Sampling sediment trap

Kimmel, B.L., Axler, R.P. and Goldman, C.R., 1977. A closing, replicate-sample sediment trap. Limnol. Oceanogr., 22 768—772. 

Where all nuclide measurements are expressed in activities. In both expressions, the first term in curly brackets corrects for Th (or Pa) supported by U in lithogenic material, and the second term in curly brackets corrects for °Th (or Pa) ingrown from authigenic U. For samples that are known to be young, such as sediment trap or core-top samples, t = 0 and this second term equals zero reflecting the lack of time for decay of authigenic U in such samples. 

Montgomery, M.T., N.A. Welschmeyer, and D.L. Kirchman. 1990. A simple assay for chitin application to sediment trap samples from the subarctic Pacific. Mar. Ecol. Prog. Ser. 64 301-308. 

Different sampling methods often result in collection of different components of the element or compound of interest. Most seawater samples are collected in bottles, filtered to remove particles and analyzed directly or after preconcentration of minor components. Particulate matter from the water column is collected by filtration or with sediment traps. Sediment samples are collected in cores that recover intact chronological sequences and are commonly subsampled, dried and ground to a powder. Pore waters are extracted from sediments by squeezing or suction, dialysis, and centrifugation. 

Zooplankton population samples for isotope analysis were composites of 50-200 individuals. Population samples are less variable in isotope composition than are samples of individuals. Replicate isotope analyses of composite samples of zooplankton or POM collected at different locations within the lake varied by no more than 0.5%. Larger organisms such as molluscs, insects, and fish were analyzed individually. Molluscs were soaked in dilute HCl to remove carbonates and then rinsed copiously with distilled water. Fish muscle was analyzed. Sediment trap material was collected in replicate cylinders (11.4-cm diameter, 76.2-cm length) suspended at 4.5-m depth. All isotope samples were dried at 60 °C before analysis. 

Field Procedures. Sedimenting Particles. A sediment trap array, moored at the sampling station, was retrieved and redeployed 15 times over the course of the main study period (early April 1982 to late March 1983). Deployment intervals averaged 3 weeks. The cylindrical acrylic traps employed were similar in design to those described by Wahlgren and Nelson (11). The standard trap used had an aspect ratio of 4.0 (16-cm diameter) and an open area of 162 cm2 with a baffle and 198 cm2 without a baffle. 

An acid-leached polyethylene terephthalate (Mylar) sheet was placed inside the circumference of the centrifuge bowl to enable rapid recovery of trapped particles. Particles and lake water (4 L), retained in the centrifuge bowl after the selfsealing device isolated the bowl, were recovered and kept at 4 °C for transport to the laboratory. Time delay from the collection to laboratory processing varied from 24 to 36 h. At typical lake-water particle concentrations of 1 mg/L, more than 0.5 g of suspended particles could be collected in 1 h. On-station time limited the number of large-volume depths sampled per cruise to six or seven. The depths chosen were selected to be representative of distinct layers of the water column and also to correspond to depths at which sediment traps were deployed. 

Sediment Traps. Sediment traps with a height diameter ratio of 10 1 were exposed in the deepest part of the lake close to the water-sampling site at 15-and 28-m depth for 15 months. The particulate material in the traps was collected approximately every 3 weeks and was subsequently freeze-dried until analysis. 

Figure 14.7 Particulate concentrations of Mn and Fe in sediment trap samples collected in the Baltic Sea from December 1999 to March 2001. The sediment trap was located at a water depth of approximately 120 m. (Modified from Pohl et al., 2004.)...

To sample the settling flux directly, free-floating multiple-sample programmable sediment traps (Pro-Trap) were deployed at all three fjords for about 16 h at each time (trap depth 60 m). The Pro-Trap system consists of four polyvinyl chloride (PVC) sediment tubes, each of 0.018 square meter exposed area (cylinder height of 80 cm, trap aspect ratio A 4 5.3), mounted on a stain-less-steel frame. Depth and angle sensors allowed defining the position of the traps in the water... 

Below about 200 m, PON concentrations tend to asymptote to similar levels of about 0.1 to 0.3 pmol kg", irrespective of the large differences in PON in the euphotic zone. Overall, PON dynamics in the aphotic zone tends to follow that of particulate organic carbon (POC), with a stoichiometric C N ratio of about 7.1 0.1 (equivalent to 16 114 2) for the particles sinking out of the euphotic zone (Schneider et al, 2003) (see also Hebei and Karl (2001) for long-term observations of the POC and PON dynamics in an oligotrophic environment). In their analysis of sediment trap samples and particles collected by in situ pumps, Schneider et al (2003) also noticed a slight increase of this ratio with depth of about 0.2 per 1000 m, so that particles sinking across 1000 m have a C N ratio very close to the 117 16 ratio proposed by Anderson and Sarmiento (1994). 

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