Effects Of Dams Research Articles

Effects of a bypass-type multistage sand-filled dam on water supply in a drought-vulnerable area in Mullocheon catchment, South Korea

Study regionMullocheon catchment, Gangwon-do, South Korea Study focusClimate change can lead to extreme droughts worldwide, and regions relying on valley streams without large reservoirs are more vulnerable to drought. To address this, a bypass-type multistage sand-filled dam (BMSD) was constructed in a drought-prone area in South Korea, specifically in the Mullocheon catchment, to supply water to a small-population village. The BMSD was connected in series with an existing small pond, and the drainage rates were integrated through a single conduit. Quantitatively analyzing the contribution of the newly constructed sand-filled dam was challenging, so this study investigated the effect of the sand dam on water supply capacity using a bed-mounted infiltration system. The contribution of the sand-filled dam to the total drainage rate was calculated using observation data. New hydrological insights for the regionThe hydraulic conductivity of the riverbed and the drainage rate of the intake pond were estimated using the observed water level and flow rate. Prior to the installation of the sand dam, from January to May 2021, the total precipitation was approximately 284.72mm, and the average drainage rate was 76.78m³/d. After the sand dam was installed, from January to May 2022, the precipitation was 165.13mm, and the average drainage rate increased by 45.4% to 124.49m³/d. It was observed that during normal periods, the supply was more than three times greater than before, and even during droughts, the supply met the residents' needs. This indicates that the sand-filled dam’s storage effect has enhanced drought resilience.

Effects of a subsurface dam on groundwater flow and salt transport in stratified coastal aquifers: Experiments and simulations

Subsurface dams are now widely used to mitigate seawater intrusion in coastal aquifers. Previous studies have mostly focused on the optimal design of subsurface dams under various conditions, but such an attempt in the context of a three-layered (a low-permeability layer in between two high-permeability layers) aquifer is lacked. In reality, many coastal aquifer exhibit such a geological layering feature. This study, using laboratory experiments and numerical simulations, filled the research gap. The results show that, the addition of a subsurface dam to a three-layered coastal aquifer may significantly prolong the particle travel times in both the freshwater zone and the saltwater wedge. Also, the saltwater-freshwater mixing zone in a stratified aquifer can be narrowed by a subsurface dam. However, this trend is reversed when the subsurface dam is located rather landward. Moreover, a subsurface dam may hinder the formation of “freshwater fingers”, which would have formed in aquifers with highly contrasting permeability coefficients between the three layers. Further analysis reveals high-level sensitivity of saltwater-freshwater mixing zone to the height and location of the subsurface dam, and the permeability of the low-permeability layer. These findings promote deeper insights into the impact of subsurface dams on the underground hydrodynamics in complex nearshore groundwater systems. More importantly, conclusions drawn from the study may help to evaluate the environmental impact and optimize the design of subsurface dams to be constructed, ultimately assisting the management of coastal fresh groundwater resources.

A novel Bayesian updating finite element model using enhanced unscented Kalman filter for time-dependent estimation of rockfill dam structure deformation

Due to the time-dependent effect of rockfill dams, the conventional time-invariant finite element method (FEM) can hardly meet practical engineering requirements. This paper proposes an updating Bayesian FEM method for accurate long-term deformation analysis. A combined FEM model is introduced accounting for both instantaneous and creep behaviors. The FEM model is then updated using a Bayesian algorithm, unscented Kalman filter (UKF). The UKF calibrates the prior FEM predictions by incorporating real-time measurement data, thus iteratively reducing discrepancies between model predictions and actual observations. To further enhance the algorithm accuracy, a power-law-based fading memory factor is proposed to mitigate measurement noise in standard UKF. For parameter identification, a slice approach of the high-dimensional covariance confidence ellipsoid is developed. The methodology is validated in Qingyuan rockfill dam, in Guangdong province, China. Results show that the updated FEM is more consistent with the actual monitoring data. The fading memory improves standard UKF performance with a lower relative root-mean-square error (RRMSE). Additionally, the slice method reveals that a specific three-parameter configuration behaves better than the others. The proposed approach can also be extended to other fields including slope and tunneling.

