Prevention Of Algal Blooms Research Articles

Influence of algal organic matter in the in-situ flotation removal of Microcystis using positively charged bubbles

Positively charged bubbles efficiently capture and remove negatively charged algal cells without relying on coagulation-flocculation. However, the efficiency is notably influenced by the presence of algal organic matter (AOM). This study investigated the impact of AOM composition on flotation performance by analyzing AOM from various growth phases of Microcystis flos-aquae. The results indicated that low-concentration AOM (<5 mg C L-1), particularly the high molecular weight (>30 kDa) fractions containing high percentages of protein during the exponential growth phase, significantly improved the flotation efficiency by >18%. A high-speed camera system illustrates the pivotal role of low-concentration protein-containing AOM in forming network structures that enhance cell capture. These protein-driven network structures, which enhance the flotation efficiency, provide valuable insights into the development of effective in-situ algal bloom prevention techniques.

The influence mechanism of water level operation on algal blooms in canyon reservoirs and bloom prevention

The water level operation of reservoirs affects the spatiotemporal patterns of water quality, light-heat, hydrodynamics and phytoplankton, which have implications for algal bloom prevention. However, the theoretical analysis and practical applications of related research are limited. Based on prototype observations and numerical modeling, data on algae, water level operation and environmental factors in the Zipingpu Reservoir from April and September in 2015 to 2017 and 2020 to 2022 were collected. An in-depth analysis of the causal mechanisms between algal blooms and water level operation was performed, and prevention strategies with practical application assessments were developed. Water level operation control in the reservoir from April to September can be divided into five stages (falling-rising-oscillating-falling-rising), with algal blooms occurring only in the second stage. The rising water level with inflow into the middle layers shapes a closed-loop circulation in the surface waters. This distributes the nutrients that were trapped in the surface layer during the first stage, helping algae avoid to phosphorus limitation and thrive in the closed loop circulation, leading to algal blooms (chlorophyll-a exceeding 10 mg/m3). There is a significant positive correlation (p < 0.05) between algal blooms and the rapid rise in water levels in the second stage, occurring within a span of three days. To contain the algal bloom, a water level operation limit of rising waters on the third day after a two-day consecutive rise in water level was examined. This was found to be effective after its practical application to the case reservoir in 2022, with chlorophyll-a concentrations consistently below 10 mg/m3. This study unveils the mechanisms through which water level operation affects algal blooms and presents a successful case of bloom prevention. Furthermore, it serves as a valuable reference for the management of canyon reservoirs.

Variation of Local Wind Fields under the Background of Climate Change and Its Impact on Algal Blooms in Lake Taihu, China

Global climate change can greatly promote the continuing expansion of algal blooms in eutrophic inland lakes. Wind fields, an important climate factor, provide an external driving force for the movement of algal blooms. Based on algal bloom satellite imageries and wind observation data from 2003 to 2022, this study explored a quantitative assessment of the variations in surface wind fields and their impacts on the algal blooms in Lake Taihu, China. The results indicate that the mean wind speed at different time scales in the Lake Taihu area presents a continuous descending tendency in recent decades, which is the probable cause for the increasing frequency and severity of algal blooms in the lake. Wind fields affect the formation, location, and severity of algal blooms in diverse and complex ways. The area and frequency of algal blooms in Lake Taihu increase with the decrease in wind speed. The 6 h mean wind speed before 12:00 LT (Local Time) on the day of the algal bloom occurrence generally follows a Gaussian distribution, with a wind speed range of (0.6 m/s, 3.4 m/s) at the 95.5% confidence level. Accordingly, the wind speeds of 0.6 m/s and 3.4 m/s are identified to be the lower and upper critical wind speed indicators suitable for the formation of algal blooms, respectively. Another meaningful finding is that the outbreak of large-scale algal blooms requires stricter wind speed conditions, with a significantly lower wind speed threshold of around 2 m/s. Our study also demonstrates that the dominant wind direction of southeast in the region may be an important cause of the continuous water-quality decline and the high frequency and severity of algal blooms in the northwest waters of the lake. These findings will contribute to further studies on the dynamic mechanism of algal blooms and provide support for water environment management and algal bloom prevention and control.

