An oligotrophic clearwater lake, initially characterized by a pronounced dominance of autotrophic phytoplankton and mostly by one species, the green alga Botryococcus, was subject to additions of dissolved organic carbon in the form of white sugar (sucrose) during two consecutive years. The hypothesis tested was that it is organic carbon per se, and not other possible effects of humic substances, that determines the differences in structure of the planktonic ecosystem between humic and clearwater lakes. The additions of DOC resulted in a significant increase in bacterial biomass and a decrease in the biomass of autotrophic phytoplankton. The biomass of mixotrophic and heterotrophic flagellates instead increased significantly, whereas no effects were found to propagate to higher trophic levels. As a result of the changes among biota, total planktonic biomass also decreased to a level typical of nearby humic lakes. We suggest that it is the carbon component of humic material and its utilization by bacterioplankton that determines the structure and function of the pelagic food web in humic lakes.

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Understanding how long-term abiotic and biotic processes are linked at a landscape level is of major interest for analyzing future impact on humans and the environment from present-day societal planning. This article uses results derived from multidisciplinary work at a coastal site in Sweden, with the aim of describing future landscape development. First, based on current and historical data, we identified climate change, shoreline displacement, and accumulation/erosion processes as the main drivers of landscape development. Second, site-specific information was combined with data from the Scandinavian region to build models that describe how the identified processes may affect the site development through time. Finally, the process models were combined to describe a whole interglacial period. With this article, we show how the landscape and ecosystem boundaries are affected by changing permafrost conditions, peat formation, sedimentation, human land use, and shoreline displacement.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-013-0407-5) contains supplementary material, which is available to authorized users.

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The transport of HCO,-, SO,'-, C1-, silica, particulate material, and organic material (total and dissolved) were compared in three rivers regulated for the expoitation of hydroelectric power and in three unregulated rivers in northern Sweden. This evaluation was done by statistical analysis of data derived from monthly sampling near the outlets of the rivers during the period 1972-1986. Significant differences due to regulation were found for particulate matter, total-P, Fe, and silica. Regulation decreased the transport by 10-50 per cent depending on the parameter and the river. The explanations for this effect are sedimentation of particles in impoundments and decreased erosion of the river bed due to the elimination of runoff during the snow melt period. The reduced transport of phosphorus may affect the productivity of the coastal zone of Bothnian Bay into which the rivers discharge.