Evaluating the continued significance of dam-induced vigorous downstream channel erosion in the context of projected climate change: a case study from Peninsular India

ABSTRACT Although erosion has naturally been driven by rainfall patterns, human activities have increasingly influenced erosion rates in recent times. However, as climate change alters precipitation, future erosion control may once again depend primarily on climate. The primary goal of this investigation was to ascertain whether the issue of escalated erosion, typically linked to downstream dam effects, could diminish in significance due to projected climatic shifts later in this century. An erosion potential index (Ep), formulated as the ratio of the mass of sediment influx from upstream to the frequency of the sediment-carrying flow events, was computed on a tributary of the Godavari River, located downstream of a dam. Using the Soil & Water Assessment Tool (SWAT), virtual experiments were conducted to distinguish the impacts of the dam from projected climate changes on river geomorphology. Two control scenarios were created using the current climate data and simulated regulated and unregulated states of the basin. Employing climate projections and various mitigation scenarios (SSPs) for the 2060s and 2090s, this study estimated Ep values exclusively under future climatic conditions in an unregulated state of the basin. Results indicate that, in the unregulated state without the existence of the upstream dam, future climate impacts on erosion outweigh the current effects of the dam, underscoring the growing influence of climate on geomorphology. It suggests that existing structural interventions may lose their geomorphic significance in the face of future climate conditions.

Impacts of hydroelectric stations on vegetation phenology in the Lancang River Basin

Hydropower projects can be critical in regulating ecological systems and managing water resources. The combined effects of natural conditions and human activities make the impact of hydropower on vegetation phenology much more complex. In this study, we selected four representative hydropower stations (Huangdeng (HD), Xiaowan (XW), Nuozhadu (NZD), and Jinghong (JH)) along the Lancang River to assess the effects of dams on vegetation phenology. The buffer zone analysis and Geodetector methods were used to evaluate the spatiotemporal variations of vegetation phenology and to analyze the possible causes of vegetation phenology. This study found that: (1) Throughout the study area, the relative contributions of factors affecting the start of the growing season (SOS) were ranked as air temperature (50.46 %), elevation (50.16 %), precipitation (49.90 %), and human activities (34.45 %). (2) The SOS of the rugged areas (HD) had been significantly delayed since water storage. The disparities of vegetation phenology in different areas had been identified by introducing the Core Impact Zone (CIZ) and the Peripheral Impact Zone (PIZ). Within the CIZ, the most pronounced delay was observed in grasslands (+6.57 days/yr). The delay days in the PIZ was 2.68 days/yr, which revealed that the effect of water storage diminished with increasing distance from the water source. (3) Human activities significantly influenced the vegetation phenology around the economically developed region (JH). This research provided new insights into the impact of hydropower development on vegetation phenology in river basins.

Distributed feather-inspired flow control mitigates stall and expands flight envelope

Multiple rows of feathers, known as the covert feathers, contour the upper and lower surfaces of bird wings. These feathers have been observed to deploy passively during high angle of attack maneuvers and are suggested to play an aerodynamic role. However, there have been limited attempts to capture their underlying flow physics or assess the function of multiple covert rows. Here, we first identify two flow control mechanisms associated with a single covert-inspired flap and their location sensitivity: a pressure dam mechanism and a previously unidentified shear layer interaction mechanism. We then investigate the additivity of these mechanisms by deploying multiple rows of flaps. We find that aerodynamic benefits conferred by the shear layer interaction are additive, whereas benefits conferred by the pressure dam effect are not. Nevertheless, both mechanisms can be exploited simultaneously to maximize aerodynamic benefits and mitigate stall. In addition to wind tunnel experiments, we implement multiple rows of covert-inspired flaps on a bird-scale remote-controlled aircraft. Flight tests reveal passive deployment trends similar to those observed in bird flight and comparable aerodynamic benefits to wind tunnel experiments. These results indicate that we can enhance aircraft controllability using covert-inspired flaps and form insights into the aerodynamic role of covert feathers in avian flight.

