Watershed Scale Phosphorus Management - The Movement of Phosphorus Downstream.

The movement of phosphorus from the landscape downstream is a complex myriad of processes, which should be thought of in terms of transport and then retention.  The transport is the downstream movement of phosphorus in surface runoff, interflow and groundwater from the landscape, and then subsequent transport in streams and rivers under base flow conditions and rainfall-runoff events, as well as through impoundments.  The retention represents the myriad of factors which [temporarily] delay the downstream transport, such as adsorption, chemisorption, biological uptake, sedimentation, etc.  The specific mechanisms are important, but what might be more important is understanding that the downstream transport occurs in pieces, i.e. spirals as defined in the stream solute workshop.  There are many studies defining transport distances in streams and rivers, but few studies have focused on two important aspects - 1) the transport distances across the landscape, and 2) the [temporary] storage resulting from those important mechanisms on the landscape and within the fluvial channel.  These aspects of phosphorus transport and retention have influenced our perception of watershed management and the lag time required to see changes in phosphorus concentrations and loads at the watershed level and in large rivers.