Nitrite-responsive hydrogel for long-term and smart control of cyanobacteria bloom

Authors

Jialiang Xiong, Ruoxiao Xie, Huiying Zhang, Jianyi Gao, Jiaping Wang, Qionglin Liang

Frequent cyanobacteria bloom has caused serious environmental consequences and economic loss, especially in aquaculture. Direct algaecide addition, the most commonly used method, suffered from the poor control and overdose of algaecide. In this manuscript, we designed a smart nitrite-responsive hydrogel (DHPG) loading algaecide (BZK@DHPG) based on selective crosslinker: a kind of dihydropyridine derivatives termed DHPL. The network of the polymer could be decomposed by the nitrite-induced cleavage of DHPL. Compared to the traditional method, BZK@DHPG can adjust releasing speed according to the concentration of NO₂⁻, the marker of cyanobacteria bloom level, and elongate the releasing time. Furthermore, BZK@DHPG could shift the effective dose of algaecide much ahead of the safety threshold, thus reducing deterioration of water quality caused by the overdose of algaecide.

Using sodium percarbonate to suppress vertically distributed filamentous cyanobacteria while maintaining the stability of microeukaryotic communities in drinking water reservoirs

Authors

Hangzhou Xu, Yiming Pang, Yizhen Li, Shasha Zhang, Haiyan Pei

The increasing frequency and intensity of blooms of toxin- and taste & odour-producing filamentous cyanobacteria in water sources is a growing global issue. Compared to the common spherical Microcystis genus, the removal of filamentous cyanobacteria is more difficult in drinking water treatment plants; hence, abatement and control of the occurrence and proliferation of harmful filamentous cyanobacteria within drinking water sources is important for water supply. In this study, the solid sodium percarbonate (SPC), Na2CO3·1.5H2O2, was used as an algaecide to eliminate the cyanobacteria distributed throughout the water column in the surface and bottom layer of a reservoir serving as a drinking water source. Results showed that although the oxidation capacity of SPC was higher in the surface water due to the higher light intensity than in the bottom water, 3.0 mg/L SPC can still suppress the harmful cyanobacteria in the bottom water after 36 h because the carbonate ion generated by SPC decomposition can act as an activator of H2O2 to generate many reactive oxygen species — including superoxide radicals, carbonate radical anions, and hydroxyl radicals — even in the light-limited environment. The obtained inactivation rates for the main cyanobacteria in this reservoir followed the order: Pseudanabaena limnetica > Raphidiopsis curvata > Cylindrospermopsis raciborskii. 3.0 mg/L SPC has a slight impact on microeukaryotic communities according to the 18S rRNA gene sequencing, while 6.0 mg/L SPC changed the composition of eukaryotic phytoplankton and zooplankton clearly. Eukaryotic co-occurrence networks showed that although the network of eukaryotic plankton in treated surface water was more compact and clustered, stability of microeukaryotes in the treated surface water was lower than for the treated bottom water, owing to the higher oxidation capacity of SPC in the surface water. The results above not only have important implications for full-scale control of harmful cyanobacteria in drinking water sources, especially filamentous cyanobacteria with vertical distributions, but also help to ensure the health and stability of the whole aquatic ecosystem.

Mitigating eutrophication and toxic cyanobacterial blooms in large lakes: The evolution of a dual nutrient (N and P) reduction paradigm

Authors

Hans W. Paerl, Karl E. Havens, Hai Xu, Guangwei Zhu, Mark J. McCarthy, Silvia E. Newell, J. Thad Scott, Nathan S. Hall, Timothy G. Otten & Boqiang Qin

