Eutrophication of lake waters in China: cost, causes, and control

Eutrophication evolution of lakes in China: Four decades of observations from space

The lake eutrophication is highly variable in both time and location, and greatly restricts the sustainable development of water resources. The lack of national eutrophication evaluation for multi-scale lakes limits the pertinent governance and sustainable management of water quality. In this study, a remote sensing approach was developed to capture 40-year dynamics of trophic state index (TSI) for nationwide lakes in China. 32% of lakes (N = 1925) in China were eutrophic and 26% were oligotrophic, and a longitudinal pattern was discovered, with the 40-year average TSI of 62.26 in the eastern plain compared to 23.72 in the Tibetan Plateau. A decreasing trend was further observed in the past four decades with a correlation of -0.16, which was mainly discovered in the Tibetan Plateau lakes (r > -0.90, p < 0.01). The contribution of climate change and human activities was quantified and varied between lake zones, with anthropogenic factors playing a dominant role in the east plain lakes (88%, N = 473) and large lakes are subject to a more complex driving mechanism (≥ 3 driving factors). The study expands the spatiotemporal scale for eutrophication monitoring and provides an important base for strengthening lake management and ecological services.

Development of a basin-scale total nitrogen prediction model by integrating clustering and regression methods

Nutrient runoff into rivers caused by human activity has led to global eutrophication issues. The Nakdong River in South Korea is currently facing significant challenges related to eutrophication and harmful algal blooms, underscoring the critical importance of managing total nitrogen (T-N) levels. However, traditional methods of indoor analysis, which depend on sampling, are labor-intensive and face limitations in collecting high-frequency data. Despite advancements in sensor allowing for the measurement of various parameters, sensors still cannot directly measure T-N, necessitating surrogate regression methods. Therefore, we conducted T-N predictions using a water quality dataset collected from 2018 to 2022 at 157 observatories within the Nakdong River basin. To account for the water quality characteristics of each location, we employed a clustering technique to divide the basin and compared a Gaussian mixture model with K-means clustering. Moreover, optimal regressor for each cluster was selected by comparing multiple linear regression (MLR), random forest, and XGBoost. The results showed that forming four clusters via K-means clustering was the most suitable approach and MLR was reasonably accurate for all clusters. Subsequently, recursive feature elimination cross-validation was used to identify suitable parameters for T-N prediction, thus leading to the construction of high-accuracy T-N prediction models. Clustering was useful not only for improving the regressors but also for spatially analyzing the water quality characteristics of the Nakdong River. The MLR model can reveal causal relationships and thus is useful for decision-making. The results of this study revealed that the combination of a simple linear regression model and clustering method can be applied to a wide watershed. The clustering-based regression model showed potential for accurately predicting T-N at the basin level and is expected to contribute to nationwide water quality management through future applications in various fields.

Low-cost IoT based system for lake water quality monitoring

Water quality monitoring is a critical process in maintaining the well-being of aquatic ecosystems and ensuring growth of the surrounding environment. Clean water supports and maintains the health, livelihoods, and ecological balance of the ecosystem as a whole. Regular assessment of water quality is essential to ensure clean and reliable water is available to everyone. This requires regular measurement of pollutants or contaminants in water that can be monitored in real-time. Hence, this research showcases a system that consists of low-cost sensors used to measure five basic parameters of water quality that are: turbidity, total dissolved solids, temperature, pH, and dissolved oxygen. The system incorporates electronics and IoT technology that are powered by a solar charged lead acid battery. The data gathered from the sensors was stored locally on a micro-SD card with live updates that could be viewed on a mobile device when in proximity to the system. Data was gathered from three different bodies of water over a span of three weeks, precisely during the seasonal transition from autumn to winter. We adopted a water sampling technique since our low-cost sensors were not designed for continuous submersion. The results show that the temperature drops gradually during this period and an inversely proportional relationship between pH and temperature could be observed. The concentration of total dissolved solids decreased during rainy periods with a variation in turbidity. The deployed system was robust and autonomous that effectively monitored the quality of water in real-time with scope of adding more sensors and employing Industry 4.0 paradigm to predict variations in water quality.

Purification Effect of Water Eutrophication Using the Mosaic System of Submerged-Emerged Plants and Growth Response

Aquatic plants play a crucial role in the sustainable management of eutrophic water bodies, serving as a valuable tool for water purification. However, the effectiveness of using aquatic plants for improving water quality is influenced by landscape considerations. In practical applications, challenges arise concerning low purification efficiency and compromised aesthetic appeal when utilizing plants for water purification. To address these issues, this study aimed to examine the impact of aquatic plants on the purification of simulated landscape water bodies, specifically focusing on the effectiveness of the mosaic system of submerged-emerged plants in remediating eutrophic water bodies. Our findings indicated that individual aquatic plants exhibited limited efficacy in pollutant (total nitrogen, total phosphorus, ammonia nitrogen, and chemical oxygen demand) removal. However, when combined in appropriate proportions, submerged plants could enhance species growth and improve the purification efficiency of polluted water bodies. Notably, the mosaic system of submerged-emerged plants neither significantly promoted nor inhibited the growth of each other, but it effectively removed pollutants from the simulated water bodies and inhibited turbidity increase. The comprehensive evaluation ranked the purification capacity as Canna indica-submerged plants combination (C + S) > Thalia dealbata-submerged plants combination (T + S) > Iris pseudacorus-submerged plants combination (I + S) > Lythrum salicaria-submerged plants combination (L + S). Both C + S and T + S configurations effectively mitigated the rise of water turbidity and offered appealing landscape benefits, making them viable options for practical applications in urban landscape water bodies. Our study highlights that a submerged-emerged mosaic combination is a means of water purification that combines landscape aesthetics and purification efficiency.

Eutrophication diminishes bacterioplankton functional dissimilarity and network complexity while enhancing stability: Implications for the management of eutrophic lakes

Eutrophication is a growing environmental concern in lake ecosystems globally, significantly impacting the structures and ecological functions of bacterioplankton communities and posing a substantial threat to the stability of lake ecosystems. However, the patterns of functional dissimilarity, network complexity, and stability within bacterioplankton communities across different trophic states, along with the underlying mechanisms through which eutrophication influences these aspects, are not well-understood. To bridge this knowledge gap, we collected 88 samples from 34 lakes spanning trophic gradients and investigated bacterioplankton communities using network analysis and multiple statistical methods. Our results reveal that eutrophication, progressing from mesotrophic to hyper-eutrophic states, reduces the putative functional dissimilarity of bacterioplankton, particularly affecting the relative proportions of functional groups such as oxygenic photoautotrophy, phototrophy, and photoautotrophy. Network complexity exhibited a unimodal pattern across increasing trophic states, peaking at mesotrophic states and then decreasing towards hyper-eutrophic conditions, while stability exhibited the opposite pattern (U-shaped), indicating a variation in response to trophic state changes. In essence, eutrophication diminishes network complexity but enhances network stability. Collectively, these findings shed light on the ecological impact of eutrophication on bacterioplankton communities and elucidate the potential mechanisms by which eutrophication drives functional dissimilarity, network complexity and stability within bacterioplankton communities. These insights carry significant implications for the ecological management of eutrophic lakes.

Cooperation of ferrous ions and hydrated ferric oxide for advanced phosphate removal over a wide pH range: Mechanism and kinetics

Excessive phosphate loading leads to eutrophication problems in rivers or lakes and causes serious environmental and economic damages, urging new technologies to reduce effluent phosphate at ultra-low levels. As a promising candidate, adsorption over metal oxides is restricted by the released hydroxide anions (OH-) through ligand exchange, which elevates pH and suppresses further adsorption. In this contribution, we found ferrous ions (Fe2+) significantly enhance phosphate removal over hydrated ferric oxide (HFO) in a wide pH range via a cooperation of adsorption and precipitation, and clarified the synergistic mechanism by a series of characterizations and the modified models of adsorption isotherms and pseudo second-order kinetics. The combination of Fe2+and HFO removed up to 51.7 mg/g of phosphate at pH 4.0, with 43.6 and 8.1 mg/g attributing to adsorption and precipitation, respectively. In comparison to HFO alone, HFO/Fe2+ system achieved 2.2-fold increase in phosphate removal, 1.9-fold increase in phosphate adsorption capacity, and 3.4-fold increase in phosphate removal rate. The enhancement is understood by that hydroxide anions released from ligand exchange over HFO are neutralized by protons produced from the oxidative precipitation of ferrous ions. The HFO/Fe2+ combining system is promising to realize advanced removal of low concentration phosphate containing wastewater, and these findings bring new insights for the development of novel phosphate removal technologies through a rational design of a combination process.

