RESUMEN

Darwin's two opposing hypotheses, proposing that non-native species closely or distantly related to native species are more likely to succeed, are known as 'Darwin's Naturalization Conundrum'. Recently, invasion ecologists have sought to unravel these hypotheses. Studies that incorporate rich observational data in disturbed ecosystems that integrate phylogenetic and functional perspectives have potential to shed light on the conundrum. Using 313 invaded plant communities including 46 invasive plant species and 531 native plant species across the Three Gorges Reservoir Area in China, we aim to evaluate the coexistence mechanisms of invasive and native plants by integrating phylogenetic and functional dimensions at spatial and temporal scales. Our findings revealed that invasive plants tended to co-occur more frequently with native plant species that were phylogenetically distant but functionally similar in the reservoir riparian zone. Furthermore, our study demonstrated that the filtering of flood-dry-flood cycles played a significant role in deepening functional similarities of native communities and invasive-native species over time. Our study highlights the contrasting effects of phylogenetic relatedness and functional similarity between invasive and native species in highly flood-disturbed habitats, providing new sights into Darwin's Naturalization Conundrum.

RESUMEN

Afforestation is an acknowledged method for rehabilitating deteriorated riparian ecosystems, presenting multiple functions to alleviate the repercussions of river damming and climate change. However, how ecosystem multifunctionality (EMF) responds to inundation in riparian afforestation ecosystems remains relatively unexplored. Thus, this article aimed to disclose how EMF alters with varying inundation intensities and to elucidate the key drivers of this variation based on riparian reforestation experiments in the Three Gorges Reservoir Region in China. Our EMF analysis encompassed wood production, carbon storage, nutrient cycling, decomposition, and water regulation under different inundation intensities. We examined their correlation with soil properties and microbial diversity. The results indicated a substantial reduction in EMF with heightened inundation intensity, which was primarily due to the decline in most individual functions. Notably, soil bacterial diversity (23.02%), soil properties such as oxidation-reduction potential (ORP, 11.75%), and temperature (5.85%) emerged as pivotal variables elucidating EMF changes under varying inundation intensities. Soil bacterial diversity and ORP declined as inundation intensified but were positively associated with EMF. In contrast, soil temperature rose with increased inundation intensity and exhibited a negative correlation with EMF. Further insights gleaned from structural equation modeling revealed that inundation reduced EMF directly and indirectly by reducing soil ORP and bacterial diversity and increasing soil temperature. This work underscores the adverse effects of dam inundation on riparian EMF and the crucial role soil characteristics and microbial diversity play in mediating EMF in response to inundation. These insights are pivotal for the conservation of biodiversity and functioning following afforestation in dam-induced riparian habitats.

Asunto(s)

RESUMEN

Interconnected river-lake systems record sedimentary organic carbon (OCsed) dynamics and watershed environmental changes, providing valuable information for global carbon budgets and watershed management. However, owing to the evolving river-lake interactions under global change, monitoring OCsed is difficult, thereby impeding the understanding of OCsed transport and fate. This study provided new insights into the dynamical mechanisms of OCsed in a typical river-lake system consisting of Dongting Lake and its seven inlet/outlet rivers (the three inlets of the Yangtze River and four tributaries) over the last century using stable isotope tracing and quantified the influences of climate change and human activities on OCsed. Results indicated that exogenous OC dominated the OCsed in the lake (58.2 %-89.0 %) and was lower in the west than in the east due to the differences in the material inputs and depositional conditions within the lake. Temporally, the distribution patterns of OCsed sources mainly responded to human activities in the basin rather than to climate change. Before 2005, the Yangtze River contributed the most OCsed (53.5 %-74.6 %), attributed to the high-intensity land use changes (path coefficient (r∂): 0.48, p-value < 0.01) and agriculture-industry activities (r∂: 0.44, p-value < 0.001) in the Yangtze River basin that increased soil erosion. After 2005, a large amount of Yangtze River OC was intercepted by the Three Gorges Dam, altering the OC exchange in the river-lake system and shifting OCsed dominance to the four tributaries (52.2 %-63.8 %). These findings highlight the active response of OCsed to the river-lake interaction evolution and anthropogenic control, providing critical information for regulating watershed management behavior under global change.

