Response of Annual Herbaceous Plant Leaching and Decomposition to Periodic Submergence in Mega-Reservoirs: Changes in Litter Nutrients and Soil Properties for Restoration

Comprehensive study of the occurrence and characteristics of organic matter, nitrogen, and phosphorus in sediments and riparian soils of a large drinking water reservoir

The contamination of nutrients has caused considerable worry about the environment, resource value, and ecological worth of drinking water reservoirs. Therefore, we comprehensively studied the abundance, sources, distribution, and environmental behavior of carbon, nitrogen, and phosphorus in Fengshuba Reservoir (FSBR) (a large drinking reservoir, China). A graded leaching technique (introduced in 2003), the European Standard, Measurement and Testing (SMT) protocol, and spectrometry combined with parallel factor analysis (EEMs-PARAFAC) were used to assess nitrogen, phosphorus forms, and spectra data in the sediment and soil phases, respectively. The study demonstrates that seasonal hydrological variation had no significant effect on the nutrient abundance and nutrient structure composition of the FSBR, while different environmental media (e.g., sediment and soil phase) exhibited considerable differences in nutrient abundance, composition, and environmental behavior. The abundance of colored dissolved organic matter (CDOM), as well as molecular weight, aromatization degree, and humification degree of dissolved organic matter (DOM) were all lower in sediments than in soils, whereas the authigenic component was greater than in soils. Microbial-derived humus (C1), terrestrial-derived humus (C2), and protein-like tryptophan (C3) were identified as the three primary fluorescence components. Principal component analysis indicated that three components were closely associated with phosphorus in the sediment phase, whereas nitrogen and phosphorus in the soil phase were mainly related to C1 and C2. In summary, soil media (drawdown area) must be carefully considered in the management and control of water environment nutrients in reservoirs.

Effect of topographical features on hydrologically connected riparian landscapes across different land-use patterns in colossal dams and reservoirs

Topographic features impact the riparian landscape, which shapes reservoir ecosystems. We know little about ecological network parameter (ENP) responses to topographical features (riparian width, stream-channel width, slope, and elevation) from three land-use areas (rural, urban, and rural-urban transitional) in larger dams and reservoirs globally. This study used a field-based approach with 305 transects on an inundated area of 58,000 km² inside the Three Gorges Dam Reservoir (TGDR) in China. We discovered that topographical features influenced ENPs differently, involving parameters of plant cover, regeneration, exotics, erosion, habitat, and stressors. As per the Pearson correlation (p < 0.05), riparian width had the most significant effect on transitional ENPs and the least impact on urban ENPs. Riparian width showed the most important influence on the parameters of exotics (with r ≤ -0.44) and erosion (r ≤ 0.56). In contrast, stream-channel widths had the greatest effect on rural ENPs and the least on urban and transitional ENPs. The erosion parameters were the most affected (r ≤ -0.26) by stream width. The slope showed relationships with the fewest ENPs in all three areas and influenced the stress (with a range of -0.51 <r < 0.85) and erosion (r ≤ -0.39) parameters. The impact of elevation was higher in urban areas and was positively correlated with the parameters of plant cover (r ≤ 0.70), erosion (r ≤ 0.58), and habitat (r ≤ 0.69). These results justify the policy emphasis on riparian areas that are managed using the same techniques, which generally ignores their topographical features.

The impact of ecotourism on ecosystem functioning along main rivers and tributaries: Implications for management and policy changes

Tourism along river basins benefits both tourists and the economy, but its management necessitates trade-offs between nature-based recreation and ecological functioning. Despite ecosystem services being helpful in managing environmental challenges, there are limited data on the impact of tourism activities on ecosystem functioning across different river types globally. This study investigates how people's recreational activities and values affect ecosystem functioning in high-order rivers. The original field data were collected from 308 transects along the main river and tributaries of the Three Gorges Dam Reservoir in China during 2019. Kruskal-Wallis tests (p < 0.01) revealed that the ecosystem functioning indices were significantly higher than the recreational activity and value indices around the rivers and that ecosystem functioning was highest around tributaries. The critical variables of ecotourism activities and ecosystem functioning identified by principal component analysis accounted for 66.49% of the total variance. The Pearson correlation coefficient strengths among tourism and ecosystem functioning parameters were correlated mildly to moderately, but they exhibited positive and negative connections with a range of r = -0.27 to 0.37 (p < 0.05). Furthermore, the distribution patterns of these parameters that were determined by hierarchical cluster analysis were diverse for both the main river and its tributaries. The findings suggest that the development and enforcement of zoning may be necessary for the long-term use of natural resources by all sectors of society. Therefore, it is imperative to raise public awareness and urge governments to adopt more progressive ecotourism policies.

