Agriculture Reference
In-Depth Information
Figure I.16 summarises the results of a study of a 14-month study of soil redox
potential carried out in a mangrove-forested tidal wetland in tropical northeastern
Australia (Boto and Wellington, 1984). Nine sites were located along a transect laid out
between two creeks; soils were sampled monthly at 5 cm intervals to a depth of 100 cm.
Sites 1 and 2 were below mean sea level, sites 3 and 9 were below mean high water and
site 6 was above the level of the mean high water spring tides.
Since no significant depth or temporal variation was detected, the means and ranges
presented are for all depths over the time course of the study. It may be seen from the Eh
values that all the bulk soils remained consistently anaerobic over the sampling period.
However some evidence of micro-scale increases in redox potential was apparent around
the roots, suggesting that oxygen was being secreted into the mangrove rhizosphere.
1.3
Soil structure and micro-relief
At a number of locations and in particular soils, the surface may be organised into
micro-relief features occurring at horizontal scales that range up to several metres or
more. These features may occur as some combination of ridges, cracks, semi-regular to
quasi-random patterns of holes, hollows and mounds. Micro-relief features may result
from purely physical processes or they may be created by the biota, either directly or
indirectly (Chapter IV) (Figure I.17). They are usually dynamic features of the landscapes
and are constantly being degraded and recreated and have considerable implications for
soil development (Chapter II.3.3.2). Such features may strongly affect the distribution
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