How Soil Is Formed - Soil: Reflections on the Basis of our Existence - page 28

It takes around eighty years and the arrival of the first blueberry and other low
shrubs and conifers for soil formation to gather genuine pace. The low air temper-
ature slows the decomposition process. Blueberry leaves and conifer needles also
contain components that degrade slowly, resulting in an accumulation of organic
matter at the surface. Dissolved organic compounds seep into the soil with rain-
water and dissolve the ions from mineral particles. The vegetation absorbs some
ions, while others collect further down in the soil or leach into the groundwater.
As time passes, the soil separates into an upper leached layer and a lower enriched
layer, though this process can be affected by the presence of earthworms, whose
burrowing mixes the soil profile. At Lyman Lake, one can study the soil formation
process during the hundred years immediately following the deposition of moraine
by the glacier. There are plenty of other places to visit for those who wish to study
the process over a longer time frame.
Podzolisation and Soil Formation in Sweden
In Sweden, the ice sheets melted around ten thousand years ago in a process mir-
roring that at Lyman Lake. In their wake, they left an unconsolidated moraine that
is the dominant soil type in Sweden. During the Ice Age, the weight of the ice
depressed the surface of the Earth's crust, which is now in a process of post-glacial
rebound as the land regains its former form. In northern Sweden, the land is ris-
ing at a rate of one centimetre per year and here, as at Lyman Lake, we can use a
natural time experiment to study the progression of the soil formation process, this
time under Scandinavian conditions.
I travelled to ￅkerb￤ck, some twenty-ive kilometres inland from the Baltic
coast in northern Sweden, to take some soil samples. A nearby patch of shingle
beach reveals the line the coast took around eight thousand years ago. Lush spruce
forest has dominated the landscape for the last three thousand years or so, having
colonised the area from the north. So stony was the ground that it was impossible
to use my soil sampler, though after much effort I managed with my colleague's
help to dig a deep enough hole to examine the soil structure. Above the mineral
soil, which was primarily moraine, lay a ten-centimetre layer of organic matter
topped by newly shed spruce needles and leaves embedded in blueberry twigs and
moss. The matter adjacent to the mineral soil had degraded into a black paste-like
substrate showing no direct evidence of needles or leaves. The upper section of the
mineral soil was greyish-white in colour, becoming reddish lower down.
Carbon dioxide emitted by plant roots and microorganisms dissolves in the
soil to form carbonic acid, which accelerates the disintegration of soil minerals.
The acidification effect is augmented by the positively charged hydrogen ions that
these life forms release in exchange for the potassium, magnesium and other posi-
tively charged ions that they need in order to grow. As the most easily weathered
minerals disintegrate and leach, the soil looks bleached because only grey quartz
remains and is resistant to disintegration. The bleached soil is called the eluviated