People in many regions worldwide are entirely dependent on groundwater resources for their water supply. More than 1.5 billion people rely mainly on groundwater for drinking water. In China, groundwater is a necessary and irreplaceable resource, which is important for quality of life as well as for economic and social development. In some cities and rural areas, groundwater is often the only source of drinking water, especially in north China such as Shandong Province.
Contamination by various pollutants might render groundwater unsuitable for consumption and therefore have negative consequences for human and animal life as well as the whole environment. Nitrate is the most frequent pollutant introduced into groundwater systems, and high nitrate levels exceeding 50 mg/L can damage human health. Nitrate pollution usually originates from non-point sources, such as intensive agriculture areas and unsewered sanitation in densely populated regions, or point sources such as irrigation of land by sewage effluent. To protect groundwater as a drinking water source and provide a reference that can be used to improve the water environment, we investigated nitrate pollution in Weifang Shandong province, which is famous as protected land where vegetables are produced in China.
We used a uniform sampling method to collect ground water in residential areas, grain and vegetable planting areas and others areas in Weifang district, Shandong Province. The nitrate content of the water was analyzed and the source identified. The results showed that the average NO^-₃-N content of groundwater from 56 wells was 28.1 mg/L, which therefore belong to Class III according to national water quality standards (GB/T 14848-93). The average NO^-₃-N content in drinking water was 23.3 mg/L, which exceeded the maximum permissible nitrate limit for drinking water of 50 mg/L (11.3 mg/L nitrate-nitrogen) recommended by the World Health Organization (WHO). The maximum nitrate-nitrogen content reached 150 mg/L. Compared with the Chinese drinking water standard (10 mg/L), the proportion exceeding the standard value was up to 73.5%, and 50% of the drinking water exceeded 20 mg/L in drinking wells. There was variation in the content of nitrate-nitrogen among different land uses including greenhouse vegetable planting areas, open-field vegetable planting areas and wheat/maize planting areas. The average nitrate-nitrogen was 62.4 mg/L. It was highest in the greenhouse vegetable planting fields, which was almost twice the average value in open-field vegetable planting areas, and lowest in the wheat-corn cropping fields. However, the average for all of the land use types exceeded the maximum permissible limit for drinking water recommended by the WHO. There was a highly significant correlation between NO^-₃ and Ca²⁺, and a significant correlation between NO^-₃ and Mg²⁺. This indicates that the nitrate source was associated with excessive nitrogen fertilizer use in the fields. The Piper diagram obtained from the ions of the water also indicated that the nitrate was associated with human activities, such as fertilizer application and sewage discharge. The δ¹⁵N in nitrate was analyzed, and the results showed that 41.5% of nitrate was from fertilizer, and 14.6% from sewage, and the remainder from fertilizer, sewage and livestock manure in the groundwater in Weifang district. The nitrate contamination of groundwater in Weifang is a serious problem which has compromised the health of the local population. Therefore, it is very urgent to decrease the contamination and particularly the excessive fertilizer inputs to improve the local water environment. Our results suggest that there is a need to develop eco-friendly approaches for the protection of the water environment.