Siliceous algae response to the “Great Acceleration” of the mid-20th century in Crawford Lake (Ontario, Canada): A potential candidate for the Anthropocene GSSP

Diatom and chrysophyte assemblages from varved sediments of meromictic Crawford Lake, Ontario record major environmental changes resulting from spatially broadening anthropogenic environmental stressors related to the “Great Acceleration” in the mid-20th century. Biannual assessment of diatom and chrysophyte assemblages over the last ~200 years allowed for rate of change analysis between adjacent samples that increased substantially during the mid-20th century, concurrent with significant generalized additive model trends. Changes in diatom and chrysophyte assemblages were likely driven by multiple anthropogenic stressors including local forestry harvesting, agriculture, and milling activities, acidic deposition from regional industrial processes, and anthropogenic climate warming. Novel siliceous algal assemblages now exist in Crawford Lake, likely related to the complexities of the above mentioned local and regional stressors. The major assemblage changes at the proposed base of the Anthropocene Epoch detected in this study support the laminated sequence from Crawford Lake as a strong potential candidate for the Anthropocene GSSP.

THE SAPROPELS OF THE UPPER VOLGA-SELIGER LANDSCAPE AND LIMNOLOGICAL AREA TVER REGION

В Верхневолжско-Селигерском ландшафтно-лимнологическом районе преобладают сапропелевые отложения биогенного и смешанного типа. На плёсах Селигера встречаются кремнеземистые среднезольные и высокозольные минерально-органические и органо-минеральные илы. В небольших и мелких озёрах района преобладают низкозольные кремнистые водорослевые сапропели. Сапропели кремнеземистого состава, содержат железа до 10 %, карбонатов - 1,5-3,0 %. Минерализация жидкой фазы составляет 1 г/л. In the Upper Volga-Seliger landscape-limnological area, sapropel deposits of hilly-moraine landscape of biogenic and mixed type predominate. On the Seliger ples, siliceous medium-ash and high-ash mineral-organic and organo-mineral silts are found. In small and shallow lakes of the Seliger system, low-ash siliceous algae sapropels predominate. Sapropels of silica composition, iron up to 10 %, carbonates - 1,5-3,0 %. Salinity of the liquid phase is 1 g/l.

What is diatomite?

Different types of biogenic remains, ranging from siliceous algae to carbonate precipitates, accumulate in the sediments of lakes and other aquatic ecosystems. Unicellular algae called diatoms, which form a siliceous test or frustule, are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments. When diatoms accumulate in large numbers in sediments, the fossilized remains can form diatomite. In sedimentological literature, “diatomite” is defined as a friable, light-coloured, sedimentary rock with a diatom content of at least 50%, however, in the Quaternary science literature diatomite is commonly used as a description of a sediment type that contains a “large” quantity of diatom frustules without a precise description of diatom abundance. Here we pose the question: What is diatomite? What quantity of diatoms define a sediment as diatomite? Is it an uncompacted sediment or a compacted sediment? We provide a short overview of prior practices and suggest that sediment with more than 50% of sediment weight comprised of diatom SiO2 and having high (>70%) porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated. Greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite, chert, and pure quartz.

Use of siliceous algae as biological monitors of heavy metal pollution in three lakes in a mining city, southeast China

In order to assess the ecological status of three lakes in a historical mining city (SE China), water metal concentrations and surface sedimentary diatoms and chrysophyte cysts were analyzed in 20 sampling sites. The significant correlations between the algal indices and the cumulative criterion unit (CCU) scores confirmed the importance of heavy metals in shaping algae communities. In the metal-polluted sites, diatom assemblages were dominated by metal-tolerant species, such as Nitzschia palea and Nitzschia perminuta. In the unpolluted samples, diatom assemblages were characterized by Cyclostephanos dubius, Discostella pseudostelligera and Aulacoseira species (mainly A. alpigena, A. granulata and A. ambigua). These dominant taxa in the unpolluted samples might be sensitive to metal contamination but tolerant of eutrophication. In addition, nonspherical cysts were much more abundant in the polluted sites, indicating that their presence should be indicative of metal contamination in this region. This study provides some clues for future metal pollution assessment through the use of siliceous algae in metal polluted lakes.

A 6-Yr Record of Nutrient Element Sedimentation and Recycling in Three North Temperate Lakes

Sedimentation of C, N, and P from the water column was assessed during the ice-free seasons of 1986–91 in three northern Wisconsin lakes. Seasonal trends in mass sedimentation were different among lakes but consistent from year to year within each lake. High rates of nutrient sedimentation were associated with spring and fall blooms of large siliceous algae. Nutrient recycling, calculated as the difference between uptake during photosynthesis and loss to sedimentation, showed seasonal trends that were related to sedimentation. Recycling within the water column was the most important source of nutrients to primary producers, accounting for 85–90% of P demand during the summer stratified period.