Effects Of Dam Construction Research Articles

Environmental fate of microplastics in alpine and canyon-type river-cascade reservoir systems: Large-scale investigation of the Yalong River in the eastern Qinghai-Tibet Plateau

Reservoirs are regarded as potential collection sites for microplastics (MPs), and ample water resources in plateau regions provide favorable natural conditions for hydroelectric power generation. However, research on the impact of cascade reservoir construction in the plateau region on the fate of MPs within the watershed is limited. In this study, the Yalong River, an alpine canyon river in the eastern Qinghai-Tibet Plateau, was selected as the research area. This study explored the distribution of MPs at various depths in water, sediment, and riverbank soil as well as the formation of “MP communities” within the river-cascade reservoir system. Furthermore, the effects of dam construction on MPs' migration in different environments were analyzed. The results revealed that the abundance of MPs in the water and sediment within the cascade reservoir area (CRA) was significantly higher than that in the river area (RA) (P < 0.001). Additionally, the trend of increasing MPs in water with decreasing altitude was notably slower in CRA. Regarding shape, the proportion of fibers in the water within the CRA was significantly lower than that in the RA, with a smaller vertical migration rate in the water than in the sediment. The proportion of MPs < 500 μm in the water within the CRA was significantly higher than that in the RA. High-density MPs were notably deposited in the reservoir sediments. The analysis of the MP communities revealed that the construction of cascade dams led to relative geographical isolation between different sampling sites, reducing the similarity of MP communities in the CRA. This study established a theoretical foundation for understanding the impact of cascade dam construction on the fate characteristics of MPs and their potential risks in plateau areas.

Whole-genome resequencing confirms the genetic effects of dams on an endangered fish Hemibagrus guttatus (Siluriformes: Bagridae): A case study in a tributary of the Pearl River

Dam construction in riverine ecosystems has fragmented natural aquatic habitats and has altered environmental conditions. As a result, damming has been demonstrated to threaten aquatic biodiversity by reducing species distribution ranges and hindering gene exchange, leading to the inability to adapt to environmental changes. Knowledge of the contemporary genetic diversity and genetic structure of fish populations that are separated by dams is vital to developing effective conservation strategies, particularly for endangered fish species. We chose the Lianjiang River, a tributary of the Pearl River, as a case study to assess the effects of dams on the genetic diversity and genetic structure of an endangered fish species, Hemibagrus guttatus, using whole-genome resequencing data from 63 fish samples. The results indicated low levels of genetic diversity, high levels of inbreeding and decreasing trend of effective population size in fragmented H. guttatus populations. In addition, there were significant genetic structure and genetic differentiation among populations, suggesting that the dams might have affected H. guttatus populations. Our findings may benefit management and conservation practices for this endangered species that is currently suffering from the effects of dam construction.

Effects of dam construction on the reproduction of the Yellow River carp (Cyprinus carpio) in lower reaches of the Yellow River, China

The construction of dams changes the natural flow of rivers, affects the integrity of river ecosystems, and causes a series of ecological and environmental problems, such as habitat fragmentation and reduction in fish resources. This study took a section of the Yellow River in China from the Xiaolangdi Dam to Gaocun as the research area. The Yellow River carp (Cyprinus carpio) was selected as an indicator species for its economic value. A habitat suitability model for the Yellow River carp coupled with a one-dimensional hydrodynamic model was built. It was used to simulate dynamic changes in the reproductive habitat suitability of the Yellow River carp before and after the construction of the Xiaolangdi Dam. We demonstrated the spatial distribution of the carp’s spawning reaches before and after the Xiaolangdi Dam construction and investigated its influence on the spawning activity and larval development of the species accordingly. The results apparently showed that the construction and operation of the Xiaolangdi Dam delayed the breeding time of the Yellow River carp and decreased its quality by 5.28%. In particular, the larval fish development was greatly affected by the dam, with the quality being reduced by 8.95%. Furthermore, the habitat suitability of the spawning reaches slightly decreased as the extent of spawning reaches decreased by 16.23%, and several spawning reaches were lost entirely. This study shed light on the response of the Yellow River carp to hydrological and physical changes in the period 1980–1990 before the construction of the Xiaolangdi Dam and 2006–2018 after the construction. Thus, it is a valuable reference for the ecological scheduling of discharges of the Xiaolangdi Dam.

