خيارات البحث
النتائج 1 - 10 من 984
Charges critiques pour la vegetation.
1993
Thimonier A. | Dupouey J.L.
Water quality, phosphorus input reductions, analytical methods and lake internal/self-purification measures: a case study of Lake Froylandsvatn, Norway.
1994
Bratli J.L.
Importance of ammonia nitrogen potentially released from sediments to the development of eutrophication in a plateau lake
2022
Ding, Shuai | Dan, Solomon Felix | Liu, Yan | He, Jia | Zhu, Dongdong | Jiao, Lixin
Sedimentary nitrogen (N) in lakes significantly influenced by eutrophication plays a detrimental role on the ecological sustainability of aquatic ecosystems. Here, we conducted a thorough analysis of the importance of N potentially released from sediments during the shift of “grass-algae” ecosystem in plateau lakes. From 1964 to 2013, the average total amount of sedimentary potential mineralizable organic nitrogen (PMON) and exchangeable N in whole Lake Dianchi were 5.50 × 10³ t and 3.44 × 10³ t, respectively. NH₄⁺-N was the main product (>90%) of sedimentary PMON mineralization. The PMON in sediments had great release potential, which tended to regulate the distribution of aquatic plants and phytoplankton in Lake Dianchi and facilitated the replacement of dominant populations. Moreover, NH₄⁺-N produced by sedimentary PMON mineralization and exchangeable NH₄⁺-N have increased the difficulty and complexity of ecological restoration in Lake Dianchi to a certain extent. This study highlights the importance of sedimentary N in lake ecosystem degradation, showing the urgent need to reduce the continuous eutrophication of lakes and restore the water ecology.
اظهر المزيد [+] اقل [-]Local environment modulates whole-transcriptome expression in the seagrass Posidonia oceanica under warming and nutrients excess
2022
Pazzaglia, Jessica | Santillán-Sarmiento, Alex | Ruocco, Miriam | Dattolo, Emanuela | Ambrosino, Luca | Marín-Guirao, Lazaro | Procaccini, Gabriele
The intensification of anomalous events of seawater warming and the co-occurrence with local anthropogenic stressors are threatening coastal marine habitats, including seagrasses, which form extensive underwater meadows. Eutrophication highly affects coastal environments, potentially summing up to the widespread effects of global climate changes. In the present study, we investigated for the first time in seagrasses, the transcriptional response of different plant organs (i.e., leaf and shoot apical meristem, SAM) of the Mediterranean seagrass Posidonia oceanica growing in environments with a different history of nutrient enrichment. To this end, a mesocosm experiment exposing plants to single (nutrient enrichment or temperature increase) and multiple stressors (nutrient enrichment plus temperature increase), was performed. Results revealed a differential transcriptome regulation of plants under single and multiple stressors, showing an organ-specific sensitivity depending on plants' origin. While leaf tissues were more responsive to nutrient stress, SAM revealed a higher sensitivity to temperature treatments, especially in plants already impacted in their native environment. The exposure to stress conditions induced the modulation of different biological processes. Plants living in an oligotrophic environment were more responsive to nutrients compared to plants from a eutrophic environment. Evidences that epigenetic mechanisms were involved in the regulation of transcriptional reprogramming were also observed in both plants’ organs. These results represent a further step in the comprehension of seagrass response to abiotic stressors pointing out the importance of local pressures in a global warming scenario.
اظهر المزيد [+] اقل [-]Indirect herbivore biomanipulation may halt regime shift from clear to turbid after macrophyte restoration
2022
Zhang, Chengxiang | Pei, Hongcui | Lu, Cai | Liu, Cunqi | Wang, Wei | Zhang, Xiaobo | Liu, Peizhong | Lei, Guangchun
Eutrophication transforms clear water into turbid water in shallow lakes. Current restoration techniques focus on re-establishing the clear-water state rather than on its maintenance. We investigated the response of submerged macrophytes to temporary grass carp (Ctenopharyngodon idella) and scraping snail (Bellamya aeruginosa) introductions. We also explored the impacts of herbivores on underwater light conditions to identify their long- and short-term potential to halt regime shift from clear to turbid after clear-water state reestablishment. Herbivores reduced both the biomass of submerged macrophytes and accumulated nutrients in the tissue of submerged macrophytes. This potentially avoided the pulse of endogenous nutrient release which would have exceeded the threshold required for the regime shift from clear to turbid. However, herbivores had a non-significant impact on submerged macrophyte-reduced light attenuation coefficient, which has a positive linear relationship with water chlorophyll a. Further, grass carp and snails enhanced the inhibition ratio of submerged macrophytes to phytoplankton by 3.96 and 2.13 times, respectively. Our study provides novel findings on the potential of herbivore introduction as an indirect biomanipulation tool for halting the regime shift of shallow lakes from clear to turbid after the restoration of submerged macrophytes.
