Fecal pellets sediments

As mentioned above, most oils are buoyant in water. However, in areas with high levels of suspended sediment, petroleum constituents may be transported to the river, lake, or ocean floor through the process of sedimentation. Oil may adsorb to sediments and sink or be ingested by zooplankton and excreted in fecal pellets that may settle to the bottom. Oil stranded on shorehnes also may pick up sediments, float with the tide, and then sink. Most of this process occurs from about 2 to 7 days after the spill. 

Over longer time scales, clay minerals can undergo more extensive reactions. For example, fossilization of fecal pellets in contact with a mixture of clay minerals and iron oxides produces an iron- and potassium-rich, mixed-layer clay called glauconite. This mineral is a common component of continental shelf sediments. Another example of an authigenic reaction is called reverse weathering. In this process, clay minerals react with seawater or porewater via the following general scheme ... 

Three mechanisms have been proposed to explain how particulate metals could be transported within such sediments so as to support the growth of Fe-Mn nodules (1) anoxic microzones, (2) bioturbation, and (3) shifts in the depth of the redox boundary over time. Anoxic microzones are present within fecal pellets and the interiors of radiolarian shells where detrital POM is still present. Metals mobilized within these microzones should be able to diffuse through the sediments for substantial distances... 

Some green clay minerals occur as ovoids, probably having formed within fecal pellets or casts of forams. They also occur as films or stains on shells, sand grains, and phosphate nodules. They are finmd in highest density in sediments of the outer continental shelves and slopes where waters are shallow (20 to 700 m) and mildly suboxic. Slow sedimentation rates are necessary to prevent burial as green clays form at very slow rates. A notable example are the green muds found on the Blake Plateau. 

The transport of cysts via shellfish transplants or relays is even more difficult to evaluate. Not only is it possible that the sediment on the shells of seed shellfish contains cysts, but ingested cysts may even survive ingestion and germinate following defecation. Many cysts fed to soft-shell clams and mussels are viable following isolation from fecal pellets (35), but experiments have yet to be performed that mimic the conditions associated with prolonged residence in the intestines of shellfish during inter or intra-state transport. 

Carbon and Phosphorus Burial Efficiencies. The estimate of diatom carbon demand (12-15 g/m2 per year) is consistent with the flux of carbon to the sediment surface. With sediment-trap fluxes corrected for resuspension, we measured a total annual deposition flux of 12.5 g of C/m2. In comparison, Eadie et al. (24) obtained 23 g of C/m2 for a 100-m station, based on three midsummer metalimnion deployments. Of our total, 83% of the carbon was associated with diatoms, and the primary diatom carbon flux was 10.3 g of C/m2. Thus, about 15-30% of the diatom carbon was regenerated in the water column during sedimentation. Approximately 10% of the diatom flux reached the sediment surface encapsulated in copepod fecal pellets the remaining 90% was unpackaged. 

Sedimentation. Some organisms may ingest dispersed oil droplets in the water column and subsequenfly deposit them as fecal pellets. In some instances, this has been estimated to be a significant form of sedimentation. 

There are, however, some problems in the direct application of such a ratio. First, relative high abundances of A7-sterols have been reported in Lake Kinneret, a normal marine salinity environment (39). Hence, A -sterols are obviously not restricted to organisms living in hypersaline environments. The relative abundance of A7- (and a8 14)-) sterols in hypersaline environments may be due to the absence of grazing zooplankton in these environments. In normal marine salinity environments A7- and A8(14)-sterols are selectively metabolised in the guts of zooplankton resulting in a selective preservation of A5-sterols in zooplankton fecal pellets, which are transported rapidly to the sediment (40,41). 

Madin, L.P., The production, composition and sedimentation of salp fecal pellets in oceanic waters, Mar. Biol., 67, 39, 1982. 

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