Deposition/resuspension cycle

The amount of P supplied by resuspension was relatively small compared with water-column standing pools and major flux vectors. Thus, resuspension of bottom sediments may not be a major mode of phosphorus resupply. The pool of resuspendable P is finite. The deposition-resuspension cycle will not increase the amount of P in this pool unless P is added from another source (e.g., by diffusion of P from lower sediment levels). However, the diffusive flux would be relatively small. The resuspendable particulate P can be recycled during spring mixing by repeated deposition and resuspension, but this cycle does not increase the amount of P in the resuspendable pool. Eadie et al. (24) reported a resuspended P flux (sediment-trap-based) of3200 mg of P/m2, 66 times our estimate here. However, this large P flux would require the resuspension of over 2.0 cm of surface sediment and much higher suspended Al levels than were measured in the water column. 

The relationship between alkalinity and FSS concentration and Andean source waters was expected because > 80% of suspended materials and dissolved solids in transport in the Amazon are derived from Andean regions (Gibbs 1972, Stallard 1980, Meade et al. 1985). Although the Andes are also the dominant source of CSS, its seasonal cycle is tied more to the river surface slope than the percent Andean water. In fact, the seasonal pattern of river slope has a nearly identical shape to CSS concentration (Devol et al. 1995). Deposition occurs during periods of low slope (low turbulence), whereas resuspension predominates during high slope (Meade et al. 1985). This changing balance would also explain the relationships between coarse particulate... 

Resuspension in rivers is driven by high bottom shear velocity associated with hydrological events that lead to high flow rates. Resuspension in estuaries is most often driven by tidally induced velocities, so that periodic resuspension and deposition cycles occur as a function of tidal cycles. Resuspension in coastal and nearshore systems is most often driven by wind-generated wave action. 

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