Eutrophication: A new wine in an old bottle?

A smartphone-based platform for point-of-use determination of alkaline phosphatase as an indicator of water eutrophication

A smartphone-based detection platform for the determination of alkaline phosphatase (ALP) is described. The method is based on the rational design of the stimulus-response of 7-methoxycoumarin-3-carboxylic acid (7-MC-3-COOH)-functionalized Eu-AMP infinite coordination polymer (ICP) nanoparticles. The blue fluorescence of 7-MC-3-COOH at 403 nm was suppressed, while the red fluorescence of Eu³⁺ at 615 nm was sensitized after the formation of 7-MC-3-COOH@Eu-AMP ICP. Upon exposure to ALP, the dephosphorylation of AMP resulted in the destruction of 7-MC-3-COOH@Eu-AMP ICP, and thereby, the blue fluorescence of 7-MC-3-COOH recovered; in the meantime, the sensitized red fluorescence was quenched. With the fluorescence intensity ratio F₆₁₅/F₄₃₀ as the signal readout, ALP can be detected within a concentration range 0.001 to 0.15 U mL^-1, and the limit of detection (LOD) was 0.00035 U mL^-1. Moreover, fluorescence color changes from red to blue could also be recognized by a portable device with the smartphone as a signal reader, and direct point-of-use testing (POUT) for ALP within a concentration range 0.005 to 0.7 U mL^-1 could be realized, with LOD of 0.0015 U mL^-1. Endowed with high sensitivity and superior reliability, the assay enabled direct monitoring of P-related water eutrophication in a freshwater lake with ALP as an indicator. Graphical abstract A smartphone-based platform for point-of-use determination of alkaline phosphatase.

Influence of tropical reservoirs eutrophication on the polyunsaturated fatty acid profile in Astyanax altiparanae (Pisces: Characidae)

The eutrophication increases the quantity of algae that are deficient in highly unsaturated fatty acids (HUFA) n3, as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), altering the bottom-up transfer of the entire food chain. Due to the importance of the fatty acids (FA) in physiological processes related to the main role of the membrane phospholipids (PL) and precursors of eicosanoids, and also the little knowledge about the influence of eutrophication in tropical ecosystems, it is important to understand how anthropogenic changes in the aquatic ecosystem affect the lipid quality, specifically n3 HUFAs. This study aimed to investigate the influence of eutrophication on the FA profile of the hepatic PL, as well as prostaglandin (PG) levels in Astyanax altiparanae females. Fish were collected in reservoirs with different eutrophication degrees: Jundiaí (Ju) reservoir and Embu-Guaçu (EG) branch, considered as mesotrophic points, and Barragem (Ba) and Aracati (Ar), branches from Guarapiranga reservoir, considered as supereutrophic and hypereutrophic points, respectively. The FA profile of the liver PL was analyzed by gas chromatography, and the concentration of liver PGE2 was analyzed using ELISA immunoassay kits. The degree of eutrophication did not alter the PG concentration and produced few modifications in the FA profile of hepatic PL. Fish collected at Ba and EG presented similar FA profiles, both with high percentages of n3 HUFA, especially DHA, in comparison to fish from Ju. However, no change was observed in the n3 HUFA profile of the fish from Ar. These data demonstrated that the FA profile in A. altiparanae seems to be more related to different physiological requirements of n3 HUFA of the species than eutrophication. So, this study contributed to findings on the trophic transfer dynamics in tropical freshwater reservoirs, where a direct effect of eutrophication on the availability of HUFA n3 to animals is not suggested.

Autogenous Eutrophication, Anthropogenic Eutrophication, and Climate Change: Insights from the Antrift Reservoir (Hesse, Germany)

Climate change is projected to aggravate water quality impairment and to endanger drinking water supply. The effects of global warming on water quality must be understood better to develop targeted mitigation strategies. We conducted water and sediment analyses in the eutrophicated Antrift catchment (Hesse, Germany) in the uncommonly warm years 2018/2019 to take an empirical look into the future under climate change conditions. In our study, algae blooms persisted long into autumn 2018 (November), and started early in spring 2019 (April). We found excessive phosphorus (P) concentrations throughout the year. At high flow in winter, P desorption from sediments fostered high P concentrations in the surface waters. We lead this back to the natural catchment-specific geochemical constraints of sediment P reactions (dilution- and pH-driven). Under natural conditions, the temporal dynamics of these constraints most likely led to high P concentrations, but probably did not cause algae blooms. Since the construction of a dammed reservoir, frequent algae blooms with sporadic fish kills have been occurring. Thus, management should focus less on reducing catchment P concentrations, but on counteracting summerly dissolved oxygen (DO) depletion in the reservoir. Particular attention should be paid to the monitoring and control of sediment P concentrations, especially under climate change.

Study on the experimental performance by electrolysis-integrated ecological floating bed for nitrogen and phosphorus removal in eutrophic water

The new-type electrolysis-integrated ecological floating beds (EEFBs) were set up to study their water removal ability due to the excellent water treatment capacity of electrolysis, this enhanced EEFBs were made of polyethylene filled with biochar substrate and in middle of the substrate placed the Mg-Al alloy served as anode and graphite served as cathode. The results show that removal rates of total nitrogen (TN), ammonia nitrogen (NH₃-N), total phosphorus (TP) and phosphate (PO₄³⁻-P) by the EEFBs increased 53.1%, 96.5%, 76.5% and 74.5%, respectively. The electrolysis reaction was the main pathway for TN and TP removals in the EEFBs. A higher concentration of hydrogen autotrophic denitrification bacteria was recorded in the substrate of the EEFBs than that in the traditional ecological floating beds (EFBs) (p < 0.05), suggesting that the electrolysis may have enhanced the NO₃⁻-N removal efficiency of the EEFBs by promoting the growth and reproduce of hydrogen autotrophic denitrification bacteria. The in-situ formation of Mg²⁺ and Al³⁺ ions from a sacrificial Mg-Al alloy anode, caused PO₄³⁻-P and other suspended matter flocculation, improved phosphorus removal and simultaneously reduced turbidity. Thus, electrolysis-integrated ecological floating bed has high nitrogen and phosphorus removal potential in eutrophic water.

Identification of Regime Shifts and Their Potential Drivers in the Shallow Eutrophic Lake Yilong, Southwest China

Regime shifts in shallow lakes can lead to great changes in ecosystem structures and functions, making ecosystem management more complicated. Lake Yilong, located in Yunnan Province, is one of the most eutrophic lakes in China. Although there is a high possibility that this lake has undergone regime shift one or more times, the presence of regime shifts and their drivers remain unknown. Here, we employed the sequential t-test analysis of regime shifts to detect the regime shifts based on the long-term (1989–2018) dataset of the lake. We further determined their potential drivers, and explored the nutrient thresholds of regime shifts and hysteresis. The results showed that during the testing period, three regime shifts occurred in 1996 (restorative type), 2009 (catastrophic type) and 2014 (restorative type). The potential key drivers for the first two regime shifts (1996 and 2009) were both related to aquaculture. The abolition of cage fish culture may have led to the restorative regime shift in 1996, and the stocking of crabs and excessive premature releasing of fry possibly caused the catastrophic regime shift in 2009. However, the third regime shift, which occurred in 2014, was possibly related to the drought and succedent hydration. These results indicate that adjustments of aquaculture strategy and hydrological conditions are critical for the lake ecosystem’s recovery. Moreover, the total phosphorus thresholds were identified to be lower than 0.046 mg/L (restorative type) and higher than 0.105 mg/L (catastrophic type), respectively. In addition, an obvious hysteresis was observed after 2014, suggesting that nutrient reduction is important for this lake’s management in the future.

Mind the gap: Coping with delay in environmental governance

Gaps between public policy goals and the state of the environment are often significant. However, while goal failures in environmental governance are studied in a number of disciplines, the knowledge on the various causes behind delayed goal achievement is still incomplete. In this article we propose a new framework for analysis of delay mechanisms in science and policy, with the intention to provide a complementary lens for describing, analysing and counteracting delay in environmental governance. The framework is based on case-study findings from recent research focusing on goal-failures in policies for climate change, hazardous chemicals, biodiversity loss and eutrophication. It is also related to previous research on science and policy processes and their interactions. We exemplify the framework with two delay mechanisms that we consider particularly important to highlight-denial of science and decision thresholds. We call for further research in the field, for development of the framework, and not least for increased attention to delay mechanisms in environmental policy review and development on national as well as international levels.

