Total nitrogen migration in Wuliangsuhai Lake during ice growth process

To study the characteristics of total nitrogen (TN) during the period of lake ice freeze-up, vertical measurements of TN are made at ice thicknesses of 0 cm, 2.5 cm, 9.5 cm, 21 cm, 31 cm, 41cm, 50 cm and 59 cm. The regularity of TN migration in Wuliangsuhai Lake during ice growth process is examined. Results show that TN migrates from ice to water during the whole growth period of ice, which gives a rise of TN in under-ice water as the ice is getting thicker. TN of water is 2.85 times more than that of ice at an ice thickness of 59 cm. The rate of ice growth determines the flux of TN migration between ice and water. Within the ice layer, the TN migration mostly occurs during the initial stage of ice formation (0-21cm), and then TN is transformed into the steady nitrogen cell with bubbles in ice. The difference in measured and calculated TN in under-ice water indicates that TN still migrates from lake water to sediment during ice growth process. The study provides a reference for controlling eutrophication pollution during the period of lake ice freeze-up.