『Abstract
　Phosphorus (P) dynamics in the agriculturally-dominated Minnesota River (USA) were examined in the lower 40 mile reach in relation to hydrology, loading sources, suspended sediment, and chlorophyll to identify potential biotic and abiotic controls over concentrations of soluble P and the recycling potential of particulate P during transport to the Upper Mississippi River. Within this reach, wastewater treatment plant (WWTP) contributions as soluble reactive P (SRP) were greatest during very low discharge and declined with increasing discharge and nonpoint source P loading. Concentrations of SRP declined during low discharge in conjunction with increases in chlorophyll, suggesting biotic transformation to particulate P via phytoplankton uptake. During higher discharge periods, SRP was constant at 〜0.115 mg l^-1 and coincided with an independently measured equilibrium P concentration (EPC) for suspended sediment in the river, suggesting abiotic control over SRP via phosphate buffering. Particulate P (PP) accounted for 66％ of the annual total P load. Redox-sensitive PP, estimated using extraction procedures, represented 43％ of the PP. Recycling potential of this load via diffusive sediment P flux under anoxic conditions was conservatively estimated as 〜17 mg m^-2 d^-1 using published regression equations. The reactive nature and high P recycling potential of suspended sediment loads in the Minnesota River has important consequences for eutrophication of the Upper Mississippi River.

Keywords: Equilibrium phosphorus concentration; Phosphorus; Redox-sensitive phosphorus; Rivers; Soluble phosphorus; Suspended sediment』

Introduction
Study site
Methods
　Biologically labile and refractory particulate phosphorus pools of suspended sediment
　Phosphorus equilibrium characteristics of suspended sediment
　Water chemistry and loading analysis
　Statistical analyses
Results
　Particulate phosphorus composition and equilibrium characteristics
　Phosphorus dynamics
　Budgetary analysis
Discussion
Acknowledgements
References

Table 1 Operationally-defined particulate phosphorus (PP) fractions

Variables	Extractant	Recycling potential
Loosely-bound PP	1 M ammonium chloride	Biologically labile; recycled via eH and pH reactions and equilibrium processes
Iron-bound PP	0.11 M sodium bicarbonate-dithionate	Biologically labile; recycled via eH and pH reactions and equilibrium processes
Labile organic PP	Persulfate digestion of the NaOH extraction	Biologically labile; recycled via bacterial mineralization of organic P and mobilization of polyphosphates stored in cells
Aluminum-bound PP	0.1 N sodium hydroxide	Biologically refractory
Calcium-bound PP	0.5 N hydrochloric acid	Biologically refractory
Refractory organic PP	Persulfate digestion of remaining particulate P	Biologically refractory
Biologically labile = Subject to recycling pathways; Biologically refractory = Low recycling potential and subject to burial

Table 2 Biologically labile and refractory particulate phosphorus (PP) fraction means (mg kg^-1; n=20), standard errors (S.E.), and percent composition for allochthonous（外来、異地性） TSS loads in the lower Minnesota River, 2005-2006

Variable	Mean	S.E.	Percent
Biologically labile PP
Loosely-bound	138	7	18.2
Iron-bound	186	6	24.5
Labile organic	56	4	7.4
Refractory PP
Aluminum-bound	59	3	7.8
Calcium-bound	203	14	26.8
Refractory organic	116	18	15.3

Fig. 9 Contribution of biologically labile (solid shades) and refractory (dotted shades) phosphorus (P) fractions to the annual average (i.e., between 2004 and 2006 for RM 39.4 and RM 3.5 combined) total P load of the lower Minnesota River James,W.F. and Larson,C.E.(2008)によるPhosphorus dynamics and loading in the turbid Minnesota River (USA): controls and recycling potentialから