Isolation of two iron-reducing facultative anaerobic electricigens and probing the application performance in eutrophication water

Purpose

Sediment microbial fuel cell (SMFC) is a promising bioremediation technology in which microbes play an important role. Electricigens as the bio-catalysts have effect on pollution control and electricity generation. It is of great significance to screen the microorganisms with the ability of generating electricity.

Methods

The SMFC anode biofilm was used as microbiological source to study the feasibility of electricigens with iron-reducing property for eutrophication water treatment. Preliminarily, we isolated 20 facultative anaerobic pure bacteria and evaluated their cyclic voltammogram (CV) through the three-electrode system and electrochemical workstation. The power generation performance of strains was verified by air-cathode microbial fuel cells (AC-MFCs) under different single carbon sources.

Result

According to its morphological, physiological, and biochemical characteristics, along with phylogenetic analysis, the two strains (SMFC-7 and SMFC-17) with electrical characteristics were identified as Bacillus cereus. Compared with SMFC-7, SMFC-17 exhibited efficient NH4+-N and NO3−-N removal and PO43−-P accumulation from eutrophic solution with a removal rate of 79.91 ± 6.34% and 81.26 ± 1.11% and accumulation rate of 57.68 ± 4.36%, respectively.

Conclusion

The isolated bacteria SMFC-17 showed a good performance in eutrophic solution, and it might be a useful biocatalyst to enable the industrialized application of SMFC in eutrophic water treatment.

Relationships between nutrient, chlorophyll a and Secchi depth in lakes of the Chinese Eastern Plains ecoregion: Implications for eutrophication management

Eutrophication and associated algal blooms are principal environmental challenges confronting lakes in China, particularly in the Eastern Plains ecoregion. The empirical relationships between nutrient and chlorophyll a (Chla) level and Secchi depth (SD) are widely used as a theoretical basis for lake eutrophication management. However, these relationships are largely influenced by hydromorphological conditions and biogeochemical processes. Thus, there is a need to establish a type-specific understanding of these interactions. In the current study, lakes in the Chinese Eastern Plains ecoregion were subdivided into four lake types according to water retention time (LRT), water depth, and water area. Regression analyses indicated that the impacts of nutrient (total nitrogen, TN; total phosphorus, TP) concentrations on summer Chla were significantly reduced in lakes with high inorganic suspended solids (ISS) (P<0.05). Meanwhile, the decrease in SD in these lakes were found to relate mainly to non-algal turbidity. In lakes characterized by both short LRT and high ISS content, the Chla exhibited limited response to nutrients. In contrast, in lakes with low ISS content and long LRT, the observed slopes of both Chla=f(TP) and SD=f(Chla) were significantly steeper (P < 0.05). The factors limiting summer algal growth and the development of type-specific nutrient criteria (TN and TP) of all four investigated lake types in the Eastern Plains ecoregion are discussed in the context of specific nutrients. Based on these results, we establish type-specific eutrophication assessment equations of TN, TP, Chla, and SD in our study lakes. Our results may provide essential information for achieving the cost-effective eutrophication management of lakes both in the Eastern Plains ecoregion and elsewhere with similar climatic and hydromorphological conditions. Moreover, we believe that the subdivision of lakes to allow type-specific eutrophication management framework may prove valuable for other ecoregions where the interpretation of empirical nutrient-Chla and SD relationships suffer from similar serious limitations.

On the Use of an IoT Integrated System for Water Quality Monitoring and Management in Wastewater Treatment Plants

The deteriorating water environment demands new approaches and technologies to achieve sustainable and smart management of urban water systems. Wireless sensor networks represent a promising technology for water quality monitoring and management. The use of wireless sensor networks facilitates the improvement of current centralized systems and traditional manual methods, leading to decentralized smart water quality monitoring systems adaptable to the dynamic and heterogeneous water distribution infrastructure of cities. However, there is a need for a low-cost wireless sensor node solution on the market that enables a cost-effective deployment of this new generation of systems. This paper presents the integration to a wireless sensor network and a preliminary validation in a wastewater treatment plant scenario of a low-cost water quality monitoring device in the close-to-market stage. This device consists of a nitrate and nitrite analyzer based on a novel ion chromatography detection method. The analytical device is integrated using an Internet of Things software platform and tested under real conditions. By doing so, a decentralized smart water quality monitoring system that is conceived and developed for water quality monitoring and management is accomplished. In the presented scenario, such a system allows online near-real-time communication with several devices deployed in multiple water treatment plants and provides preventive and data analytics mechanisms to support decision making. The results obtained comparing laboratory and device measured data demonstrate the reliability of the system and the analytical method implemented in the device.

Contribution of heavy metal in driving microbial distribution in a eutrophic river

Urban rivers represent an important source of freshwater. Accelerated urban development has resulted in imbalances in the water ecological environment and even eutrophication. Moreover, both natural and anthropogenic sources result in frequent heavy metal pollution in urban rivers. However, the combined impact of eutrophication and heavy metal pollution on the diversity and structure of the river microbial communities has not been adequately addressed. The microbial community distribution and predicted functions were examined in six water and sediment samples from the Laojingshui (LJS) River using metagenomic sequencing. The results showed that there were distinct differences in the microbial composition along the river. Redundancy analysis (RDA) revealed that the redox potential (Eh) was the most influential factor, explaining 76.5% of the variation (p = 0.002), and the heavy metals Zn and Cu explained 4.5 and 3.9%, respectively (p < 0.05). The results revealed that high nitrogen and phosphorus concentrations may have affected the proliferation of opportunistic plant species, such as Eichhornia crassipes, but Eh and heavy metals may have had greater impacts than N and P on the microorganisms in the water and sediment. The sensitivities of Deltaproteobacteria, Acidobacteria, Gemmatimonadetes and Nitrospira were most significant under Zn and Cu contamination when accompanied by eutrophic conditions. The expression ratio of the CYS (Cystain) gene might explain why the spatial distribution of each metal differed. This study suggests that heavy metals in eutrophication water continue to be the main factors determining the composition of microbial community, so the treatment of eutrophic water still needs to attach great importance to the complex pollution of heavy metals.

Characteristics of microbial eukaryotic community recovery in eutrophic water by using ecological floating beds

Ecological floating beds can rapidly remove nutrients (nitrogen and phosphorus) from eutrophic water, but we still know little about whether this process can simultaneously recover microbial eukaryotic communities. To fill this gap, planktonic microbial eukaryotic communities were investigated using 18S rRNA high-throughput gene sequencing during nutrient removal by floating beds of Canna indica L. We found that nutrient concentrations were high in both the control and treatment groups during period 1 (days 0-5) but rapidly decreased in the treatment group during period 2 (days 6-9) and period 3 (days 10-18). However, the microbial eukaryotic species richness and community compositions were similar between the control and treatment groups during periods 1 and 2 but showed small differences during period 3. The microbial eukaryotic co-occurrence networks between the control and treatment groups also showed similar degree centrality and interconnected eukaryotic members. We found that some abundant fungi species significantly responded to nutrient variations, but a large number of abundant ciliates were insensitive to nutrient removal. Our findings suggest that ecological floating beds can rapidly remove nutrients in eutrophic waters but that it is difficult to quickly and simultaneously improve microbial eukaryotic communities. This result reveals the critical influence of nutrient pollution on aquatic ecosystems and therefore on long-term and comprehensive aquatic habitat restoration, as aquatic macrophyte recoveries should be conducted after nutrient controls have been implemented.