اظهر المزيد [+] اقل [-]Effects of river-lake disconnection and eutrophication on freshwater mollusc assemblages in floodplain lakes: Loss of congeneric species leads to changes in both assemblage composition and taxonomic relatedness
2022
Jiang, Xiaoming | Li, Zhengfei | Shu, Fengyue | Chen, Jing
River floodplain ecosystems host one of the highest freshwater molluscan biodiversity on Earth. However, multiple human disturbances, such as loss of hydrological connectivity and deterioration of water quality, are seriously threatening most floodplain lakes throughout the world. Given the high imperilment rate of freshwater molluscs but the scarcity of studies examining the anthropogenic effects on this fauna, we test the response of mollusc assemblages to river-lake disconnection and eutrophication in 30 lakes in the Yangtze River floodplain, China. The species richness of entire Mollusca, Gastropoda and Bivalvia and 6 dominant families were all much lower at disconnected lakes than that in connected lakes, and decreased with increasing water eutrophication. The assemblage structure differed significantly among four lake groups for datasets based on entire Mollusca, Gastropoda and Bivalvia, indicating the serious impacts of hydrological disconnection and eutrophication. Moreover, the connected lakes showed significantly lower values of average taxonomic distinctness (Δ⁺) but higher values of variation in taxonomic distinctness (Λ⁺) than disconnected lakes. Such variations were triggered by the extirpation of congeneric and endemic species (mainly from families Unionidae and Viviparidae), which giving a waring of the loss of mollusc endemism in this region. In general, the present study showed that river-lake disconnection and deterioration of water quality resulted in serious biodiversity declines of both gastropods and bivalves in the Yangtze River floodplain lakes. A systematic approach including restoration of river-lake connectivity and habitats and improvement of water quality should be implemented in the conservation planning in this large river floodplain.
اظهر المزيد [+] اقل [-]Fate of dissolved inorganic nitrogen in turbulent rivers: The critical role of dissolved oxygen levels
2022
Liu, Ming | He, Yixin | Cao, Li | Zhi, Yue | He, Xianjin | Li, Tao | Wei, Yanyan | Yuan, Xiaobing | Liu, Bingsheng | He, Qiang | Li, Hong | Miao, Xiaojun
Dissolved inorganic nitrogen (DIN) is considered the main factor that induces eutrophication in water, and is readily influenced by hydrodynamic activities. In this study, a 4-year field investigation of nitrogen dynamics in a turbulent river was conducted, and a laboratory study was performed in the approximately homogeneous turbulence simulation system to investigate potential mechanisms involved in DIN transformation under turbulence. The field investigation revealed that, contrary to NO⁻₃ dynamics, the NH⁺₄ concentrations in water were lower in flood seasons than in drought seasons. Further laboratory results demonstrated that limitation of dissolved oxygen (DO) caused inactive nitrification and active denitrification in static river sediment. In contrast, the increased DO levels in turbulent river intensified the mineralization of organic nitrogen in sediment; moreover, ammonification and nitrification were activated, while denitrification was first activated and then depressed. Turbulence therefore decreased NH⁺₄ and NO⁻₂ concentrations, but increased NO⁻₃ and total DIN concentrations in the overlying water, causing the total DIN to increase from 0.4 mg/L to maximum of 1.0 and 1.7 mg/L at low and high turbulence, respectively. The DIN was maintained at 0.7 and 1.0 mg/L after the 30-day incubation under low and high turbulence intensities (ε) of 3.4 × 10⁻⁴ and 7.4 × 10⁻² m²/s³, respectively. These results highlight the critical role of DO in DIN budgets under hydrodynamic turbulence, and provide new insights into the DIN transport and transformation mechanisms in turbulent rivers.
اظهر المزيد [+] اقل [-]Exploring use of a commercial passive sampler in a closed static chamber to measure ammonia volatilization
2022
Jaeman, Sabrina | Nurulhuda, Khairudin | Amin, Adibah Mohd | Sulaiman, Muhammad Firdaus | Man, Hasfalina Che
Studies have indicated that up to 47% of total N fertilizer applied in flooded rice fields may be lost to the atmosphere through NH₃ volatilization. The volatilized NH₃ represents monetary loss and contributes to increase in formation of PM₂.₅ in the atmosphere, eutrophication in surface water, and degrades water and soil quality. The NH₃ is also a precursor to N₂O formation. Thus, it is important to monitor NH₃ volatilization from fertilized and flooded rice fields. Commercially available samplers offer ease of transportation and installation, and thus, may be considered as NH₃ absorbents for the static chamber method. Hence, the objective of this study is to investigate the use of a commercially available NH₃ sampler/absorbent (i.e., Ogawa® passive sampler) for implementation in a static chamber. In this study, forty closed static chambers were used to study two factors (i.e., trapping methods, exposure duration) arranged in a Randomized Complete Block Design. The three trapping methods are standard boric acid solution, Ogawa® passive sampler with acid-coated pads and exposed coated pads without casing. The exposure durations are 1 and 4 h. Results suggest that different levels of absorbed NH₃ was obtained for each of the trapping methods. Highest level of NH₃ was trapped by the standard boric acid solution, followed by the exposed acid-coated pads without casing, and finally acid-coated pads with protective casing, given the same exposure duration. The differences in absorbed NH₃ under same conditions does not warrant direct comparison across the different trapping methods. Any three trapping methods can be used for conducting studies to compare multi-treatments using the static chamber method, provided the same trapping method is applied for all chambers.
