Geoscience Reference
In-Depth Information
(a)
(b)
Figure 7.8
Rugose crusts, western NSW, Australia: (a) surface comprised of BSC, exposed silts and quartz pebbles, in dry
condition; (b) surface largely covered by bryophyte crust. Note the marked surface roughness and considerable depression storage
capacity.
The role of BSCs is further complicated because the soil
fertility benefits that they confer may foster more abun-
dant soil invertebrates able to contribute to soil bioporos-
ity. Unsurprisingly, given the variation in soil properties
and BSC types, the literature reveals no clear consensus
about the effects of crusts on surface water balance or in-
filtration (Eldridge and Greene, 1994). It is possible that
the effects of crusts are indeed different in rain events of
varying size. Mild water repellency of some crusts may
reduce the soil uptake of water from small events, but the
together with roughening of the surface, may promote wa-
ter retention in larger events. The swelling of polysaccha-
ride sheaths during wetting evidently blocks pore spaces
within the crust and may contribute to the partitioning
of water into surface ponding or overland flow (Kidron,
Yaalon and Vonshak, 1999). The surface roughness, lower
flow speeds and greater surface detention and depression
storage capacity all seem likely to contribute to this. More-
over, it is important to recall the patchy nature of many
dryland surfaces, referred to at the start of this chapter.