RESUMEN

Understanding the long-term variations in basins that undergo large-scale hydroelectric projects is crucial for effective dam operation and watershed management. In this study, comprehensive analyses were conducted on a dataset spanning over 20 years (1998-2018) of hydrological regime and physicochemical parameters from the Yangtze River basin to evaluate the potential impacts of the Three Gorges Dam. Water level significantly increased from 128.75±58.18 m in 2002 to 136.78±55.05 m in 2005, and the mean flow velocity significantly decreased from 2004 to 2010. However, no significant change in the flow was observed in the basin. Meanwhile, remarkable fluctuations in physicochemical parameters, including dissolved oxygen, chemical oxygen demand, conductivity, hardness, and alkalinity, were mainly observed during impoundment (2003-2009). After that, the above parameters tended to stabilize, and some even returned to their original levels. The dam's retention effect significantly reduced the suspended solids (SS) in both up- and downstream, to only one-third of the pre-operation level. And total phosphorus and chemical oxygen demand also significantly decreased with the decline of SS. Particularly, ammonium also showed a significant downward trend, with the up- and downstream of the dam falling by 36.8 % and 26.1 %, respectively. However, the increasing total nitrogen (7.5 % and 20.0 % up- and downstream of the dam, respectively) still threatened the water quality of the basin, especially in the estuaries. Additionally, the significant decline in dissolved oxygen downstream (from 8.53±1.08 mg/L to 8.11±1.36 mg/L) also exacerbated the hypoxia in the Yangtze River estuary. The results demonstrated the long-term impact of the construction of the Three Gorges Dam on the environmental elements of the Yangtze River basin, which provides reference data and guidance for the construction of big dams in major rivers in the future.

Asunto(s)

RESUMEN

Large-scale water conservancy projects benefit human life but have modified the landscape and provided opportunities for alien plant invasions. Understanding the environmental (e.g., climate), human-related (e.g., population density, proximity to human activities), and biotic (e.g., native plant, community structure) factors driving invasions is essential in the management of alien plants and biodiversity conservation in areas with intense human pressure. To this end, we investigated the spatial patterns of alien plant species distribution in the Three Gorges Reservoir Area (TGRA) of China and distinguished the role of the external environment and community characteristics in determining the occurrence of alien plants with differing levels of known invasion impacts in China using random forest analyses and structural equation models. A total of 102 alien plant species belonging to 30 families and 67 genera were recorded, the majority being annual and biennial herbs (65.7%). The results showed a negative diversity-invasibility relationship and supported the biotic resistance hypothesis. Moreover, percentage coverage of native plants was found to interact with native species richness and had a predominant role in resisting alien plant species. We found alien dominance was mainly the result of disturbance (e.g., changes in hydrological regime), which drove native plant loss. Our results also demonstrated that disturbance and temperature were more important for the occurrence of malignant invaders than all alien plants. Overall, our study highlights the importance of restoring diverse and productive native communities in resistance to invasion.

Asunto(s)

RESUMEN

As the largest hydroelectric project in the world, the Three Gorges Dam (TGD) is expected to have significant environmental and ecological impacts on riparian vegetation in the Yangtze River Basin (YRB). However, existing studies have mainly focused on small segments of the YRB. In addition, few studies have quantified the responses of riparian vegetation to both climatic factors and dam construction. In this study, we investigated riparian vegetation dynamics over the entire YRB before, during, and after the construction of TGD from 1982 to 2015 using the normalized difference vegetation index (NDVI). Furthermore, the effects of climatic factors and dam construction on riparian vegetation were quantitatively analyzed using path analysis. The results demonstrate that the YRB has experienced a generally greening trend after TGD construction. The impacts of climate change on riparian vegetation have exhibited notable spatial heterogeneity and temperature is the main climatic factor that affects riparian vegetation growth. Moreover, TGD becomes the major contributor to riparian vegetation dynamics in the YRB after TGD construction. TGD has not only directly enhanced riparian vegetation but also indirectly affected riparian vegetation by regulating the microclimate. This study highlights the significance of anthropogenic interference when evaluating the relationships between riparian vegetation and climatic factors, providing useful insights for the effective management and conservation of large-scale riparian ecosystems.

