ABSTRACT
The role of phosphorus (P) inputs in accelerating eutrophication of freshwaters is well documented. The total load of P to a river can broadly be divided into point source inputs, typically dominated by sewage treatment effluents, and diffuse sources, often dominated by agriculture. There is a general increase in P transport in the order of rivers draining forested -native ecosystems, intensively managed agriculture, and urban settings. Point sources enter the river more continually through the year than do non-point sources, which are subject to large seasonal variation, typically as a function of overland flow. Changes in the forms and amounts of P during transport in streams and rivers can greatly influence the eventual impact of P loss on the degree of eutrophic response of receiving waters. These changes are mediated by physical (sediment deposition and resuspension and flow regimes), abiotic (P sorption and desorption), and biotic (microbial and plant uptake) processes. Such riverine processes influence the long-term transport and receiving water body response to P, where there may be a time-lag (years or decades) before improvements in water quality, or regeneration of diverse habitats, might become apparent even after P inputs are minimized. Clearly, implementation of effective conservation measures must consider fluvial system response behavior, where sinks may become sources of P with only slight changes in watershed management and hydrologic response.
