James,W.F. and Larson,C.E.(2008): Phosphorus dynamics and loading in the turbid Minnesota River (USA): controls and recycling potential. Biogeochemistry, 90, 75-92.


 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』

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

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