Effects Of Dams Research Articles

Genetic diversity and structure of Brycon henni in regulated and non-regulated water flow rivers of the Colombian Andes

The sabaleta, Brycon henni, is a medium-size fish species found in the Andean range of the Magdalena-Cauca river basin in Colombia, where it is a fishery resource. Recruitment of sabaleta has affected construction of dams with unknown consequences on its genetic diversity and structure. Understanding the current genetic architecture in the dam-influenced areas compared to non-regulated water flow systems is crucial to diagnose the impact of human interventions and formulate proper management strategies. In this study, we evaluated the genetic structure and diversity of B. henni by using a set of microsatellites in individuals from 14 localities to identify the number of distinct genetic pools. We used various approaches to compare populations between regulated and non-regulated areas in the Magdalena-Cauca basin, and identified eleven well-differentiated and highly diverse population groups with marked genetic structures at local and regional levels. Genetic diversity of B. henni was very similar among non-regulated and dam-regulated water flow areas; however, one of the populations in non-regulated areas showed evidence of a founder effect associated with recent introductions. The effect of dams on the genetic structure of B. henni in the Magdalena-Cauca basin was negligible, probably due to their recent construction. Future reduction of genetic diversity and the loss of unique populations is expected due to the combined effect of geographic isolation and population declines. Thus, monitoring programs are necessary to detect changes in the genetic structure of fish populations to develop useful conservation actions.

Characterizing the response of the coastal Rio Grande to upstream damming

Dams are major obstructions to the flow of water and the transport of sediment in rivers. Much work has shown the construction of dams, and storage of sediment in reservoirs, can lead to significant changes in the morphodynamic behavior of alluvial rivers; however, in most cases, the effect of damming has a finite downstream limit as sediment is supplied back to the river through channel bed/bank erosion and/or tributary inputs. Here we present a study of a natural experiment that isolates one source of sediment downstream of a dam – the lower Rio Grande, which has no major tributary inputs of sediment over a ~450 km reach, from Falcon Dam to the coast. Analysis of the morphology and topography of the Rio Grande shows that prior to damming in the 1950s the coastal Rio Grande was a kinematically active channel with large, subaerial point bars. Subsequent to damming, lateral migration of the river shut down and exposed point bars shrunk in size, becoming static and vegetated. Bathymetric survey data show meter-scale incision of the channel bed for hundreds of kilometers downstream of the dam. Entrenchment of the river is also evidenced by the development of steep banks on the inner portions of channel bends. Damming also impacted the interaction between the river and the floodplain, resulting in the formation of persistent gullies incised into the channel banks, suggesting transport of water and sediment is net positive into, not out of, the channel. Based on all of these observations we conclude that the full ~450 km reach of the Rio Grande, from Falcon Dam to the coast, became net degradational following dam closure. We conclude that the presence of such a long degrading reach is caused by the exposure of bedrock in the Rio Grande channel for nearly 100 km downstream of the dam, which, combined with the lack of tributaries, limits downstream sediment supply to the river. Our results provide new insights into the response to damming for rivers with no tributary sediment input and thin alluvial cover, and more broadly to the kinematic and channel geometry responses to a major drop in water discharge and sediment supply for coastal meandering rivers.

Coastal Dynamics in Estuaries and Deltas under the Combined Effects of Large Dams Built Upstream and Rising Sea Levels

Examines in Marine Biology & Oceanography Coastal Dynamics in Estuaries and Deltas under the Combined Effects of Large Dams Built Upstream and Rising Sea Levels Jean Albergel1* and Yadh Zahar2 1University of Montpellier, UMR LISAH, IRD, France 2University of Carthage, VDEC lab, LR01ES20, Tunisia *Corresponding author: Jean Albergel, UMR LISAH-IRD, 2 Place Pierre Viala - 34060 Montpellier Cedex 1, France Submission: January 09, 2023;Published: January 23, 2023 DOI: 10.31031/EIMBO.2023.05.000611 ISSN 2578-031X Volume5 Issue3

Impacts of the Victoria Nile Bujagali hydropower dam on fisheries and livelihoods