RESUMEN

There are many studies that have examined the impact of the Three Gorges Dam (TGD) on changes in meteorological data, and most of them concluded that the TGD significantly reduced precipitation without taking into account the negative trends that had already existed before the impoundment. In this study, the investigation focused on the monthly precipitation data, and the Mann-Kendall (MK) trend analysis was conducted to show that the TGD had little effect on the trends of the precipitation data. Monthly data (1980-2018) from 19 stations upstream and downstream of the TGD and 5 stations located far from the main river were extracted. The analysis and results showed that although the linear long-term (1980-2018) precipitation trend upstream of the TGD was downward, the MK trend analysis showed that the precipitation trends became upward after impoundment. This situation existed even for station data located outside the region. Also, the analysis of monthly trends in different seasons showed that in spring and winter, there was only a very weak downward trend in monthly precipitation, while in summer and autumn, the trends were upward with steeper slopes. Following the upward trends of the monthly precipitation, the TGD generally positively intensified the monthly precipitation trends upstream and downstream of the dam, with the exception of a few months when total precipitation amounts were consistently low. In contrast to the trend analysis, which showed small and insignificant variations in precipitation data, the 12-month SPEI analysis showed a significant deterioration (about 20%) in the wetness index after impoundment both upstream and downstream of the TGD, while this situation did not occur outside the region. Thus, the TGD has extended dry periods both upstream and downstream of the dam over the past two decades.

Asunto(s)

RESUMEN

BACKGROUND: Snail abundance varies spatially and temporally. Few studies have elucidated the different effects of the determinants affecting snail density between upstream and downstream areas of the Three Gorges Dam (TGD). We therefore investigated the differential drivers of changes in snail density in these areas, as well as the spatial-temporal effects of these changes. METHODS: A snail survey was conducted at 200 sites over a 5-year period to monitor dynamic changes in snail abundance within the Yangtze River basin. Data on corresponding variables that might affect snail abundance, such as meteorology, vegetation, terrain and economy, were collected from multiple data sources. A Bayesian spatial-temporal modeling framework was constructed to explore the differential determinants driving the change in snail density and the spatial-temporal effects of the change. RESULTS: Volatility in snail density was unambiguously detected in the downstream area of the TGD, while a small increment in volatility was detected in the upstream area. Regarding the downstream area of the TGD, snail density was positively associated with the average minimum temperature in January of the same year, the annual Normalized Difference Vegetation Index (NDVI) of the previous year and the second, third and fourth quartile, respectively, of average annual relative humidity of the previous year. Snail density was negatively associated with the average maximum temperature in July of the previous year and annual nighttime light of the previous year. An approximately inverted "U" curve of relative risk was detected among sites with a greater average annual ground surface temperature in the previous year. Regarding the upstream area, snail density was positively associated with NDVI and with the second, third and fourth quartile, respectively, of total precipitation of the previous year. Snail density was negatively associated with slope. CONCLUSIONS: This study demonstrated a rebound in snail density between 2015 and 2019. In particular, temperature, humidity, vegetation and human activity were the main drivers affecting snail abundance in the downstream area of the TGD, while precipitation, slope and vegetation were the main drivers affecting snail abundance in the upstream area. These findings can assist authorities to develop and perform more precise strategies for surveys and control of snail populations.

Asunto(s)

