This study developed a pilot-scale vertical-baffled solid-phase denitrification reactor (VbSPDR) incorporating polycaprolactone (PCL) and ceramsite as fillers to balance organic carbon release and denitrification consumption. The Box-Behnken design was employed to assess the effects of hydraulic retention time (HRT), temperature, and influent nitrate concentration on nitrate removal efficiency and COD accumulation. Optimal conditions yielded a 95 % nitrate removal rate at 33 degrees C, an HRT of 1.22 h, and an influent nitrate concentration of 19 mg/L. Conversely, effluent COD concentration was minimized and dropped 2.5 mg/L at 13 degrees C, an HRT of 0.39 h, and an influent nitrate concentration of 19 mg/L. The PCL layer enriched hydrolysis-acidification and heterotrophic denitrifying bacteria by unclassified_f__Comamonadaceae and Acidovorax, while heterotrophic genera Phreatobacter thrived in ceramsite layer, enhancing the metabolism of COD over-released from PCL. These findings indicate that inorganic fillers can effectively enhance nitrate removal and controll effluent COD under varied operational parameters.

Increasing algal blooms in lakes promote algal particle aggregation, deposition, and decomposition, driving hypoxia across the sediment-water interface (SWI). This hypoxic environment favors pollution-tolerant benthic organisms, such as Limnodrilus hoffmeisteri. Massively settled algal particles are often disturbed and transported by these benthic organisms, potentially influencing environmental conditions and phosphorus (P) exchange across the SWI. Our study investigates the synergistic effects of algal particle decomposition and bioturbation on internal P loading. The results demonstrate that the burrowing of L. hoffmeisteri during its active phase enhances sediment oxygenation, while sustained algal decomposition exacerbates hypoxia. Ultimately, the anaerobic state across the SWI is synergistically enhanced during algal degradation and benthic faunal decay. Redox-sensitive P (Fe-P) dissolution remains the primary pathway for P release across the SWI. Additionally, the decomposition of organic P (Org-P) over longer timescales and its enrichment in the subsurface sediment also present significant potential for P release. The organic matter derived from algal particle deposition drives P cycling processes, affecting the Fe-S-P cycle by facilitating sulfate reduction processes on the one hand. On the other hand, bioturbation accelerate the mineralization rate of Org-P, promoting P release across the SWI. Our findings suggest that effective management of P in eutrophic lakes should consider bioturbation, particularly in littoral areas with dense algal accumulation.

The intensification of organic matter pollution is a critical issue in lake eutrophication research. Typically for macrophyte-dominated lakes of cold-arid regions, the increasing organic matter pollution, aggravating eutrophication status, and intensifying global changes amplify uncertainties in the evolution of lake ecosystems. This study investigates seasonal migration and transformation mechanisms of organic matter in Lake Ulansuhai, a macrophyte-dominated cold-arid eutrophic lake. Our findings revealed that Lake Ulansuhai exhibits persistently high organic matter concentrations in water and sediment, with dissolved organic matter dominating in the water column. Unlike subtropical lakes, organic matter burial in Lake Ulansuhai was significantly higher, peaking in winter, while mineralization occurred throughout spring, summer, and autumn. Summer conditions—elevated temperatures and algal-sourced organic matter—further accelerated mineralization. In addition, the accumulation of algal-sourced organic matter in the sediment and rapid consumption of algal-sourced organic matter in the water suggests an escalating trend in algal blooms. The warming trend of the area might intensify mineralization of buried organic matter through earlier ice melt and higher seasonal temperatures. These processes would in turn increase carbon emissions and promote a potential trend of transitioning to an algal-dominated turbid state. Future studies should give more focus on these accelerated organic matter cycling processes in similar cold-arid eutrophic lakes under an intensified global change trend.