AbstractThe Upper Victoria Nile (UVN) flows from Lake Victoria into Lake Kyoga, spanning 117 km and supports a diverse aquatic fauna that sustains livelihoods of riverside communities. The UVN is habitat to critically endangered (Labeo victorianus), near threatened (Oreochromis variabilis and Oreochromis esculentus), and rare species (Neochromis simotes). Four hydropower dams were built on the UVN to provide energy for industrial and socioeconomic development, notwithstanding consequential environmental and socioeconomic impacts. The impacts of Bujagali hydropower (BHP) dam on fisheries and livelihoods were assessed biannually (April and September) from 2006 to 2019, using fishing effort, species abundance, catch composition, and economic beach revenue at upstream, mid‐reservoir, and downstream transects. The fishing boats increased from 31 in 2009 to 293 in 2019 and fishers from 83 to 500 over the monitoring period. Maximum annual catch of 461.4 t was recorded in 2014 and lowest of 54.2 t in 2009. In all transects, Protopterus aethiopicus and Labeo victorianus were least in the commercial catches and the use of Mormyrus kannume juveniles as bait for Nile perch fishery corresponded with increased catches from 3.3 t in 2009 to 148.2 t in 2019. Women were mostly engaged in post‐harvest activities such as fish drying, smoking, and food vending. These observations suggest coupling effects of the hydropower dam and ineffective fisheries management. The harvest of M. kannume wild stocks for bait should be banned and research in possible domestication of the species undertaken. There is a need to strengthen fisheries enforcement to curb illegal effort and overexploitation and to implement conservation actions to mitigate potential biodiversity impacts from the hydropower dam operations.

Reservoirs regulated by small dams have a similar warming effect than lakes on the summer thermal regime of streams

Small dams account for the majority of reservoirs throughout the world, yet little is known about their effects on stream temperatures. Given that water temperature is vital for maintaining the integrity of aquatic ecosystems, studying the effects of small dams is important. This study aims to understand the effect of small dams on summer stream temperatures in a protected area in southern Quebec, Canada. We assessed the effect of small surface-release dams on four attributes of the thermal regimes (magnitude, frequency and duration of warm events, and rate of change) of streams by comparing water temperature measured in the main tributary upstream and in the main outlet downstream of the reservoir. We also compared the thermal effects of reservoirs to those of natural lakes of similar size. Using a generalized additive model, we identified key determinants of stream temperature to assess the influence of reservoir and natural lake characteristics on the thermal regime of streams. In August 2020, we observed an average warming of 3.7 °C downstream of reservoirs regulated by small dams compared to conditions upstream of the reservoir. During this period, the warming effect of reservoirs was not significantly different from the warming effect of natural lakes (3.4 °C). In addition to the drainage area, distance to an upstream water body, and the proportion of the watershed occupied by water bodies were the primary determinants of stream temperature in August, demonstrating the importance of nearby water bodies on stream thermal regimes. Given their warming effect, small waterbodies may limit the available habitat for species that are sensitive to warm temperatures. As the construction of small dams is accelerating at the global scale, a clear understanding of the cumulative effects of small lakes and reservoirs on stream temperature is required to ensure the sound management of aquatic ecosystems.

Microbial community structure and denitrification responses to cascade low-head dams and their contribution to eutrophication in urban rivers

Low-head dams are one of the most common hydraulic facilities, yet they often fragment rivers, leading to profound changes in aquatic biodiversity and river eutrophication levels. Systematic assessments of river ecosystem structure and functions, and their contribution to eutrophication, are however lacking, especially for urban rivers where low-head dams prevail. In this study, we address this gap with a field survey on microbial community structure and ecosystem function, in combination with hydrological, environmental and ecological factors. Our findings revealed that microbial communities showed significant differences among the cascade impoundments, which may be due to the environment heterogeneity resulting from the cascade low-head dams. The alternating lentic–lotic flow environment created by the low-head dams caused nutrient accumulation in the cascade impoundments, enhancing environmental sorting and interspecific competition relationships, and thus possibly contributing to the reduction in sediment denitrification function. Decreased denitrification led to excessive accumulation of nutrients, which may have aggravated river eutrophication. In addition, structural equation model analysis showed that flow velocity may be the key controlling factor for river eutrophication. Therefore, in the construction of river flood control and water storage systems, the location, type and water storage capacity of low-head dams should be fully considered to optimize the hydrodynamic conditions of rivers. To summarize, our findings revealed the cumulative effects of cascade low-head dams in an urban river, and provided new insights into the trade-off between construction and decommissioning of low-head dams in urban river systems.

