16 June 2008

War and soil!

There was an unusual little paper in Geoderma’s last issue (Hupy & Schaetzl, 2008: Soil development on the WWI battlefield of Verdun, France. Geoderma 145: 37-49. DOI: 10.1016/j.geoderma.2008.01.024). While soil science is pretty far from what I do on a daily basis now, I had great interest in the subject when I was an undergrad and still finds it fascinating. Furthermore, I visited Verdun in 1994 and saw the remains of the battlefield and was amazed how little it had recovered - craters were absolutely everywhere and vast areas were cordoned off with warnings about un-exploded ammunition.  A study combining the two topics would be just up my alley!

Anyway, H&S studied soil development in and adjacent to artillery craters at three sites, corresponding to the three major soil types in the battlefield.  These in turn are related to the underlying geology and geomorphology of the area.  The area is structurally defined by a series of NE-SW running cuestas creating a sets of valleys and ridges.  In the valleys low-lying poorly drained areas have soils suffering from waterlogging (Pseudogleys), while the ridges have soils influenced by the shallow limestone bedrock (Brunified Rendzina and Calcareous Brown).  

The data were collected from the disturbed soil profiles (in the craters) compared to the ‘undisturbed’ profiles (adjacent to the craters). In 3 study sites, one for each major soil type  in the area, 3 soil profiles were dug in each of 3 craters for a total of 27 soil profiles.

At the end of the battle, no soil horizons were likely to exist in the area due to the intensive ‘bomturbation’ of the area. H&S found that a measurable amount of soil development have occurred since the disturbance in 1916: The crater bottoms have accumulated a thick layer of organic matter, the freshly exposed (in 1916) limestone bedrock have been weathered and its byproducts leached down-profile.  Weathering at the crater bottoms have occurred at a faster rate than elsewhere, most likely due to run-off accumulating in the crater bottoms.  Also earthworm activity was found to have moved humus-rich material into cracks and fractures in the limestone, thereby increasing the area exposed to leaching by humic acids.  

This means that soil formation has now been enhanced in crater bottoms located at the ridge crests due to 1) water being focused in the craters and 2) organic matter being collected at the crater bottoms.  In the valleys between the cuesta ridges soil formation has slowed as the crater bottoms are more or less permanently below the water table.  Soil formation has also increased on the slopes of the ridges, as the craters delay the run-off and increase the infiltration of surface water into the soils, thereby enhancing soil formation.

The vegetation in the area has generally not been restored to its pre-war state of beech, hornbeam and oak, due to the scale of the devastation.  Pine has been planted in heavily visited areas due to the soft lighting created by pine trees.  H&S try to make the claim that the soil development in the 88 years since the battle can be used as indicators of landscape recovery/resilience, in the absence of re-colonizing vegetation.  

However, it’s not clear to me exactly how.  Their data seems to show to me that while the same soil-forming processes are acting now as before the battle, the location of the resulting soils are different, for example as evidenced by the  development of soils in the crater bottoms on ridge crests.  Consequently reovery hasn’t been particularly successful (as I see it), but this is never really spelled out by H&S.  However, I still like the paper simply for being curious about soil development in a heavily bombarded area!

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