Displacement and Livelihoods through the Construction of Small Dams: Legacies of Magunje Dam in Hurungwe District, Mashonaland West Province, Zimbabwe

This article examines the experiences of people in rural areas who are displaced by the construction of small dams. Scholarship on dam construction has generally focused on the impact of big dams on communities. Yet, this study argues, small dam construction projects also impact those living on the site and vicinity of small dams. Using Magunje Dam in Hurungwe District of Zimbabwe as a lens, the study traces the experiences of the changed livelihoods of communities that resisted being moved and those who were relocated to other places. By taking this approach, the study establishes the complex impact of the Magunje Dam project on the evicted people and argues that those who are affected by small dam projects sometimes suffer unwanted consequences and their challenges are difficult to remedy because they occupy the fringes of society. Their challenges go unnoticed, especially after receiving paltry compensation. The study shows that displacement and involuntary resettlement destabilise the family fabric. Through the lenses of the Impoverishment Risks and Reconstruction model (IRR), the effects of dam construction on rural people are unpacked. Data was obtained through qualitative research methodologies.

Genetic Diversity and Population Differentiation of Chinese Lizard Gudgeon (Saurogobio dabryi) in the Upper Yangtze River

Dam construction on the upper Yangtze River has dramatically altered riverine ecosystems and caused habitat fragmentation of fishes, which might influence the genetic structure of fish populations. In this study, we examined the possible genetic effects of dam construction on Chinese lizard gudgeon (Saurogobio dabryi) populations in the upper Yangtze River, China. Seven populations were sampled, and genetic structure was analyzed using single nucleotide polymorphism (SNP) markers through the specific locus amplified fragment sequencing (SLAF-seq) method. The numbers of SNPs were lower in the upstream populations than in the downstream populations. Genetic similarity was increased from downstream to upstream. The upstream populations of S. dabryi might be more vulnerable to genetic drift than those downstream. Structure analysis indicated three distinct genetic groups of S. dabryi in the upper Yangtze River, among which the genetic differentiation values (Fst) were at a high level. The genetic differentiation of S. dabryi exhibited a close correlation with spatial distance. We did not detect a significant correlation between isolation time and genetic differentiation, suggesting that impacts of dams on the genetic structure of S. dabryi can be relatively minimal on a short time scale. The results quantify the genetic diversity and population structure patterns of S. dabryi after habitat fragmentation caused by dams, which will provide a reference for resource protection and management of this species in the upper Yangtze River.

Review of Effects of Dam Construction on the Ecosystems of River Estuary and Nearby Marine Areas

Dams have made great contributions to human society, facilitating flood control, power generation, shipping, agriculture, and industry. However, the construction of dams greatly impacts downstream ecological environments and nearby marine areas. The present manuscript presents a comprehensive review of the influence of human activities on the environment, especially the effect of dam construction on the ecosystems of river estuaries and nearby marine areas, so as to provide a scientific basis for ecological environment protection. To summarize these impacts, this review used recent studies to comprehensively analyze how dam construction has affected river hydrology, geomorphology, and downstream ecosystems globally. Effects of dams on ecosystems occur through reduced river flow, reduced sediment flux, altered water temperature, changed estuary delta, altered composition and distribution of nutrients, altered structure and distribution of phytoplankton populations, habitat fragmentation, and blocked migration routes in river sections and adjacent seas. Effects of dam construction (especially the Three Gorges Dam) on the Yangtze River were also reviewed. Performing community and mitigation planning before dam construction, exploring new reservoir management strategies (including targeted control of dam storage and flushing sediment operations), banning fishing activities, and removing unnecessary dams (obsolete or small dams) are becoming crucial tools for ecosystem restoration.