What drives the changing characteristics of phytoplankton in urban lakes: Climate, hydrology, or human disturbance?

Phytoplankton in shallow urban lakes are influenced by various environmental factors. However, the long-term coupling effects and impact pathways of these environmental variables on phytoplankton remain unclear. This is an emerging issue due to high urbanization and the resultant complex climate, lake hydrology and morphology, human interference, and water quality parameter changes. This study used Tangxun Lake, the largest urban lake in the Yangtze River Economic Belt, as an example to assess for the first time the individual contributions and coupled effects of four environmental variables and fourteen indicators on chlorophyll-a (Chla) concentrations under two scenarios from 2000 to 2019. Additionally, the influence pathways between the environmental variables and Chla concentration were quantified. The results indicated that the Chla concentration was most affected by lake hydrology and morphology, as were the total nitrogen, total phosphorus, and transparency. Especially after urbanization (2015-2019), the coupling effect of human interference, lake hydrology and morphology, and water quality parameters was strongest (18%). This is mainly due to fluctuations in the lake water level and an increase in the shape index of lake morphology, large amounts of nutrients were input, which reduced lake transparency and indirectly changed the Chla content. In addition, due to the rapid development of Wuhan city, the expansion of construction land has led to an increase in impervious surface area and a decrease in lake area. During periods of intense summer rainfall, a substantial amount of pollutants entered the lakes through surface runoff, resulting in decreased lake transparency, and elevated concentrations of nitrogen and phosphorus, indirectly increasing the Chla content. This study provides a scientific basis for aquatic ecological assessment and pollution control in urban shallow lakes.

Increased invasion of submerged macrophytes makes native species more susceptible to eutrophication in freshwater ecosystems

Invasion and eutrophication are considered to pose serious threats to freshwater biodiversity and ecosystem function. However, little is known about the synergistic effects of invasion density and nutrient concentration on native submerged macrophytes. Here, we selected a common invasive species (Elodea nuttallii) and two native plants (Hydrilla verticillata and Potamogeton maackianus) to elucidate the effects of invasion density and eutrophication on native submerged plants. We found that (1) high nutrient concentrations inhibited the growth of both invasive and native species, but E. nuttallii, with a wide ecological niche, was more tolerant to eutrophication than the two native species. (2) High invasion density had a remarkable negative effect on the growth of the two native species under the medium and high nutrient concentrations. (3) Medium and high invasion densities of E. nuttallii made native macrophytes more susceptible to eutrophication. (4) The two native macrophytes had species-specific responses to medium and high invasion densities under medium and high nutrient concentrations. Specifically, a high invasion density of E. nuttallii significantly delayed the growth of H. verticillata rather than P. maackianus. Thus, it is necessary to consider the synergistic effects of invasion with eutrophication when assessing invasion in freshwater ecosystems. And our results implied that invasion with eutrophication was a powerful factor determining the results of interspecific competition among submerged macrophytes, which could change the biodiversity, community structure and functions of freshwater ecosystems.

Occurrence of polyhalogenated carbazoles and the combined effects with heavy metals on variation in bacterial communities in estuarine sediments

Carbazole (CZ) and eight polyhalogenated carbazoles (PHCZs) were quantified by GC-MS in sediments of 12 estuaries, the interface linking large industrial and living areas to the Bohai Sea, China. These pollutants, heavy metals, and environmental factors caused integrated exposure to sediment bacteria. Four PHCZ congeners were detectable, with ΣPHCZs ranging from 0.56 to 15.94 ng/g dw. The dominant congeners were 3,6-dichlorocarbazole (36-CCZ) and 3-chlorocarbazole (3-CCZ), with a mean contribution of 72.6 % and 20.2 %. Significant positive correlations were found between 36-CCZ and both total organic carbon and heavy metals. Redundancy analysis of microbial variation implicated no impacts from PHCZs. Correlation analysis demonstrated an increase in abundance of Rhodocyclaceae but a decrease in Bacteroides-acidifaciens-JCM-10556 with presence of PHCZs, suggesting that these bacteria can be used as potential contamination indicators. The combined exposure of heavy metals, nutrients, and PHCZs may also increase toxicity and biological availability, adversely affecting the ecosystem and human health.

A novel total phosphorus concentration retrieval method based on two-line classification in lakes and reservoirs across China

Phosphorus is widely recognized as a nutrient that restricts growth and is the primary contributor to eutrophication in 80 % of water bodies. Consequently, the Chinese government has consistently prioritized monitoring and controlling total phosphorus (TP) levels. The remote estimation of TP in lakes and reservoirs at a national scale is a challenging task due to TP being a non-optically active parameter. Currently, there is a lack of developed TP inversion models specifically designed for lakes and reservoirs in China. For solving this problem, a novel two-line classification method drawn on scatter plots based on the natural logarithm of TP (Ln(TP)) and B33/B9 was proposed and used to classify 1211 measured samples obtained from field cruises in 105 lakes and reservoirs across China from 2012 to 2022 into three categories, Class 1, Class 2, and Class 3. Results demonstrate that the proposed classification method has the ability to enhance the correlation between Ln(TP) and 43 basic potential single band and band combinations. Specifically, the correlation range improved from (-0.31,0.15) to (-0.77,0.24) in Class 1, (-0.81, 0.36) in Class 2, and (-0.74, 0.52) in Class 3. Additionally, the classification method also improved the correlation range between Ln(TP) and 820 band ratios, from (-0.32, 0.32) to (-0.83, 0.82) in Class 1, (-0.86, 0.86) in Class 2, and (-0.86, 0.86) in Class 3. These datasets were subsequently utilized as input for eXtreme Gradient Boosting (XGBoost) models. Finally, well performing XGBoost models in Class 1 (R2 = 0.76, RMSE = 0.3, MAPE = 12 %), Class 2 (R2 = 0.84, RMSE = 0.49, MAPE = 38 %), and Class 3 (R2 = 0.74, RMSE = 0.46, MAPE = 14 %) were used to map TP of 563 large lakes and reservoirs (≥20 km2) across China using MODIS images from 2005, 2010, 2015, and 2020. This study presents a novel approach for estimating non-optically active parameters through remote sensing on a national scale.

Integrating ecosystem services closely related to human well-being into the restoration and management of deep lakes facing multiple stressors: Lessons from long-term practice in Qiandao Lake, China

Deep-lake (reservoir) ecosystems provide valuable ecosystem services (ES) and generate significant ecosystem service values (ESV); however, reservoir ecosystems have suffered great losses from environmental changes and human activities. Currently, studies on ES and its correlations with stressors remain insufficient and the integration of ES into ecological restoration and management poses numerous challenges. Here, we combined four types of stressors with six ES closely related to human well-being to discuss their interactions in Qiandao Lake (a representative deep lake in China). Our results indicate that all ESV showed a consistent growth trend throughout the study period, reaching 5203.8 million CNY in 2018, and the cultural service value surpassed the provisioning service value for the first time in 2004. Almost all the ESV were limited during the cyanobacterial bloom in Qiandao Lake. Redundancy analysis and partial least squares structural equation modeling jointly revealed that socioeconomic development was the most important direct driver of the increase in ESV (0.770) and that hydro-meteorological conditions (0.316) and pollutant loads (0.274) positively affected ESV by mediating lake trophic status. The trophic status of the lake is the result of the interaction of multiple stressors, which has a negative impact on ESV. Therefore, to continuously protect the provisioning and cultural service values of deep-lake ecosystems from damage, the government must rationally formulate SED goals and reduce pollutant loads during lake development, operation, and utilization. This work provides valuable insights into the interactions between ES, which are closely related to human well-being, and stressors in deep-lake ecosystems.

