Juying Jiao

Seed morphology characteristics in relation to seed loss by water erosion in the Loess Plateau

The role of water erosion on seed loss and on plant establishment and distribution is unknown on the Chinese Loess Plateau, which suffers serious soil erosion. The seed susceptibility of 16 local species to removal by water erosion from loess slopes was determined by rainfall simulation experiments. The experiments were performed on slopes with gradients of 10°, 15°, 20° and 25° for a 60-min duration at an intensity of 50 mm/h, 100 mm/h and 150 mm/h, respectively. The total seed removal rate obviously increased with rainfall intensity but did not obviously change with slope gradient, and the responses were varied among the species. The morphological characteristics affecting seed loss of the various species are quite different. Our experiments showed that the seed removal from some species are mainly due to seed weight, some species are mainly affected by seed shape, some are affected by appendage, some by surface structure, some by the comprehensive effects of the different morphological characteristics, while seeds having mucilage secretion are not easily moved by water erosion. We argued that the seed removal during water erosion can clearly effect seed redistribution and deposition, and consequently, species composition and vegetation spatial distribution.

Factors affecting distribution of vegetation types on abandoned cropland in the hilly-gullied Loess Plateau region of China

A study was conducted in the forest-steppe region of the Loess Plateau to provide insight into the factors affecting the process of vegetation establishment, and to provide recommendations for the selection of indigenous species in order to speed up the succession process and to allow the establishment of vegetation more resistant to soil erosion. Four distinctive vegetation types were identified, and their distribution was affected not only by the time since abandonment but also by other environmental factors, mainly soil water and total P in the upper soil layers. One of the vegetation types, dominated by Artemisia scoparia, formed the early successional stage after abandonment while the other three types formed later successional stages with their distribution determined by the soil water content and total P. It can be concluded that the selection of appropriate species for introduction to accelerate succession should be determined by the local conditions and especially the total P concentration and soil water content.

Changes in sediment discharge in a sediment-rich region of the Yellow River from 1955 to 2010: implications for further soil erosion control

The well-documented decrease in the discharge of sediment into the Yellow River has attracted considerable attention in recent years. The present study analyzed the spatial and temporal variation of sediment yield based on data from 46 hydrological stations in the sediment-rich region of the Yellow River from 1955 to 2010. The results showed that since 1970 sediment yield in the region has clearly decreased at different rates in the 45 sub-areas controlled by hydrological stations. The decrease in sediment yield was closely related to the intensity and extent of soil erosion control measures and rainstorms that occurred in different periods and sub-areas. The average sediment delivery modulus (SDM) in the study area decreased from 7,767.4 t/(km2 ·a) in 1951–1969 to 980.5 t/(km2·a) in 2000–2010. Our study suggested that 65.5% of the study area with the SDM below 1,000 t/(km2·a) is still necessary to control soil deterioration caused by erosion, and soil erosion control measures should be further strengthened in the areas with the SDM above 1,000 t/(km2·a).

Effects of Revegetation on Soil Organic Carbon Storage and Erosion-Induced Carbon Loss under Extreme Rainstorms in the Hill and Gully Region of the Loess Plateau

Background: The Loess Plateau, an ecologically vulnerable region, has long been suffering from serious soil erosion. Revegetation has been implemented to control soil erosion and improve ecosystems in the Loess Plateau region through a series of ecological recovery programs. However, the increasing atmospheric CO2 as a result of human intervention is affecting the climate by global warming, resulting in the greater frequency and intensity of extreme weather events, such as storms that may weaken the effectiveness of revegetation and cause severe soil erosion. Most research to date has evaluated the effectiveness of revegetation on soil properties and soil erosion of different land use or vegetation types. Here, we study the effect of revegetation on soil organic carbon (SOC) storage and erosion-induced carbon loss related to different plant communities, particularly under extreme rainstorm events. Materials and methods: The erosion-pin method was used to quantify soil erosion, and soil samples were taken at soil depths of 0–5 cm, 5–10 cm and 10–20 cm to determine the SOC content for 13 typical hillside revegetation communities in the year of 2013, which had the highest rainfall with broad range, long duration and high intensity since 1945, in the Yanhe watershed. Results and discussion: The SOC concentrations of all plant communities increased with soil depth when compared with slope cropland, and significant increases (p < 0.05) were observed for most shrub and forest communities, particularly for natural ones. Taking the natural secondary forest community as reference (i.e., soil loss and SOC loss were both 1.0), the relative soil loss and SOC loss of the other 12 plant communities in 2013 ranged from 1.5 to 9.4 and 0.30 to 1.73, respectively. Natural shrub and forest communities showed greater resistance to rainstorm erosion than grassland communities. The natural grassland communities with lower SOC content produced lower SOC loss even with higher soil loss, natural secondary forest communities produced higher SOC loss, primarily because of their higher SOC content, and the artificial R. pseudoacacia community with greater soil loss produced higher SOC loss. Conclusions: These results indicate that natural revegetation is more effective in enhancing SOC storage and reducing soil erosion than artificial vegetative recovery on hillsides. However, natural secondary forest communities, with higher SOC content and storage capacity, may also contribute to larger SOC loss under extreme rainstorms.

