The biotransformation of soil phosphorus in the water level fluctuation zone could increase eutrophication in reservoirs

Synthesis and Application of 1,8-Naphthalimide Derivatives Fluorescent Probe for Sequential Recognition of Cu2+ and H2PO4. J Fluoresc 2025;35:2685-2694. [PMID: 38613712 DOI: 10.1007/s10895-024-03692-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A naphthalimide Schiff base fluorescent probe (BSS) was designed and synthesized from 4-bromo-1,8-naphthalic anhydride, and its structure was characterized by 1HNMR, 13CNMR, FTIR, and MS. Fluorescence emission spectra showed that probe BSS could realize the "turn-off" detection of Cu2+ in acetonitrile solution, detection process with strong specificity and excellent anti-interference of other metal ions. In the fluorescence titration experiments, fluorescence intensity of BSS showed a good linear relationship with the Cu2+ concentration (0-10 µmol/L), and the detection limit was up to 7.0 × 10- 8 mol/L. Meanwhile, BSS and Cu2+ could form a 1:1 complex (BSS-Cu2+) during the reaction process. Under the same detection conditions, complex BSS-Cu2+ had specific fluorescence recovery properties for H2PO4- and the whole process was not only fast (6 s) but also free of interference from other anions, with a detection limit was as low as 5.7 × 10- 8 mol/L. In addition, complex BSS-Cu2+ could be successfully applied to the detection of H2PO4- in actual water samples, which with excellent application prospects.

Changes of riparian soil-plant system phosphorus responding to hydrological alternations of Three Gorges Reservoir

The anti-seasonal hydrological alternation in the Three Gorges Reservoir (TGR) significantly impacts the release of phosphorus (P) from the riparian soil-plant system, posing a threat to the aquatic environment. To investigate this issue, riparian soils and plants in three tributaries of the central TGR were sampled at three distinct stages: early exposure, final exposure, and soon after inundation receded. Soil properties, P forms, and plant P content were analyzed. A significant decrease in exchangeable P and organic P during exposure, and a decrease in aluminum/iron-bound P during inundation were observed. These changes were linked to the mineralization of organic matter and the reduction of iron oxides. Compared to bioavailable inorganic P, bioavailable organic P contributed more to the total soil P release during the exposure-inundation cycle. Plant P uptake accounted for 76.08% of the bioavailable P released by the soil during exposure. During inundation, plant P release significantly exceeded soil P release. Therefore, the soil-plant system could act as a P "sink" during exposure and a P "source" during inundation. The hydrological alternation of the TGR was the primary driver of this "source-sink" transformation. To mitigate P release in riparian zones, recycling plant materials and establishing monitoring sites are recommended.

Identifying factors influencing reservoir eutrophication using interpretable machine learning combined with shoreline morphology and landscape hydrological features: A case study of Danjiangkou Reservoir, China

Reservoir nearshore areas are influenced by both terrestrial and aquatic ecosystems, making them sensitive regions to water quality changes. The analysis of basin landscape hydrological features provides limited insight into the spatial heterogeneity of eutrophication in these areas. The complex characteristics of shoreline morphology and their impact on eutrophication are often overlooked. To comprehensively analyze the complex relationships between shoreline morphology and landscape hydrological features, with eutrophication, this study uses Danjiangkou Reservoir as a case study. Utilizing Landsat 8 OLI remote sensing data from 2013 to 2022, combined with a semi-analytical approach, the spatial distribution of the Trophic State Index (TSI) during flood discharge periods (FDPs) and water storage periods (WSPs) was obtained. Using Extreme Gradient Boosting (XGBoost) and SHapley Additive exPlanations (SHAP), explained the relationships between landscape composition, landscape configuration, hydrological topography, shoreline morphology, and TSI, identified key factors at different spatial scales and validated their reliability. The results showed that: (1) There is significant spatial heterogeneity in the TSI distribution of Danjiangkou Reservoir. The eutrophication levels are significant in the shoreline and bay areas, with a tendency to extend inward only during the WSPs. (2) The importance of landscape composition, landscape configuration, hydrological topography, and shoreline morphology to TSI variations during the FDPs are 25.12 %, 29.6 %, 23.09 %, and 22.19 % respectively. Besides shoreline distance, the Landscape Shape Index (LSI) and Hypsometric Integral (HI) are the two most significant environmental variables overall during the FDPs. Forest and grassland areas become the most influential factors during the WSPs. The influence of landscape patterns and hydrological topography on TSI varies at different spatial scales. At the 200 m riparian buffer zone, the increase in cropland and impervious areas significantly elevates eutrophication levels. (3) Morphology complexity, shows a noticeable threshold effect on TSI, with complex shoreline morphology increasing the risk of eutrophication.