Incorporating the life stages of fish into habitat assessment frameworks: A case study in the Baihetan Reservoir

Although it is widely accepted that the construction of dams may alter fish habitats, few studies have followed the life cycles of fish and combined the environmental conditions with the ecological behaviors and habit preferences of fish during reproductive processes to assess its effects of dam construction. In this study, we call for more sophisticated and holistic assessment framework, including effectiveness of technologies intended to mitigate environmental impacts in different life stages. An assessment framework that considers the swimming ability, perception ability of water flow and environmental preference of different fish species during migration, spawning and hatching was proposed. We used the Baihetan Reservoir as an example environment to assess the impoundment effect on the habitat of a tributary upstream of the reservoir. We observed shifts in the habitats of target fish in different life stages which is dominated by reservoir operation of the Baihetan Dam. Combined with the response of fish activities to impoundment, the selection of suitable positions for artificial breeding and release projects and the outlet of the fish transportation system were recommended measures to improve the migration possibilities. Our reassessment results also demonstrated the theoretical possibility and feasibility of joint improvements in spawning and hatching periods using instream structures. Our framework provides a complete set of “assessment-solution” processes for developers and managers to address the aquatic ecological degradation caused by resource development, and its use is strongly recommended for assessments or assessments of damming effects in other regions and on other fish species.

Effects of Dam Construction in the Wang River on Sediment Regimes in the Chao Phraya River Basin

The Wang River is one of the major tributaries of the Chao Phraya River (CPR) system in Thailand as the key riverine sediment source supplying the Chao Phraya Delta that has experienced severe shoreline retreat in the past six decades. Historical and observed river flow and sediment data measured during 1929–2019 were used to assess the variation in total sediment load along the Wang River and evaluate the effects of three major dam constructions on sediment supplied from the Wang River to the CPR. Results indicated that sediment loads increased toward downstream. Variation in long-term total sediment load (TSL) along the river suggested that construction of the Kiew Lom Dam in 1972 did not cause a reduction in sediment yield in the Wang River Basin because it impounded less than 20% of the average annual runoff, while the Mae Chang and Kiew Koh Ma Dams caused downstream sediment reduction. These three dams are located in the upper and middle river basins, and their effects on sediment load in the Wang River are ameliorated by additional sediment supplied from the lower basin. Results confirmed that construction of these three major dams in the Wang River did not greatly impact sediment supply from the Wang River to the CPR system. The dam site and sediment load variation along the river are the primary factors controlling the impact of the dam construction.

Effects of dam construction and fish invasion on the species, functional and phylogenetic diversity of fish assemblages in the Yellow River Basin

An understanding of the consequences of human-mediated disturbances from multi-facet diversity (i.e. species, functional and phylogenetic) perspectives is of great significance in biodiversity assessment and conservation planning. Most previous studies have concentrated on anthropogenic effects on species diversity in the Yellow River Basin (YRB) in China, but information on anthropogenic effects on phylogenetic and functional facets is still pending. Here, we identified the temporal changes in species, functional, and phylogenetic alpha diversity of fish assemblages in 18 reaches (i.e. 15 mainstream reaches and 3 tributaries) of the YRB under the background of long-term cascade hydropower construction and widespread introduction of non-native fish species. The results showed that native fishes experienced a sharp decline through time, with an average of 25.6 (extirpation rate 46.7%) native species extirpated per sub-region, and 89 of 182 (48.9%) native species extirpated across the whole basin during the period considered. However, the number of non-native fish species substantially increased, with an average increase of 8.6 species (invasion rate 26.9%) per sub-region. Furthermore, the percentage of non-native species showed a significant unimodal relationship with average altitude, with highest invasion rates (ca. 70%) in upstream reaches. The extirpation rate was negatively related to altitude, increasing from upstream to downstream reaches. Interestingly, the functional diversity indices (FEve, FDiv, FDis, RaoQ) and phylogenetic diversity indices (Δ+ and Λ+) of the entire fish fauna significantly increased through time, whereas these indices based on native fish fauna only did not change. Such increases in functional and phylogenetic diversities were mainly triggered by introductions of non-native species, which were functionally distinct and phylogenetically distant from native species, and extirpation of congeneric endemic species. In general, the present study revealed anthropogenic impacts on the multi-faceted diversity of fish assemblages in a large river and highlighted the negative effects of cascaded hydropower developments and non-native fish invasions on native fish. Moreover, evaluating the responses of multi-faceted diversity to anthropogenic disturbances is a suitable means to understand assemblage reorganization and to assess how such impacts lead to the decline of biodiversity. The complementary information derived from using the multi-faceted diversity approach indicate functional and phylogenetic diversity measures could be implemented in biodiversity planning in the sediment-laden and ecologically important Yellow River Basin.