RESUMEN

BACKGROUND: The area of Oncomelania hupensis snail remains around 3.6 billion m2, with newly emerging and reemergent habitats continuing to appear in recent years. This study aimed to explore the long-term dynamics of snail density before and after the operation of Three Gorges Dam (TGD). METHODS: Data of snail survey between 1990 and 2019 were collected from electronic databases and national schistosomiasis surveillance. Meta-analysis was conducted to estimate the snail density. Joinpoint model was used to identify the changing trend and inflection point. Inverse distance weighted interpolation (IDW) was used to determine the spatial distribution of recent snail density. RESULTS: A total of 3777 snail survey sites with a precise location of village or beach were identified. For the downstream area, snail density peaked in 1998 (1.635/0.11 m2, 95% CI: 1.220, 2.189) and fluctuated at a relatively high level before 2003, then declined steadily from 2003 to 2012. Snail density maintained lower than 0.150/0.11 m2 between 2012 and 2019. Joinpoint model identified the inflection of 2003, and a significant decreasing trend from 2003 to 2012 with an annual percentage change (APC) being - 20.56% (95% CI: - 24.15, - 16.80). For the upstream area, snail density peaked in 2005 (0.760/0.11 m2, 95% CI: 0.479, 1.207) and was generally greater than 0.300/0.11 m2 before 2005. Snail density was generally lower than 0.150/0.11 m2 after 2011. Snail density showed a significant decreasing trend from 1990 to 2019 with an APC being - 6.05% (95% CI: - 7.97, - 7.09), and no inflection was identified. IDW showed the areas with a high snail density existed in Poyang Lake, Dongting Lake, Jianghan Plain, and the Anhui branch of the Yangtze River between 2015 and 2019. CONCLUSIONS: Snail density exhibited a fluctuating downward trend in the Yangtze River basin. In the downstream area, the operation of TGD accelerated the decline of snail density during the first decade period, then snail density fluctuated at a relatively low level. There still exists local areas with a high snail density. Long-term control and monitoring of snails need to be insisted on and strengthened.

Asunto(s)

RESUMEN

Damming alters downstream sediment supply relationships and erosion in the estuarine delta. Given that sediment grainsize serves as a key parameter for the ability to adsorb heavy metals from water, the assessment of estuarine heavy metal risk needs to get connected initially. Hence, fine suspended sediment (<63 µm) in the Yangtze River estuary (YRE) was divided into four grainsize fractions to simulate the surface suspended sediment concentration (SSC) and grainsize composition before and after the completion of the Three Gorges Dam (TGD). Representative months were selected for flood peak reduction (October) and runoff compensation in the dry season (March) to maximize the scheduling impact of the TGD on runoff and riverine sediment input to the YRE. An improved Water Quality Index (WQI) approach was proposed to assess the combined risk alteration of five heavy metals in six estuarine sensitive targets due to TGD-induced sediment characteristics. The results demonstrated that TGD significantly but tardily reduced the SSC and the proportion of fine sediment in the YRE, decreasing the risk of heavy metals resuspension. Seasonally, the total SSC became higher in the flood season than in the dry season during post-TGD period. However, the fine SSC in the flood season was averaged only 59.7% of that in the dry season due to the pronounced grainsize coarsening effect. As the significant reduction in fine SSC overcomes the increase in heavy metal content per unit of SS, the integrated resuspension risk declined significantly, particularly for Pb and Cr. Spatially, the risk reduction for sensitive targets near the turbidity maximum zone (TMZ) is 8.4 times greater than for inner river channel. However, undiminished anthropogenic metal inputs to the YRE signified greater pressures on the depositional environment.

Asunto(s)

RESUMEN

The global demand for sand and gravel is at 50 billion tons per year, far exceeding global resource capacities. It reached 7.6 billion tons in 2021 in the Yangtze River Basin (YRB), China. However, production is severely limited in the YRB. Therefore, the incongruity between the supply and demand of river sand is prominent. Wise management of decreasing sand resources in the YRB has become critical since the Three Gorges Dam became operational in 2003. This study synthesized spatial and temporal changes in sand mining activities and quantities along the Yangtze River and its major tributaries from 2004 to 2020. Results from the study show that the mining amount during the period reached 76.2 million tons annually. At the same time, riverine suspended sediment discharge (SSD) downstream of the Three Gorges Dam decreased largely. SSD reduction leads to riverbed erosion, further limiting the riverine sand and gravel sources for mining. Thus, alternative sand and gravel resources, as well as optimizing supply/demand balance, are necessary for sustainable development. There is an urgent need to assess the relationship between river sand resources and exploitation in the YRB for creating a sand and gravel data management system in order to cope with the increasing incongruity between their supply and demand.