Impacts of Stressors on Riparian Health Indicators in the Upper and Lower Indus River Basins in Pakistan

Riparian zones along rivers and streams provide ecosystem services that may change over time as disturbances increase and deteriorate these buffer zones globally. The effect of stressors on ecosystem services along the rivers in underdeveloped countries is unclear, which impacts the environment directly in the form of riparian health indicators (RHIs). This study fills this gap and measures the impact of stressors on RHIs (parameters of habitat, plant cover, regeneration, exotics, and erosion) in the Indus River basin (IRB) in Pakistan. Data on 11 stressors and 27 RHIs were collected using a field-based approach in 269 transects in the upper and lower Indus basins (UIB and LIB) in 2020 and analyzed using multivariate statistical methods. The Kruskal-Wallis tests (p < 0.05) indicated that RHIs varied significantly under the influence of stressors in the UIB and LIB. However, their highest mean values were found in the UIB. Principal component analysis revealed the key RHIs and stressors, which explained 62.50% and 77.10% of the variance, respectively. The Pearson correlation showed that stressors had greater impacts on RHIs in LIB (with r ranging from -0.42 to 0.56). Our results also showed that stressors affected RHI indices with r ranging from -0.39 to 0.50 (on habitat), -0.36 to 0.46 (on plant cover), -0.34 to 0.35 (on regeneration), -0.34 to 0.56 (on erosion), and -0.42 to 0.23 (on exotics). Furthermore, it was confirmed by the agglomerative hierarchical cluster that indices and sub-indices of RHIs and stressors differ across the UIB and LIB. These findings may serve as guidance for managers of large rivers and ecosystem service providers to minimize the environmental impact of stressors in terms of RHIs.

Nature-based tourism influences ecosystem functioning along waterways: Implications for conservation and management

Nature-based tourism has an influence on ecosystem functioning around watercourses, but this influence lacks scientific evidence. Additionally, strategic and operational management of streams necessitates trade-offs between the recreational activities and values of tourists and riparian zone hospitality services. This paper aims to assist environmentalists and planners by exploring the effects of tourism-based recreational activities on ecosystem functioning along the drawdown zone. The study uses multivariate statistical techniques to delineate the relevant global tourism issues for planners. Kruskal-Wallis tests (p < 0.01) were conducted using quantitative data from 284 transects within the Three Gorges Dam Reservoir in China. The results revealed higher ecosystem function indices than tourism indices. Indicators of tourism contributed both positively and negatively to ecological indicators, with the Pearson correlation coefficients ranging from minor to moderate (r = ̶ 0.24 to 0.38, p < 0.05). Principal component analysis revealed that the critical variables of ecosystem functioning and tourism activities explained 72.26 % of the overall variance. Nevertheless, hierarchical cluster analysis revealed that these indicators responded differently in the upstream, midstream, and downstream sections. Our findings suggest that policymakers should consider the different characteristics of riparian zones in future planning, as doing so will improve both national and global strategic and operational management.

Environmental literacy affects riparian clean production near major waterways and tributaries

Although environmental illiteracy threatens the functioning of landscapes throughout the world, it is frequently ignored. The traditional wisdom assumes that suspicions will evaporate when the public and government authorities are provided with new information. Despite significant efforts to enhance riparian corridor output, limited data are available on the effect of environmental literacy metrics (ELMs) on clean production elements (CPEs) across various streams (e.g., main rivers and tributaries) within impoundments. This study examined such effects within the China Three Gorges Dam Reservoir area (TGDRA) by collecting 336 transects that assessed the breadth of effects on 58,000 km² in 2019. The network visualization revealed 7234 papers published over the last 121 years, each of which focused on themes such as plant cover, regeneration, exotics, erosion, habitat, and stressors. The bar graph showed that the general public lacked understanding of environmental literacy (e.g., knowledge, attitudes, and behavior), which influenced plant cover elements most in tributary zones but had little direct effect on regeneration. Locals' environmental literacy had the greatest impact on CPEs, with Pearson correlation coefficients ranging from -0.69 <r < 0.96 in the main river zones. Moreover, public employees' environmental literacy had a stronger correlation with CPEs (-0.58 <r < 0.83) within the main river regions. Farming systems, exposed soil, dominant grass regeneration, and instream structures, including pollution, were among the most notable CPEs within the TGDRA. According to hierarchical approaches, CPEs and ELMs change substantially across stream types. CPEs and ELMs vary significantly around main rivers and tributaries, requiring efforts to raise the public understanding of the worldwide impacts of stream health on humans.

An Insight into Abiotic Stress and Influx Tolerance Mechanisms in Plants to Cope in Saline Environments

Simple Summary

This review focuses on plant growth and development harmed by abiotic stress, primarily salt stress. Salt stress raises the intracellular osmotic pressure, leading to hazardous sodium buildup. Plants react to salt stress signals by regulating ion homeostasis, activating the osmotic stress pathway, modulating plant hormone signaling, and altering cytoskeleton dynamics and cell wall composition. Understanding the processes underlying these physiological and biochemical responses to salt stress could lead to more effective agricultural crop yield measures. In this review, researchers outline recent advances in plant salt stress control. The study of plant salt tolerance processes is essential, both theoretically and practically, to improve agricultural output, produce novel salt-tolerant cultivars, and make full use of saline soil. Based on past research, this paper discusses the adverse effects of salt stress on plants, including photosynthesis suppression, ion homeostasis disturbance, and membrane peroxidation. The authors have also covered the physiological mechanisms of salt tolerance, such as the scavenging of reactive oxygen species and osmotic adjustment. This study further identifies specific salt stress-responsive mechanisms linked to physiological systems. Based on previous studies, this article reviews the current methodologies and techniques for improving plant salt tolerance. Overall, it is hoped that the above-mentioned points will impart helpful background information for future agricultural and crop plant production.

