Soils temperature and moisture are variables whose knowledge is required to Determine the energy and water budgets in the biosphere. The thermal and hydric regimes of soils beneath each ecosystem, present considerable variations, according to their mineralogy, the local climate and vegetation. In this context, soil temperatures and moistures were measured under three ecosystems existing over the eastern portion of the Amazon Region, namely: native forest (Caxiuana's National Forest, 01° 42' 30" S and 51° 31' 45" W), pasture area (Soure, 00° 43' 25" S and 48° 30' 29" W) and cultivated area (Igarape-Acu, 01° 07' 59" S and 47° 36' 55" W). Field data at the forest and pasture sites were collected between December, 2001 and February, 2005; while at the cultivated area, the monitoring was limited to the August, 2003 to February, 2005, period. These observations of soil physical variables were analyzed taken into consideration the simultaneously measured meteorological variables such as the incoming solar radiation flux and pluviometric precipitation, which directly impacted the soil variables at each site selected for study. The soil temperatures were monitored by means of thermal sondes at 0.05, 0.2 and 0.5 m depths. Heat fluximeters, measured heat flux at 0.05 and 0.2 m depth levels. The upper 0.3 m soil layer bulk moisture was measured by double probe Time Domain Reflectometer (TDR) sondes at each site. Analyses were made, considering the soil responses during the local dry and rainy seasons at these three representative ecosystems of eastern Amazonia. Apparent thermal diffusivity estimates were made by the amplitude and phase methods, using the daily heating pulse propagation data in these soils. The results showed quite different values. However, the first approach seemed to be more reliable and suitable to numerical modeling. As expected, considering their small vegetation cover, the soil temperatures at the upper levels, presented larger variations at the pasture and cultivated sites. Unexpectedly, the temperatures at 0.5 m depth beneath the forest showed larger amplitude variations than at 0.2 and 0.05 m depths. The numerical modeling of time variations of temperature, as function of depth, for each soil was made through the harmonic method. The results showed that the first harmonic represented over 90% of the total variation of the observed daily pulse of temperature for the pasture and cultivated areas at 0.2 and 0.05 m depths. Similar performance of the modeling was observed for the forest at 0.05 and 0.20 m levels. The magnitude of heat fluxes beneath the pasture and cultivated sites reached values six times larger than those observed beneath the soil of the forest. The results also show that, for the upper 0.30 m layer of soils, the bulk moisture beneath the forest is larger than under the other ecosystems studied in this work. This result apparently is due to the forest's protection against the soils surface evaporation. An analysis of the seasonal and daily behavior of the soils temperature and moisture in response to the incoming solar radiation and precipitation are presented. Case studies of the rate of soil moisture losses after significant water recharge by precipitation events were also analyzed. Some estimates of daily water depletion and even, night recharge of moisture by rising water from lower layers to the 0.30 m layer were made. This work analyzed the largest time series of soil temperature and moisture data taken at high sampling rates, available so far, for eastern Amazonia. It was possible to characterize the differences of these physical variables regimes, beneath three important ecosystems in this Region. Further studies of the minerals and organic materials in these soils, as well as the foliar area and biomass indexes of their vegetation covers, would improve the comprehension of the regimes described in this work.
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