An operational approach for large-scale mapping of water clarity levels in inland lakes using landsat images based on optical classification

Water clarity is a critical parameter of water, it is typically measured using the setter disc depth (SDD). The accurate estimation of SDD for optically varying waters using remote sensing remains challenging. In this study, a water classification algorithm based on the Landsat 5 TM/Landsat 8 OLI satellite was used to distinguish different water types, in which the waters were divided into two types by using the ad(443)/ap(443) ratio. Water type 1 refers to waters dominated by phytoplankton, while water type 2 refers to waters dominated by non-algal particles. For the different water types, a specific algorithm was developed based on 994 in situ water samples collected from Chinese inland lakes during 42 cruises. First, the Rrs(443)/Rrs(655) ratio was used for water type 1 SDD estimation, and the band combination of (Rrs(443)/Rrs(655) - Rrs(443)/Rrs(560)) was proposed for water type 2. The accuracy assessment based on an independent validation dataset proved that the proposed algorithm performed well, with an R2 of 0.85, mean absolute percentage error (MAPE) of 25.98%, and root mean square error (RMSE) of 0.23 m. To demonstrate the applicability of the algorithm, it was extensively evaluated using data collected from Lake Erie and Lake Huron, and the estimation accuracy remained satisfactory (R2 = 0.87, MAPE = 28.04%, RMSE = 0.76 m). Furthermore, compared with existing empirical and semi-analytical SDD estimation algorithms, the algorithm proposed in this paper showed the best performance, and could be applied to other satellite sensors with similar band settings. Finally, this algorithm was successfully applied to map SDD levels of 107 lakes and reservoirs located in the Middle-Lower Yangtze Plain (MLYP) from 1984 to 2020 at a 30 m spatial resolution, and it was found that 53.27% of the lakes and reservoirs in the MLYP generally show an upward trend in SDD. This research provides a new technological approach for water environment monitoring in regional and even global lakes, and offers a scientific reference for water environment management of lakes in the MLYP.

Revealing the hidden burden for lake management: the sediment phosphorus storage pools in Eastern Plain Lake Zone, China

As one of the essential components in ecosystems, lakes play a major role in the global phosphorus (P) cycle. It is helpful for further understanding of the inside lake P geochemical cycle to research P pollution and storage in lakes, which is of positive significance for lake eutrophication restoration. In this study, we investigated the total phosphorus concentrations (TPC) of water and sediments from 37 lakes in the Eastern Plain Lake Zone (EPL) of China, evaluated the P pollution degree of lakes, and estimated P storage in lake sediments with quantitative data of lake area and number. The results indicate that the total phosphorus concentrations of water (TPCW) and total phosphorus concentrations of the surface sediments (0-1 cm, TPCSS) in EPL were high, the mean values were 0.11 mg·L-1 and 869.85 mg·kg-1 respectively, with obvious differences between urban and rural areas, as well as between different river basins. Over half (56.76% and 70.27% respectively) of the lakes reached severe pollution levels in water and surface sediments. There were 16224 lakes (> 0.01 km2) with a total area of 21662.37 km2 in the EPL, and the P storage in the lake sediments (0-30 cm) was about 4.87 ± 2.08 Tg (1 Tg = 1 × 1012 g), accounting for about 2.74% of the basin soil. TPCW and TPCSS of lakes in the EPL were significantly positively correlated, may suggest a close nutrient cycling relationship between the lake water and the sediment. During periods of high winds and waves, the stored P in the top sediments in the EPL may continue to participate in the internal P geochemical cycle and migrate to the overlying water, posing a potential pollution hazard. Therefore, it is crucial to take into account the sediment P pools when formulating effective lake phosphorus management strategies.

A graph-based modeling framework for tracing hydrological pollutant transport in surface waters

Anthropogenic pollution of hydrological systems affects diverse communities and ecosystems around the world. Data analytics and modeling tools play a key role in fighting this challenge, as they can help identify key sources as well as trace transport and quantify impact within complex hydrological systems. Several tools exist for simulating and tracing pollutant transport throughout surface waters using detailed physical models; these tools are powerful, but can be computationally intensive, require significant amounts of data to be developed, and require expert knowledge for their use (ultimately limiting application scope). In this work, we present a graph modeling framework - which we call HydroGraphs - for understanding pollutant transport and fate across waterbodies, rivers, and watersheds. This framework uses a simplified representation of hydrological systems that can be constructed based purely on open-source data (National Hydrography Dataset and Watershed Boundary Dataset). The graph representation provides a flexible intuitive approach for capturing connectivity and for identifying upstream pollutant sources and for tracing downstream impacts within small and large hydrological systems. Moreover, the graph representation can facilitate the use of advanced algorithms and tools of graph theory, topology, optimization, and machine learning to aid data analytics and decision-making. We demonstrate the capabilities of our framework by using case studies in the State of Wisconsin; here, we aim to identify upstream nutrient pollutant sources that arise from agricultural practices and trace downstream impacts to waterbodies, rivers, and streams. Our tool ultimately seeks to help stakeholders design effective pollution prevention/mitigation practices and evaluate how surface waters respond to such practices.

Polymer-based nanocomposite adsorbents for resource recovery from wastewater

Developing mitigation mechanisms for eutrophication caused by the uncontrolled release of nutrients is in the interest of the scientific community. Adsorption, being operationally simple and economical with no significant secondary pollution, has proven to be a feasible technology for resource recovery. However, the utility of adsorption often lies in the availability of effective adsorbents. In this regard, polymer-based nanocomposite (PNC) adsorbents have been highly acclaimed by researchers because of their high surface area, multiple functional groups, biodegradability, and ease of large-scale production. This review paper elaborates on the functionality, adsorption mechanisms, and factors that affect the adsorption and adsorption-desorption cycles of PNC adsorbents toward nutrient resources. Moreover, this review gives insight into the application of recovered nutrient resources in soil amendment.

Novel assessment tools for inland aquaculture in the western Godavari delta region of Andhra Pradesh

The production of fisheries and shrimp has been twice every 10 years for the previous five decades, making it the most rapidly expanding food industry. This growth is due to intensive farming and the conversion of agriculture into aquaculture in many parts of South Asia. Furthermore, intensive aquaculture generates positive economic growth but leads to environmental degradation without proper monitoring. Unfortunately, technical innovation is less in aquaculture than agricultural and manufacturing industries. The advent of remote sensing and soft computing has expanded various opportunities for utilizing and integrating technological advances in civil and environmental disciplines. This paper presents the aquaculture scenario in the western Godavari delta region of Andhra Pradesh and proposes various novel assessment tools to monitor the aquaculture environment. An experimental investigation was carried out on the physicochemical characteristics of the inland aquaculture ponds to evaluate water quality in the aquaculture ponds. Furthermore, to assess the intensity of inland aquaculture, the current work concentrates on the potential application of remote sensing and soft computing approaches. Geospatial models of kriging and inverse distance weighing (IDW) show higher performance in estimating ammonia levels in the intensive aquaculture groundwaters with coefficient of determination (R2) values of 0.947 and 0.901, respectively. Teaching learning-based optimization (TLBO) and adaptive particle swarm optimization (APSO), two of the five soft computing techniques utilized in the study, perform better than the others. Additionally, it was found that remote sensing-based assessment tools and soft computing prediction models were both trustworthy, accurate, and easy to use. Furthermore, these methods could assist in the real-time evaluation of inland aquaculture waters by stakeholders and policymakers.

Long-term spatial-temporal monitoring of eutrophication in Lake Burdur using remote sensing data

Lake eutrophication continues to be one of the major environmental challenges in lakes worldwide. This study is about using a remote sensing approach to monitor long-term chlorophyll-a (Chl-a) concentrations and the trophic state index (TSI) in Lake Burdur, Türkiye. Surface reflectance from Landsat 5, Landsat 7, and Landsat 8 satellite image collections were evaluated with an empirical equation to estimate a 38-year-long (1984-2021) time series of the lake's median Chl-a concentrations. Pixel quality masking was applied to retain only acceptable quality information and exclude images affected by cloud cover, icing, and other environmental factors from the analysis. The results were analyzed based on annual, seasonal, and monthly temporal averages. Over a period of 38 years, Chl-a concentrations were found to vary between 58.7 and 196.4 mg/m³. Notably higher concentrations were recorded in 2010 and 2021, while lower concentrations were observed between 1991 and 1993. A substantial increase in Chl-a concentration was evident from 2002 to 2010. The maximum concentration of Chl-a during the first two decades of the analysis was 130 mg/m³, which increased to 200 mg/m³ during the last two decades. Landsat-derived TSI values suggested that Lake Burdur has been mostly hypertrophic for the entire study period.

