Abstract
The 137Cs technique of quantifying soil erosion is used to provide field data to compare with the empirical model USLE/RUSLE for predicting long-term erosion rates in afforested lands. Caesium-137 from atmospheric nuclear-weapons tests in the 1950s and 1960s, deposited worldwide on the land surface by precipitation, has become an important tool for assessing soil erosion and sedimentation in a wide variety of environments. The underlying hypothesis to support the use of 137Cs measurements to estimate rates of erosion or sedimentation is the assumption that a reliable relationship can be established between the degree of increase or depletion of the soil caesium-137 inventory relative to the baseline or reference inventory and the total depth of soil loss or accumulation. The reference inventory is usually established by sampling adjacent, stable sites, where neither erosion nor deposition has occurred. Where sample inventories are lower than the local reference inventory, erosion may be inferred. Similarly, sample inventories beyond the reference level are indicative of deposition. Estimation of sediment production by erosion has traditionally been solved through the use of empirical models as USLE and its corrected version RUSLE (Renard et al., 1997), and extensive work has been done regarding calibration and validation of its main parameters under Uruguayan local conditions (Clérici y García Prèchac, 2001). The results of a trial run of the technique on Eucalyptus forested microcatchment (97 ha) are presented. The expected distribution of deposition was derived from the reference sample activity: 373,5 Bq/m2. Evidence of soil erosion in the catchment’s middle slope was deduced whereas soil cores from the lower slope had more than expected activity indicating deposition. Results indicate a good agreement between the 137Cs data and USLE/ RUSLE predicted erosion in the slope.
Highlights
Since 1998 researchers from the Universidad de la República (UdelaR) Agricultural Engineering Network carry on investigation in connection with hydrological and environmental variables under different land uses, with a focus on soil and water resources in afforested areas
The viability and potential of the caesium-137 technique in Uruguayan afforested areas has been demonstrated by the results presented here
The obtained results in terms of net erosion rates fall within the expected range, given the characteristics of soil and vegetal cover and well below the referenced maximum soil erosion threshold
Summary
Since 1998 researchers from the Universidad de la República (UdelaR) Agricultural Engineering Network carry on investigation in connection with hydrological and environmental variables under different land uses, with a focus on soil and water resources in afforested areas. Micro-watersheds under diverse land uses and management practices were considered as case study units for which the most widespread-used hydrological variables were monitored and recorded, so to speak quantity and quality of rainfall and runoff waters, extreme storm events runoff peaks, distribution of rainfall and water interception, monitoring of water table levels, soil loss measurements in the watershed area. This very model, subject of extensive parameter calibration proceedings aiming to adapt the equation to local conditions (Puentes, 1981; García Préchac et al, 1999; Terra y García Préchac, 2001, Clérici y García Préchac, 2001), has become the most widespread tool to determine soil sheet erosion rates in Uruguay
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