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Rainfall redistribution through the vegetation canopy plays a key role in the hydrological cycle. Although there have been studies on the heterogeneous patterns of rainfall redistribution in some ecosystems, the understanding of this process in different stages of forest succession remains insufficient. Therefore, this study investigated the change tendency of rainfall redistribution and rainwater chemistry in a subtropical succession forest area in South China, based on 22 years (2001-2022) of monitoring 740 valid rainfall events. Results showed that at the event scale throughfall ratio showed in order broadleaf forest (BF) < mixed forest (MF) < pine forest (PF), and stemflow ratio showed in order BF > MF > PF. At the interannual scale, annual gross rainfall considerably shifted over time, which directly induced the variable accumulation of annual throughfall and annual stemflow. In the last 22 years, annual variability of throughfall presented in order MF (CV, 9.7 %) < BF (15.6 %) < PF (16.1 %), and annual variability of stemflow presented in order MF (CV, 38.6 %) < PF (50.9) < BF (56.2 %). The spatial variability of stemflow was always greater than that of throughfall. Besides, the difference of rainwater chemistry fluxes (TN, TP and K+) among the three forest types were found and they changed over time. Throughfall was characterized with high chemistry fluxes compared to open rainfall followed by stemflow. On average, TN and TP fluxes of throughfall presented in order BF < MF < PF, while K+ flux of throughfall presented in order BF > MF > PF. The above results indicated that the patterns of rainfall redistribution often changed over time. The event-scale accumulation of throughfall and stemflow potentially induced the interannual-scale variability. Both water volume and chemistry of throughfall and stemflow depended on the effect of rainfall and forest factors. This study provided insight into the rainfall redistribution process by linking the long-term changing of rainfall pattern and subtropical forest succession sequence. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) transported by surface runoff has been identified as an important role of the global carbon cycle. Despite there being many studies on DOC concentration and flux, but little information is available in semi-arid catchments of the Loess Plateau Region (LPR). The primary goal of this study was to quantify DOC exported from a sequence of runoff events during the concentrated rainfall season. In addition, factors that affect DOC export from a small headwater catchment will be investigated accordingly. Runoff discharge and DOC concentration were monitored at the outlet of the Yangjuangou catchment in Yanan, Shaanxi Province, China. The results showed that DOC concentration was highly variable (1.91-34.70 mg L-1), with event-based DOC concentrations ranging from 4.08 to 15.66 mg L-1. The mean monthly DOC flux loading from the catchment was 94.73-110.17 kg km-2 from June to September, while the event-based DOC flux ranged from 0.08 to 2.81 kg km-2. Intra-events of rainfall amount and runoff discharge led to event-based/monthly differences in DOC concentration and flux. Hysteresis analysis showed a nonlinear relationship between DOC concentration and discharge in the runoff process. Our results highlighted the advantages of high-frequency monitoring for DOC export and indicated that DOC export from a catchment is largely influenced by the interaction of rainfall and antecedent conditions for a rainfall event. Engineering and scientists can take advantage of the derived results to better develop advanced field monitoring work. In addition, release of DOC runoff can take quantified during hydrological and biogeochemical processes within catchments in LPR. [ABSTRACT FROM AUTHOR]

Wet carbon deposition is a critical node of the global carbon cycle, but little is known about dissolved organic and inorganic carbon (DOC and DIC) variation and flux in semi arid area of the Loess Plateau Region (LPR). In this study, concentration of DOC and DIC in rainfall was monitored in the period of July to September 2015 at Yangjuangou catchment in the LPR. Results showed that the Volume-Weighted Mean (VWM) concentration of DOC and DIC were 24.62 and 4.30 (July), 3.58 and 10.52 (August), 1.01 and 5.89 (September) mg C L-1. VWM concentrations of DOC and DIC for the concentrated rainy season (July-September) in the studied region were 7.06 and 7.00 mg C L-1, respectively. In addition, the monthly deposition flux of DOC and DIC were 541.64/94.60, 131.03/385.03, and 44.44/259.16 mg C m-2 for July, August and September. The estimated annual wet carbon depositions were 1.91, 1.89 g C m-2 yr-1 for DOC and DIC, which were higher than those of other sites and lower than those in the tropical and sub-tropical sites. Furthermore, the loess dust deposition process provides soil parental material in soil formation process and might be another source of carbon at the LPR. Therefore, the given results reflect characteristics of wet carbon deposition process during concentrated rainfall season in a semi-arid catchment of the LPR. Our preliminary results suggest that further investigation is needed on carbon source and deposition flux from atmosphere at long term temporal and large scale for revealing the global carbon cycle. [ABSTRACT FROM AUTHOR]

Soil and water losses in agriculture are major environmental problems worldwide, especially on the Loess Plateau, China. Summer fallow management may help to control soil erosion and conserve water. This study investigated the effects of wheat stubble on runoff, infiltration, and soil loss in laboratory plots under simulated rainfall. The treatments comprised wheat stubble cover (WS) and traditional plowing (TP) in runoff plots (4.0m ×1.0 m) with threeslope gradients (5, 10, and 15°) under simulated rainfall at 80mmh-1 for 1 h. The runoff volume from WS plots was significantly less than that from TP. The runoff reduction with WS ranged from 91.92 to 92.83% compared with TP. The runoff rates varied with the runoff volume in the same manner. The infiltration amount was higher with WS (94.8-96.2% of rainwater infiltrated) than TP (35.4-57.1 %). The sediment concentration was significantly lower with WS than TP. Compared with TP (304.31-731.23 gm-2), the sediment losses were reduced dramatically in WS (2.41-3.78 gm-2) and the sediment loss slightly increased with slope; however, it was greatly increased as slope increased in TP. These results revealed that the stubble cover was the main factor reducing runoff and sediment losses and improving infiltration and that stubble showed a great potential to control erosion and conserve soil and water resources during the summer fallow period in the Loess Plateau region. [ABSTRACT FROM AUTHOR]

Soil and water losses in agriculture are major environmental problems worldwide, especially on the Loess Plateau, China. Summer fallow management may help to control soil erosion and conserve water. This study investigated the effects of wheat stubble on runoff, infiltration, and soil loss in laboratory plots under simulated rainfall. The treatments comprised wheat stubble cover (WS) and traditional plowing (TP) in runoff plots (4.0 m × 1.0 m) with three slope gradients (5°, 10°, and 15°) under simulated rainfall at 80 mm h-1 for 1 h. The runoff volume from WS plots was significantly less than that from TP. The runoff reduction with WS ranged from 91.92-92.83% compared with TP. The runoff rates varied with the runoff volume in the same manner. Under WS, sediment losses (2.41-3.78 g m-2) were reduced dramatically compared with TP (304.31-731.23 g m-2). The sediment concentration was also significantly lower with WS than TP. The infiltration amount was higher with WS (94.8-96.2% of rainwater infiltrated) than TP (35.4-57.1%). Thus, stubble cover can help to control erosion and conserve soil and water resources. [ABSTRACT FROM AUTHOR]