Characteristics of runoff processes and nitrogen loss via surface flow and interflow from weathered granite slopes of Southeast China

Rainfall intensity and slope gradient are two of the most important factors affecting the variations of runoff nitrogen(N).However,the effects of slope gradient and rainfall intensity on N loss via surface flow and interflow on weathered granite slopes are poorly understood.In this study,12 artificial rainfalls(three rainfall intensities and four slope gradients)were simulated to investigate the coupling loss characteristics of surface flow–interflow–total nitrogen(TN),nitrate nitrogen(NO_3^--N)and ammonia nitrogen(NH_4^+-N)on weathered granite slopes.The results show that slope gradient has a greater impact on the surface flow when the rainfall intensity is relatively large.The effect gradually weakens with the decrement of rainfall intensity.The interflow yield increases firstly with the prolongation of rainfall duration,then tends to be stable and finally decreases.The total surface flow percentage increases with rainfall intensity while it decreases with increasing slope gradient with a range of 10.88%-71.47%.The TN loss concentration of the surface flow continually decreases with rainfall duration while that of the interflow shows different fluctuations.However,the TN loss loads of both surface flow and interflow increase with increasing rainfall intensity and slope gradient.The NO_3^--N concentration of interflow is much higher than that of the surface flow.The NH_4^+-N concentration is always less than that of NO_3^--N with no significant difference between surface flow and interflow.The percentages of the TN,NO_3^--N,and NH_4^+-N total loss load and concentration of surface flow and interflow were analyzed.The results show that N loss via both surface flow and interflow occurs mainly in the form of NO_3^--N.Most of the N loss is caused by interflow which is the preferential path of runoff nutrient loss.These findings provide data support and underlying insights for the control of runoff and N loss on the weathered granite slopes.

Comparison of nitrogen losses by runoff from two different cultivating patterns in sloping farmland with yellow soil during maize growth in Southwest China

The loss of N in farmland is an important cause of agricultural non-point source pollution, which seriously impacts the aquatic environment. A two-year(2017–2018) experiment was conducted to investigate the characteristics of runoff and N losses under different tillage practices. Taking downslope ridge planting and cross ridge planting as the experimental treatments,the characteristics of surface runoff, interflow, and N losses in sloping farmlands with yellow soil were studied throughout the maize growth period. As the rainfall increased, the surface runoff and interflow also increased. The surface runoff and N losses in the surface runoff of downslope ridge planting were significantly higher than those of cross ridge planting. The interflow volumes and N losses in the 0–20 and 20–40 cm soil layers of the cross ridge planting were significantly higher than those of the downslope ridge planting. The total N(TN) losses from surface runoff accounted for 54.95–81.25% of the N losses from all pathways. Therefore, we inferred that surface runoff is the main pathway of N losses. Dissolved total N(DTN) was the main form of N loss under different tillage measures, as it accounted for 55.82–94.41% of the TN losses,and dissolved organic N accounted for 52.81–87.06% of the DTN losses. Thus, we inferred that dissolved N is the main form of N loss. Future research must focus on the prevention and control of the N losses during the maize seedling stage to reduce the environmental pollution caused by ammonium N through runoff.

Groundwater Contribution to Surface Water Contamination in a North German Low Land Catchment with Intensive Agricultural Land Use

The contribution of groundwater (GW) to the nitrate loads in surface waters (SW) was exemplarily studied for the river Augraben with a catchment area of 89.9 km2, located in north eastern Germany. The study uses available GW and SW quality data in order to develop a relationship between SW and GW in the Augraben catchment. The calculated ratio of base flow varies from 40% to 80% using various filtering methods of hydrograph separation methods (without taking into account the drainage) in comparison to a calculated GW infiltration of 5% - 7% applying Darcy’s law (upper unconfined aquifer). Drainage was estimated as the difference in base flow obtained through filtering methods of hydrograph separation and the Darcy’s law. Results on the basis of monitoring data and hydrograph separation in quick flow and base flow showed that during winter periods, high concentration in SW has been found parallel to periods of higher GW flow with a strong correlation between SW and GW concentrations. These findings also coincided with the non-vegetation period, i.e. low nitrogen uptake by plants. Overall, nitrate-nitrogen loads at the SW monitoring point (Bei Lindenberg represents the 85% area of the catchment) were 193.5, 97.72, and 122 tons for the year 2010, 2011 and 2012 respectively. Measured GW concentrations in the catchment differ strongly, depending on land use, with elevated concentrations in agricultural areas compared to monitoring points in grass land and in forest areas. In one GW monitoring station, NO3 concentrations exceed the maximum permissible limits (MPL) according to EU water quality standards (MPL = 50 mg/l NO3), up to factor two. High ammonia concentrations at another station may be due to excessive application of manure. The contribution of the different sub-catchments to nitrate load in SW can be ranked in decreasing order in Zone B, D, A and C. Drainage and interflow proved to be a major contributor with 55% - 65% of total load in SW. With the applied method a robust estimation of GW contribution to nitrate loads is feasible using typically available monitoring data of German environmental authorities.