Cyanobacterial harmful algal blooms (CyanoHABs) are an increasingly common feature of large, eutrophic lakes. Non-N₂-fixing CyanoHABs (e.g., Microcystis) appear to be proliferating relative to N₂-fixing CyanoHABs in systems receiving increasing nutrient loads. This shift reflects increasing external nitrogen (N) inputs, and a > 50-year legacy of excessive phosphorus (P) and N loading. Phosphorus is effectively retained in legacy-impacted systems, while N may be retained or lost to the atmosphere in gaseous forms (e.g., N₂, NH₃, N₂O). Biological control on N inputs versus outputs, or the balance between N₂ fixation versus denitrification, favors the latter, especially in lakes undergoing accelerating eutrophication, although denitrification removal efficiency is inhibited by increasing external N loads. Phytoplankton in eutrophic lakes have become more responsive to N inputs relative to P, despite sustained increases in N loading. From a nutrient management perspective, this suggests a need to change the freshwater nutrient limitation and input reduction paradigms; a shift from an exclusive focus on P limitation to a dual N and P co-limitation and management strategy. The recent proliferation of toxic non-N₂-fixing CyanoHABs, and ever-increasing N and P legacy stores, argues for such a strategy if we are to mitigate eutrophication and CyanoHAB expansion globally.

A systematic literature review of forecasting and predictive models for cyanobacteria blooms in freshwater lakes

Authors

Benny Zuse Rousso, Edoardo Bertone, Rodney Stewart, David P. Hamilton

Cyanobacteria harmful blooms (CyanoHABs) in lakes and reservoirs represent a major risk for water authorities globally due to their toxicity and economic impacts. Anticipating bloom occurrence and understanding the main drivers of CyanoHABs are needed to optimize water resources management. An extensive review of the application of CyanoHABs forecasting and predictive models was performed, and a summary of the current state of knowledge, limitations and research opportunities on this topic is provided through analysis of case studies. Two modelling approaches were used to achieve CyanoHABs anticipation; process-based (PB) and data-driven (DD) models. The objective of the model was a determining factor for the choice of modelling approach. PB models were more frequently used to predict future scenarios whereas DD models were employed for short-term forecasts. Each modelling approach presented multiple variations that may be applied for more specific, targeted purposes. Most models reviewed were site-specific. The monitoring methodologies, including data frequency, uncertainty and precision, were identified as a major limitation to improve model performance. A lack of standardization of both model output and performance metrics was observed. CyanoHAB modelling is an interdisciplinary topic and communication between disciplines should be improved to facilitate model comparisons. These shortcomings can hinder the adoption of modelling tools by practitioners. We suggest that water managers should focus on generalising models for lakes with similar characteristics and where possible use high frequency monitoring for model development and validation.

Cyanobacteria in inland waters: new monitoring, reporting, modelling and ecological research

 

Authors

Simon M. Mitrovic, Tsuyoshi Kobayashi and Daniel L. Roelke

Cyanobacteria in freshwater environments are a natural part of the phytoplankton community but can cause human health and ecosystem issues through the production of toxins (Paerl et al. 2001). The toxins produced by cyanobacteria (cyanotoxins) are
varied, and include hepatotoxins, neurotoxins, cytotoxins and skin irritants (Bartram and Chorus 1999; Wiegand and Pflugmacher 2005). Cyanotoxins can have adverse effects on human health, particularly by exposure through drinking water (Carmichael et al. 2001) or recreation (such as swimming; Pilotto et al. 1997). Cyanotoxins are also known to affect livestock and native animals drinking contaminated water (Stewart et al. 2008) and aquatic organisms such as fish (Drobac et al. 2016), zooplankton (Bownik 2016) and aquatic macrophytes (Mitrovic et al. 2004, 2005). The risks from cyanotoxins increase with the density of cyanobacterial blooms, so understanding the drivers of cyanobacterial growth and dominance, as well as the risks of cyanotoxins, is important for management. Cyanobacterial blooms are anticipated to expand and change their distribution, frequency and intensity in inland waters with increasing global warming and climate change (Paerl and Huisman 2009). This is concerning due to the potential impact of blooms in new locations and increased bloom intensity in previously affected areas. This special issue of the Journal brings together papers that use new and diverse scientific tools available for monitoring, reporting and modelling cyanobacterial growth, as well as ecological research on cyanobacteria and their toxins that can help expand our research and management capabilities. These approaches to the monitoring of cyanobacteria within waterways may give further insights into risks and management approaches.

