Land use changes diminish soil water storage in highland ecosystems of central Argentina

Abstract:

The rivers which provide water to over two million people are born in the highlands of central Argentina, above 1900 m a.s.l. Disturbances caused by livestock and fire regimes, mostly anthropogenic, are important modulators of the vegetation cover and soil integrity. The aim of the present study was to analyze water dynamics in highland ecosystems of central Argentina, in sites with contrasting vegetation covers, though similar topography. In the context of the “trade-off infiltration hypothesis”, it was predicted that in these seasonal mountain sites with frequent fog events the loss of vegetation structure and impairment of soil functioning caused by grazing and fire would reduce the infiltration opportunities and soil water storage. Our results showed that sites with more structured vegetation presented edaphic features that enhanced infiltration opportunities and soil water storage capacity due to deeper soil profiles. On the other hand, sites with a higher root biomass and soil properties that benefit soil water storage capacity were dominated by plants with potentially higher transpiration rates. Fog was an extra input of water all year round when a vertical structure allowed its interception, suggesting that the input by this means is greater in sites with structured vegetation. Additionally, fog may cause an indirect effect over soil water status by suppressing direct soil evaporation and plant transpiration. Superficial soil water content was highest at sites where the vegetation cover was more structured and soils deeper. This can be explained by the positive effect of the structured vegetation on edaphic properties that enhance infiltration opportunities and soil water storage capacity; as well as by the extra input of water by a higher fog interception. Likewise, sites with deeper soils presented more days along the year with a groundwater table present. In summary, this study supports the trade-off infiltration hypothesis. Even though sites with less structured vegetation and with more compacted soils were dominated by plants with a thrifty water strategy, this did not lead to a higher accumulation of water in the soil profile in comparison to sites with a more preserved vegetation-soil complex.