Salinity Dynamics in Subsoiled Soils of the Northwest of the Argentine Pampean Plain

Aims: The objective of the present work was to evaluate the annual evolution of the electrical conductivity and the reaction of the soil, in a Natraqualf of the northwest of the Argentine Pampean Plain, treated with a subsoiler and sowing of wheatgrass. Methodology: Four treatments were established in plots of 400 m2: natural pasture; pasture with wheatgrass (Thynopirum ponticum); natural pasture with subsoiling and wheatgrass pasture with subsoiling. Soil samples were extracted at depths of 0-15 cm, 15-30 cm and 30-45 cm, in January, April, July and October. The edaphic parameters analyzed were: pH, electrical conductivity and bulk density. In October, the dry matter production was determined by treatment. The monthly variation of the depth of the groundwater and its chemical characteristics was measured. Results: The depth of the water table fluctuated between 1.30 m and 0.70 m. The implantation of wheatgrass combined with subsoiling produced a decrease in electrical conductivity from 23.7 dS.m-1 to 3.4 dS.m-1 at 0-15 cm, and from 18.3 dS.m-1 to 7.9 dS.m-1 at 15-30 cm. Soil pH decreased almost one unit in the first 30 cm of depth of the treatments that included wheatgrass. The bulk density was reduced from 1.39 to 1.03 g.cm-3 in the treatment with subsoiling and wheatgrass, and 1.09 g.cm-3 in the wheatgrass treatment without subsoiling. The salt concentration and reaction of the soil at more than 30 cm did not show significant changes in the course of the work. Conclusion: The implantation of wheatgrass, combined with the use of a “mole plow” subsoiler, in the studied soil, produces a significant decrease in the salt content and soil pH in the first 30 cm of depth. At more than 30 cm the salt concentration and reaction of the soil is determined by the groundwater.

Effects of polyphenols on plankton assemblages and bacterial abundance representative of a pampean shallow lake: an experimental study

Shallow lakes are complex environments that play an important role in ecology. Their relationships with the surrounding areas make these lentic water bodies susceptible to alterations in response to human activity. For example, the input of polyphenols could be critical in altering species interactions. The shallow lakes located in the pampean plain of Argentina are major reservoirs of diversity, with the environmental habitats of the Salado River basin in particular having become impacted by human activities. The aim of this work was to evaluate the effects of different polyphenol concentrations (i.e. tannins) on changes in the plankton assemblages and on the abundance of bacteria in San Miguel del Monte Lake. Factorial experiments under laboratory conditions (4 tannin concentration levels and 4 response times) revealed that high tannin concentrations affected neither the phyto- and zooplankton assemblages nor bacterial abundances. Major changes both in assemblages and in the bacterioplankton abundances were dependent on exposure time. We found that the initial food web of grazers shifted to detritivorous feeding, thus producing a simplification of the community toward early succession. Although no effects of polyphenols were registered here, what proved striking was the resilience of the system and the capability to support high tannin concentrations throughout the experiment. Therefore, future investigations are necessary to elucidate the key role of such humic substances in the structuring of plankton assemblages of shallow lakes from strongly impacted areas, such as those found in the pampean region.