Quantifying the dependence of cyanobacterial growth to nutrient for the eutrophication management of temperate-subtropical shallow lakes

Authors

Wei Zou, Guangwei Zhu, Yongjiu Cai, Hai Xu, Mengyuan Zhu, Zhijun Gong, Yunlin Zhang, Boqiang Qin

The increasing global occurrence of cyanobacterial blooms, attributed primarily to human-induced nutrient enrichment, significantly degrades freshwater ecosystems and poses serious risks to human health. The current study examined environmental variables and cyanobacterial biovolume (B_Cyano) of 28 shallow lakes in the eastern China plains during the spring and summer of 2018. We used a 95% quantile regression model to explore season-specific response of B_Cyano to total nitrogen (TN), or total phosphorus (TP), and robust linear relationships were observed between log(B_Cyano+0.001) and log(TN), or log(TP) in both spring and summer periods. Based on these regressions, regional-scale and season-specific TN and TP thresholds are proposed for these lakes to ensure the safety for recreational waters and drinking water source. However, actual B_Cyano for a given concentration of TN (or TP) for many observations were considerably lower than the results of the 95% regression model predict, indicating that other factors significantly modulated nutrient limitation of B_Cyano. Generalized additive model and quantile regression model were used together to explore potentially significant modulating factors, of which lake retention time, macrophytes cover and N: P ratio were identified as most important. Thus, it is necessary to develop type-specific nutrient thresholds with the consideration of these significant modulating factors. Furthermore, nutrient-B_Cyano relationships of our studied lakes with lake retention time>100 days and no macrophyte were further explored and nutrient thresholds of this lake type were proposed. Nutrient thresholds proposed in this study may play an essential role in achieving a cost-effective eutrophication management for shallow lakes both in the eastern China plains and elsewhere with similar climatic background. On a broader scale, the approaches and findings of this study may provide valuable reference to formulate reasonable nutrient reduction targets for other ecoregions with different climatic conditions.

Mitigating eutrophication and toxic cyanobacterial blooms in large lakes: The evolution of a dual nutrient (N and P) reduction paradigm

Authors

Hans W. Paerl, Karl E. Havens, Hai Xu, Guangwei Zhu, Mark J. McCarthy, Silvia E. Newell, J. Thad Scott, Nathan S. Hall, Timothy G. Otten, Boqiang Qin

Cyanobacterial harmful algal blooms (CyanoHABs) are an increasingly common feature of large, eutrophic lakes. Non-N₂-fixing CyanoHABs (e.g., Microcystis) appear to be proliferating relative to N₂-fixing CyanoHABs in systems receiving increasing nutrient loads. This shift reflects increasing external nitrogen (N) inputs, and a > 50-year legacy of excessive phosphorus (P) and N loading. Phosphorus is effectively retained in legacy-impacted systems, while N may be retained or lost to the atmosphere in gaseous forms (e.g., N₂, NH₃, N₂O). Biological control on N inputs versus outputs, or the balance between N₂ fixation versus denitrification, favors the latter, especially in lakes undergoing accelerating eutrophication, although denitrification removal efficiency is inhibited by increasing external N loads. Phytoplankton in eutrophic lakes have become more responsive to N inputs relative to P, despite sustained increases in N loading. From a nutrient management perspective, this suggests a need to change the freshwater nutrient limitation and input reduction paradigms; a shift from an exclusive focus on P limitation to a dual N and P co-limitation and management strategy. The recent proliferation of toxic non-N₂-fixing CyanoHABs, and ever-increasing N and P legacy stores, argues for such a strategy if we are to mitigate eutrophication and CyanoHAB expansion globally.

