Vertical gradients in particle distribution and its elemental composition under oxic and anoxic conditions in a eutrophic lake, Scharmützelsee, NE Germany
Kleeberg, Andreas; Schubert, Hendrik
Archiv für Hydrobiologie Volume 148 Number 2 (2000), p. 187 - 207
published: Apr 14, 2000
ArtNo. ESP141014802008, Price: 29.00 €
Two vertical profiles of soluble and suspended components were registered at the deepest location of the eutrophic Lake Scharmützel (29.5 m) - one in May under oxic conditions, and one under anoxic conditions during stratification in September 1997. The sequential accumulation of soluble components from May to September was illustrated by decreasing partition coefficients, i. e. by the quotients of elemental concentration of particulate and water phase for Al, Si, Ca, Cu, Mn, Fe, P, and N. Particle counting and in-situ photographs neither showed significant differences between May and September nor in the vertical percentual distribution of the four size classes. All size classes increased with depth in the epilimnetic layer. The aggregates are formed by very small particles. They are not effectively removed from any lake compartment, and they accumulate at steady-state to high concentrations in the thermocline and in the hypolimnion in transient maxima at middepth under anoxic conditions. In September the coincident particulate P and Fe transient maxima at 15 m depth were evidence for a cosedimentation of Fe and P even under anoxic conditions, which, can be substantially less than particle removal. FeS precipitation was responsible for efficient Fe removal below 18 m water depth at an apparent pK of 2.76. As a result, the partition coefficient for S and particulate S increased. The Fe: P ratio decreased, contributing to a more rapid release and recycling of P already in the water column.