THE EFFECT OF TEMPERATURE ON SPECIFIC GROWTH RATE AND ACTIVATION ENERGY OF MICROCYSTIS AND SYNECHOCOCCUS ISOLATES RELEVANT TO THE ONSET OF NATURAL BLOOMS

A comparative study of metatranscriptomic assessment methods to characterize Microcystis blooms

Harmful algal blooms are increasing in duration and severity globally, resulting in increased research interest. The use of genetic sequencing technologies has provided a wealth of opportunity to advance knowledge, but also poses a risk to that knowledge if handled incorrectly. The vast numbers of sequence processing tools and protocols provide a method to test nearly every hypothesis, but each method has inherent strengths and weaknesses. Here, we tested six methods to classify and quantify metatranscriptomic activity from a harmful algal bloom dominated by Microcystis spp. Three online tools were evaluated (Kaiju, MG-RAST, and GhostKOALA) in addition to three local tools that included a command line BLASTx approach, recruitment of reads to individual Microcystis genomes, and recruitment to a combined Microcystis composite genome generated from sequenced isolates with complete, closed genomes. Based on the analysis of each tool presented in this study, two recommendations are made that are dependent on the hypothesis to be tested. For researchers only interested in the function and physiology of Microcystis spp., read recruitments to the composite genome, referred to as "Frankenstein's Microcystis", provided the highest total estimates of transcript expression. However, for researchers interested in the entire bloom microbiome, the online GhostKOALA annotation tool, followed by subsequent read recruitments, provided functional and taxonomic characterization, in addition to transcript expression estimates. This study highlights the critical need for careful evaluation of methods before data analysis.

Seasonal dynamics of water bloom-forming Microcystis morphospecies and the associated extracellular microcystin concentrations in large, shallow, eutrophic Dianchi Lake

The increasing occurrence of Microcystis blooms is of great concern to public health and ecosystem due to the potential hepatotoxic microcystins (MCs) produced by these colonial cyanobacteria. In order to interpret the relationships between variations of Microcystis morphospecies and extracellular MC concentrations, the seasonal dynamics of phytoplankton community composition, MC concentrations, and environmental parameters were monitored monthly from August, 2009 to July, 2010. The results indicated that Microcystis dominated total phytoplankton abundance from May to December (96%-99% of total biovolume), with toxic Microcystis viridis and non-toxic Microcystis wesenbergii dominating after July (constituting 65%-95% of the Microcystis population), followed by M. viridis as the sole dominant species from November to January (49%-93%). Correlation analysis revealed that water temperature and nutrient were the most important variables accounting for the occurrence of M. wesenbergii, while the dominance of M. viridis was related with nitrite and nitrate. The relatively low content of MCs was explained by the association with a large proportion of M. viridis and M. wesenbergii, small colony size of Microcystis populations, and low water temperature, pH and dissolved oxygen. The extracellular MC (mean of 0.5±0.2μg/L) of water samples analyzed by enzyme-linked immunosorbent assay (ELISA) demonstrated the low concentrations of MC in Dianchi Lake which implied the low potential risk for human health in the basin. The survey provides the first whole lake study of the occurrence and seasonal variability of Microcystis population and extracellular MCs that are of particular interest for water quality monitoring and management.

Environmental factors influencing cyanobacteria community structure in Dongping Lake, China

The present study was conducted to provide a detailed understanding of the variation in cyanobacterial communities of Dongping Lake, which is the final water volume adjusting and storing lake in the east route of the South-to-North Water Diversion Project in China. The spatial and temporal distribution of cyanobacteria was assessed from May 2010 to October 2012 based on monthly samples collected from three stations. Over the 30-month survey, 15 genera and 25 species of cyanobacteria were identified, with cyanobacterial abundance at each monitoring station ranging from undetected to 3.04x10(7) cells/L, average of 4.27x10(6) cells/L. The dominant cyanobacterial species were Pseudanabaena limnetica and Aphanizomenon issatschenkoi and not the usual bloom-forming genera such as Microcystis and Anabaena. Cyanobacterial community structure and water quality variables exhibited substantial changes over the period of survey. Redundancy analysis, Pearson correlations, and regression analysis were applied to analyze the relationships among the variables. The results suggested that temperature and chemical oxygen demand were key drivers of the cyanobacterial community composition in Dongping Lake. In addition, the concentration of inorganic nitrogen in the lake had a profound effect on the cyanobacterial abundance as a non-limiting factor in warm periods.