Review: Toward management of urban ponds for freshwater biodiversity

Authors

Beat Oertli, Kirsten M. Parris

Many cities around the world are expanding and this trend in urbanization is expected to sharply increase over coming decades. At the same time, the integration of green and blue spaces is widely promoted in urban development, potentially offering numerous benefits for biodiversity. This is particularly relevant for urban waterbodies, a type of ecosystem present in most cities. However, site managers often lack the knowledge base to promote biodiversity in these waterbodies, which are generally created to provide other ecosystem services. To address this, our review presents guidelines for promoting biodiversity in urban ponds. We found a total of 516 publications indexed in ISI Web of Sciences related to this topic, of which 279 were retained for the purposes of our review. The biodiversity of urban ponds, measured by species richness, appears to be generally lower than in rural ponds; however, urban ponds often support threatened species. Furthermore, if well managed, urban ponds have the potential to support a much greater biodiversity than they currently do. Indeed, this review shows that a range of urban factors can impair or promote pond biodiversity, including many that can easily be controlled by site managers. Local factors include design (surface area, pond depth, banks and margins, shade, shoreline irregularity), water quality (conductivity, nutrients, heavy metals), and hydroperiod and biotic characteristics (stands of vegetation, fish, invasive species). Important regional factors include several indicators of urbanization (roads, buildings, density of population, impervious surfaces, car traffic), and the presence of other wetlands or green spaces in the surrounding landscape. We considered each of these factors and their potential impact on freshwater biodiversity. Taking into account the management measures listed in the publications reviewed, we have proposed a framework for the management of urban ponds, with guidelines to promote biodiversity and other ecosystem services, and to avoid ecosystem disservices or the creation of ecological traps. At the city scale, the biodiversity of a pondscape benefits from a high diversity of pond types, differing in their environmental characteristics and management.

Assessing future water–sediment interaction and critical area prioritization at sub-watershed level for sustainable management

Authors

Ashish Pandey, Santosh S. Palmate

Changes in the response of water and sediment have brought imbalances in present land resources as well as future management practices. Such critical areas need to be identified and prioritized for conservation and protection interventions. The Betwa River basin, located in the central part of India, has natural resources problems due to hydrologic changes. Thus, the present study has been focused on water–sediment interaction and prioritization of critical areas identified from a simulation using the Soil and Water Assessment Tool (SWAT). A downscaled and bias-corrected CMIP5 global climate model dataset has been used to simulate the water and sediment yields of the river basin. The analysis period was grouped into a 20-year period starting with a baseline of 1986 (from 1986 to 2005) and four future horizons, i.e. horizon 2020 (2020–2039), horizon 2040 (2040–2059), horizon 2060 (2060–2079) and horizon 2080 (2080–2099). Based on the sediment yield obtained from the SWAT simulation, identification of an empirical relationship and prioritization of critical areas were carried out. Results show that the relationship between annual water and sediment yields has a good correlation (R² = 0.75) for horizon 2020; however, a low correlation (R² = 0.63) was observed for horizon 2060. The analysis reveals that the water–sediment interaction will be affected due to changes of monsoon precipitation in future. Based on priority treatment, the critical sub-watersheds were identified and prioritized for the baseline as well as future climate horizons. Analysis shows that the sediment yield of sub-watersheds SW-5, SW-6, SW-11, SW-17, SW-18, SW-34 and SW-45 has increased with changing climate conditions. Further, these sub-watersheds would undergo changes in erosion class from moderate to very severe. Thus, the identified critical sub-watersheds for the baseline as well as for future climate conditions need to be considered for prioritization and management. The present approach can be used for sub-watershed-level sustainable planning and management.

 

Do benthic algae provide important information over and above that provided by macrophytes and phytoplankton in lake status assessment? – Results from a case study in Norway

Authors

Susanne C. Schneider, Dag Hjermann, Hanne Edvardsen

To test if phytobenthic algae provide additional important information to macrophytes and phytoplankton for lake monitoring, we sampled two large lakes in Norway. In each lake, we analyzed water chemistry and phytoplankton above the deepest site, recorded macrophytes and non-diatom phytobenthic algae at 20 sites around the shoreline and estimated site-specific nutrient input from land cover. Since no ready-to-use phytobenthos index exists for lakes in Norway, we tested the PIT index developed for rivers, commonly perceived signs of disturbance such as high algal cover, and taxon richness as well as similarity patterns. Both lakes were nutrient poor, but had potential local nutrient inputs (villages, agriculture). In neither of the lakes did phytobenthos indicate a worse overall ecological status than macrophytes and phytoplankton. Our data therefore, did not suggest that it would be useful to add phytobenthos into surveillance monitoring of lakes in Norway. There was a loose correlation between macrophyte and phytobenthic site-specific taxon richness and similarities. This means that macrophytes and phytobenthos do indeed give partly redundant information. High algal cover was found at sites with both high and low phosphorus input. Using algal cover as indicator of site-specific nutrient input is therefore overly simplistic. Urban and cultivated areas were associated with a more eutrophic PIT. This indicates that the PIT, despite being developed for lotic waters, may be used to detect site specific nutrient input in lakes.