『Abstract
In areas of intensive crop production, continual phosphorus (P)
applications as P fertilizer and farmyard manure have been made
at levels exceeding crop requirement. As a result, surface soil
accumulations of P have occurred to such an extent that loss of
P in surface runoff and a high risk for P transfer into groundwater
in concentrations exceeding the groundwater quality standard has
become a priority management concern. Phosphorus content of groundwater
was determined in order to examine dissolved P concentration and
species in the groundwater and mineral solubility in a semi-arid
region of southern Malayer, western Iran. The speciation for P
in groundwater was calculated using geochemical speciation model
PHREEQC. The concentration of total P in the groundwater (0.01-2.56
mg P l-1) and estimated concentrations of HPO42- (49.5-89％), H2PO4- (1.5-17.3％), CaHPO4+
(5.7-36.1％), and CaPO4- (1.4-12.2％)
varied considerably amongst the groundwater. Results suggest that
the concentration of P in the groundwater could be primarily controlled
by the solubility of octacalcium phosphate and β-tricalcium phosphate.
Large amounts of P fertilizer, inadequate management of P fertilization,
and low irrigation efficiency, coupled with sandy soils in some
parts of the study area could be mainly responsible for the greater
P in the groundwater. In general, the greater the dissolved P
concentration in the groundwater, the closer the solution was
to equilibrium with respect to the more soluble Ca-phosphate minerals.
The groundwater P content could be potentially used to identify
areas where management approaches, such as P applied and crop
type planted, could be adjusted to different types of soils, geology
and topography.
Keywords: Phosphorus; Saturation index; Phosphorus solubility;
Speciation; Groundwater pollution』
Introduction
Materials and methods
Study area
Sampling method
Water analysis
Speciation and saturation indices
Results and discussion
Chemical characterization of groundwater
Phosphorous concentration in groundwater
Sources of high P in soils and groundwater
Factors controlling dissolved P concentration
Phosphate speciation and mineral solubility
Conclusion
Acknowledgments
References