suggests that it is unlikely that a priori classifications of dams based on their structural attributes can replace site‐specific and cumulative impact assessments. The results also shed light on the need for better understanding of how SHP attributes shape their ecological effects, so that a full assessment of the potential environmental impacts of the wide range of "small" dams is possible.

Patterns and drivers of water quality changes associated with dams in the Tropical Andes

Abstract. The Tropical Andes is a biodiversity hotspot facing pressure from planned and ongoing hydropower development. However, the effects of dams on the region's river ecosystems, as mediated by physicochemical changes in the water quality, are poorly known. Colombia is unique among its peers in South America with respect to managing central public environmental databases, including surface water quality data sets associated with the environmental monitoring of dams. To assess the relationship between hydropower and Colombian river conditions, we analyze monitoring data associated with 15 dams, focusing on oxygen availability, thermal regimes and sediment losses because these properties are influenced directly by river damming and impose fundamental constraints on the structure of downstream aquatic ecosystems. We find that most Colombian dams (7 of 10) seasonally reduce concentrations of total suspended solids by large percentages (50 %–99 %) through sediment trapping. Most dams (8 of 15) also, via the discharge of warm reservoir surface waters, seasonally increase river temperatures by 2 to 4 ∘C with respect to upstream conditions. A subset of four dams generate downstream hypoxia (< 4 mg L−1) and water that is 2 to 5 ∘C colder than inflows, with both processes driven by the turbination and discharge of cold and anoxic hypolimnetic waters during periods of reservoir stratification. Reliance on monitoring data likely leads us to under-detect impacts: many rivers are only sampled once or twice per year, which cannot capture temporal shifts across seasons and days (i.e., in response to hydropeaking). Despite these blind spots, the monitoring data point to some opportunities for planners and hydropower companies to mitigate downstream ecological impacts. These findings highlight the importance of implementing environmental monitoring schemes associated with hydrologic infrastructure in developing countries.

Riverine inputs, spatiotemporal variations, and potential sources of phthalate esters transported into the Bohai Sea from an urban river in northern China

The effects of anthropogenic activities on pollutant transport and inputs to the sea remain unclear. This study aimed to evaluate the impacts of sewage discharge and dam interception on riverine inputs, spatiotemporal variations, and potential sources of phthalate esters (PAEs) throughout the Haihe River, one of the largest rivers in northern China. Based on seasonal observations, the yearly inputs of the total concentrations of 24 PAE species (Σ24PAEs) from the Haihe River to the adjacent Bohai Sea were in the range of 5.28–19.52 tons, a considerable amount compared with those of other large rivers worldwide. The value of Σ24PAEs in the water column ranged from 1.17 to 15.46 μg/L and showed the following overall seasonal pattern: normal season > wet season > dry season, with dibutyl phthalate (DBP) (31.0 ± 11.9 %), di (2-ethylhexyl) phthalate (DEHP) (23.4 ± 14.1 %), and diisobutyl phthalate (DIBP) (17.2 ± 5.4 %) as the dominant components. Σ24PAEs were higher in the surface layer, slightly lower in the intermediate layer, and higher in the bottom layer. Σ24PAEs increased from the suburban section to the urban and industrial sections, which may indicate the effects of runoff, biodegradation, regional urbanization, and industrialization levels. The Erdaozha Dam intercepted 0.29–1.27 tons of Σ24PAEs inputs into the sea, but induced a substantial quantity accumulated behind the dam. The dominant sources of PAEs were the basic residential necessities (18.2–25.5 %) and industrial production (29.1–53.0 %). This study provides insights into the direct effects of sewage discharge and river dams on the inputs and variations in the PAEs entering the sea, which can be leveraged to manage and control PAEs in megacities.