Programming rumen microbiome development in calves with the anti-methanogenic compound 3-NOP

The aim of this study was to establish a distinctive rumen microbial and fermentation profile using the anti-methanogenic compound 3-NOP to assess dam effect, and nutritional intervention of the juvenile offspring on microbial structure and function of rumen up to 12 months of age, once the treatment was withdrawn. Forty-eight pregnant heifers (H) and their future offspring (C) were allocated to either Control (-) or 3-NOP (+) treatment resulting in four experimental groups: H+/C+, H+/C-, H-/C + and H-/C-. Animals were treated from 6 weeks prior to calving until weaning, with the offspring monitored until 12 months of age. Rumen fluid samples and methane measurements using the Greenfeed system were collected during the trial. Results supported the mode of action of the compound, with a shift in fermentation from acetate to propionate, increases in branched chain fatty acids and formic acid in the 3-NOP treated animals. Similar shifts in microbial populations occurred in 3-NOP treated animals with lower abundances of rumen methanogen populations, increases of bacterial groups Succiniclasticum spp, Candidatus Saccharimonas. Fibrobacter and the families Prevotellaceae and Succinivibrioacea. and the protozoa Entodinium. Early life intervention had an enduring impact on the rumen microbial structure of young animals up to 28 weeks post weaning, however the effect was diminished once 3-NOP was withdrawn. Interestingly, a group of young animals emitted significantly less methane (15%) than the animals that did not receive the treatment during their juvenile stage. Our results suggest a higher resemblance of the young calf microbiome to a low methane adult and that early life colonisation of the rumen persists through to later life with the pre-weaning microbiome comprising ~ 65% of the yearling animal. Further research needs to be performed to determine the timing and dose of 3-NOP for new-born calves that can sustain a reduction in methane emissions after the treatment is withdrawn, under extensive grazing or controlled conditions.

Monitoring Coastal Evolution and Geomorphological Processes Using Time-Series Remote Sensing and Geospatial Analysis: Application Between Cape Serrat and Kef Abbed, Northern Tunisia

The monitoring of coastal evolution (coastline and associated geomorphological features) caused by episodic and persistent processes associated with climatic and anthropic activities is required for coastal management decisions. The availability of open access, remotely sensed data with increasing spatial, temporal, and spectral resolutions, is promising in this context. The coastline of Northern Tunisia is currently showing geomorphic process, such as increasing erosion associated with lateral sedimentation. This study aims to investigate the potential of time-series optical data, namely Landsat (from 1985–2019) and Google Earth® satellite imagery (from 2007 to 2023), to analyze shoreline changes and morphosedimentary and geomorphological processes between Cape Serrat and Kef Abbed, Northern Tunisia. The Digital Shoreline Analysis System (DSAS) was used to quantify the multitemporal rates of shoreline using two metrics: the net shoreline movement (NSM) and the end-point rate (EPR). Erosion was observed around the tombolo and near river mouths, exacerbated by the presence of surrounding dams, where the NSM is up to −8.31 m/year. Despite a total NSM of −15 m, seasonal dynamics revealed a maximum erosion in winter (71% negative NSM) and accretion in spring (57% positive NSM). The effects of currents, winds, and dams on dune dynamics were studied using historical images of Google Earth®. In the period from 1994 to 2023, the area is marked by dune face retreat and removal in more than 40% of the site, showing the increasing erosion. At finer spatial resolution and according to the synergy of field observations and photointerpretation, four key geomorphic processes shaping the coastline were identified: wave/tide action, wind transport, pedogenesis, and deposition. Given the frequent changes in coastal areas, this method facilitates the maintenance and updating of coastline databases, which are essential for analyzing the impacts of the sea level rise in the southern Mediterranean region. Furthermore, the developed approach could be implemented with a range of forecast scenarios to simulate the impacts of a higher future sea-level enhanced climate change.