Dam inundation reduces ecosystem multifunctionality following riparian afforestation in the Three Gorges Reservoir Region

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.

Response of phosphorus fractions transformation and microbial community to carbon-to-phosphorus ratios during sludge composting

Phosphorus (P) is one of the essential nutrient elements for plant growth and development. Sludge compost products can be used as an important source of soil P to solve the shortage of soil P. The difference in the initial carbon-to-phosphorus ratio (C/P) will lead to difference in the bacterial community, which would affect the biological pathway of P conversion in composting. However, few studies have been reported on adjusting the initial C/P of composting to explore P conversion. Therefore, this study investigated the response of P component transformations, bacterial community and P availability to C/P during sludge composting by adjusting initial C/P. The results showed that increasing C/P promoted the mineralization of organic P and significantly increased the content of the labile P. High C/P also increased the relative content of available P, especially when the C/P was at 45 and 60, it reached 60.51% and 60.47%. High C/P caused differences in the community structure, and improved the binding ability of microbial network modules and the competitiveness of microbial communities. Additionally, high C/P strengthened the effect of microbial communities on the transformation of P components. Finally, the study showed that C/P was the main contributor to P content variation (64.7%) and indirectly affected P component conversion by affecting the microbial community. Therefore, adjusting the C/P is crucial to improve the P utilization rate of composting products.

Arsenic mobilization across the sediment-water interface of the Three Gorges Reservoir as a function of water depth using DGT and HR-Peepers, a preliminary study

The artificial regulation of the Three Gorges Reservoir (TGR) creates large water level fluctuation zones (WLFZ) that may change the behavior of metals and metalloid in sediment, particularly redox sensitive elements. Mobilization of As, Fe and Mn across the sediment-water interface (SWI) in the TGR as a function of different water depth (periodically and permanently submerged sediments, respectively) was in situ determined by diffusive gradients in thin films (DGT) and high-resolution dialysis technique (HR-Peeper), respectively. The results showed that the mobilization of As was significantly affected by Fe/Mn especially Mn, across the SWI. Duo to the oxic-anoxic transitional state in near bottom water, the reduced Fe and Mn in sediment pore water could be oxidized and precipitated again, leading to the co-precipitation of As with Fe/Mn oxides (hydroxides). Consequently, concentrations of As, Fe and Mn in labile phases and pore water were generally low across the SWI, then they sharply increased at a few centimeters below the SWI. Considering different water depth, various trends were found in labile phase, whereas concentrations of As, Fe and Mn in pore water in permanently submerged sediments were significantly higher than those in periodically submerged sediments. The dry-re-wetting alternation processes in the WLFZ may play vital roles in the resupply capacity of sediments as it was found that periodically submerged sediments with longer re-wetting time had higher Fe/Mn resupply capacity than those with shorter re-wetting times and permanently submerged sediments.