اظهر المزيد [+] اقل [-]Significant influence of phosphorus resources on the growth and alkaline phosphatase activities of Microcystis aeruginosa
2021
Xie, En | Su, Yuping | Deng, Songqiang | Kontopyrgou, Maria | Zhang, Dayi
It is well-accepted that phosphorus, particularly orthophosphate, is a determinant factor in aquatic eutrophication. However, numerous kinds of phosphorus sources exist in real world scenario, and limited studies have characterized the pairwise relationships among abundant different phosphorus sources and the physiological behaviour of algae. The present study developed a high-throughput assay to investigate the effects of 59 different phosphorus sources (equal initial concentration of total phosphorus) on the growth and alkaline phosphatase (AKP) activities of Microcystis aeruginosa, a model cyanobacteria whose predominance holds sway in lake eutrophication. M. aeruginosa cultivated with nucleoside monophosphates (NMPs) had higher growth, relative AKP activities and residual orthophosphate, which were positively intercorrelated. Oppositely, non-NMPs cultivation of M. aeruginosa led to negative relationships between the relative AKP activities and their growth or residual orthophosphate. These results indicated distinct mechanisms for M. aeruginosa to utilize different phosphorus sources in real-world scenario, and both phosphorus source and content are determinant factors on the growth and physiological behaviour of M. aeruginosa. Given the complicated and vast phosphorus pool in the natural environment, phosphorus resources might significantly alter the abundance and physiological behaviour of M. aeruginosa and other bloom-forming algae, then influence the phytoplanktonic community structure and affect the possibility and intensity of algal bloom. Our work hints the underestimation of the restriction factors in lake eutrophication and provides a new tool to study the driven forces of phytoplanktonic community dynamics as phosphorus from both internal and external sources.
اظهر المزيد [+] اقل [-]Species-specific isotope tracking of mercury uptake and transformations by pico-nanoplankton in an eutrophic lake
2021
Cossart, Thibaut | Garcia-Calleja, Javier | Worms, Isabelle A.M. | Tessier, Emmanuel | Kavanagh, Killian | Pedrero, Zoyne | Amouroux, David | Slaveykova, Vera I.
The present study aims to explore the bioaccumulation and biotic transformations of inorganic (iHg) and monomethyl mercury (MMHg) by natural pico-nanoplankton community from eutrophic lake Soppen, Switzerland. Pico-nanoplankton encompass mainly bacterioplankton, mycoplankton and phytoplankton groups with size between 0.2 and 20 μm. Species-specific enriched isotope mixture of ¹⁹⁹iHg and ²⁰¹MMHg was used to explore the accumulation, the subcellular distribution and transformations occurring in natural pico-nanoplankton sampled at 2 different depths (6.6 m and 8.3 m). Cyanobacteria, diatoms, cryptophyta, green algae and heterotrophic microorganisms were identified as the major groups of pico-nanoplankton with diatoms prevailing at deeper samples. Results showed that pico-nanoplankton accumulated both iHg and MMHg preferentially in the cell membrane/organelles, despite observed losses. The ratios between the iHg and MMHg concentrations measured in the membrane/organelles and cytosol were comparable for iHg and MMHg. Pico-nanoplankton demethylate added ²⁰¹MMHg (~4 and 12% per day depending on cellular compartment), although the involved pathways are to further explore. Comparison of the concentrations of ²⁰¹iHg formed from ²⁰¹MMHg demethylation in whole system, medium and whole cells showed that 82% of the demethylation was biologically mediated by pico-nanoplankton. No significant methylation of iHg by pico-nanoplankton was observed. The accumulation of iHg and MMHg and the percentage of demethylated MMHg correlated positively with the relative abundance of diatoms and heterotrophic microorganisms in the pico-nanoplankton, the concentrations of TN, Mg²⁺, NO₃⁻, NO₂⁻, NH₄⁺ and negatively with the concentrations of DOC, K⁺, Na⁺, Ca²⁺, SO₄²⁻. Taken together the results of the present field study confirm the role of pico-nanoplankton in Hg bioaccumulation and demethylation, however further research is needed to better understand the underlying mechanisms and interconnection between heterotrophic and autotrophic microorganisms.
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