Phylogeography and genetic diversity of the Scapholeberis kingii species complex (Cladocera: Daphniidae) in China

There is increasing interest in the diversity and phylogeography of aquatic invertebrate zooplankton in the Eastern Palearctic, yet this topic remains largely unexplored in China. Here, we investigated the lineage diversity and phylogeography of an important cladoceran taxon, the Scapholeberis kingii (Cladocera: Daphniidae) species complex, members of which live in the surface layers of freshwater ecosystems. We identified only the S. smirnovi morphospecies from this species complex in 29 of 491 Chinese water bodies examined. Its phylogenetic position was verified using both a mitochondrial (mitochondrial cytochrome c oxidase subunit I; COI) and a nuclear marker (the nuclear large subunit ribosomal RNA gene; 28S). Pronounced geographical separation among three S. smirnovi mitochondrial lineages was observed in China: only a single lineage (Lineage A) was present in the Eastern Plain, whereas Lineages B and C were restricted to the Inner Mongolia-Xinjiang Plateau and the Qinghai-Tibetan Plateau respectively. This deep mtDNA divergence and the substantial genetic differentiation among S. smirnovi populations from different regions is likely a result of the rapid uplift of the Qinghai-Tibetan Plateau and associated ecological changes. This study contributes to an understanding of the genetic diversity of the S. kingii complex, a key component of neustonic zooplankton.

Beneath the surface: spatial and temporal trends in water quality and its impacts on algal community composition in the Albemarle Sound, North Carolina

Urban and agricultural expansion and intensification pose a critical threat to water quality and aquatic ecosystems. Increased nutrient loading into waterways combined with warming temperatures due to climate change have increased eutrophication and algal blooms. The relationship between land use, nutrient availability, and algal growth can vary dramatically across space and time, but few studies have captured this variation. The goal of this research is to assess water quality across time and disparate land uses, and its influence on algal community composition in the Albemarle Sound, a brackish water estuary in North Carolina. We collected water quality data from 21 sites across the sound, visiting six sites in Chowan County biweekly and 15 other sites twice between June and August 2020. Water samples from each site were tested for nitrate, phosphate, ammonia, bicarbonate, and total phosphorus (TP). Preserved algal samples from the six Chowan County sites were enumerated under a microscope to estimate genus richness and biomass. In the Chowan County sites, phosphorus increased and nitrate decreased over the course of the summer. Across all sites, TP increased with development and agricultural land use. These results suggest that sources of nitrogen and phosphorus in the sound differ. Algal richness increased with nitrate concentration and decreased with precipitation while biomass increased with water temperature. Our results indicate that climate change impacts, particularly increasing temperatures and extreme precipitation, influence how land use, water quality, and algal community composition interact. These data demonstrate the co-benefits of mitigating climate change in developing management strategies to reduce algal blooms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10452-023-10008-y.

Environment-friendly nitrogen management practices in wetland paddy cultivation

A large amount of nitrogen (N) fertilizer is required for paddy cultivation, but nitrogen use efficiency (NUE) in paddy farming is low (20–40%). Much of the unutilized N potentially degrades the quality of soil, water, and air and disintegrates the functions of different ecosystems. It is a great challenge to increase NUE and sustain rice production to meet the food demand of the growing population. This review attempted to find out promising N management practices that might increase NUE while reducing the trade-off between rice production and environmental pollution. We collected and collated information on N management practices and associated barriers. A set of existing soil, crop, and fertilizer management strategies can be suggested for increasing NUE, which, however, might not be capable to halve N waste by 2030 as stated in the “Colombo Declaration” by the United Nations Environment Program. Therefore, more efficient N management tools are yet to be developed through research and extension. Awareness-raising campaign among farmers is a must against their misunderstanding that higher N fertilizer provides higher yields. The findings might help policymakers to formulate suitable policies regarding eco-friendly N management strategies for wetland paddy cultivation and ensure better utilization of costly N fertilizer.

Microbial Fuel Cell-Based Biosensors and Applications

The sustainable development of human society in today's high-tech world depends on some form of eco-friendly energy source because existing technologies cannot keep up with the rapid population expansion and the vast amounts of wastewater that result from human activity. A green technology called a microbial fuel cell (MFC) focuses on using biodegradable trash as a substrate to harness the power of bacteria to produce bioenergy. Production of bioenergy and wastewater treatment are the two main uses of MFC. MFCs have also been used in biosensors, water desalination, polluted soil remediation, and the manufacture of chemicals like methane and formate. MFC-based biosensors have gained a lot of attention in the last few decades due to their straightforward operating principle and long-term viability, with a wide range of applications including bioenergy production, treatment of industrial and domestic wastewater, biological oxygen demand, toxicity detection, microbial activity detection, and air quality monitoring, etc. This review focuses on several MFC types and their functions, including the detection of microbial activity.

Spatiotemporal variation and driving factors of water quality in Yunnan-Guizhou plateau lakes, China

The Yunnan-Guizhou Plateau (YGP) lakes are the typical plateau rift lakes and an important water source in southwest China. However, there is a scarcity of research on its spatiotemporal water quality variations and driving factors, especially on long-term scales. Herein, multiple water quality indicators for 11 natural lakes on the YGP were measured from 2005 to 2020. In this study, the effects of natural lake attributes, human activities, and meteorological conditions on water quality were also analyzed. The results showed that the water quality of the YGP lakes tended to degrade, and was divided into heavy, medium, and light pollution types. Total phosphorus (TP), total nitrogen (TN), permanganate index (COD_Mn), and biochemical oxygen demand (BOD₅) increased by 14.69%, 14.44%, 22.61%, and 11.26%, respectively, from 2005 to 2020. Natural attributes of lakes and land use types were the main reasons for the spatial heterogeneity of water quality in YGP. In contrast, the temporal evolution of lake water quality was mainly related to human activities and climatic conditions. The smaller the water/ terrestrial area ratio, water storage capacity, and water depth, the easier the eutrophication and the worser the water quality of YGP lakes. Land degradation accelerated the deterioration of water quality in plateau lakes, while ecological land played an improving role. This study summarizes the water quality changes and influencing factors in YGP lakes over the past 15 years, which can provide a scientific database reference for water environment protection in YGP.

Integrated transcriptomic and metabolomic analysis of Microcystis aeruginosa exposed to artemisinin sustained-release microspheres

Artemisinin sustained-release microspheres (ASMs) have been shown to inhibit Microcystis aeruginosa (M. aeruginosa) blooms. Previous studies have focused on inhibitory mechanism of ASMs on the physiological level of M. aeruginosa, but the algal inhibitory mechanism of ASMs has not been comprehensively and profoundly revealed. The study proposed to reveal the toxicity mechanism of ASMs on M. aeruginosa based on transcriptomics and metabolomics. After exposure to 0.2 g·L^-1 ASMs for 7 days, M. aeruginosa biomass was significantly inhibited, with an inhibition rate (IR) of 47 % on day 7. Transcriptomic and metabolomic results showed that: (1) 478 differentially expressed genes (DEGs) and 251 differential metabolites (DMs) were obtained; (2) ASMs inhibited photosynthesis by blocking photosynthetic pigment synthesis, destroying photoreaction centers and photosynthetic carbon reactions; (3) ASMs reduced L-glutamic acid content and blocked glutathione (GSH) synthesis, leading to an imbalance in the antioxidant system; (4) ASM disrupted nitrogen metabolism and the hindered synthesis of various amino acids; (5) ASMs inhibited glyoxylate cycle and TCA cycle. This study provides an important prerequisite for the practical application of ASMs and a new perspective for the management of harmful algal blooms (HABs).