Spatial variation of soil phosphorus in the water level fluctuation zone of the Three Gorges Reservoir: Coupling effects of elevation and artificial restoration

The water level fluctuation zone (WLFZ) is a distinctive and important component of the reservoir ecosystem. Due to periodic inundation, the fraction, spatial distribution, and chemical reactivity of soil phosphorus (P) within the WLFZ can potentially impact the loading of P into reservoir waters. However, a detailed study of this subject is lacking. In this study, the soil P in the WLFZ of the Three Gorges Reservoir, China, was examined using a combination of chemical sequential extraction, 31P NMR, and adsorption experiments. The results of chemical sequential extraction showed that HCl-Pi constituted the largest P pool among all P forms, with a mean concentration of 338 mg/kg. The content of HCl-Pi decreased significantly toward the dam, while the content of Res-P decreased in the opposite direction. The highest contents of most P forms and total P were observed at an elevation of 160 m. 31P NMR measurements showed that NaOH-EDTA Pi detectable in WLFZ soils at 145 m, 160 m, and 175 m elevation consisted mainly of orthophosphate and pyrophosphate, while NaOH-EDTA Po contained phosphate monoesters and phosphate diesters, accounting for 1.4 % to 46.2 % of NaOH-EDTA TP. Adsorption experiments showed that soil P in the WLFZ was a potential P source for reservoir waters, with chemisorption being the dominant mechanism of P sequestration. The adsorption equilibrium concentration of WLFZ soil was lower at higher elevations (>170 m) compared to lower elevations (<150 m), exhibiting a decrease in the average maximum adsorption from 271 mg/kg to 192 mg/kg. Statistical analysis suggested that Ca and Fe content, particle size, elevation, and artificial restoration were key factors affecting the fraction and content of soil P in the WLFZ. Our findings contribute to an improved understanding of the behavior of soil P in the WLFZ of large reservoirs and its potential contribution to the reservoir waters.

Changing temporal and spatial patterns of methane emission from rivers by reservoir dams: a review

Dams built on rivers can bring economic benefits to local production and are considered to be environmentally friendly. However, in recent years, many researchers found that the establishment of dams has created excellent conditions for the production of methane (CH₄) in rivers, making it change from a "weak source" of rivers to a "strong source" of dams. In particular, reservoir dams have a great impact on CH₄ emission in rivers within their regions in terms of time and space. Spatially, the sedimentary layer and water level fluctuation zone of reservoirs are the main direct and indirect causes of CH₄ production. Temporally, the synergetic effect between water level adjustment of the reservoir dam and environmental factors leads to large changes in the substances of the water body, impacts on the production and transport of CH₄. Finally, the generated CH₄ is emitted into the atmosphere through several important emission modes: molecular diffusion, bubbling, and degassing. The contribution of CH₄ emitted from reservoir dams to the global greenhouse effect cannot be ignored.

Biogeochemical dynamics of particulate organic phosphorus and its potential environmental implication in a typical "algae-type" eutrophic lake

Organic phosphorus (P_o) plays a very important role in the process of lake eutrophication, but there is still a lack of knowledge about the internal cycle of P_o in suspended particulate matter (SPM) dominated by algal debris. In this study, the characterization of bioavailable P_o by sequential extraction and enzymatic hydrolysis showed that 45% of extracted TP was P_o in SPM of Lake Dianchi, and 43-98% of total P_o in H₂O, NaHCO₃ and NaOH fractions was enzymatically hydrolyzable P_o (EHP, H₂O-EHP: 31-53%). Importantly, labile monoester P was the main organic form (68%) of EHP, and its potential bioavailability was higher than that of diester P and phytate-like P. According to the estimation of P pools in SPM of the whole lake, the total load of P_i plus EHP in the H₂O extract of SPM was 74.9 t and had great potential risk to enhance eutrophication in the lake water environment. Accordingly, reducing the amount of SPM in the water during the algal blooming period is likely to be a necessary measure that can successfully interfere with or block the continuous stress of unhealthy levels of P on the aquatic ecosystem.