CRWS-mountain Project:Coordinate remediation techniques and devices for water-soil pollution in mountain areas in China

Rural environmental governance is an important strategy to achieve the goal of building"green liveable villages"in China.However,studies on technology and devices for pollution remediation focus mainly on urban areas;in this regard,few studies have focused on rural areas,especially mountainous or hilly areas with interflow.Coordinate remediation techniques and devices for water-soil restoration in mountain areas(CRWS-mountain),a subproject of the"environmental monitoring and remediation in rural areas"project(ERM-rural project),was undertaken to develop techniques and devices for coordinating the restoration of water and soil in rural mountainous and hilly areas with interflow.The CRWS-mountain project will attempt to explore the mechanisms of pollutant transportation and transformation in the interflow-soil-surface water system,establish in-situ and heterotopic remediation systems in landfill,towns and surrounding areas,and construct a comprehensive system for"polluted soilinterflow-surface water"by integrating all the technologies and devices at Yanting,a typical rural mountainous hilly area in Sichuan,Southwest China.We expect that after using this comprehensive system,the water quality will meet the requirements for local water function zoning.The operation cost is 10%lower than that of the existing urban equipment.

A Diffusion Wave Based Integrated FEM-GIS Model for Runoff Simulation of Small Watersheds

In this paper, an integrated model based on Finite Element Method (FEM) and Geographical Information Systems (GIS) has been presented for the runoff simulation of small watersheds. Interception is estimated by an exponential model based on Leaf Area Index (LAI). Philip two term model has been used for the estima-tion of infiltration in the watershed. For runoff estimation, diffusion wave equations solved by FEM are used. Interflow has been simulated using FEM based model. The developed integrated model has been applied to Peacheater Creek watershed in USA. Sensitivity analysis of the model has been carried out for various pa-rameters. From the results, it is seen that the model is able to simulate the hydrographs with reasonable ac-curacy. The presented model is useful for runoff estimation in small watersheds.

Displomacy and Foreign Trade laying New Look of Motherland, Enhancing Foreign Interflow and Spurring Dip HALF A CENTURY OF CCPI' OVERSEAS EXHIBITIONS

Fifty years ago, just after the foundingof new China, the Chinese Governmentwas invited to participate in twointernational industrial fairs in India andPakistan. The 30 member delegationbrought exhibits of metallurgy,machinery, chemicals, textiles,

Effects of rainfall intensities and slope gradients on nitrogen loss at the seedling stage of maize(Zea mays L.)in the purple soil regions of China

Loss of soil nitrogen has been reported to reduce soil productivity and result in eutrophication.The objective of this work was to understand the mechanisms of nitrogen loss at the maize seedling stage from purple soil in the sloping farmlands of southwest China.The characteristics of nitrogen loss were explored in experiments simulating rainfall conditions during the maize seedling stage at different rainfall intensities(60 mm/h,90 mm/h,and 120 mm/h)and slope gradients(10°,15°,and 20°).The results showed that the runoff and sediment yield increased with time.The surface runoff and sediment yield increased with the rainfall intensity and slope gradient.Nitrogen losses increased in the surface runoff and sediment but decreased in the interflow as the rainfall intensity and slope gradient increased.Dissolved total nitrogen(DTN)was the main form of nitrogen in the surface runoff and interflow,and nitrate nitrogen(NO3-N)was the main form of DTN.The surface runoff and sediment accounted for less than half of the TN losses.Thus,interflow was the main pathwayfor nitrogen loss.The regression lines between the surface runoff and forms of nitrogen losses in the runoff and interflow were linear.The results indicated that an increasing rainfall intensity and slope gradient generally increased the surface runoff,sediment,andnitrogen losses.However,the opposite trend was observed for the interflow and its nitrogen losses.

EFFECTS OF SUBSTITUTION OF MINERAL NITROGEN WITH ORGANIC AMENDMENTS ON NITROGEN LOSS FROM SLOPING CROPLAND OF PURPLE SOIL

Nitrogen loss from purple soil can lead to large negative impacts to the environment considering the wide distribution of this soil type in the upper reaches of the Yangtze River.Therefore,nitrogen loss patterns from sloping cropland of purple soil in the Sichuan Basin with the following fertilization regimes were studied in a wheat-maize rotation system:100%organic fertilizer(OM),using pig manure to replace 30%of mineral N(OMNPK)and crop residue to replace 15%of the mineral N(CRNPK)plus standard mineral fertilization(NPK)and no fertilizer control.The cumulative hydrological N loss could be as high as 45 kg·ha^(−1) N.The interflow accounted for up to 90%of the total N loss followed by sediment and overland flow losses.The high N loss via interflow found in this study highlighting that sloping cropland of purple soil may be one of the hot spots of N leaching.Compared to the NPK regime,organic substitution regimes(i.e.,OM,OMNPK and CRNPK)decreased total hydrological N loss loadings by 30%−68%.In addition,they can maintain annual crop yields and decrease yield-scaled total hydrological N losses by 18%−71%.In conclusion,long-term substitution of mineral N with organic amendments can maintain high crop productivity and reduce environmental N loss loadings,and thereby recommended as good N management practices to minimize the risk of agricultural non-point source pollution in the purple soil region of China.