Depositional fluxes of metals and phytoplankton in Windermere as measured by sediment traps1

Abstract

Monthly sediment trap samples collected from a deep water station (42 m) in Windermere for a period of 1 year were analyzed for 0.5 M HCl extractable and total Fe, Mn, Al, Pb, Cu, Zn, total C, N, and total solids. Concomitant algal counts showed the year to be fairly typical in terms of the known sequence of phytoplankton.The annual depositional fluxes are compared with previously determined values based on sediment studies. The ratio of the annual trap to sediment flux for Al (≤ 1) indicates the absence of local sediment resuspension. The ratios for Fe, Pb, and Zn (1.1, 1.4, and 1.5, but not significantly > 1) suggest some possible biogeochemical cycling at the sediment‐water interface. The deposition of Fe, Al, and Pb is predominantly associated with detrital material and occurs mainly during winter. The behavior of Zn is largely independent of other variables examined. The ratios for C (1.8), total solids (2.2), N (3.2), Mn (8.6), and Cu (9.5) are all significantly > 1. The C and N values are thought to reflect the microbial breakdown of organic matter at the sediment surface and more particularly the preferential degradation of proteinaceous (i.e. N rich) material. The major influence on the deposition and recycling of Mn is its well known redox cycle involving oxidative precipitation and reductive remobilization. Cu undergoes an independent deposition‐remobilization cycle, probably related to uptake by diatoms and their rapid microbial decomposition after sedimentation.