Removal and recovery of phosphorus from secondary effluent using layered double hydroxide-biochar composites

Removal of phosphorus (P) from wastewater and its recovery as a fertilizer are solutions to both P pollution control and resource recycling for agriculture. In this study, various layered double hydroxide biochar composites (LDH/BCs), namely, Zn-Al-LDH/BC, Mg-Al-LDH/BC, and Mg-Fe-LDH/BC, were synthesized to remove P from secondary effluents and then applied as fertilizers. Batch experiments showed that LDH/BCs could adsorb P in fast kinetics, with adsorption capacities ranging 35.19-55.76 mg P/g. A dynamic experiment was performed under different column heights and flow rates, and the results fitted well with Thomas model (R² > 0.90). These LDH/BCs effectively removed P in the continuous mode, even when treating secondary effluents. Furthermore, when the used LDH/BCs applied as fertilizers, the adsorbed Mg-Al-LDH/BC and Mg-Fe-LDH/BC stimulated crop growth; however, Zn-Al-LDH/BC did not. These differences were attributed to not only the availability of P, but also the stimulation or inhibition of photosynthetic pigment synthesis in crops by adsorbents. Overall, we synthesized LDH/BCs, which effectively removed and recovered P from secondary effluents, and investigated the factors influencing the effects of LDH/BCs on crops. We suggest that both P availability and physiological influences of adsorbents on crops should be considered when using adsorbents as fertilizers.

Unveiling the role of dissolved organic matter on phosphorus sorption and availability in a 5-year manure amended paddy soil

Dissolved organic matter (DOM) is an active component of organic manure that is widely used in agroecosystems to increase nutrient availability and consequently enhance crop yields. However, the ways in which soil DOM characteristics are influenced by organic manure and how it contributes to crop yield and soil P availability remains unclear. Here, we conducted a 5-year field experiment and demonstrated that partial replacement of chemical P fertilizer with swine manure could maintain high rice yield and soil available P levels and increase P fertilizer use efficiency (PUE) in comparison to chemical fertilization, even when the total P input was reduced. This suggests that organic manure application can significantly mobilize soil P and increase P availability. Structural equation modeling analysis indicated that the soil pH and humification degree of DOM, rather than DOM content, directly decreased maximum P adsorption capacity. The combined results of the optical spectroscopy and ultrahigh-resolution mass spectroscopy obtained from the laboratory validation experiment based on the DOM-removed soil demonstrated that manure-derived DOM competing with P for adsorption was one of the main reasons for the increase in soil P availability and that the effective DOM components were N-containing lignins, tannins, and condensed polycyclic aromatics with higher O/C and lower H/C ratios. Overall, our results provide solid evidence that soil DOM characteristics are influenced by manure application and facilitate soil P availability, which could help guide the sustainable P management and manure application in agroecosystems.

Characteristics of Ions Composition and Chemical Weathering of Tributary in the Three Gorges Reservoir Region: The Perspective of Stratified Water Sample from Xiaojiang River

River water chemistry offers information on watershed weathering and responds to the global carbon cycle. Watershed weathering processes and water chemistry in stratified water are still unclear in Xiaojiang River, as a major tributary of the Three Gorges Reservoir (TGR) which is the largest reservoir in the world. Major ions of river water at different depths were measured to reveal the ionic composition and chemical weathering properties by principal component analysis and stoichiometry in Xiaojiang River. Ca2+−HCO3− dominated the hydrochemical facies of river. Surface river water had the lowest total dissolved solid (146 mg/L) compared to other layers of water. According to principal component analysis, the major ions were divided into two principal components. PC1 was the weathering end-member of rocks, including the main ions except K+ and NO3–N, and PC2 may be the mixed end-member of atmospheric input and anthropogenic input. From stoichiometry, carbonate weathering dominated the cationic composition, with a contribution ratio of 56.7%, whereas atmospheric input (15.2%) and silicates weathering (13.9%) had similar extent of contribution. Compared with other major tributaries of TGR, Xiaojiang had more intense chemical weathering processes. The weathering rates of carbonates and silicates were 19.33 ± 0.68 ton/km2/year and 3.56 ± 0.58 ton/km2/year, respectively. Sulfuric acid as a proton may have participated less in the weathering processes of Xiaojiang River. The CO2 consumption budgets for silicates and carbonates weathering were 0.8 ± 0.2 × 109 mol/year and 2.8 ± 0.2 × 109 mol/year, respectively. These results enrich the watershed weathering information of TGR tributaries and provide data support for understanding the global carbon cycle.