Abstract

Salinity is significant abiotic stress that affects the majority of agricultural, irrigated, and cultivated land. It is an issue of global importance, causing many socio-economic problems. Salt stress mainly occurs due to two factors: (1) soil type and (2) irrigation water. It is a major environmental constraint, limiting crop growth, plant productivity, and agricultural yield. Soil salinity is a major problem that considerably distorts ecological habitats in arid and semi-arid regions. Excess salts in the soil affect plant nutrient uptake and osmotic balance, leading to osmotic and ionic stress. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, the production of enzymes, compatible solutes, metabolites, and molecular or genetic networks. Different plant species have different salt overly sensitive pathways and high-affinity K⁺ channel transporters that maintain ion homeostasis. However, little progress has been made in developing salt-tolerant crop varieties using different breeding approaches. This review highlights the interlinking of plant morpho-physiological, molecular, biochemical, and genetic approaches to produce salt-tolerant plant species. Most of the research emphasizes the significance of plant growth-promoting rhizobacteria in protecting plants from biotic and abiotic stressors. Plant growth, survival, and yield can be stabilized by utilizing this knowledge using different breeding and agronomical techniques. This information marks existing research areas and future gaps that require more attention to reveal new salt tolerance determinants in plants—in the future, creating genetically modified plants could help increase crop growth and the toleration of saline environments.

Invasive Plants and Species Richness Impact Litter Decomposition in Riparian Zones

Natural ecosystems generally include litter decomposition as part of the natural cycle since the material properties and the environment greatly influence the decomposition rate. The invasion of exotic plants alters the species diversity and growth characteristics of plant communities, but its impact on litter decomposition is unknown in the riparian zone. This study examines how invasive plants affect the early stages of litter decomposition and how species richness impacts them. This experiment involved a random litter mixture of exotic (Alternanthera philoxeroides and Bidens pilosa) and native species in the riparian zone of the Three Gorges Dam Reservoir in China. There were 43 species mixture types, with various species richness ranging from 1 to 6. Litterbags were placed in the hydro-fluctuation zone and terrestrial zone, where they decomposed over the course of 55 days. Invasive plants decompose rapidly compared to native plants (35.71% of the remaining mass of the invasive plant). The invasive plant A. philoxeroides has the potential to accelerate native plant decomposition (0.29 of non-added synergetic effect), but Bidens pilosa cannot. Nonetheless, species richness had little effect on the decomposition rate. These effects are dependent upon differences in chemical functional characteristics among the species. The initial traits of the plants, specifically C, N, and C/N, were significantly and linearly correlated with the loss of mixed litter mass and mixing effect strength (P < 0.01). In addition, submergence decomposition conditions reduce the disturbance of invasive plants and predict decomposition rates based on litter characteristics. Invasive plants can therefore impact the material cycle of an ecosystem. There is a need to examine decomposition time, which may also involve considering other factors.

Plant-soil interactions and C:N:P stoichiometric homeostasis of plant organs in riparian plantation

Carbon (C), nitrogen (N), and phosphorus (P) stoichiometric ratios give valuable insight into ecosystem function. The purpose of the present study is to probe into the C, N, and P stoichiometric characteristics in various organs and their relationships with soil factors of the dominant deciduous conifer plant species (Taxodium ascendens and Taxodium distichum) during afforestation in the riparian zone of Three Gorges Reservoir. The results showed only a small change in the concentration of C in different plant organs and soils. T. ascendens contained mean N and P concentrations of 7.63 and 1.54 g/kg in fine roots, 5.10 and 0.56 g/kg in stems, and 15.48 and 2.30 g/kg in leaves, respectively. Whereas T. distichum had a mean N and P concentration of 7.08 and 1.37 g/kg in fine roots, 4.84 and 0.59 g/kg in stems, and 16.89 and 2.23 g/kg in leaves. The N:P ratios in all organs were below 14, indicating that N may have inhibited tree growth. The fine roots P and N:P of T. distichum were weak plasticity and weak homeostasis, and those of T. ascendens were plasticity and weak plasticity. Their stems and leaves adhere to strict homeostasis. N concentrations were significantly positively related to P concentrations in every tissue (except the stems of T. ascendens), and C concentrations were significantly positively associated with P concentrations in the stems and leaves of T. ascendens and T. distichum (p < 0.05). Likewise, soil P and fine root P were positively associated (p < 0.01). This study contributes to the understanding of deciduous conifer plant stoichiometry. It demonstrates N, P, and N:P stoichiometric homeostasis in T. ascendens and T. distichum, which can withstand flooding and are suitable for vegetation restoration in the hydro-fluctuation zone.