A study of the cycling of manganese and other elements in a seasonally anoxic lake, Rostherne Mere, U.K

The vertical distribution of sulphate, dissolved sulphide, alkalinity, pH, total iron and manganese, Fe(II) and Mn(II) and humic substances was monitored for a year in a seasonally anoxic lake, Rostherne Mere, U.K. During summer stratification Mn(II), probably of sediment origin, accumulated in the hypolimnetic bottom waters to a concentration of 50μm. Release occurred in two stages and appeared to be related to the supply of organic material to the sediment. No ferrous iron or dissolved sulphide were detected in the water column, although they were measured in the interstitial waters of the sediment. Ferrous sulphide formation in the sediment controls the iron(II) and dissolved sulphide concentrations and so minimises the concentration gradients at the sediment-water interface. Electron acceptors other than oxygen are capable of oxidising ferrous and sulphide ions in the water column. pH and alkalinity were the only other chemical components to show appreciable variation with depth, reflecting the biological processes of photosynthesis, respiration and decomposition. Iron and humic substances simultaneously increased in the surface waters after a major flood indicating that they are both present in the solution in contact with the soils of the catchment.