Influence of coexisting calcium and magnesium ions on phosphate adsorption onto hydrous iron oxide

Removal of phosphorus (P) from municipal wastewater is of vital importance to the control of eutrophication in receiving freshwater bodies. Typical cations such as Ca²⁺ and Mg²⁺ generally exist in municipal wastewater, and they may affect the sorption behavior and mechanism of iron oxide-based materials for aqueous phosphate (H_xPO₄^x - 3, x = 0, 1, 2, or 3 depending on solution pH). To better apply iron oxide-containing materials as adsorbents to eliminate H_xPO₄^x - 3 in municipal wastewater, a hydrous ferric oxide (HFEO) was prepared and characterized at first and then the impact of coexisting Ca²⁺ and Mg²⁺ on the uptake of H_xPO₄^x - 3 by HFEO was studied. The results showed that, without coexisting Ca²⁺ and Mg²⁺, the kinetic data for H_xPO₄^x - 3 sorption onto HFEO were better described by the Elovich model (R² = 0.953) than the pseudo-second-order (R² = 0.838) and pseudo-first-order (R² = 0.641) models, and the isotherm data were fitted better with the Dubinin-Radushkevich (R² = 0.966) and Freundlich (R² = 0.953) models than with the Langmuir (R² = 0.924) model. The ligand exchange of the Fe-bound hydroxyl group with H_xPO₄^x - 3 and the generation of Fe-O-P bonding played a key role in the uptake of H_xPO₄^x - 3 by HFEO in the absence of Ca²⁺ and Mg²⁺. Coexisting Ca²⁺ and Mg²⁺ greatly improved the adsorptive removal of H_xPO₄^x - 3 by HFEO, including the adsorption capacity and initial adsorption rate. According to the Langmuir isotherm equation, the predicted maximum H_xPO₄^x - 3 adsorption capacity for HFEO at pH 7 in the presence of 2 mmol/L Ca²⁺ (24.7 mg P/g) or 2 mmol/L Mg²⁺ (18.4 mg P/g) was much larger than that without coexisting Ca²⁺ and Mg²⁺ (10.7 mg P/g). The formation of aqueous CaHPO₄⁰ and MgHPO₄⁰ species firstly and then the adsorption of the formed CaHPO₄⁰ and MgHPO₄⁰ species on the HFEO surface to generate the HPO₄^2--bridged ternary complexes (i.e., Fe(OPO₃H)Ca⁺ and Fe(OPO₃H)Mg⁺) had an important role in the improvement of H_xPO₄^x - 3 adsorption onto HFEO by coexisting Ca²⁺ and Mg²⁺.

Using Microcystin Gene Copies to Determine Potentially-Toxic Blooms, Example from a Shallow Eutrophic Lake Peipsi

Global warming, paired with eutrophication processes, is shifting phytoplankton communities towards the dominance of bloom-forming and potentially toxic cyanobacteria. The ecosystems of shallow lakes are especially vulnerable to these changes. Traditional monitoring via microscopy is not able to quantify the dynamics of toxin-producing cyanobacteria on a proper spatio-temporal scale. Molecular tools are highly sensitive and can be useful as an early warning tool for lake managers. We quantified the potential microcystin (MC) producers in Lake Peipsi using microscopy and quantitative polymerase chain reaction (qPCR) and analysed the relationship between the abundance of the mcyE genes, MC concentration, MC variants and toxin quota per mcyE gene. We also linked environmental factors to the cyanobacteria community composition. In Lake Peipsi, we found rather moderate MC concentrations, but microcystins and microcystin-producing cyanobacteria were widespread across the lake. Nitrate (NO3-) was a main driver behind the cyanobacterial community at the beginning of the growing season, while in late summer it was primarily associated with the soluble reactive phosphorus (SRP) concentration. A positive relationship was found between the MC quota per mcyE gene and water temperature. The most abundant variant-MC-RR-was associated with MC quota per mcyE gene, while other MC variants did not show any significant impact.

Strategies for Sustainable and Circular Management of Phosphorus in the Baltic Sea Region: The Holistic Approach of the InPhos Project

Despite the significant reduction of phosphorus (P) discharge in the Baltic Sea in the last decades, obtained through the implementation of some approaches within the Helsinki Convention, eutrophication is still considered the biggest problem for the Baltic Sea environment. Consequently, the reduction of P load is an urgent need to solve, but the complexity of both the environmental and legislative context of the area makes this process difficult (more than in the past). Eutrophication is an intricate issue requiring a proper framework of governance that is not easy to determine in the Baltic Sea Region where the needs of several different countries converge. To identify the most suitable strategy to reduce the eutrophication in the Baltic Sea, the InPhos project (no. 17022, 2018–2019, funded by the European Institute of Innovation & Technology (EIT) Raw Materials) adopted a holistic approach considering technical, political, economic, environmental and social aspects of P management. With the aims to raise awareness about the P challenge, foster the dialogue among all the stakeholders, and find solutions already developed in other countries (such as Germany and Switzerland) to be transferred in the Baltic Sea Region, the InPhos project consortium applied the methodology proposed in this paper, consisting of three main phases: (i) analysis of the available technologies to remove P from waste streams that contribute to eutrophication; (ii) analysis of the main streams involving P in Baltic Sea countries to highlight the potential of more sustainable and circular P management; (iii) study of the current context (e.g., already-existing initiatives and issues). This approach allowed us to identify four categories of recommendations and practical actions proposed to improve P management in the Baltic Sea region. During the project, the consortium mainly addressed social aspects. Following steps beyond the project will be more quantitative to determine the techno-economic feasibility of circular P management in selected demo cases in the region.

Automated Determination of Dissolved Reactive Phosphorus at Nanomolar to Micromolar Levels in Natural Waters Using a Portable Flow Analyzer

Automated in-field methods for measuring dissolved reactive phosphorus (DRP) over a large concentration range are in high demand for the purpose of better understanding the biogeochemistry of phosphorus in the river-estuary-coast continuum to the open ocean. Here, an automated portable and robust analyzer was described for the determination of nanomolar to micromolar levels of DRP in natural waters. The quantification of DRP was based on classic phosphomolybdenum blue (PMB) chemistry. All the components of the analyzer were computer-controlled using LabVIEW-based laboratory-programmed software. When equipped with a 3 cm Z-type flow cell, the system demonstrated linearity with concentrations up to 12 μmol L^-1, a sampling rate of 20 h^-1, a limit of detection of 0.11 μmol L^-1, and relative standard deviations (RSDs) of 0.4-4.6% (n = 11-576). When a solid-phase extraction cartridge was combined with the analyzer, the PMB formed from the sample was automatically concentrated on the hydrophilic-lipophilic balanced sorbent. The concentrated PMB compound was eluted with NaOH solution and measured in the spectrophotometric system. Under optimal conditions, the nanomolar-level mode afforded a sampling rate of 8 h^-1, a limit of detection of 1.7 nmol L^-1, and RSDs of 3.0-5.7% (n = 11-120). The system exhibited advantages that included a wide linear range, high sensitivity and reproducibility, low reagent consumption, and insignificant interference from salinity, silicate, arsenate, and other P-containing compounds. The system was successfully applied for discrete sample analysis, fixed site online monitoring, and the real-time underway measurement of DRP in riverine-estuarine-coastal waters.

A Review and Perspective of eDNA Application to Eutrophication and HAB Control in Freshwater and Marine Ecosystems

Changing ecological communities in response to anthropogenic activities and climate change has become a worldwide problem. The eutrophication of waterbodies in freshwater and seawater caused by the effects of human activities and nutrient inputs could result in harmful algae blooms (HABs), decreases water quality, reductions in biodiversity and threats to human health. Rapid and accurate monitoring and assessment of aquatic ecosystems are imperative. Environmental DNA (eDNA) analysis using high-throughput sequencing has been demonstrated to be an effective and sensitive assay for detecting and monitoring single or multiple species in different samples. In this study, we review the potential applications of eDNA approaches in controlling and mitigating eutrophication and HABs in freshwater and marine ecosystems. We use recent studies to highlight how eDNA methods have been shown to be a useful tool for providing comprehensive data in studies of eutrophic freshwater and marine environments. We also provide perspectives on using eDNA techniques to reveal molecular mechanisms in biological processes and mitigate eutrophication and HABs in aquatic ecosystems. Finally, we discuss the feasible applications of eDNA for monitoring biodiversity, surveying species communities and providing instructions for the conservation and management of the environment by integration with traditional methods and other advanced techniques.