Recovery of phosphorus from eutrophic water using nano zero-valent iron-modified biochar and its utilization

Effective removal and recovery of phosphorus (P) from the aquatic environment was of great significance for eutrophication control and P recovery. This study investigated the effects of different environmental conditions on P adsorption by biochar (BC) and the feasibility of applying the P-laden BC as a fertilizer for plant growth. The nano zero-valent iron (nZVI) modified reeds BC prepared at 700 °C (Fe-700-BC) had the maximum P adsorption capacity of 95.2 mg g^-1, which was higher than those prepared at 300, 500, and 900 °C. The addition of Fe-700-BC reduced the concentration of total phosphorus (TP) in the overlying water, in which the soluble reactive phosphorus (SRP) almost completely removed, as well as had a certain inhibitory effect on the growth of algae. Simultaneously, Fe-700-BC reduced the contents of different fractions of P (weakly adsorbed inorganic phosphorus (WA-Pi), potential active inorganic phosphorus (PA-Pi), and Fe/Al-bound inorganic phosphorus (Fe/Al-Pi)) by adsorbing the soluble P released from the sediments, especially in the case of disturbance. Fe-700-BC had no significant effect on the diversity and richness of the microbial community in the sediment. Moreover, P-laden BC was safe and environmentally friendly for application in the soil and tended to increase stem and root length, fresh and dry weight at low doses (0.5 wt%) in wheat planting experiments. The present work could provide a reference for solving the problems related to eutrophication and P deficiency.

Effectiveness and mechanism of aluminum/iron co-modified calcite capping and amendment for controlling phosphorus release from sediments

The effectiveness and mechanism of aluminum/iron co-modified calcite (Al/Fe-CA) for the control of phosphorus (P) liberation from sediments was investigated. The results showed that Al/Fe-CA possessed good sorption performance for phosphate, and the maximum phosphate sorption capacity for Al/Fe-CA could reach 27.0 mg/g. The major mechanisms involved the surface adsorption of phosphate on calcite, the precipitation between phosphate and Ca²⁺ leached from calcite, and the ligand exchange between Al/Fe-bound hydroxyl groups and phosphate to form the Al-O-P and Fe-O-P inner-sphere complexes. The re-releasing risk of Al/Fe-CA-bound P under the circumstances of normal pH (5-9) and reducing environment was very low. Al/Fe-CA addition could significantly reduce the risk of P releasing from sediment to overlying water (OL-water), and the inactivation of mobile P, reactive soluble P (SRP) and diffusive gradient in thin-films (DGT)-labile P in sediment by Al/Fe-CA had a great part in the suppression of sediment-P liberation to OL-water by the Al/Fe-CA amendment. Al/Fe-CA capping and fabric-wrapped Al/Fe-CA capping both could greatly reduce the risk of P releasing from sediment into OL-water, and the formation of a static layer with low concentrations of SRP and DGT-labile P in the upper sediment was the key to sustaining a high P controlling efficiency. When the applied mode of Al/Fe-CA varied from capping to amendment, although the inactivation efficiency of DGT-labile P in the overlying water and upper sediment by Al/Fe-CA would decrease to a certain degree, the inactivation efficiency of DGT-labile P in the lower sediment by Al/Fe-CA would increase. Results of this study suggest that Al/Fe-CA has the high potential to be used as an active capping or amendment material for the management of internal P loading in surface water bodies.