The ongoing lateral expansion of peatlands in Finland.

Peatlands are the most dense terrestrial carbon stock and since the last glacial epoch northern peatlands have accumulated between 400 and 1000 Gt of carbon. Although the horizontal development history of the peatlands during the Holocene has been previously researched, these studies have overlooked the current peatland margins. This has led to a long-standing view that the lateral expansion of the peatlands has halted or significantly slowed down. However, no concentrated effort focusing on the recent development of the peatland margins has been conducted. To fulfil this knowledge gap, we studied the development of peatland margins in five Finnish peatlands. In addition, we studied the effect of peatland subsoil characteristics and past forest fires on the peatland expansion. We sampled 15 transects with a total of 47 peat cores utilizing 14 C radiocarbon dating on the basal layers of these peat cores. Our results show that the Northern peatlands are still expanding with four of our study sites having recent, post-1950's basal ages in the peatland margins. In addition, the rate of peatland lateral expansion has increased during the last 1500 years in our study sites, challenging the current knowledge of the recent peatland expansion dynamics. We recorded lateral expansion rates of 0.1-6.4 cm/year from the sites studied. The rate of lateral expansion was restricted by local characteristics, especially the steepness of subsoil (p = .0108). Forest fires likely played an important role as the trigger for lateral expansion in southern study sites with large number of charcoal found at the basal layer of the peat cores. Depending on the scope of this recent lateral expansion across the vast northern peatlands, the effect on the carbon balance could be significant and should be taken into account when estimating the development of carbon pools in these crucial ecosystems.

Spatial and Temporal Patterns in Black Carbon Deposition to Dated Fennoscandian Arctic Lake Sediments from 1830 to 2010.

Black carbon (BC) is fine particulate matter produced by the incomplete combustion of biomass and fossil fuels. It has a strong climate warming effect that is amplified in the Arctic. Long-term trends of BC play an important role in assessing the climatic effects of BC and in model validation. However, few historical BC records exist from high latitudes. We present five lake-sediment soot-BC (SBC) records from the Fennoscandian Arctic and compare them with records of spheroidal carbonaceous fly-ash particles (SCPs), another BC component, for ca. the last 120 years. The records show spatial and temporal variation in SBC fluxes. Two northernmost lakes indicate declining values from 1960 to the present, which is consistent with modeled BC deposition and atmospheric measurements in the area. However, two lakes located closer to the Kola Peninsula (Russia) have recorded increasing SBC fluxes from 1970 to the present, which is likely caused by regional industrial emissions. The increasing trend is in agreement with a Svalbard ice-core-BC record. The results suggest that BC deposition in parts of the European Arctic may have increased over the last few decades, and further studies are needed to clarify the spatial extent of the increasing BC values and to ascertain the climatic implications.

Impacts of eutrophication on diatom life forms and species richness in coastal waters of the Baltic Sea.

Increased nutrient and sediment loading can affect the functioning and biodiversity of coastal ecosystems. Lacking long-term monitoring data, paleolimnological techniques enable the estimation of habitat and diversity change through time. Using these methods we assessed the effects of eutrophication on diatom community structure and species richness over the past ca. 200 years in coastal waters of the Gulf of Finland. The abundance of planktonic diatoms has increased markedly because of increased eutrophication and turbidity. The loss of benthic habitats resulted in a clear decrease in diatom species richness after a threshold of 400-600 microg L(-1) total dissolved nitrogen; no unimodal pattern between diversity and productivity was observed in our data. The urban sites displayed a marked decrease in species richness starting in the late 19th century with increased urbanization. A clear recovery was visible after the cessation of point source loading by the mid-1980s at two sites, whereas at the third site no recovery was detected because of diffuse loading from the large catchment. Changes in the rural sites were minor and did not start until the 1940s.

Multiple mining impacts induce widespread changes in ecosystem dynamics in a boreal lake.

In order to satisfy the needs of constant economic growth, the pressure to exploit natural resources has increased. Since accessible mineral resources are becoming scarce, the mining industry is constantly looking for novel techniques to allow commercial exploitation of lower-grade deposits. However, mining can have considerable impacts on freshwater ecosystems. Here, we present the ecological damage inflicted by mine water originating from the massive Terrafame Talvivaara polymetal mine (central Finland), where bioheap leaching is being applied to high-sulphur low-grade ore. We found that saline mine water has turned the lake meromictic, and sediment is heavily contaminated. As a result, important zooplankton and phytoplankton groups have been significantly altered. As the exploitation of poor-grade deposits is the future of the mining industry globally, water management should be taken to a higher level in order to proceed towards a sustainable mining sector.

Reliability of temperature signal in various climate indicators from northern Europe.

We collected relevant observational and measured annual-resolution time series dealing with climate in northern Europe, focusing in Finland. We analysed these series for the reliability of their temperature signal at annual and seasonal resolutions. Importantly, we analysed all of the indicators within the same statistical framework, which allows for their meaningful comparison. In this framework, we employed a cross-validation procedure designed to reduce the adverse effects of estimation bias that may inflate the reliability of various temperature indicators, especially when several indicators are used in a multiple regression model. In our data sets, timing of phenological observations and ice break-up were connected with spring, tree ring characteristics (width, density, carbon isotopic composition) with summer and ice formation with autumn temperatures. Baltic Sea ice extent and the duration of ice cover in different watercourses were good indicators of winter temperatures. Using combinations of various temperature indicator series resulted in reliable temperature signals for each of the four seasons, as well as a reliable annual temperature signal. The results hence demonstrated that we can obtain reliable temperature information over different seasons, using a careful selection of indicators, combining the results with regression analysis, and by determining the reliability of the obtained indicator.

Quantifying background nutrient concentrations in coastal waters: a case study from an urban embayment of the Baltic Sea.

Successful management of damaged coastal ecosystems requires reliable scientific evidence of their past state. Here we demonstrate that the sediment record of biotic indicators can be used to quantitatively reconstruct nutrient concentrations preceding the short time span covered by monitoring records. We generated a diatom-based weighted-averaging partial least squares transfer function model for total dissolved nitrogen with a prediction accuracy of 0.09 microg L(-1) (log10 units). The model was applied to sediment core data from Laajalahti Bay, an urban embayment in Helsinki, Finland, where its performance was validated against a approximately 30 yr record of water-quality data and known land-use changes in the watershed. The model tracked well the trends in the nutrient record, although it underestimated very high nutrient concentrations in this highly impacted embayment. The generally good agreement between the actual and predicted values implies that the approach has considerable potential in assessing background nutrient concentrations in coastal waters.

Climate-driven regime shifts in the biological communities of arctic lakes.

Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread species changes and ecological reorganizations in algae and invertebrate communities since approximately anno Domini 1850. The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes are primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. The widespread distribution and similar character of these changes indicate that the opportunity to study arctic ecosystems unaffected by human influences may have disappeared.