Numerically Simulated Water Movement in Reclaimed Multi-Layered Soil Backfilled with Yellow River Sediments

The Yellow River interlayer filling reclamation technology can effectively improve the quality of destroyed cultivated land in the condition of limited soil resources. However, it is a conundrum to choose the appropriate sandwich strategy according to the amount of soil that can be backfilled. This study using the Hydrus-1D model to simulate water movement in reclaimed multiple-layered soils were to understand the mechanism of interlayer, and predict the optimal profile for reclaimed with Yellow River sediments. Simulations were performed on 18 soil profiles that were divided into a control check (CK) and two general scenarios that the total thickness of soil were 50 and 60 cm. Treatments in both scenarios exhibited interaction of different positions and thicknesses of soil interlayer. Results showed that removing part of the subsoil overlying the sediment placed it between sediment layers will improve the infiltration character of the conventional reconstructed soil profiles (T50-0 and T60-0). Moreover, changing the thickness of the interlayers affected infiltration character and soil water-holding capacity more than changes in the position of the layers for same total thickness of native soil. The optimal reconstructed soil profiles for scenarios 1 and 2 were T50-6 (interlayer thickness of 20 cm and located at a position of 30 cm) and T60-9 (interlayer thickness of 30 cm and located at a position of 30 cm), which could have a better infiltration character that were more closed to the native farmland.

Uranium isotopic constraints on the nature of the prehistoric flood at the Lajia site, China

The catastrophic landslide-dam outburst flood, possibly caused by the same earthquake that destroyed the well-dated Lajia archaeological site, in the upper reaches of the Yellow River in China, may provide an accurate constraint on the age of the first Chinese dynasty (Xia Dynasty), which, according to Chinese ancient documents, has been associated with flood-control activities. The key link between the destructive earthquake and the megaflood is a flood-related blackish sand layer (BSL) covering the Lajia site on terraces high above the Yellow River channel. However, the BSL, which mainly consists of debris of local schist, may have originated from mudflows in local gullies rather than an outburst flood from the Yellow River that swept predominantly schist debris from channel slopes and/or a landslide dam. The composition of the fine particles in the BSL can help to discriminate the provenance of the BSL because an outburst flood would consist of suspended particles from the Yellow River, while a mudflow origin would incorporate fine particles from the local gullies. However, the similar geological origin between the Yellow River sediments and the Quaternary eolian loess and Tertiary reddish clay sediments that feed the local gullies precludes the application of traditional geochemical source tracers. This work shows that the 234U/238U activity ratio, which reflects the comminution age, of the fine particles in the BSL is very similar to that of the Yellow River sediments but not to the sediments in the local gullies, supporting an outburst flood origin of the BSL. Thus, the emergence of the Xia Dynasty can be constrained to be shortly after the sudden destruction of the Lajia site, if the outburst flood is the same event that initiated nationalization as described in the Chinese ancient documents.

Heavy Mineral Variability in the Yellow River Sediments as Determined by the Multiple-Window Strategy

In this study, heavy mineral analysis was carried out in different size fractions of the Yellow River sediment to extract its end-members. It shows that heavy mineral contents, species, and compositions vary in different grain sizes. Distribution curve of heavy mineral concentration (HMC) and particle size frequency curve are in normal distribution. In most samples, the size fraction of 4.5–5.0 Φ contains the maximum HMC (18% on average). Heavy mineral assemblages of the Yellow River are featured by amphibole + epidote + limonite + garnet. Amphibole content is high in coarse fraction of >3.0 Φ and reaches its peak value in 3.5–4.5 Φ. Epidote is rich in a size fraction of >3.5 Φ, and increase as the particle size becomes fine. Micas content is high in coarse subsamples of <3.0 Φ, but almost absent in fine grains of >4.0 Φ. Metallic minerals (magnetite, ilmenite, hematite, and limonite) increase as the sediment particle size become fine, and reach the peak in silt (>4.0 Φ). Other minerals such as zircon, rutile, tourmaline, garnet, and apatite account for about 15%, and mainly concentrate in fine sediment. Further analysis reveals that similarity value between the most abundant grain size group and wide window grain size group is high (0.978 on average). The grain size of 4.0–5.0 Φ ± 0.5 Φ is suitable to carry out detrital mineral analysis in the Yellow River sediments. Our study helps to eliminate cognitive bias due to narrow grain size strategy, and to provide heavy mineral end-members of the Yellow River sediment for provenance discrimination in the marginal seas of East China.