Variation of cyanobacteria with different environmental conditions in Nansi Lake, China

Nansi Lake is located on the east line of the South-to-North Water Diversion Project in China. A comprehensive study was carried out to investigate the spatial and temporal distribution of cyanobacteria in the lake from June 2008 to May 2011 based on monthly sample monitoring from five stations. The effect of environmental factors on cyanobacterial abundance was also evaluated. The cyanobacterial community contained 15 genera and 23 species. The cyanobacterial abundance of each monitoring station ranged from 0 to 1.53 x 10(7) cells/L with an average of 1.45 x 10(6) cells/L, which accounted for 11.66% of the total phytoplankton abundance. The dominant species of cyanobacteria were Pseudanabaena (32.94%) and Merismopedia (19.85%), not the bloom-forming algae such as Microcystis and Anabaena. In addition, the cyanobacterial community structure and water quality variables changed substantially over the survey period. Redundancy analysis (RDA) suggested that temperature and phosphorus were important environmental factors that affected cyanobacteria. Temperature was the most important factor affecting cyanobacterial abundance. The effect of phosphorus on cyanobacterial abundance was more notable in warm periods than in periods with low temperature.

Estimating cyanobacterial bloom transport by coupling remotely sensed imagery and a hydrodynamic model

The ability to forecast the transport of harmful cyanobacterial blooms in the Laurentian Great Lakes is beneficial to natural resource managers concerned with public health. This manuscript describes a method that improves the prediction of cyanobacterial bloom transport with the use of a preoperational hydrodynamic model and high temporal resolution satellite imagery. Two scenarios were examined from separate cyanobacterial blooms in western Lake Erie, USA. The first scenario modeled bloom position and extent over the span of 13 days. A geographic center, or centroid, was calculated and assigned to the bloom from observed satellite imagery. The bloom centroid was projected forward in time, and the projected position was compared to the final observed bloom centroid. Image pixels flagged as cyanobacterial bloom were compared between the initial image and the final image, and this was assumed as persistence. The second bloom scenario was modeled for a period of 12 days, and the results were framed in an ecological context in an effort to gain further understanding of cyanobacterial bloom dynamics. These modeling techniques can be incorporated into an operational forecasting system.

Tailoring dam structures to water quality predictions in new reservoir projects: assisting decision-making using numerical modeling

Selection of reservoir location, the floodable basin forest handling, and the design of dam structures devoted to water supply (e.g. water outlets) constitute relevant features which strongly determine water quality and frequently demand management strategies to be adopted. Although these crucial aspects should be carefully examined during dam design before construction, currently the development of ad hoc limnological studies tailoring dam location and dam structures to the water quality characteristics expected in the future reservoir is not typical practice. In this study, we use numerical simulation to assist on the design of a new dam project in Spain with the aim of maximizing the quality of the water supplied by the future reservoir. First, we ran a well-known coupled hydrodynamic and biogeochemical dynamic numerical model (DYRESM-CAEDYM) to simulate the potential development of anoxic layers in the future reservoir. Then, we generated several scenarios corresponding to different potential hydraulic conditions and outlet configurations. Second, we built a simplified numerical model to simulate the development of the hypolimnetic oxygen content during the maturation stage after the first reservoir filling, taking into consideration the degradation of the terrestrial organic matter flooded and the adoption of different forest handling scenarios. Results are discussed in terms of reservoir design and water quality management. The combination of hypolimnetic withdrawal from two deep outlets and the removal of all the valuable terrestrial vegetal biomass before flooding resulted in the best water quality scenario.