Search

Abstract: The isolated Easter Island (Rapa Nui) is an outstanding example of land degradation caused by land use in a sensitive ecosystem. The focus of the investigation was placed on Poike peninsula, the most eastern part of Rapa Nui. While Poike peninsula was once supplied with fertile soils, in large areas desertification takes place today. Detailed analysis of soil profiles allowed the reconstruction of the history and of causes and effects of soil erosion and gullying in the context of land use history and cultural evolution. The results of the stratigraphic analysis prove that from the beginning of human settlement around AD 300/600 until AD 1280 the agriculture on Poike peninsula was characterised by sustainable land use and a traditional type of agro-forestry. Soil erosion was not significant. At around AD 1280 the woodland on Poike, dominated by the endemic palm Jubaea sp., was cleared by slashing and burning. Intensive farming on the upper slopes of the volcanic peninsula resulted in sheet erosion lasting until the 20th century. Settlements and ceremonial places which were built around AD 1300 on downslope areas were buried soon by sediments. Agriculture ceased around AD 1400 on downslope areas as the fertile soils were completely eroded. From AD 1400 until the late 19th century sheet erosion and the accumulation of fine-layered sediments migrated upslope. On average 8.6 Mg of soil per hectare and per year were reworked by erosion (eroded and accumulated within the catchment). Gullying began on Rapa Nui with the sudden increase in the number of sheep during the early 20th century. Gullies are still developing on the island and their ongoing enlargement created extended badlands on Poike which pose a significant problem for ecological and archaeological conservation strategies. Gullying rates exceed 190 Mg ha−1 y−1. [Copyright &y& Elsevier]

Abstract: Analysis of contemporary and past gully erosion and infilling processes allowed to reconstruct the long-term evolution of a permanent gully system under cropland. An active and a buried gully under cropland were investigated. The recent sediment deposits within the active gully, adjacent to the buried gully, showed that the recent gully was filling in at a mean rate of 6.4 cm a−1. In the buried gully, several erosion and deposition phases could be identified and the type of deposited sediments revealed a complex infilling history. Charcoal, pottery and brick fragments of different sizes were found at all depths of the gully infilling. Their age indicates that the first gully incised after the midst of the 17th century, most probably in the second half of the 18th century or the early 19th century. Gully morphology and analogy with the processes in the recent gully indicate that the buried gully filled in rapidly. Overall, five cycles of cut and fill occurred in 350 years or less and four cycles even within little less than a few decades, indicating that gully development and infilling under cropland can be very rapid processes. [Copyright &y& Elsevier]

The clayey Ultisols in low hilly area in southeastern China were called for agricultural reclamation to meet the increasing food demand. However, little attention was given to soil erosion during land use planning due to lack of information on the amount of soil erosion and how to restore the severely eroded bare soils. The objectives were to estimate the long-term influences of reforestation on soil and water erosion and nutrient losses on a severely eroded bare land derived from Quaternary red clay. The results indicated that reforestation using integrative measures decreased surface runoff and soil erosion on the severely eroded land. On the severely eroded bare land, annual runoff varied from 303 to 1056 mm and annual total soil loss from 53 to 256 tons ha−1. After reforestation, soil erosion dramatically reduced to 2–43 tons ha−1 year−1 from 1988 to 1990 and became negligible since then. The high level of soil erosion was attributed to high rainfall erosivity, readily transportable particles due to the presence of pseudo sand on the bared soil surface formed in the dry season and due to clay dispersion occurring in the long rainy season, and the gully landform. Depositional soil loss accounted for the high proportion of soil loss, while enrichment ratios (ER) of soil nutrients in the suspensional sediment were greater than 1. The results suggest that soil erosion has to be taken into account when planning to convert the clayey soils in the low hilly area for agricultural use, and integrative measures to reforest are key to prevent soil erosion on the severely eroded bared land. [Copyright &y& Elsevier]