Cooperative interactions between nitrogen fixation and phosphorus nutrition in legumes

Legumes such as soybean are considered important crops as they provide proteins and oils for humans and livestock around the world. Different from other crops, leguminous crops accumulate nitrogen (N) for plant growth through symbiotic nitrogen fixation (SNF) in coordination with rhizobia. A number of studies have shown that efficient SNF requires the cooperation of other nutrients, especially phosphorus (P), a nutrient deficient in most soils. During the last decades, great progress has been made in understanding the molecular mechanisms underlying the interactions between SNF and P nutrition, specifically through the identification of transporters involved in P transport to nodules and bacteroids, signal transduction, and regulation of P homeostasis in nodules. These studies revealed a distinct N-P interaction in leguminous crops, which is characterized by specific signaling cross talk between P and SNF. This review aimed to present an updated picture of the cross talk between N fixation and P nutrition in legumes, focusing on soybean as a model crop, and Medicago truncatula and Lotus japonicus as model plants. We also discuss the possibilities for enhancing SNF through improving P nutrition, which are important for high and sustainable production of leguminous crops.

Eutrophication induces functional homogenization and traits filtering in Chinese lacustrine fish communities

Rapid anthropogenic nutrient enrichment has caused widespread ecological problems in aquatic ecosystems and the resulting eutrophication has dramatically changed fish communities throughout the world. However, few studies addressed how fish communities responded to eutrophication in terms of multidimensional functional and taxonomic structure, especially how eutrophication acted as an environment filter on functional traits. The aim of the present study was to investigate the effects of eutrophication on fish species composition, community metrics and species functional traits in 26 shallow lakes from the middle reaches of Yangtze River basin, China. This study validated that eutrophication is an important factor shaping the fish community structure. Regression analyses showed that eutrophication favored higher total biomass and lower functional diversity of fish communities but had little effect on species richness. Despite the fact that some pelagic zooplanktivorous species were more abundant in the most eutrophic lakes, multivariate analyses of the relationships between species traits and environmental variables revealed weak relationships between feeding traits and eutrophication. In contrast, species with a benthic life stage were negatively associated with eutrophication while those with a large body size and high absolute fecundity showed the opposite trend. Due to demersal habitat degradation, and to a lesser degree, to changes in trophic resources availability, eutrophication caused functional simplification of fish communities by increasing functional traits homogeneity among the most tolerant species. Some relationships between functional traits and eutrophication well established in the western palearctic have not been observed in this study, emphasizing the importance of biases resulting from specific evolutionary histories. This work will provide useful insights on on-going restoration and management of shallow lakes in the Yangtze River basin.

Analysis of water quality indexes and their relationships with vegetation using self-organizing map and geographically and temporally weighted regression

Natural vegetation has been proved to promote water purification in previous studies, while the relevant laws has not been excavated systematically. This research explored the relationships between vegetation cover and water quality indexes in Liaohe River Basin in China combined with self-organizing map (SOM) and geographically and temporally weighted regression (GTWR) innovatively and systematically based on the distributing heterogeneity of water quality conditions. Results showed that the central and northeast regions of the study area had serious organic and nutrient pollution, which needed targeted treatment. And SOM verified that high vegetation coverage with retention potential of organic and inorganic pollutants as well as nutrients improved water quality to some degree, while the excessive discharges of pollutants still had serious threats to nearby water environment despite the purification function of vegetation. GTWR indicated that the waterside vegetation was beneficial for dissolved oxygen increasing and contributed to the decreasing of organic pollutants and inorganic pollutants with reducibility. Natural vegetation also obsorbed nutrients like TN and TP to some degree. However, the retential potential of nitrogen and organic pollutants became not obvious when there were heavy pollution, which demonstrated that pollution sources should be controlled despite the purification function of vegetation. This study implied that natural vegetation purified water quality to some degree, while this function could not be revealed when there was too heavy pollution. These findings underscore that the pollutant discharge should be controlled though the natural vegetation in ecosystem promoted the purification of water bodies.

Polymer-based nanocomposite adsorbents for resource recovery from wastewater

Adsorption is alternative technique for recovery of nutrient resources with no/less secondary pollution. PNC adsorbents are effective for removal and recovery of nutrient resources, and reusing nutrients as fertilizer could prevent eutrophication.

Enhanced soil erosion threatens fluvial tufa landscapes after an Ms 7.0 earthquake in the Jiuzhaigou World Heritage Site, southwestern China

Tufa is a porous freshwater deposit comprising primarily calcite (CaCO₃) and organic matter. Massive tufa depositions can spread for up to several kilometers, forming tufa landscapes that have been recognized as national parks and World Heritage Sites. Previous studies have suggested that enhanced soil erosion owing to human activities (e.g., deforestation and agriculture) is one of the major causes of fluvial tufa decline in many places worldwide. In 2017, an Ms 7.0 earthquake occurred in Jiuzhaigou, which greatly increased soil erosion in the catchment. We compared the water chemistry and tufa deposition before and after the earthquake to understand the impact of soil erosion on tufa landscapes in Jiuzhaigou. After the earthquake, we found that high turbidity greatly reduced the aesthetic value of the lakes. Enhanced soil erosion increased NO₃^-, dissolved organic carbon (DOC), and PO₄^3- concentrations in surface water, which may worsen the problems of increased algal biomass and marsh development. Enhanced soil erosion reduced alkalinity, HCO₃^-, and the saturation index of calcite (SIc), thereby decreasing the potential to generate new calcite. Enhanced soil erosion may also increase the annual tufa deposition rates by increasing the soil and organic materials in the sediment. In addition, the tufa sediment affected by enhanced soil erosion was loose, highly porous, and contained numerous diatoms. This study provides observational data to explain the impact mechanisms of soil erosion on tufa landscapes and assess the necessity and achievements of artificial soil erosion control.

Optimization of constructed wetlands on purifying black-odorous water and their potential purification mechanism

Black-odorous water has become a common and widespread problem in recent decades. In this study, nine constructed wetlands (CWs) with different flow types, filters, plants, and hydraulic loadings were designed according to an orthogonal array (L₉ (3⁴), and were used for the purification of black-odorous water in summer and winter. The results showed that CWs are regarded as effective to purify black-odorous water in both seasons. Microbial degradation is the major removal pathway of pollutants in CWs during summer, while the joint effect of biodegradation and adsorption is the main treatment route during winter. Flow type and hydraulic loading appear to be the most important factors impacting the purification performance of CWs, by changing the redox condition of systems and retention time of contaminants, respectively. 'Vertical flow-zeolite filter-high loading' is proposed as the best parameter selection for CWs on the purification of black-odorous water: among them, CWs with vertical flow have better oxygen transport capacity that is conductive to aerobic processes of pollutants, zeolite substrates may adsorb more nitrogen via ion exchange, higher hydraulic loadings can extend the contact time between contaminants and filters, and regulate the water temperature for microbial activity.

Water footprint and virtual water trade analysis in water-rich basins: Case of the Chaohu Lake Basin in China

Water footprints and virtual water are widely used as essential tools for water use and conservation analysis of basins worldwide. Despite the importance of water-rich basins as the main force for water-saving, water use analysis has been mainly for water-scarce basins rather than water-rich basins in the existing literature. To fill the gap, in this paper, we investigate the water footprint and virtual water trade in a water-rich basin, namely the Chaohu Lake Basin in China, from 2007 to 2017 using input-output analysis. The results show that: (1) Water use efficiency in the Chaohu Lake Basin was significantly improved. The overall trend of the water intensity was declining, decreasing by 10.21 % in 2017 versus 2012; (2) The internal and external water footprints showed an upward trend, and the growth rate of total water footprint was 36.66 %; (3) The basin was a net virtual water exporter, but the net export flows of virtual water has decreased significantly. The virtual water net export flow decreased by 0.12 billion m³ in 2017 versus 2012; (4) Water resources in the basin were mainly used locally, and its supply to other provinces was minimal. Compared with some water-scarce basins such as the Heihe River Basin and Haihe River Basin, the Chaohu Lake Basin shows significant gaps in the virtual water export flow per capita and behaves differently in the proportion of virtual water transfer. Based on the above findings, we conclude with some guidance and implications for local governments and policymakers.