The environmental licensing of hydroelectrics and the interface with migratory fish and aquaculture in Brazil

In this review, we present a background on the Brazilian Federal Legislation on the environmental licensing of hydroelectric plants focusing on the procedure of the repair of environmental damage caused by dams to migratory fish. To that end, the Brazilian electrical matrix was first addressed, thus highlighting the significant contribution of the energy produced by hydroelectric projects. To better contextualize the characteristics of the legislation, separate sections concerning illustrative reports of the effects of dams on migratory fish and the current panorama of aquaculture in Brazil and in the world were included. In this review, we also present a discussion on the specific legislation concerning a mitigation measure, the “fish restocking programs,” which have the potential to promote fishing and aquaculture, but still lack a scientific basis on their effectiveness and correct application. An assessment of this historical process in Brazil indicates that different mitigation measures imposed to obtain operating licenses by hydroelectric plants vary among different hydroelectric projects and that this heterogeneity in the conditions imposed may have effects (of unknown proportions) on local fish communities. Considering the absence of a specific device foreseen in the law that requires the owner or concessionaire of dams in watercourses to provide for fish restocking programs or specific ichthyofauna conservation programs, the issue seems to depend on the discretion of the licensing agency to demand that the hydroelectric plant operators carry out the reintroduction of fish in their reservoirs. This review concludes that there are political and scientific issues to be debated and explored in order to improve public policies on this topic of extreme relevance for society.

Modelling and assessing how small hydropower facilities affect sediment transport by using fuzzy inference systems

Small dams for power generation are increasingly being built around the world, and the reported impact caused by these structures on sediment transport varies widely, ranging from substantial to minimal or non-existent alterations among different dams. Such variability is still poorly understood. In this study, we present an original application of fuzzy inference systems (FIS) to extract knowledge concerning the effect of small dams on sediment transport, providing understandings of how different variables related to watershed characteristics, dam characteristics and hydrological variations can affect sedimentological responses of these structures. Numerous small dams have been built, and many more are in development or proposed, in rivers that drain into the Pantanal, a world-renowned tropical wetland, where we apply the methodology. Data on 23 hydropower facilities from the uplands of the Pantanal region were used, with a total of 535 records. The models presented very good results (NS equal to 0.92 for the most detailed FIS model) and provided a better understanding of the phenomenon through their explicit linguistic rules. The upstream suspended sediment concentration (SSC) is the most determinant variable for the alteration caused by dams. Higher SSC entering the reservoir is related to higher sediment retention. Vegetation cover and soil type of the drainage area of dams also influence the alterations on SSC caused by these structures. Dams located in basins with greater vegetation cover tend to affect less sediment transport, and dams located in basins with high percentages of agriculture and pasture tend to alter more. FIS models also confirmed that the size of dams is directly proportional to their capacity to alter sediment transport. The methodologies developed for the interpretation of fuzzy rules proved to be useful for assessing how small dams affect sediment transport along river systems.

A transgenerational study on the effect of great-granddam birth month on granddaughter EBV for production traits in Italian Simmental cattle

Heat tolerance is a key feature of resilient animals. Offspring of animals that suffer environmental stress during pregnancy could show physiological, morphological, and metabolic modifications. This is due to a dynamic reprogramming of the epigenetics of the mammalian genome that occurs in the early life cycle. Thus, the aim of this study was to investigate the extent of the transgenerational effect of heat stress during the pregnancy of Italian Simmental cows. The effects of dam and granddam birth months (as indicator of pregnancy period) on their daughter and granddaughter estimated breeding values (EBV) for some dairy traits as well as of the temperature-humidity index (THI) during the pregnancy were tested. A total of 128,437 EBV (milk, fat, and protein yields, and somatic cell score) were provided by the Italian Association of Simmental Breeders. The best birth months (of both dam and granddam) for milk yield and protein yield were May and June, whereas the worst were January and March. Great-granddam pregnancies developed during the winter and spring seasons positively affected the EBV for milk and protein yields of their great-granddaughters; in contrast, pregnancies during summer and autumn had negative effects. These findings were confirmed by the effects of maximum and minimum THI in different parts of the great-granddam pregnancy on the performances of their great-granddaughters. Thus, a negative effect of high temperatures during the pregnancy of female ancestors was observed. Results of the present study suggest a transgenerational epigenetic inheritance in Italian Simmental cattle due to environmental stressors.