Dimethyl sulfides are ubiquitous odorous substances in eutrophic freshwater bodies. In this study, a simple headspace solid-phase microextraction-gas chromatography-flame photometric detection method was developed to detect three representative algal-derived dimethyl sulfides in freshwater lake water samples: dimethyl monosulfide (DMS), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS). The effects of extraction fiber, temperature, pH, ionic strength, and sample volume were investigated orthogonally, and the optimized method was applied to analyze surface water samples from Lake Ulansuhai in Inner Mongolia, China. Optimal extraction was obtained with a 50/30 µm DVB/CAR/PDMS extraction fiber, 20% ion concentration, 87 min extraction time, and 50 °C extraction temperature. The correlation coefficients of the standardized working curves for DMS, DMDS, and DMTS were 0.9967, 0.9907, and 0.9994, respectively, indicating good linear relationships. Limits of detection were in the nanogram range, and the recoveries of the spiked standards for DMS, DMDS, and DMTS were 97.22~99.07%, 93.39~99.34%, and 91.17~99.25%, with relative standard deviations of 5.18~5.94%, 3.08~6.25%, and 2.56~5.47%, respectively. This method is stable and reliable, and can be used for the determination of volatile sulfides in freshwater lake water.

As the second deepest lake in Africa, Lake Tanganyika plays an important role in supplying fish protein for the catchment’s residents and is irreplaceable in global biodiversity. However, the lake’s water environment is threatened by socioeconomic development and rapid population growth along the lake. This study analyzed the spatial scale effects and seasonal dependence of land use types and landscape metrics on water quality in 16 sub-basins along northeastern Lake Tanganyika at different levels of urbanization. The results revealed that land use types had a higher influence on water quality in urban areas than that in rural areas; the explanatory variance in the urban area was 0.78–0.96, while it was 0.21–0.70 in the rural area. The explanatory ability of land use types on water quality was better at the buffer scale than at the sub-watershed scale, and the 500 m buffer scale had the highest explanatory ability in the urban area and rural area both in the rainy season and dry season, and artificial surface and arable land were the main contributing factors. And this phenomenon was more obvious in dry season than in rainy season. We identified that CONTAG was the key landscape metric in urban area and was positively correlated with nutrient variables, indicating that water quality degraded in less fragmented landscapes. The sub-watershed scale had the highest explained ability, while in rural area, the 1500 m buffer scale had the highest explained ability and IJI had the highest explanatory variance, which had a negative effect on water quality. Research on the relationship between land use and water quality would help assess the water quality in the unmonitored watershed as monitoring is expensive and time-consuming in low-income area. This knowledge would provide guideline to watershed managers and policymakers to prioritize the future land use development within Lake Tanganyika basin.

Nitrogen (N) and phosphorus (P) metabolism is becoming an increasingly complex process during urbanization due to increasing rates of consumption and emission worldwide. Understanding the urban N and P metabolism helps identifying production capacity, consumption demand, and the impact of N and P emissions on the environment, providing a scientific basis for decision-making in sustainable utilization of N and P resources. Quantifying and mapping the source, path, and sinks of N and P in an urban system is the premise of controlling emissions. In this paper, we used the substance flow analysis (SFA) method to describe the N and P metabolism processes in the urban system of Dar es Salaam (Tanzania) in 2017, and used the scenario-based analysis method to understand the impact of different N and P metabolisms on potentially recoverable N and P sources by 2030. The results showed that the urban system of Dar es Salaam receives a total input flow of 28,101.8 tN/year and 3,379 tP/year, with a total output flow of 18,859.6 tN/year and 1,849.3 tP/year with net stock changes of 9,242.2 t/year for N and 1,529.7 t/year for P, respectively. We noticed that increased human activities largely represented the city's waste released after the household consumption, and would become the main causes of N and P emissions. In addition to this, 59.38%, 31.25%, and 9.38% of N flow quantification quality were at high, medium, and low levels, respectively, while 74.07%, 11.11%, and 14.81% of P flow quantification quality were at high, medium, and low levels, respectively. Our results suggest that implementing integrated nutrient management measures, such as changes in people's diets and the use of washing products, and improved management and technologies of manure, sewage, and landfill leachate treatment, would be the most effective approach to resolve the urban nutrient emissions in Dar es Salaam.

