Stemflow influences on the formation of solution pipes in Bermuda eolianite

• Autores: Stanley R. Herwitz
• Localización: Geomorphology, ISSN 0169-555X, Vol. 6, Nº 3, 1993, pág. 253
• Idioma: inglés
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• Resumen

  • Soil-filled pipes consisting of calcite casings were found in all of the eolianite formations of Bermuda except the Rocky Bay Formation. The pipes are cylindrical in shape, taper vertically downwards, and occur in aggregated clusters. They are most commonly exposed in areas of shoreline erosion in the form of soil-filled cylindrical rims of calcite projecting up from the surrounding host eolianite. In the early literature on the geology of Bermuda, it was suggested that these features were fossilized stumps of the Bermuda palmetto tree Sabal bermudiana. In the study presented here, this hypothesis is rejected on the basis of the morphology and stratigraphic position of these geomorphic features and their basal area and areal density compared with existing natural stands of S. bermudiana. The soil-filled pipes of Bermuda, however, cannot be simply explained as random solutional features that correspond to points where percolating soil water happened to converge and cause localized subsurface dissolution.

    In situ measurements of stemflow from indigenous tree species suggest that the soil-filled solution pipes of Bermuda may be the product of stemflow drainage from particular tree species. Stemflow from S. bermudiana was the most acidic, with pH values as low as 4.29 compared to the gross rainfall in the open, which had a pH of 5.58. The crowns of the Bermuda cedar (Juniperus bermudiana) and the subtropical tree species Eugenia axillaris had the most significant funnelling effect. Stemflow volumes from individual trees representing these two species were 20 times greater than the volume of water that would have been collected in rain gauges with orifice areas equivalent to the trees' trunk basal areas.

    Tree species capable of acidifying intercepted rainwater and funnelling large quantities down their trunks as stemflow may be the cause of subsurface dissolution loci extending vertically downward through Bermuda's soluble eolianite formations. Stemflow from long-lived trees representing these species could account for the diameters, the cyclindrical shape, the vertical orientation, and the soil-filled interiors of the pipes. Successive generations of these trees in preferred habitats could explain their clustered distribution and high areal densities (>103 pipes/ha).