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[en] Highlights: • Present day methods deliver new knowledge about socio-ecological past of the lake. • Long term investigation reveals shifting goal setting of restoration over time. • Different, intertwined temporal scales complicate lake restoration endeavors. • Interannual weather variability influences restoration endeavors. • Prevailing understandings influence the anticipated futures of the lake. - Abstract: The history and future of the restoration efforts at the hypereutrophic southern Finnish lake, Tuusulanjärvi, are investigated. The interdisciplinary study is conducted within a modified DPSIR- framework, which allows us to both trace back and envision the future of the dynamics of the complex socio-ecological processes involved in restoration. The study covers the time period from the early 1970s up to 2030. The longitudinal study integrates environmental historical, limnological, and futures studies. The analyses reveal the multiple time scales of social and ecological processes present in long term restoration, the changing perceptions of and emphasis on restoration goals and outcomes over time, and the challenges that incidental and uncertain parameters, such as weather conditions, pose to sustainable and efficient restoration endeavors.
[en] Ascertaining the phosphorus (P) release processes in polymictic lakes is one of the methodologically most complex questions in limnology. In the current study, we combined short- and long-term investigations to elucidate the role of sediments in the P budget in a chain of eutrophic lake basins. We quantified the internal loading of P in three basins of Lake Peipsi (Estonia/Russia) for two periods characterized by different external P loadings using radiometrically dated sediment cores (long-term studies). The relationships between different water quality variables and the internal P loading, and the external P loading were studied. Our short-term studies aimed at elucidating the possible mechanisms behind variations in internal P loading included examination of the surficial sediments, i.e., seasonal measurements of redox potential, sediment pore water P concentrations and diffusive fluxes. Our results provided evidence for a potentially high importance of internal P loading in regulating water quality. The sediment core analyses revealed an increase in the internal P loading during the period of lower external P loading coinciding with the general deterioration in the lake water quality (i.e, higher concentrations of soluble reactive phosphorus, total phosphorus and biomass of cyanobacteria). Increase in wave action between the two studied periods appeared to cause more frequent sediment resuspension, and thus be the most likely reason for the variations in internal P loading. Our short-term measurements indicated that resuspension events can be followed by a considerable increase in the diffusive fluxes. - Highlights: • Short- and long-term studies of sediment phosphorus (P) release were combined. • Internal P loading increased during the period of decreased external P loading. • An increase in internal P loading apparently caused deterioration of the lake water quality. • Resuspension event is followed by an increase in diffusive fluxes. • Increase in wave action was the most likely reason behind an increase in internal P loading.