Search results for "järvet"
showing 10 items of 116 documents
Järvisedimenttien iänmääritys lyijyajoituksella
2013
Radioaktiivisuudella tarkoitetaan epästabiilin ytimen hajoamista toiseksi ytimeksi. Käytännössä ydin voi hajota kolmella perusprosessilla; alfa-, beeta tai gammahajoamisella, joista gammahajoamisessa virittyneen ytimen viritystila purkautuu emittoimalla gammahiukkasen, fotonin, jonka energia vastaa viritystilan tai viritystilojen välistä energiaa. Lyijyn isotoopin 210Pb (puoliintumisaika noin 22 vuotta) gammahajoamiseen perustuvalla lyijyajoituksella voidaan määrittää järvenpohjien sedimenttikerrosten ikä syvyyden funktiona. Sedimentteihin 210Pb kertyy kahdella tavalla: hajoamalla radioaktiivisesti maaperässä olevasta radiumista sekä ilmakehästä suoraan esimerkiksi sateiden välityksellä tai…
Toxicity of Mining-Contaminated Lake Sediments to Lumbriculus variegatus
2021
AbstractBoreal lakes with soft water and low buffering capacity are susceptible to excess ion loading resulting from metal mining. The impact of two Finish mining sites in downstream lakes was assessed with a chronic sediment toxicity test using a laboratory-reared freshwater Lumbriculus variegatus (Oligochaeta). The test organisms were exposed to mining-contaminated natural lake sediments and hypolimnion water (HLW) or artificial freshwater (AFW) as overlying water in two independent experimental setups. In both test setups, growth and reproduction of L. variegatus were lower in sediments from the lakes receiving high amount of mining effluents from the mines nearby. In the biomining site,…
Cyanobacteria and their metabolites in mono- and polidominant shallow eutrophic temperate lakes
2022
Monodominant (one species dominates) or polidominant (multiple species dominate) cyanobacterial blooms are pronounced in productive freshwater ecosystems and pose a potential threat to the biota due to the synthesis of toxins. Seasonal changes in cyanobacteria species and cyanometabolites composition were studied in two shallow temperate eutrophic lakes. Data on cyanobacteria biomass and diversity of dominant species in the lakes were combined with chemical and molecular analyses of fifteen potentially toxin-producing cyanobacteria species (248 isolates from the lakes). Anatoxin-a, saxitoxin, microcystins and other non-ribosomal peptides formed the diverse profiles in monodominant (Planktot…
Vertical stratification patterns of methanotrophs and their genetic controllers in water columns of oxygen-stratified boreal lakes
2021
ABSTRACT The vertical structuring of methanotrophic communities and its genetic controllers remain understudied in the water columns of oxygen-stratified lakes. Therefore, we used 16S rRNA gene sequencing to study the vertical stratification patterns of methanotrophs in two boreal lakes, Lake Kuivajärvi and Lake Lovojärvi. Furthermore, metagenomic analyses were performed to assess the genomic characteristics of methanotrophs in Lovojärvi and the previously studied Lake Alinen Mustajärvi. The methanotroph communities were vertically structured along the oxygen gradient. Alphaproteobacterial methanotrophs preferred oxic water layers, while Methylococcales methanotrophs, consisting of putative…
Variability in δ13C values between individual Daphnia ephippia: Implications for palaeo-studies
2018
The stable carbon isotope ratio (δ13C value) of Daphnia spp. resting egg shells (ephippia) provides information on past changes in Daphnia diet. Measurements are typically performed on samples of ≥20 ephippia, which obscures the range of values associated with individual ephippia. Using a recently developed laser ablation-based technique, we perform multiple δ13C analyses on individual ephippia, which show a high degree of reproducibility (standard deviations 0.1–0.5‰). We further measured δ13C values of 13 ephippia from surface sediments of three Swiss lakes. In the well-oxygenated lake with low methane concentrations, δ13C values are close to values typical for algae (−31.4‰) and the rang…
Unveiling distribution patterns of freshwater phytoplankton by a next generation sequencing based approach.
2012
The recognition and discrimination of phytoplankton species is one of the foundations of freshwater biodiversity research and environmental monitoring. This step is frequently a bottleneck in the analytical chain from sampling to data analysis and subsequent environmental status evaluation. Here we present phytoplankton diversity data from 49 lakes including three seasonal surveys assessed by next generation sequencing (NGS) of 16S ribosomal RNA chloroplast and cyanobacterial gene amplicons and also compare part of these datasets with identification based on morphology. Direct comparison of NGS to microscopic data from three time-series showed that NGS was able to capture the seasonality in…
Comprehensive dataset of shotgun metagenomes from oxygen stratified freshwater lakes and ponds
2021
Stratified lakes and ponds featuring steep oxygen gradients are significant net sources of greenhouse gases and hotspots in the carbon cycle. Despite their significant biogeochemical roles, the microbial communities, especially in the oxygen depleted compartments, are poorly known. Here, we present a comprehensive dataset including 267 shotgun metagenomes from 41 stratified lakes and ponds mainly located in the boreal and subarctic regions, but also including one tropical reservoir and one temperate lake. For most lakes and ponds, the data includes a vertical sample set spanning from the oxic surface to the anoxic bottom layer. The majority of the samples were collected during the open wate…