Isotopic biomonitoring of N pollution in rivers embedded in complex human landscapes

The dynamic and hierarchical structure of rivers, together with disruption of the natural river continuum by human activities, makes it difficult to identify and locate sources of nutrient pollution affecting receiving waters and observe its dispersion, thus impairing monitoring efforts. The identification of reliable indicators of anthropogenic nitrogen inputs in catchments is therefore key to achieving effective management of polluted rivers. We tested the capacity of N isotopic signatures (δ¹⁵N) of epilithon and snails to provide useful indications of organic and inorganic anthropogenic N inputs in three Mediterranean rivers differing in terms of surrounding land use and physicochemical conditions. We used a combined approach based on (i) analysis of nutrient concentrations in water, (ii) CORINE land cover classification and drainage patterns in catchments and (iii) isotopic analysis of river biota to verify whether isotopic variations were indicative of anthropic activities in the watershed, the associated alteration of water quality, and the consequent impact on snail abundance and diversity. Variation in the δ¹⁵N of epilithon within and between rivers reflected localised and diffuse N inputs from inorganic and organic sources. Negative epilithon δ¹⁵N values (<0‰) indicated inorganic pollution from agriculture. Values between 4‰ and 8‰ and those above 8‰ respectively indicated moderate organic pollution from urban areas, and high organic pollution, mostly from waste waters. The diversity and abundance of snails decreased with increasing water pollution. While their isotopic variations reflected between-river differences, they failed to indicate within-river variations in anthropogenic N inputs, since the proportion of epilithon in their diet varied along the rivers. Concluding, epilithon was a reliable indicator of anthropogenic N sources across a wide range of nutrient concentrations and anthropogenic inputs, and the proposed approach allowed us to determine the nature of nitrogen pollutants, their sources, location and dispersion along rivers embedded in complex human landscapes.

Deriving a Bayesian Network to Assess the Retention Efficacy of Riparian Buffer Zones

Bayesian networks (BN) have increasingly been applied in water management but not to estimate the efficacy of riparian buffer zones (RBZ). Our methodical study aims at evaluating the first BN to predict the RBZ efficacy to retain sediment and nutrients (dissolved, total, and particulate nitrogen and phosphorus) from widely available variables (width, vegetation, slope, soil texture, flow pathway, nutrient form). To evaluate the influence of parent nodes and how the number of states affects prediction errors, we used a predefined general BN structure, collected 580 published datasets from North America and Europe, and performed classification tree analyses and multiple 10-fold cross-validations of different BNs. These errors ranged from 0.31 (two output states) to 0.66 (five states). The outcome remained unchanged without the least influential nodes (flow pathway, vegetation). Lower errors were achieved when parent nodes had more than two states. The number of efficacy states influenced most strongly the prediction error as its lowest and highest states were better predicted than intermediate states. While the derived BNs could support or replace simple design guidelines, they are limited for more detailed predictions. More representative data on vegetation or additional nodes like preferential flow will probably improve the predictive power.

Conversion of municipal wastewater-derived waste to an adsorbent for phosphorus recovery from secondary effluent

The sustainable management and recirculation of phosphorus resources are essential to our human lives. In this work, phosphorus removal and recovery from secondary effluent were achieved using municipal wastewater-derived materials as adsorbents. Through modification with 0.5 M NaOH for 30 min, iron containing sludge that originated from the coagulation pretreatment of municipal wastewater was successfully converted to phosphorus adsorbent. The maximal adsorption capacity of the prepared adsorbent was estimated to be 22 mg-P/g, and the adsorption performance remained stable in the pH range of 5-8. FeO(OH) was identified as the key adsorption site, and the ligand exchange mediated chemical adsorption was the main mechanism for phosphorus removal by the prepared material. Moreover, a laboratory-scale continuous-flow adsorption column experiment showed that the surplus phosphorus in secondary effluent could be readily reduced to <0.1 mg/L. By pyrolysis of P-laden alkali-treated iron sludge under oxygen limited conditions, the phosphorus was recovered and successfully applied to support wheat growth. This work provides valuable information for both the sustainable management of phosphorus streams in wastewater and cyclic utilization of waste sludge.

Linker-Eliminated Nano Metal-Organic Framework Fluorescent Probe for Highly Selective and Sensitive Phosphate Ratiometric Detection in Water and Body Fluids

Phosphate is an important anion in both the aquatic environment and biological systems. The search for a selective and sensitive phosphate ratiometric fluorescent probe to quantify the phosphate level in water samples and body fluids is of great significance for the protection of the ecological environment and human health. Here, a porphyrin-based nano metal-organic framework (NMOF), PCN-224, was successfully exploited as a simple but highly sensitive and selective single-component ratiometric fluorescent probe with accurate composition and measurable structure for the quantitative determination of phosphate, based on the interesting double-emission fluorescence of the porphyrin ligand itself. Compared with other zirconium-based NMOF probes for phosphate, the reduced number of connections for ZrO clusters with the ligand in PCN-224 obtained by a linker-elimination strategy simultaneously provides more active recognition sites for phosphate, which effectively improves the sensitivity of the zirconium-based NMOF probes. The detection limit of the probe is only 54 nM. Additionally, the accuracy of the ratiometric detection based on this probe was further proved by the detection of phosphate in human serum and drinking water.

Using hydrodynamic and water quality variables to assess eutrophication in a tropical hydroelectric reservoir

Few studies have examined the influence of reservoir hydrodynamics on the water quality of its limnological zones. In this study, the relationships between the operational phases and the water quality of the limnological zones were assessed for the Amazonian reservoir Tucuruí. Limnological zones were clustered by means of an artificial neural network technique, and inputs used were water quality variables, measured at twelve stations between 2006 and 2016. Generalized Linear Models (GLMs) were then used to identify the influence of the operational phases of the reservoir on the water quality of its limnological zones. The GLM with a gamma-distributed response variable indicated that Chlorophyll-a concentrations in the riverine and transitional zones differed notably from those observed in the lacustrine zone. Chlorophyll-a concentrations were significantly lower during the operational falling water phase than in the low water phase (p < 0.05). The GLM with an inverse Gaussian-distributed response variable indicated that Secchi depth was significantly lower in the riverine than in the lacustrine limnological zone (p < 0.05). Our results suggest that more eutrophic conditions occur during the operational rising water phase, and that the area most vulnerable to eutrophication is the transitional zone. We demonstrate that the use of GLMs is suitable for determining areas and operational phases most vulnerable to eutrophication. We envisage that this information will be useful to decision-makers when monitoring the water quality of hydroelectric reservoirs with dendritic patterns and dynamic operational phases.

Using Machine-Learning Algorithms for Eutrophication Modeling: Case Study of Mar Menor Lagoon (Spain)

The Mar Menor is a hypersaline coastal lagoon with high environmental value and a characteristic example of a highly anthropized hydro-ecosystem located in the southeast of Spain. An unprecedented eutrophication crisis in 2016 and 2019 with abrupt changes in the quality of its waters caused a great social alarm. Understanding and modeling the level of a eutrophication indicator, such as chlorophyll-a (Chl-a), benefits the management of this complex system. In this study, we investigate the potential machine learning (ML) methods to predict the level of Chl-a. Particularly, Multilayer Neural Networks (MLNNs) and Support Vector Regressions (SVRs) are evaluated using as a target dataset information of up to nine different water quality parameters. The most relevant input combinations were extracted using wrapper feature selection methods which simplified the structure of the model, resulting in a more accurate and efficient procedure. Although the performance in the validation phase showed that SVR models obtained better results than MLNNs, experimental results indicated that both ML algorithms provide satisfactory results in the prediction of Chl-a concentration, reaching up to 0.7 R²_CV (cross-validated coefficient of determination) for the best-fit models.

Sensors Applied for the Detection of Pesticides and Heavy Metals in Freshwaters

Water is essential for every life living on the planet. However, we are facing a more serious situation such as water pollution since the industrial revolution. Fortunately, many efforts have been done to alleviate/restore water quality in freshwaters. Numerous sensors have been developed to monitor the dynamic change of water quality for ecological, early warning, and protection reasons. In the present review, we briefly introduced the pollution status of two major pollutants, i.e., pesticides and heavy metals, in freshwaters worldwide. Then, we collected data on the sensors applied to detect the two categories of pollutants in freshwaters. Special focuses were given on the sensitivity of sensors indicated by the limit of detection (LOD), sensor types, and applied waterbodies. Our results showed that most of the sensors can be applied for stream and river water. The average LOD was72.53±12.69 ng/ml (n=180) for all pesticides, which is significantly higher than that for heavy metals (65.36±47.51 ng/ml,n=117). However, the LODs of a considerable part of pesticides and heavy metal sensors were higher than the criterion maximum concentration for aquatic life or the maximum contaminant limit concentration for drinking water. For pesticide sensors, the average LODs did not differ among insecticides (63.83±17.42 ng/ml,n=87), herbicides (98.06±23.39 ng/ml,n=71), and fungicides (24.60±14.41 ng/ml,n=22). The LODs that differed among sensor types with biosensors had the highest sensitivity, while electrochemical optical and biooptical sensors showed the lowest sensitivity. The sensitivity of heavy metal sensors varied among heavy metals and sensor types. Most of the sensors were targeted on lead, cadmium, mercury, and copper using electrochemical methods. These results imply that future development of pesticides and heavy metal sensors should (1) enhance the sensitivity to meet the requirements for the protection of aquatic ecosystems and human health and (2) cover more diverse pesticides and heavy metals especially those toxic pollutants that are widely used and frequently been detected in freshwaters (e.g., glyphosate, fungicides, zinc, chromium, and arsenic).