Asunto(s)

RESUMEN

High sediment flux in large rivers provide sufficient dilution to the heavy metals' concentration. However, sediment starvation caused by hydrological engineering in recent decades has been reported worldwide. Thus, a study is necessary on the influences of recent declining sediment flux on heavy metal pollution change in the suspended sediments. In this study, heavy metal concentrations and speciation (Cd, Pb, Zn, Cu, Co, Ni, and Cr) in suspended sediments were investigated downstream the Three Gorges Dam (TGD) during dry and flood seasons. Substantial changes of Pb, Zn, Cd, and Cu along the river channel were found which were constrained by the dilution efficiency of suspended sediment during the dry season. High proportion of labile fraction revealed anthropogenic sources of heavy metal. Moreover, the historical trend of metal content illustrated TGD construction together with anthropogenic influx both contribute to the increasing environmental risk in the Yangtze River basin.

Asunto(s)

RESUMEN

Dams are often regarded as greenhouse gas (GHG) emitters. However, our study indicated that the world's largest dam, the Three Gorges Dam (TGD), has caused significant drops in annual average emissions of CO2, CH4 and N2O over 4300 km along the Yangtze River, accompanied by remarkable reductions in the annual export of CO2 (79%), CH4 (50%) and N2O (9%) to the sea. Since the commencement of its operation in 2003, the TGD has altered the carbonate equilibrium in the reservoir area, enhanced methanogenesis in the upstream, and restrained methanogenesis and denitrification via modifying anoxic habitats through long-distance scouring in the downstream. These findings suggest that 'large-dam effects' are far beyond our previous understanding spatiotemporally, which highlights the fundamental importance of whole-system budgeting of GHGs under the profound impacts of huge dams.

RESUMEN

Pharmaceuticals and personal care products (PPCPs) are a group of emerging anthropogenic pollutants. Here we investigated the occurrence and concentrations of 35 typical PPCPs in water, sediment, and freshwater mollusks (Hyriopsis cumingii, Unio douglasiae, Sinanodonta woodiana, Lamprotula leai and Corbicula fluminea) of the Dongting Lake downstream of the Three Gorges Dam. As results, 33 PPCPs were detected in water and sediment of the lake. Ketoprofen (not detected (ND)-292.8 ng/L, mean 91.1 ng/L) and roxithromycin (13.7-141.9 ng/L, mean 30.4 ng/L) were the primary PPCPs measured in lake water, while ibuprofen (ND-105.0 ng/g, mean 30.0 ng/g) and ketoprofen (ND-142.9 ng/g, mean 27.6 ng/g) were dominant in the sediment. Distinct seasonal difference in PPCP compositions was observed in both water and sediment of the Dongting Lake, potentially associated with the water-level fluctuations driven by the Three Gorges Dam operations. Ketoprofen and ibuprofen were also frequently detected in the soft tissues of freshwater mollusks, with concentrations of 42.5-1206.6 and 44.9-992.7 ng/g, respectively. Significant species-specific accumulation characteristics of PPCPs in mollusks were observed, with the highest total contents being reported for Corbicula fluminea (3.18 ± 1.13 µg/g). Moreover, gonads of mollusks were identified as the target organ to accumulate these compounds. Correlation analysis further revealed the strong associations of PPCP concentrations in mollusks with those in water and sediment, suggesting the importance of controlling dissolved and sedimentary bioavailability of PPCPs for ecological risk management in this freshwater lake ecosystems.

Asunto(s)

RESUMEN

A massive increase in dam construction has decreased fluvial sediment discharge at a global scale. In order to explore potential effects of the Three Gorges Dam (TGD) on floodplain lakes in the middle Yangtze reaches (central China), this study investigated phosphorus forms (i.e., Ca-bound phosphorus, Fe/Al-bound phosphorus, and organic phosphorus) and trace elements (i.e., Sc, Ba, Be, Pb, and Zn) in a 210Pb-dated sediment core collected from East Dongting Lake, a hydrologically open lake proximal to the TGD. Sedimentary records revealed that the fluxes of phosphorus in different forms and trace elements were high before 2005. Thereafter, the fluxes of Ca-bound phosphorus, Sc, Ba, and Be declined sharply, probably due to declining supply of riverine detritus from the upstream after the TGD operation. In contrast, the fluxes of Fe/Al-bound phosphorus and heavy metals remained high after 2005, indicating the impacts of industrial sewage inputs. Our results underscore that river damming and anthropogenic pollution have altered sedimentary geochemical composition in East Dongting Lake. This phenomenon might be widespread in similar floodplain lakes due to increasing human disturbance during recent decades.

