Earth Surface Processes and Landforms最新文献

Radiocarbon dates from alluvial sections provide maximum deposit ages because of the time lag between formation of the dated material and deposition at the sample site, potentially producing decade- to century-long biases in the dates of historic events, paleoclimatic change, fire histories, and paleoearthquakes. This bias, called the inherited age, combines the inbuilt age distribution, which reflects the age composition of the vegetation of the source area, and the residence time distribution, which includes transport and interim storage prior to final deposition. We tackle inherited age and its components by comparing charcoal dates from two modern fires in southern California, the 2020 Bobcat Fire and the 2013 Grand Fire, with a well-dated late Holocene terrace deposit in the Pallett Creek watershed. Fifty-six radiocarbon dates from the modern fires provide an inbuilt age distribution with a median of 25 years pre-fire (320-year 95% range). An inherited age distribution calculated from 175 terrace deposit dates is older, with a median age of ~90 years (850-year 95% range). Comparing inherited ages calculated from organic-rich versus clastic terrace deposits reveals a slight facies dependence suggesting longer residence times in clastic deposits. We develop a modeled inherited age that incorporates larger calibration uncertainties in pre-1950s samples by combining the modern fire sample distribution with the pre-bomb portion of the calibration curve. The modeled inherited age is younger than the terrace deposit inherited age by only 21 years, indicating inbuilt age, not long residence times, dominates inherited age in this setting. The results imply that paleoearthquakes and climatic event age estimates in the Western Transverse Ranges are up to a century too old. More broadly, dating charcoal from modern fires can constrain inherited age and the resulting distributions can improve the accuracy of dates of past environmental and tectonic events.

Improper management of sugarcane cultivation may cause severe soil erosion, especially in lateritic red soil hilly areas. Crop straw return to the field can effectively improve the soil structure, but there is a lack of evaluation studies of the soil and water conservation benefits of sugarcane leaf mixing and return to the field, and the underlying regulatory mechanism has rarely been described. Thus, we conducted a series of simulated rainfall experiments to investigate the impact of returning different mixed sugarcane leaf weights (0, 3, 6, 9, 12 and 15 t/ha) to the field on erodible lateritic red soil slopes that support sugarcane production under various slopes (5°, 10°, 15° and 20°) in different rainfall events (60 and 120 mm/h). The results indicated that returning sugarcane leaves into farmland could effectively regulate the process of runoff and sediment production on lateritic red soil slopes, and the optimal mixing amount was 9 t/ha. Under a low rainfall intensity, the erosion process was mainly affected by the slope, and the benefits of applying the sugarcane leaf mixing treatment to the slope to reduce runoff and sediment could reach 13.37–53.04% and 23.86–77.55%, respectively. However, under a high rainfall intensity, the sugarcane leaf mixing amount was the main influencing factor, the benefits for reducing runoff and sediment could reach 4.64–38.72% and 30.87–93.14%, respectively. The sugarcane leaf mixing amount exhibited a linear relationship with the Reynolds number (R² > 0.63), whereas the runoff velocity (R² > 0.96), Froude number (R² > 0.94) and drag coefficient (R² > 0.85) exhibited well-fitting exponential function relationship with it. This study provides a reference for future endeavours regarding the inhibition mechanisms of sugarcane leaves mixed and returned to the field for decreasing slope erosion.