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Rice terraces are crucial for agriculture in China's southern mountainous regions. Land use and land cover change (LUCC) in these areas impact hydrology, but our understanding is limited. In this study, we applied the hydrological assessment tool SWAT to a selected small watershed in the rice terrace-dense area of central Hunan province, China. This study covered four LUCC periods over the past 40 years and was simulated at annual and monthly scales. The results showed that from 1980 to 2020, the areas of paddy fields and drylands decreased by 4.19% and 5.76%, respectively, while the areas of forests and construction land increased by 1.14% and 92.48%, respectively. During the past period, LUCC led to a decrease of 1.77% and 2.49% in runoff and infiltration, respectively, and an increase of 1.03% in ET. However, the water yield remained almost unchanged, indicating that the rice terrace plays a positive role in maintaining stable watershed water yield under LUCC. The results of the sub-basin analysis indicated that the transformation of paddy fields and forests directly determines the trend of hydrological changes. Land use type had the most significant impact on the runoff of the rice-terrace watershed, with the proportions of paddy fields and forests being the most influential factors. Paddy fields significantly influenced the stability of runoff at the watershed scale, suggesting that a high paddy field ratio doesn't ensure sustainability. This study offers valuable insights for managing small watershed terraces, land use planning, and achieving sustainable development in the watershed. [ABSTRACT FROM AUTHOR]

This study seeks to clarify the content characteristics, spatial distribution, potential sources and ecological risks of nitrogen, phosphorus and some heavy metals (As, Hg, Cd, Cr, Cu, Pb, Zn and Ni) in the sediments of Yueliang Lake. Nitrogen, phosphorus and heavy metals were analyzed in the surface and core sediments of Yueliang Lake. The present situation of heavy metal pollution and the degree of potential ecological risk in sediments was evaluated by the geo-accumulation index (Igeo) and potential ecological risk index (RI). The correlation (CA) and principal component analysis (PCA) methods were used to analyze the potential sources of the main pollutants among the heavy metals. The results show that the total nitrogen (TN = 2305 mg/kg) and total phosphorus (TP = 530 mg/kg) in the surface sediments of Yueliang Lake are at medium and low levels, respectively. The average content of organic matter was 2.17%, and the nutrient ratio was 6.90–11.92, which was significantly higher in the northwest than in the middle and east of Yueliang Lake, indicating that the organic matter was a mixture of endogenous aquatic plants and exogenous terrestrial plants in the sediments. From two evaluation indices (RI and Igeo) calculated using element contents, the heavy metals in the surface sediments were at a moderate ecological risk level. The level of Hg was moderately polluted, Pb and Cd were at the mildly polluted level, and Cu, Zn, As, Cr and Ni were at pollution-free levels. Except for Hg, the other elements in the core sediment are basically not polluting, and the whole is at the level of slight ecological risk. The sources of heavy metals in the sediments are roughly divided into three categories. The first category is natural sources, including Cr, Ni, As, Zn and Cu. The second category includes Cd and Hg and the main sources are highly related to energy development and agricultural activities. The third category is light Pb pollution caused by vehicular traffic and coal-related industrial activities. Therefore, the pollution problems caused by tourism development and agricultural activities should be considered in the future development of the Yueliang Lake area. [ABSTRACT FROM AUTHOR]

Riparian phreatophytes in hyperarid areas face selection pressure from limiting groundwater availability and high transpiration demand. We examined whole-plant water use and hydraulic traits in Populus euphratica and Tamarix ramosissima seedlings to understand how they adapt to groundwater variations. These species coexist in the Tarim River floodplain of western China. Measurements were performed on 3-year-old seedlings grown in lysimeters simulating various groundwater depths. P. euphratica had relatively greater leaf area-specific water use due to its comparatively higher sapwood area to leaf area ratio (Hv). A high Hv indicates that its sapwood has a limited capacity to support its leaf area. P. euphratica also showed significantly higher leaf-specific conductivity (ksl) than T. ramosissima but both had similar sapwood-specific conductivities (kss). Therefore, it was Hv rather than kss which accounted for the interspecific difference in ksl. When groundwater was not directly available, ksl and Hv in P. euphratica were increased. This response favors water loss control, but limits plant growth. In contrast, T. ramosissima is more capable of using deep groundwater. Stomatal sensitivity to increasing leaf-to-area vapor pressure deficit was also higher in P. euphratica. Overall, P. euphratica is less effective than T. ramosissima at compensating for transpirational water loss at a whole-plant level. For this reason, P. euphratica is restricted to riverbanks, whereas T. ramosissima occurs over a wide range of groundwater depths. [ABSTRACT FROM AUTHOR]