Sedimentary phosphorus accumulation and distribution in the continuum of three cascade dams (Creuse River, France)

Dam construction leads to both sediment discontinuities and the creation of internal phosphorus (P) loads in reservoirs capable of supporting eutrophication. Today, majority of large rivers are dammed and numerous of these infrastructures are constructed in cascade. However, few studies focus on the cumulative effect of the presence of dam on sediment P mobility and bioavailability in downstream reservoirs and rivers parts or throughout the continuum. The influence of three cascade dams has been studied herein on the sedimentary P distribution in surface bed sediments along a 17-km fluvial continuum of the Creuse River (Massif Central, France). The sediments (17 samples) were analyzed for their physical (grain size, specific surface area) and chemical (pH, contents of P, Fe, Al, Ca, Mn, organic matter (OM), and P fractionation) characteristics. Results indicated an amount of P 3 to 7 times higher in dam sediments (1.59 ± 0.51 mgP/g DW) than in free-flowing river sections (0.27 ± 0.11 mgP/g DW). Unexpectedly, sedimentary TP content did not decrease from the first to the third reservoir. The spatial variations of sediment characteristics between river and reservoirs were correlated with the retention of particles sized under 200 μm within the reservoirs. In reservoir sediment, P was mainly associated with the ascorbate fraction (P associated with the redox-sensitive Fe/Mn precipitates). Inside each dam reservoir, longitudinal variations of the sedimentary P distribution were mainly due to the increase of amorphous Fe precipitate content accumulated in fine sediments toward the dam, as characterized by a low Fe-Asc/P-Asc molar ratio. In the river sections, P distribution (mainly associated with HCl and ascorbate fractions) was not significantly influenced by cascade dams.

Assessment of iron-modified calcite/zeolite mixture as a capping material to control sedimentary phosphorus and nitrogen liberation

Calcite/zeolite mixture (CZ) can be used to construct a capping layer for the simultaneous management of phosphorus (P) and nitrogen (N) liberation from sediments into the overlying water (OVER-water). However, its control efficiency of sedimentary P release still needs to be improved. To address this issue, an iron-modified CZ (Fe-CZ) was synthesized, characterized, and employed as a capping material to simultaneously prevent P and N release from sediments into OVER-water. Batch and microcosm incubation experiments were performed to study the efficiency and mechanism for the control of P and N release from sediments by capping Fe-CZ. Results showed that sediment capping with Fe-CZ resulted in the significant reduction of soluble reactive P (SRP) and ammonium-N (NH₃-N) in OVER-water, with reduction rates of 77.8-99.7% and 54.0-96.7%, respectively. Furthermore, the Fe-CZ capping layer decreased the SRP concentration in the pore water (PORE-water) at depth of 0-30 mm and reduced the concentration of PORE-water NH₃-N at depth of 0-50 mm. Moreover, the Fe-CZ capping layer gave rise to the great decrement of the concentration of the labile P measured by DGT (diffusive gradient in thin films) technology (P-DGT) in the profile of OVER-water and sediment. Additionally, the Fe-CZ capping resulted in the reduction of redox-sensitive P (P-BD) in the 0-50 mm sediment and caused the transformation of P-BD to calcium-bound P (P-HCl) and residual P (P-RES) in the 0-10 mm sediment as well as to P-RES in the 10-20 mm sediment. Results of this work indicate that the Fe-CZ capping has a high potential for the simultaneous management of P and N release from sediments, and the decrease of the contents of sediment P-DGT, sediment P-BD, PORE-water SRP and PORE-water NH₃-N as well as the conversion of mobile P to more stable P in the top sediment should have a significant role in the simultaneous interception of sedimentary P and N liberation into OVER-water by the Fe-CZ capping.

Algal Bloom Occurrence and Effects in Russia

Eutrophication caused by the entry of nutrients into a water body may lead to algal bloom. Russia possesses the world’s second highest supply of renewable freshwater resources and has faced the problem of eutrophication for many years. Nevertheless, as far as we know, no general analysis of Russia’s algal bloom situation has been before carried out. We have analyzed mass media and scientific reports about algal outbreaks from 2016 to 2018, which allowed us to determine the geographical distribution of algal blooms in Russia, as well as the major effects of eutrophication. As a result, we showed that algal blooms happened in all major climate zones and all federal districts. Cyanobacteria are the most frequently reported photosynthetic organisms comprising algal blooms in freshwater reservoirs located in the continental part of Russia and in the Baltic Sea. Dinoflagellate dominated blooms are more characteristic for the coastal parts of the northeastern Pacific Ocean. The largest number of reports comes from the south of the European part of Russia. However, we did not find significant correlations between state statistics data on factors possibly affecting eutrophication (e.g., population, arable land area, fertilizers, livestock, air temperature, etc.) and the number of algal outbreaks in the regions. Mass media analysis showed that algal blooms attract considerable public attention in Russia, which requires the scientific community to actively participate in solving the problem.

Nitrate sources and processes in the surface water of a tropical reservoir by stable isotopes and mixing model

Nitrate is one of the primary nutrients associated with sedimentation and fuels eutrophication in reservoir systems. In this study, water samples from Bukit Merah Reservoir (BMR) were analysed using a combination of water chemistry, water stable isotopes (δ²H-H₂O and δ¹⁸O-H₂O) and nitrate stable isotopes (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-). The objective was to evaluate nitrate sources and processes in BMR, the oldest man-made reservoir in Malaysia. The δ¹⁵N-NO₃^- values in the river and reservoir water samples were in the range +0.4 to +14.9‰ while the values of δ¹⁸O-NO₃^- were between -0.01 and +39.4‰, respectively. The dual plots of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- reflected mixing sources from atmospheric deposition (AD) input, ammonium in fertilizer/rain, soil nitrogen, and manure and sewage (MS) as the sources of nitrate in the surface water of BMR. Nitrate stable isotopes suggested that BMR undergoes processes such as nitrification and mixing. Denitrification and assimilation were not prevalent in the system. The Bayesian mixing model highlighted the dominance of MS sources in the system while AD contributed more proportion in the reservoir during both seasons than in the river. The use of δ¹³C, δ¹⁵N, and C:N ratios enabled the identification of terrestrial sources of the organic matter in the sediment, enhancing the understanding of sedimentation associated with nutrients previously reported in BMR. Overall, the nitrate sources and processes should be considered in decision-making in the management of the reservoir for irrigation, Arowana fish culture and domestic water supply.

Phosphorus leaching from riparian soils with differing management histories under three grass species

Plants release carbon-based exudates from their roots into the rhizosphere to increase phosphorus (P) supply to the soil solution. However, if more P than required is brought into solution, additional P could be available for leaching from riparian soils. To investigate this further, soil columns containing a riparian arable and buffer strip soil, which differed in organic matter contents, were sown with three common agricultural and riparian grass species. The P loads in leachate were measured and compared with those from unplanted columns, which were 0.17 ± 0.01 and 0.89 ± 0.04 mg kg^-1 for the arable and buffer strip soil, respectively. A mixture of ryegrass and red fescue significantly (p ≤ .05) increased dissolved inorganic P loads in leachate from the arable (0.23 ± 0.01 mg kg^-1 ) and buffer strip soil (1.06 ± 0.05 mg kg^-1 ), whereas barley significantly reduced P leaching from the buffer strip soil (0.53 ± 0.08 mg kg^-1 ). This was dependent on the dissolved organic C released under different plant species and on interactions with soil management history and biogeochemical conditions, rather than on plant uptake of P and accumulation into biomass. This suggested that the amount and forms of P present in the soil and the ability of the plants to mobilize them could be key factors in determining how plants affect leaching of soil P. Selecting grass species for different stages of buffer strip development, basing species selection on root physiological traits, and correcting soil nutrient stoichiometry in riparian soils through vegetative mining could help to lower this contribution.

