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Due to the coupled or interconnected relationships among frequent climate extremes, unique geological conditions, discontinuous soil distribution, rugged geomorphology, and highly heterogeneous landscapes in different karst watersheds, few studies were conducted to decouple the relative magnitudes of the climate, lithology, soil, topography, and landscape on soil erosion in karst regions. The objective of this study was to quantify the relative importance of these influencing factors on runoff and sediment yield (SY) in 40 typical karst watersheds in southwest China. To address this issue, the Pearson correlation and random forest were first to select the dominant factors influencing runoff and SY. Subsequently, the partial least squares‐structural equation model (PLS‐SEM) was used to decouple the complex relationships among runoff, SY and their potential influencing factors. Results showed that climate, lithology, soil, topography and landscape could explain 79% of the runoff variation, and only climate factors have significant impact on runoff for heterogeneous karst watersheds (P < 0.01, path coefficient (β) = 0.589). The explanation of five factors to SY variability is 59%, and the landscape has the greatest impact on SY (P < 0.01, β = −0.458). Different from runoff, climatic factors have no significant influence on SY. By elucidating a complex coupled relationship framework, this study can provide a scientific basis for the formulation of soil and water loss program, and the optimization of land resources and ecological environment sustainable development in karst watersheds. Plain Language Summary: The variations of runoff and sediment yield (SY) among heterogeneous watersheds are expected to be influenced by climate, lithology, soil, topography and landscape, which are generally interconnected and coupled. Therefore, it is important to decouple the complex relationship between runoff, SY and their potential influencing factors, especially in karst areas where ecologically fragile regions experience severe soil erosion. The results show that only climate factors play a significant influence on runoff. Unlike runoff, all factors have significant effects on SY except climate factors. Interestingly, landscape factors have the greatest influence on SY. Our findings are conducive to better understanding the hydrological and sediment transport characteristics of karst watersheds, and provide scientific basis for soil erosion control and sustainable development of ecological environment. Key Points: We decoupled the effects of climate, lithology, soil, topography and landscape on runoff and sediment yield (SY)Climate and landscape exerted the largest influence on runoff and SY, respectivelyLithology, soil, topography, and landscape significantly affected SY rather than runoff variability [ABSTRACT FROM AUTHOR]

Non-point source pollution is severe in the Yimeng Mountainous Area of China. Few studies have been conducted to identify and predict phosphorus loss at a watershed scale in this region. The objectives of this study were to identify the characteristics of phosphorus loss and further to develop regression models to estimate phosphorus losses of different forms based on the dataset of measured rainfall, runoff, and sediment of 24 rainfall events during the period of 2010-2011 in a typical small watershed from Yimeng Mountainous Area. The results revealed that phosphorus (P) loss differed considerably with phosphorus forms. The dissolved inorganic phosphorus (DIP) was the dominant form of the total dissolved phosphorus (TDP) loss by runoff, accounting for 72 %. The ratio of particulate phosphorus (PP) to total phosphorus (TP) was 65 %, which indicated that most of phosphorus loss was transported by eroded sediment. Similar to soil loss, rainfall properties influenced phosphorus loss greatly and most of the phosphorus loss was produced by only a few heavy storms. The concentrations of different phosphorus forms during a rainfall event varied with similar trends and reached the maxima prior to the peak runoff. Phosphorus losses of different forms were influenced by rainfall kinetic energy, runoff volume, and sediment loss significantly. DIP, TDP, and TP could be predicted with rainfall kinetic energy and runoff volume satisfactorily ( NSE ≥ 0.92). PP was estimated with rainfall kinetic energy, runoff volume, and sediment loss of rainfall event well ( NSE = 0.90). Further studies are necessary to assess the performance of the developed models under different conditions. [ABSTRACT FROM AUTHOR]

This contribution analyzes the similarities and differences between the measured activities of Cs and excess Pb (Pb) in the cultivated brown and cinnamon soils of the Yimeng Mountain area, discusses the influence of soil texture on the measurement of Pb, and presents differences between the two types of soils. Fields A and B were selected to represent the fields that contain cultivated brown and cinnamon soils, respectively. From either study field, one site of sectioned core and six bulk cores were collected to measure Cs levels, Pb levels, and the particle-size composition of soil samples. Three undisturbed soil samples were collected to measure capillary and aeration porosities. The Cs inventories for the two study fields are very similar. The Cs is a man-made radionuclide, which means that its measured levels for soils are unaffected by soil texture. In contrast, levels of the naturally occurring Pb of soils from Field A were lower than those of Field B by about 50%. In contrast to aquatic sediments, levels of Pb in terrestrial surface soils are affected by the emanation of Rn from the soils. It can be assumed that the coarser the soils, the greater the emanation of Rn; in addition, the lower the measured Pb, the greater the underestimate of this value. The cultivated brown soils in Field A are coarser than the cultivated cinnamon soils in Field B. As a result, Rn in Field A will diffuse more easily into the atmosphere than that in Field B. As a consequence, the measured Pb in soils from Field A is much lower than the actual value, whereas the value measured for Field B is much closer to the actual value. [ABSTRACT FROM AUTHOR]

Studies on the transportation and flux of various kinds of heavy metals in runoff and sediment of five typical landuse types in West Tiaoxi catchment showed that the losses of Cu (0.21 mg.m-2.min-1), Zn (0.45 mg.m-2.min-1), and Pb (0.15 mg.m-2.min-1) in mulberry and that of Cr (0.06 mg.m-2.min-1) in paddy field were larger in surface runoff, while their losses in pinery were very small. Suspended thin particles played the main role on transporting heavy metals in surface runoff under all kinds of land uses. The losses from runoff were much lower than that from sediment, which only occupied 0.1%-4.9%, and the loss rate of Cu from runoff and sediment was higher than that of Cr, Pb and Zn.

Five typical land covers in West Tiaoxi catchment were studied on phosphorous loss in artificial rainstorm runoff. Triple duplication experiments were carried out under the artificial rain condition with intensity of 2 mm.min-1 lasting 32 minutes in 3 m2 plot. Transportation and flux of various species of phosphorous in runoff and sediments were investigated. The results showed that phosphorous losses amount and rate were different among five types of land covers. The loss of total phosphorous in runoff of mulberry garden was the largest, which was five times higher than that of paddy and pinery field. The majority of total phosphorous in runoff was particulate phosphorous. Losses of dissolved phosphorous in vegetable plots and mulberry gardens were much higher than bamboo plot and paddy field. Loss of dissolved inorganic phosphorous in runoff was the main part of dissolved phosphorus, which pinery was much higher than others. Total amounts of phosphorous loss from top 10 cm layer of 5 kinds of soils were estimated as high as 2.57-4.89 g.m-2, of which phosphorous loss through sediment of runoff accounted for more than 97%. The rate of total phosphorous losses were ranged in 0.45-4.11 mg.(m2.min)-1 in runoff, which was much lower than that of 72.82-135.96 mg.(m2.min)-1 in sediment of runoff.