Unlike reservoirs located in the regions with warm and temperate climate,Siberian reservoirs have a stable ice cover during the winter period(near 6 months); as a result they have seasonal changes in the natural cycles of substances and their water-sediment exchange.Novosibirsk Reservoir is the largest artificial reservoir in the Ob river basin,which is completely covered with ice from mid-November to late April.Hydrological regime and morphometric characteristics of Novosibirsk reservoir are the typical for the lowland water bodies and it performs seasonal flow regulation of the Ob River.The total volume of the reservoir is 8.86 km3,the average depth is about 9 m,the maximal depth-25 m.Novosibirsk reservoir is the main source of water supply for Novosibirsk,the largest city in Siberia.We evaluated fluxes of dissolved manganese(Mn(Ⅱ))from the bottom sediments to the water and fluxes of adsorbed forms of manganese(Mn(Ⅳ))from water to the bottom,which are controlled by changes of ox-red conditions in different seasons of 2013-2014.The maximum flux of the dissolved manganese is observed from late February to mid-April(before ice floating),as well as in the period of maximum development of the biota in August-early September,when there are strong reducing conditions in the sediments and bottom water.Results of our research show that at this time sediments make significant contribution to manganese input into the water of the Novosibirsk reservoir(up to 250-400%respect to the river discharge – the main source of Mn in the reservoir),while in other seasons,this contribution does not exceed 10-30%.Additionally,in the winter-spring period we observed the clearly expressed vertical distribution of the dissolved manganese; and Mn concentrations were in the reverse of the dissolved oxygen concentrations.At that time,vertical changes of dissolved manganese from the bottom to the water surface ranged from 140 to 4 ppb,exceeding the Russian national water quality criteria in whole water column,except for the surface layer.Manganese sedimentation(Mn(Ⅳ))from the water column to the bottom takes place in the composition with suspended matter.The greatest fluxes of suspended manganese were in August-September(0.3-0.5 g/m2day),during the spring flood these fluxes rich only 0.05-0.2 g/m2day,and in the rest time(especially in the ice cover period)fluxes are very weak or practically absent.