Measurement on physical parameters of raindrop energy

Rainfall erosivity factor (R) is one of the most commonly used factors in soil erosion models. While rainfall energy (E) is the most elementary physical parameter to predict R. Based on comparative analysis of previous soil erosion models and rainfall erosivity factor measuring methods, integrated application of modern photogrammetric techniques, image analytic methods and automatic control theories, this paper provided a new method based on image analytic to calculate the rainfall energy and R factor, which obtains raindrops volume and velocity by means of modern photogrammetric technique. Results show that this method can improve both efficiency and accuracy of rainfall energy calculation and other rainfall physical parameters measurement.

Soil Seed Bank and Standing Vegetation of Abandoned Croplands on Chinese Loess Plateau: Implications for Restoration

Vegetation succession depends on the availability of suitable propagules in the soils, and an understanding of soil seed banks is important for effective vegetation restoration of abandoned croplands. Aims of this study were to identify characteristics of soil seed bank, relationship with standing vegetation, and potential significance of soil seed bank for vegetation restoration in abandoned croplands on the hilly-gullied Loess Plateau. Results of field survey, germination, and correspondence analysis showed that density of soil seed bank ranged from almost 900 through almost 6470 seeds m−2 at 0–5 cm depth and almost 120 through almost 2470 seeds m−2 at 5–10 cm depth, with species richness of 7–14. Early successional species dominated soil seed bank, while later successional species occurred only at low densities. Similarity between soil seed bank and standing vegetation was low (with an average of 0.261). Most important variables contributing to the variation of the standing vegetaion included soil water, extractable P, soil seed bank density, and aspect. Soil seed bank alone explained 32% of vegetation community variation. Potential for vegetation restoration from soil seed banks is limited, and it is recommended to transplant some later successional species into abandoned croplands to accelerate succession.

Have conservation measures improved Yellow River health

The Yellow River is the second-longest river in China with a length of 5,464 km (3,395 mi). It originates from the eastern Qinghai–Tibet Plateau flows eastward through the Loess Plateau, and empties into the Bohai Sea. The whole river basin, which covers approximately 752,443 km2 (290,520 mi2), was regarded as “the cradle of Chinese Civilization” (Zhu et al. 2004) and has played an important role in regional economic development. However, extreme floods, hyperconcentrated sediment flow, and water shortages have been ongoing environmental problems that the Chinese national government must face and resolve in the Yellow River Basin. The Yellow River is well known worldwide due to its extraordinarily high suspended sediment concentration. The Loess Plateau, located in the upper-middle reaches of the Yellow River, contributed approximately 90% of the sediment in the mainstream. Additionally, catastrophic floods that occurred frequently in the tributaries during summer months brought hyperconcentrated sediment flow to the main stem of the river. Large amounts of sediment deposition have made the Yellow River a “suspended” river in which the channel bottom reaches up to 10 m (33 ft) above ground. The continual elevation of the river bed has resulted in a great decline of sediment transport capacity.