Asunto(s)

RESUMEN

Hydropower dam constructions and operations have dramatically changed the original hydrological regime of natural rivers. Because of significantly slashed and suspended sediments blocked by damming, discharged "clear" water was found to play a strong undercutting effect on the riverbank and to exacerbate riparian soil erosion on the downstream near dams. Yet, it is still an unsettled issue whether the instability of riparian soil structure would be simply correlated negatively with the distance to a dam. In this study, soils along the downstream riparian zone of a huge dam on the River Yangtze, China, were sampled to examine the distance effect on the riparian soil structural stability. Water-stable aggregates were fractionated by the wet-sieving method. Mean weight diameter (MWD) and geometric mean diameter (GMD) were used to indicate riparian soil stability. Further, the fractal dimension (D) and soil erodibility parameter (K) were used to represent the likelihood of riparian erosion. Our results revealed that riparian soil structural stability demonstrated a high spatial heterogeneity along the River Yangtze, and was less affected by the spatial distance to the dam. Rather, the soil stability was primarily influenced by a river shape index (sinuosity) and local edaphic properties. The river sinuosity index demonstrated a positive relationship with soil structural stability. Additionally, soil organic matter was found as a major edaphic factor in stabilizing soil structure. The results indicated that river sinuosity plays a crucial role in stabilizing soil by accumulating soil organic matters. Our findings implied that the potential negative impact of damming effect on soil stability may be attenuated by maintaining a higher sinuosity of the river. Against the risk of riparian soil erosion along the dammed river, the configuration of river morphology shall be considered as one of the potential managements in offsetting the negative impacts of damming.

Asunto(s)

RESUMEN

Herein, a two-dimensional (2-D) vertically-averaged hydrodynamic model was applied to study the heavy metal particle footprints pre- and post-Three Gorges Dam (TGD) in Poyang Lake. Two defined indexes-Reserve Impact Index (σRII) and Species Impact Index (ηSII) were applied to assess the potential impact of the copper footprint on nature reserves and sensitive species quantitatively. The results demonstrated that the movement speed, distribution, and trajectory of copper particle footprints differed enormously pre- and post-TGD. By contrast, the post-TGD footprints were more complex because of the dam-induced variations in hydrology and meteorology. TGD had both pros and cons for the copper footprint on the reserves based on the results of σRII. It had changed the way for the transport of heavy metals and altered the patterns of exposure risk in the reserves. Sustainable management of Poyang Lake could be achieved by optimizing daily monitoring works. The ηSII for Finless Porpoises do not differ significantly between scenarios, but the ηSII for Siberian White Cranes increased by 0.92 and 0.83 for the two periods pre- and post-TGD, respectively. Heavy metals in food sources and the excreta of Siberian White Cranes could be of great concern in future studies. This study provides a theoretical basis for the in-depth study of the TGD-induced impact on Poyang Lake and provides a reference for the long-term treatment of Poyang Lake and the protection of key species.

Asunto(s)