Effects of Fertilization Approaches on Plant Development and Fertilizer Use of Citrus

Fertilization is an important part of citrus crop management. However, limited details are available about the fertilization approach on citrus plant development. A pot experiment for the fertilization approaches and fertigation levels were conducted in this study. Four fertilization approaches, namely, drip fertigation (DF), broadcast fertilization (CK+), hole fertilization (HF) and pour fertilization (PF) were tested. The fertigation level treatment included 100% (DF-337.5), 80% (DF-270), 60% (DF-202.5) and 40% (DF-135) fertilizer supply with DF, and the 100% fertilizer supply with broadcast fertilization were served as control (CK). The results showed that DF not only increased the absorptions of nitrogen (N), phosphorus (P) and potassium (K) but also promoted citrus plant height, stem diameter and dry weight. In fruit quality, DF had the highest fruit total soluble solid (TSS) and titratable acidity (TA) contents. For fertilizer loss, DF had the lowest N and K leaching losses of 9.26% and 4.05%, respectively, and the lowest N and K runoff losses among the approaches. Isotopic tracing with 15N indicated that DF had the highest fertilizer use efficiency. Based on the analysis of fertigation levels, DF approach with 60% fertilizer reduction could improve citrus plant development. Therefore, DF promoted citrus plant growth and fruit quality by accelerating fertilizer utilization and impairing fertilizer loss. The fertilizer amount in citrus production could be reduced significantly using DF.

Selective capture of ammonium ions from municipal wastewater treatment plant effluent with a nickel hexacyanoferrate electrode

Currently, intercalation materials such as Prussian blue analogs have attracted considerable attention in water treatment applications due to their excellent size-based selectivity toward cations. This study aimed to explore the feasibility of using a nickel hexacyanoferrate (NiHCF) electrode for selective NH₄⁺ capture from effluent from a municipal wastewater treatment plant. To assess the competitive intercalation between NH₄⁺ and other common cations (Na⁺, Ca²⁺), a NiHCF//activated carbon (AC) hybrid capacitive deionization (CDI) cell was established to treat mixed-salt solutions. The results of cyclic voltammetry (CV) analysis showed a higher current response of the NiHCF electrode toward NH₄⁺ ions than toward Na⁺ and Ca²⁺ ions. In a single-salt solution with NH₄⁺, the optimized operating voltage of the hybrid CDI cell was 0.8 V, with a higher salt adsorption capacity (51.2 mg/g) than those obtained at other voltages (0.1, 0.4, 1.2 V). In a multisalt solution containing NH₄⁺, Na⁺, and Ca²⁺ ions, the selectivity coefficients of NH₄⁺/Ca²⁺ and NH₄⁺/Na⁺ were 9.5 and 4.9, respectively. The feasibility of selective NH₄⁺ capture using the NiHCF electrode in a hybrid CDI cell was demonstrated by treating the effluent from a municipal wastewater treatment plant (WWTP). The intercalation preference of the NiHCF electrode with the WWTP effluent was NH₄⁺>K⁺>Na⁺>Ca²⁺>Mg²⁺, and NH₄⁺ showed the highest salt adsorption capacity among the cations during consecutive cycles. Our results revealed that cations with smaller hydrated radii and lower (de)hydration energies were more favorably intercalated by the NiHCF electrode. The results provide important knowledge regarding the use of intercalation-type electrodes for selective nutrient removal and recovery from wastewater.

Responses of multiple facets of macroinvertebrate alpha diversity to eutrophication in floodplain lakes

The accelerated eutrophication of freshwater lakes has become an environmental problem worldwide. Increasing numbers of studies highlight the need to incorporate functional and phylogenetic information of species into bioassessment programms, but it is still poorly understood how eutrophication affects multiple diversity facets of freshwater communities. Here, we assessed the responses of taxonomic, phylogenetic and functional diversity of benthic macroinvertebrates to water eutrophication in 33 lakes in the Yangtze River floodplain in China. Our results showed that macroinvertebrate assemblage structure was significantly different among four lake groups (river-connected, macrophyte-dominated, macrophyte-algae transition, and algae-dominated). Three taxonomic, two phylogenetic and two functional diversity indices were significantly different among the lake groups. Except for the increasing trend of Lambda⁺, these metrics showed a clear decreasing trend with increasing levels of eutrophication, with highest values detected in river-connected and macrophyte-dominated lakes, followed by macrophyte-algae transition lakes and algal-dominated lakes. Although differing in the number and identity of key environmental and spatial variables among the explanatory models of different diversity indices, environmental factors (eutrophication-related water quality variables) played more important role than spatial factors in structuring all three facets of alpha diversity. The predominant role of environmental filtering can be attributed to the strong eutrophication gradient across the studied lakes. Among the three diversity facets, functional diversity indices performed best in portraying anthropogenic disturbances, with variations in these indices being solely explained by environmental factors. Spatial factors were mostly weak or negligible in accounting for the variation in functional diversity indices, implying that trait-based indices are robust in portraying anthropogenic eutrophication in floodplain lakes. However, variation in some taxonomic and phylogenetic diversity indices were also affected by spatial factors, indicating that conservation practitioners and environmental managers should use these metrics with caution when providing solutions for addressing eutrophication in floodplain lakes.

Implementation of P-Reactive Layer for Improving Urban Water Quality: Kinetic Studies, Dimensioning and Economic Analysis

Urbanization and climate change affecting water quality are the most critical problems that humanity has to encounter globally. Undoubtedly, urban water bodies are heavily contaminated by phosphorus (P). This study aims to identify the mechanisms and efficiency of the P sorption process for selected reactive materials (Autoclaved Aerated Concrete (AAC), Filtralite® Nature P, lightweight expanded clay aggregate (Leca®), limestone, opoka, and zeolite) with surface water as adsorbate and dimension of P-reactive reactive layer supported with economic analysis. Four kinetic models were used to know the sorption mechanism: pseudo-first order, pseudo-second order, Elovich, and intra-particle diffusion model. Calculating the P-reactive layer was based on dimensioning rain retention spaces standards. The pseudo-second model provided the best description of the adsorption kinetics of most materials. The sorption properties obtained after 72 h showed the reduction of 83, 81, 59, 53, 37, and 36% for AAC, opoka, Filtralite® Nature P; limestone, Leca®, and zeolite, respectively. Depending on the volume, the P-reactive layer can remove 29–77 or 61–163 g of P-PO4. The unit cost of removing P-PO4 by the P-reactive layer range from 49.57 to 85.53 €/P-PO4 g. For these reasons, reactive materials seem to be an effective way of removing P from the urban water environment worldwide from both environmental and economic points of view.

Impact of Magnesium Sources for Phosphate Recovery and/or Removal from Waste

As the population continues to rise, the demand for resources and environmentally friendly management of produced wastes has shown a significant increase in concern. To decrease the impact of these wastes on the environment, it is important to utilize the wastes in producing and/or recovering usable products to provide for the sustainable management of resources. One non-renewable and rapidly diminishing resource is phosphorus, which is used in several products, the most important being its use in manufacturing chemical fertilizer. With the increase in demand but reduction in availability of naturally occurring mineral phosphorus, it is important to investigate other sources of phosphorus. Phosphorus is most commonly recovered through struvite (magnesium ammonium phosphate) precipitation. The recovery of phosphorus from various wastewater has been well established and documented with recovery rates mostly above 90%. However, one of the major drawbacks of the recovery is the high cost of chemicals needed to precipitate the phosphorus. Since the external magnesium needed to achieve struvite precipitation accounts for around 75% of the total chemical cost, applicability of low-cost magnesium sources, such as bittern or seawater, can help reduce the operational cost significantly. This paper investigates the different magnesium sources that have been used for the recovery of phosphorus, highlighting the different approaches and operating conditions investigated, and their corresponding phosphorus recovery rates. An investigation of the economic aspects of the magnesium sources used for removal/recovery show that costs are dependent on the raw waste treated, the source of magnesium and the location of treatment. A review of published articles on the economics of phosphorus removal/recovery also indicates that there is a lack of studies on the economics of the treatment processes, and there is a need for a comprehensive study on life cycle assessment of such processes that go beyond the technical and economical aspects of treatment processes.

Development of remote sensing algorithm for total phosphorus concentration in eutrophic lakes: Conventional or machine learning?