Ecological water diversion is an important method to improve water quality in lakes and reservoirs. But the environmental effects, from the ecological water diversion project (EWDP) to the internal release of sediment nutrients, remain unclear. In this study, an indoor simulation of an EWDP with different treatment scenarios with water transfer proportions of 25%, 50%, 75% and 100% was conducted to study the effects of water diversion on sediment nitrogen and phosphorus release in Lake Wanshandang. Our results showed that the flux of NH3–N released from the sediments in the western and eastern areas of Lake Wanshandang was significantly reduced after water transfer treatment, and the degree of reduction increased with increased water transfer. Specifically, the release flux of NH3–N in the sediment in the western area decreased from 18.02 mg/(m2/d) to −2.25 mg/(m2/d) when the transferred water reached 100% replacement of the original overlying water. The effect of water transfer treatment on the release flux of SRP from sediment varied greatly throughout the lake. After treatment, the SRP release flux in the western and central areas increased significantly, while it decreased in the eastern area. The NH3–N and SRP concentrations changed from 0.12–0.27 mg/L and 0.02–0.049 mg/L to 0.28–0.84 mg/L and 0.01–0.066 mg/L before and after the water transfer treatment. Our statistical analysis showed that the change in NH3–N and SRP release fluxes after treatment was significantly negatively correlated (p < 0.05) with concentrations of NH3–N or SRP in the overlying water before and after water transfer. We suggest the increase in NH3–N and SRP concentrations in the overlying water after the water transfer treatment led to the subsequent decreased NH3–N or SRP release flux, while the decrease in SRP concentration in overlying waters enhanced SRP release from the sediment. The differences in the concentrations of nitrogen and phosphorus between the original overlying water and the transferred incoming water are important factors affecting the release of nutrients from sediment.

The high concentration of salt in organic wastewater has a strong inhibitory effect on the removal of pollutants. A method for the efficient removal of trace pollutants in high-salinity organic wastewater was developed. This study investigated the effect of the combination of permanganate [Mn(VII)] and calcium sulfite [S(IV)] on pollutant removal in hypersaline wastewater. The Mn(VII)-CaSO3 system removed more pollutants from high-salinity organic wastewater than from normal-salinity wastewater. Chloride (increasing from 1 M to 5 M) and low concentration of sulfate (increasing from 0.05 M to 0.5 M) significantly enhanced the system's resistance to pollutants under neutral conditions. Despite the fact that Cl− can combine with the free radicals in the system and reduce their efficiency in removing pollutants, the presence of chloride ions greatly enhances the electron transfer rate in the system, promoting the conversion of Mn(VII) to Mn(III) and significantly increasing the reaction rate of Mn(III) as the primary active species. Therefore, chloride salts can greatly enhance the removal of organic pollutants by Mn(VII)-CaSO3. Although sulfate does not react with free radicals, a high concentration of sulfate (1 M) will affect the formation of Mn(III), which greatly weakens the removal effect of the entire system on pollutants. The system can still have a good pollutant removal effect with mixed salt. Altogether, this study demonstrates that the Mn(VII)-CaSO3 system offers new possibilities for the treatment of organic pollutants in hypersaline wastewater.

Increased algal blooms and loss of aquatic vegetation are critical environmental issues associated with shallow lakes worldwide. The increase in organic matter (OM) in both macrophyte-dominated areas (MDAs) and algaedominated areas (ADAs) has exacerbated these problems. Most OM in water is concentrated as suspended particulate matter (SPM), which eventually migrates to the sediment. However, the detailed origins and fates of OM in water-SPM-sediment systems with coexisting MDAs and ADAs remain unclear. Therefore, in this study, we conducted monthly field investigations in Lake Taihu, focusing on OM-migration patterns in an MDA and an ADA. The C/N mass ratios, 813C contents, and OM compositions of the water, SPM, and sediment were analyzed. Our findings revealed that autochthonous sources of OM prevailed in water, whereas terrestrial sources prevailed in SPM and sediment. Rapid decomposition processes of microbial- and algae-derived dissolved OM were discovered along the water-SPM-sediment pathways in both areas. A trend towards a shift from macrophytes to algae in the MDA was also discovered. Overall, the entire lake underwent a burial process of OM in both types of areas, with mineralization mostly occurring during the algal-bloom seasons and more strongly in the ADA. Furthermore, we deduced that a decrease in the OM-burial rate, but an increase in the mineralization rate, might occur after a complete shift from a macrophyte- to an algae-dominated status. Such a shift might change the carbon-cycle process in eutrophic shallow lakes and should be given more attention in future research.

