Expansion Of Cyanobacterial Blooms Research Articles

Hypoxia and its feedback response to algal blooms and CH4 emissions in subtropical reservoirs

Anthropogenic nutrient input stimulates surface eutrophication and algal blooms and thus exacerbates oxygen depletion and hypoxia in aquatic ecosystems. However, existing studies have paid little attention on the understanding of the feedback relationships among oxygen consumption, algal succession and greenhouse gas effect after river damming, particularly in Three Gorges Reservoir. This field work investigated the thermal stratification, water quality and phytoplankton in four tributaries (Pengxi Bay (PXB), Daning Bay (DNB), Shennong Bay (SNB), and Xiangxi Bay (XXB)) of the Three Gorges Reservoir (TGR) in spring (April 25-28, 2022), and explored the drivers of hypoxia and its feedback response to algal blooms and methane (CH4) emissions. The results showed that during the observation period, DO, thermal stratification, and algal blooms were more severe in PXB. The high Chemical Oxygen Demand (CODMn) (11.27 mg•L-1) and Dissolved Organic Carbon (DOC) content (7.56 mg•L-1) in PXB were the main causes of the progressive hypoxia. Furthermore, stronger density stratification in PXB inhibited the vertical supply of DO and accelerated bottom hypoxia. But the downslope density current replenished bottom DO in the upper reaches of the DNB, SNB, and XXB. The CH4 concentration was generally higher in hypoxia zone, especially in where cyanobacteria are the dominant species (eg., PX03 and PX04). Dam construction led to the succession of algal-dominant species, exerting a significant influence on the river carbon cycle. The expansion of cyanobacterial blooms and the consequence of metabolic substrates increase are gradually increasing oxygen deprivation, even hypoxia, and enhancing CH4 production in rivers. These findings suggest that the succession of algal-dominant species caused by river damming has a pronounced positive feedback effect on reservoir hypoxia processes and greenhouse effect.

Global expansion of toxic and non-toxic cyanobacteria: effect on ecosystem functioning

The recent invasion and proliferation of toxic cyanobacteria in diverse aquatic habitats is a well-known worldwide phenomenon. The expansion of cyanobacterial blooms have the potential to significantly alter the structure of the native community and to modify ecosystem functioning. Public and scientific attention was primarily given to the effect on the water quality due to a variety of toxic compounds that some species produce. However, the expansion of toxic and non-toxic cyanobacteria to a wide geographic range may have an impact on the ecosystems, trophic cascades and geochemical cycles. Here we briefly summarize the geographic expansion of cyanobacteria species. We further deliberate the physiological advantages of the invading cyanobacterial species and the ecological effect of cyanotoxins. We discuss recent studies on the contribution of cyanotoxins to the invasion process and the impact toxin producing cyanobacteria have on their newly invaded habitats, the effect of alien cyanobacteria on zooplankton and fish and on the diversity and complexity of the microbial community.

Spatial scale of cyanobacterial blooms in Old Providence Island, Colombian Caribbean

The frequency and expansion of cyanobacterial blooms have increased in coastal waters worldwide. These may be facilitated by excessive nutrient input and global warming, exerting negative consequences in marine ecosystems, communities and habitats. Although reports of cyanobacterial blooms are frequent, their causes, consequences and spatial extent are not completely understood, hence restricting regional management actions. From 2009 to 2012 we examined the spatial extent of cyanobacterial blooms in the reef systems off Providencia Island, Colombia. We also identified the main taxa involved in those blooms and evaluated bloom cover within substrate types. Blooms of benthic cyanobacteria consisted of complex microbial consortia belonging to the genera Okeania, Lyngbya, Symploca, Phormidium, Oscillatoria or Spirulina. Cyanobacteria were present in different ecosystems, geomorphological zones and substrate types, particularly at the northwest, east and southeast portions of the island. The soft bottoms, sea grasses and reef ecosystems around Providencia Island are subject to cyanobacterial blooms of varying intensity. There is a strong need to further study the frequency, scale and duration of these events to understand their impact on an ecosystem basis and on the services these provide.

Dynamics of cyanobacterial bloom formation during short-term hydrodynamic fluctuation in a large shallow, eutrophic, and wind-exposed Lake Taihu, China

Short-term hydrodynamic fluctuations caused by extreme weather events are expected to increase worldwide because of global climate change, and such fluctuations can strongly influence cyanobacterial blooms. In this study, the cyanobacterial bloom disappearance and reappearance in Lake Taihu, China, in response to short-term hydrodynamic fluctuations, was investigated by field sampling, long-term ecological records, high-frequency sensors and MODIS satellite images. The horizontal drift caused by the dominant easterly wind during the phytoplankton growth season was mainly responsible for cyanobacterial biomass accumulation in the western and northern regions of the lake and subsequent bloom formation over relatively long time scales. The cyanobacterial bloom changed slowly under calm or gentle wind conditions. In contrast, the short-term bloom events within a day were mainly caused by entrainment and disentrainment of cyanobacterial colonies by wind-induced hydrodynamics. Observation of a westerly event in Lake Taihu revealed that when the 30 min mean wind speed (flow speed) exceeded the threshold value of 6 m/s (5.7 cm/s), cyanobacteria in colonies were entrained by the wind-induced hydrodynamics. Subsequently, the vertical migration of cyanobacterial colonies was controlled by hydrodynamics, resulting in thorough mixing of algal biomass throughout the water depth and the eventual disappearance of surface blooms. Moreover, the intense mixing can also increase the chance for forming larger and more cyanobacterial colonies, namely, aggregation. Subsequently, when the hydrodynamics became weak, the cyanobacterial colonies continuously float upward without effective buoyancy regulation, and cause cyanobacterial bloom explosive expansion after the westerly. Furthermore, the results of this study indicate that the strong wind happening frequently during April and October can be an important cause of the formation and expansion of cyanobacterial blooms in Lake Taihu.

Contributions of meteorology to the phenology of cyanobacterial blooms: Implications for future climate change

Cyanobacterial blooms are often a result of eutrophication. Recently, however, their expansion has also been found to be associated with changes in climate. To elucidate the effects of climatic variables on the expansion of cyanobacterial blooms in Taihu, China, we analyzed the relationships between climatic variables and bloom events which were retrieved by satellite images. We then assessed the contribution of each climate variable to the phenology of blooms using multiple regression models. Our study demonstrates that retrieving ecological information from satellite images is meritorious for large-scale and long-term ecological research in freshwater ecosystems. Our results show that the phenological changes of blooms at an inter-annual scale are strongly linked to climate in Taihu during the past 23 yr. Cyanobacterial blooms occur earlier and last longer with the increase of temperature, sunshine hours, and global radiation and the decrease of wind speed. Furthermore, the duration increases when the daily averages of maximum, mean, and minimum temperature each exceed 20.3 °C, 16.7 °C, and 13.7 °C, respectively. Among these factors, sunshine hours and wind speed are the primary contributors to the onset of the blooms, explaining 84.6% of their variability over the past 23 yr. These factors are also good predictors of the variability in the duration of annual blooms and determined 58.9% of the variability in this parameter. Our results indicate that when nutrients are in sufficiently high quantities to sustain the formation of cyanobacterial blooms, climatic variables become crucial in predicting cyanobacterial bloom events. Climate changes should be considered when we evaluate how much the amount of nutrients should be reduced in Taihu for lake management.