Algal bloom prevention: Noteworthy public education

Algal bloom prevention: Noteworthy public education

Nitrogen addition enhances terrestrial phosphorous retention in grassland mesocosms

Nitrogen (N) and phosphorus (P) are fundamental for plant biomass production in grasslands, are often co-limiting, and have become major freshwater pollutants. By factorially applying gradients of N and P to field-based grassland mesocosms, we tested for saturating thresholds of plant uptake as nutrients increase and whether simultaneous and potentially additive growing-season demand reduces flows of dissolved nutrients to subsurface leachate. We quantified the seasonality of nutrient losses, differences in uptake by functional group (grasses, forbs), the impacts of increasing nutrients on root:shoot ratios, and contrasted vegetated and unvegetated treatments to isolate edaphic influences. Overall, most added nutrients were retained by plants and soil–80% for N and 99% for P. Co-limitation dynamics were powerful but asymmetrical with N additions reducing P in leachate, but P having little influence on N. N retention was primarily influenced by season—most N was lost prior to peak biomass when plant demand was presumably lower. Nutrients reduced root:shoot ratios by increasing foliage but with no detectable effect on retention, possible because root biomass remained unchanged. Similarly, there was no impact of functional group on nutrient loss. Despite substantial plant uptake, leachate concentrations of N and P still exceeded regional levels for safe drinking water and prevention of algal blooms. This work reveals how nutrient co-limitation can accelerate the capture of P by N in grasslands, indicating that plant uptake can significantly reduce dissolved subsurface nutrients. However, the offseason flows of N and the failure to meet regional water-quality standards despite capture levels as high as 99% reveal that vegetative-based solutions to nutrient capture by grasslands are important but likely insufficient without complimentary measures that reduce inputs.

Heavy Metals Exacerbate the Effect of Temperature on the Growth of Chlorella sp.: Implications on Algal Blooms and Management

With the accelerated urbanization and rapid development of the industrial and agricultural sectors, concern about the pollution of water environments is becoming more widespread. Algal blooms of varying sizes are becoming increasingly frequent in lakes and reservoirs; temperatures, nutrients, heavy metals, and dissolved oxygen are the factors that influence algal bloom occurrence. However, knowledge of the combined effect of heavy metals and temperature on algal growth remains limited. Thus, this study investigated how specific concentrations of heavy metals affect algal growth at different temperatures; to this end, two heavy metals were used (0.01 mg/L Pb2+ and 0.05 mg/L Cr6+) at three incubation temperatures (15, 25, and 30 °C) with the alga Chlorella sp. A higher incubation temperature contributed to a rise in soluble proteins, which promoted algal growth. The density of algal cells increased with temperature, and catalase (CAT) decreased with increasing temperature. Chlorella sp. growth and catalase activity were optimal at 30 °C (algal cell density: 1.46 × 107 cell/L; CAT activity: 29.98 gprot/L). Pb2+ and Cr6+ significantly promoted Chlorella sp. growth during incubation at 25 and 30 °C, respectively. At specific temperatures, 0.01 mg/L Pb2+ and 0.05 mg/L Cr6+ promoted the production of soluble proteins and, hence, the growth of Chlorella sp. The results provide a useful background for the mitigation and prevention of algal blooms.

Preemptive warning and control strategies for algal blooms in the downstream of Han River, China

Riverine blooms have become a challenging global environmental problem owing to strong disturbances from intensified human activities and the construction or operation of hydraulic projects. Previous studies mainly paid attention to algal blooms in the lakes and reservoirs, while less focused on the prediction and prevention of algal blooms in large rivers. As one of the highly regulated rivers in China, the downstream of Han River frequently occurred consecutive algal blooms in recent decades, was selected as the case study. Firstly, algal blooms in the downstream of Han River during 1992–2021 were investigated to find out the key environmental factors governing algal blooms. Secondly, the distribution lag model was applied to ascertain the time lag between key environmental factors and algal growth in January-April 2021. Thirdly, a random forest machine learning (RFML) model was established for prediction and early warning of river algal bloom. Finally, the threshold of controllable hydro-meteorological conditions and control strategies for the algal bloom prevention was proposed. Results reveal that: (1) The importance ranking of key environmental variables for algal bloom are antecedent air temperature, total phosphorus, flow discharge, total nitrogen, solar radiation and river turbidity; (2) The time-lag between algal growth and the key environmental drivers is the previous 1–5 days period; (3) The RFML model based on antecedent environmental variables can effectively predict the concentration of Chl-a; (4) The diatom bloom is very possible to outbreak if the 5-day sliding accumulated temperature is more than 43.13 °C and the average flow discharge is less than 780 m3/s. Our study may provide potential scientific guidance for the preemptive warning and control strategies of riverine blooms.