Effects of an amazonian dam on taxonomic, functional and phylogenetic diversity of non-volant small mammals

Effects of an amazonian dam on taxonomic, functional and phylogenetic diversity of non-volant small mammals

Economic impacts of large dams on downstream brickmaking in developing countries

Large dams have positive and negative impacts, including disrupting brickmaking on the floodplains downstream due to flow regulation and sediment reduction, affecting the supply of essential construction material, notably in developing countries. In this study, we introduce an analytical framework to assess the economywide effects of large dams on downstream brickmaking, focusing on Traditional Fired Clay Brick (TFCB). The framework includes three steps: characterizing the impacts on river flow and sediment load using river system modeling and secondary data, understanding the role of TFCB production in the economy based on survey and economic data, and quantifying the economywide impacts of changes in TFCB production using dynamic computable general equilibrium modeling. We demonstrate the functionality of the approach by conducting a case study of the impacts of the Grand Ethiopian Renaissance Dam (GERD) on the Sudanese economy due to changes in TFCB production by comparing two scenarios: “with GERD” and “no GERD.” Results show that Sudan’s accumulated (2023–2050) discounted (at 0.5% annually) Gross Domestic Product (GDP) at factor cost would decline by US$ 6 billion (−0.38%) due to a reduction in TFCB production. Consumer flexibility regarding brick types and the ability of alternative brick sources to fill the demand gap are key determinants of the impacts.

Bayesian approach to estimate variance components and genetic parameters of average daily gains and Kleiber ratios in crossbred cattle.

The present study aimed to estimate variance components and genetic parameters of the average daily gains from birth to 3-months (ADG1), 3- to 6-months (ADG2), 6- to 9-months (ADG3) and 9- to 12-months (ADG4) of age and corresponding Kleiber ratios (KR1, KR2, KR3 and KR4, respectively) in Jersey crossbred calves. Data for this study were collected from National Dairy Research Institute, Eastern Regional Station, Kalyani, West Bengal, India during 2013 to 2021. Genetic parameters for the traits were estimated using Bayesian procedure through Gibbs sampling by fitting six animal models. The deviance information criterion (DIC) was employed to determine the most appropriate model for each trait under investigation. Direct heritability estimates for ADGs and KRs ranged from 0.19 (ADG3) to 0.59 (ADG2) and 0.14 (KR3) to 0.72 (KR1), respectively. Significant maternal heritability ( ) was observed for average daily gains (17-24%) and Kleiber ratios (13-18%) at different age intervals under the best model. Estimates of permanent environmental effects ( ) of dam for ADG1, ADG2, KR2 and KR4 were only 1-4% of the total phenotypic variance in this study. Large negative estimates of correlations, ranging from -0.87 to -0.98, between direct and maternal ) effects for ADGs and KRs (except KR3) at different age intervals were observed. Total heritability ( ) and maternal repeatability ) of the studied traits ranged 0.05-0.28 and 0.01-0.14, respectively. The moderate to high heritability estimates for all traits in this study indicate the possibility of genetic progress for these traits through selective breeding program.

Use of long-term underwater camera surveillance to assess the effects of the largest Amazonian hydroelectric dam on fish communities

The increase in the construction of mega dams in tropical basins is considered a threat to freshwater fish diversity. Although difficult to detect in conventional monitoring programs, rheophilic species and those reliant on shallow habitats comprise a large proportion of fish diversity in tropical basins and are among the most sensitive species to hydropower impacts. We used Baited Remote Underwater Video (BRUV), an innovative, non-invasive sampling technique, to record the impacts caused by Belo Monte, the third largest hydropower project in the world, on fishes inhabiting fast waters in the Xingu River. BRUV were set in a river stretch of ~ 240 km for 7 years, 2 before and 5 after the Belo Monte operation. We explored the spatial and temporal variation in fish diversity (α, β, and γ) and abundance (MaxN) using generalized additive models. We also investigated the variation of environmental variables and tested how much information we gained by including them in the diversity and abundance models. Belo Monte altered the flow regime, water characteristics, and fishery yield in the Xingu, resulting in changes in the fish community structure. Temporally, we observed sharp declines in α diversity and abundance, far exceeding those from a previous study conducted with more conventional sampling methods (i.e., catch-based) in the region. γ-diversity was also significantly reduced, but we observed a non-expected increase in β diversity over time. The latter may be associated with a reduction in river connectivity and an increase in environmental heterogeneity among river sectors. Unexpected signs of recovery in diversity metrics were observed in the last years of monitoring, which may be associated with the maintenance of flow levels higher than those previously planned. These results showed that BRUV can be a useful and sensitive tool to monitor the impacts of dams and other enterprises on fish fauna from clear-water rivers. Moreover, this study enhances our comprehension of the temporal variations in freshwater fish diversity metrics and discusses the prevalent assumption that a linear continuum in fish-structure damage associated with dam impoundments may exhibit temporal non-linearity.

