The effects of rainfall regimes and terracing on runoff and erosion in the Three Gorges area, China.

Changes in natural rainfall regimes have taken place and are expected to become more pronounced in future decades. These changes are also likely to be accompanied by changes in crop management practices. The main purpose of this study was to analyze runoff and soil loss in relation to rainfall regimes and terracing in the Three Gorges area, China. Based on 10 years of field observation and k-mean clusters, 101 rainfall events were grouped into three rainfall regimes. Rainfall regime I was the group of events with strong rainfall intensity, high frequency, and short duration. Rainfall regime III consisted of events with low intensity, long duration, and high rainfall amount. Rainfall regime II was the aggregation of events of high intensity and amount, and less frequent occurrence. The results showed that event runoff coefficients were not significantly different among rainfall regimes. However, the average soil erosion rates in rainfall regimes I and II were significantly higher than that in regime III. The average erosion rates under rainfall regimes I, II, and III were 21.6, 39.7, and 9.8 g m-2, respectively. The effect of rainfall regime on soil erosion also was changed by terracing. On unterraced cropland, soil erosion rate in rainfall regime I is significantly higher than that in regime III. However, the situation did not exist in unterraced orchard. Terracing significantly reduced runoff and soil erosion, and compensated the effects of rainfall regime on soil erosion, which indicated that runoff and erosion in terraced system may be little influenced by climate change. Based on these results, it was suggested more attention should be paid to the timing of rainfall events in relation to crop development and the high erosion on unterraced citrus orchard to control soil erosion in this area.

[Runoff and nitrogen loss characteristics in soil-epikarst system on a karst shrub hillslope]. / 喀斯特灌丛坡地土壤-è¡¨å±‚å²©æº¶å¸¦äº§æµåŠæ°®ç´ æµå¤±ç‰¹å¾.

With the development of the binary structure of karst landforms, surface water is largely drained with rapid loss of nutrients. However, the pathway and mechanism of nutrient loss remain elusive. From a three-dimensional (vegetation-soil-epikarst system) perspective of a critical zone in karst area, this study conducted rainfall induced runoff and nitrogen loss monitoring during monsoon in karst shrub slopes. Isotope-based (D and 18O) hydrograph separation method was applied to partition the ratio of 'old' and 'new' water in main hydrological path. The main results were summarized as follows. Deep percolation and interflow were the dominant hydrological pathways, accoun-ting for 71% and 9% of total rainfall amount, respectively. In contrast, surface runoff occupied less than 2%. Both deep percolation and interflow were dominated with 85% and 61% of old water, respectively. The highest nitrate concentration occurred in deep percolation (1.97 mg·L-1), while the highest ammonium nitrogen concentration occurred in interflow (1.18 mg·L-1). Deep percolation contributed 89.4% of total nitrogen loss, which was significantly higher than that of surface runoff and interflow. Old water ratio showed a significant positive correlation with nitrate nitrogen concentration, ammonium nitrogen concentration, and total nitrogen loss, suggesting it might be the main agent driving nitrogen migration for the whole soil-epikarst system in karst hillslopes. The results would provide scientific basis for rational allocating water resources and developing nutrient loss control technology in karst region of southwestern China.

Neuronal-derived Ccl7 drives neuropathic pain by promoting astrocyte proliferation.

Recent studies suggest that peripheral nerve injury converts resting spinal cord astroglial cells into an activated state, which is required for the development and maintenance of neuropathic pain. However, the underlying mechanisms of how resting astrocytes are activated after nerve injury remain largely unknown. Astroglial cell proliferation and activation could be affected by endogenous factors including chemokines, growth factors, and neurotropic factor. Chemokine (C-C motif) ligand 7 (Ccl7) is essential in facilitating the development of neuropathic pain; however, the mechanism is unknown. In the present study, we found that Ccl7 promoted astrocyte proliferation and thus contributed toward neuropathic pain. Spinal nerve ligation increased the expression in the spinal cord of neuronal Ccl7. Behavioral analyses showed that knockdown of Ccl7 alleviated spinal nerve ligation-induced neuropathic pain. Further in-vitro study showed that neuronal-derived Ccl7 was sufficient for the proliferation and activation of astroglial cells. We found a novel mechanism of Ccl7 stimulating the proliferation and activation of spinal cord astrocytes that contributes toward neuropathic pain.