Quantitative assessment of the effects of human activities on phytoplankton communities in lakes and reservoirs

Global algal blooms have been severely threatening safety of drinking water and development of socio-economy. Effective prevention and accurate control of algal blooms require a quantitative assessment of the influence of human activities and identification of priority areas. However, previous studies on the quantitative assessment of the effects of human activities on algal communities are lacking, severely hindering the effective and precise control of algal blooms. This paper proposes a quantitative assessment model to evaluate the impact intensity of human activities on phytoplankton. Applications showed that the proliferation of phytoplankton were more limited by nutrients such as total phosphorus and ammonia where waters are less influenced by human activities, yet were less limited by these nutrients where there are highly intensive human activities. The density of phytoplankton in waters increased with an increase in human activity intensity, particularly in concentrated agricultural areas, which are priority areas for the prevention and control of algal blooms. The methodologies can clearly identify key areas for algal bloom prevention and control and can provide scientific evidence for water and nutrient management throughout the world, reducing the risk of algal blooms and ensuring aquatic ecosystem health and potable water safety.

Lab-scale Evaluation of Spiral Vortex Artificial Circulation

When phosphorus and nitrogen concentrations are high in lakes and reservoirs, enough for algae to grow, algal bloom prevention needs to be approached by circulation of stagnant water. A new circulation technology ‘Spiral vortex artificial circulation’ was developed that transports water to the surface without any hose and also provides sufficient oxygen as the water circulates. Artificial thermal and dissolved oxygen stratification was created in a water tank, and thermometers and DO meters were placed at each layer to evaluate the technology’s efficiency by comparing how fast the stratification broke. Two types of booster were used: a flow booster which promotes thorough mixing and a 12 cm flat round booster that protects the bottom of water column from disturbing, yet circulates the surface. Impeller speed was set at 60 rpm and 180 rpm to compare speed difference thus total of four experiments were conducted. The stratified water was completely mixed in two experiments with flow booster. However when 12 cm flat round booster was used at 60 rpm, even after 100 minutes of operation the stratification was not broken whereas it took 75 minutes at 180 rpm. The same or similar settings can be applied in situ without disturbing the benthic zone; if not, nutrients could be released to water bodies which might lead serious eutrophication. The further technology evaluation is in progress for improving its algal bloom suppression and energy efficiency since all technologies required to be environmentally sustainable.

Impacts of water level rise on algal bloom prevention in the tributary of Three Gorges Reservoir, China

Water level fluctuation plays an important role in algal blooms within the side arms. Field observations of the impacts of fluctuations of water level in Xiangxi Bay (XXB), one of the tributaries of the TGR, were analyzed from 2008 to 2010.Water level rise can result in increases as well as decreases in Chl. a, which depends on the water circulation patterns in the XXB. Those effective/ineffective water circulation patterns in preventing algal blooms in the XXB were based on the tributary inflow but also from the intrusion flow from the TGR. Flow velocity, thermal structure, hydrodynamic characteristics including water age, the turbulent eddy viscosity, the buoyancy frequency, the mixing depth, and the ratio of the euphotic depth and the mixed layer depth were evaluated for these scenarios. It is showed that the effective water circulation patterns in the XXB occurred when there was a converging of the inflow from the upstream with an intrusive overflow, lower-interflow, underflow or the combination from the TGR mainstream. Larger daily WL fluctuation and a longer duration of WL rise would enhance algal bloom prevention in the XXB. These results can provide assistance in managing the operation of water levels in TGR.