Phosphorus is a limiting nutrient in freshwater ecosystems. Therefore, the estimation of total phosphorus (TP) concentration in eutrophic water using remote sensing technology is of great significance for lake environmental management. However, there is no TP remote sensing model for lake groups, and thus far, specific models have been used for specific lakes. To address this issue, this study proposes a framework for TP estimation. First, three algorithm development frameworks were compared and applied to the development of an algorithm for Lake Taihu, which has complex water environment characteristics and is a representative of eutrophic lakes. An Extremely Gradient Boosting (BST) machine learning framework was proposed for developing the Taihu TP algorithm. The machine learning algorithm could mine the relationship between FAI and TP in Lake Taihu, where the optical properties of the water body are dominated by phytoplankton. The algorithm exhibited robust performance with an R² value of 0.6 (RMSE = 0.07 mg/L, MRE = 43.33%). Then, a general TP algorithm (R² = 0.64, RMSE = 0.06 mg/L, MRE = 34.13%) was developed using the proposed framework and tested in seven other lakes using synchronous image data. The algorithm accuracy was found to be affected by aquatic vegetation and enclosure aquaculture. Third, compared with field investigations in other studies on Lake Taihu, the Taihu TP algorithm showed good performance for long-term TP estimation. Therefore, the machine learning framework developed in this study has application potential in large-scale spatio-temporal TP estimation in eutrophic lakes.

Novel insights into molecular composition of organic phosphorus in lake sediments

Organic phosphorus (Po) plays a key role in eutrophication and ecological equilibrium in lake systems. However, characterizing the composition of Po in lake sediments has been a bottleneck hindering further understanding of the biogeochemical cycle of Po. Here, multiple methods of 31P NMR spectroscopy and molecular weight (MW) ultrafiltration were combined to detect Po composition characteristics from a novel angle in ten lake sediments of China. The results showed that sediment Po mainly consisted of monoester (mono-P, 14±8.8% of the NaOH-EDTA total P on average), diester (di-P, 1.4±1.4%) and phosphonate (phos-P, 0.1±0.1%), while the abundance of Po was largely underestimated by 31P NMR methods. Some specific species of mono-P were successfully determined, and the contents of these species followed a decreasing order: inositol hexakisphosphate (IHP6) > RNA mononucleotides (RNA-mnP) > β-glycerophosphate (β-gly) > D-glucose 6-phosphate (Glu-6) > α-glycerophosphate (α-gly), which was largely dependent upon their bioreactivity. A significant relationship between MW and Po components was observed despite the great differences among sediment samples. For refractory Po components, IHP6 was mainly rich in the MW < 3 kDa while phos-P was almost only detected in the MW > 3 kDa, which largely attributed to their metal binding affinities and characteristics. The abundance of bioreactive Po species (α-gly, β-gly, Glu-6, di-P) in high MW (HMW, > 3 kDa) were all higher than that of low MW (LMW, < 3 kDa) due to microbial degradation and self-assembly. If the HMW organic molecules were biologically and chemically more reactive than its LMW counterparts, the high percentage of α-gly, β-gly, glu-6 and di-P in the HMW portion would highlights their high reactivity from the perspective of MW. These insights revealed the dynamics of the MW distribution of Po components and provide valuable information to better understand the Po composition and bioreactivity in sediments.

Influence of N:P Ratio of Water on Ecological Stoichiometry of Vallisneria natans and Hydrilla verticillata

Eutrophication is one of the major threats to shallow lake ecosystems, because it causes large-scale degradation of submerged plants. N:P ratio is an important indicator to estimate nutrient supply to water bodies and guide the restoration of submerged plants. The massive input of N and P changes the structure of aquatic communities and ecological processes. However, the mechanism underlying the influence of changes in N and P content and the N:P ratio of a water body on the growth of submerged plants is still unclear. In this study, we simulated gradients of water N:P ratio in lakes in the middle-lower reaches of the Yangtze River using outdoor mesocosm experiments. Using established generalized linear models (GLM), the effects of total nitrogen (TN) content and N:P ratio of water, phytoplankton and periphytic algae biomass, and relative growth rate (RGR) of plants on the stoichiometric characteristics of two widely distributed submerged plants, Hydrilla verticillata and Vallisneria natans, were explored. The results reveal that changes in water nutrient content affected the C:N:P stoichiometry of submerged plants. In a middle-eutrophic state, the stoichiometric characteristics of C, N, and P in the submerged plants were not influenced by phytoplankton and periphytic algae. The P content of H. verticillata and V. natans was positively correlated with their relative growth rate (RGR). As TN and N:P ratio of water increased, their N content increased and C:N decreased. These results indicate that excessive N absorption by submerged plants and the consequent internal physiological injury and growth inhibition may be the important reasons for the degradation of submerged vegetation in the process of lake eutrophication.

Insights into the highly efficient treatment of dyeing wastewater using algal bloom derived activated carbon with wide-range adaptability to solution pH and temperature

Here, a low-cost acid-base and temperature tolerant algal bloom derived activated carbon (ABAC) was successfully prepared to remove rhodamine B (RhB) from water. The ABAC exhibited maximum adsorption capacity of RhB (1101 ± 11 mg/g), higher than that of laboratory-prepared rape straw activated carbon (176 ± 5 mg/g) and commercial activated carbon (489 ± 5 mg/g). It is attributed to larger surface area and mesoporous structure of the ABAC. Furthermore, the effective adsorption of RhB by using ABAC was achieved at a wide range of solution pH (3.2-10.8) and temperature(25-50 °C). The mass transfer resistance of RhB adsorption process well depicted by Langmuir model was controlled by external mass transfer. The adsorption process involved both secondly chemisorption (H-bonds and π-π interaction) and dominated physisorption. Four dyes in river water were efficiently removed. This work provides a promising approach for developing high-absorption biomass materials for actual dye wastewater treatment.

Effects of Warming and Phosphorus Enrichment on the C:N:P Stoichiometry of Potamogeton crispus Organs

The loss of submerged macrophytes from freshwater ecosystems is accelerating owing to the combined effects of eutrophication and climate change. Submerged macrophytes depend on spring clear water; however, increased water temperatures and excessive phosphorus (P) inputs often lead to the dominance of phytoplankton. It is still not clear how the stoichiometric characteristics of carbon (C), nitrogen (N), and P in different tissues of submerged macrophytes respond to P enrichment and temperature increases. In this study, we established 36 mesocosm ecosystems to explore the effects of warming and P addition on the leaf, turion, stem, and seed stoichiometry of Potamogeton crispus. The results revealed that different functional plant organs show distinct responses to P addition and warming, which demonstrates the importance of evaluating the responses of different submerged macrophyte organs to environmental changes. In addition, interactive effects between P addition and warming were observed in the leaf, turion, and seed C:N:P stoichiometry, which highlights the importance of multifactorial studies. Our data showed that warming caused a decrease in the C content in most organs, with the exception of the stem; P addition increased the P content in most organs, with the exception of seed; N content in the turion and seed were influenced by interactive effects. Collectively, P addition could help P. crispus to resist the adverse effects of high temperatures by aiding growth and asexual reproduction, and asexual propagules were found to be more sensitive to P enrichment than sexual propagules.

Nitrogen Transport/Deposition from Paddy Ecosystem and Potential Pollution Risk Period in Southwest China

Nitrogen (N) losses through runoff from cropland and atmospheric deposition contributed by agricultural NH3 volatilization are important contributors to lake eutrophication and receive wide attention. Studies on the N runoff and atmospheric N deposition from the paddy ecosystem and how the agriculture-derived N deposition was related to NH3 volatilization were conducted in the paddy ecosystem in the Erhai Lake Watershed in southwest China. The critical period (CP) with a relatively high total N (TN) and NH4+-N deposition occurred in the fertilization period and continued one week after the completion of fertilizer application, and the CP period for N loss through surface runoff was one week longer than that for deposition. Especially, the mean depositions of NH4+-N in the CP period were substantially higher than those in the subsequent period (p < 0.01). Moreover, agriculture-derived NH4+ contributed more than 54% of the total NH4+-N deposition in the CP period, being positively related to NH3 volatilization from cropland soil (p < 0.05). The N concentrations were higher in the outlet water of ditches and runoff in May than in other months due to fertilization and irrigation. Therefore, to reduce the agricultural N losses and improve lake water quality, it is important to both reduce agricultural NH4+-N deposition from NH3 volatilization and intercept water flow from the paddy fields into drainage ditches during the CP.