Responses of macroinvertebrate functional trait structure to river damming: From within-river to basin-scale patterns

Revealing how aquatic organisms respond to dam impacts is essential for river biomonitoring and management. Traditional examinations of dam impacts on macroinvertebrate assemblages were frequently conducted within single rivers (i.e., between upstream vs. downstream locations) and based on taxonomic identities but have rarely been expanded to level of entire basins (i.e., between dammed vs. undammed rivers) and from a functional trait perspective. Here, we evaluated the effects of dams on macroinvertebrate assemblages at both the within-river and basin scales using functional traits in two comparable tropical tributaries of the Lancang-Mekong River. At different scales, maximum body size, functional feeding groups (FFG), voltinism and occurrence in drift respond significantly to dam impact. Armoring categories varied significantly between downstream sites and upstream sites, and oviposition behavior, habits and adult life span significantly differed between rivers. The key traits at the within-river scale resembled to those at the between-river scale, suggesting that within-river trait variation could further shape functional trait structure at the basin scale in dammed rivers. Furthermore, water nutrients and habitat quality induced by dams showed the most important role in shaping trait structure, although trait-environment relationships varied between the two different scales. In addition, the trait-environment relationships were stronger in the dry season than in the wet season, suggesting a more important role of environmental filtering processes in the dry season compared with the wet season. This study highlights the utility of the trait-based approach to diagnose the effects of damming and emphasizes the importance of spatial scale to examine dam impacts in riverine systems.

Regulation effect of slit-check dam against woody debris flow: Laboratory test

Woody debris flows (i.e., debris flows carrying wood) are common in mountainous and forested areas. They can cause more severe hazards due to the effects of LW (woody debris larger than 1 m in length and 10 cm in width) compared to debris flows without LW. Mitigation structures for debris flows have considered little of the regulating effect on LW and the influence of LW on the regulation effect of sediment. Thus, model tests were conducted to discuss the regulation effects of slit-check dams on woody debris flow. Research results demonstrated that slit-check dams can effectively regulate woody debris flows without overflows. Once overflow occurs, sediment trapping efficiency and the wood retention rate dramatically decrease. The sediment trapping efficiency of slit-check dams on debris flows without LW shared a linear relationship with the relative opening width, the height-to-width ratio of the opening, and the opening density. However, this was also influenced by the wood retention rate for woody debris flow. A logarithmic relationship between the sediment trapping rate and wood retention rate was obtained. The wood retention rate is mainly determined by the ratio of the LW length to the opening width, the ratio of the LW length to the channel width and the opening density of the slit-check dam. Three draining patterns of woody debris flows at the slit-check dam and three clogging types of LW at the openings of the slit-check dam were observed. Some design criteria for the structure parameters of the slit-check dam were proposed. These research results promote a better understanding of the regulation effect of slit-check dams on woody debris flows and provide a basis for the optimal design of slit-check dams.

Heritability and genetic trend of body weight in dogs of different breeds in Sweden.

High body weight (BW) in dogs has been associated with developmental as well as degenerative diseases, but the heritability of BW in dog breeds is largely unknown. The aim of the current study was to estimate heritability and genetic change (genetic trend) for BW in a range of dog breeds in Sweden. Body weight registrations from 19 dog breeds (with n ranging from 412 to 4,710) of varying body size, type and usage were collected from 2007 to 2016. The average BW of the breeds was 8 to 56 kg. The BW registrations were performed when the dogs were 12 to 24 mo of age (18 to 30 mo for one large-sized breed) in connection with an official radiographic screening program for hip dysplasia. Collected weight records were used to estimate heritability and genetic trends for BW. Several statistical models were used. The preliminary model included the fixed effects of breed (P < 0.001), sex (P < 0.001), year of screening (P < 0.001), litter size (P = 0.06), parity of the dam (P = 0.03) and linear regression on age at screening (P < 0.001), the latter five effects all nested within breed, and the random effects of litter and dam. Season of birth and the quadratic effect of age were also tested, but were not significant (P > 0.10). For the genetic analysis, various mixed linear models were tested within breed with different combinations of random effects; the most complex model included random effects of litter, direct additive, and maternal genetic effects, and maternal permanent environmental effects. The average heritability for BW over all 19 breeds was 51%, with a range of 35% to 70%, and the additive genetic coefficient of variance was around 9%. Maternal heritability was 5% to 9% and litter variance was below 10% with one exception (15% in Shetland Sheepdogs). For nine breeds, there was a genetic trend of increasing BW, whereas seven breeds had a genetic trend of decreasing BW. The largest absolute genetic change over a 10-yr period was around 0.6 kg or about 2% of the mean. In conclusion, given the small genetic changes in spite of the high heritability, it seems that there is generally a very weak selection, if any, for BW in the included dog breeds.

