Geoscience Reference
In-Depth Information
HUMID ENVIRONMENTS
ARID ENVIRONMENTS
High
evaporation
High rainfall
Dominantly endolithic
biofilms
Mainly epilithic
biofilms
Dense vegetation
cover
Low
evaporation
Low
rainfall
Sparse vegetation
cover
Bedrock with
common surface
outcrops
Thin soil
Thick soil
Bedrock with only occasional surface outcrops
Leaching and runoff of weathering products
Weathering products often build up in situ
Weathering rate heavily influenced by variability in precipitation
and evaporation over time and space
Precipitation an important control of weathering rate
Vegetation and biofilms usually have indirect influence on
weathering
Vegetation and biofilms usually have direct influence on weathering
Weathering system characterised by equilibrium conditions
Weathering system characterised by non-equilibrium conditions
Figure 6.3
A conceptual diagram summarising the major elements of arid versus humid weathering systems.
drylands. This chapter aims to explore recent progress in
these three areas, after an introduction to the key facets
of arid environments as relevant to weathering systems,
some theoretical underpinnings to weathering research
and a review of current study methods, which are allow-
ing us unprecedented insights into weathering systems in
arid and other environments.
other terrestrial environments, which has a clear influence
on weathering systems (Figure 6.3). For one thing, the lack
of soils makes bare rock surfaces more common and thus
small-scale weathering landforms (which develop pre-
dominantly on bare rock surfaces) more frequent. While
the lack of moisture and soils is generally coupled with
sparse vegetation, the vegetation that does survive under
these conditions often has a more clear-cut influence on
weathering than it does in other environments. For ex-
ample, plants exploit crevices in rocks in order to find
moisture, shelter and anchorage in moisture-limited and
soil-poor environments. In so doing, they can cause weath-
ering through root growth pressures and chemical effects
of associated endophytic bacteria (Puente, Li and Bashan,
2009). Of much more widespread importance is the rela-
tive importance of rock surface biofilms (mixed commu-
nities of lower plants and microorganisms) to weathering.
Such biofilms, because of the harsh growth conditions
in arid environments, often have very intimate connec-
tions with the underlying rock and, as a result, can play
a large role in both chemical and physical weathering
6.2
What makes arid environments
unusual in terms of weathering systems?
Arid environments possess three very important character-
istics, which have a dominant influence on their weather-
ing systems, i.e. extreme environmental conditions (Chap-
ters 1), nonequilibrium conditions (or variation over time,
Chapter 2) and a diversity of environmental conditions
(or variation over space, Chapter 3 and 4). Arid environ-
ments are extreme environments in the sense that they are
highly moisture-limited. This lack of moisture is matched
