Research On Spatial Distribution And Numerical Simulations Of Migration For 3-Nitrogen In Groundwater Of The North China Plain

Temporal and spatial distribution of 3-nitrogen contamination in groundwater of the North China plain is unclear. The nitrogen pollution assessment and analyses of its pollution distribution pattern in this area was needed. According to the hydrogeologic conditions of the North China plain, we selected two geologic across-sections in this region from the piedmont plain to the central plains to obtain the nitrogen contents in groundwater samples four times. The data of nitrogen contents for four times from 2010 to 2013 in groundwater samples along two geologic across-sections were estimated and the nitrogen pollution status was analyzed systematically. At last, according the nitrogen pollution status, the groundwater numerical modeling is applied to study on the vertical migration of total nitrogen in the groundwater, select total nitrogen in Baoding for typical pollutant in typical area. Analyze the main control factors of the vertical migration of total nitrogen. The results showed that:Along the typical geologic cross-sections of the North China plain, ammonia exceeded most seriously drinking water standard, among ammonia, nitrate, and nitrate in groundwater, the total amount of ammonia, nitrate, and nitrate concentrations increased with time for those 3 years overall. Spatially, the average concentrations of nitrate and ammonia in the piedmont plain were higher than those in the central plains, while the average concentrations of nitrite in the piedmont plain was far lower than those in the central plains. Furthermore, in the vertical direction, the concentrations of ammonia, nitrate, and nitrate in groundwater decreased generally with depth. Finally, total nitrogen concentrations in groundwater in different types of wells vary while they presented higher in those irrigation and monitoring wells, and, however, the ammonia contamination in the drinking wells is relatively serious, which would bring about a risk to human health.Contamination risk of deeper groundwater from total nitrogen sources in surface depends on hydro-geological conditions. The considerable influencing factor of vertical migration for total nitrogen is the permeability coefficient of shallow water, which depends on the soil type and underground environment. The exploitation of shallow water, in some extent, promotes vertical migration of total nitrogen, while the exploitation of deep water has little effect. The "skylight" can promote the vertical migration of total nitrogen. Effect of hydrodynamic dispersion was strengthened with the existence of pumping Wells, thus to play a promoting role of total nitrogen vertical migration. Effect of adsorption biodegradation reduced the total solute of vertical migration, weakened the vertical migration effect of total nitrogen. The permeability coefficient of shallow layer, adsorption coefficient and dispersion degree are identified as the main control factors of nitrogen pollution vertical migration in the typical area of the North China Plain. this provides a relatively clear guidance to the implementation of the nitrogen pollution prevention and control work of groundwater in the typical area of the North China Plain.