The effect of source of protein fed during pregnancy and lactation on the development of characteristics of metabolic syndrome in male offspring of obese Wistar rats.

Gestational obesity has major negative impacts on both mothers and their offspring. More than two-thirds of women of reproductive age in the United States are overweight and/or obese. We previously reported that the source of protein in the maternal diet influences the phenotype of offspring born to normal-weight dams. However, whether it has the same effect in obese mothers was unclear. The casein- and soya protein-based diets were fed to obese pregnant Wistar rats and compared for their effects on characteristics of the metabolic syndrome in male offspring. Dams randomized to either a casein (CD) or soya protein (SD) diet (n 12). Pups were weaned to either a CD or SD for 16 weeks. Offspring of SD dams had higher birthweight (P < 0⋅01). Glucose metabolism was not altered at birth but fasting blood glucose (FBG) (P < 0⋅02), insulin (P < 0⋅0002), insulin/glucose ratio (P < 0⋅03), and HOMA-IR index (P < 0⋅0002) were higher in offspring of SD dams at week 17. The pulse rate was higher in dams (P < 0⋅03). Food intake and body weight of offspring were affected by interactive effects of time and dams' diet (P < 0⋅05). Food intake was not influenced by maternal diet, but it was higher in pups weaned to SD dams (P < 0⋅03) The results of this study indicate that although the source of protein in the maternal diet is still an influencing factor in the outcome of the pregnancy in obese mothers, gestational obesity may mask this effect possibly by imposing general detrimental effects on measured parameters regardless of the source of protein in maternal diet.

Effects of feeding fodder beet or kale in winter to dams and their heifer offspring on the heifer growth and production

Context Fodder beet (FB) is a widely used winter feed in New Zealand’s southern regions due to its high yield, consistent quality, and environmental benefits. However, FB is low in crude protein, phosphorus and fibre, and a survey showed that many dairy farmers were concerned that feeding FB may have negative impacts on lifetime performance. Aim To determine whether winter feeding FB or kale (Ka) to dairy cows, and then their heifer offspring at 1 and 2 years old, affects the heifer performance from birth until the end of their first lactation. Methods In June–August 2017, pregnant dairy cows were fed FB or kale over winter and then 140 of the resultant heifer offspring were divided into four treatment groups at 9–11 months old according to their dam’s winter diet and offered either FB or kale, with pasture baleage. The groups were as follows (dam crop–heifer crop): FB–FB, FB–Ka, Ka–FB, Ka–Ka. The heifers’ subsequent performance (growth, stature, milk production, and reproduction) was measured to the end of their first lactation (May 2020), and blood mineral status was monitored from May 2018 to May 2019. This observational study has its limitations, but is useful for generating hypotheses to test in more controlled research. Key results Heifers grazing FB in winter (June–August) 2018 had lower blood plasma urea and phosphate concentrations than did heifers grazing kale, despite similar dietary crude protein contents. Treatments had no effect on milk production. However, the heifer liveweights were affected and there was an indication of poorer reproductive performance. The FB–FB heifer treatment group had a lower average liveweight than the FB–Ka heifers from 1 to 2.8 years old. Conclusions Although no impact on milk production for the first lactation was observed, the key results suggest possible negative impacts of feeding heifers FB during winter, particularly if their dam also wintered on FB. Implications The combined effects of FB dam and heifer winter diets on lifetime productivity warrant further investigation to help develop sustainable FB feeding systems. When feeding FB, we recommend that farmers test their crops and supplements to ensure that sufficient nutrition, in particular protein and phosphorus are provided.