Soil Quality Change after Reclaiming Subsidence Land with Yellow River Sediments

With continuous population growth and decreasing cultivated land area, China’s food security is greatly threatened. Additionally, coal mining in China is primarily underground mining, which causes land subsidence and destroys existing cultivated land. This effect aggravates the contradiction between a growing population and a shrinking area of cultivated land. The purpose of this study was to introduce a method of filling reclamation with Yellow River sediments to restore farmland and realize the sustainable utilization of cultivated land. The properties of the soil and crop yields in reclaimed farmland were assessed. This study examined farmland reclaimed with Yellow River sediments at an experimental site located in Jining City, Shandong Province, China. Filling reclamation procedures with Yellow River sediments were applied. The reclaimed farmland (RF) and unaltered farmland (CK) were continuously monitored for three years, and the soil was sampled six times. A total of 180 soil samples were collected from RF and CK. The soil properties were measured at three depths: 0–20 cm, 20–50 cm, and 50–80 cm. Crop yields were monitored regularly. The results indicate that filling reclamation with Yellow River sediments is an effective method for restoring farmland. The RF and CK soils were weakly alkaline, non-saline soils. The RF soil was suitable for the growth of local crops. With an increasing number of farming years, both the quality of cultivated land and crop yields have increased. Therefore, filling reclamation with Yellow River sediments is an effective way to realize the sustainable utilization of cultivated land.

Optimal Thickness of Soil Cover for Reclaiming Subsided Land with Yellow River Sediments

The cultivated land area per capita in China is relatively small compared to the world average. However, most of the coal output is coming from underground mining, resulting in land subsidence and the destruction of existing cultivated land. The Yellow River is known as a ground-suspended river due to its large sediment concentration. Using unpolluted Yellow River sediment to reclaim the coal mine subsidence not only solves the problem of sediment deposition, but also solves the problem of shortage of filling material. Some experimental studies revealed low soil productivity as a result of thin soil cover. To ensure crop growth and production in land reconstructed with Yellow River sediments, determining the optimal thickness of soil cover over the sediment is extremely important. There were four experimental treatments and one control treatment. Each treatment was repeated three times. The control treatment was an original soil profile with 30 cm topsoil plus 110 cm subsoil. The four experimental treatments with different thickness of soil covers had the same thickness of topsoil (30 cm) and Yellow River sediments (60 cm), and different thickness of subsoil, which were 10, 30, 40, and 50 cm, respectively. Thus, the total thicknesses of soil cover (topsoil plus subsoil) were 40 cm, 60 cm, 70 cm, and 80 cm, respectively. The topsoil, subsoil, and Yellow River sediments were collected from Liangshan County. The soil type is fluvo-aquic. Maize (Zea mays L.) is the main crop in Liangshan County. A greenhouse experiment was conducted to investigate the growth of maize. The results showed that (1) the peroxidase (POD) activity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content of maize leaf decreased with an increasing thickness of soil, while soluble protein (SP) and leaf relative water content (RWC) increased. (2) The dry biomasses of the shoot and root system in T70 and T80 were not significantly different from those in the control (3) Increased soil thickness is conducive to the storage of more water and available nutrients. Considering the time and cost of reconstruction, 70 cm is the optimal thickness of soil cover on Yellow River sediment to ensure maize growth.