The response of zooplankton and phytoplankton from the North American Great Lakes to filtration

Filtration of ballast water was investigated as a means of minimizing the introduction of nonindigenous zooplankton and phytoplankton by ships visiting the North American Great Lakes-St. Lawrence Seaway system (GLSLSS). An automatic backwash screen filtration (ABSF) system with nominal filtration options of 25, 50 or 100 μm was mounted on the deck of an operating Seaway-sized dry bulk carrier, the MV Algonorth. Water was pumped through the ABSF with a deck mounted pump at 341 m³ hr⁻¹ during routine ship operations in the GLSLSS, and effectiveness of the various screen pore sizes at removing taxonomic categories of zooplankton and phytoplankton was measured using matched treatment and control ballast tanks. The smallest pore sizes (25 and 50 μm) performed better than the 100 μm pore size at removing biological material. There was no difference in the filtration efficiency of the 25 and 50 μm screens relative to macro- or microzooplankton in these tests, but this result was probably due to low densities of macrozooplankton, and soft-bodied (aloricate) characteristics of the microzooplankton present. The 25 and 50 μm pore sizes were subjected to more controlled tests on board a stationary barge platform equipped with triplicate 700 L catchment bins moored in Duluth Harbor of Lake Superior. In these tests, filter pore size, organism size and rigidity influenced zooplankton removal efficiency by the ABSF. The 25 μm screen reduced both macrozooplankton and microzooplankton significantly more than the 50 μm screen. Zooplankton width was more determinative of filtration performance than length, and both filters removed loricate species of rotifers significantly more efficiently than aloricate species of the same length and width size classes. The 25 and 50 μm ABSF also significantly reduced algal densities, with the exception of colonial and filamentous green algae (50 μm only). Filter efficiency relative to algal particles was influenced by filter pore size, organism morphology and structure, and intake density, while algal particle size was not determinative. This research provides compelling evidence that 25 or 50 μm filtration is a potentially powerful means of reducing densities of organisms discharged by ships operating in the Great Lakes but an additional treatment step would be necessary to effectively minimize risk and meet the International Maritime Organization's discharge standards associated with organisms of all sizes in the water column.     

Inferring long-term nutrient changes in southeastern Ontario lakes: comparing paleolimnological and mass-balance models

Lake eutrophication continues to be a major concern in many lake regions, but long-term monitoring data are often lacking. Therefore, indirect proxy methods must be used to infer these missing data sets. Two methods were applied to infer pre-industrial and present-day lakewater total phosphorus concentrations (TP) in a suite of 50 hardwater lakes in southern Ontario (Canada). One method inferred TP from the diatom species composition in the tops (present-day inferences) and bottoms (pre-1850 inferences) of sediment cores. The other method applied the Lakeshore Capacity Model (LCM), which is a mass-balance model based on phosphorus export coefficients that relate lakes and their watershed characteristics to epilimnetic nutrient concentrations. Diatom-based estimates of preindustrial to present-day change show that 78% of the lakes increased in TP (29% significantly) and 8% decreased. According to model error, 63% of the lakes have not significantly changed. LCM estimates show that 56% of the lakes have increased in TP, and the remainder (44%) have not changed. The average inferred increase in TP was similar for both models, but a lake-by-lake comparison indicated marked differences in model output. In particular, a paired comparison of diatom-based and LCM-based inferences of preindustrial TP shows no correlation. It is suggested that lake managers be thorough when collecting data for either model, and model selection should be carefully considered. The LCM and diatom-based models perform better in regions that are geologically similar to where the respective models were calibrated. Advantages and disadvantages of each model are further discussed.     

Assessing the condition of the Missouri, Ohio, and Upper Mississippi rivers (USA) using diatom-based indicators

Diatom-based indicators were developed to assess environmental conditions in the Missouri, Ohio, and Upper Mississippi rivers. Disturbance gradients, comprising the first two principal components derived from a suite of stressor variables, included a trophic gradient (Trophic) and a gradient reflecting agriculture and other development activities (Ag/Dev). Diatom-based indicators were developed by creating models using weighted average calibration and regression-based transfer functions to relate planktonic and periphytic diatom species assemblages to each disturbance gradient. The most predictive disturbance models combined phytoplankton and periphyton assemblages into a single bioindicator model (observed versus inferred: Trophic $ r_{\text{boot}}^{2} = 0. 5 6 $ ; Ag/Dev $ r_{\text{boot}}^{2} = 0. 7 0 $ ). The geographic applicability of bioindicators was assessed by limiting sample geographical range during model calibrations. Geographic scale was limited by creating bioindicators using samples from: (a) each river, and (b) combined Mississippi/Missouri samples excluding Ohio River sites which were chemically unique. Indicator performance decreased with geographically restrictive models, therefore river basin-wide models, developed across all three rivers, is recommended. The most effective diatom-based disturbance bioindicators for this great river ecosystem could be applied using phytoplankton, periphyton, or combined assemblages to infer both trophic and agriculture/development disturbances.     