Examining Disruptions of Social Systems due to Large Dam Projects in the North East

The vulnerability of the tribals to lose more than the commodity value of land due to large dam projects in the North East has not been given due attention both in policy space and empirical research. Also, the question of whether the living standards of the already displaced tribals have improved after dam construction has not been treated with rigour. The paper tries to disaggregate the social disruption effects of large dam construction along the lines of gender, religious identity and ethnic conflicts and question the conventional economics of resettlement. The study examines the claimed effects (and benefits) of large dams on tribal communities made in non-empirical papers and government documents using available real-world examples from the north-east. The study also validates the findings from the literature through a sentiment analysis of newspaper articles and a public opinion survey of dams in the north-east. This crossexamination is expected to serve as a foundation for further empirical research.

Taxonomic and functional responses of macroinvertebrate communities to dam construction in a non-wadeable river

Damming and impoundment are among the main flow-related alterations in rivers worldwide. However, compared to the highland river sections where the impacts associated with dams have been largely studied, still scarce evidence is available in scientific literature for large, lowland rivers. In this study, the ecological effects of a hydropower dam in the Po River (Italy) on the taxonomic and functional responses of benthic macroinvertebrates were examined by comparing one station upstream of the dam with one downstream station over a six-year period. Weak and not significant differences were observed for taxon richness, abundance and community composition. By contrast, community-level proportion of macroinvertebrates associated with water velocity increased during medium and high flow condition and decreased during low flow condition in downstream stations. Such differences were also mirrored by the Flow-T index, that is a biomonitoring index recently developed to assess hydraulic conditions in rivers. Results of this study support the adoption of stressor-specific metrics in river biomonitoring.

Effects of Beaver Dams on Stream and Riparian Conditions on Public Lands in the United States' Inland Northwest

Se utilizó el diseño experimental “before-after control-impact” (BACI, por sus siglas en inglés) para evaluar simultáneamente cómo el hábitat del arroyo, las comunidades de macroinvertebrados, la temperatura del arroyo y las condiciones ribereñas respondieron a la construcción de presas por parte de los castores dentro de un tramo del arroyo. El resumen de las condiciones que describen los tramos de arroyo con represas de castores y sin represas, sugirieron que 13 de las 18 métricas evaluadas difirieron. Después de tener en cuenta la selección de los castores de tramos de arroyo de menor pendiente y con menos cobertura forestal, el número de parámetros de arroyo y ribera que diferían significativamente se redujo a cinco. Las presas de los castores aumentaron el área y la profundidad de las charcas, a pesar de no aumentar la frecuencia de madera de más de 10 cm de diámetro. Esto sugiere que los castores utilizan en sus presas trozos de madera más pequeños de lo que estiman la mayoría de los programas de monitoreo. Los cambios en las condiciones del arroyo y de la ribera ocasionados por la presencia de castores fueron insuficientes para alterar las métricas de macroinvertebrados utilizadas habitualmente para evaluar la calidad del agua. La existencia de presas de castores en un tramo se asoció con una menor cobertura vegetal y leñosa a lo largo del borde del arroyo. La reducción de la cobertura de arbustos y la presencia de presas de castores, contracorriente, probablemente influyeron en los pequeños aumentos observados en la temperatura del agua. El hecho de que los castores tendieran a construir presas en tramos con niveles freáticos elevados podría haber minimizado el aumento de la temperatura del agua. De acuerdo a la tasa de ocupación de los castores que se encontró en este estudio, se deberían esperar cambios en las condiciones del arroyo y de la ribera debido a nuevas presas de castores entre el cinco y el 15% de los tramos de arroyo similares a los de este estudio durante las próximas dos décadas. El creciente número de castores que ocupan tramos de arroyos representa un importante enfoque de restauración pasiva que mejorará la calidad de los sistemas acuáticos en los terrenos públicos.