Performance-based analysis of earth dams: a case study of Hajji Qushan watershed, Iran

Recently, land-use change, as well as climate change through seasonal floods, have caused increasing damage to the Hajji Qushan watershed. Therefore, to reduce the peak discharge of floods, the construction of earth dams is necessary and inevitable. This study aimed to evaluate the effect of embankment structures on the reduction of peak discharge and their effects on the downstream flow regime. For this purpose, to present a favorite rainfall-runoff model and to route the mainstream channel, the HEC–HMS model was utilized. The required data included data from three rain gauge stations and two hydrometric stations. To delineate the boundaries of the watershed, ArcGIS 10.3 (HEC–GeoHMS extension) was implemented. To extract the digital elevation model (DEM), 10-m contour lines were used. The results showed the lack of satisfactory effects of dam construction on the reduction of peak flood discharge. The location of dam construction, reservoir capacity, and watershed area were of the factors that determined the possible reduction of flood risk.

Effects of dam construction on the main-stream river, a lesson from Ba Lai dam, Ben Tre province

Water can make a substantial contribution to human life for drinking as well as purposes related to human life and human nature. Because of increasing demand for water, there is a need for dam construction in preparation for agricultural purposes, drinking, industry and also flood control, power generation, etc. Simultaneously, they have had a considerable impact on the environment. A large range of potential impacts and hazards linked to the exploitation of dams and reservoirs, such as: (i) Major change in flow regime, thermal regime, physico-chemical cycles, (ii) reduction or loss of biological diversity, particular in aquatic species, (iii) greenhouse gas emissions, (iv) increases in the number of infectious disease and accumulation of heavy metals in food web...Therefore, there are various potential health risks of the environment and residents. However, whilst dam effects are very well documented elsewhere in the world, little or no information about negative effects of dams on the environment is available from Vietnam. Consequently, this paper provides a brief review of the environmental impact of dam constructions and after that, we will investigate some strategies to deal with the effects for Vietnam. By the way, we give some insight into ​​the first studies on the impacts of dams on the environment, which focuses on aquatic species was also noted in paper.

Is core bacterial community more vulnerable to environmental changes in dammed river?

It is well known that dam construction has a potential to impact water quality, resulting other related changes on bacterial community structure and diversity. Yet, effects of dam construction on planktonic and sediment bacterial structure are much more fragmentary. Through sampling of water and sediments along a dammed river between winter and summer, bacterial community were investigated using Illumina high-throughput sequencing. Core bacterial community, including Proteobacteria (55.29%), Firmicutes (25.29%), Bacteroidetes (17.22%), Verrucomicrobia (1.27%) and Gemmatimonadetes (0.93%), were maintained among water and sediments and between seasons. Mantel test showed the core bacterial community was less sensitive to environmental variable. However, a few of dominant microbe, such as class Alphaproteobacteria and family Sphingomonadaceae in core community were still tightly correlated with physiochemical properties according to correlation analysis. Physiochemical characteristics in water and sediment were mainly affected by season fluctuations. Changes in sediment texture has been attributed to the dam construction. This study suggests a potential to detect possible biological indicators of human and natural pressures in riverine system.

