Examining the dynamics of phytoplankton biomass in Lake Tanganyika using Empirical Orthogonal Functions

The spatial and seasonal variations in phytoplankton concentrations can be pronounced in large tropical lakes and can have a direct impact on the regional communities in developing nations. Given the complex hydrodynamics and ecology of the African Great Lakes, there is a clear need for spatial databases to address their inter-annual and seasonal variability. In the past, phytoplankton studies in these extensive ecosystems focused mostly on point stations or lake transects repeated over several years. In the present work, satellite based reflectanceswere used to determine anomalies in chlorophyll related reflectance bands over a 7-year period for the whole of Lake Tanganyika. Empirical Orthogonal Function analysis was used to define regions with similar temporal co-variation of phytoplankton biomass. Using AutoRegressive Integrated Moving Average modelling techniques, it was possible to determine differences in phytoplankton dynamics and link these to climate and lake basin characteristics. An important shift in the phytoplankton seasonalitywas observed at the end of 2000, in concomitance to changes in wind and air temperatures which favoured entrainment of nutrients present in the deeper lake waters. This shift confirms the high sensitivity of the lake to climate change. The combination of extensive satellite based measurements with modelling approaches that consider both spatial and temporal dynamics is an important contribution to the understanding of long term changes in this important freshwater ecosystem

Relationships between wetland ecotones and inshore water quality in the Ugandan coast of Lake Victoria

Much of the lake shore in Lake Victoria is covered by extensive wetlands, often dominated by dense papyrus stands that extend out over the lake waters. These wetlands, their extension and management play a role in the physical, chemical and biological conditions of the inshore waters. Continuous transects along 180 km of shoreline together with spatial grids of sampling sites in eight bays were performed in the Ugandan inshore waters in order to analyze the relationships between the wetland characteristics and water quality. Measurements of extension of the wetland ecotones, water temperature (T), pH, Secchi disk depth (SD), dissolved oxygen (DO), total nitrogen (TN), total phosphorous (TP), dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and chlorophyll-a (CHL) were made in each sampling area. Data of T, pH and DO collected during the transects showed that the water characteristics of the bays differ from the open shoreline. Moreover, the magnitude of these physical–chemical differences is strongly conditioned by the dimension of the bordering wetlands. Bays with extensive wetlands ecotones were characterized by cooler, more acidic and poorly oxygenated waters. TN : TP ratios and especially DIN : SRP ratios decreased with the wetland presence along the coastline, showing a higher probability of N limitation in the inshore waters where large wetlands are present. Results point to denitrification processes in the wetland ecotones as the cause of this trend. The distribution of CHL was found to be highest in the presence of two significant point loading sources: a river (in Katonga Bay) and a major population centre (Kampala, in Murchison Bay). The reduction of external P loading is shown as an important step in the management of the eutrophication process of Lake Victoria inshore waters

Optimized extraction of daily bio-optical time series derived from MODIS/Aqua imagery for Lake Tanganyika, Africa

Lake Tanganyika is one of the world’s great freshwater ecosystems. In recent decades its hydrodynamic characteristics have undergone important changes that have had consequences on the Lake’s primary productivity. The establishment of a long-term Ocean Color dataset for Lake Tanganyika is a fundamental tool for understanding and monitoring these changes. We develop an alternative approach to create a regionally calibrated dataset of chlorophyll-a concentrations (CHL) and attenuation coefficients at 490 nm (K490) for the period from July 2002 to December 2006 using daily calibrated radiances retrieved from the MODIS-Aqua sensor. Standard MODIS Aqua Ocean Color products were found to not provide a suitable calibration for high altitude lakes such as the Lake Tanganyika. The optimization of the extraction process and the validation of the dataset were performed with independent sets of in situ measurements. Our results show that for geographical, atmospheric and optical conditions of Lake Tanganyika: (i) the coastal aerosol model set with a high relative humidity (90%) performs the best for the atmospheric correction; (ii) a significant correlation between in situ data and CHL estimates using the MODIS specific 0C3 algorithm is possible; (iii) K490 estimates provide a good level of significance. The development of a validated time series of bio-optical properties provides an important information base for the study of lake dynamics and interannual trends

The microalgae Tetraselmis suecica in mesocosms under different light regimes

Pigment profiles and pheopigment accumulation of the microalga Tetraselmis suecica were studied under different spectral irradiances. Irradiance conditions typical of coastal waters with (‘clear’) and without (‘coloured’) chromophoric dissolved organic matter (C-DOM) were simulated in mesocosm cultures. The lag, growth and stationary phases were found to follow a logistic model, as light limitation controlled growth where maximum carrying capacity and incremental growth were sensitive to irradiance conditions, both being higher in mesocosms with full irradiance conditions (clear sea conditions without attenuation due to C-DOM). Through daily measurements of chlorophylls, carotenoids and pheopigments, it was found that the highest concentrations of pigments occurred in the growth phase: in particular in the clear sea conditions. Lower concentrations of lutein were measured in the coloured mesocosms showing their protective function against photo-oxidation. Pheopigment concentrations increased linearly throughout the experiment, being highest in the mesocosm with clear sea conditions. In general, clear sea conditions, including ultraviolet irradiance, showed the higher production of primary and secondary pigments, demonstrating the high tolerability of T. suecica to a range of solar irradiance conditions

Longitudinal Assessment of Intravoxel Incoherent Motion Diffusion-Weighted MRI Metrics in Cognitive Decline.