Regulation of self-renewal in normal and cancer stem cells

Mutations can confer a selective advantage on specific cells, enabling them to go through the multistep process that leads to malignant transformation. The cancer stem cell hypothesis postulates that only a small pool of low-cycling stem-like cells is necessary and sufficient to originate and develop the disease. Normal and cancer stem cells share important functional similarities such as 'self-renewal' and differentiation potential. However, normal and cancer stem cells have different biological behaviours, mainly because of a profound deregulation of self-renewal capability in cancer stem cells. Differences in mode of division, cell-cycle properties, replicative potential and handling of DNA damage, in addition to the activation/inactivation of cancer-specific molecular pathways confer on cancer stem cells a malignant phenotype. In the last decade, much effort has been devoted to unravel the complex dynamics underlying cancer stem cell-specific characteristics. However, further studies are required to identify cancer stem cell-specific markers and targets that can help to confirm the cancer stem cell hypothesis and develop novel cancer stem cell-based therapeutic approaches.     

p53 Loss in Breast Cancer Leads to Myc Activation,Increased Cell Plasticity,and Expression of a Mitotic Signature with Prognostic Value

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Algal assemblages for large river monitoring: Comparison among biovolume,absolute and relative abundance metrics

Periphyton and phytoplankton samples were collected and analyzed from 393 locations in three mid-continent (US) great rivers: the Upper Mississippi, Missouri and Ohio. From the 410 taxa identified, 303 taxa were common enough for multivariate analyses. Algae assemblages were quantified by multiple metrics including biovolume (based on algal shape formulae and cell measurements), relative biovolume, cell density, relative cell density, entity density (based on numbers of colonies, filaments or free-living cells), and relative entity density. Relationships between algal metrics and both water quality (e.g., nutrients, ionic properties, physicochemical parameters) and landscape-scale stressor data (e.g., proportions watershed with agriculture and urban development, impoundment, pollution point-sources) were examined using multivariate analyses. Overall, algal metrics were more closely related to water quality than to landscape stressors. Phytoplankton cell density was the best indicator of water quality with 45% of the variance in the taxonomic data explained. We suspect that relationships between periphyton and water quality were weaker because water grab samples did not reflect the prevailing conditions to which the periphyton had been exposed. Phytoplankton also had a slightly stronger relationship to landscape-scale stressor data than did periphyton. Biovolume metrics were the best periphytic indicators of water quality and stressors. Absolute algal metrics, especially cell density, consistently had stronger relationships to water quality and stressors than relative (percentage-based) metrics.     

Pelagic phytoplankton community change‐points across nutrient gradients and in response to invasive mussels

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Laurentian Great Lakes Phytoplankton and Their Water Quality Characteristics,Including a Diatom-Based Model for Paleoreconstruction of Phosphorus

Recent shifts in water quality and food web characteristics driven by anthropogenic impacts on the Laurentian Great Lakes warranted an examination of pelagic primary producers as tracers of environmental change. The distributions of the 263 common phytoplankton taxa were related to water quality variables to determine taxon-specific responses that may be useful in indicator models. A detailed checklist of taxa and their environmental optima are provided. Multivariate analyses indicated a strong relationship between total phosphorus (TP) and patterns in the diatom assemblages across the Great Lakes. Of the 118 common diatom taxa, 90 (76%) had a directional response along the TP gradient. We further evaluated a diatom-based transfer function for TP based on the weighted-average abundance of taxa, assuming unimodal distributions along the TP gradient. The r² between observed and inferred TP in the training dataset was 0.79. Substantial spatial and environmental autocorrelation within the training set of samples justified the need for further model validation. A randomization procedure indicated that the actual transfer function consistently performed better than functions based on reshuffled environmental data. Further, TP was minimally confounded by other environmental variables, as indicated by the relatively large amount of unique variance in the diatoms explained by TP. We demonstrated the effectiveness of the transfer function by hindcasting TP concentrations using fossil diatom assemblages in a Lake Superior sediment core. Passive, multivariate analysis of the fossil samples against the training set indicated that phosphorus was a strong determinant of historical diatom assemblages, verifying that the transfer function was suited to reconstruct past TP in Lake Superior. Collectively, these results showed that phytoplankton coefficients for water quality can be robust indicators of Great Lakes pelagic condition. The diatom-based transfer function can be used in lake management when retrospective data are needed for tracking long-term degradation, remediation and trajectories.