Assessing response of sediment load variation to climate change and human activities with six different approaches

Understanding the relative contributions of climate change and human activities to variations in sediment load is of great importance for regional soil, and river basin management. Considerable studies have investigated spatial-temporal variation of sediment load within the Loess Plateau; however, contradictory findings exist among methods used. This study systematically reviewed six quantitative methods: simple linear regression, double mass curve, sediment identity factor analysis, dam-sedimentation based method, the Sediment Delivery Distributed (SEDD) model, and the Soil Water Assessment Tool (SWAT) model. The calculation procedures and merits for each method were systematically explained. A case study in the Huangfuchuan watershed on the northern Loess Plateau has been undertaken. The results showed that sediment load had been reduced by 70.5% during the changing period from 1990 to 2012 compared to that of the baseline period from 1955 to 1989. Human activities accounted for an average of 93.6 ± 4.1% of the total decline in sediment load, whereas climate change contributed 6.4 ± 4.1%. Five methods produced similar estimates, but the linear regression yielded relatively different results. The results of this study provide a good reference for assessing the effects of climate change and human activities on sediment load variation by using different methods.

Variation in the sediment deposition behind check-dams under different soil erosion conditions on the Loess Plateau, China: Sediment deposition behind check-dams in different erosion conditions

Tomaintain a reasonable sediment regulation system in themiddle reaches of the YellowRiver, it is critical to determine the variation in sediment deposition behind check-dams for different soil erosion conditions. Sediment samples were collected by using a drilling machine in the Fangta watershed of the loess hilly–gully region and the Manhonggou watershed of the weathered sandstone hilly– gully (pisha) region. On the basis of the check-dam capacity curves, the soil bulk densities and the couplet thickness in these two small watersheds, the sediment yields were deduced at the watershed scale. The annual average sediment deposition rate in the Manhonggou watershed (702.0mm/(km·a)) from 1976 to 2009 was much higher than that in the Fangta watershed (171.6mm/(km·a)) from 1975 to 2013. The soil particle size distributions in these two small watersheds were generally centred on the silt and sand fractions, which were 42.4% and 50.7% in the Fangta watershed and 60.6% and 32.9% in the Manhonggou watershed, respectively. The annual sediment deposition yield exhibited a decreasing trend; the transition years were 1991 in the Fangta watershed and 1996 in the Manhonggou watershed (P < 0.05). In contrast, the annual average sediment deposition yield was much higher in the Manhonggou watershed (14011.1 t/(km·a)) than in the Fangta watershed (3149.6 t/(km·a)). In addition, the rainfalls that induced sediment deposition at the check-dams were greater than 30mm in the Fangta watershed and 20mm in the Manhonggou watershed. The rainfall was not the main reason for the difference in the sediment yield between the two small watersheds. The conversion of farmland to forestland or grassland was the main reason for the decrease in the soil erosion in the Fangta watershed, while the weathered sandstone and bare land were the main factors driving the high sediment yield in theManhonggou watershed. Knowledge of the sediment deposition process of check-dams and the variation in the catchment sediment yield under different soil erosion conditions can serve as a basis for the implementation of improved soil erosion and sediment control strategies, particularly in semi-arid hilly–gully regions. Copyright

Influence of Afforestation on the Species Diversity of the Soil Seed Bank and Understory Vegetation in the Hill-Gullied Loess Plateau, China

The Chinese Loess Plateau region has long been suffering from serious soil erosion. Thus, large-scale afforestation has continued during the past decades in order to control soil erosion. Afforestation can dramatically alter nutrient cycles, affect soil-carbon storage, and change hydrology. However, it is unknown how afforestation influences species diversity of the soil seed bank and understory vegetation compared with spontaneous restoration of abandoned land. Forest land with trees planted 30 years ago, abandoned slope land restored spontaneously for 30 years, and the corresponding slopes with remnant natural vegetation were selected as sampling sites. The species richness both in the soil seed bank and vegetation was significantly higher on the afforested slope compared to the spontaneously restored abandoned land. The species similarity between the afforested slope and the remnant slope land was high both in the soil seed bank and standing vegetation compared to the abandoned land. The soil seed bank density varied from 1778 ± 187 to 3896 ± 221 seeds/m2, and more than half of it was constituted by annual and biennial species, with no significant difference among sampling habitats. However, the afforested slope had higher seed density of grass and shrub/subshrubs compared to the abandoned slope. The present study indicates that in the study region, characterized by serious soil erosion, afforestation can better facilitate vegetation succession compared to spontaneously restoration of abandoned slope land.