Afrocymbella barkeri sp. nov. (Bacillariophyta), a common phytoplankton component of Lake Challa, a deep crater lake in East Africa

A new freshwater diatom, Afrocymbella barkeri Cocquyt & Ryken sp. nov., is described from Lake Challa, a deep and unproductive crater lake near Mt Kilimanjaro in equatorial East Africa, based on light and electron microscopic observations. This tropical diatom is a representative of the rather small genus Afrocymbella with only 12 known species and with a distribution restricted to the African Rift. Taxa belonging to this genus are heteropolar and characterized by dorsiventral valves curved along the pervalvar axis and the presence of small pseudosepta and septa on the open girdle bands. Afrocymbella barkeri was common only towards the end of the dry and windy season corresponding to northern hemisphere summer, when deep water-column mixing caused upwelling of nutrient-rich water from the hypolimnion. This taxon was observed free living in the water column during mixing, but the presence of a small apical pore field at the foot pole, along with some cells with mucilage stalks, suggests that its primary habitat probably involves attachment to a substrate

Ammonia and chromate interaction explains unresolved Hyalella azteca mortality in Flanders' sediment bioassays

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Mixtures of sediment chemical contaminants at freshwater sampling sites across Europe with different contaminant burdens

Extended chemical analyses of fluvial sediments were undertaken to establish the key pollutant pressures and mixtures present across nine European Union inland waterways. A wide range of chemical components and physical parameters were investigated including substances from the EU Priority List and Watch List. The data set was examined for key indicator compounds, however it was found that a wide range of pollution pressures were present in the different sediments including organic hydrocarbons, metal(loid)s, nutrients, polycyclic aromatic hydrocarbon (PAH), polychlorinated biphenyl (PCB) compounds, perfluoroalkyl and polyfluoroalkyl substances and pesticides, some of which exceeded regulatory guidance at different sampling points. The presence of such a wide range of compounds underpins the complex chemical composition of sediments that have acted as sinks for many decades absorbing contaminants from urban, industrial and agricultural sources. This dataset has been used to describe average overall toxicity of the sediments sampled, a calculation which was based on key components identified by Principal Component Analysis (PCA) and for those that had existing freshwater sediment regulatory values. A total of 33 components were used including PCBs, PAHs, metal(iod)s and pesticides. This analysis reflected the contamination of each site, with most indicating some level of toxicity during the sampling period. Watch List chemicals triclosan (TCS) and diclofenac (DIC) were also investigated; levels were relatively low, typically 10–100's ng L−1, however they were present at all sampling sites. The dataset is available as a resource for future chemical, and toxicological, sediment analysis comparisons