Characteristics of deep drainage and soil water in the mobile sandy lands of Inner Mongolia, northern China

Quantification of deep drainage and the response of soil water content to rainfall patterns are critical for an effective management strategy of soil water conservation and groundwater utilization. However, there has been little information on how rainfall characteristics influence soil water dynamics and deep drainage in mobile sandy lands. We used an underground chamber to examine the responses of deep drainage and soil water content in mobile sandy lands to rainfall characteristics in Inner Mongolia during the growing seasons of 2010, 2011 and 2012. Results showed that rainfall in this area was dominated by small events （〈5 mm）, which increased soil water con- tent in the surface soil layers （0-40 cm）, but did not increase soil water content in the deeper soil layers （greater than 40 cm）. Soil water content at the 0-100 cm depth increased significantly when the total amount of rain was 〉20 mm. Rainfall amount, intensity and the duration of dry intervals were significantly related to the soil water content in different soil layers. Deep drainage was significantly correlated with rainfall amount and intensity, but not with the duration of dry intervals. The coefficients of deep drainage in the mobile sandy lands ranged from 61.30% to 67.94% during the growing seasons. Our results suggested that rainfall infiltration in the mobile sandy lands had considerable potential to increase soil water storage while recharging the groundwater in this region.

Soil water movement and deep drainage through thick vadose zones on the northern slope of the Tianshan Mountain: Croplands vs.natural lands

Regional aridity is increasing under global climate change,and therefore the sustainable use of water resources has drawn attention from scientists and the public.Land-use changes can have a significant impact on groundwater recharge in arid regions,and quantitative assessment of the impact is key to sustainable groundwater resources management.In this study,the changes of groundwater recharge after the conversion of natural lands to croplands were investigated and compared in inland and arid region,i.e.,the northern slope of the Tianshan Mountain.Stable isotopes suggest that soil water in topsoil(<2 m)has experienced stronger evaporation under natural lands than croplands,and then moves downward as a piston flow.Recharge was estimated by the tracer-based mass balance method,i.e.,chloride and sulfate.Recharge rates under natural conditions estimated by the chloride mass balance(CMB)method were estimated to be 0.07 mm/a in deserts and 0.4 mm/a in oases.In contrast,the estimated groundwater recharge ranged from 61.2 mm/a to 44.8 mm/a in croplands,indicating that groundwater recharge would increase significantly after land changes from natural lands to irrigated croplands in arid regions.Recharge estimated by the sulfate mass balance method is consistent with that from the CMB method,indicating that sulfate is also a good tracer capable of estimating groundwater recharge.

Nitrate Leaching in an Irrigated Wheat-Maize Rotation Field in the North China Plain

Soil water deep drainage and nitrate (NO-3) leaching losses below the root zone were investigated in a 1 ha wheat-maize rotation field under traditional agricultural management that local farmers generally follow in the North China Plain, using the soil water balance method and NO3-N concentration in suction samples. Water drainage, and NO3-N distribution and leaching losses exhibited pronounced spatial and temporal variability. Soil water deep drainage and NO3-N leaching loss mostly occurred during the sum…

Influences of flow rate and baffle spacing on hydraulic characteristics of a novel baffle dropshaft

Due to limited flow capacity and the instability of the asymmetric structure of traditional baffle dropshafts,a novel baffle dropshaft with a symmetric structure,adopting the construction shield well directly,is proposed for large-range flow discharge in deep tunnel drainage systems.In this study,a two-phase flow field of the novel baffle dropshaft with three different baffle spacings was simulated at seven different flow rates with a three-dimensional(3D)numerical model verified with experiments,to study hydraulic characteristics of this novel baffle dropshaft.The results show that the novel baffle dropshaft has a remarkable energy dissipation effect.Baffle spacing of the novel baffle dropshaft has a greater effect on flow patterns and baffle pressure distributions than the comprehensive energy dissipation rate.Flow rate is a critical issue for the selection of baffle spacing in the design.Some guidance on baffle spacing selection and structure optimization for the application of this novel baffle dropshaft in deep tunnel drainage systems is proposed.

On-farm gains and losses of soil organic carbon in terrestrial hydrological pathways:A review of empirical research

Theoretical estimates of soil carbon sequestration in Australian farming systems often do not coincide with measured values of soil carbon,possibly due to post sequestration carbon losses.Carbon loss through soil erosion is one of several pathways of sequestered carbon loss from agricultural systems.Specific details on different loss pathways,especially carbon loss through terrestrial hydrological pathways on a farm scale,are sparse.In this article,we review the Australian and global literature on terrestrial on farm carbon gains and losses in hydrological pathways.Catchment scale,landscape scale and modelling studies are not the focus of this review and are only briefly addressed.Carbon fractions associated with soil erosion and runoff include particulate organic and inorganic carbon,dissolved organic carbon(DOC),dissolved inorganic carbon(DIC),dissolved CO_(2)-C and dissolved CH4-C.Temperate climatic zones with approximately 500 mm of annual rainfall may receive from 6.4 to 29.5 kg ha^(−1) of DOC in rainfall(with concentration of 1.28-5.9 mg L^(−1) of DOC in rainwater).Carbon addition(net)to a field through irrigation water can range from 4.6 to 30.8 kg ha^(−1).The carbon losses through runoff and erosion may vary from below detection limits to 1072 kg ha^(−1) yr^(−1) and these values are significant proportions of SOC sequestration rates reported in literatures.Organic carbon enrichment ratios in eroded sediments range from 0.39 to 5.Total organic carbon concentrations in deep drainage below farming lands range from negligible to 90 mg L^(−1).Management practices that may influence soil carbon losses in erosion and runoff include changing land use,tillage,ground cover,farm layout and slope,furrow length and vegetative buffer strips in the tail end of the field.The literature surveyed indicated that a large knowledge gap existed in Australia with respect to empirical data on soil carbon lost through erosion and runoff because most studies focussed on nutrients other than carbon.The new carbon farming initiative measure means,a better understanding on the farm level carbon losses through runoff across different farming systems is essential to better predict the SOC sequestration potential.Other gaps include carbon losses in the form of carbon dioxide and methane emissions associated with the irrigation network(head ditches,tail drains etc.),on farm water bodies and sediment depositional sites,farm level carbon gains through irrigation and flooding.Carbon losses in deep drainage and its impact on whole soil profile denitrification and the associated mechanisms and biochemical changes of carbon,and carbon and nitrogen interactions during on-farm transport and storage within on-farm dams needs further investigation.