Water quality degradation of urban rivers has become a serious constraint to the sustainable development of big cities in sub-Saharan Africa, and few systematic quantitative studies have been conducted on this issue. Here, we studied three main urban rivers: Mzinga River, Kizinga River, and Msimbazi River in Dar es Salaam, the largest port city on the west coast of the Indian Ocean. The spatial and temporal changes of the physicochemical parameters including DO, pH, oxidation–reduction potential (ORP), electrical conductivity (EC), total dissolved solids (TDS), turbidity, total nitrogen (TN), total dissolved nitrogen (TDN), dissolved inorganic nitrogen (DIN), chemical oxygen demand (COD Mn ), total phosphorus (TP), total dissolved phosphorus (TDP), soluble reactive phosphate (SRP), and water quality index ( WQI ) were investigated. The results showed that the middle and lower reaches of the three rivers were severely polluted with N (nitrogen) and P (phosphorus) with pollution increasing from the upstream to the downstream. WQI results showed that the water quality of Msimbazi River was in the “poor” category and fluctuated temporally and spatially. Principal component analyses (PCA) implied that redox status and N were the main factors affecting the water quality of the rivers. Unregulated discharges of untreated municipal and industrial wastewaters were the main drivers of water quality degradation in the rivers. Rapid urbanization characterized by population explosion and the small handicraft industry aggravated the situation. Source control and end treatment are urgently needed to prevent the water quality of the urban rivers in Dar es Salaam from deteriorating further.

Mediating the anoxic ammonia oxidation with manganese oxide (MnOx) can reduce the requirements of dissolved oxygen (DO) concentrations in constructed wetlands (CWs) and improve the removal of ammonium nitrogen (NH4+-N). Recent studies that employed natural manganese ore and/or mine waste as substrates in CWs may develop potentially negative environmental effects due to leachates. However, removing NH4+-N by anoxic ammonia oxidation is influenced by the crystal form of MnOx. In this study, a novel clinoptilolite-based amorphous-MnO2 (amorphous-MnO2/clinoptilolite) was synthesized by the sol-gel method as an alternative substrate to improve the efficiency of anoxic ammonia oxidation and reduce the impact of Mn ion leaching. According to the anoxic ammonia oxidation experiment of clinoptilolite, amorphous-MnO2/clinoptilolite, and manganese ore on NH4+-N, the amounts of NH4+-N removed were 24.55 mg/L/d, 44.55 mg/L/d, and 11.04 mg/L/d, respectively, and the initial NH4+-N concentration was 49.53 mg/L. These results indicated that the amorphous-MnO2/clinoptilolite had both the adsorption and the anoxic ammonia oxidation performance. The recycling experiment demonstrated that the effect of anoxic ammonia oxygen mediated by amorphous-MnO2 would not diminish with the gradual saturation of clinoptilolite for NH4+-N. Furthermore, the anoxic ammonia oxidation consumed NH4+-N in the clinoptilolite, which restored the adsorption capacity of the clinoptilolite and simultaneously decreased the leakage of manganese ions in the process, making it environmentally friendly. Therefore, the amorphous-MnO2/clinoptilolite provided an excellent substrate material for the constructed wetland under an anoxic environment, which greatly improved the nitrogen removal capacity compared to existing substrate materials.

The traditional coagulation process in drinking water treatment cannot effectively remove the organic precursors of highly toxic iodinated disinfection by-products (I-DBPs). This study proposes a combination of zero-valent iron (ZVI) and peroxymonosulfate (PMS) to remove the organic precursor of I-DBPs during the coagulation stage. This study investigated the degradation of iopamidol (IPM), a typical organic precursor of I-DBPs, by the combination of ZVI/peroxymonosulfate (PMS) and the influence on the generation of I-DBPs during disinfection. IPM was effectively decomposed by ZVI/PMS, because of the formation of hydroxyl (HO center dot) and sulfate (SO4 center dot-) radicals. SO4 center dot- was a major contributor (>64.7 %) to the degradation. The anions (Cl- and SO42-) in the conventional coagulants have a weak effect on the removal of IPM by the ZVI/PMS process, while the common cations (Fe3+) further enhance the removal of IPM by the ZVI/PMS process. The formation of I-THMs was obviously decreased during the chlorination of IPM in the presence of the ZVI/PMS process (14.4 mu g/L) compared to that in the presence of the ZVI process (258.1 mu g/L) and the chlorination alone process (29.7 mu g/L). The formation of I-THMs was increased by more than 1.7-fold in the presence of natural organic matter (NOM). The presence of Fe3+ further reduced the formation of I-DBPs to below the limit of quantitation (LOQ). Therefore, it is feasible to use the ZVI/PMS process to degrade IPM in the coagulation stage of drinking water treatment, and it can also reduce the I-DBPs formed by subsequent disinfection.

