Pm. Haygarth et al., SHORT-TERM CHANGES IN THE MOLYBDATE REACTIVE PHOSPHORUS OF STORED SOIL WATERS, Journal of environmental quality, 24(6), 1995, pp. 1133-1140
Precise determination of molybdate reactive phosphorus (MRP) in waters
is needed to accurately quantify sources of bioavailable phosphorus (
P) entering into fresh water systems. Leachate waters from soils were
collected from lysimeters to study the short-term stability of MRP dur
ing sample storage from 2 h up to 32 d. The effects of different chemi
cal preservatives (iodine, sulfuric acid, and mercury) were different
in different soil water types, sometimes causing an increase in MRP a
few days after storage. The effects of storage environment (refrigerat
ion, freezing, outside, darkness, and in ambient laboratory conditions
) also varied between soil types, with the least changes noted in samp
les stored in the ambient laboratory conditions and under refrigeratio
n. Larger vessels (25 L) retained MRP more effectively than smaller ve
ssels (30 mt) and teflon-polytetrafluoroethylene (PTFE) was the vessel
material preferred to polyethylene and polythene. The mechanisms resp
onsible for the changes are thought to be a complex interaction betwee
n biological (microbial incorporation/release), chemical (adsorption/d
esorption and hydrolysis), and physical (presence/absence of particle
material) factors. The conclusions were that different waters behave d
ifferently, that losses are rapid (hours and days) and that rapid anal
ysis is essential to provide a correct assessment of water quality.