Trends in normalized difference vegetation index time series in differently regulated cascade reservoirs in Wujiang catchment, China

Dam construction is economically and ecologically important for power generation and water capture. However, the effects of cascade dams with various regulation types (i.e., daily, weekly, seasonal, yearly) on vegetation coverage are still need to be clarified. In the current study, we investigated the effects of dam construction on vegetation coverage and predicted the dynamic trends of vegetation at the sub-catchment (i.e., the catchment removing the overlapping catchment of the upstream reservoir) and buffer scale of each reservoir. MODIS Terra normalized difference vegetation index (NDVI) composites (MOD13Q1, 2000–2019) were used to study spatial and temporal changes in riparian vegetation coverage. At the sub-catchment scale, the long-term mean NDVI increased significantly from upstream to downstream from 2000 to 2019, and the NDVI mutation point (i.e., turning point) was consistent with the construction year of the corresponding dam. At the temporal scale, the vegetation trend predictions indicated a greater degree of degradation (23 %–61 %) than in the past (2000–2019; 3 %–32 %). Our findings also showed that reservoir vegetation degradation was associated with regulation type, i.e., daily reservoirs experienced a higher degree of vegetation degradation. Each cascade reservoir exhibited higher past vegetation degradation within the 0–1 km buffer zone compared to the sub-catchment. However, future degradation was predicted to be much higher in the sub-catchment than in the 0–1 km buffer zone, indicating the potential impact of damming on vegetation from adjacent areas (i.e., 0–1 km buffer) with gradual expansion to more distant areas (i.e., sub-catchment) over time. A potential cascade effect of upstream dams on sub-catchment vegetation of downstream dams was also observed. This study provides a reference for watershed management and ecological civilization construction. Relevant laws and policies should be established in areas surrounding reservoirs to help mitigate dam-induced degradation of vegetation communities, especially in reservoirs with short retention times.

Characterization of the impacts of hydro-dams on wetland inundations in Southeast Asia

Inundations of wetlands play a significant role in wetland ecosystems, but they are vulnerable to hydrological alterations. In Southeast Asia, many hydro-dams, which significantly alter the hydrology, have been built, but little is known about the influences of dams on wetland inundations. In this study, we quantified the characteristics of inundations and related the alterations to the dams by distinguishing them from influences of climate variabilities and local human activities. A multi-sensor approach using Landsat 8, Sentinel-1, and MODIS was devised to delineate the weekly inundations of 362 Southeast Asian wetlands from 2014 to 2021. The four hydrological characteristics (cyclical patterns, trends, intra-annual variability, and amplitude of inundations) were quantified, and the alteration of the characteristics caused by dams was separated from climate variabilities and local human activities using correlation analysis and logistic regression models. The results found that cyclical patterns, trends, intra-annual variability, and amplitude of wetland inundations changed significantly over the period, but the magnitudes vary significantly depending on their geographic locations with respect to the dams. Findings showed that dams critically affect the wetlands even though dams are located distantly from the dams. This indicates that wetlands should be monitored and conserved for reducing the influences of dams. This study advances our understanding of the effects of dams on wetlands by using the multi-sensor approach and distinguishing them from climate variabilities and local human activities.

Coupled effects of dam, hydrology, and estuarine filtering on dissolved organic carbon and optical properties in the reservoir-river-estuary continuum

The land–ocean aquatic continuum is affected notably by damming, yet the effects of changing dissolved organic carbon (DOC) and optical properties in the reservoir zone of dammed rivers on the downstream waterbodies remain unclear. This was studied in the Minjiang River (SE China) in the normal, wet, and dry seasons, using the measurements of DOC, absorption spectroscopy, and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). The DOC and absorption spectral slope (S275-295) increased while the absorption coefficient (a280) and DOC-specific UV absorbance (SUVA254) decreased in the surface water of the reservoir. This indicated removals of chromophoric dissolved organic matter (CDOM) and potential additions of autochthonous constituents with lower aromaticity and molecular weight. The discharge of more humified DOC from the middle and deep outlets of the reservoir was evident in the adjacent downstream station in the wet season. The DOC and optical indices were generally stable in the downstream river zone in the normal and dry seasons, suggesting that these signals from the reservoir could persist downstream. In contrast, the downstream DOC and CDOM showed evident additions in the wet season, which might be related to enhanced inputs from the surrounding soils and residential areas in the rainy and hot summer. The absorption coefficient and humic-like components correlated strongly with salinity in the estuarine zone, indicating they were mainly conservative in the estuary of this study. This suggested that the refractory DOC from the reservoir and river zones could pass the estuary and contribute to the carbon storage in the coastal ocean. In contrast, the protein-like components did not correlate significantly with salinity, indicating more active modifications of labile constituents in the estuary. Overall, our results have implications for assessing the effects of damming on DOC and optical properties across the land–ocean aquatic continuum.

Trend analysis and forecasting of streamflow using random forest in the Punarbhaba River basin.