铁氧化物和锰氧化物均可在缺氧条件下介导氨氮(NH4+-N)的氧化去除,这2项技术被称为铁氨氧化(Feammox)和锰氨氧化(Mnammox).此外,金属氧化物对总磷(TP)也有去除能力,因此,在人工湿地中具有良好的应用前景.为比较铁矿基和锰矿基人工湿地的脱氮除磷效果,本研究建立了铁矿基人工湿地(CW-Fe)、锰矿基人工湿地(CW-Mn)和砾石对照组人工湿地(CW-C)3组人工湿地.结果表明,CW-Fe和CW-Mn的脱氮除磷性能均优于CW-C.尽管锰矿对NH4+-N的吸附作用最强,但CW-Fe却表现出了更优越的NH4+-N长期去除性能.在基质对NH4+-N的吸附饱和后,CW-Fe对NH4+-N的去除率仍有39.93％～62.4％,而CW-Mn只有29.15％～35.4％.由于铁矿和锰矿溶出的金属离子能与磷酸盐结合形成稳定的沉淀,从而有效去除TP,CW-Fe和CW-Mn均有优异的TP去除性能.CW-Mn的TP去除率最高,为95.26％,其次是CW-Fe,为79.97％.在微生物方面,具有还原铁氧化物和氧化NH4+-N潜力的Bacillus和Exiguobacterium在CW-Fe中均得到了显著富集.结合水质数据及脱氮相关功能菌的分析,推测出Feammox中可能更倾向于将NH4+-N直接氧化为N2,而Mnammox则是更倾向于先将NH4+-N氧化为NOx-N.本研究可为探索同步脱氮除磷的低能耗污水处理工艺及人工湿地中基质的选择提供案例参考.

Since the mineral, phosphorus (P), has dual properties of being limited resources for use, and being a pollutant for studying sustainable management of anthropogenic P flows in wetlands and soils, currently P receives the highest interests among researchers around the world. This study has successfully mapped P flows for a reference year (2017) and a future year (2030) using different scenarios of food production and consumption system (hereafter 'system') in the Mwanza region (Tanzania). The results showed that the total P input and output for 2017 alone were 9770 t and 7989 t, respectively. However, as high as 1781 tP accumulated in the system and the potentially recyclable P found, is yet to be recovered due to economic reasons and the lack of market. The main anthropogenic P input to the system occurred via imported feed, fertilizer, and crop food, accounting for about 99.72 % of the total input flow. The output was comprised of animal products exported with 3428 tP, and various P-contained wastes which were lost to water bodies with 4561tP. Analysis of the 2030 scenario showed that setting P management objectives from different perspectives such as the total P budget balance, potential recyclable P, and P emission, can help develop differentially preferred management strategies and measures in the Mwanza region. The combination of diet change, precision feeding, and integrated waste management practices presents the best prospects for decreasing P budget and losses, and the amount of P that can be potentially recovered from the system. We propose a package of integrated P management measures for the Mwanza region. Given the similarity of regional socio-economic development background around the Lake Victoria basin, the model can be used to guide the study of anthropogenic P flow analysis in other areas along the shore of Lake Victoria (Africa).

