The characteristics of sinking materials and the formation of bottom deposits in a eutrophic lake

Summary

Investigations carried out in the eutrophic lake Mikolajki were aimed at discovering seasonal variations and spatial differentiation and also the chemical composition of tripton sedimentation. Sediment traps placed in different stations in the lake and at different depths were used for measuring the amount of sinking tripton. Considerable variations were found in the amount of sinking tripton over the yearly cycle, but very small differentiation between one site and another. Both the amount and the composition of tripton are directly dependent on mass appearances of phytoplankton dominants and their chemical composition. It was found that about 1500 g of dry mass of tripton reaches 1 m² of the bottom surface over the course of a year. The energy value of tripton was examined by burning samples in an oxygen calorimetric bomb, and parallel to this by calculation from the composition of organic matter (proteins, fats, carbohydrates — proximate analysis). Comparison of the two methods showed that caloritic values obtained from calculations on the basis of organic matter composition are greater — estimated on an average by 30%. It was found that about 2000 Kcal reach 1 m² of bottom surface in a year. Comparing the number of calories contained in 1 g of plankton organic matter (5,6 Kcal) with the number of calories in 1 g of tripton organic matter collected from immediately below the epilimnion it was found that energy losses of up to 43% take place in the trophogenic zone over the course of a year. The maximum value occurs during the summer and is 70%. Energy losses in the hypolimnion were calculated in a similar way, and give the figure of 4%. The amount of energy obtained from gross primary production of the pelagial per 1 m² of surface and the amount of energy contained in tripton were compared. The difference found between these values was held to be due to the passage of organic matter produced in the littoral to the pelagial. This transfer took place chiefly in the form of dissolved matter, which may pass into particulate form and then sink. The method consisting of forming an artificial chronological horizon in the deposits was used to investigate the processes taking place in the most recent layer of bottom deposits and their increase during the course of one year.