Soil Moisture Response to Rainfall in Forestland and Vegetable Plot in Taihu Lake Basin,China

Soil moisture and its spatial pattern are important for understanding various hydrological,pedological,ecological and agricultural processes.In this study,data of rainfall and soil moisture contents at different depths(10 cm,20 cm,40 cm and 60 cm) in forestland and vegetable plot in the Taihu Lake Basin,China were monitored and analyzed for characteristics of soil moisture variation and its response to several typical rainfall events.The following results were observed.First,great temporal variation of soil moisture was observed in the surface layer than in deeper layer in vegetable plot.In contrast,in forestland,soil moisture had similar variation pattern at different depths.Second,initial soil moisture was an important factor influencing the vertical movement of soil water during rainfall events.In vegetable plot,simultaneous response of soil moisture to rainfall was observed at 10-and 20-cm depths due to fast infiltration when initial soil was relatively dry.However,traditional downward response order occurred when initial soil was relatively wet.Third,critical soil horizon interface was an active zone of soil water accumulation and lateral movement.A less permeable W-B soil horizon interface(40-cm depth) in vegetable plot can create perched water table above it and elevate the soil water content at the corresponding depth.Fourth,the land cover was an effective control factor of soil moisture during small and moderate rainfall events.In the forestland,moderate and small rainfall events had tiny influences on soil moisture due to canopy and surface O horizon interception.Fifth,preferential flow and lateral subsurface interflow were important paths of soil water movement.During large and long duration rainfall events,lateral subsurface flow and preferential flow through surface crack or soil pipe occurred,which recharged the deep soil.However,in more concentrated large storm,surface crack or soil pipe connected by soil macropores was the main contributor to the occurrence of preferential flow.Findings of this study provide a theoretical foundation for sustainable water and fertilizer management and land use planning in the Taihu Lake Basin.

Soil Respiration of Biologically-Crusted Soils in Response to Simulated Precipitation Pulses in the Tengger Desert, Northern China

Soil respiration(SR) is a major process of carbon loss from dryland soils, and it is closely linked to precipitation which often occurs as a discrete episodic event. However, knowledge on the dynamic patterns of SR of biologically-crusted soils in response to precipitation pulses remains limited. In this study, we investigated CO_2 emissions from a moss-crusted soil(MCS) and a cyanobacterialichen-crusted soil(CLCS) after 2, 4, 8, 16, and 32 mm precipitation during the dry season in the Tengger Desert, northern China.Results showed that 2 h after precipitation, the SR rates of both MCS and CLCS increased up to 18-fold compared with those before rewetting, and then gradually declined to background levels; the decrease was faster at lower precipitation amount and slower at higher precipitation amount. The peak and average SR rates over the first 2 h in MCS increased with increasing precipitation amount, but did not vary in CLCS. Total CO_2 emission during the experiment(72 h) ranged from 1.35 to 5.67 g C m-2 in MCS, and from 1.11 to3.19 g Cm^(-2) in CLCS. Peak and average SR rates, as well as total carbon loss, were greater in MCS than in CLCS. Soil respiration rates of both MCS and CLCS were logarithmically correlated with gravimetric soil water content. Comparisons of SR among different precipitation events, together with the analysis of long-term precipitation data, suggest that small-size precipitation events have the potential for large short-term carbon losses, and that biological soil crusts might significantly contribute to soil CO_2 emission in the water-limited desert ecosystem.

Decadal Variability of Extreme Precipitation Days over Northwest China from 1963 to 2012

Daily precipitation data from 153 meteorological stations over Northwest China during summer from 1963 to 2012 were selected to analyze the spatiotemporal distribution of extreme summer precipitation frequency.The results show that the extreme precipitation frequency was regional dependent.Southern Gansu,northern Qinghai,and southern Shaanxi provinces exhibited a high extreme precipitation frequency and were prone to abrupt changes in the frequency.Northwest China was further divided into three sub-regions（northern,central,and southern） based on cluster analysis of the 50-yr extreme precipitation frequency series for each meteorological station.The extreme precipitation frequency changes were manifested in the northern region during the late 1970 s and in the central region from the end of the 1980 s to the 1990 s.The southern region fluctuated on a timescale of quasi-10 yr.This study also explored the mechanism of changes in extreme precipitation frequency.The results demonstrate that stratification stability,atmospheric water vapor content,and upward motion all affected the changes in extreme precipitation frequency.