Understanding various biogeochemical processes, especially in eutrophic sediments, necessitates fine-scale phosphorus (P) measurements in pore waters. To the best of our knowledge, the fine-scale distributions of P across the sediment profiles of Lake Nansi have rarely been investigated. Herein we evaluated the dynamic distributions of labile P and Fe across the sediment-water interface (SWI) of Lake Nansi at two-dimensional (2D) and sub-millimeter resolution, using well-established colorimetric diffusive gradients in thin films (DGT) methodology. The concentrations of labile P in all investigated sediment profiles exhibited strong spatial variations, ranging from 0 to 1.50 mg/L with a considerable number of hotspots. Lake Nanyang (0.55 +/- 0.21 mg/L) had the highest mean concentration of labile P, followed by Lake Dushan (0.38 +/- 0.19 mg/L), Lake Weishan (0.28 +/- 0.21 mg/L), and Lake Zhaoyang (0.18 +/- 0.09 mg/L). The highest concentrations of labile P were always detected in Lake Dushan, which had been subjected to excessive exogenous P pollution. The co-distributions of labile P and Fe in the majority of the sediment of Lake Nansi confirmed highly positive correlations (P < 0.01), suggesting that the mobility of labile P throughout the SWI was likely governed by iron redox processes. The apparent diffusion fluxes of P across the SWI ranged from -7.7 to 33.6 mu g/m(2)center dot d, with a mean value of 5.26 +/- 7.80 mu g/m(2)center dot d. Positive apparent fluxes for labile P were recorded in most sediment cores, demonstrating the strong upward mobility of P from the sediment to the overlying water. Our results provided accurate and extensive information regarding the micro-distribution and dynamic exchange of labile P across the SWI. This allows for a better understanding of eutrophication processes and the implementation of P management strategies in Lake Nansi.

Heavy metal pollution in sediments is a common environmental issue in small- and medium-sized reservoirs not only in China but also worldwide; however, few interpretations of the pollution pattern exist. Based on the analyses of accumulation characteristics, ecological risks, and source apportionments of eight heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn) in sediments, we derived a paradigm to describe the pollution pattern of heavy metals in sediments of a typical small- and medium-sized Tongjiqiao Reservoir. The results showed high levels of Cd, Hg, and As pollutants in the surface and upper sediment layers of the pre-dam area. Additionally, As, Cd, Hg, and Pb pollutants peaked in the middle layers of the inflow area, indicating a high ecological risk in these areas. The positive matrix factorization results implied that industrial, agricultural, and transportation activities were the main sources of heavy metals. The heavy metal pollution pattern exhibited three distinct stages: low contamination, rapid pollution, and pollution control. This pattern explains the heavy metal pollution process in the sediments and will provide scientific guidance for realizing the green and sustainable operation and development of the reservoir.

The phyllosphere pH helps shape the plant microbiome and strongly influences aboveground interactions in plant canopies. Yet little is known about the distribution of pH at a microscale within the macrophyte phyllosphere and the factors promoting them because achieving high-resolution quantitative imaging of phyllosphere pH is a great challenge. Here, new ratiometric pH nano-optodes were prepared by firstly encapsulating the self-synthesized lipophilic dyes (8-acetoxypyrene-N1, N3, N6-trioctadecyl-1, 3, 6-tri-trisulfonamide) to poly(1-vinylpyrrolidone-co-styrene) nanoparticles, and then immobilizing the resulting nanoparticles in polyurethane hydrogel on transparent foils. The nano-optodes presented reversible and fast response (t95 < 80 s) to the pH range from 7.0 to 11.0, with merits of good spatial resolution, photobleaching/leaching resistance and negligible cross-sensitives toward temperature, O2 and ionic strength (< 100 mM). The nano-optodes together with a self-designed phyllosphere chamber were further applied to directly measure the pH distributions at a microscale around single leaves of V. spiralis grown in natural sediment. The pronounced pH microheterogeneity and leaf basification within the V. spiralis phyllosphere were quantitatively visualized. We also provided direct empirical evidence that the dynamic of the phyllosphere pH at high resolution was significantly controlled by the shifting light intensity and temperature. Implementation of the nano-optodes holds great potential for various laboratory applications, which will provide an in-depth insight into phyllosphere activities on the microscale.