Effect of Check Dams on Sediment Concentration in a Watershed in the Loess Hilly Area During a Heavy Rain Event

ABSTRACTUnderstanding the changes of sediment concentration in rivers, especially under heavy rains, is of great significance to accurately evaluate the effectiveness of soil and water conservation measures in the Loess Hilly Area. On July 26, 2017, an extremely heavy rain (maximum rain intensity of 66.6 mm/h, the highest rainfall of 256.8 mm in 10 h, and a return period of 100 years) occurred over the 821 km2 Xiaoli River watershed in the Wuding River watershed. In order to understand the sediment concentration during the heavy rain event, 10 dam‐controlled catchments in the center of the rainstorm (3 in the Xiaoli River watershed and 7 in its adjacent watersheds) without drainage and damage were selected. All the retained runoff and sediment in the check dams were measured by the cross‐sectional survey according to the flood marks left by the heavy rain. Combined with the observed runoff and sediment transport data by the hydrological station at the outlet of the Xiaoli River watershed as well as the deposited sediment investigated in the watershed during the heavy rain event, the change of sediment concentration and the role of check dam were analyzed. Results showed that under heavy rain, all the sediment concentrations of runoff in the dam‐controlled catchments ranged from 344 to 552 kg/m3, suggesting that the sediment retaining effect of slope measures (woodland, grassland, and terrace) is limited and cannot prevent the occurrence of hyperconcentrated flows. The gully measures (check dams) in the Xiaoli River watershed can hold a large amount of sediment under heavy rain and make the runoff no longer a hyperconcentrated flow at the watershed outlet. In order to control the transport of hyperconcentrated flows to the downstream, more attention should be paid to the construction of check dams while carrying out vegetation ecological construction in the Loess Hilly Area.

228 Evaluation of sire vs. dam influences on age at first parturition in Brahman heifers

Abstract The objective of this study was to determine if sire or dam had a stronger impact on age at first parturition of Brahman heifers (n = 833) born between 2000-2021. Typically, in Bos taurus heifers, puberty occurs between 10 to 12 mo of age leading to parturition of the first calf occurring around 24 mo of age. However, in Bos indicus cattle, puberty is achieved between 15 to 17 mo of age leading to a first calf around 36 mo of age. The ability of heifers to achieve pubertal status earlier plays a vital role in reproductive success. For selection purposes, knowing if early pubertal attainment is influenced more by the sire or dam is important for herd management. For this study, to minimize any epigenetic and environmental changes, all heifers originated and were developed at the Texas A&M AgriLife Research Center at Overton. Sire groups (SG) and dam groups (DG) were established based on the number of offspring used in the study. Sire groups were comprised of SG-1 (1+ calves sired; n = 58 sires), SG-2 (5+ calves sired; n = 44 sires), SG-3 (10+ calves sired; n = 31 sires), SG-4 (15+ calves sired; n = 23 sires), SG-5 (20+ calves sired; n = 17 sires), and SG-6 (25+ calves sired; n = 12 sires). Dam groups consisted of DG-1 (1+ calves; n = 489 dams), DG-2 (2+ calves; n = 215 dams), DG-3 (3+ calves; n = 81 dams), DG-4 (4+ calves; n = 38 dams), and DG-5 (5+ calves; n = 9 dams). Statistical analysis (PROC GLM; SAS 9.4) included the fixed effect of sire group (dam group) and all dams (sires) utilized in that grouping. Significance for age at first calving was considered at P < 0.05. Mean separation for age was performed using LSmeans. Sire significantly impacted age at first calving in SG-1 (P = 0.0173) vs dam effect (P = 0.3993; n = 489 dams), SG-2 (P = 0.0159) vs dam effect (P = 0.5476; n = 481 dams), SG-3 (P = 0.0023) vs dam effect (P = 0.2532; n = 439 dams), SG-4 (P = 0.0022) vs dam effect (P = 0.3997; n = 400 dams), SG-5 (P = 0.0002) vs dam effect (P = 0.0602; n = 361 dams), and SG-6 (P = 0.0005) vs dam effect (P = 0.1058; n = 305 dams). The dam impact on age at first calving was never significant in the dam groupings but sires did impact age at first calving in two groups: DG-1 (P = 0.3993) vs sire effect (P = 0.0173; n = 58 sires), DG-2 (P = 0.4823) vs sire effect (P = 0.0173; n = 56 sires), DG-3 (P = 0.3011) vs sire effect (P = 0.3420; n = 49 sires), DG-4 (P = 0.3911) vs sire effect (P = 0.6278; n = 40 sires), and DG-5 (P = 0.3042) vs sire effect (P = 0.9159; n = 23 sires). In summary, evaluation of sire and dam influences on age at first parturition for female offspring demonstrates that the ability to calve at an earlier age is influenced by the sire but not the dam. Further studies into the mechanisms for the transmission of this trait are warranted.