RESUMEN

Suspended sediments in the estuary play an important role in regulating the erosion-accretion and shaping the geomorphological patterns. Yet, it can be strongly impacted by the human activities. Constructions of basin and estuarine engineering in the Yangtze River Estuary (YRE), including constructions of Three Gorges Dam (TGD) further upstream of the Yangtze River and Deep Waterway Project (DWP) in the estuary, have greatly modified the distribution of estuarine suspended sediment concentration (SSC). In this study, we retrieved the surface water SSC in the YRE from a total of 149 Landsat-TM/ETM+/OLI images (from 1984 to 2020) and 515 GOCI images (from 2011 to 2020) to obtain its long-term dynamics. The results indicate that the SSC estimation model performed well with a mean absolute percentage error of 12.83% and a root mean square error of 0.027 g/L. The SSC in the YRE demonstrated an overall declining pattern over the past 37 years, particularly during the flood season, which was related to the decrease in the sediment discharge of Yangtze River. The SSC in different sub-regions across the entire YRE responded differently to the reduced sediment discharge caused by the impoundment of the TGD. The SSC in the inner estuary responded promptly with a 40.3% decline noted immediately after the impoundment of the TGD, whereas hysteresis of SSC changes was found in the estuarine turbidity maximum zone (TMZ) and have begun to decline by 20.0-30.0% in the recent 5 years. Constructions of local estuarine engineering, such as the DWP also exert important controls on the estuarine SSC dynamics by blocking the lateral transport of suspended sediments between the shoal and the river channel. Our results highlight the strong influence of engineering constructions on the SSC dynamics in the world large river-influenced estuaries.

Asunto(s)

RESUMEN

Litter decomposition is an important soil nutrient source that promotes vegetation in deteriorated riparian zones worldwide. The periodic submergence and sediment burial effects on two prominent annual herbaceous plants (Echinochloa crusgali and Bidens tripartite) are little known in mega-reservoir settings. Our study focuses on the mass and carbon loss and nutrient release from E. crusgali and B. tripartitle litter and changes in soil properties, which are important for riparian zone rehabilitation in the Three Gorges Dam Reservoir, China. This study adopted the litter bag method to explore the nutrient change characteristics and changes in soil properties at different sediment burial depths under flooding scenarios. Three burial depths (0 cm, 5 cm, and 10 cm) were used for these two plants, and the experiment lasted for 180 days. The results revealed that the litter decay rate was high at first in the incubation experiment, and the nutrient loss rate followed the pattern of K > P > N > C. The relationship between % C remaining and % mass remaining was nearly 1:1, and the total amount of P exhibited a leaching-enrichment-release state in the decomposition process. Nutrients were changed significantly in the soil and overlying water at the first decomposition stage. Still, the total soil nutrient change was insignificant at the end, except for the 10 cm burial of B. tripartitle. Moreover, oxidation-reduction potential was the main factor in the litter decomposition process at different burial depths. This study indicated that sediment deposition reduced litter mass loss, slowed down the release of N and P, and retained more C, but promoted the release of K. Conclusively, in litter decomposition under waterlogging, the total soil nutrient content changed little. However, litter does more to the soil than that. Therefore, it is necessary to study the residual soil litter's continuous output after the water level declines for restoration purposes.

RESUMEN

The construction of dams has caused riparian habitat degradation and ecosystem service loss globally. It is critical to assess the response of riparian plant communities to inundation gradients for their conservation. Recent evidence suggests that plant community assemblages are governed by flooding stress, soil nutrient availability, climate (environmental filtering) and dispersal, speciation, local extinction (dispersal filtering), but it remains unclear which dominates the riparian ecosystem regulated by a dam. Thus, this article aims to elucidate the relative importance of environmental and dispersal filtering to variations in plant communities to understand community assembly mechanisms in riparian ecosystems. Here we used plant community data related to four elevations in the riparian zone of the Three Gorges Dam Reservoir in China to show that species richness and diversity, community height, and the cover of total, annual, and exotic plant categories decreased, while the cover of perennial and native plant groups increased under higher flooding stress. Community composition varied substantially with elevation, and species composition tended to converge with increased inundation, characterized by flood-tolerant species. The community composition underwent stronger environmental filtering at low elevations and stronger dispersal filtering at high elevations, with stronger environmental filtering across riparian ecosystems. Therefore, we conclude that dam inundation drives community assemblages of riparian plants by the combined effects of environmental and dispersal filtering. Still, their relative contribution varies between elevations, and environmental filtering is more important in shaping community assembly. This study is the first to confirm that plant community assembly in the dam-regulated riparian area is determined by both niche-based and stochastic processes. Thus, we highlighted the importance of considering inundation intensity, propagule sources, and river connectivity when implementing restoration projects.

Asunto(s)