Ecological preferences and distribution of Aulacoseira species in southeastern Brazilian reservoirs with varying trophic states were studied. One hundred and fourteen plankton samples (winter and summer) from 57 sites located in 16 reservoirs were analysed. Ten water quality parameters were measured. Ten Aulacoseira species were identified using light, scanning and transmission electron microscopy, and new information on their ecological preferences is provided here. Our results indicate that trophic gradient is the main driver of species distribution. Principal components analysis and calculation of weighted average nutrient optima revealed three indicator taxa, Aulacoseira tenella characteristic for oligotrophic waters and two varieties of Aulacoseira granulata (nominate and var. angustissima) typical for eutrophic reservoirs. This is the first ecological study of Aulacoseira in Brazil, adding information on the distribution of this genus in the tropics, and highlighting the need for species-level identification and regional studies to improve the use of diatoms in water quality assessment.

High Arctic ecosystems and Indigenous livelihoods are tightly linked and exposed to climate change, yet assessing their sensitivity requires a long-term perspective. Here, we assess the vulnerability of the North Water polynya, a unique seaice ecosystem that sustains the world’s northernmost Inuit communities and several keystone Arctic species. We reconstruct mid-to-late Holocene changes in sea ice, marine primary production, and little auk colony dynamics through multi-proxy analysis of marine and lake sediment cores. Our results suggest a productive ecosystem by 4400–4200 cal yrs b2k coincident with the arrival of the first humans in Greenland. Climate forcing during the late Holocene, leading to periods of polynya instability and marine productivity decline, is strikingly coeval with the human abandonment of Greenland from c. 2200–1200 cal yrs b2k. Our long-term perspective highlights the future decline of the North Water ecosystem, due to climate warming and changing sea-ice conditions, as an important climate change risk.

Aim: The study aimed at (a) contributing to a spatial evaluation of the Billings Complex water quality; (b) associating information on the geochemistry of the surface sediments; and (c) providing, based on previous studies, a temporal evaluation of the Complex's water quality since the Pinheiros River pumping restriction; Methods: sampling was performed at 12 sites: 2 in the Central body (CB), 3 in the Taquacetuba branch (TQ), 3 in the Rio Pequeno branch (RP) and 4 in the Rio Grande Reservoir (RG). Water samples were taken along a vertical profile during the winter (August 2009) and summer (February 2010) and in the surface sediments (2 cm) during the winter. Physical and chemical characteristics of water and sediments were evaluated. Lamparelli's Trophic State Index (TSI) was calculated; Results: limnological variability was mostly affected by the season. The spatial heterogeneity of the Complex was more pronounced during winter, with greater differences among its compartments. Nitrogen was higher in the winter, whereas in the summer there was a substantial phosphorus increase along with a nitrogen decrease. The most degraded compartments, associated with the highest nutrient levels, were CB and TQ. In contrast, the upstream region of the RP branch was considered a reference site (the least impacted) for the Complex; Conclusion: The Billings Complex ranged from mesotrophic (RP) or eutrophic (RG) to super-eutrophic (CC, TQ). High TSI variation also occurred within compartments and/or depending on the season, mainly associated with the human management of the Complex. The surface sediments underlined the differences observed between the extremes in the Billings Complex water quality, as well as providing additional information on other impacts that was not observed from the water analysis. A slight improvement in the water quality of the Central body and the Taquacetuba branch has been observed since 2009, possibly associated with the Pinheiros River flotation project.Resumo: Objetivos: Este estudo visa a (a) contribuir com a avaliação espacial da qualidade da água do Complexo Billings; (b) associar informações sobre a geoquímica dos sedimentos superficiais e (c) com base em literatura, fornecer uma avaliação temporal da qualidade da água no Complexo desde a restrição do bombeamento do Rio Pinheiros; Métodos: As amostragens foram realizadas em 12 locais: 2 no Corpo Central (CB), 3 no Braço Taquacetuba (TQ); 3 no Braço Rio Pequeno (RP) e 4 na Represa Rio Grande (RG). A coleta da água foi realizada ao longo do perfil vertical no período de inverno (agosto/2009) e verão (fevereiro/2010) e a dos sedimentos superficiais (2 cm), no inverno. Foram avaliadas características físicas e químicas da água e dos sedimentos, e foi calculado o índice de estado trófico (IET) de Lamparelli; Resultados: As condições limnológicas foram primordialmente influenciadas pelos períodos climáticos. No inverno, a heterogeneidade no Complexo foi mais definida com separação de seus compartimentos espaciais. Maior disponibilidade das formas nit...

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