High-frequency in-situ monitoring of nutrients in lakes is increasingly becoming relevant to understand event-driven nutrient pulses better. These pulses are essential for phytoplankton development but are usually not captured during conventional sampling programs. In-situ monitoring of nutrients in lakes has been lagging despite the role of nutrients in eutrophication. We evaluated an in-situ wet chemistry soluble reactive phosphorus (SRP) analyzer to establish a methodological basis for high-frequency measurements of SRP. The device (based on the molybdate blue method) was evaluated in laboratory and field tests by comparing it with conventional laboratory analysis. The results of the in-situ analyser during laboratory were similar to the conventional analysis (R2 > 0.995, NSE = 0.989, PBIAS = 8.4 %). Repeated measurements by the in-situ analyzer in a 0.1 mg L-1 test solution had a mean and standard deviation of 0.1005 ± 0.0047 and a MAPE of 3.39, indicating the stability of the measurements. During field tests in a hypertrophic lake with anoxic hypolimnion, the in-situ analyzer SRP concentrations were lower and divergent from the laboratory analysis; due to potential interference of the in-situ analyzer's reagents by sulfides. Under aerobic conditions during field tests, the in-situ P results of a eutrophic, mixed shallow lake were similar to those from water samples analyzed in the laboratory (R2 = 0.562 – 0.812, NSE = 0.397 – 0.707, PBIAS = -8.5 – 24.6 %). There was no difference in SRP concentration among the unfiltered, 0.2 µm, and 10 µm pore size filtered samples; filter pore size did not play a role in the measured SRP concentrations. The in-situ SRP analyzer revealed previously unobserved phenomena, e.g., multiple strongly discontinuous SRP peaks reaching almost 0.1 mg L-1; it therefore, offers a solid methodological basis for high-frequency monitoring of SRP. Incorporating high-frequency in-situ nutrient analysis in lake monitoring provides insights into lakes' short-term nutrient dynamics. Such information is essential for understanding the effects of extreme events like droughts, storms, and heat waves.

Tidal flow constructed wetlands (TFCWs) offer a promising method to treat domestic wastewater in rural areas. However, TFCWs are usually severely restricted by denitrification. This study aimed to explain the nitrogen removal process in TFCWs and provide an effective method to increase nitrogen removal. TFCWs filled zeolite (Z-TFCW) was established in this work, and its pollutants (NH4+-N, NOx--N, and COD) removal performance, layered effect, microbial community characteristics, the in-situ regeneration process of Z-TFCW, and the two-way influent mechanisms were investigated. The results showed that under the downflow influent, the Z-TFCW effluent NH4+-N, NOx--N, and COD concentrations were 9.79 +/- 0.62 mg.L-1, 24.25 +/- 1.53 mg.L-1, and 24.04 +/- 2.68 mg.L-1, respectively. In the influent and flood period, NH4+-N was adsorbed rapidly by zeolite. Then, they were released into the biofilm and oxidized to NOx--N during the drain period. The generated NOx--N was leached to the bottom layer during the next cycle of influent, and most of them were adsorbed by the bottom biofilm for denitrification. Furthermore, the proportion of COD/NOx--N in the top, middle, and bottom layers of Z-TFCW was 12.9, 3.1, and 1.0, respectively. Layered effect and microbial community analysis represented that COD limited the denitrification of Z-TFCW. The two-way influent optimized the distribution path of carbon sources for denitrification in Z-TFCW and enhanced nitrogen removal. Therefore, the NOx-N- effluent concentration decreased by 50.31 %.

Nowadays, the ubiquitous distribution and increasing abundance of P+III in waterbodies have caused serious concerns regarding its bioavailability and potential toxicity. However, our knowledge on these issues is relatively limited. We addressed previously unknown effects of P+III on three dominate algae species i.e. Microcystic aeruginosa (M. aeruginosa), Chlorella pyrenoidesa (C. pyrenoidesa) and Cyclotella. sp in eutrophic waterbodies in China. Remarkable declines in biomass, specific growth rate and Chl-a of algae cells treated with 0.01-0.7 mg/L P+III as sole or an alternative P source were observed, indicating P+III had an inhibitory effect on the algal growth. Besides, the intracellular enzyme activities e.g superoxide dismutase (SOD) and malondialdehyde (MDA) were significantly increased with P+III stress. M. aeruginosa and Cyclotella. sp cells seemed to be more sensitive to P+III toxicity than C. pyrenoidesa since cell membrane suffered more serious stress and destruction. These findings combined, it confirmed P+III could not be utilized as bioavailable P, but had certain toxicity to the tested algae. It indicated that the increased P+III abundance in eutrophic waterbodies would accelerate the algal cell death, which could have a positive effect against algal blooms. Our results provide new insights into assessing the ecological risks of P+III in aquatic environments.