Plankton metabolism and sedimentation in a small boreal lake — a long-term perspective

We used weekly or biweekly data from the years 1990–2009 to analyse variation in primary production (PP), chlorophyll a (Chl) and respiration (R) of plankton, and organic matter sedimentation (S) in a small boreal lake with intense water colour. PP and S had a decreasing trend over the study period while no trend was found in Chl and R. PP and R were in balance except during the last five years when R > PP. The results indicated that light limited PP, while occasionally phosphorus, nitrogen and/or dissolved inorganic carbon could also act as limiting factors. The decrease in S coincided with that of PP although during the last five years allochthonous organic matter load seemed to compensate for the decrease in PP. Weather and hydrological conditions were the key drivers in modifying the properties of the lake while the metabolic processes were intercorrelated, and R correlated strongly with water temperature.