Streamflow rate changes due to damming are hydro-ecologically sensitive in present and future times. Very less studies have done an investigation of the damming effect on the streamflow along with future forecasting, which can be the solution for the existing problems. Therefore, this study aims to use the Pettitt test as well as standard normal homogeneity test (SNHT) to discover trends in streamflow with the future situation in the Punarbhaba River in Indo-Bangladesh from 1978 to 2017. Trend was spotted using Mann-Kendall test, Spearman's rank correlation approach, innovative trend analysis, and a linear regression model. The current work additionally uses advanced machine learning techniques like random forest (RF) to estimate flow regimes using historical time series data. 1992 appears to be a yard mark in this continuum of time series datasets, indicating a significant transformation in the streamflow regime. The MK test as well as Spearman's rho was used to find a significant negative trend for the average (-0.57), maximum (-0.62), and minimum (-0.48) flow regimes. The consistency of the flow regime has been losing consistency, and the variability of flow regime has increased from 2.1 to 6.7% of the average water level, 1.5 to 6.5% of the maximum streamflow, and 3.1 to 5.8% of the minimum streamflow in the post-change point phase. The forecast trend using random forest for streamflow up to 2030 are negative for all four seasons with a flow volume likely to be reduced by 0.67% to-5.23%. Annual and monthly streamflows revealed very negative tendencies, according to the conclusions of unique trend analysis. Flow declination of this magnitude impacts downstream habitat and environment. According to future estimates, the seasonal flow will decrease. Furthermore, the outcome of this research will give a wealth of data for river management and other places with comparable environment.

Study on the sediment and phosphorus flux processes under the effects of mega dams upstream of Yangtze River

The upper Yangtze River (UYR) plays an important role in water supply, hydropower generation, environmental and ecological protection. Constructions of Mega cascade reservoirs have significantly affected the transport of sediment and P, but the evolution of sediment and P in the mega cascade reservoirs of the UYR is unclear. This study investigated the variations in sediment load and total P (TP) flux based on the flow and sediment data from 1990 to 2019 and TP concentrations from 2005 to 2019. In addition, the proportion of sediment load and TP flux from tributaries, variations in the concentrations of particulate P (PP) and dissolved P, trapping effect of dams, and statistical uncertainties were analyzed and discussed. The main results are as follows: (1) the sediment load and TP flux evidently decreased after the impoundment of reservoirs in the UYR and Jinsha River, and the contribution rate of TP flux from main tributaries (except Wu River) to mainstream increased by 3.82–24 %; (2) the error of TP flux calculated by daily and monthly data is within 30 %, which shows that the uncertainty range is clear at some degree attributed to the different monitoring frequency, and the concentration of PP in flood season is greater than that in non-flood season; (3) the total retention rates of sediment and TP in the Three Gorges Reservoir and Gezhouba were 86.78 %, and 49.83 % (2009–2012), respectively, but decreased to 82.85 % and 15.26 % (2013–2019), and the values in Xiangjiaba and Xiluodu were 97.83 % and 60.27 % (2013–2019). The retention rates of newly built reservoirs (Wudongde and Baihetan) were predicted using an empirical method, and the results revealed that new dams would facilitate long-term reduction in sediment downstream.

Effect of river damming on nutrient transport and transformation and its countermeasures

In recent decades, damming has become one of the most important anthropogenic activities for river regulation, and reservoirs have become hotspots for biogeochemical cycling. The construction of dams changes riverine hydrological conditions and alters the physical, chemical, and biological characteristics of rivers, eventually leading to significant variations in nutrient cycling. This review mainly explores the effects of river damming on nutrient transport and transformation, including i) nutrient (N, P, Si, and C) retention in reservoirs, ii) greenhouse gas (GHG) emissions, and iii) interactions between the nutrient stoichiometry ratio and the health of the reservoir ecosystem. The important drivers of nutrient transport and transformation, such as river connectivity, hydraulic residence time, hydropower development mode, microbial community variation, and anthropogenic pollution, have also been discussed. In addition, strategies to recover from the negative effects of damming on aquatic ecosystems are summarized and analyzed. To provide theoretical and scientific support for the ecological and environmental preservation of river-reservoir systems, future studies should focus on nutrient accumulation and GHG emissions in cascade reservoirs.