Response of the nitrogen load and its driving forces in estuarine water to dam construction in Taihu Lake, China.

To regulate the water level and minimize the occurrence of water eutrophication in shallow lakes, dams and gates are often constructed in rivers. However, this practice may result in a deterioration of water quality in some estuaries. In the present study, using the correction of Nemerow pollution index (CNPI) and a redundancy analysis (RDA), water samples from different dammed rivers around Taihu Lake were compared to assess the pollution risk and identify the factors responsible for water eutrophication. The average total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) concentrations, and chemical oxygen demand (CODMn) were 2.45 ± 2.28, 0.08 ± 0.06, 43.01 ± 18.75, and 10.78 ± 4.86 mg L-1, respectively. The CNPI values indicated that approximately 76.47% of the estuarine water was moderately polluted (1 < CNPI < 7.28). A positive correlation was observed between dam construction and nutrient concentrations (e.g., rTN = 0.38, p < 0.05; rTP = 0.89, p < 0.01). Under the effects of dam construction, land use change, estuary shape, and meteorological conditions, there was a clear spatial variation of the TN concentrations. Dams that were closed all year round accelerated the TN accumulation in the water around them. The pollution risk in a trumpet-shaped estuary was higher than that in other regions (t = 2.92, p = 0.02). Endogenous release of pollutants was an important factor that may have a priming effect on algal blooms and should be given more attention. In Wuli Lake, exogenous pollution was the dominant pollutant source. A total of 74.49% of the nitrogen losses with the runoff into the estuarine water in 2018 were derived from urban domestic sewage and constructed land, with the load being 4.40 times higher than in 2000. The RDA results revealed that dam construction was the main factor (43.70%) affecting water quality, while meteorological conditions, land use types, estuary shape, and other factors contributed 56.30%. Scientific regulation and control of dam operation is important to protect the water environment of Taihu Lake.

Impact of river discharge seasonality change on tidal duration asymmetry in the Yangtze River Estuary

The Yangtze River Estuary (YRE) is one of the world’s largest river-tidal systems with rapidly changing hydrology and morphology following the construction of multiple dams. The effects of dam construction may extend to the region close to the coast, where channel stability depends on the asymmetry of the tide. Here, we focus on the possible effects of changing discharge regimes on tidal asymmetry in the YRE. Specifically, we focus on the difference in duration between ebb and flood, quantified as tidal duration asymmetry, because it has strong implications for residual sediment transport and can be derived from available water level data. To cope with nonstationary tides under the influence of a time-varying river discharge, a nonstationary harmonic analysis tool (NS_TIDE) is applied to explore the spatiotemporal variations in tidal duration asymmetry, under the influence of different combinations of tidal constituents. Tidal duration asymmetry initially increases, then slightly decreases, in an upstream direction. It experiences significant seasonal variations in response to rapidly varying discharge: tides are more asymmetric upstream of Zhenjiang in the dry season and more asymmetric downstream in the wet season. The combined effects of discharge regulation and morphological changes cause seasonal alterations in tidal duration asymmetry. In the wet season, reduced river discharge caused by water storage and climate change enhance the asymmetry upstream (+11.74% at Wuhu, +7.19 at Nanjing) while the asymmetry is weakened downstream (−2.90% at Zhenjiang, −7.19 at Jiangyin) following the TGD’s operation. Downstream channel erosion caused by post-TGD lower sediment loads has become the dominant factor weakening tidal asymmetry in most parts of the YRE in the dry season. Understanding these evolutions of tidal duration asymmetry under the hydrological and morphological effects has important implications for the management of estuarine ecosystem and navigation.