Spatial patterns of water quality impairments from point source nutrient loads in Germany's largest national River Basin (Weser River)

We employed the well-established Horton-Strahler, hierarchical, stream-order (ω) scheme to investigate scaling of nutrient loads (P and N) from ~845 wastewater treatment plants (WWTPs) distributed along the river network in urbanized Weser River, the largest national basin in Germany (~46K km²; ~8.4 million population). We estimated hydrologic and water quality impacts at the reach- and basin-scales, at two steady river discharge conditions (median flow, Q_R50; low-flow, Q_R90). Of the five WWTPs class-sizes (1 ≤ k ≤ 5), ~68% discharge to small low-order streams (ω < 3). We found large variations in capacity to dilute WWTP nutrient loads because of variability in (1) treated wastewater discharge (Q_U) within and among different class-sizes, and (2) river discharge (Q_R) within low-order streams (ω < 3) resulting from differences in drainage areas. For Q_R50, reach-scale water quality impairment assessed by nutrient concentration was likely at 136 (~16%) locations for P and 15 locations (~2%) for N. About 90% of these locations were lower-order streams (ω < 3). At Q_R50 and only with dilution, basin-scale cumulative nutrient loads from multiple upstream WWTPs increase impaired locations to 266 (~32% of total) for P. Considering in-stream uptake decreased P-impaired streams to 225 (~27%), suggesting the dominant role of dilution in the Weser River basin. Role of in-stream uptake diminished along the flow paths, while dilution in larger streams (4 ≤ ω ≤ 7) minimizes the impact of WWTP loads. Under Q_R90 conditions [(Q_R50/Q_R90) ~ 2.5], water quality impaired locations will likely double for the basin-scale analyses. Long-term water quality data suggested that diffuse sources are the primary contributors for water quality impairments in large streams. Our data-modeling synthesis approach is transferable to other urbanized river basins and extends understanding of point source impacts on water quality across spatial scales.

Contrasting exchanges of nitrogen and phosphorus across the sediment-water interface during the drying and re-inundation of littoral eutrophic sediment

High water level fluctuations (WLFs) lead to periodic drying and re-inundation of sediments in the littoral area of eutrophic lakes. In this study, a series of littoral sediment cores were dried for different periods (5-30 d) and rewetted for 48 h. The sediment cores that dried for 30 d were then re-inundated for 90 d. The exchanges of nitrogen (N) and phosphorus (P) across the sediment-water interface (SWI) and the mechanisms were studied. The results showed that ammonium nitrogen (NH₄⁺-N) fluxes increased after 5-25 d of drying, which was followed by an obvious decrease after 30 d of drying. The decreased NH₄⁺-N fluxes remained at low levels during the 90 d re-inundation period. The soluble reactive P (SRP) fluxes decreased significantly after 15 d of drying. However, further re-inundation increased the SRP fluxes to their initial levels. The decreased water content and porosity, the oxidation of the sediment during drying, and the associated transformations of the N and P fractions in the sediment from drying to re-inundation influenced the exchanges of NH₄⁺-N and SRP across the SWI. The decrease of labile NH₄⁺-N in the sediment during drying was non-reversible, while the transformations between redox sensitive P (Fe-P) and aluminum-bound P were more likely to be reversible from drying to re-inundation. The increase of Fe-P during drying and dissolution of Fe-P during the re-inundation were responsible for the development of SRP fluxes from drying to re-inundation. Therefore, the periodic drying and re-inundation of the littoral eutrophic sediments reduced the release of NH₄⁺-N but accelerated the release of SRP from the sediment. This should be given more consideration for the remediation and management of eutrophication in the lake and other similar lakes with high WLFs.

Analysis of Biogenic Secondary Pollution Materials from Sludge in Surface Waters

Many countries of the world, including Lithuania, are making an effort to reduce surface water pollution. State monitoring data show that almost 80% of the lakes in Lithuania have an increased amount of sludge. One of the reasons for this increase in sludge is an excessive amount of biogenic material in the water. It is known that even after the source of pollution is removed, the condition of the lake water does not improve; rather, the condition of the lake water worsens due to the secondary pollution of sludge in the water. A study was conducted to determine the impact of secondary sludge pollution on water. For this study, 5 sludge samples were taken from different lakes in Lithuania. Fresh water was poured on the sludge samples, the concentrations of N_t, NO₂-N, NO₃-N, NH₄-N, PO₄-P, P_t, the pH and the changes in the electric conductivity (C) were measured in the water within 28 h. Research has shown that the thickness of the sludge layer influences the total amounts of nitrogen, phosphorus, and organic matter present in the sludge. As the thickness of the sludge layer increases in a lake, the total concentrations of nitrogen, total phosphorus and organic matter increase. Studies have also shown that the concentrations of all biogenic substances in water increase, with the exception of total phosphorus. This finding shows that organic phosphorus is "locked" in sludge, and no secondary pollution occurs from this source. Moreover, the electrical conductivity values of the water influence the release of biogenic substances from sludge in the water.

Assessing the Ecological Sensitivity of Coastal Marine Ecosystems: A Case Study in Xiamen Bay, China

Coastal marine ecosystems are sensitive to anthropogenic stressors and environmental change. The Chinese Government proposed an ecosystem-based marine spatial planning scheme called the “Marine Ecological Red Line” (MERL), aimed at protecting ecologically sensitive areas. The assessment and mapping of ecosystem sensitivity provide important tools for regional MERL and setting conservation priorities. In this study, an integrated framework for the comprehensive sensitivity assessment of coastal marine ecosystems was proposed. This framework had two components: endogenous sensitivity and exogenous sensitivity. A weighted summation method was used along with a GIS-based spatial analysis to calculate regional sensitivity quantitatively. Taking Xiamen Bay in China as a case study, the approach integrated spatial data on the distribution of marine habitats and multiple human activities. An index system (including 26 indicators) was established for the case study. Five areas with different levels of sensitivity were delineated. In the study region of 1281 km2, areas with extremely high and high sensitivity covered 87 km2 and 235 km2, respectively, and were hypothesized to be priority areas of conservation and regulation. Areas with the highest sensitivity were located closer to Jiulongjiang Estuary and along the coastline of Xiang’an. Areas with lower sensitivity were also mapped in Tong’an Bay, representing possible areas that could accommodate future industrial or intensive human use. Comparative analyses between endogenous sensitivity and exogenous sensitivity allowed the presence of development-protection conflict zones to be identified. The results provide an important scientific basis for MERL decisions. In addition, targeted management strategies were proposed for Xiamen Bay. This study presents an operational approach to provide relevant scientific knowledge on the process of ecosystem-based marine spatial planning, facilitating policy-making decisions in sustainable coastal and marine management.

Simultaneous control of nitrogen and phosphorus release from sediments using iron-modified zeolite as capping and amendment materials

The use of zeolite as a geo-engineering tool has a high potential to control nitrogen (N) release from sediments, but its efficiency for controlling sedimentary phosphorus (P) release still need to be further increased. To address this issue, this work synthesized an iron-modified zeolite (IM-Z) by coating iron onto the surface of natural zeolite (NAT-Z) and then the as-obtained IM-Z was utilized as a geo-engineering material to block the upward mobilization of N and P from sediments to the overlying water. The efficiencies of IM-Z covering and amendment to prevent the liberation of N and P from sediments were evaluated, and the controlling mechanism was explored. Capping and amendment with IM-Z not only resulted in the tremendous reduction of the levels of ammonium-N (NH₄⁺-N) and reactive soluble P (RSP) in the overlying water, but also led to the decrease of the contents of NH₄⁺-N and RSP in the pore water. More importantly, sediment capping and amendment with IM-Z resulted in the formation of a static layer in the upper sediment directly below the sediment-water interface, with very low concentration of RSP in the pore water. In addition, IM-Z capping and addition effectively immobilized the diffusive gradients in thin films (DGT)-labile P in the overlying water and sediment. Furthermore, the decrease of the DGT-labile Fe concentrations in the overlying water as well as the top sediment were also observed after IM-Z capping and addition. Nearly 70% of P bound by IM-Z is stable and difficult to be released back into the overlying water under common pH and anoxic conditions. The adsorption of pore water NH₄⁺-N on IM-Z, the immobilization of pore water RSP and DGT-labile P by IM-Z and the uptake of DGT-labile Fe on IM-Z played a significant role in the simultaneous control of NH₄⁺-N and RSP liberation. Compared to NAT-Z, the efficiency of IM-Z to block the liberation of sedimentary P was higher. Results of this study demonstrate that IM-Z is suitable for use in the simultaneous interception of the upward transportation of NH₄⁺-N and RSP from sediments into the overlying water.

