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Gravitational mass wasting on steep slopes plays an important role in permanent gully development. This is typically driven by hydrological processes in the head cut and the hydromechanical response within the soil mass. In this study, erosion intensities were observed in the head cuts of two permanent gullies in the mollisol region of Northeast China during the rainy and snow melting seasons. To understand the physical process, soil water storage and drainage capacity, and suction stress during the 111 d of the rainy season and 97 d of the snow melting season, critical parameters such as soil moisture, temperature, and precipitation were investigated. This analysis also examined the increase in pore water pressure, dissipation properties, and hydromechanical properties of the mollisols. Under the same confining stress, the mollisols in the interrupted head cut of Gully No. II increased more rapidly and dissipated pore water pressure more than at the uninterrupted head cut of Gully No I. The combination of the soil water characteristic curve and the hydraulic conductivity function indicates that the mollisols of Gully No. II had a higher air entry pressure and saturated hydraulic conductivity during the wetting and drying cycles than Gully No. I. The head cut area of Gully No. II exhibited rapid water infiltration and drainage responses during rain events, with a high soil water storage capacity during torrential rain, rainstorms, and snow melting seasons. The absolute suction stresses within the mollisols of Gully No. II was lower than that in Gully No. I, which could lead to high erosion per unit of steep slope area. Soil loss from gravitational mass wasting on steep slopes is closely related to soil suction stress and we observed a correlation between erosion per unit gully bed area and the soil water storage. These findings have deepened our understanding of the physical process of permanent gully development from the perspective of the hydrological and hydromechanical behavior of gully head cuts. [ABSTRACT FROM AUTHOR]

The increasing discharge of dyes and antibiotic pollutants in water has brought serious environmental problems. However, it is difficult to remove such pollutants effectively by traditional sewage treatment technologies. Semiconductor photocatalysis is a new environment-friendly technique and is widely used in aqueous pollution control. TiO 2 is one of the most investigated photocatalysts; however, it still faces the main drawbacks of a poor visible-light response and a low charge-separation efficiency. Moreover, powder photocatalyst is difficult to be recovered, which is another obstacle limiting the practical application. In this article, g-C 3 N 4 /TiO 2 heterojunction is simply immobilized on a glass substrate to form an all-solid-state Z-scheme heterojunction. The obtained thin-film photocatalyst was characterized and applied in the visible-light photodegradation of colored rhodamine B and tetracycline hydrochloride. The photocatalytic performance is related to the deposited layers, and the sample with five layers shows the best photocatalytic efficiency. The thin-film photocatalyst is easy to be recovered with stability. The active component responsible for the photodegradation is identified and a Z-scheme mechanism is proposed., Competing Interests: The authors declare no conflict of interest.