The Effect of Hydraulic Characteristics on Algal Bloom in an Artificial Seawater Canal: A Case Study in Songdo City, South Korea

Algal blooms have threatened the environmental functions of artificial seawater canals. Generally, water quality in a canal is managed by periodically circulating water from the sea into the canal. However, hydraulic characteristics from the canal design can interrupt the removal of algal blooms by water circulations in the canal. Accordingly, this study analyzed the effect of the hydraulic characteristics on algal blooms in an artificial seawater channel in Central Park, New Songdo City, Korea using a 3-D hydrodynamic model. Nutrients and velocity in stagnant areas in the canal were spatio-temporally measured. Algal bloom locations based on field monitoring mainly corresponded with areas of stagnant water and high vorticity in the z-direction, as determined by the numerical simulations. These results support that high vorticity interrupts the transfer water to the outer area when the canal water is in a stagnant condition. A high value of z-direction vorticity resulted in increased nutrient (total nitrogen (T-N) and total phosphorus (T-P)) availability, and sequentially increases the probability of algal bloom events. In this regard, this study will give a contribution to prevention of algal blooms in the artificial seawater canal.

Water Stratification Affects the Microeukaryotic Community in a Subtropical Deep Reservoir

Producers, consumers, and decomposers are the three key functional groups that form the basis of all ecosystems. But, little is known about how these functional groups coexist with each other in aquatic environments, particularly in subtropical reservoirs. In this study, we describe the nature of microeukaryotic communities in a subtropical deep reservoir during the strongly stratified period. Denaturing gradient gel electrophoresis gel band sequencing, pyrosequencing, and light microscopy were used together to facilitate an in-depth investigation of the community structure of phytoplankton, zooplankton, and fungi. Our results showed that thermal and oxygen stratification shaped the composition of the phytoplankton, zooplankton, and fungi populations in the reservoir. Stratification was evident among ecological functional groups in autumn: producers and consumers were overwhelmingly dominant in the epilimnion characterized by high temperatures and oxygen levels, whereas decomposers were inclined to inhabit the hypolimnion. These results contribute to our understanding of the relationship of ecosystem functional groups in the man-made aquatic systems and have important practical implications for reservoir management. Results suggest that the strategies for the control of eutrophication and harmful algal bloom prevention should focus on a fuller understanding of the consequences of both thermal stratification and vertical distribution of microplankton.

Temperature-induced activation of freshwater Cyanophage AS-1 prophage

Synechococcus sp. IU 625 is one of the freshwater cyanobacteria responsible for harmful algal blooms (HAB). Cyanophages can serve as natural control agents and may be responsible for algal bloom prevention and disappearance. Cyanophage AS-1, which infects Synechococcus sp. IU 625 (Anacystis nidulans) and Synechococcus cedrorum, plays an important role in the environment, significantly altering the numbers of its hosts. Since seasonal (temperature-dependent) lytic induction of cyanobacterial prophage has been proposed to affect seawater algal blooms, we investigated if the AS-1 lytic cycle could be induced by a shift to high temperature. Our hypothesis was confirmed, as more phages were released at 35°C than at 24°C, with maximal induction observed with a shift from 24 to 35°C. Furthermore, transmission electron microscopy (TEM) images provide direct evidence of lysogenic to lytic conversion with temperature shift. Thus, temperature is an important inducer for AS-1 conversion from lysogenic to lytic cycle and could have applications in terms of modulating cyanobacterial populations in freshwater aquatic environments. The study gives insight into the effect of climate change on the interaction between cyanophage and cyanobacteria in freshwater ecosystems.

A First Generation Stochastic Bioeconomic Analysis of Algal Bloom Control in a Coastal Lagoon (Sacca di Goro, Po River Delta)

Abstract. In this work we have developed a very simple stochastic mathematical model of Ulva spp. growth to quantitatively evaluate the economic costs of algal harvesting and the related benefits in terms of avoided‘economic loss’of clam production due to an effective prevention of algal blooms and the consequent anoxic crises. Algal growth was simulated by means of a discrete time difference equation of Ulva biomass where the finite growth rate depends only upon water temperature. In order to explicitly include environmental variability, a seasonal autoregressive model calibrated on available data was used to simulate water temperature. Different harvesting scenarios were analysed in terms of the number of harvesting vessels employed and the threshold biomass of Ulva at which vessels start to operate. Costs of algal harvesting and disposal, as well as monetary damages resulting from the collapse of clam production as a consequence of algal blooms, were assessed by interviewing the managers of the Clam Fishermen's Union of Goro. A Monte Carlo approach was used to estimate the mean and total statistical distribution of costs and benefits of different harvesting strategies. Our analysis shows that the most cost‐effective management policy is attained with 4–6 vessels operating at low algal density able to harvest as much Ulva as possible with intensive and short interventions at the beginning of the seasonal growth.