River nutrient water and sediment measurements inform on nutrient retention, with implications for eutrophication

The consideration of nutrients in pollution dynamics is important for environmental management and conservation. Developing countries are yet to appreciate the aquatic ecosystem pollution impacts on their economies and as such, information on water pollution dynamics is limited. This study assessed the spatio-temporal dynamics of nutrient loading and retention in stream water and sediments in the Bloukrans River system, Eastern Cape province, South Africa over the course of the wet and dry season. Sediment and water samples were analysed for total phosphorus (TP) and nitrogen (TN) concentrations, and were used in combination with river flow discharge, to determine nutrient loads. The study results highlight that river discharge plays a significant role in temporal differences in sediment and water column nutrient concentrations. The mean sediment nutrient concentration was high for the dry season, with high values being observed for the urban river system. Nutrient loads were high above the sewage treatment works outflow (i.e. urban sites), as such, a decreasing trend was observed with increasing distance from the urban environment. Nutrient loads were generally high for the dry season in comparison to the wet season indicating organic matter retention (i.e. accumulation from burst sewage pipes) most likely due to low flows. While it was evident that the ageing wastewater infrastructure contributed to the observed state of the Bloukrans River, the high natural nutrient retention capacity seemed to mitigate eutrophication of downstream aquatic ecosystems. As such, the nutrient retention capacity and management of the system is central to the entire Bloukrans River catchment management practices. Therefore, the study contributes to our understanding of water and sediment nutrient pollution dynamics in an arid temperate river landscape where vast spatio-temporal differences in base flow characterise the riverscape.

Modeling the Ecological Impact of Phosphorus in Catchments with Multiple Environmental Stressors

The broken phosphorus (P) cycle has led to widespread eutrophication of freshwaters. Despite reductions in anthropogenic nutrient inputs that have led to improvement in the chemical status of running waters, corresponding improvements in their ecological status are often not observed. We tested a novel combination of complementary statistical modeling approaches, including random-effect regression trees and compositional and ordinary linear mixed models, to examine the potential reasons for this disparity, using low-frequency regulatory data available to catchment managers. A benthic Trophic Diatom Index (TDI) was linked to potential stressors, including nutrient concentrations, soluble reactive P (SRP) loads from different sources, land cover, and catchment hydrological characteristics. Modeling suggested that SRP, traditionally considered the bioavailable component, may not be the best indicator of ecological impacts of P, as shown by a stronger and spatially more variable negative relationship between total P (TP) concentrations and TDI. Nitrate-N ( < 0.001) and TP ( = 0.002) also showed negative relationship with TDI in models where land cover was not included. Land cover had the strongest influence on the ecological response. The positive effect of seminatural land cover ( < 0.001) and negative effect of urban land cover ( = 0.030) may be related to differentiated bioavailability of P fractions in catchments with different characteristics (e.g., P loads from point vs. diffuse sources) as well as resilience factors such as hydro-morphology and habitat condition, supporting the need for further research into factors affecting this stressor-response relationship in different catchment types. Advanced statistical modeling indicated that to achieve desired ecological status, future catchment-specific mitigation should target P impacts alongside multiple stressors.

Phytoplankton Blooms, Red Tides and Mucilaginous Aggregates in the Urban Thessaloniki Bay, Eastern Mediterranean

We investigated the plankton community composition and abundance in the urban marine environment of Thessaloniki Bay. We collected water samples weekly from March 2017 to February 2018 at the coastal front of Thessaloniki city center and monthly samples from three other inshore sites along the urban front of the bay. During the study period, conspicuous and successive phytoplankton blooms, dominated by known mucilage-producing diatoms alternated with red tide events formed by the dinoflagellates Noctiluca scintillans and Spatulodinium pseudonoctiluca, and an extensive mucilage aggregate phenomenon, which appeared in late June 2017. At least 11 known harmful algae were identified throughout the study, with the increase in the abundance of the known harmful dinoflagellate Dinophysis cf. acuminata occurring in October and November 2017. Finally, a red tide caused by the photosynthetic ciliate Mesodinium rubrum on December 2017 was conspicuous throughout the sampling sites. The above-mentioned harmful blooms and red tides were linked to high nutrient concentrations and eutrophication. This paper provides an overview of eutrophication impacts on the response of the unicellular eukaryotic plankton organisms and their impact on water quality and ecosystem services.

Demonstrated transfer of cyanobacteria and cyanotoxins along a freshwater-marine continuum in France

The frequency of cyanobacterial proliferations in fresh waters is increasing worldwide and the presence of associated cyanotoxins represent a threat for ecosystems and human health. While the occurrence of microcystin (MC), the most widespread cyanotoxin, is well documented in freshwaters, only few studies have examined its occurrence in estuarine waters. In this study we evaluated the transfer of cyanobacteria and cyanotoxins along a river continuum from a freshwater reservoir through an interconnecting estuary to the coastal area in Brittany, France. We sampled regularly over 2 years at 5 stations along the river continuum and analysed for phytoplankton and cyanotoxins, together with physico-chemical parameters. Results show that cyanobacteria dominated the phytoplanktonic community with high densities (up to 2 × 10⁶ cells mL^-1) at the freshwater sites during the summer and autumn periods of both years, with a cell transfer to estuarine (up to 10⁵ cells mL^-1) and marine (2 × 10³ cells mL^-1) sites. While the temporal variation in cyanobacterial densities was mainly associated with temperature, spatial variation was due to salinity while nutrients were non-limiting for cyanobacterial growth. Cyanobacterial biomass was dominated by several species of Microcystis that survived intermediate salinities. Intracellular MCs were detected in all the freshwater samples with concentrations up to 60 μg L^-1, and more intermittently with concentrations up to 1.15 μg L^-1, at the most upstream estuarine site. Intracellular MC was only sporadically detected and in low concentration at the most downstream estuarine site and at the marine outlet (respectively <0.14 μg L^-1 and <0.03 μg L^-1). Different MC variants were detected with dominance of MC-LR, RR and YR and that dominance was conserved along the salinity gradient. Extracellular MC contribution to total MC was higher at the downstream sites in accordance with the lysing of the cells at elevated salinities. No nodularin (NOD) was detected in the particulate samples or in the filtrates.

Nitrogen and phosphorus removal comparison between periphyton on artificial substrates and plant-periphyton complex in floating treatment wetlands

Artificial substrates (ASs) and floating treatment wetlands (FTWs) have been widely used in the treatment of polluted surface water. In fact, periphyton on ASs functions in nutrient removal, while the plant-periphyton complex functions in FTWs. However, the nutrient removal performance of the periphyton on ASs and the plant-periphyton complex in FTWs has not been systematically compared. Thus, ASs and FTWs were established in a mesocosm experiment to compare nitrogen and phosphorus removal between the two ecological treatment techniques. The results showed that the total nitrogen removal efficiency was 60.4% in the AS treatments and 65.3% in the FTWs, while the total phosphorus removal efficiency was 83.7% in the AS treatments and 39.45% in the FTWs. Periphyton on the ASs absorbed 2.5 g N m^-2 and 0.85 g P m^-2, accounting for 20.8% of the N removal and 18.7% of the P removal. Sedimentation contributed to 71.3% of the N removal and 56.1% of the P removal in the AS treatments. For the plant-periphyton complex in the FTWs, 25.1% of the N and 53.0% of the P accumulated in plant tissue. Most of the reduced N (47.1%) was removed by other pathways, which was likely the effect of periphyton attached on plant roots and floating rafts. The nutrient removal efficiencies and pathways of AS and FTW treatments showed different characteristics, providing a reference for the selection of treatment measures for polluted surface water remediation.