BACKGROUND: Advanced diffusion-based MRI biomarkers may provide insight into microstructural and perfusion changes associated with neurodegeneration and cognitive decline. PURPOSE: To assess longitudinal microstructural and perfusion changes using apparent diffusion coefficient (ADC) and intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) parameters in cognitively impaired (CI) and healthy control (HC) groups. STUDY TYPE: Prospective/longitudinal. POPULATION: Twelve CI patients (75% female) and 13 HC subjects (69% female). FIELD STRENGTH/SEQUENCE: 3 T; Spin-Echo-IVIM-DWI. ASSESSMENT: Two MRI scans were performed with a 12-month interval. ADC and IVIM-DWI metrics (diffusion coefficient [D] and perfusion fraction [f]) were generated from monoexponential and biexponential fits, respectively. Additionally, voxel-based correlations were evaluated between change in Montreal Cognitive Assessment (ΔMoCA) and baseline imaging parameters. STATISTICAL TESTS: Analysis of covariance with sex and age as covariates was performed for main effects of group and time (false discovery rate [FDR] corrected) with post hoc comparisons using Bonferroni correction. Partial-η RESULTS: Significant differences were found for the main effects of group (HC vs. CI) and time. For group effects, higher ADC, IVIM-D, and IVIM-f were observed in the CI group compared to HC (ADC: 1.23 ± 0.08 DATA CONCLUSION: These findings demonstrate that longitudinal differences between CI and HC cohorts can be measured using IVIM-based metrics. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 2

Preliminary Assessment of Intravoxel Incoherent Motion Diffusion-Weighted MRI (IVIM-DWI) Metrics in Alzheimer\u27s Disease

Background: Alzheimer\u27s disease (AD) is a progressive neurodegenerative disease that affects aging populations. Current MRI techniques are often limited in their sensitivity to underlying neuropathological changes. Purpose: To characterize differences in voxel-based morphometry (VBM), apparent diffusion coefficient (ADC), and intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) metrics in aging populations. Additionally, to investigate the connection between cognitive assessments and neuroimaging metrics. Study Type: Prospective/cross-sectional. Population: In all, 49 subjects, including 13 with AD dementia, 12 with mild cognitive impairment (MCI), and 24 healthy controls (HC). Field Strength/Sequence: 3T/magnetization-prepared rapid acquisition gradient echo (MP-RAGE) and IVIM-DWI. Assessment: All participants completed a cognitive screening battery prior to MRI. IVIM-DWI maps (pure diffusion coefficient [D], pseudodiffusion coefficient [D*], and perfusion fraction [f]) were generated from a biexponential fit of diffusion MRI data. VBM was performed on the standard T1-weighted MP-RAGE structural images. Group-wise templates were used to compare across groups. Statistical Tests: Analysis of covariance (ANCOVA) with gender and age as covariates (familywise error [FWE] corrected, post-hoc comparisons using Bonferroni correction) for group comparisons. Partial-η2 and Hedges\u27 g were used for effect-size analysis. Spearman\u27s correlations (false discovery rate [FDR]-corrected) for the relationship between cognitive scores and imaging. Results: Clusters of significant group-wise differences were found mainly in the temporal lobe, hippocampus, and amygdala using all VBM and IVIM methods (P \u3c 0.05 FWE). While VBM showed significant changes between MCI and AD groups and between HC and AD groups, no significant clusters were observed between HC and MCI using VBM. ADC and IVIM-D demonstrated significant changes, at P \u3c 0.05 FWE, between HC and MCI, notably in the amygdala and hippocampus. Several voxel-based correlations were observed between neuroimaging metrics and cognitive tests within the cognitively impaired groups (P \u3c 0.05 FDR). Data Conclusion: These findings suggest that IVIM-DWI metrics may be earlier biomarkers for AD-related changes than VBM. The use of these techniques may provide novel insight into subvoxel neurodegenerative processes. Level of Evidence: 2. Technical Efficacy Stage: 2 J. MAGN. RESON. IMAGING 2020;52:1811–1826

L'italiano della canzone

Il volume esamina le caratteristiche dell'attuale italiano per musica, che \ue8 molto cambiato non solo rispetto alle tradizionali arie d'opera e alla canzone della prima met\ue0 del Novecento, ma anche nel corso di questi ultimi decenni, in cui la cosiddetta \u201cmusica leggera\u201d ha assunto un\u2019importanza sempre maggiore. Il problema di fondo, per\uf2, \ue8 uguale da secoli: l\u2019italiano \ue8 la lingua della musica per eccellenza, ma nello stesso tempo, quando \ue8 cantato, deve spesso rinunciare al proprio ritmo naturale. Infatti, la musica costringe a selezionare in modo drastico le parole utilizzabili alla fine dei versi e, pi\uf9 in generale, i testi di canzone devono di solito sottomettersi a regole che li rendono molto meno efficaci se sono considerati di per s\ue9, come fossero poesie tradizionali. Il volume passa in rassegna le scelte stilistiche, i metodi e talvolta gli stratagemmi con cui le canzoni moderne affrontano il problema