Landscape patterns of carbon fluxes in natural and disturbed ice-wedge-polygon tundra

ABSTRACT The degradation of ice-rich permafrost ecosystems due to climate change and infrastructure development strongly impacts carbon exchange dynamics in tundra landscapes. This study investigates the effects of surficial geology and infrastructure disturbances from road dust and flooding on vegetation and trace gas fluxes in polygonal ice-wedge tundra in arctic Alaska. We compared CO2 and CH4 fluxes from closed-chamber measurements at common landform elements (polygon centers, troughs, and rims) at a natural site and a disturbed site within the Prudhoe Bay Oil Field. Relationships among environmental parameters, plant species composition, and trace gas fluxes were assessed through nonmetric multidimensional scaling. Map extrapolations showed spatial variations in midsummer landscape-level ecosystem productivity and CH4 efflux at the various geologic landforms. Highest carbon uptake occurred in ice-rich drained thaw lake basins with aquatic, graminoid-dominated polygon troughs. In contrast, wet, featureless areas associated with more recently drained, ice-poor thaw lake basins showed a net carbon loss even during summer. The damming effect of road infrastructure led to deeply flooded, minimally vegetated troughs with low ecosystem respiration and high CH4 fluxes close to the road. This work highlights the importance of the complex interactions among surficial geology, landform elements, vegetation type, and disturbance factors in understanding carbon exchange dynamics in ice-rich permafrost environments.

Gravity dam displacement monitoring using in situ strain and deep learning

AbstractRecent studies in dam displacement monitoring primarily focus on single‐response monitoring or model updating using advanced techniques. Few studies involve the combination analysis of displacement with other synchronized responses utilizing their monitoring characteristics. In situ strain data provide a strength‐safety perspective for dam displacement monitoring. The challenge lies in that estimating displacement directly using limited discrete strain data may be misleading. This paper analyzes the relationship between displacement and global, and multipoint local strains from the perspective of the differences in load effects of gravity dams, and indicates that introducing appropriate state factors improves the estimation. A displacement estimation model driven by strain data and state factors is developed using stacked convolutional neural network, and the variable relationships within the model are interpretated via accumulated local effects. Incorporating specific strength criteria, a novel displacement monitoring indicator based on the tensile safety of the dam heel is proposed. A case study of a gravity dam showcases the effectiveness of the proposed approach in comparison with the solely strain‐based model and the traditional hydrostatic‐seasonal‐time factors‐based model.