Assessment of freshwater discharge into a coastal bay through multi-basin ensemble hydrological modelling

Coastal basins of the Brittany peninsula (France) are hydrological hot spots. A high level of nutrient pollution affects many of these basins and causes algal blooms in several coastal bays; nine have been a specific focus of the European Commission since 2007. The flux of each contributing basin flowing into these bays must be examined to assess the conditions and explore mitigation options. However, this task encounters a large lack of data since most of the basins are ungauged. In this context, this study developed a method which facilitates transposition of hydrographs from gauged basins to ungauged neighbouring basins of interest. Inverting a simple geomorphology-based transfer function of the gauged basin which describes travel time through channels enables the net rainfall time-series to be estimated from the discharge time-series of donor basins. To estimate the net rainfall of a given ungauged catchment, several net rainfall time series of gauged catchments are averaged. The resulting net rainfall is then transposed onto the ungauged target basin and convoluted by its own transfer function to estimate the hydrograph. This allows the transposition of as many hydrographs as there are different donor basins. This ensemble prediction enables the proportion of prediction uncertainty that is due to the heterogeneity in hydrological behaviour to be estimated. Moreover, the time-series of the donor basins are combined to estimate the ungauged net rainfall time-series. This provides a discharge prediction which values all available measurements. The method was applied to the highly controversial Saint Brieuc Bay, where it was possible to quantify the contribution of each coastal basin, even those influenced by dams, and ultimately the entire volume of fresh water entering the bay at an hourly time step. This work opens perspectives to additionally refine estimation of the associated nutrient fluxes.

Effects of seasonality, trophic state and landscape properties on CO2 saturation in low-latitude lakes and reservoirs

The role of tropical lakes and reservoirs in the global carbon cycle has received increasing attention in the past decade, but our understanding of its variability is still limited. The metabolism of tropical systems may differ profoundly from temperate systems due to the higher temperatures and wider variations in precipitation. Here, we investigated the spatial and temporal patterns of the variability in the partial pressure of carbon dioxide (pCO₂) and its drivers in a set of 102 low-latitude lakes and reservoirs that encompass wide gradients of precipitation, productivity and landscape properties (lake area, perimeter-to-area ratio, catchment size, catchment area-to-lake area ratio, and types of catchment land use). We used multiple regressions and structural equation modeling (SEM) to determine the direct and indirect effects of the main in-lake variables and landscape properties on the water pCO₂ variance. We found that these systems were mostly supersaturated with CO₂ (92% spatially and 72% seasonally) regardless of their trophic status and landscape properties. The pCO₂ values (9-40,020 μatm) were within the range found in tropical ecosystems, and higher (p < 0.005) than pCO₂ values recorded from high-latitude ecosystems. Water volume had a negative effect on the trophic state (r = -0.63), which mediated a positive indirect effect on pCO₂ (r = 0.4), representing an important negative feedback in the context of climate change-driven reduction in precipitation. Our results demonstrated that precipitation drives the pCO₂ seasonal variability, with significantly higher pCO₂ during the rainy season (F = 16.67; p < 0.001), due to two potential main mechanisms: (1) phytoplankton dilution and (2) increasing inputs of terrestrial CO₂ from the catchment. We conclude that at low latitudes, precipitation is a major climatic driver of pCO₂ variability by influencing volume variations and linking lentic ecosystems to their catchments.

Impact of Urban Stormwater Runoff on Cyanobacteria Dynamics in A Tropical Urban Lake

Worldwide, eutrophication and cyanobacteria blooms in lakes and reservoirs are a great concern for water resources management. Coupling a catchment hydrological model and a lake model has been a strategy to assess the impact of land use, agricultural practices and climate change on water quality. However, research has mainly focused on large lakes, while urban reservoirs and their catchments, especially in tropical regions, are still poorly studied despite the wide range of ecosystem services they provide. An integrated modelling approach coupling the hydrological model Storm Water Management Model SWMM and the lake ecological model DYRESM-CAEDYM is proposed for Lake Pampulha (Brazil). Scenarios of increased imperviousness of the catchment and of reduction in the load of nutrients and total suspended solids (TSS) in dry weather inflow were simulated. Runoff water quality simulations presented a fair performance for TSS and ammonium (NH4+) while the dynamics of total phosphorus (TP) and nitrate (NO3−) were poorly captured. Phytoplankton dynamics in the lake were simulated with good accuracy (Normalized Mean Absolute Error, NMAE = 0.24 and r = 0.89 in calibration period; NMAE = 0.55 and r = 0.54 in validation period). The general trends of growth, decline and the magnitude of phytoplankton biomass were well represented most of the time. Scenario simulations suggest that TP reduction will decrease cyanobacteria biomass and delay its peaks as a consequence of orthophosphate (PO43−) concentration reduction in the lake surface layers. However, even decreasing TP load into Lake Pampulha by half would not be sufficient to achieve the water quality objective of a maximum concentration of 60 µg chla L−1. Increased imperviousness in the catchment will raise runoff volume, TSS, TP and NO3− loads into Lake Pampulha and promote greater cyanobacteria biomass, mainly in the beginning of the wet season, because of additional nutrient input from catchment runoff. Recovering Lake Pampulha water quality will require the improvement of the sanitation system. The lake water quality improvement will also require more sustainable and nature-based solutions for urban drainage in order to reduce non-point pollution through infiltration and retention of stormwater and to enhance natural processes, such as chemical sorption, biodegradation and phytoremediation. The integrated modelling approach here proposed can be applied for other urban reservoirs taking advantage of existing knowledge on Lake Pampulha.

Hydrogeological modelling for the watershed management of the Mar Menor coastal lagoon (Spain)

The Mar Menor is the largest lagoon along the Spanish Mediterranean coast. It suffers from eutrophication and algal blooms associated with intensive agricultural activities and urban pressure in the surrounding Campo de Cartagena plain. A balanced discharge of groundwater, carrier of algal nutrients such as nitrate, is essential to ensure the integrity of the coastal lagoon and the availability of groundwater resources inland. We here present a 3D hydrogeological model of the unconfined Quaternary aquifer that discharges into the lagoon. The model couples both surface water balance and groundwater dynamics and has been calibrated to available data in the period 2000-2016. The calibrated model allows understanding of the current state of the aquifer and its link to the lagoon. The potential discharge has been quantified in both space and time and falls between 69.5 and 84.9 hm³/yr during dry and wet periods, respectively (with values of nitrate discharge of 11.4-11.8 Mkg/yr in the absence of aquifer sink terms, e.g., leakage to deeper aquifers and pumping from groundwater wells). The predictive capabilities of the calibrated model can be used to test the impact of different integrated management scenarios on the surface-groundwater dynamics of the catchment. Three plausible management scenarios are proposed that include localized and distributed groundwater pumping (drains and groundwater wells, respectively). Results show the effectiveness of the scenarios in reducing the groundwater and nitrate discharge into the lagoon. The disadvantages of the proposed scenarios, including potential seawater intrusion, need to be balanced with their relative merits for the sustainable development of the region and the survival of the Mar Menor ecosystem. The modelling approach proposed provides a valuable tool for the integrated and holistic management of the Campo de Cartagena-Mar Menor catchment and should be of great interest to similar hydrological systems with high ecological value.

Integration of Membrane Bioreactor and Nanofiltration for the Treatment Process of Real Hospital Wastewater in Ho Chi Minh City, Vietnam

Hospital wastewater contains pharmaceutical residues, chemicals, and pathogens that cause coloration and nourish pathogenic microorganisms. The objective of the study was to evaluate the effectiveness of a medical wastewater treatment system at Military Hospital 175 (Ho Chi Minh City, Vietnam) that combined a membrane bioreactor (MBR) system with nanofiltration (NF). The influent of the system was the wastewater discharged from the operating rooms of the hospital. The system has a capacity of 50 L/day and operates at three organic load rates (OLR) of 0.5, 1.5 and 2.5 kgCOD/m3day (COD: Chemical oxygen demand), in which each load rate operates for 40 days. The results showed that most nutritional criteria generally achieved positive results. Specifically, the average COD removal was shown to be consistently high throughout the three phases at 94%, 93.3%, and 92.7%, respectively. For removal of nitrogen, the system demonstrated efficiencies of 75%, 79%, and 83%, respectively, to three phases. The log removal value (LRV) for Escherichia coli and coliform bacteria were higher than four throughout the study period. The average removal efficiency for color and total iron was approximately 98% and 99%, respectively. The water quality after treatment, especially after NF, meets the Vietnamese standard of grade A. The arrangement in which the MBR preceded NF was also found to limit the amount of soil and solids entering subsequent treatment, which therefore improved the efficiency of NF, as demonstrated by the stability of post-NF transmembrane pressures throughout three cycles renewed by two backwashes.