Qiangguo Cai

Effect of rainfall regime and slope on runoff in a gullied loess region on the Loess Plateau in China

Runoff was measured from seven plots with different slopes nested in Tuanshangou catchment on the Loess Plateau to study effect of slopes on runoff in relation to rainfall regimes. Based on nine years of field observation and K-mean clusters, 84 rainfall events were grouped into three rainfall regimes. Rainfall regime A is the group of events with strong rainfall intensity, high frequency, and short duration. Rainfall regime C consists of events with low intensity, long duration, and infrequent occurrence. Rainfall regime B is the aggregation of events of medium intensity and medium duration, and less frequent occurrence. The following results were found: (1) Different from traditional studies, runoff coefficient neither decreased nor increased, but presented peak value on the slope surfaces; (2) For individual plot, runoff coefficients induced by rainfall regime A were the highest, and those induced by rainfall regime C were the lowest; Downslope, the runoff coefficients induced by three rainfall regimes presented the same changing trend, although the peak value induced by regime A occurred on a shorter slope length compared to those by regime B and C; (3) Scale effect on runoff induced by rainfall regime A was the least, and that induced by rainfall regime C was the largest. These results can be explained by the interactions of crusting, soil moisture content, slope length and gradient, and erosion units, etc., in the context of different rainfall regimes.

Using 137Cs to study spatial patterns of soil erosion and soil organic carbon (SOC) in an agricultural catchment of the typical black soil region, Northeast China

Understanding the spatial pattern of soil organic carbon (SOC) is of great importance because of global environmental concerns. Soil erosion and its subsequent redistribution contribute significantly to the redistribution of SOC in agricultural ecosystems. This study investigated the relationships between (137)Cs and SOC over an agricultural landscape, and SOC redistribution was conducted for an agricultural catchment of the black soil region in Northeast China. The spatial patterns of (137)Cs and SOC were greatly affected by the established shelterbelts and the developed ephemeral gullies. (137)Cs were significantly correlated with SOC when (137)Cs were >2000 Bq m(-2), while no relation was observed between them when (137)Cs were <2000 Bq m(-2). Factors other than soil erosion such as vegetative productivity, mineralization of SOC, landscape position and management induced their spatial difference of (137)Cs and SOC. Using (137)Cs technique to directly study SOC dynamics must be cautious in the black soils. The net SOC loss rate across the entire catchment during 1954-2010 was 92.8 kg ha(-1) yr(-1), with around 42% of the eroded SOC being redeposited within the catchment. Such information can help guide shelterbelt establishment or other land management to reduce SOC loss in the agricultural ecosystems.

A review on rill erosion process and its influencing factors

Rills are frequently observed on slope farmlands and rill erosion significantly contributes to sediment yields. This paper focuses on reviewing the various factors affecting rill erosion processes and the threshold conditions of rill initiation. Six factors, including rainfall, runoff, soil, topography, vegetation and tillage system, are discussed. Rill initiation and network are explored. Runoff erosivity and soil erodibility are recognized as two direct factors affecting rill erosion and other types of factors may have indirect influences on rill erosion through increasing or decreasing the effects of the direct factors. Certain conditions are necessary for rill initiation and the critical conditions are different with different factors. Future studies should be focused on 1) the dynamic changes of rill networks; 2) the combined effect of multiple factors; and 3) the relationships of threshold values with other related factors.

Temporal variations of ecological security with soil and water loss stress in black soil region of northeast China: a case study on Baiquan County

The deterioration of ecological situation with serious soil and water loss in black soil region of northeast China has attracted more attention due to its significant role on food security of China. To investigate the temporal characteristics of ecological status in typical black soil areas, Baiquan County is selected. Based on the model of Press-Status-Response (P-S-R), indicators are established and the ecological security situations with soil and water loss of Baiquan County are evaluated for the years of 1979, 1990, 2000 and 2005. The results show that the ecological insecurity indicator changes from 0.701 to 0.435 from 1979 to 2005, with a decrease of 37.9% for Baiquan County. And the contributions of physical and human factors to the temporal variations of the ecological security are discussed in detail. Moreover, several problems are recognized to be the potential threats to the ecological security in Baiquan county, including reduction of the effective thickness, excessive application of the fertilizer and low efficiency of the agricultural irrigation system. It is found that effective soil and water loss control actions have made great contribution to the improvement of the ecological security in Baiquan county. All these results and discussions are very helpful for the further investigation on the quantitative relationship between soil and water loss and ecological security in black soil region of northeast China.