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doi: 10.1002/ldr.3400010302pmid: N/A
Soil degradation is usually a complex process in which several features of soil deterioration can be recognized. Soil degradation may lead to the loss of land or soil; limitations to normal soil functions; decrease of soil fertility and ‘productive capacity’.
doi: 10.1002/ldr.3400010303pmid: N/A
A hydroelectric dam currently under construction is likely to have significant adverse impacts on riparian forest bordering the Turkwel River in northern Kenya. The forest is dominated by Acacia tortilis which depends upon river flooding. The River has a seasonal and highly ‘flashy’ flow regime, and floods are vital to recharge the floodplain aquifer. Flood regime, bruchid beetle infestation of Acacia pods, and the role of domestic herbivores in killing beetle larvae and grazing seedlings are important influences on Acacia regeneration. The riparian forest is a vital element in the grazing ecology of Turkana pastoralists, particularly in the dry season and in times of drought. Dam construction threatens the degradation of the forest both through reduced survival of existing trees and reduced regeneration. Such degradation would have serious implications for the Turkana.
doi: 10.1002/ldr.3400010304pmid: N/A
The principal objective of this investigation was to quantify erosion rates for five agricultural fields in three separate study areas in Saskatchewan. The radionuclide tracer caesium‐137 (137Cs) was used to quantify net erosion and net deposition within the landscape over a 30‐year period. Uneroded (native) sites were used to establish the mean background level of 137Cs in each of the study areas. The assumption being that agricultural sites with 137Cs areal activities greater than the native site were subject to deposition, and sites with 137Cs less than the native control site were subject to erosion. A linear proportionality model was used to convert the loss or gain of 137Cs to net soil erosion or deposition. Results have indicated that accelerated (anthropogenic) erosion has been commonplace on arable land in Saskatchewan, even on near‐level fields (< 1.3 degrees). The net integrated sediment output from the five agricultural fields ranged from — 0.6 t th−1 y−1 to — 6.8 t ha−1 y−1 (where negative values represent erosion). What is more alarming is that between 40 and 75 per cent of all sites sampled within individual fields had erosion rates in excess of the generally accepted rate of soil formation (1.0 t ha−1 y−1). Also, in one highly eroded field (Crystal Springs medium sloping site) 65 per cent of the sites sampled exceeded the upper tolerable erosion rate of 11.0 t ha−1 y−1. These results indicate significant degradation of the non‐renewable soil resource has occurred over the past 30 years and is still presently active. Land degradation by accelerated erosion would result in reductions in effective rooting depth, soil moisture holding capacity, essential nutrient stores, and would adversely effect the physical structure of the topsoil. The major reason for accelerated erosion on arable land in Saskatchewan is the practice of summer fallowing, where the field is left in a ‘bare’ state and repeatedly tilled every second or third year. During a fallow period, or prior to crop emergence during a cropping year, fields are subject to wind and water erosion. On near‐level fields wind would be the dominant transport agent, while on sloping fields inter‐rill and rill erosion would be the primary forces of erosion. It is suggested that the appropriate conservation farming response would be to increase application of surface mulches and possibly to decrease the frequency of summer fallowing. Without such efforts long‐term sustainable agricultural production in the Prairies of Canada is considered to be a tenuous land use practice.
doi: 10.1002/ldr.3400010305pmid: N/A
Temporal and spatial changes in land use, vegetation cover, deforestation and reforestation in the Zambian Copperbelt were studied using a combination of aerial photograph analysis, literature review and inquiries among relevant government institutions.
doi: 10.1002/ldr.3400010306pmid: N/A
Land degradation in the middle and upper Yangtze has caused loss of cultivable land, sediment deposition in reservoirs and changes in the runoff: sediment yield relationships of major tributaries. The Jialin River and the Dukou‐Pingshan sector of the Jingsha River together contribute over 75 per cent of all the sediment carried by the Yangtze at Yichang. As the Jialin catchment has the highest rates of erosion per unit area, high sediment discharges from that river exert a major influence on peak summer sediment discharges on the Yangtze. Even though land degradation is increasing in severity, there is no clear overall pattern or trend in variations in sediment yield since 1950. Some tributaries are affected by major reservoir construction and soil conservation works, others are not.
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