What is the pollution limit? Comparing nutrient loads with thresholds to improve water quality in Lake Baiyangdian

Ecological thresholds are useful indicators for water quality managers to define limits to nutrient pollution. A common approach to estimating ecological thresholds is using critical nutrient loads. Critical nutrient loads are typically defined as the loads at which the phytoplankton chlorophyll-a exceeds a certain concentration. However, national policies, such as in China, use chemical indicators (nitrogen and phosphorus concentrations) rather than ecological indicators (phytoplankton chlorophyll-a) to assess water quality. In this study, we uniquely define the critical nutrient loads based on maximum allowable nutrient concentrations for lake Baiyangdian. We assess whether current and future nutrient loads in this lake comply with the Chinese Water Quality standards. To this end, we link two models (MARINA-Lakes and PCLake+). The PCLake+ model was applied to estimate the critical nutrient loads related to ecological thresholds for total nitrogen, total phosphorus and chlorophyll-a. The current (i.e., 2012) and future (i.e., 2050) nutrient loads were derived from the water quality MARINA-Lakes model. Nitrogen loads exceeded the nitrogen threshold in 2012. Phosphorus loads were below all ecological thresholds in 2012. Ecological thresholds are exceeded in 2050 with limited environmental policies, and urbanization may increase nutrient loads above the ecological thresholds in 2050. Recycling and reallocating animal manure is needed to avoid future water pollution in Lake Baiyangdian. Our study highlights the need for effective policies for clean water based on policy-relevant indicators.

Functional Investigation of Plant Growth Promoting Rhizobacterial Communities in Sugarcane

Plant microbiota are of great importance for host nutrition and health. As a C₄ plant species with a high carbon fixation capacity, sugarcane also associates with beneficial microbes, though mechanisms underlying sugarcane root-associated community development remain unclear. Here, we identify microbes that are specifically enriched around sugarcane roots and report results of functional testing of potentially beneficial microbes propagating with sugarcane plants. First, we analyzed recruitment of microbes through analysis of 16S rDNA enrichment in greenhouse cultured sugarcane seedlings growing in field soil. Then, plant-associated microbes were isolated and assayed for beneficial activity, first in greenhouse experiments, followed by field trials for selected microbial strains. The promising beneficial microbe SRB-109, which quickly colonized both roots and shoots of sugarcane plants, significantly promoted sugarcane growth in field trials, nitrogen and potassium acquisition increasing by 35.68 and 28.35%, respectively. Taken together, this report demonstrates successful identification and utilization of beneficial plant-associated microbes in sugarcane production. Further development might facilitate incorporation of such growth-promoting microbial applications in large-scale sugarcane production, which may not only increase yields but also reduce fertilizer costs and runoff.

Biochar-induced priming effects in soil via modifying the status of soil organic matter and microflora: A review

Biochar (BC) application has the potential to be integrated into a carbon-trading framework owing to its multiple environmental and economic benefits. Despite the increasing research attention over the past ten years, the mechanisms of BC-induced priming effects on soil organic carbon mineralization and their influencing factors have not been systematically considered. This review aims to document the recent progress in BC research by focusing on (1) how BC-induced priming effects change the soil environment, (2) the factors governing the mechanisms underlying BC amendment effects on soils, and (3) how BC amendments alter soil microbial communities and nutrient dynamics. Here, we carried out a detailed examination of the origins of different biochar, its pyrolysis conditions, and potential interactions with various factors that affect BC characteristics and mechanisms of C mineralization in primed soil. These findings clearly addressed the strong linkage between BC properties and abiotic factors that leads to change the soil microclimate, priming effects, and carbon stabilization. This review offers an overview of a fragmented body of evidence and the current state of understanding to support the application of BC in different soil environments with the aim of sustaining or improving the agricultural crop production.

New insights into eutrophication management: Importance of temperature and water residence time

Eutrophication and harmful cyanobacterial blooms threaten water resources all over the world. There is a great controversy about controlling only phosphorus or controlling both nitrogen and phosphorus in the management of lake eutrophication. The primary argument against the dual nutrients control of eutrophication is that nitrogen fixation can compensate the nitrogen deficits. Thus, it is of great necessary to study the factors that can significantly affect the nitrogen fixation. Due to the difference of climate and human influence, the water quality of different lakes (such as water temperature, N:P ratio and water residence time) is also quite different. Numerous studies have reported that the low N:P ratio can intensify the nitrogen fixation capacities. However, the effects of temperature and water residence time on the nitrogen fixation remain unclear. Thus, 30 shallows freshwater lakes in the eastern plain of China were selected to measure dissolved N₂ and Ar concentrations through N₂: Ar method using a membrane inlet mass spectrometer to quantify the nitrogen fixation capacities and investigate whether the temperature and water residence time have a great impact on nitrogen fixation. The results have shown that the short lake water residence time can severely inhibit the nitrogen fixation capacities through inhibiting the growth of nitrogen-fixing cyanobacteria, changing the N:P ratio and resuspending the solids from sediments. Similarly, lakes with low water temperature also have a low nitrogen fixation capacity, suggesting that controlling nitrogen in such lakes is feasible if the growth of cyanobacteria is limited by nitrogen.

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

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.

Treating carbon-limited wastewater by DWTR and woodchip augmented floating constructed wetlands

Floating constructed wetlands (FCWs) have attained tremendous popularity for water purification purposes. However, FCW functions establishment in nutrients removal from carbon-limited wastewater, especially in cold weather, is still a challenge. Here, two drinking water treatment residual (DWTR) based biocarriers (B-I: DWTR cakes, B-II: DWTR cakes combined with woodchips) have been augmented into FCW to enhance the nutrients (N and P) removal performance. Compared to the traditional FCW, the intensified FCWs simultaneously achieved higher N and P removal efficiencies, with average pollutants removal of 52.16 ± 11.51% for TN and 92.72 ± 1.61% for TP in FCW-I and 57.65 ± 9.43% for TN and 92.17 ± 2.55% for TP in FCW-II, respectively, while their removal in FCW-III of 27.74 ± 7.11% for TN and 17.91 ± 9.27% for TP. B-II performed best in overcoming the negative influence of low temperature in nutrients removal. Mass balance budget indicated that most P was enriched in DWTR based biocarriers. Thus it is feasible to recycle and recover P from the surface water. Furthermore, P in the sediment can be changed from active P to stable P, mitigating the internal P release risk. This study can help to expand the understanding of the intensified FCWs and promote the practical application of FCWs.

Improved soil-crop system management aids in NH3 emission mitigation in China

High ammonia (NH3) emissions from fertilized soil in China have led to various concerns regarding environmental safety and public health. In response to China's blue skies protection campaign, effective NH3 reduction measures need to consider both mitigation efficiency and food security. In this context, we conducted a meta-analysis (including 2980 observations from 447 studies) to select effective measures based on absolute (AV) and yield-scaled (YSAV) NH3 volatilization reduction potential, with the aim of establishing a comprehensive NH3 mitigation framework covering various crop production sectors, and offering a range of potential solutions. The results showed that manipulating crop density, using an intermittent irrigation regime for paddy field rice, applying N as split applications or partially substituting inorganic fertilizer N with organic N sources could achieve reductions in AV and YSAV reduction of 10-20 %; adopting drip irrigation regimes, adding water surface barrier films to paddy fields, or using double inhibitor (urease and nitrification), slow-release or biofertilizers could achieve 20-40 % mitigation; plastic film mulching, applying fertilizer by irrigation or using controlled-release fertilizers could yield 40-60 % reduction; use of a urease inhibitor, fully substituting fertilizer N with organic N, or applying fertilizer by deep placement could decrease AV and YSAV by over 60 %. In addition, use of soil amendments, applying suitable inorganic N sources, or adopting crop rotation, intercropping or a rice-fish production model all had significant benefits to control AV. The adoption of any particular strategy should consider local accessibility and affordability, direct intervention by local/government authorities and demonstration to encourage the uptake of technologies and practices, particularly in NH3 pollution hotspot areas. Together, this could ensure food security and environmental sustainability.