Duripan

Abstract: Vernal pools are small depressional wetlands found in seasonal climates throughout the world. In California, they are among the few ecosystems still dominated by native flora and are critical habitat for numerous endemic and rare species. In this study, we show that geology is a dominant control on the physical and chemical hydrology of contrasting vernal pools on clay-rich and hardpan soils, the two most common types of vernal pools in the Central Valley, California. The vernal pools on clay-rich soils formed on alluvium derived primarily from sedimentary and metasedimentary rocks of marine origin and deposited in relatively low-gradient environments. The clay-rich soils are fine grained and moderately to strongly saline and sodic. The vernal pools on clay-rich soils are perched surface-water systems in which surface waters are relatively saline, sodic, and turbid and in which primary productivity may be nitrogen and light limited. The vernal pools on hardpan soils formed on alluvium derived primarily from coarse-grained igneous rocks and deposited in relatively high-gradient environments. Surface soils are coarse grained and underlain by a clay-rich argillic horizon and a silica- and iron- cemented duripan. The vernal pools on hardpan soils are surface-water and perched ground-water systems in which surface waters are relatively fresh and non-turbid and in which primary productivity may be phosphorus limited. While surficially similar, these vernal pools differ in their physical and chemical hydrology, and therefore should be treated differently in resource conservation, restoration, and management efforts.

Abstract: The objective of the present study was to make the physical and chemical characterization of soils developed on sediments of the Barreiras group, in southern Bahia, as well as soils formed from rocks of the crystalline basement, which were taken as reference. For this purpose, soil horizon samples from two representative toposequences of the Coastal Plain were selected and analyzed: (1) eutrophic argisolic Red Latosol, latosolic dystrophic Yellow Argisol, duric orthic Ferrocarbic Spodosol; (2) dystrophic abruptic Yellow Argisol, dystrophic typic Yellow Argisol and duric orthic carbic Spodosol. Physical characteristics determined were texture, water dispersed clay, flocculation degree, and bulk density. The chemical analysis carried out were the following: pH in H2O and in KCl, Mg2+, K+, Na+, Al3+, H+ + Al3+, P, organic C and sulfuric acid attack. The soils of the two different topographic sequences differed regarding morphological and physical (texture) characteristics, mainly in the manifestation of the cohesive character. The Argisols inserted where the plateau was wider and less dissected presented a higher textural gradient and more pronounced cohesion state. The bulk density values for the cohesive horizons as well as for the fragipan and duripan were high and were inversely related with the organic matter content. The main micromorphological characteristics observed in the dense horizons of the Yellow Argisols were: low porosity and biological activity, and presence of illuviation argilans, confirming the presence of a textural B horizon.