Boa Esperança's Dam Reservoir Ichthyofauna

Objective: The the present study investigated the composition and structure of the fish assemblage of the reservoir of Boa Esperança, located in the main body of the Parnaíba River, aiming to contribute to the expansion of knowledge on fish diversity of anthropic ecosystems and subsidizing management actions for the conservation of the diversity of inland waters. Method: Traps installation points were randomly chosen in order to include the greatest possible amount of aquatic microhabitats found in the Boa Esperança dam lake, on the Parnaíba river, in order to capture the greatest possible fish diversity. Samples were collected every two months, between September 2013 and October 2014 (SISBIO 42018-2 OF 12/12/2013), in which standardized gill nets were used (from 3 to 10 cm between opposite). Research results and discussions: The result of the fauna inventory was a total of 823 specimens, subdivided into 6 orders, 20 families and 39 species. The most abundant species upstream was the "Arenga" Pellona flavipinnis, with 198 specimens captured, accounting for 24% of the total capture in both systems. In the downstream stretch, it was the "Pacu" Myleus asterias, corresponding to 6.8% of the total capture in both systems, with 14 endemic species. Research implications: Implications of the research: The results obtained serve to show the impacts caused by the construction of the dam on the local ichthyofauna. Originality/Value: This study contributes to the understanding of the effect of dams on the maintenance, preservation and modification or not of the ichthyofauna existing in the rivers where they are implemented. It also serves as a basis for future analyses of the effects of dams on riverside populations that use the local ichthyofauna as a source of subsistence.

Environment DNA Reveals Fish Diversity in a Canyon River within the Upper Pearl River Drainage.

Investigating fish diversity in canyon rivers through conventional fish surveys is challenging due to precipitous conditions, including steep slopes, rapid water flow, and complex habitats. Additionally, intensive construction of dams has further complicated the understanding of contemporary fish diversity in these rivers. In this study, we used the environmental DNA (eDNA) technique to assess fish diversity and examine the effects of dams on fish diversity in the Mabiehe River, a canyon river in the upper reaches of the Pearl River drainage. Water samples from 15 sampling sites were collected, yielding 9,356,148 valid sequences. Utilizing the NCBI public database, a total of 60 freshwater fish species were identified, with Carassius auratus, Cyprinus carpio, and Pelteobagrus fulvidraco being the most dominant species in the Mabiehe River. We also detected one nationally protected fish species, three provincially protected fish species, and six exotic species in this river. Furthermore, eDNA analyses demonstrated that the lotic river sections harbor more species and greater diversity than dammed sections, suggesting that dams might exert significant impacts on local fish diversity. Overall, this study supports the effectiveness of the eDNA technique as a complementary tool to traditional field surveys for monitoring fish biodiversity in canyon rivers.

Temporal Changes in the Effect of Damming on the Degree of Hydrological and Ecological Alteration in Floodplain River and Wetland

Temporal Changes in the Effect of Damming on the Degree of Hydrological and Ecological Alteration in Floodplain River and Wetland

Size-dependent effects of dams on river ecosystems and implications for dam removal outcomes.

Understanding the relationship between a dam's size and its ecological effects is important for prioritization of river restoration efforts based on dam removal. Although much is known about the effects of large storage dams, this information may not be applicable to small dams, which represent the vast majority of dams being considered for removal. To better understand how dam effects vary with size, we conducted a multidisciplinary study of the downstream effect of dams on a range of ecological characteristics including geomorphology, water chemistry, periphyton, riparian vegetation, benthic macroinvertebrates, and fish. We related dam size variables to the downstream-upstream fractional difference in measured ecological characteristics for 16 dams in the mid-Atlantic region ranging from 0.9 to 57 m high, with hydraulic residence times (HRTs) ranging from 30 min to 1.5 years. For a range of physical attributes, larger dams had larger effects. For example, the water surface width below dams was greater below large dams. By contrast, there was no effect of dam size on sediment grain size, though the fraction of fine-grained bed material was lower below dams independently of dam size. Larger dams tended to reduce water quality more, with decreased downstream dissolved oxygen and increased temperature. Larger dams decreased inorganic nutrients (N, P, Si), but increased particulate nutrients (N, P) in downstream reaches. Aquatic organisms tended to have greater dissimilarity in species composition below larger dams (for fish and periphyton), lower taxonomic diversity (for macroinvertebrates), and greater pollution tolerance (for periphyton and macroinvertebrates). Plants responded differently below large and small dams, with fewer invasive species below large dams, but more below small dams. Overall, these results demonstrate that larger dams have much greater impact on the ecosystem components we measured, and hence their removal has the greatest potential for restoring river ecosystems.