Abstract. Runoff formation at an experimental plot (1600 m 2 ), a field (0.06 km 2 ), and a small catchment (1.36 km 2 ) with a shallow groundwater table and a dense drainage system in the agricultural North Huaihe River Plain (China) was analysed based on the observed rainfall, runoff, and groundwater table data of 30 storm events that occurred during the 1997 to 2008 flood seasons. The surface runoff was collected and measured at the outlet of the furrow of the experimental plot, whereas the total runoff was collected and measured at the outlets of the drainage ditches of the field and the small catchment. The present study showed that the relatively narrow range of rainfall amounts resulted in significantly different runoff amounts at the 3 scales. When the groundwater is close to the surface, the runoff amount is a large percentage of the total rainfall. The difference in rainfall and runoff amounts was regressed against changes in the groundwater table, and a significant linear relationship was determined. Significant rainfall-runoff relationships were indicated for the events divided into 3 groups according to the initial groundwater table depths (as indicators of the antecedent moisture conditions): less than 0.5 m, more than 2.1 m, or between 0.5 m and 2.1 m. These findings suggest that saturation excess surface flow dominated the runoff response, particularly when the groundwater table was shallow. For almost all events, the groundwater table rose above the bottom of the drainage ditch. The total runoff amounts were larger both at the field and at the catchment than at the plot with only the surface runoff collected, which shows a considerable contribution of subsurface flow. Groundwater table depth, which indicates antecedent moisture conditions and influences lateral sub-surface flow to the drainage ditches, is an important parameter that influences runoff formation in catchments, including the study area with a shallow groundwater table and a dense drainage system.

Reducing nitrogen (N) loss from agricultural soils as surface runoff is essential to prevent surface water contamination. The objective of 3-year study, 2007–09, was to evaluate surface runoff and N loss from different cropping systems. There were four treatments, including one single-crop cropping system with winter wheat (Triticum aestivum L.) followed by summer fallow (wheat/fallow), and three double-cropping systems: winter wheat/corn (Zea mays L.), wheat/cotton (Gossypium hirsutum L.), and wheat/soybean (Glycine max L. Merrill). The wheat/fallow received no fertiliser in the summer fallow period. The four cropping systems were randomly assigned to 12 plots of 5 m by 2 m on a silty clay soil. Lower runoff was found in the three double-cropping systems than the wheat/fallow, with the lowest runoff from the wheat/soybean. The three double-cropping systems also substantially reduced losses of ammonium-N (NH4+-N), nitrate-N (NO3–-N), dissolved N (DN), and total N (TN) compared with the wheat/fallow. Among the three double-cropping systems, the highest losses of NO3–-N, DN, and TN were from the wheat/cotton, and the lowest losses were from the wheat/soybean. However, the wheat/soybean increased NO3–-N and DN concentrations compared with wheat/fallow. The losses in peak events accounted for >64% for NH4+-N, 58% for NO3–-N, and 41% for DN of the total losses occurring during the 3-year experimental period, suggesting that peak N-loss events should be focussed on for the control of N loss as surface runoff from agricultural fields.

In order to solve the problem that shallow water source wells in northern pastoral areas are prone to freezing in winter, which brings inconvenience to drinking water for local residents. shallow water source wells are taken as the research object. Through field experiments indoor and software simulations, the key factors to prevent freezing of water source wells are discovered by obtained temperature distribution pattern of water source wells,A photovoltaic heating system compatible with existing solar water extraction systems in pastoral areas is designed. It is found that the temperature distribution of water source wells is “steep-slow- slow” in the field and extreme conditions. The steep-rising areas are located at 0.0-1.3m, 0.0-0.8m away from the wellhead, and the temperature rising rates in the steep-rising areas are 10.58 C/m and 15.75 C/m, respectively. Increasing the temperature of “steep rise zone” is very important to improve the water surface temperature of water source wells. The ANSYS software was used to simulate the temperature field of the water source well under extreme conditions (-40℃), and compared with the indoor simulation results to verify its accuracy. A photovoltaic heating system compatible with the existing solar water lifting system in the pastoral area was designed which can generate 1659.52J heat a day larger than 412.2J heat dissipation per day under extreme conditions which is calculated by software model. Theoretically this system can meet antifreeze requirements. An indoor anti-freezing experiment of solar heating for a freezing period (3 months) was carried out. It was found that the temperature at the water surface of the water source well was about 0℃, which verified the feasibility of the solar heating system.