Geoscience Reference
In-Depth Information
Table 12.9 Colloidal (1 lm-1 nm) and dissolved (\1 nm) molybdate-reactive phosphorus
(MRP) and major cation concentrations in runoff, generated by simulated sprinkler irrigation onto
three semiarid, arable soils (Turner et al.
2004
)
Filter size
Portneuf
Warden
Greenleaf
MRP, % of MRP \1 lm1lm-1 nm
13-22 (18)
11-39 (24)
37-56 (45)
\1 nm
78-87 (82)
61-89 (76)
44-63 (55)
lM
MRP 1 lm-1 nm 0.5-3.1 (1.4) 0.2-1.5 (0.5) 0.3-0.7 (0.5)
\1 nm 2.1-16.6 (6.8) 0.5-5.8 (1.8) 0.4-0.8 (0.6)
Al 1 lm-1 nm 2.2-22.2 (9.3) ND
a
-4.5 (1.5) 1.1-7.8 (4.1)
\1 nm ND-0.7 (ND) ND-3.0 (0.7) ND-3.0 (1.1)
Ca 1 lm-1 nm 3.5-61.1 (31.7) 0.5-12.7 (7.2) 2.5-10.5 (8.2)
\1 nm 62.1-156.2 (127.8) 2.3-15.0 (9.0) 53.2-68.9 (62.1)
Fe 1 lm-1 nm 0.7-5.4 (2.2) ND-2.2 (0.7) 0.5-13.1 (4.5)
\1 nm ND-0.2 (ND) ND-1.6 (0.4) ND-0.2 (ND)
K 1 lm-1 nm 2.6-14.1 (6.1) 1.0-17.1 (7.4) \0.3-1.5 (0.8)
\1 nm 19.7-63.7 (35.6) 4.9-28.9 (16.9) 29.9-30.1 (38.1)
Mg 1 lm-1 nm 2.1-7.8 (5.4) ND-3.7 (2.1) 3.3-7.8 (5.4)
\1 nm 13.2-40.3 (27.6) 0.8-3.7 (2.5) 12.8-18.5 (15.6)
Si 1 lm-1 nm 5.0-59.5 (27.1) 0.7-14.2 (5.3) 4.6-22.1 (13.5)
\1 nm 13.9-51.3 (35.6) 4.6-16.0 (8.2) 19.6-29.2 (24.6)
Values are the range of concentrations from runoff generated on dry and wet soils, with the mean
value in parentheses. Values for the Portneuf soil are flow-weighted means of six samples taken
at 5-min intervals during 30 min of continuous runoff. Values for the Warden and Greenleaf soils
are means of samples taken from each of two subplots after 30 min of continuous runoff
a
Not detectable (less than the limit of detection)
12.4.1 Surface Runoff
Transport of contaminants by surface runoff is illustrated in the experimental
results of Turner et al. (
2004
), which deal with the colloid-mediated transfer of
phosphorus (P) from a calcareous agricultural land to watercourses. Colloidal
molybdate-reactive phosphorus (MRP) was identified by ultrafiltration associated
with particles between 1 lm and 1 nm in diameter. Colloidal P compounds can
constitute a substantial component of the filterable MRP in soil solution and
include primary and secondary P minerals, P occluded or adsorbed on or within
mineral or organic particles, and biocolloids (Kretzschmar et al.
1999
).
The experiments were conducted on three plots of semiarid soils from the
western United States, characterized by various concentrations of CaCO
3
and
organic carbon. Surface runoff, generated by simulated sprinkler irrigation, was
applied twice on each plot: first to yield a moisture content of 2-5 % then again on
the same plot at a moisture content of 17-29 %. Colloidal (1 lm-1 nm) and
dissolved (\1 nm) MRP and major cation concentrations in the generated runoff
are presented in Table
12.9
. In the runoff colloids, MRP concentrations range
between 0.16 and 3.07 lM, constituting 11-56 % of the MRP in the \l lm