Effects of hydropower dam construction on sulfur distribution and sulfate-reducing prokaryotes assemblage

River damming is significant for hydropower production, but also alters the ecological conditions, and especially affects the microbial community. Sulfate-reducing prokaryotes (SRPs) make vital contributions to biogeochemical sulfur cycle, but the information on the effects of dam construction on the SRPs assemblage are unclear. Here, a comprehensive survey was conducted by collecting water and sediment samples along horizontal and vertical profiles from six sites at the Xiaowan Reservoir on the Lancang River, China. We used 16S rRNA gene amplicon sequencing and qPCR assay with dsrB gene to study the composition and activity of SRPs. The results indicated that river damming accumulated nutrients in the middle layer of the reservoir, and the impoundment provided an anaerobic and high nutrient available environment, which is beneficial for the survival of SRPs. The abundance and diversity of SRPs in water and sediments at the bottom of the reservoir were higher than those in the other sites. The network analyses revealed a synergistic effect between SRPs and other dominant bacteria in water column, which was more complex than in sediments. Moreover, a relatively higher sulfate reduction activity was found in the middle and lower layers of the water profile according to dsrB gene analysis.

Community characteristics of aquatic organisms and management implications after construction of Shihutang Dam in the Gangjiang River, China

ABSTRACTLiu X, Hu X, Ao X, Wu X, Ouyang S. 2017. Community characteristics of aquatic organisms and management implications after construction of Shihutang Dam in the Gangjiang River, China. Lake Reserv Manage. 34:42–57.The Ganjiang River is the largest river in Jiangxi Province, China, and plays a significant role in maintaining and replenishing the aquatic biodiversity for Poyang Lake and the Yangtze River. Understanding the effects of dam construction on aquatic biodiversity is critical because of the increasing number of dams and their adverse environmental impacts on the Ganjiang River. In this study, community structure of aquatic organisms and physicochemical parameters in the Shihutang Dam were investigated during March, July, and December 2015. We found that species number, density, and biomass of phytoplankton upstream of the dam were greater than downstream of the dam. Moreover, analysis of aquatic biodiversity showed that phytoplankton, zooplankton, and macrozoobenthos upstream of the dam were more abundant and richer than downstream of the dam, and fish downstream of the dam were more abundant and the fish community richer than upstream of dam. Fish life habits revealed that resident fish were the dominant species, but the proportion of migratory fish was low. Additionally, species composition of aquatic organisms was related to dissolved oxygen, turbidity, water depth, some nutrients, and velocity, based on redundancy analysis. The study showed that aquatic organism community structure was influenced by the Ganjiang River dam. We therefore proposed a series of dam management strategies, such as establishing artificial fish spawning substrate and implementing eco-hydraulic regulations. These dam management strategies can play an important role in protecting aquatic biodiversity and sustaining the resources in the Ganjiang River.

Effects of dam construction and increasing pollutants on the ecohydrological evolution of a shallow freshwater lake in the Yangtze floodplain

Large river-floodplain systems which provide a variety of societal, economic and biological benefits are undergoing extensive and intensive human disturbance. However, floodplain lakes responses to multiple stressors are poorly understood. The Yangtze River and its floodplain which provide water and food resources for more than 300 million people are an important region in China. Hydrological regulation as well as socio-economic development have brought profound negative influence on this ecologically important area. To improve understanding of decadal-scale responses of floodplain lakes to multiple stressors, lake sediment proxies including particle size, geochemical elements, diatoms and chironomids were analysed in a lead-210 dated core from Futou Lake. The analyses show that dams constructed in 1935 and the early 1970s stabilized hydrological conditions in Futou Lake and impeded the interaction with the Yangtze River, resulting in a decrease in major elements (e.g., Mg, Al, Fe) transported into the lake and an increase of macrophyte-related chironomids (C. sylvestris-type, P. penicillatus-type and Paratanytarsus sp.). After the late 1990s, further decreases in major elements and increases in median grain size are attributed to the erosion of the Yangtze riverbed and declining supply of major elements-enriched sediments from the upper Yangtze caused by the impoundment of the Three Gorges Dam. Chironomid and diatom assemblages indicate that hydrological stabilization caused by dam constructions stimulated the growth of macrophytes, which may be important in buffering against an ecosystem state change towards a phytoplankton-dominated and turbid state with ongoing eutrophication. However, a recent increase in Zn, TP and the emergence of eutrophic diatom and chironomid species indicate initial signs of water quality deterioration which may be related to the combined effects of hydrological stabilization and aquaculture. Over all, the sediment record from Futou Lake emphasizes the importance of interactions between hydrological change and pollutant loads in determining floodplain lake ecosystem state.

