Cyanobacterial mass occurrences in freshwater lakes are generally formed by Anabaena, Microcystis, and Planktothrix, which may produce cyclic heptapeptide hepatotoxins, microcystins. Thus far, identification of the most potent microcystin producer in a lake has not been possible due to a lack of quantitative methods. The aim of this study was to identify the microcystin-producing genera and to determine the copy numbers of microcystin synthetase gene E (mcyE) in Lake Tuusulanjärvi and Lake Hiidenvesi in Finland by quantitative real-time PCR. The microcystin concentrations and cyanobacterial cell densities of these lakes were also determined. The microcystin concentrations correlated positively with the sum of Microcystis and Anabaena mcyE copy numbers from both Lake Tuusulanjärvi and Lake Hiidenvesi, indicating that mcyE gene copy numbers can be used as surrogates for hepatotoxic Microcystis and Anabaena. The main microcystin producer in Lake Tuusulanjärvi was Microcystis spp., since average Microcystis mcyE copy numbers were >30 times more abundant than those of Anabaena. Lake Hiidenvesi seemed to contain both nontoxic and toxic Anabaena as well as toxic Microcystis strains. Identifying the most potent microcystin producer in a lake could be valuable for designing lake restoration strategies, among other uses.

Estuaries are often seen as natural filters of riverine nitrate, but knowledge of this nitrogen sink in oligotrophic systems is limited. We measured spring and summer dinitrogen production (denitrification, anammox) in muddy and non-permeable sandy sediments of an oligotrophic estuary in the northern Baltic Sea, to estimate its function in mitigating the riverine nitrate load. Both sediment types had similar denitrification rates, and no anammox was detected. In spring at high nitrate loading, denitrification was limited by likely low availability of labile organic carbon. In summer, the average denitrification rate was ~138 μmol N m. The corresponding estuarine nitrogen removal for August was ~1.2 t, of which ~93% was removed by coupled nitrification−denitrification. Particulate matter in the estuary was mainly phytoplankton derived (> 70% in surface waters) and likely based on the riverine nitrate which was not removed by direct denitrification due to water column stratification. Subsequently settling particles served as a link between the otherwise uncoupled nitrate in surface waters and benthic nitrogen removal. We suggest that the riverine nitrate brought into the oligotrophic estuary during the spring flood is gradually, and with a time delay, removed by benthic denitrification after being temporarily 'trapped' in phytoplankton particulate matter. The oligotrophic system is not likely to face eutrophication from increasing nitrogen loading due to phosphorus limitation. In response, coupled nitrification−denitrification rates are likely to stay constant, which might increase the future export of nitrate to the open sea and decrease the estuary's function as a nitrogen sink relative to the load.

In order to establish a baseline for proxy-based reconstructions for the Young Sound–Tyrolerfjord system (Northeast Greenland), we analysed the spatial distribution of primary production and sea ice proxies in surface sediments from the fjord, against monitoring data from the Greenland Ecosystem Monitoring Programme. Clear spatial gradients in organic carbon and biogenic silica contents reflected marine influence, nutrient availability and river-induced turbidity, in good agreement with in situ measurements. The sea ice proxy IP25 was detected at all sites but at low concentrations, indicating that IP25 records from fjords need to be carefully considered and not directly compared to marine settings. The sea ice-associated biomarker HBI III revealed an open-water signature, with highest concentrations near the mid-July ice edge. This proxy evaluation is an important step towards reliable palaeoenvironmental reconstructions that will, ultimately, contribute to better predictions for this High Arctic ecosystem in a warming climate.

The effects of biomanipulation were studied in ten Finnish lakes to determine responses in fish and plankton communities and water quality after mass removal of cyprinids. From 1997 to 2001, the fish communities shifted from the dominance of large cyprinids to an explosion of small cyprinids and a higher proportion of piscivores in effectively biomanipulated lakes (>200 kg ha )1 3 yr )1 ). The biomass of cyanobacteria decreased, and the duration of the blooms shortened and shifted towards the autumn. Decreased concentrations and slower cycling of nutrients and increased grazing by cladocerans probably affected the declined biomass of cyanobacteria. Less intensive sediment disturbance and increased phosphorus-retention in fast growing fish biomass may have turned the role of the fish assemblage from 'nutrient recycler' to 'nutrient storage'. Increased potential grazing pressure, higher proportion of edible algae, and lower chlorophyll a:total phosphorus ratio indicated strengthened herbivore control. A high mass removal catch in relation to trophic state, low background turbidity, and bearable external loading favoured the successful biomanipulation, whereas intensive cyprinid reproduction, high nutrient loading and non-algal turbidity hindered the recovery. Three important issues should be noticed before biomanipulation in Finland: (1) careful selection of target lake, (2) well-planned, effective and long-lasting biomanipulation and (3) sustainable management of piscivores.

The eastern north coast of Greenland is considered to be highly sensitive to the ongoing Arctic warming, but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability. Here we present a detailed investigation of 11 biogenic proxies preserved in surface sediments from the remote High Arctic Wandel Sea shelf, the entrance to the Independence, Hagen, and Danmark fjords. The composition of organic matter (organic carbon, C:N ratios, δ13C, δ15N, biogenic silica, and IP25) and microfossil assemblages revealed an overall low primary production dominated by benthic diatoms, especially at the shallow sites. While the benthic and planktic foraminiferal assemblages underline the intrusion of chilled Atlantic waters into the deeper parts of the study area, the distribution of organic‐walled dinoflagellate cysts is controlled by the local bathymetry and sea ice conditions. The distribution of the dinoflagellate cyst Polarella glacialis matches that of seasonal sea ice and the specific biomarker IP25, highlighting the potential of this species for paleo sea ice studies. The information inferred from our multiproxy study has important implications for the interpretation of the biogenic‐proxy signal preserved in sediments from circum‐Arctic fjords and shelf regions and can serve as a baseline for future studies. This is the first study of its kind in this area.