FIELD-EVALUATION OF A VALVED SEDIMENT TRAP

An internally valved sediment trap designed to isolate sinking particu late matter from free-swimming animals, temporally subsample particle flux, and minimize washout of solid and dissolved material is describe d. The trap is controlled by a single microprocessor capable of suppor ting multiple traps as well as other instrumentation on a single array . Test deployments of valved and nonvalved control traps, along with t hree other conventional cylindrical trap designs, were undertaken duri ng a series of six 1-week experiments in Dabob Bay, Washington. Treate d traps containing biocide-spiked (HgCl2 or Formalin) bottom brine lay ers (80 parts per thousand NaCl brine), brine layers alone, and only s eawater (untreated) were deployed on multitrap arrays. Fluxes of mater ial > 850 mum in size (almost exclusively large zooplankton) caught in biocide- and brine-treated valved traps were reduced by an average of 88% relative to non-valved control traps; all other open traps collec ted > 850-mum fluxes equivalent to controls. The type of treatment had a significant effect on the > 850-mum mass flux, with Formalin-treate d traps >HgCl2 approximately NaCl brine much greater than untreated. F luxes of < 850-mum material were reduced in treated valved traps and a veraged 39% less than fluxes caught in VERTEX-style particle intercept or traps. Organic C: total N ratios were higher in material caught in valved traps than in all other types, primarily due to reduced nitroge n fluxes. Reduced fluxes of the primarily autochthonous biochemicals ( pigments, amino acids, and lipids) measured by valved relative to cont rol traps indicate significant exclusion (> 80%) of zooplankton < 850 mum from valved traps.