DAMS IN TIME OF WATER NATIONALISM

A dam, in most cases is a large, impressive concrete structure. A commanding number of large dams exist with over 45000 estimated in the world. It is important to understand such a concrete structure not only from a technical perspective, but also from the view of local community in the region of the dam. Also, it is important to know the international impact of a dam on a river basin and the measures necessary for implementing a dam, as well as the positive and negative effects of dam construction itself. Preliminary measures aim to characterize a river regarding natural, geological, geographical patterns, human geographical distribution, and food production. Prospective trends, such as the need for augmented water volumes for a water-fed agriculture, industrialization, energy, and river transportation, can influence decisions connected to dam building. Recently, climate change, a phenomenon considered as human-induced, at least partially, and the prospect of a water-stressed world, are another elements that affect decisions about build dams, especially regarding water security and green energy and a renewable resource under threat. This paper presents the main administrative requirements for a team involved in dam construction, including their specific tasks and interactions. The main aim of this paper is to establish political meaning of dams, and their capacity to influence economics, society, and the environment in an interconnected world.

Paleoreconstruction of organic carbon inputs to an oxbow lake in the Mississippi River watershed: Effects of dam construction and land use change on regional inputs

AbstractWe use a dated sediment core from Lake Whittington (USA) in the lower Mississippi River to reconstruct linkages in the carbon cycling and fluvial sediment dynamics over the past 80 years. Organic carbon (OC) sources were characterized using bulk (δ13C, ramped pyrolysis‐oxidation (PyrOx) 14C, δ15N, and TN:OC ratios) and compound‐specific (lignin phenols and fatty acids, including δ13C and 14C of the fatty acids) analyses. Damming of the Missouri River in the 1950s, other hydrological modifications to the river, and soil conservation measures resulted in reduced net OC export, in spite of increasing OC concentrations. Decreasing δ13C values coincided with increases in δ15N, TN:OC ratios, long‐chain fatty acids, and lignin‐phenol concentrations, suggesting increased inputs of soil‐derived OC dominated by C3 vegetation, mainly resulting from changes in farming practices and crop distribution. However, ramped PyrOx 14C showed no discernible differences downcore in thermochemical stability, indicating a limited impact on soil OC turnover.

Forest pattern dynamics and landscape connectivity changes in the Manwan Basin after dam construction in the Lancang River, China

Regional habitat quality and landscape connectivity can be greatly impaired by dam construction and subsequent land-use changes. This study examined landscape pattern and connectivity changes in the Manwan Basin from 1974 to 2006 to quantify the effects of dam construction. Landscape pattern indices and kernel density estimation (KDE) were used to analyze forest pattern dynamics, while the probability of connectivity (PC) index was applied to evaluate landscape connectivity changes. The results showed that forest area decreased by nearly 20 %, while the number of forest patches increased more than sixfold from 1974 to 2006 in the Manwan Basin. During the study period, forest fragmentation mainly occurred in the western and northern parts of the Manwan Basin. Due to the changes in the forest landscape pattern, landscape connectivity decreased by an average of 54.74 %. In addition, we detected changes to key stepping-stone patches by calculating the percentage importance of each resource patch. The results showed that 300.38 km2 of high-importance forest patches transformed to medium- and low-importance patches from 1974 to 2006.