Environmental Engineering Reference
In-Depth Information
0.6
P-
occluded
0.4
P
Ca
P
non-occluded
0.2
P
O
0.0
10
2
10
3
10
4
10
5
10
6
10
7
FIGURE 8.8
Soil P fractions measured across the Hawaiian archipelago chronosequence provided
general support for the Walker and Syers model of the relative shifts in P pools during soil develop-
ment. P
Ca
5
calcium phosphates and P
O
5
P bound to organic matter. (From
Crews et al. 1995
.)
to test the Walker and Syers model of soil P
transformations over time and its implica-
tions for ecosystem structure and function.
Their results generally supported the Walker
and Syers model as primary mineral P
declined rapidly and P was increasingly
incorporated into occluded P pools over
Time.
increase P availability through multiple pathways. First, acids can increase chemical
weathering of P-containing minerals as described earlier. Second, as with other organic
matter, organic acids can compete with phosphates for sorption sites on clays, thereby
reducing P binding sites.
Aquatic Systems
Inland waters are active sites of storage and transformation of the P that enters these
systems from point and nonpoint sources. There are three ultimate fates of all elements
that enter a water body. The P can be stored in sediments (buried), exported downstream,
or lost to the atmosphere. For P, there are very few examples where atmospheric loss is
reported to be substantial. Thus, the two primary fates of P are hydrologic export and
burial. The proportion of P that is lost to sediment burial and hence not transported down-
stream varies substantially between and within types of inland waters. Lakes have
some of the highest retentions (approaching 100%) while retention is generally lowest in
fast-moving streams and rivers. Variation in nutrient retention between and within inland
