Climatic controls of soil moisture dynamics in an arid steppe of northern Patagonia, Argentina

Abstract

Long‐term dynamics of soil moisture (SM) in the surface (0–30 cm) and subsurface (30–60 cm) soil layers of an arid steppe in northern Patagonia were studied in relation to climatic variables. SM was evaluated gravimetrically at four depths at monthly intervals. The dynamics of SM at surface and subsurface layers were described as a function of precipitation, soil, and air temperatures using stepwise regression models. Predicted SM at both layers were validated using a set of SM values measured at other location of the northern Patagonian steppe. A seasonal pattern of wet (SM > 10%) and dry (SM < 5%) periods in soil was observed. In the surface soil, SM was related to heavy precipitation events (>10 mm), falling mainly in the cold season, and to air temperatures. In the subsurface soil, SM was correlated with precipitation events (>10 mm) of the previous 4 months and with air temperatures. A significant (p < .05) reduction of SM below 3% occurred during the thermally favorable growing seasons in the upper layer (0–15 cm) contrasted with attenuated variations in the subsurface layers. The stepwise model produced good predictions of SM (0–15 cm) observed at the location used for validation. However, it overestimated in some degree SM in the 45–60 cm layer when SM was <9% and slightly underestimated the values when SM was >9%. These differences may be attributed to the effect of plant water uptake or to deep percolation losses, a frequent phenomenon in the Patagonian steppe. The shifting patterns of SM at surface and deeper soil layers have implications in the regulation of the biological activity of different plant functional types that explore the soil at different depths. The activity of plant functional types with shallow roots may be limited during the warm season.